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[ilovemygaydad]

title: until we meet again

pairing: demus (deceit/remus)

summary: a zombie apocalypse isn’t the place to be catching feels. unfortunately, dc is doing exactly that with a mysterious man that he met in an alley.

word count: 4.1k

warnings: remus, deceit, sympathetic deceit, zombie apocalypse, mentions of cuts and bruises, swearing, heated making out sessions, implied nudity, weapons, threats, almost attempted murder, mentions of broken glass, mentions of casual sex, mentions of hickeys, innuendos, fainting (once), mentions of STDs, death mentions, crying, sadness, anxiety, sort of breakups? it really isn’t one but idk, sexual attraction, possibly something else

***this fic obviously has a lot of triggers in it, so if you have any questions or concerns, or if you need a summary of parts with specific triggers, please send me an ask! your safety is my number one priority here, and i would hate for anybody to be engaging in unsafe reading practices!***

a/n: so this is... new for me. i’ve never written this ship or this kind of au, nor have i had deceit be the main character (in a serious manner, at least), and i’ve never attempted remus seriously, either. i hope i didn’t fuck up the descriptions of sexual attraction and making out because idk what i’m doing as a sex repulsed asexual! rip me i guess lol. also shoutout to @adultmorelikeadolt for listening to me ramble about this and proof reading it <3 they’re the real mvp here, so check their stuff out, too!!! also, this got way longer than i thought... whoops?

a/n 2: this is heavily based off of death valley by fall out boy! you can listen to it here

Commission Info

consider buying me a coffee

---

DC breathed a heavy sigh of relief as soon as the beat-up VW bus screeched to a stop inside of the checkpoint station. It had been far too long since the last one, and each mile that ticked off on the odometer made him increasingly anxious. The dense forests of Maine were the perfect hiding spots for zombies or bandits, which Virgil so fantastically liked to point out every time that it got dark. Yet they trudged deeper and deeper into the state, driving towards the safety of Canada.

But finally, they had made it.

Roman threw the bus into park and hopped out of the driver’s seat, and the others piled out of the back right after. The checkpoint station was huge--easily one of the largest in the country--but its size made sense given that it was one of two in the entirety of New England. DC gazed around the part of the checkpoint that he could see, and he was in awe at how normal it looked. Other than the giant fences and sentries, it looked like an average New England town. If he hadn’t known any better, he would have believed that there had never been a zombie outbreak in the first place.

Neat, uniform streets of houses stretched before him with shops-turned-supply-stations interspersed between them. Children were outside playing, and adults were going about their days with only a slightly heightened level of concern. Unlike all of the other stations they’d passed through on their way from Miami, it was clean and calm, and a person didn’t have to worry about being pickpocketed or stabbed on their way back from getting their rations.

The guards advanced on them, and Patton talked to the officers as they searched the bus for illegal contraband. Once the bus was clear, they were ushered into the nearest building--a small, gray brick cube that looked more like a sad excuse for a shed than anything--and were tested for the virus. With the exception of Logan fainting, the group was completely cleared to continue into the checkpoint without issue. A guide was designated to them for their month-long stay both to help them become familiar with the checkpoint and to dissuade any of the residents from becoming hostile towards the newcomers.

They drove fifteen minutes into the checkpoint to the visitor park, which was where they were allowed to park the bus. Although their guide, whose name was Remy, offered them a tour, they politely declined. They had been on the road for nearly six days, only stopping to rest or refuel, which might have been circumnavigated had it not been for the Pittsburgh checkpoint being on lockdown.

Long story short, they were tired and really just needed to sleep.

Well, everyone else needed to sleep. DC was too keyed up from the trip to feel anything other than restless, so as soon as he was sure the others were asleep and that the sun had set, he snuck out of the bus and took to the darkest alleys of the checkpoint. He moved with expert silence through the night. His feet took him far from the bus to a more desolate area. Similarly to a normal city, the checkpoint had a dilapidated section of buildings that the more unfortunate people lived, which seemed proportional to the size of the area. 

It was eerily silent amidst the ruined structures. Aside from the occasional rat skittering across an alley, it was completely, utterly quiet.

Footsteps echoed just behind DC. Those footsteps were not his own.

Lightning fast, DC had his stalker pinned against the crumbling brick wall. He expected a fight back, but the man was merely grinning at him in glee. Electric green eyes stared at him with an unnerving amount of energy.

“The last time someone pinned me against a wall, both parties ended up without clothes on,” the man giggled, leaning his head as far forward as DC’s hold would allow. His mustache twisted along with each movement of his mouth. “I wouldn’t mind if this interaction ended the same way.”

DC decided to ignore that comment. “Why were you following me?”

“‘Cause you’re new! We never get visitors.”

That seemed fair. People tended to stay at their original checkpoints.

“And I think you’re hot.”

“Oh, and that makes stalking me so much better. I’m not disgusted by you right now.”

The man’s odd smile grew. “People usually are, so I’m not surprised.”

DC didn’t even know how to reply. He opened and closed his mouth, scouring his brain for a comeback, when a rogue hand tugged on his belt loop. Before he could even process what was happening, their positions had been reversed. 

Oh, shit.

“You’re so pretty when you’re pretending to be tough!” The man was surprisingly strong, and his hands held DC firmly in place regardless of how much he struggled. “I wonder what it would be like when you’re angry. Just fully animalistic.”

“Fuck you,” DC spat.

“Promise?”

Logan probably would have been worried about how aggressively DC rolled his eyes. “In your dreams.”

“Who says we can’t make dreams a reality?” the man whispered in a voice that sent a chill running through DC’s blood. Was this man seriously flirting with him? Was he seriously flirting back?

“I don’t give myself up so easy to dirty street dwellers.”

The man smirked, and a dark glitter flashed in his eyes. “I put the ‘d’ in dirt, baby. I can show you if you’d like.”

DC was suddenly glad that the scars covering the left half of his face were gnarly enough to distract from any blushing.

“Come on,” the man crooned. “Come with me, and I can show you a good time.”

“No. No, I can’t.” DC rushed, and to his surprise, he was immediately let go.

“Okay.” The man took a step back, allowing DC an escape route.

“Okay?”

The man gestured down the alley, still smiling. “You are free to go. I can’t keep you here.”

“Oh,” DC said. “Okay.”

As DC walked away, the man called, “Good bye!” He pretended that he didn’t hear.

---

For some godforsaken reason, DC found himself sitting on a dumpster in the alley the next day. Being out at night didn’t affect him much as he tended to prefer sleeping during the day, and he had yet to be caught by either guards or the rest of his group. Still, he hadn’t exactly been expecting to want to return to the place where he had met the strange man.

But he had, so there he was, sitting on a dumpster lid and staring up at the sky.

“BOO!” a voice suddenly shouted behind DC, and he barely managed to catch  himself before he could be sent tumbling to the pavement. The same giggling from the night before echoed through the alley as the man skipped around the dumpster, stopping right in front of DC. “Hiya!”

“Hello.”

“I can’t believe you came back! People don’t usually want to be in this area of the checkpoint.”

“Well,” DC said, shrugging. “I’ve been told that I’m very usual.”

The man laughed, setting his elbow on the edge of the dumpster to place his chin in his palm. “You’re so funny!”

“Thanks.” DC tried to imagine what the man had found so funny, but his train of thought was cut short when the man moved again. He crossed his arms on the dumpster edge and rested his chin on DC’s crossed legs, looking up through his thick lashes. It took every ounce of restraint not to make a strangled noise at the very, very intimate position.

“So... Why did you come back?”

There was a second that DC considered lying, but he knew deep down that this man would be able to tell. “You.”

“Oh,” the man said breathily as if all of the air had been knocked out of his lungs.

“Kiss me?”

The tone of the man’s voice (the man--DC didn’t even know his name) turned dark, and he said, “God, yes.”

They moved quickly, and the second that DC’s boots hit the pavement, he was pressed back against the dumpster with a searing kiss. He hadn’t felt such an intense fire under his skin since before the apocalypse--since before he’d sworn off feelings altogether. A sharp flash of teeth ran across his lip before biting down so hard that DC was surprised his skin didn’t break. In retaliation, he thread his fingers in the other man’s hair and tugged, which elicited a surprised moan out of his companion. 

If DC’s skin had been on fire before, he was burning now, and he took advantage of the distraction to deepen the kiss further. Too soon, the other man pulled away, grinning dangerously with shining green eyes. His cheeks held a heavy flush that matched the red swell of his lips. 

“Do you want to take this somewhere more appropriate?” he asked in a husky voice that nearly made DC’s knees give out.

“Please.”

---

DC continued to sneak out to meet up with the strange man. It was fun and extremely enjoyable, so why wouldn’t he go back? He had to spend the month in the checkpoint anyway; it made sense to find something to do (literally) in his free time. Once his time was up, he would leave, and everything would go back to normal.

He could forget any of these meetings ever happened.

He would.

Because they were merely for sex. Nothing else.

They didn’t mean anything.

DC turned his head to look at the man next to him. They still didn’t know each others’ names. They were two strangers who happened to cross paths in a dingy alley. Nothing more than the product of long lines of choices. A high that they just couldn’t get enough of.

The man’s eyes were closed, and his breathing was even and deep. In the moonlight that shined through the broken window, the gray streak in his hair glimmered like a silver lake. The soft part of his lips was starkly juxtaposed with the harsh bruises and scrapes on his skin. If it were any other time, DC would have described him as stunning.

Wait.

...

No.

No. No, He wasn’t thinking like that. Sure, the man was attractive, but that was it. He was a good fuck--a good time during the god damn zombie apocalypse. DC wasn’t some fucking teenage YA protagonist yearning for the pretty bad boy. It wasn’t like he’d fallen in love with this crass, borderline violent stranger.

Holy shit, DC had fallen in love, and he had no idea what to do with himself.

The man’s eyes fluttered open and met his gaze. He yawned and propped himself onto his elbow, grinning his usual Cheshire smile. DC’s heart pounded heavily in his chest.

“Ready for another round?” the man teased as he traced the hickeys on DC’s neck.

“I-I’ve gotta go!” DC scrambled off of the stained mattress, throwing on his clothes with urgency.

“What?”

“I just--I have to go.”

The man couldn’t even get another word in before the door to his room slammed closed.

---

The following three days were spent moping, napping, and pointedly not leaving the bus. Mostly napping. Definitely not moping.

He didn’t want to think about the pretty man from the alley. No part of his mind wanted to be reminded of soft lips and green eyes and burning passion. It was so damn tiring to confront the horrible reality of DC being in love. 

Because this was the apocalypse.

And he was going to leave in a couple of weeks.

The apocalypse was neither the time nor place to grow attached to a man who skulked around in alleys like the rat bastard that he was.

But god, he had fallen hard. DC would close his eyes and see a silver streak and tan, calloused hands and shiny scars. Memories of sharp teeth on sensitive skin mingled with the sensation of hot flashes in his blood, quickening his heart rate as he wished to go back and be held and loved. What deity had he angered in a past life to deserve the burden of emotions? Why couldn’t he have just stayed in the bus on the second day instead of going to the alley? How was he supposed to move on?

A sad, strangled noise escaped his throat as he contemplated his existence.

The back door of the bus swung open, and DC stilled, pretending to be asleep. He was luckily turned away from the door, so his tear-streaked face wasn’t visible to whomever opened the door. They clambered in and shut the door with a heavy thunk. They sat, of course, right behind DC’s back.

“Dee, I know you’re awake,” Virgil said. “I could hear you sobbing from outside.”

“I know what you’re talking about, Virgil. I was crying.”

Virgil huffed out a short laugh. “Wow, double lies. That’s pretty impressive.”

“Don’t go away.”

“Alright. I won’t.”

DC turned to glare at Virgil. There was no reason to hide his obvious crying when Virgil had already called him out on it. “I hate you.”

Virgil smiled sympathetically. “I know, Dee, but you’ve been in this slump for days now. Even Logan is starting to notice that you’re upset. What’s wrong?”

“I just...” he trailed off, trying to think of what he wanted to say. “I met someone.”

“We all have met people in the checkpoint, dude. We don’t know anybody here--oh. Oh, you met someone.” Virgil’s eyes went wide as the realization hit him like a truck. “You fell for them.”

“Yeah, well, it doesn’t matter anymore. I ran away.”

“You what?!” Virgil screeched.

“Please, continue acting so incredibly melodramatic. It suits you,” DC grumbled. He rolled his eyes and turned away. 

Virgil scoffed. “I can’t believe how fucking stupid you are! I might as well have a god damn rock for a friend.”

“Your words are so kind.”

“I’m sorry that you threw away your own fucking happiness because you’re afraid of love! You had it, DC. You found someone, and you want to just throw it away!”

DC pulled himself up, throwing a harsh look at Virgil. “We have less than two weeks left in this checkpoint. When that time is up, we will leave, and I will never see him again. Continuing to see him will only bring me more distress, not to mention that I have no idea if he even feels anything for me aside from sexual attraction.”

“Dude, can you shut the fuck up for a second? Seriously, for the past few weeks, you were happier than I’d seen you since well before the apocalypse.” Virgil let out a heavy sigh. “At least apologize. I know you like to keep up your morally-gray schtick, but he deserves to hear why you ran away.”

There were a few seconds of angry silence before DC spat, “I love when you’re right!”

Virgil merely smiled and pat his shoulder, climbing out of the van.

The sun wouldn’t be setting for a few hours, so DC had plenty of time to figure out what the fuck he was supposed to say.

---

It felt like major déjà-vu for DC to be sitting on the same dumpster, hoping that the man would show up. Sure, he could have just traveled to the man’s odd little apartment, but it was far more difficult to make a quick escape from a building than it was an alley. Thus, DC had settled to take his chances of sitting on the dumpster should his partner (fuck buddy? significant other???) be furious. 

Anger was a pretty valid response given the circumstances.

It had been a couple of hours since he’d arrived, and it was a bit chilly. He shivered, pulling his old leather jacket closer around him. His eyes squeezed shut as if he could will away the cold air. Canada’s weather was going to be an absolute bitch if Maine was bordering on unbearable for DC.

“Oh,” a familiar voice exclaimed from in front of the dumpster, and DC’s eyes snapped open. The man had his hands on his hips in a childlike pose, but the glimmer in his eyes bordered on murderous. “Y’know, I was starting to think I’d have to hunt you down myself, but you just waltzed back in like the idiot you are!” He shifted slightly, and the moonlight caught the metal of the knife in his hand.

“Don’t wait!” DC cried when the man lifted his arm in preparation to strike. “I didn’t want to apologize. Please, you don’t have to hear me out!”

“I do? I didn’t realize that I was under the jurisdiction of lying bastards!” The man laughed, but it was dark and lacking any humor.

“I love you,” DC blurted before he could stop himself. He clamped his hands over his mouth in horror.

I love you. The words hung in the air like a child’s mobile. They couldn’t be retracted; they couldn’t be taken back. Each syllable stuck in reality. I love you.

“Oh,” the man said, staring at DC in shock. “You aren’t lying.”

“Yes,” he lied. “I am. I wasn’t scared of my feelings. My friends and I won’t leave in a week and a half, and after that...”

The man let the knife drop to the pavement with a heavy clatter, moving to take DC’s hands. “We’re going to die. It’s just a matter of time before it happens, but what we do with that time is up to us.” He paused, and a wicked smirk twisted his lips. “Who you do is also a choice to make.”

DC choked out a laugh because it was so familiar to hear a stupid innuendo coming from this man’s lips. Love coursed through his veins for all of the stupidest reasons, but it felt so good. Virgil had been right--he was happy. He was purely, simply happy. For once, the apocalypse was on the back of his mind, and he was enjoying existence.

“I won’t have to leave,” he murmured despite himself. “It will last.”

“We’ll burn that bridge when we get to it. Let’s make every second of this next week and a half count, okay?”

Maybe Virgil had been right about DC being an idiot, too, because he nodded and said, “Okay.”

---

There were only twelve hours remaining before DC had to leave the Maine checkpoint station.

There were only twelve hours remaining before DC had to leave the only person that he’d ever truly loved.

They were laying together on the man’s mildly disgusting mattress. The man--yes, he was still known as the man because they decided anonymous identities would be best--was lightly tracing his fingers down the bare skin of DC’s back, which would have been soothing if they hadn’t been acutely aware of the clock running out. 

“You should come with us,” DC whispered. He’d been mulling the idea around in his mind for a while, but he hadn’t known how to bring it up.

“What?”

“Come with us,” he repeated fervently, sitting up. “The rest of the group wouldn’t mind one more person, and we could easily take you across the border.”

“No.”

It was DC’s turn to say, “What?”

“No,” the man sighed as he sat up as well. “I can’t go with you.”

“Why not?!”

“Look around!” He gestured at the debris-filled room. Glass and rock littered most of the floor, and the rest was covered in clothes and containers of food. “I have no worth. I despise using the characteristics of ‘good’ and ‘bad,’ but it isn’t fair to such kind people to have to take on someone like me.”

“They’d be happy to let you tag along--”

“I know, but I have to make it on my own.” His green eyes sparked with determination. “I’ll make it on my own.”

“Will you promise? I don’t care if it’s meaningless, but... it’ll make it easier to leave if I have reassurance that you’ll find me.” DC let his fingers intertwine with the other man’s in an attempt to forget about the pit in his stomach.

“I promise.”

---

One Year Later

Things had finally started settling down for the group. Nearly all of them had been able to secure some sort of job, and they had a roof over their heads that wasn’t attached to a vintage bus. Things were good. DC was happy, healthy, and safe.

A bit lonely, but he still had his friends.

He knew deep down that the man he’d met in Maine wouldn’t make it to Canada. DC had left him with a map marked with where the group was going to end up, but without a mode of transportation, the whispered promises to find each other would stay in the crumbling ruins of an apartment complex. That was okay, even if his heart still held on to the green-eyed stranger like there was a chance of being together.

When he’d eventually told the others of his fling, they’d all been supportive in their own ways. Patton gave him a long hug and whispered gentle reassurances into his ears, and Roman had told him that anything was possible until proven impossible. Logan scolded him about being reckless, claiming that he would have been pissed that DC had survived the apocalypse for so long just to be taken down by potential STDs. Even though Virgil had already known, he still offered a shoulder to cry on. DC would never admit it, but he appreciated how loved he felt.

He shook his head to clear his mind. It was nearly two in the morning; he should’ve been trying to sleep instead of dwelling on the past. Logan always liked to preach about circadian rhythm and all that jazz.

Whatever. DC cut his losses and went to the tiny kitchen, throwing a pot of water on the stove to boil. He took out his mug and a packet of chamomile tea that Patton had stocked for his insomnia as he waited. At least he was trying to coax his body into sleep. Virgil usually just listened to news stations on the radio until the sun rose. Old, paranoid habits died hard, he supposed.

A knock at the door pulled DC out of his thoughts. They never received any visitors, and they definitely were never this late at night. Cautiously, he grabbed the heavy flashlight from its spot next to the hall closet. He prepared to swing at whoever was outside and peered out of the peephole.

Bright green eyes stared back at him, and the flashlight clattered to the ground, barely missing his foot. He flung the door open because there was no way that he was seeing things right, but standing less than a meter away was the man from Maine. DC couldn’t believe his eyes. It couldn’t be real.

“Hey,” the man said as though they had never been apart.

“Holy shit.”

The man giggled, playfully setting his fists on his hips. “I traveled nearly three hundred miles to see you, and this is the greeting I get?”

DC wasn’t able to respond as Roman’s tired voice appeared behind him. “Dee, wha’s goin’ on?”

“Dee? Oh, that’s a cute nickname!” The man turned to Roman and said, “Hi! I’m his boyfriend.”

That sobered DC up fast. “He’s the one from Maine.” My boyfriend.

“Oh! Holy shit!” Roman’s eyes went wide with realization. 

“Roman, this is...?”

“Remus,” the man supplied.

“Roman, this is Remus.” The name felt like gold on his tongue. “Remus, this is my friend, Roman.” 

Roman held out his hand, which Remus shook. “I can’t believe you made it. How’d you even find us?”

“I secretly embedded a tracker in Dee’s skin before he left!” Roman looked horrified, and Remus cackled at the response. “Just kidding! He told me that you were going to Moncton, and I just asked around about a VW bus for a while until I found you.”

“Right...” It seemed that Roman had become thoroughly uncomfortable by Remus’ sense of humor. “I’m gonna go back to bed.” He paused, making direct eye contact with his friend. “And DC? Don’t be loud or whatever.”

“We won’t,” he assured at the same time that Remus said, “No promises!”

As soon as the door to Roman’s room was shut, DC threw himself into Remus’ arms. “You actually did it.”

“I did,” he said. “I promised.”

“I didn’t think you’d actually make it!” DC cried, feeling hot tears brim in his eyes.

“I didn’t either, Dee. I really didn’t.”

“I love you.”

Remus’ fingers tangled in his hair. “I love you, too.”

And maybe DC cried, but that was okay. He had someone to wipe the tears away, now.

now with a part 2 minific

[carlosebanegas-blog]

Managing Control Forces.

Managing Control Forces. As airplanes evolved from stick and wire contraptions to awesome supersonic machines, the pilot at the center of it all has not changed. Desirable maximum and minimum levels of pilot stick, yoke, and rudder pedal control forces required to steer and maneuver are much the same, but the engineering solutions that bring these forces about have changed with the times. Desirable Control Force Levels. In 1936 and 1937, NACA research pilots and engineers Melvin N. Gough, A. P. Beard, and William H. McAvoy used an instrumented cockpit to establish maximum force levels for control sticks and wheels. In lateral control the maximums for one hand are 30 pounds applied at a stick grip and 80 pounds applied at the rim of a control wheel. In longitudinal control the maximums are 35 pounds for a stick and 50 pounds for a wheel. Lower forces are desirable and easily attainable with modern artificial feel systems. The Federal Aviation Administration allows higher forces for transport-category airplanes under FAR Part 25. Seventy-five pounds is allowed for temporary application. However, the data compilation for the handbook accompanying MIL-STD-1797, a current military document, shows that a little over 50 percent of male pilots and fewer than 5 percent of female pilots are capable of this force level. Gough-Beard-McAvoy force levels are generally used as maximum limits for conventional stick, yoke, and rudder pedal controllers, but much lower control force levels are specified for artificial-feel systems and for side-stick controls operated by wrist and forearm motions. Background to Aerodynamically Balanced Control Surfaces. When airplanes and their control surfaces became large and airplane speeds rose to several hundred miles per hour, control forces grew to the point where even the Gough Beard-McAvoy force limits were exceeded. Pilots needed assistance to move control surfaces to their full travels against the pressure of the air moving past the surfaces. An obvious expedient was to use those same pressures on extensions of the control surface forward of the hinges, to balance the pressure forces that tried to keep the control surfaces faired with the wing. The actual developmental history of aerodynamically balanced control surfaces did not proceed in a logical manner. But a logical first step would have been to establish a background for design of the balances by developing design charts for the forces and hinge moments for unbalanced control surfaces. That step took place first in Great Britain. Glauert’s calculations were based on thin airfoil theory. W. G. Perrin followed in the next year with the theoretical basis for control tab design. The next significant step in the background for forces and hinge moments for unbalanced control surfaces was NACA pressure distribution tests on a NACA 0009 airfoil, an airfoil particularly suited to tail surfaces. The trends with control surface hinge position along the airfoil chord match Glauert’s thin airfoil theory exactly, but with lower flap effectiveness and hinge moment than the theoretical values. Ames and his associates developed a fairly complex scheme to derive three-dimensional wing and tail surface data from the two-dimensional design charts. That NACA work was complemented for horizontal tails by a collection of actual horizontal tail data for 17 tail surfaces, 8 Russian and 3 each Polish, British, and U.S. Full control surface design charts came later, with the publication of stability and control handbooks in several countries. Horn Balances. The first aerodynamic balances to have been used were horn balances, in which area ahead of the hinge line is used only at the control surface tips. In fact, rudder horn balances appear in photos of the Moisant and Bleriot XI monoplanes of the year 1910. It is doubtful that the Moisant and Bl´eriot horn balances were meant to reduce control forces on those tiny, slow airplanes. However, the rudder and aileron horn balances of the large Curtiss F-5L flying boat of 1918 almost certainly had that purpose. Wind-tunnel measurements of the hinge moment reductions provided by horn balances show an interesting characteristic. Control surface hinge moments arise from two sources: control deflection with respect to the fixed surface and angle of attack of the fixed or main surface. The relationship is given in linearized dimensionless form by the equation hinge moment coefficient equals to the derivative of the hinge moment coefficient with respect to the control surface deflection times control surface deflection with respect to the fixed surface plus the derivative of the hinge moment coefficient with respect to angle of attack of the fixed or main surface times the angle of attack of the fixed or main surface, where the hinge moment coefficient is the hinge moment divided by the surface area and mean chord aft of the hinge line and by the dynamic pressure. Both derivatives are normally negative in sign. A negative derivative of the hinge moment coefficient with respect to the control surface deflection means that when deflected the control tends to return to the faired position. A negative derivative of the hinge moment coefficient with respect to angle of attack of the fixed or main surface means that when the fixed surface takes a positive angle of attack the control floats upward, or trailing edge high. Upfloating control surfaces reduce the stabilizing effect of the tail surfaces. It was discovered that horn balances produce positive changes in the derivative of the hinge moment coefficient with respect to angle of attack of the fixed or main surface, reducing the up floating tendency and increasing stability with the pilot’s controls free and the control surfaces free to float. This horn balance advantage has to be weighed against two disadvantages. The aerodynamic balancing moments applied at control surface tips twist the control surface. Likewise, flutter balance weights placed at the tips of the horn, where they have a good moment arm with respect to the hinge line, lose effectiveness with control surface twist. A horn balance variation is the shielded horn balance, in which the horn leading edge is set behind the fixed structure of a wing or tail surface. Shielded horn balances are thought to be less susceptible to accumulating leading-edge ice. Shielded horn balances are also thought to be less susceptible to snagging a pilot’s parachute lines during bailout. Overhang or Leading-Edge Balances. When control surface area ahead of the hinge line is distributed along the span of the control surface, instead of in a horn at the tip, the balance is called an overhang or a leading-edge balance. Overhang design parameters are the percentage of area ahead of the hinge line relative to the total control surface area and the cross-sectional shape of the overhang. Experimental data on the effects of overhang balances on hinge moments and control effectiveness started to be collected as far back as the late 1920s. Some of these early data are given by Abe Silverstein and S. Katzoff. Airplane manufacturers made their own correlations of the effects of overhang balances, notably at the Douglas Aircraft Company. As in many other disciplines, the pressure of World War II accelerated these developments. Root and his group at Douglas found optimized overhang balance proportions for the SBD-1 Dauntless dive bomber by providing for adjustments on hinge line location and overhang nose shape on the SBD-1 prototype, known as the XBT-2. Root wrote a NACA Advance Confidential Report in May 1942 to document a long series of control surface and other modifications leading to flying qualities that satisfied Navy test pilots. For example, in 1 of 12 horizontal tail modifications that were flight tested, the elevator overhang was changed from an elliptical to a “radial,” or more blunt, cross-section, to provide more aerodynamic balancing for small elevator movements. This was to reduce control forces at high airspeeds. Overhang aerodynamic balance, in combination with spring tabs, continue in use in Douglas transport airplanes, from the DC-6 and DC-7 series right up to the elevators and ailerons of the jet-powered DC-8. The DC-8’s elevator is balanced by a 35-percent elliptical nose overhang balance. Remarkably constant hinge moment coefficient variations with elevator deflection are obtained up to a Mach number of 0.96. George S. Schairer came to the Boeing Company with an extensive control surface development background at Convair and in the Cal Tech GALCIT 10-foot wind tunnel. Although early B-17s had used spring tabs, Schairer decided to switch to leading-edge balances for the B-17E and the B-29 bombers. The rounded nose overhang balances on the B-29s worked generally well, except for an elevator overbalance tendency at large deflection angles. Large elevator angles were used in push-overs into dives for evasive action. William Cook remarks, “A World War II B-29 pilot friend of mine was quite familiar with this characteristic, so the fact that he got back meant this must have been tolerable.” However, overhang balance was not effective for the B-29 ailerons. Forces were excessive. The wartime and other work on overhang aerodynamic balance was summarized by the NACA Langley Research Department. The Toll report remains a useful reference for modern stability and control designers working with overhang aerodynamic balances and other aerodynamic balance types as well. Frise Ailerons. The hinge line of the Frise aileron, invented by Leslie George Frise, is always at or below the wing’s lower surface. If one sees aileron hinge brackets below the wing, chances are that one is looking at a Frise aileron. Frise ailerons were used on many historic airplanes after the First World War, including the Boeing XB-15 and B-17, the Bell P-39, the Grumman F6F-3 and TBF, and the famous World War II opponents – the Spitfire, Hurricane, and Focke-Wulf 190 fighters. Frise ailerons were applied to both the Curtiss-Wright C-46 Commando and the Douglas C-54 Sky master during World War II, to replace the hydraulic boost systems used in their respective prototypes. With the hinge point below the wing surface, an arc drawn from the hinge point to be tangent to the wing upper surface penetrates the wing lower surface some distance ahead of the hinge line, thus establishing an overhang balance. The gap between the aileron and wing can be made as narrow as desired by describing another arc slightly larger than the first. This in fact is typical of the Frise aileron design. The narrow wing-to-aileron gap reduces air flow from the high-pressure wing under surface to the lower pressure wing upper surface, reducing drag. The Frise aileron is less prone to accumulate ice for that same reason. It was promoted by the U.S. Army Air Corps Handbook for Airplane Designers as an anti-icing aileron. The relatively sharp Frise aileron nose develops high velocities and low static pressures when projecting below the wing lower surface, when the aileron goes trailing-edge up. This generally overbalances the up-going aileron. On the other hand, the overbalanced-up aileron is connected by control cables or pushrods to the down-going aileron on the other side of the wing. The sharp Frise nose on that side is within the wing contour; the down aileron is underbalanced. By connecting the up and down sides through the pilot’s controls the combination is made stable, with lowered control forces relative to ailerons without aerodynamic balance. The sharp nose of the Frise aileron, protruding below the wing’s lower surface for trailing edge-up deflections, has been thought to help reduce adverse yaw when rolling. The trailing edge-up aileron is on the down-going wing in a roll. In adverse yaw, the down-going wing moves forward, while the airplane yaws in a direction opposite to that corresponding to a coordinated turn. Flow separation from the Frise aileron sharp nose is supposed to increase drag on the down-going wing, pulling it back and reducing adverse yaw. This happens to some extent, but for normal wing plan forms with aspect ratios above about 6, adverse yaw is actually dominated by the aerodynamic yawing moment due to rolling, and is little affected by Frise ailerons. Adverse yaw must be overcome by good directional stability complemented by rudder deflection in harmony with aileron deflection. A Frise aileron design used on the Douglas SBD-1 Dauntless. This design was the seventh and final configuration tested in 1939 and 1940. Nose shape, wing-to-aileron gap, hinge line position, and gap seal parameters were all varied. Flight test evidence of Frise aileron oscillations on a Waco XCG-3 glider due to alternate stalling and unstalling of the sharp nose at extreme up-aileron travels. The upper photo shows the bulky roll rate recorder. The lower photo is a rate of roll trace for two abrupt full aileron rolls. Aileron oscillations are shown by the ripples at the peak roll rate values. Frise ailerons turned out to have problems on large airplanes, where there is a long cable run from the control yoke to the ailerons. In the development of the Waco XCG-3 glider in 1942, the sharp nose of its Frise ailerons alternately stalled and unstalled when the ailerons were held in a deflected position. This created severe buffeting. The aileron nose stalled at the largest angle, reducing the balancing hinge moment. Control cable stretch allowed the aileron to start back toward neutral. But as the aileron angle reduced the nose unstalled, the aerodynamic balance returned, and the aileron started back toward full deflection, completing the cycle. The fix for the XCG-3 was to limit up-aileron angles from 30 to 20 degrees and to round off the sharp nose to delay stalling of the nose. Modified Frise ailerons, with noses raised to delay stalling, had been tested in Britain by A. S. Hartshorn and F. B. Bradfield as early as 1934. The advantages of raised-nose Frise ailerons were verified in NACA tests on a Curtiss P-40. Beveled trailing edges were added to the raised-nose Frise ailerons on the P-40, to make up for loss in aerodynamic balance at small deflections. Lateral stick force remained fairly linear and very low up to a total aileron deflection of 48 degrees, giving a remarkably high dimensionless roll rate of 0.138 at 200 miles per hour. Aileron Differential. The larger travel of one aileron relative to the other is called aileron differential. Aileron differential is a method of reducing control forces by taking advantage of hinge moment bias in one direction. At positive wing angles of attack, the hinge moment acting on both ailerons is normally trailing-edge up, and we say the ailerons want to float up. Assume that the up-going aileron is given a larger travel than the down-going aileron for a given control stick or wheel throw. Then, the work done by the trailing-edge-up hinge moment acting on the up-going aileron can be nearly as great as the work the pilot does in moving the down-going aileron against its up-acting hinge moment, and little pilot force is needed to move the combination. The differential appropriate for up-float is more trailing-edge-up angle than down. Typical values are 30 degrees up and 15 degrees down. The floating hinge moment can be augmented, or even reversed, by fixed tabs. Aileron up-float, associated with negative values of the hinge moment derivative, is greatest at high wing angles of attack. Neglecting accelerated flight, high wing angles of attack occur at low airspeeds. Thus, aileron differential has the unfortunate effect of reducing aileron control forces at low airspeeds more than at high airspeeds, where reductions are really needed. In addition to the force-lightening characteristic of aileron differential, increased up relative to down aileron tends to minimize adverse yaw in aileron rolls, which is the tendency of the nose to swing initially in the opposite direction to the commanded roll. Adverse yaw in aileron rolls remains a problem for modern airplanes, especially those with low directional stability, such as tailless airplanes. Where stability augmentation is available, it is a more powerful means of overcoming adverse yaw than aileron differential. Balancing or Geared Tabs. Control surface tabs affect the pressure distribution at the rear of control surfaces, where there is a large moment arm about the hinge line. A trailing-edge-up tab creates relative positive pressure on the control’s upper surface and a relative negative pressure peak over the tab-surface hinge line. Both pressure changes drive the control surface in the opposite direction to the tab, or trailing-edge-down. When a tab is linked to the main wing so as to drive the tab in opposition to control surface motion, it is called a balancing or geared tab. Balancing tabs are used widely to reduce control forces due to control surface deflection. They have no effect on the hinge moments due to wing or tail surface angle of attack. Airplanes with balancing tabs include the Lockheed Jet star rudder, the Bell P-39 ailerons, and the Convair 880M. Trailing-Edge Angle and Beveled Controls. The included angle of upper and lower surfaces at the trailing edge, or trailing edge angle, has a major effect on control surface aerodynamic hinge moment. This was not realized by practicing stability and control engineers until well into the World War II era. For example, a large trailing-edge angle is now known to be responsible for a puzzling rudder snaking oscillation experienced in 1937 with the Douglas DC-2 airplane. Quoting from an internal Douglas Company document of July 12, 1937, by L. Eugene Root: The first DC-2s had a very undesirable characteristic in that, even in smooth air, they would develop a directional oscillation. In rough air this characteristic was worse, and air sickness was a common complaint.... It was noticed, by watching the rudder in flight, that during the hunting the rudder moved back and forth keeping time with the oscillations of the airplane. It is common knowledge that the control surfaces were laid out along airfoil lines. Because of this fact, the rearward portion of the vertical surface, or the rudder, had curved sides. It was thought that these curved sides were causing the trouble because of separation of the air from the surface of the rudder before reaching the trailing edge. In other words, there was a region in which the rudder could move and not hit “solid” air, thus causing the movement from side to side. The curvature was increased towards the trailing edge of the rudder in such a way as to reduce the supposedly “dead” area.... The change that we made to the rudder was definitely in the wrong direction, for the airplane oscillated severely.... After trying several combinations on both elevators and rudder, we finally tried a rudder with straight sides instead of those which would normally result from the use of airfoil sections for the vertical surfaces. We were relieved when the oscillations disappeared entirely upon the use of this type of rudder. The Douglas group had stumbled on the solution to the oscillation or snaking problem, reduction of the rudder floating tendency through reduction of the trailing-edge angle. Flat sided control surfaces have reduced trailing-edge angles compared with control surfaces that fill out the airfoil contour. We now understand the role of the control surface trailing edge angle on hinge moments. The wing’s boundary layer is thinned on the control surface’s windward side, or the wing surface from which the control protrudes. Conversely, the wing’s boundary layer thickens on the control surface’s leeward side, where the control surface has moved away from the flow. Otherwise stated, for small downward control surface angles or positive wing angles of attack the wing’s boundary layer is thinned on the control surface bottom and thickened on the control’s upper surface. The effect of this differential boundary layer action for down-control angles or positive wing angles of attack is to cause the flow to adhere more closely to the lower control surface side than to the upper side. In following the lower surface contour the flow curves toward the trailing edge. This curve creates local suction, just as an upward-deflected tab would do. On the other hand, the relatively thickened upper surface boundary layer causes the flow to ignore the upper surface curvature. The absence of a flow curve around the upper surface completes the analogy to the effect of an upward-deflected tab. The technical jargon for this effect is that large control surface trailing-edge angles create positive values of the derivative of the hinge moment coefficient with respect to the control surface deflection and the derivative of the hinge moment coefficient with respect to angle of attack of the fixed or main surface, which are , the floating and restoring derivatives, respectively. The dynamic mechanism for unstable lateral-directional oscillations with a free rudder became known on both sides of the Atlantic a little after the Douglas DC-2 experience. Unstable yaw oscillations were calculated in Britain for a rudder that floated into the wind. This was confirmed in two NACA studies. The aerodynamic connection between trailing-edge angle and control surface hinge moment, including the floating tendency, completed the story. Following the success of the flat-sided rudder in correcting yaw snaking oscillations on the Douglas DC-2, flat-sided control surfaces became standard design practice on Douglas airplanes. William H. Cook credits George S. Schairer with introducing flat-sided control surfaces at Boeing, where they were used first on the B-17E and B-29 airplanes. Trailing edge angles of fabric-covered control surfaces vary in flight with the pressure differential across the fabric. A Douglas C-74 transport was lost in 1946 when elevator fabric bulging between ribs increased the trailing-edge angle, causing pitch oscillations that broke off the wing tips. C-74 elevators were metal-covered after that. Understanding of the role of the trailing-edge angle in aerodynamic hinge moments opened the way for its use as another method of control force management. Beveled control surfaces, in which the trailing-edge angle is made arbitrarily large, is such an application. Beveled control surfaces, a British invention of World War II vintage, work like balancing tabs for small control surface angles. The beveled-edge control works quite well for moderate bevel angles. As applied to the North American P-51 Mustang, beveled ailerons almost doubled the available rate of roll at high airspeeds, where high control forces limit the available amount of aileron deflection. But large bevel angles, around 30 degrees, acted too well at high Mach numbers, causing overbalance and unacceptable limit cycle oscillations. Beveled controls have survived into recent times, used for example on the ailerons of the Grumman/Gulfstream AA-5 Tiger and on some Mooney airplanes. Corded Controls. Corded controls, apparently invented in Britain, are thin cylinders, such as actual cord, fastened to control surfaces just ahead of the trailing edge. They are used on one or both sides of a control surface. Corded controls are the inverse of beveled controls. Bevels on the control surface side that projects into the wind produce relative negative pressures near the bevel that balance the control aerodynamically, reducing operating force. On the other hand, cords on the control surface side that projects into the wind create local positive pressures on the surface just ahead of the cord. This increases control operating force. Cords on both sides of a control surface are used to eliminate aerodynamic overbalance. On one side they act as a fixed trim tab. Very light control forces have been achieved by cut and try by starting with aerodynamically overbalanced surfaces, caused by deliberately oversized overhang balances. Quite long cords correct the overbalance, providing stable control forces. In the cut and try process the cords are trimmed back in increments until the forces have been lightened to the pilot’s or designer’s satisfaction. Adjustable projections normal to the trailing edge, called Gurney flaps, act as one-sided cord trim tabs. Spoiler Ailerons. Spoiler ailerons project upward from the upper surface of one wing, reducing lift on that wing and thus producing a rolling moment. Spoiler ailerons are often the same surfaces used symmetrically to reduce lift and increase drag on large jet airplanes for rapid descents and to assist braking on runways. Spoiler ailerons are generally used either to free wing trailing edges for full-span landing flaps or to minimize wing twist due to aileron action on very flexible wings. The aerodynamic details of spoiler operation are still not completely understood, even after years of experiment and theoretical studies. The aerodynamics of a rapidly opened spoiler has two phases, the opening and steady-state phases. Experimental or wind-tunnel studies of rapidly opening upper-wing surface spoilers show a momentary increase in lift, followed by a rapid decrease to a steady-state value that is lower than the initial value. At a wind speed of 39 feet per second, the initial increase is over in less than a half-second, and steady-state conditions appear in about 3 seconds. Results from the computational fluid dynamics method known as the discrete vortex method also predict the momentary increase in lift and associate it with a vortex shed from the spoiler upper edge in a direction that increases net airfoil circulation in the lifting direction. A subsequent shed vortex from the wing trailing edge in the opposite direction reduces circulation to the steady-state value. While suggestive, experimental flow visualization results do not exist that confirm this vortex model. The Yeung, Xu, and Gu experiments show that providing small clearances between the spoiler lower edge and the wing upper surface reduces the momentary increase in lift following spoiler extension. This is consistent with a small shed vortex from the spoiler lower edge of opposite rotation to the vortex shed at the upper edge. A clearance between spoiler and wing surface of this type has also been used to reduce buffet. Separation behind an opened spoiler on a wing upper surface causes distortion of the external or potential flow that is similar to the effect of a flap-type surface with trailing-edge-up deflection. In the latter case, streamlines above the wing are raised toward the wing trailing edge. The effective wing camber is negative in the trailing-edge region, causing a net loss in circulation and lift. The difference in the two cases is that the effective wing trailing edge in the spoiler case is somewhere in the middle of the separated region, instead of at the actual trailing edge, as in the flap-type surface case. The hinge moments of ordinary hinged-flap and slot lip spoiler ailerons are high; brute hydraulic force is used to open them against the airstream. Retractable arc and plug spoiler ailerons are designed for very low hinge moments and operating forces. Although aerodynamic pressures on the curved surfaces of these ailerons are high, the lines of action of these pressures are directed through the hinge line and do not show up as hinge moments. Hinge moments arise only from pressure forces on the ends of the arcs and from small skin friction forces on the curved surfaces. A very early application of plug ailerons was to the Northrop P-61 Black Widow, which went into production in 1943. The P-61 application illustrates the compromises that are needed at times when adapting a device tested in a wind tunnel to an actual airplane. The plug aileron is obviously intended to work only in the up position. However, it turned out not to be possible to have the P-61 plug ailerons come to a dead stop within the wing when retracting them from the up position. The only practical way to gear the P-61 plug ailerons to the cable control system attached to the wheel was by extreme differential. Full up-plug aileron extension on one side results in a slight amount of down-plug aileron angle on the other side. The down-plug aileron actually projects slightly from the bottom surface of the wing. Down-plug aileron angles are shielded from the airstream by a fairing that looks like a bump running span wise. Plug-type spoiler ailerons are subject to nonlinearities in the first part of their travel out of the wing. Negative pressures on the wing’s upper surface tend to suck the plugs out, causing control overbalance. Centering springs may be needed. There can be a small range of reversed aileron effectiveness if the flow remains attached to the wing’s upper surface behind the spoiler for small spoiler projections. Nonlinearities at small deflections in the P-61 plug ailerons were swamped out by small flap-type ailerons, called guide ailerons, at the wing tips. Early flight and wind-tunnel tests of spoilers for lateral control disclosed an important design consideration, related to their chord wise location on the wing. Spoilers located about mid-chord are quite effective in a static sense but have noticeable lags. That is, for a forward-located spoiler, there is no lift or rolling moment change immediately after an abrupt up-spoiler deflection. Since airfoil circulation and lift are fixed by the Kutta trailing edge condition, the lag is probably related to the time required for the flow perturbation at the forward-located spoiler to reach the wing trailing edge. Spoilers at aft locations, where flap-type ailerons are found, have no lag problems. Another spoiler characteristic was found in early tests that would have great significance when aileron reversal became a problem. Spoiler deflections produce far less wing section pitching moment for a given lift change than ordinary flap-type ailerons. The local section pitching moment produced by ailerons twists the wing in a direction to oppose the lift due to the aileron. This is why spoilers are so common as lateral controls on high-aspect ratio wing airplanes. Open slot-lip spoilers on the Boeing 707. Note the exposed upper surface of the first element of the flaps. The open spoilers destroy the slot that ordinarily directs the flow over the flap upper surface, reducing flap effectiveness. The reduced lift improves lateral control power when the spoilers are used asymmetrically or the airplane’s braking power when deployed symmetrically on when the ground. Slot-lip spoiler ailerons are made by hinging the wing structure that forms the upper rear part of the slot on slotted landing flaps. Since a rear wing spar normally is found just ahead of the landing flaps, hinging slot-lip spoilers and installing hydraulic servos to operate them is straightforward. There is a gratifying amplification of slot-lip spoiler effectiveness when landing flaps are lowered. The landing flap slot is opened up when the slot-lip spoiler is deflected up, reducing the flap’s effectiveness on that side only and increasing rolling moment. Internally Balanced Controls. Another control surface balance type that appeared about the same time as beveled controls was the internally balanced control. This control is called the Westland-Irving internal balance in Great Britain. Internally balanced controls are intended to replace the external aerodynamic balance, a source of wing drag because of the break in the wing contour. In the internally balanced control the surface area ahead of the hinge line is a shelf contained completely within the wing contour. Unless the wing is quite thick and has its maximum thickness far aft, mechanical clearance requires either that the shelf be made small, restricting the available amount of aerodynamic balance, or control surface throws be made small, restricting effectiveness. By coincidence, internally balanced controls appeared about the same time as the NACA 65-, 66-, and 67-series airfoil sections. These are the laminar flow airfoils of the 1940s and 1950s. Internally balanced ailerons are natural partners of laminar flow airfoil sections, since aerodynamic balance is obtained without large drag-producing surface cutouts for the overhang. Not only that, but the 66 and 67 series have far aft locations of wing maximum thickness. This helps with the clearance problem of the shelf inside of the wing contour. An internal balance modification that gets around the mechanical clearance problem on thin airfoils is the compound internal balance. The compound shelf is made in two, or even three, hinged sections. The forward edge of the forward shelf section is hinged to fixed airplane structure, such as the tail or wing rear spar. The first application of the compound internal balance appears to have been made by William H. Cook, on the Boeing B-47 Stratojet. Internally balanced elevators and the rudder of the Boeing B-52 have compound shelves on the inner sections of the control surfaces and simple shelves on the outer sections. Compound internal balances continue to be used on Boeing jets, including the 707, 727, and 737 series. The 707 elevator is completely dependent on its internal aerodynamic balance; there is no hydraulic boost. According to Cook, in an early Pan American 707, an inexperienced co-pilot became disoriented over Gander, New found land, and put the airplane into a steep dive. The pilot, Waldo Lynch, had been aft chatting with passengers. He made it back to the cockpit and recovered the airplane, putting permanent set into the wings. In effect, this near-supersonic pullout proved out the 707’s manual elevator control. The 707’s internally balanced ailerons are supplemented by spoilers. The later Boeing 727 used dual hydraulic control on all control surfaces, but internal aerodynamic balance lightens control forces in a manual reversion mode. An electrically driven adjustable stabilizer helps in manual reversion. At least one 727 lost all hydraulic power and made it back using manual reversion. Internally balanced controls were used on a number of airplanes of the 1940s and 1950s. The famous North American P-51 Mustang had internally balanced ailerons, but they were unsealed, relying on small clearances at the front of the shelf to maintain a pressure differential across the shelf. The Curtiss XP-60 and Republic XF-12 both used internally balanced controls, not without operational problems on the part of the XP-60. Water collected on the seal, sometimes turning to ice. Flying or Servo and Linked Tabs. Orville R. Dunn gave 30,000 pounds as a rule-of-thumb upper limit for the weight of transport airplanes using leading-edge aerodynamic balance. Dunn considered that airplanes larger than that would require some form of tab control, or else hydraulically boosted controls. The first really large airplane to rely on tab controls was the Douglas B-19 bomber, which flew first in 1941. The B-19 used pure flying or servo tab control on the rudder and elevator and a plain-linked tab on the ailerons. In a flying tab the pilot’s controls are connected only to the tab itself. The main control surfaces float freely; no portion of the pilot’s efforts go into moving them. A plain-linked tab on the other hand divides the pilot’s efforts in some proportion between the tab and the main surface. The rudder of the Douglas C-54 Sky master transport uses a linked tab. Roger D. Schaufele recalls some anxious moments at the time of the B-19’s first flight out of Clover Field, California. The pilot was Air Corps pilot Stanley Olmstead, an experienced hand with large airplanes. This experience almost led to disaster, as Olmstead “grabbed the yoke and rotated hard” at liftoff, as he had been accustomed to doing on other large airplanes. With the flying tab providing really light elevator forces, the B-19 rotated nose up to an estimated 15 to 18 degrees, in danger of stalling, before Olmstead reacted with forward control motion. Flying tabs are quite effective in allowing large airplanes to be flown by pilot effort alone, although the B-19 actually carried along a backup hydraulic system. A strong disadvantage is the lack of control over the main control surfaces at very low airspeeds, such as in taxi, the early part of takeoffs, and the rollout after landing. The linked tab is not much better in that the pilot gets control over the main surface only after the tab has gone to its stop. Still, by providing control for the B-19, the world’s largest bomber in its time, flying and linked tabs, and the Douglas Aircraft Company engineers who applied them, deserve notice in this history. An apocryphal story about the B-19 flying tab system illustrates the need for a skeptical view of flying tales. MIT’s Otto Koppen was said to have told of a B-19 vertical tail fitted to a B-23 bomber, an airplane the size of a DC-3, to check on the flying tab scheme. The point of the story is that the B-23 flew well with its huge vertical tail. Koppen said this proved that a vertical tail could not be made too large. Unfortunately, this never occurred. Orville Dunn pointed out that the B-23 came years after the B-19, and it didn’t happen. Spring Tabs. Spring tabs overcome the main problem of flying tabs, which do not provide the pilot with control of the main surface at low speeds, as when taxiing. In spring tabs, the pilot’s linkage to the tab is also connected to the main surface through a spring. If the spring is quite stiff, good low-speed surface control results. At the same time, a portion of the pilot’s efforts goes into moving the main surface, increasing controller forces. Spring tabs have the useful feature of decreasing control forces at high airspeeds, where control forces usually are too heavy, more than at low airspeeds. At low airspeeds, the spring that puts pilot effort into moving the main surface is stiff relative to the aerodynamic forces on the surface; the tab hardly deflects. The reverse happens at high airspeeds. At high airspeeds the spring that puts pilot effort into moving the main surface is relatively weak compared with aerodynamic forces. The spring gives under pilot load; the main surface moves little, but the spring gives, deflecting the tab, which moves the main surface without requiring pilot effort. The earliest published references to spring tabs appeared as Royal Air craft Establishment publications. NACA publications followed. But the credit for devising a generalized control tab model that covers all possible variations belongs to Orville R. Dunn. The Dunn model uses three basic parameters to characterize spring tab variations, which include the geared tab, the flying tab, the linked tab, and the geared spring tab. Although the derivation of pilot controller force equations for the different tab systems involve only statics and the virtual work principle, the manipulations required are surprisingly complex. As is typical for engineering papers prepared for publication, Dunn provides only bare outlines of equation derivations. Readers of the 1949 Dunn paper who want to derive his final equations should be prepared for some hard labor. Dunn concluded that spring tabs can produce satisfactory pilot forces on subsonic transport-type airplanes weighing up to several million pounds. At the time of Dunn’s paper, spring tabs had indeed been used successfully on the Hawker Tempest, the Vultee Vengeance rudder, all axes of the Canberra, the rudder and elevator of the Curtiss C-46 Commando, the Republic XF-12, and the very large Convair B-36 bomber. They also would be used later on the Boeing B-52 Stratofortress. Dunn’s account of the DC-6 development tells of rapid, almost overnight, linkage adjustments during flight testing. The major concerns in spring tab applications are careful design and maintenance to minimize control system static friction and looseness in the linkages. The B-19 experience encouraged Douglas engineers to use spring tabs for many years afterwards. Both the large C-124 and C-133 military transports were so equipped. The DC-6, 7, 8, and 9 commercial transports all have some form of spring tab controls, the DC-8 on the elevator and the DC-9 on all main surfaces, right up to the latest MD-90 version. In that case, the switch was made to a powered elevator to avoid increasing horizontal tail size to accommodate the airplane’s stretch. A powered elevator avoids tab losses and effective tail area reductions because tabs move in opposition to elevator travel. The Douglas DC-8 and -9 elevator control tabs are actually linked tabs, in which pilot effort is shared between the tab and the elevator. This gives the pilot control over the elevator when on the ground. The DC-8 and -9 elevator linked tabs are inboard and rather small. The inboard linked tabs are augmented by outboard geared tabs, which increase the flutter margin over single large linked tabs. The DC-9 elevator controls are hybrid in that hydraulic power comes in when the link tab’s deflection exceeds 10 degrees. Spring tabs serve a backup purpose on the fully powered DC-8 ailerons and rudder and on the DC-9 rudder. The tabs are unlocked automatically and used for control when hydraulic system pressure fails. The same tab backup system is used for the Boeing 727 elevator. The spring tab design for the elevators of the Curtiss C-46 Commando was interesting for an ingenious linkage designed by Harold Otto Wendt. Elevator surfaces must be statically balanced about their hinge lines to avoid control surface flutter. Spring tabs should also be statically balanced about their own hinge lines. Spring tab balance weights and the spring mechanisms add to the elevator’s weight unbalance about its hinge line. Wendt’s C-46 spring tab linkage was designed to be largely ahead of the elevator hinge line, minimizing the amount of lead balance required to statically balance the elevator. Spring tabs appear to be almost a lost art in today’s design rooms. Most large airplanes have hydraulic systems for landing gear retraction and other uses, so that hydraulically operated flight controls do not require the introduction of hydraulic subsystems. Furthermore, modern hydraulic control surface actuators are quite reliable. Although spring tab design requires manipulation of only three basic parameters, designing spring tabs for a new airplane entails much more work for the stability and control engineer than specifying parameters for hydraulic controls. Computer-aided design may provide spring tabs with a new future on airplanes that do not really need hydraulically powered controls. Springy Tabs and Down springs. Sometimes called “Vee” tabs, springy tabs first appeared on the Curtiss C-46 Commando twin-engine transport airplane. Their inventor, Roland J.White, used the springy tab to increase the C-46’s allowable aft center of gravity travel. White was a Cal Tech classmate of another noted stability and control figure, the late L. Eugene Root. Springy tabs increase in a stable direction the variation of stick force with airspeed. A springy tab moves in one direction, with the trailing edge upward. It is freely hinged and is pushed from neutral in the trailing-edge-upward direction by a compression spring. An NACA application mounted the springy tab on flexure pivots. The springy tab principle of operation is that large upward tab angles are obtained at low airspeeds, where the aerodynamic moment of the tab about its own hinge line is low compared with the force of the compression spring. Upward tab angle creates trailing-edgedown elevator hinge moment, which must be resisted by the pilot with a pull force. Pull force at low airspeed is required for stick-free stability. The C-46 springy tabs were called Vee tabs because the no-load-up deflection was balanced aerodynamically by the same down rig angle on a trim tab on the opposite elevator. The C-46 springy tabs were also geared in the conventional sense. The compression spring that operated the C-46’s springy tab was a low-rate or long-travel spring with a considerable preload of 52 pounds. Tab deflection occurred only after the preload was exceeded, making the system somewhat nonlinear. Schematic diagram of the elevator trim and vee-tab installations on the Curtiss C-46 Commando. The vee tab augments static longitudinal stick-free stability. Springy tabs were also used successfully on the Lockheed Electra turboprop. Although White is considered the springy tab’s inventor and was the applicant for a patent on the device, it may have been invented independently by the late C. Desmond Pengelly. Springy tabs are not in common use currently because of potential flutter. Irreversible tab drives are preferred to freely hinged tabs from a flutter standpoint. A flutter-conservative means of accomplishing the same effect as a springy tab is the down spring. This is a long-travel spring connected between the elevator linkage and airplane fixed structure. The stick or yoke is pulled forward by the long-travel spring with an essentially constant force. Elevator aerodynamic hinge moment, which would normally fair the elevator to the stabilizer, is low compared with the spring force, and the pilot is obliged to use pull force to hold the elevator at the angle required for trim. As with the springy tab, this provides artificial stick-free stability. Down springs are often found in light airplanes. If the yoke rests against its forward stop with the airplane parked, and a pull force is needed to neutralize yoke travel, either a down spring is installed or, less likely, the elevator has mass unbalance. All-Movable Controls. All-movable tail surfaces became interesting to stability and control designers when high Mach number theory and transonic wind-tunnel tests disclosed poor performance of ordinary flap-type controls. Effectiveness was down, and hinge moments were up. More consistent longitudinal and directional control over the entire speed range seemed possible with all-moving surfaces. However, application of all-moving or slab tail surfaces had to await reliable power controls. One of the first all-moving tail applications was the North American F-100 Super Sabre. According to William E. Cook, a slab horizontal tail was considered for the B-52 and rejected only because of the unreliability of hydraulics at the time. In modern times, there is the Lockheed 1011 transport, with three independent hydraulic systems actuating its all-moving horizontal tail. Of course, modern fighter airplanes, starting with the F-4 in the United States; the Lightning, Scimitar, and Hawk in Britain; and the MiG-21 in Russia, have all-moving horizontal tails. An interesting application is the all-moving tail on a long series of Piper airplanes, beginning with the Comanche PA-24 and continuing with the Cherokee and Arrow series. A geared tab is rigged in the anti-balance sense. The geared tab adds to both control force and surface effectiveness. Fred Weick credits John Thorp with this innovation, inspired by a 1943 report by Robert T. Jones. Mechanical Control System Design Details. Connections between a pilot and the airplane’s control surfaces are in a rapid state of evolution, from mechanical cables or push rods, to electrical wires, and possibly to fiber optics. Push rod mechanical systems have fallen somewhat into disuse; flexible, braided, stainless steel wire cable systems are now almost universal. In an unpublished Boeing Company paper, William H. Cook reviews the mature technology of cable systems: The multi-strand 7×19 flexible steel cables usually have diameters from 1/8 to 3/16 inch. They are not easily damaged by being stepped on or deflected out of position. They are usually sized to reduce stretch, and are much over-strength for a 200-pound pilot force. The swaged end connections, using a pin or bolt and cotter pin, are easily checked. The turnbuckles which set tension are safety-wired, and are easily checked. A Northwest Airlines early Electra crashed due to a turnbuckle in the aileron system that was not secured with safety wire wrap. Since the cable between the cockpit and the control is tensioned, the simplest inspection is to pull it sideways anywhere along its length to check both the tension and the end connections. In a big airplane with several body sections this is good assurance. To avoid connections at each body section joint, the cable can be made in one piece and strung out after joining the sections. The avoidance of fittings required to join cable lengths also avoids the possibility of fittings jamming at bulkheads. Since the cable is rugged, it can be installed in a fairly open manner.... Deterioration of the cables from fatigue, as can happen in running over pulleys, or from corrosion, can be checked by sliding a hand over its length. If a strand of the 7×19 cable is broken, it will “draw blood.” A recurrent problem in all mechanical flight control systems is possible rigging in reverse. This can happen on a new airplane or upon re-rigging an old airplane after disassembly. Modern high-performance sailplanes are generally stored in covered trailers and are assembled only before flying. Sailplane pilots have a keen appreciation of the dangers of rigging errors, including reversals. Preflight checks require the ground crew to resist pilot effort by holding control surfaces and to call out the sense of surface motions, up or down, right or left. A few crossed cable control accidents have occurred on first flights. The aileron cables were crossed for the first flight of Boeing XB-29 No. 2, but the pilot aborted the takeoff in time. Crossed electrical connections or gyros installed in incorrect orientations are a more subtle type of error, but careful preflight procedures can catch them, too. Hydraulic Control Boost. Control boost by hydraulic power refers to the arrangement that divides aerodynamic hinge moment in some proportion between the pilot and a hydraulic cylinder. A schematic for an NACA experimental boosted elevator for the Boeing B-29 airplane shows the simple manner in which control force is divided between the pilot and the hydraulic boost mechanism. Boosted controls were historically the first hydraulic power assistance application. By retaining some aerodynamic hinge moments for the pilot to work against two things are accomplished. First, the control feel of an unaugmented airplane is still there. The pilot can feel in the normal way the effects of high airspeeds and any buffet forces. Second, no artificial feel systems are needed, avoiding the weight and complexity of another flight subsystem. Hydraulic power boost came into the picture only at the very end of World War II, on the late version Lockheed P-38J Lightning, and only on that airplane’s ailerons. After that, hydraulic power boost was the favored control system arrangement for large and fast airplanes, such as the 70-ton Martin XPB2M-1 Mars flying boat, the Boeing 307 Stratoliner, and the Lockheed Constellation series transports, until irreversible power controls took their place. Early Hydraulic Boost Problems. Early hydraulic boosted controls were notoriously unreliable, prone to leakage and outright failures. Among other innovative systems at the time, the Douglas DC-4E prototype airplane had hydraulic power boost. Experience with that system was bad enough to encourage Douglas engineers to face up to pure aerodynamic balance and linked tabs for the production versions of the airplane, the DC-4 or C-54 Sky master. A similar sequence took place at the Curtiss-Wright plant in St. Louis, where the Curtiss C-46Commandowasdesigned.Atagrossweightof45,000 pounds, the C-46 exceeded O.R. Dunn’s rule of thumb of 30,000 pounds for the maximum weight of a transport with leading-edge aerodynamic balance only. Thus, the CW-20, a C-46 prototype, was fitted initially with hydraulic boost having a 3:1 ratio, like those on the Douglas DC-4E Sky master prototype and the Lockheed Constellation. However, maintenance and outright failure problems on the C-46’s hydraulic boost were so severe that the Air Materiel Command decreed that the airplane be redesigned to have aerodynamically balanced control surfaces. The previous successful use of aerodynamic balance on the 62,000-pound gross weight Douglas C-54 motivatedtheAirCorpsdecree.Thiswasthestartofthe“C-46BoostEliminationProgram,” which kept one of this book’s authors busy during World War II. Another airplane with early hydraulically boosted controls was the Boeing 307 Stratoliner. Hydraulic servos were installed on both elevator and rudder controls. Partial jamming of an elevator servo occurred on a TWA Stratoliner. This was traced to deformation of the groove into which the piston’s O ring was seated. The airplane was landed safely. Irreversible Powered Controls. An irreversible power actuator for aerodynamic control surfaces is in principle much simpler than hydraulic control boost. There is no force balancing linkage between the pilot and the hydraulic cylinder to be designed. Irreversible powered controls are classic closed loops in which force or torque is applied until a feedback signal cancels the input signal. They are called irreversible because aerodynamic hinge moments have no effect on their positions. An easily comprehended irreversible power control unit is that in which the control valve body is hard-mounted to the actuation or power cylinder. Pilot control movement or electrical signals move the control valve stem off center, opening ports to the high pressure, or supply hydraulic fluid and low pressure, or sump hydraulic fluid. Piping delivers high-pressure fluid to one side of the piston and low-pressure fluid to the other. The piston rod is anchored to structure and the power cylinder to the control surface. When the power cylinder moves with respect to structure in response to the unbalanced pressure it carries the control valve body along with it. This centers the control valve around the displaced stem, stopping the motion. The airplane’s control surface has been carried to a new position, following up the input to the control valve in a closed-loop manner. The first irreversible power controls are believed to have been used on the Northrop XB-35 and YB-49 flying wing airplanes. Irreversibility was essential for these airplanes because of the large up-floating elevon hinge moment at high angles of attack, as the stall was approached. This was unstable in the sense that pilot aft-yoke motion to increase the angle of attack would suddenly be augmented by the elevon’s own up-deflection. One of the N9MflyingscalemodelsoftheNorthropflyingwingswaslostduetoelevonup-float. The YB-49’s irreversible actuators held the elevons in the precise position called for by pilot yoke position, eliminating up-float. Other early applications of irreversible power controls were to the de Havilland Comet; the English Electric Lightning P1.A, which first flew in 1954; and the AVRO Canada CF-105 Arrow, which first flew in 1958. Howard believes that the Comet application of irreversible powered controls was the first to a passenger jet. The U.K. Air Registration Board “made the key decision to accept that a hydraulic piston could not jam in its cylinder, a vital factor necessary to ensure the failure-survivability of parallel multiple-power control connections to single surfaces.” While irreversible power controls are simple in principle, it was several years before they could be used routinely on airplanes. The high powers and bandwidths associated with irreversible power controls, as compared with earlier boosted controls, led to system limit cycling and instabilities involving support structures and oil compressibility. These problems were encountered and solved in an ad hoc manner by mechanical controls engineer T. A. Feeney for the Northrop flying wings on a ground mockup of the airframe and its control system, called an iron bird. An adequate theory was needed for power control limit cycle instability, to explain the roots of the problem. This was presented by D. T. McRuer at a symposium in 1949 and subsequently published. The post–World War II history of gradual improvements in the design of irreversible power controls is traced by Robert H. Maskrey and W. J. Thayer. They found that Tinsley in England patented the first two-stage electromechanical valve in 1946. Shortly afterwards, R. E. Bayer, B. A. Johnson, and L. Schmid improved on the Tinsley design with direct mechanical feedback from the second-stage valve output back to the first stage. Engineers at the MIT Dynamic Analysis and Controls Laboratory added two improvements to the two-stage valve. The first was the use in the first stage of a true torque motor instead of a solenoid. The second improvement was electrical feedback of the second-stage valve position. In 1950, W. C. Moog, Jr., developed the first two-stage servo valve using a frictionless first-stage actuator, a flapper or vane. Valve bandwidths of up to 100 cycles per second could be attained. The next significant advance was mechanical force feedback in a two-stage servo valve, pioneered by T. H. Carson, in 1953. The main trends after that were toward redundancy and integration with electrical commands from both the pilot and stability augmentation computers. In general, satisfactory irreversible power control designs require attention to many details, as described by Glenn. In addition to the limit cycling referred to previously, these include minimum increment of control, position and time lags, surface positioning accuracy, flexibility, spring back, hysteresis, and irreversibility in the face of external forces. Artificial Feel Systems. Since irreversible power controls isolate the pilot from aerodynamic hinge moments, artificial restoration of the hinge moments, or “artificial feel,” is required. Longitudinal artificial feel systems range in complexity from simple springs, weights, and stick dampers to computer-generated reactive forces applied to the control column by servos. A particularly simple artificial feel system element is the bob weight. The bob weight introduces mass unbalance into the control circuit, in addition to the unbalances inherent in the basic design. That is, even mass-balanced mechanical control circuits have inertia that tends to keep the control sticks, cables, and brackets fixed while the airplane accelerates around them. Bob weights are designed to add the unbalance, creating artificial pilot forces proportional to airplane linear and angular accelerations. They also have been used on airplanes without irreversible power controls, such as the Spitfire and P-51D. The most common bob weight form is a simple weight attached to a bracket in front of the control stick. Positive normal acceleration, as in a pull-up, requires pilot pull force to overcome the moment about the stick pivot of increased downward force acting on the bob weight. There is an additional pilot pull force required during pull-up initiation, while the airplane experiences pitching acceleration. The additional pull force arises from pitching acceleration times the arm from the center of gravity to the bob weight. Without the pitching acceleration component, the pilot could get excessive back-stick motions before the normal acceleration builds up and tends to pull the stick forward. In the case of the McDonnell Douglas A-4 airplane’s bob weight installation, an increased pitching acceleration component is needed to overcome over control tendencies at high airspeeds and low altitudes. A second, reversed bob weight is installed at the rear of the airplane. The reversed bob weight reduces the normal acceleration component of stick force but increases the pitching acceleration component. Another interesting artificial feel system element is the q-spring. As applied to the Boeing XB-47 rudder the q-spring provides pedal forces proportional to both pedal deflection and airplane dynamic pressure, or q. Total pressure is put into a sealed container having a bellows at one end. The bellows is equilibrated by static pressure external to the sealed container and by tension in a cable, producing a cable force proportional to the pressure difference, or q. Pilot control motion moves an attachment point of that cable laterally, providing a restoring moment proportional to control motion and to dynamic pressure. It appears that a q-spring artificial feel system was first used on the Northop XB-35 and B-49 flying wing elevons, combined with a bob weight. Q-spring artificial feel system versions have survived to be used on modern aircraft, such as the elevators of the Boeing 727, 747, and 767; the English Electric Lightning; and the McDonnell Douglas DC-10. Hydraulic rather than pneumatic springs are used, with hydraulic pressure made proportional to dynamic pressure by a regulator valve. In many transport airplanes the force gradient is further modulated by trim stabilizer angle. Stabilizer angle modulation, acting through a cam, provides a rough correction for the center of gravity position, reducing the spring force gradient at forward center of gravity positions. Other modulations can be introduced. Advanced artificial feel systems are able to modify stick spring and damper characteristics in accordance with a computer program, or even to apply forces to the stick with computer-controlled servos. Fly-by-Wire. In fly-by-wire systems control surface servos are driven by electrical inputs from the pilot’s controls. Single-channel fly-by-wire has been in use for many years, generally through airplane automatic pilots. For example, both the Sperry A-12 and the Honeywell The Boeing 767 elevator control system, possibly the last fly-by-cable or mechanical flight control system to be designed for a Boeing transport. Each elevator half is powered by three parallel hydro mechanical servo actuators. Cam overrides and shear units allow separation of jammed system components. C-1 autopilots of the 1940s provided pilot flight control inputs through cockpit console controls. However, in modern usage, fly-by-wire is defined by multiple redundant channel electrical input systems and multiple control surface servos, usually with no or very limited mechanical backup. According to Professor Bernard Etkin, a very early application of fly-by-wire technology was to the Avro Canada CF-105 Arrow, a supersonic delta-winged interceptor that first flew in 1958. A rudimentary fly-by-wire system, with a side-stick controller, was flown in 1954 in a NASA-modified Grumman F9F. The NASA/Dryden digital fly-by wire F-8 program was another early development. You can consult Schmitt and Tomayko for the interesting history of airplane fly-by-wire. The Boeing 767 is probably the last design from that company to retain pilot mechanical inputs to irreversible power control actuators, or fly-by-cable. The 767 elevator control schematic shows a high redundancy level, with three independent actuators on each elevator, each supplied by a different hydraulic system. Automatic pilot inputs to the system require separate actuators, since the primary surface servos do not accept electrical signals. The Boeing 777 is that company’s first fly-by-wire airplane, in which the primary surface servos accept electrical inputs from the pilot’s controls. With the Boeing 777, flyby-wire can be said to have come of age in having been adopted by the very conservative Boeing Company. Fly-by-wire had previously been operational on the Airbus A320, 330, and A340 airplanes shows the redundancy level provided on the Boeing 777 control actuators. PFC refers to primary flight control computers, the ACE are actuator control electronic units, the AFDC are autopilot flight director Controls, the PSA are power supplies, and the FSEU are secondary control units. Note the cross-linkages of the ACEs to the hydraulic power sources. Redundancy level provided on the Boeing 777 Transport. P.F.C. is the primary flight computer, A.C.E. the actuator control electronics, A.F.D.C. the autopilot flight director, P.S.A. the conditioned power, and F.S.E.U. the flap slat electronics unit. McLean gives interesting details on the 777 and A320 fly-by-wire systems: Boeing 777. To prevent pilots exceeding bank angle boundaries, the roll force on the column increases as the bank angle nears 35 degrees. FBW enables more complex inter-axis coupling than the traditional rudder cross feed for roll/yaw coordination which results in negligible sideslip even in extreme maneuvers...the yaw gust damper ...senses any lateral gust and immediately applies rudder to alleviate loads on the vertical fin. The Boeing 777 has an FBW system which allows the longitudinal static margin to be relaxed – a 6 percent static margin is maintained...stall protection is provided by increasing column control forces gradually with increases in angle of attack. Pilots cannot trim out these forces as the aircraft nears stall speed or the angle of attack limit. Airbus 320. Side stick controllers are used. The pitch control law on that aircraft is basically a flight path rate command/flight path angle hold system and there is extensive provision of flight envelope protection...the bank angle is limited to 35 degrees.... There is pitch coordination in turns. A speed control system maintains either VREF or the speed which is obtained at engagement. There is no mechanical backup.... Equipment has to be triplicated, or in some cases quadruplicated with automatic “majority voters” and there is some provision for system reconfiguration. The two cases illustrate an interesting difference in transport fly-by-wire design philosophy. Boeing 777 pilots are not restricted from applying load factors above the limit, except by a large increase in control forces. Wings could be bent in an emergency pullout. Airbus control logic prevents load factors beyond limit. The McDonnell Douglas F/A-18 Hornet represents a move in the direction of completely integrated flight control actuators. Pilot inputs to the F/A-18’s all-moving horizontal tail or stabilator are made through two sets of dual solenoid-controlled valves, a true “fly-by-wire” system. A mechanical input from the pilot is applied only in the event of a series of electrical failures and one hydraulic system failure. The General Dynamics F-16 Integrated Servo Actuator made by the National Water lift Company. This actuator design is typical of an entirely fly-by wire flight control system. The actuator uses mechanical rate and position feedback, although electrical feedback has been tried. Internal hydro mechanical failure detection and correction, using three independent servo valves, causes the piping complexity. The General Dynamics F-16 is a completely fly-by-wire airplane, incorporating fully integrated servo actuators, known by their initials as ISAs. Each actuator is driven by three electrically controlled servo valves. There are no mechanical valve inputs at all from the pilot. Of course, the servo valves also accept signals from a digital flight control computer. The complexity seen in the ISA schematic is due to the failure detection and correction provisions. Only two of the three servo valves operate normally. A first failure of one of these valves shifts control automatically to the third servo valve. A first failure of the third servo valve locks the actuator on the sum of the first two. The F-16 servo actuators also are used as primary surface actuators on the Grumman X29A research airplane. Integrated servo actuators of equivalent technology were developed by Moog, Inc., for the Israeli Lavi fighter airplane. The Northrop/Lear/Moog design for the B-2 Stealth bomber’s flight controls represents another interesting fly-by-wire variant. On this quite large airplane part of the servo control electronics that normally resides in centralized flight control computers has been distributed close to the control surfaces. Digital flight control surface commands are sent by data bus to actuator remote terminals, which are located close to the control surfaces. The terminals contain digital processors for redundancy management and analog loop closure and compensation circuits for the actuators. Distributing the flight control servo actuator feedback functions in this manner saves a great deal of weight, as compared with using centralized flight control computers for this function. Other modern fly-by-wire airplanes include the McDonnell Douglas C-17, the Lockheed Martin F-117 and F-22, the NASA/Rockwell Space Shuttle orbiter, the Antonov An-124, the EF 2000 Eurofighter, the MRCA/Tornado, the Dassault Breguet Mirage 2000 and Rafale, the Saab JAS-39, and the Bell Boeing V-22. Remaining Design Problems in Power Control Systems. The remarkable development of fully powered flight control systems to the point where they are trusted with the lives of thousands of air travelers and military crew persons every day took less than 15 years. This is the time between the Northrop B-49 and the Boeing 727 airplanes. However, there are a few remaining mechanical design problems. Control valve friction creates a null zone in response to either pilot force or electrical commands. Valve friction causes a particular problem in the simple type of mechanical feedback in which the control valve’s body is hard-mounted to the power cylinder. Feedback occurs when power cylinder motion closes the valve. However, any residual valve displacement caused by friction calls for actuator velocity. This results in large destabilizing phase lags in the closed loop. Another design problem has to do with the fully open condition for control valves. This corresponds to maximum control surface angular velocity. That is, the actuator receives the maximum flow rate that the hydraulic system can provide. The resultant maximum available control surface angular velocity must be higher than any demand made by the pilot or an autopilot. If a large upset or maneuver requires control surface angular velocity that exceeds the fully open valve figure, then velocity limiting will occur. Velocity limiting is highly destabilizing. Control surface angles become functions of the velocity limit and the input amplitude and frequency and lag far behind inputs by the human or automatic pilot. The destabilizing effects of velocity limiting have been experienced during the entire history of fully powered control systems. A North American F86 series jet was lost on landing approach when an air-propeller–driven hydraulic pump took over from a failed engine-driven pump. When airspeed dropped off near the runway, the air-propeller–driven pump slowed, reducing the maximum available hydraulic flow rate. The pilot went into a divergent pitch oscillation, an early pilot-induced oscillation event. Reported actuator velocity saturation incidents in recent airplanes include the McDonnell Douglas C-17, the SAAB JAS-39, and the Lockheed Martin/Boeing YF-22. Safety Issues in Fly-by-Wire Control Systems. Although fully fly-by-wire flight control systems have become common on very fast or large airplanes, questions remain as to their safety. No matter what level of redundancy is provided, one can always imagine improbable situations in which all hydraulic or electrical systems are wiped out. Because of the very high-power requirements of hydraulic controls, their pumps are driven by the main engines. This makes necessary long high-pressure tubing runs between the engines and the control surfaces. The long high-pressure hydraulic lines are subject to breakage from fatigue; from wing, tail, and fuselage structural deflections; and from corrosion and maintenance operations. The dangers of high-pressure hydraulic line breakage or leaking, with drainage of the system, could be avoided at some cost in weight and complexity with standby emergency electrically driven hydraulic pumps located at each control surface. An additional safety issue is hydraulic fluid contamination. Precision high-pressure hydraulic pumps, valves, and actuators are sensitive to hydraulic fluid contamination. In view of rare but possible multiple hydraulic and electrical system failures, not to mention sabotage, midair collisions, and incorrect maintenance, how far should one go in providing some form of last-ditch backup manual control? Should airplanes in passenger service have last-ditch manual control system reversion? If so, how will that be accomplished with side-stick controllers? In the early days of hydraulically operated controls and relatively small airplanes the answer was easy. For example, the 307 Stratoliner experience and other hydraulic power problems on the XB-47 led Boeing to provide automatic reversion to direct pilot control following loss in hydraulic pressure on the production B-47 airplanes. Follow-up trim tabs geared to the artificial feel system minimized trim change when the hydraulic system was cut out. Also, when hydraulic power was lost, spring tabs were unlocked from neutral. Manual reversion saved at least one Boeing 727 when all hydraulic power was lost, and a United Airlines Boeing 720 made a safe landing without electrical power. The last-ditch safety issue is less easily addressed for commercial airplanes of the Boeing 747 class and any larger superjumbos that may be built. Both Lockheed L1011 and Boeing 747 jumbos lost three out of their four hydraulic systems in flight. The L1011 had a fan hub failure; the 747 flew into San Francisco approach lights. A rear bulkhead failure in Japan wiped out all four hydraulic systems of another 747, causing the loss of the airplane. In another such incident the crew, headed by Delta Airlines Captain Jack McMahan, was able to save a Lockheed 1011 in 1977 when the left elevator jammed full up, apparently during flight control check prior to takeoff at San Diego. There is no cockpit indicator for this type of failure on the 1011, and the ground crew did not notice the problem. McMahan controlled the airplane with differential thrust to a landing at Los Angeles. This incident was a focus of a 1982 NASA Langley workshop on restructurable controls. Workshop attendees discussed the possible roles of real-time parameter identification and rapid control system redesign as a solution for control failures. Thus, although fully mechanical systems can also fail in many ways, such as cable misrig or breakage, jammed bell cranks, and missing bolts, questions remain as to the safety of modern fly-by-wire control systems. The 1977 Lockheed 1011 incident, a complete loss in hydraulic power in a DC-10 in 1989, and other complete control system losses led to the interesting research in propulsion-controlled aircraft. Managing Redundancy in Fly-by-Wire Control Systems. While redundancy is universally understood to be essential for safe fly-by-wire flight control systems, there are two schools of thought on how to provide and manage redundancy. Stephen Osder defines the two approaches as physical redundancy, which uses measurements from redundant elements of the system for detecting faults, and analytic redundancy, which is based on signals generated from a mathematical model of the system. Analytic redundancy uses real-time system identification techniques, or normal optimization techniques. Physical redundancy is the current technology for fly-by-wire, except for isolated subsystems. The key concept is grouping of all sensors into sets and using the set outputs for each of the three redundant computers. Likewise, each of the computers feeds all three redundant actuator sets. Voting circuitry outputs the mid value of the three inputs to the voting system. Fail-operability is provided, a necessity for fly-by-wire systems. The practical application of physical redundancy requires close attention to communications among the subsystems. Unless signals that are presented to the voting logic are perfectly synchronized in time, incorrect results will occur. In the real world, sensors, computers, and actuators operate at different data rates. Special communication devices are needed to provide synchronization. Additional care is required to avoid fights among the redundant channels resulting from normal error buildup, and not from the result of failures. The situation with regard to analytic redundancy is still uncertain, since broad applications to production systems have not been made. By replacing some physical or hardware redundant elements with software, some weight savings, better flexibility, and more reliability are promised. However, a major difficulty arises from current limitations of vehicle system identification and optimization methods to largely linearized or perturbation models. If an airplane is flown into regions where aerodynamic nonlinearities and hysteresis effects are dominant, misidentification could result. Misidentification with analytic redundancy could also arise from the coupled nature of the sensor, computer, and actuator subsystems. Osder gives as an example a situation where an actuator position feedback loop opening could be misdiagnosed as a sensor failure, based on system identification. An analytic redundancy application to reconfiguring a system with multiple actuators is given by Jiang. The proposed system uses optimization to reconfigure a prefilter that allocates control among a set of redundant actuators and to recompute feedback proportional and integral gains. A somewhat similar analytic redundancy scheme, using adaptive control techniques, is reported by Hess. Baumgarten reported on reconfiguration techniques focusing on actuator failures. The best hope for future practical applications of analytical redundancy rests in heavy investments in improved methods of system identification. This appears to be the goal of several programs at the Institute of Flight Mechanics of the DLR. Electric and Fly-by-Light Controls. Fully electrical airplane flight control systems are a possibility for the future. Elimination of hydraulic control system elements should increase reliability. Failure detection and correction should become a simple electronic logic function as compared with the complex hydraulic arrangement seen in the F-16’s ISA. Fly-by-light control systems, using fiber optic technology to replace electrical wires, are likewise a future possibility. Advanced hardware of this type requires no particular advances in basic stability and control theory.

[technicallyfadingdreamer]

RF Adapters Gain Bandwidth While Lowering Return Loss

From laboratory test setups to the transmitting equipment connected to base-station antennas, coaxial and waveguide adapters have been guiding RF and microwave signals for a long time. These adapters have increased flexibility by establishing connections between different or dissimilar connectors. At the same time, they have steadily continued to make electrical and mechanical progress in order to meet new performance goals set by modern and emerging applications. RF connectors suppliers have been able to continuously augment adapter performance by using newer materials, improved manufacturing methods and plating techniques, precision assembly processes, and clever impedance transformer designs.

Traditionally, waveguide-to-coaxial adapters have been a right-angle solution for applications requiring transition. In many situations, however, it is desirable to have connectors inline with the waveguide. By employing the latest RF techniques coupled with precision assembly methods, RLC Electronics has developed in-line adapters also popularly known as end-launch adapters. According to RLC's Director of Marketing, Peter Jeffery, the only advantage here is mechanical and there is also a disadvantage: very narrow bandwidth. Further details on this customer-specific solution were unavailable.

Numerous firms have taken more standard approaches (see Table). Space Machine & Engineering Corp., for instance, has readied a standard series of end-launch waveguide-to-coaxial adapters that incorporate its proprietary matching structure into the waveguide. To obtain broader bandwidth, the company has developed double-ridge waveguide-to-coaxial endlaunch adapters covering sizes WRD750 through WRD200 (Fig. 1). The adapters boast a maximum voltage standing wave ratio (VSWR) of 1.5:1. Doubleridge waveguides for end-launch-style adapters also have been developed by AR RF/Microwave Instrumentation, Cobham Defense Electronic Systems, and QuinStar Technology. Both AR and QuinStar also offer these adapters with rectangular waveguides using a variety of coaxial connectors.

Among the additional proponents of end-launch-style waveguideto- coaxial adapters are Advanced Technical Materials, A-INFO, Flann Microwave, Maury Microwave, Microwave Engineering Corp., and Unique Broadband Systems. Aside from achieving a low profile with short length and low loss and VSWR, Microwave Engineering's design permits its end-launch adapters to operate over multi-octave bandwidths at high power levels.

Developers of end-launch adapters also provide right-angle models. RLC, for example, has been making standard waveguide-to-coaxial adapters in a variety of configurations for applications in the 3.3-to-40-GHz range with options for a broadband or band-specific model. Broadband waveguide-to-coaxial adapters maintain superior electrical specifications over the entire bandwidth. In contrast, band-specific models offer enhanced electrical performance for a specified bandwidth around the center frequency.

The firm's WAD series comprises 50-Ω coaxial-connector types including N, SMA, and K male or female. The adapters' average power-handling capability is 300 W for N, 60 W for SMA, and 25 W for K-type connectors with the waveguide flange as standard. Although insertion loss ranges to just 0.05 dB between 3.3 and 8.2 GHz, it begins to climb as the frequency goes higher. Hence, insertion loss rises to 0.1 dB between 10 and 18 GHz and climbs to 0.15 dB as frequency scales beyond 18 GHz. Likewise, VSWR is 1.2:1 between 3.3 and 8.2 GHz, but deteriorates to 1.35:1 with frequency ascending to 18 GHz and beyond.

The manufacturer also has introduced right-angle solder-free adapters that can handle frequencies to 11 GHz from -65 to 165C. The 50-Ω UG-27 C/U adapters are rated for operating voltages to 1000 V RMS with a maximum dielectric withstanding voltage of 2000 V RMS at 60 Hz at sea level. They flaunt a VSWR of 1.15:1 from DC to 6 GHz and 1.35:1 from 6 to 11 GHz, respectively. Featuring silver and gold center contact plating, the adapters come with albaloy, nickel, and silver body plating.

For their relatively small size and good electrical performance, SMA connectors are commonly found in wireless systems, military/aerospace equipment, test and measurement setups, and Global Positioning System (GPS) antennas. Because these connectors use threaded coupling, they require operator time especially in test environments. It takes time to make the threaded connection and then torque the coupling prior to test. To save time and simplify the testing process, Molex has developed two versions of SMA jack to SMA slide on the plug adapter. While a floating-panel-mount version targets test fixtures (73251-2130), the knurled-body version is designed for use on the end of test cables for production testing (73251-2380).

This adapter mates with standard SMA as per MIL-STD-348A. To create constant ground, it uses a berylliumcopper (BeCu) spring on the SMA push-on side. According to the company, this 50-Ω adapter boasts a maximum VSWR of 1.25:1 to 18 GHz. Its body is stainless-steel passivated while the center contact is gold plated.

To ease interconnections in system applications, Response Microwave has launched a new line of coaxial adapters in frequency ranges from DC through 50 GHz with impedances of both 50 and 75 Ω. The 75-Ω BNC , 1.0/2.3, and 1.6/5.6 in-series adapters are specifically tailored for telecommunications and networking infrastructure, explains Peter A. Alfano, the company's Director of Business Development. Alfano points out that the in-series and between-series adapters offer popular interfaces like SMA, SSMA, SMB, 2.4 mm, 2.9 mm, 3.9 mm, SMP, N, 7/16, BNC, TNC, MCX, MMCX, 1.0/2.3, and 1.5/5.6. Plus, there are coupling options like thread-on, push-on, and quick disconnect (Fig. 2). These adapters also come in a variety of configurations, such as in-line, right angle, T, and U-link. They are available in both stainless-steel and brass housings with silver, gold, nickel, or ternary plating options.

With the proliferation of WiFi and broadband infrastructure for telecommunications and high-speed data communications, a tremendous need has arisen for a variety of connectors to test cables in the field. RF Connectors' Vice President of Marketing, Manny Gutsche, points out that the unavailability of any unique interconnection in the field can pose a problem and delay testing. To simplify this task, RF adaptors a division of RF Industrieshas crafted a universal adapter kit labeled RFA-4028-WIFI.

This kit comprises the Unidapt RF cable tester with an assortment of 30 universal adapters, which include male and female MMCX, N, reverse-polarity (RP) TNC, RP SMA, TNC, BNC, and SMA connector interfaces. By screwing any two interface adapters in this kit to a universal center, Gutsche says that scores of different adapters can be made in seconds. All adapters feature machined brass, silver-plated bodies, gold-plated contacts, and Teflon insulation. They also are sold separately. Without the tester, the universal adapter kit is labeled RFA-4024-WIFI (Fig. 3).

Other suppliers offering such universal kits include Bomar Interconnect Products and MegaPhase. To address the needs of technicians and engineers in the broadcast field, Bomar has readied a 42-piece adapter kit, called ADPT4RP, that contains the parts most often needed by technicians in on-site antenna installations. The product consists of two male and two female Type N, BNC, UHF, TNC, TNC reverse-thread (RT), TNC-RP, SMA, and SMA-RP 50-Ω coaxial parts as well as eight universal adapters and two flat wrenches. These parts are fabricated using precision-machined brass with corrosion-resistant gold bodies, Teflon insulators, and gold-plated contacts. For its part, MegaPhase's universal adapter kit includes tools to properly terminate three different-length cable sub-assemblies with various connector combinations.

An F connector is a fitting that connects a coaxial cable to an electronic device or a wall jack.

Traditional coaxial cables were once the standard means of connecting a television to an antenna or cable TV access point. But they are less common now that high-definition and ultra-high-definition televisions make prevalent use of HDMI, fiber optical, and ethernet cables for many of their connections. Still, coaxial cables have their purposes, and your video system may still use them.

A coaxial cable used to bring electronic signals to a television or other electronic device terminates in an F connector. There are several ways these F connectors can be attached to coaxial cable. Professional installers use a coaxial cable stripper, which strips all three layers of the cable at once. Then, they slip on the F connector and secure it with a coaxial cable tool, which presses the connector onto the cable and crimps it at the same time.

Choosing the proper BNC connector to suit the cable for your project usually comes with a price. The price typically needs to be an appropriate assessment of the intending cable. A major issue plaguing most corporate organizations and teams is choosing the right cable. BNC cables remain one of the most used cable types across different industries. This article presents all you need to know about the BNC cable. You will learn about Siamese cables, connectors, benefits, and applications of other types of cables.

There are many definitions of the BNC acronym. Other names include Barrel Nut connector, Bayonet Navy connector, Bayonet Nipple connector, and British Naval Connector. Nevertheless, they are popularly known as the “Bayonet Neill-Concelman.”

Bayonet Neill-Concelman (BNC) is used as a socket and plug for video signals, audio signals, power, and networking systems. These devices are known to offer the best connection to devices. They have a powerful bond with any device of choice.

An IEC connector refers to a type of electronic cable that meet the International Electrotechnical Commission (IEC) standards. The specification for IEC connectors is IEC-60320. The connectors mount with cables are commonly referred to as female connectors or sockets, whereas the connectors mount with panels are known as male connectors or plugs. IEC-60320 is a standard for male and female connectors used in cables and electric devices such as computers, workstations, laptops, printers and so on. Note that the IEC-60320 standard applies to different range and types of electrical devices. There is a range of standardized connectors that differ in regards to current capacities, temperature ratings and number of conductors. The main purpose of these cables is to attach an electronic appliance to its power source.

The RCA connector was invented in the 1940s and was first used to connect an amplifier to a phonograph. They are sometimes referred to as phono connectors due to this original purpose, even though they can be used to carry both audio and video from many different devices. By the 1950s, the RCA connector had largely replaced the tip ring sleeve (TRS) connector in most high fidelity audio systems, and they remained popular even after the introduction of digital audio and video. Most audio-visual equipment comes equipped with RCA connectors, and some speakers do as well.

There are two types of RCA connectors that are used together to make solid electrical connections. Female RCA connectors are typically located on devices. These connectors typically protrude from a device and have one contact on the exterior surface and another in the center. Male RCA connectors are typically found on cable ends and contain an outer sleeve contact in addition to a central pin connection. There are also numerous other configurations, such as extension cables that have one male and one female RCA connector, splitters that can connect a monaural output to a stereo input, and converters that include female RCA connectors and a male TRS connector.

Do you find it difficult to identify what RF connector type you're going to use in an application? If so, don’t worry. In this article, you will learn about the different types of RF connectors and what applications they are commonly used for.

RF connectors are connectors that are designed to work at radio frequencies for signal transmission of products like radios, antennas, coaxial cables, etc. However, these connectors have a variety of types.

The Type N connector is a threaded, weatherproof, medium sized connector for durable applications that can easily handle frequencies up to 11 Ghz. This type of connector follows MIL-STD-348 and widely used in lower frequency microwave systems where ruggedness and low cost are needed.

DIN Connectors were originally brought into line in the 1970s. It is an electrical connector, and its architecture has multiple pins that are under a protective circular sheath. Normally, a full-sized DIN Connector contains three to 14 pins with a diameter of 13.2 millimetres.

The term Din connector doesn’t refer to a specific cable. Instead, it requires all the connectors that meet the Din standard.

The circular connector is another name for Din Connector in computer electronics. It’s also used for a digital interface such as musical instrument digital interfaces MIDI.

There are mainly two types of DIN connector. We will discuss them briefly one by one.

? Circular connector

? Loudspeaker connector

CIRCULAR CONNECTOR

Circular connectors consist of a family of male plugs. They have the same feature of 13.2 diameter metal shield with a notch that limits the orientation in which the plug and socket can connect.

There are seven common patterns, which can be any number from three to eight pins. When some high range equipment uses seven-pin connectors, then the outer two carries digital system data. If the equipment is incompatible, then the outer two pins from plug should unscrew. That is why we fit them into standard five pins 180” sockets without data connections. We are going to produce more new products.

[lisungr]

The working principle of the salt spray test chamber

Application Field: The salt spray test machine is also called the salt spray test chamber, the full name is the salt spray test chamber, which is mainly used to test the corrosion resistance of the samples. At present, it is widely used in the aerospace industry, automotive electronics, electronics and electrical, mobile phone digital, plastic products, metal materials and other industries to test its corrosion resistance. It also simulates the extreme conditions under natural conditions or working conditions to understand the samples to perform temperature conditions.

Standard: It meets the following standards: IEC60068-2-11 (GB/T2423.17), GB/T10125, GB/T1771, ISO9227, ASTM-B117, GB/T2423-18, QBT3826, QBT3827, IEC 60068-2-52, ASTM-B368, MIL-STD-202, EIA-364-26, GJB150, DIN50021-75, ISO3768, ISO 9227, 3769, 3770; CNS 3627, 3885, 4159, 7669 etc.

Working principle of the salt spray test chamber: The working principle of the salt spray test chamber is relatively simple, mainly compressing the corrosive solution into an air spray, spraying the sample, and wrapping the spray on all sides of the sample as much as possible. This test can be performed continuously or cyclically until the sample is corroded. , And then record the corrosion time as the corrosion resistance of the sample. The longer the time, the better the corrosion resistance of the sample.

Generally, the corrosion solution in the salt spray test chamber is mainly 5% sodium chloride solution or 0.26 grams of copper chloride per liter added to the sodium chloride solution as the salt spray corrosion solution. In addition, the salt spray test chamber can independently control the sedimentation volume and spray volume of the salt spray to ensure constant test temperature, convenient operation and stable test environment. Therefore, it is often used to test the corrosion resistance of daily necessities or industrial products.

The test chamber can reach any temperature point from room temperature to 50℃ in the test working space, and keep it constant. Conduct salt spray corrosion tests on materials or products in a cabinet with a specified volume under constant temperature and relative humidity. The material used to manufacture this equipment is imported corrosion-resistant PVC plastic sheet, which does not react with salt-containing solutions or acidic salt-containing solutions, and does not affect the test results. In the design of this equipment, the internal and external pressures are balanced, and the salt spray can settle freely in the box and can be adjusted to the range specified by the national standard.

The YWX/Q-010 Salt spray test chamber of Shanghai LISUN is mainly composed of a cabinet, a spray system, a heating system and a control system. 

YWXQ-010 Salt Spray Test Chamber[/caption]

Lisun Instruments Limited was found by LISUN GROUP in 2003. LISUN quality system has been strictly certified by ISO9001:2015. As a CIE Membership, LISUN products are designed based on CIE, IEC and other international or national standards. All products passed CE certificate and authenticated by the third party lab.

Our main products are Goniophotometer, Surge Generator, EMC Test Systems, ESD Simulator, EMI Test Receiver, Electrical Safety Tester, Integrating Sphere, Temperature Chamber, Salt Spray Test, Environmental Test Chamber, LED Test Instruments, CFL Test Instruments, Spectroradiometer, Waterproof Test Equipment, Plug and Switch Testing, AC and DC Power Supply.

Please feel free to contact us if you need any support. Tech Dep: Service@Lisungroup.com, Cell/WhatsApp: +8615317907381 Sales Dep: Sales@Lisungroup.com, Cell/WhatsApp: +8618917996096

[xpresscareurgent]

Most walk in clinics that offer STD testing Washington DC operate extended hours. You can walk in at a time convenient to you – before work, on lunch, or after work. You can be sure of a hassle-free and completely confidential testing experience.

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Price: [price_with_discount] (as of [price_update_date] - Details) [ad_1] cable management The drive has a nifty groove that goes around its shell, serving as convenient storage for the detachable USB cable.  When not in use, simply disconnect the cable, easily wrap it around the HD710 Pro, and get going.  This greatly reduces the risk of annoying cable misplacement and clutter, further enhancing your experience. Ergonomic waterproof port cover Unlike other so-called external durable drives, the HD710 Pro has an easy to use USB port cover.  No fiddling, no pressing to find the right angle until it's finally closed.  Our engineers pay attention to every detail, and the HD710 Pro's tab cover is one-touch easy but totally secure and waterproof. Specification: Capacity: 1TB / 2TB / 4TB / 5TB(optional) Color: Yellow/Black/Blue/Red(optional) Dimensions(L x W x H): 133.3 x 98.5 x 21.5mm / 5.2 x 3.8 x 0.8"  (1TB)                                       133.3 x 98.5 x 26.7mm / 5.2 x 3.8 x 1.01" (2TB/4TB/5TB) Weight: 270g/9.5oz(1TB),390g/13.7oz (2TB/4TB/5TB) Interface: USB 3.1 (backward compatible with USB 2.0) Texture Plastic/Anti-shock Silicone Operating Temperature: 5–50°C/41–121°F Operating Voltage: DC 5V, 900mA System requirements: for Windows XP/Vista/7/8/8.1/10, Mac OS X 10.6 or later, Linux Kernel 2.6 or later Package list: 1 * HDD 1 * USB 3.1 cable 1 * Quick Start Guide Note:  1. HDDtoGo free software only compatible with Windows. 2. Compatibility with specific host devices may vary and could be affected by system environment. 3. Connecting via USB 2.0 requires plugging in to two USB ports for sufficient power delivery. A USB Y-cable will be needed. HD710P dust and water proof ratings apply only when the USB port cover is firmly closed. Takes shocks like a true warrior with military-grade toughness The HD710 Pro holds up against shocks, drops, and vibrations thanks to its extra-rugged triple-layered construction. We test it to US Army MIL-STD-810G 516.6, meaning it can easily take falls from 1.5 meters. Your data is safe, so feel free to go out there and take on more challenges Guarded by durable triple-layered construction No matter what you store inside, the HD710 Pro's exterior delivers supreme protection. It has three primary layers coating it, from tough silicone, through a shock absorbing buffer, the tough plastic shell that's closest to the drive itself and holds it firmly in place. Exclusive Shock vibration sensing technology Lesser external drives keep trying to work even if they fall or encounter a shock, resulting in errors and bad sectors. The HD710 Pro features Shock sensors that immediately stop all drive activity if a shock is detected. Once vibrations fully end, activity resume. You're kept fully informed with a clear status indicator. Pick your capacity With 1TB, 2TB, 4TB, and 5TB, you get the flexibility of great external storage for your needs. In any case, you have plenty of room for your experiences, be they 4K videos of your weekend outings, essential work materials, or game library. [ad_2]

[rapidtesting]

Sexually Transmitted Diseases (STDs) are fatal infections that occur in people due to insecure sexual activities, and occasionally through non-sexual contacts.

[vsplusonline]

Amidst Lockdown, students gear up for JEE/NEET with Prime Academy, a leading coaching institute - Times of India

New Post has been published on https://apzweb.com/amidst-lockdown-students-gear-up-for-jee-neet-with-prime-academy-a-leading-coaching-institute-times-of-india/

Amidst Lockdown, students gear up for JEE/NEET with Prime Academy, a leading coaching institute - Times of India

Getting into top institutions, like the IIT, AIIMS, NIT etc, is a cherished dream for most of the science students. Though this lockdown has announced doom for most of the sectors, it has helped sincere students significantly by giving them extra study hours. The students are able to practice more problems and spend extra time understanding the concepts in depth. Online classes for JEE / NEET have reached the study table of students, giving them multiple advantages by saving commuting time and energy.

If a student is aspiring to be a doctor, or an engineer, and has just appeared for his 10th board examinations, then it’s the best time to get into the groove and start preparations for competitive exams like JEE / NEET. Many top rankers start their preparation as early as 8th standard ! With a dedicated 6 hrs a day of study and right mentorship, this journey becomes very easy and fun filled if it is planned well. “Students should get a strong command over the basics and fundamental concepts of all the topics. Once they are thorough with the concepts, they should attempt the practice problems by setting a clock, which helps them strike the right balance between speed and accuracy.” said Lalit Kumar, an IIT Bombay graduate, CMD Prime Academy.

“The difference between successful students and the not so successful ones is not the students’ lack of intelligence or talent, but the lack of determination and right mentorship. A strong team of permanent and consistent faculty & unmatched success ratio in JEE are the USP of Prime. That makes Prime Academy the best IIT coaching institute in Pune” said DC Pandey sir, the most renowned author for Physics across the country, who enrolled his own son in Prime Academy and took the charge as the mentor.

Click https://youtu.be/s-7NjEzZ5D4 for the important tips by physics maestro, DC Pandey sir.

Team Prime: United since ages

During lockdown, online education is the only option and it has made it very easy for a student to choose the right classes, even if they stay in far off locations. You are one click away from the demo lectures of virtual classrooms, wherein you will get first-hand experiences of quality education and which will help decide on the best coaching class for engineering and medical exams.

“My daughter Rhythem Sood has just finished her 10th board and has been attending online sessions by Prime Academy. Not only am I happy but I am surprised to see the comfort with which she solves even complex problems. She has also developed a keen interest in the subjects. As a parent I am doing my duty to enroll her with the best coaching class for IIT JEE and providing her all necessary resources. She also follows her teachers religiously and tries her best to make us all proud.” said the father of a 10th appeared student, whose elder son Swarit Sood was also a Prime Academy student and is now pursuing B.Tech from IIT Bombay.

Last year Mustafa Chasmai aced Pune by securing an All India Rank of 91 in IIT JEE Advanced. He was the only student from Pune to make it to the International Physics Olympiad camp in 2019. He shared many important tips and tricks which are very helpful for JEE/NEET aspirants. Click https://youtu.be/BmOxfPdyzWo to know about tips to crack IIT JEE. Few Q&A are as follows:

Q: What were the key points which helped you to crack IIT JEE by superseding 99.999% of the nation?

Mustafa: Early start was the key. Most of the maths/science topics of 11th /12th std are included in 9th std books. Instead of superficially finishing those topics, I joined the foundation course for class 9th and over there I was taught those topics in depth. Subsequently I could afford to solve higher level problems of physics/maths in 11th when most of my batch mates were trying to learn very basic concepts only. That gave me lots of time to practice and analyze many mock tests. All thanks to the plan chalked out by my father and Prime Academy’s teachers.

Q. Don’t you think that IIT JEE preparation in 9th std puts a child under lots of pressure.

M: It’s the other way round. When you start your IIT JEE preparation in the 9th standard, you get 4 years to prepare as compared to those who get just 2 years, by starting in the 11th std. In 9th/10th I didn’t have any pressure of scoring in competitive exams. I simply enjoyed the scientific details and logical reasoning behind every concept. If you get good and experienced teachers, then JEE preparation becomes very interesting and fun filled.

Q: Why did you choose Prime Academy, when there are many big institutes in Pune?

M: It’s a myth that a big coaching is a good coaching. For a student what matters is teachers. My brother had done 2-year coaching at Prime and gave me very strong and encouraging feedback about its IITian faculty team, which is with Prime since the last 10 years. Out of 238 students in my batch, more than 200 cleared JEE Mains and around 80 cleared JEE Advanced. I guess one should simply ignore marketing stunts of coaching institutes and rather focus only on faculty and success ratio.

Click https://youtu.be/xIoMUtRq8b4 to get important tips about “How to choose the best coaching class for JEE/NEET”

Siblings in Computer science at IIT are very rare, but students taught by Prime faculties have done it multiple times. Unique feat was achieved by Sachdeva brothers as both of these APS Pune kids graduated in Computer Science from IIT Bombay. Sushant Sachdeva helped Pune to shine on the world map by cracking All India Rank 1 in IIT JEE. He is the only student in the history of Pune to top the whole nation in the country’s most reputed exam! His younger brother, Prashant Sachdeva also followed in his footsteps by cracking AIR 75. “Prof. Lalit was one of the best teachers that I have studied under when preparing for IIT JEE. I am sure many others will benefit from his dedication towards students.” said Sushant Sachdeva, a recipient of the President gold medal in IIT Bombay. Check the testimonials of top ranks like AIR 1, 22, 37, 44, 71, 75, 91 etc https://primeacademypune.com/testimonials

After establishing deep roots in IIT JEE training, Prime started guiding students for NEET as well. Results were no different as right from the first batch students came up with flying colours even in NEET. https://bit.ly/timesofindia1 covered the story of hardworking NEET students. For its trailblazing contribution in education, Prime Academy was also awarded as the Best Tutorials in Western Maharashtra by Times group in 2019, this being the latest accolade in its long list of awards.

Prime Academy has been dealing with online lectures and video recordings since 2013 and that gives them an edge to cater students in this Lockdown through virtual classes. Click https://youtu.be/pN1-hyiO9AM to get a glimpse of lectures by Prime Academy faculty. “Post COVID19, we immediately switched to online lectures. Instead of conducting just one lecture a day, now we are involved with students almost for the whole day. Nowadays in the morning we share a 90 minutes video lecture, which is followed by a live (online) session of 2 hours. In-between students revise the topic and solve an assignment sheet. Students clarify their doubts through our online platforms. After every topic a unit test is conducted which is followed by an analysis to identify the scope of improvement.” said Lalit Kumar.

“Amidst lockdown parents are unable to visit the offices of the educational institutes. Neither are they confident in enrolling for a two year course, as they lack the much required confidence to join an unvisited organization, nor are we confident that students will be able to cope up with our lectures, without taking any well-invigilated entrance test. So we recommend students to attend a few lectures just as a demo, without doing any financial transaction. Once a comfort factor is developed from both sides, we offer them the admission” said Vivek Prakash, Head operations, Prime Academy. Prime Academy has launched a 45 days summer course, starting from 16 May. Many important and tricky topics would be covered in such a way that students even with average academic record will be able to crack tough problems of JEE / NEET standard. Students can enroll for this at a nominal cost. “These 45 days will tune their thought process with the requirements of competitive exams and education in general.” said Nishant Guurav, an IIT Kanpur graduate, Head Academics, Prime Academy. Click www.primeacademypune.com to register for a free lecture series at Prime Academy.

Once the lockdown is over, these online lectures will be converted into conventional offline classroom coaching. For those who can’t visit Pune, few of our online batches will continue even post lockdown. Leverage this lockdown to gain the edge!

Disclaimer: This article has been produced on behalf of Prime Academy by Mediawire team.

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[womenscare]

Medical Abortions - Orlando Clinic

Daytime Clinic Same Day Second Trimester | Late Term Abortion Medical Abortion Services

Now Offering One Hour Abortion Pill Procedure – 3 to 12 weeks – Using the Abortion Pill Method – Quick – Pain Free – Immediate Appointments Available – Email 24hourabortion@gmail.com

Introduction

The Orlando, Tampa and Ft. Lauderdale Outpatient and In-Clinic Medical Offices perform first trimester, second trimester and late term abortions.

We have specialized in the induction of second trimester abortion and late termination of pregnancy using out patient and in clinic abortion pill methods for nearly 30 years.

The Percentage of Late Term Abortions account for 1.3% of the total number of abortions in the US. Our Abortion Clinics are one of the few in the US to perform these rare but necessary procedures.

The Abortion Pills that are used to terminate First Trimester, Second Trimester and Late Term Abortions are the same.

First trimester abortions (3 to 14 werks) can be performed in an outpatient setting and second trimester (14.1 to 28 weeks), third trimester (28.1 weeks or further) and late term abortions are completed in second trimester or late abortion clinics.

Our Women’s Center Services include the following:

Medical Abortion Pill Procedures from 3 to 24 weeks

In Clinic Surgical Abortion Services from 3 to 24 weeks

Extensive Evaluation Of Women With Congenital Fetal Abnormalities or Anomalies Incompatible With Life

Referrals To Other Second Trimester and Late Termination Of Pregnancy Clinics when required

Extensive Before and After Procedural Counseling

IV Sedation – For Comfort and Not Remembering Surgical Procedures

Birth Control (Women Condom, Emergency Contraception, Cervical Cap & IUD Insertion)

Ultrasound

Free Pregnancy Testing (walk in)

STD testing and treatment

Well Women Exams (incl Pap Smear)

Women further in gestation (24.1 weeks or greater) are referred to a proper facility in Florida or referred to medical facilities in Maryland, Washington D.C., Northern Virginia, New York, Colorado, California, Washington State or New Mexico.

Large cities in Florida that our Clinics Abortions serve include Jacksonville, Miami, Tallahassee, Gainesville, St Petersburg, Hialeah, and St. Petersburg.

Women travel from from many cities in the US and around the world for the second trimester and late term medication pill.

US cities include Charlotte, Atlanta, Houston, Philadelphia, Chicago, Boston, Phoenix, Los Angeles, Detroit, Nashville, Raleigh-Durham, NYC, and the entire State of New York.

We receive referrals from Abortion Clinics in KY, TN, IL, MS, MO, PA, AZ, NY, TX, MD, NYC, GA, AL, NC, VA, DC and the UK among others.

Women from South America, Canada, Europe, Asia, the Middle East, Carribean, Australia, Africa, and the far Pacific travel thousands of miles to be evaluated and undergo the safe One Day Abortion Pill Procedure at our Florida Abortion Clinics.

Surgical or Medical Abortions are one of the most common medical procedures performed in the United States.

Approximately ⅔ of the morbidity and mortality associated with abortions around the world is due to botched and illegal second trimester and late term abortions.

The majority of deaths related to abortion are hemorrage (massive blood loss) and infection. All abortions should be performed under a safe and medically supervised environment.

Surgical abortions are associated with rare complications that are rare today but still occur. These include uterine perforation, cervical lacerations, bowel and bladder injuries, retained tissue, heavy bleeding, and death. These complications occur less than 1% of the time in experienced hands.

Maternal mortality (death) associated with abortion procedures are 11 to 14 times less than having a full term birth.

Due to the unavailability of Mifepristone (RU486, Mifeprex, Mifegyne, Early Option, French Pill) in the late 80’s and early 90’s, the combined use of Methotrexate and Misoprostol (Cytotec), or Misoprostol alone were used to perform medical abortion procedures.

There are only a few abortion clinics in the USA that specialize in performing third trimester abortions

There is no upper limit of pregnancy that Misoprostol alone cannot be used to terminate pregnancies in a safe and effective manner.

Mifepristone

Mifepristone was first approved in the US for termination of early pregnancies in Sept. 2000. It works by blocking the hormone Progesterone from binding to its receptors on the wall of the Uterus (womb)

Progesterone is required to maintain and continue the growth of the pregnancy. The absence of progesterone causes the breakdown of the pregnancy tissue that is attached to the Uterine wall. This in turn causes separation (detachment) of the fetus.

The modern day Abortion Pill (non-surgical) Process uses the combination of Mifepristone and Misoprostol. Using both pills has a higher success terminating pregnancies compared to Misoprostol alone or Methotrexate and Misoprostol between the 3rd and 10th weeks of pregnancy (94 to 98%; vs 85 to 96%; vs 88 to 97%).

The success rate is higher (97 to 99%) among Abortion Pill Medical Doctors and Medical Facilities with years of experience with using Misoprostol alone.

Misoprostol / Cytotec Medical Abortion Pill: The Facts

Misoprostol is a synthetic prostaglandin medication marketed as Cytotec. It is FDA approved to prevent gastric ulcers.

Its main functions are the following:

Protects from developing Gastric Ulcers

Causes Uterine Contractions

Diarrhea

Abdominal Pain

Misoprostol MOA (Mechanism Of Action)

Prostaglandins cause stimulation of its receptors on the acid secreting cells in the stomach lining. This decreases secretion of acid and forms a thickened mucous layer that protects the stomach lining from acid exposure

Prostaglandins bind to their receptors located on the uterine wall and causes uterine contractions and induction of labor.

Cervical Priming (softening) of the cervix.

The Cervix opens (dilation) due to Misoprostol causing the breakdown of its connective tissue (collagen).

Misoprostol is only FDA approved for preventing or treating gastric ulcers in patients who have prolonged exposure to the administration of non-steroidal anti-inflammatory drugs (NSAIDs).

Misoprostol causes uterine (womb) contractions and is used in several areas of female reproductive health:

Induce labor

Postpartum Hemorrhage (heavy bleeding after delivery (vaginal or C-section)

Misoprostol alone is used for induction of labor to terminate pregnancies in any trimester of pregnancy. It causes passage of the fetus and all gestational tissue

Cervical Priming prior to the following:

IUD insertion – Misoprostol / Cytotec tablets are inserted inside of the vagina or placed underneath the tongue 2 to 3 hours prior to IUD insertion.

This allows minimal to no pain or discomfort when inserting the IUD through the Cervix

Incomplete Abortions – partial passage of pregnancy tissue. Fetal tissue remains inside the cavity of the uterus.

Missed Abortion- non viable fetus inside uterus longer than 5 weeks

Hysteroscopy (scope inserted through the cervix to diagnose and treat various GYN issues inside the uterus

First Trimester and Second Trimester Abortion. Prepares cervix for use of surgical abortion instruments that are used to facilitate removal of pregnancy tissue

Misoprostol / Cytotec can be used for induction of labor in full term pregnancies

Up To How Many Weeks Of Pregnancy (Upper Limit) Can Cytotec/Misoprostol be used For Abortion?

Cytotec/Misoprostol is used to perform medical abortion pill pregnancy terminations in abortion clinics for patients who are 3 to 24 weeks or further (i.e. abortions at 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36 weeks).

In the third trimester of pregnancy (28.1 weeks or further), there is generally a therapeutic medical reason for pregnancy termination. This should include maternal (physical or mental) health issues, rape, incest or fetal congenital abnormalities or anomalies that are incompatible with life

The use of RU 486 (Mifeprex/Mifepristone) in second trimester and late term abortions when taken 36 to 48 hours prior to giving Misoprostol accelerates the completion time of the procedure compared to using Misoprostol alone (6 to 8 hours vs

10 to 18 hours).

The process is completed 99% of the time within 24 hours without compromising safety

[addictionrecoveryassistance]

Detox Centers In Olympia Washington 98501

Contents

Featured substance detox support

Heal. grow. change

Addiction treatment business

Affected person realize

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[lord-pigasus]

The (cis)Women’s March on Washington

The women’s march this saturday was monumental. With three and a half million people participating worldwide it was a triumph of getting people into the streets. My wife and I went to the Washington DC march with a group of 15 women from tennessee and were blown away by the amount of people there. We were packed in like sardines, filling the national mall and all it’s side streets. With 700,000 people, we couldn’t even march, we just poured into the streets and went every direction. But, just getting people to show up isn’t enough to win the fight against fascism. We must keep this momentum growing. We must channel this momentum into other forms of action that directly improve the lives of oppressed people. Most importantly, we need to defend all of the oppressed people in this nation, not just the women in your circle. This was the biggest failing of the march. The voices of black, disabled, indigenous, queer, and latina women were hard to hear over the endless rows of straight white allies. As a trans person at the march i felt no solidarity from the other marchers, only thinly veiled hostility. My wife and I arrived early into a forming crowd of marchers about one block away from the main stage. The crowd was totally dead so we decided to lead some chants to get the energy up. WHO”S STREETS? OUR STREETS! WHO”S COUNTRY? OUR COUNTRY! WHO”S BODIES? OUR BODIES! WHO”S BODIES? OUR BODIES! Seconds after the chanting died down, a woman standing in front of me said “of course it’s always a man to lead the first chant” and when I tried to correct her she ignored me, pretending that i wasn’t even there. From that point on, i was constantly misgendered. One woman even told me that if i wanted to not be misgendered that I should have worn a dress. That woman was allowed to wear pants and so was every other woman in the march, but trans women always have to jump through extra hoops just to be treated with human dignity. We always have to prove our womanhood to people who only want to commodify our voices. Among a sea of half a million cis women, i felt invisible and silenced. Signs like “ovaries before brovaries”, “if men had periods, tampons would be free” , and the infinite variations of “pussy grabs back” were based on equating womanhood with having a vagina. This cisnormative gender ideal is blatant body policing and transphobia. It’s insulting and exclusionary towards trans marchers. Not all women have a uterus, and women aren’t the only people with a uterus. And even though we don’t have cisnormative bodies and identities, we still need feminism to fight for us in these next four years. We rely on Planned Parenthood for STD testing, birth control, and abortions. We can’t find jobs, and when we do we’re paid far less than the cis. We are being tormented in our schools, kicked out of our homes, and murdered in the streets. Planned Parenthood, NARAL, the march leadership, and every cis woman who attended one of the marches need to think long and hard about who their rhetoric is for, and who it hurts. Until there is trans, non-binary, and intersex leadership, i have a hard time believing that these groups are fighting for my rights. WHO”S BODIES? CIS BODIES! WHO”S BODIES? CIS BODIES!

[fenyutas]

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[xpresscareurgent]

You can even find clinics offering free HIV testing in DC. Even if you don’t want to avail of the free HIV testing facility, you can visit a private STD testing center near you to get tested in a reliable and professional manner. The top DC testing labs ensure a high level of patient confidentiality while ensuring that your privacy concerns are also addressed appropriately.