#dh 4 aerocycle

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FLIGHTLINE: 199 - US ARMY VTOL EXPERIMENTS #1 - FLYING PLATFORMS

-The de Lackner HZ-1 Aerocycle, one of a pair of flying platforms commissioned by the US Army in the 1950s.

FLIGHTLINE: 199 - US ARMY VTOL EXPERIMENTS #1 - FLYING PLATFORMS

During the 1950s, a number of single-soldier platforms were built for the US Army, but none proved successful enough for production

HILLER VZ-1 PAWNEE Originally conceived of by Charles Zimmerman and built by Hiller Aircraft Company's Advanced Research Division (A.R.D.) under a 1953 Office of Naval Research contract (the ONR was acting as a technical agent for the Army), the HO-1 (later redesignated the VZ-1) was essentially a platform over a ducted fan (a fan or series of fans inside an enclosure or "duct" which improves the efficiency of the blades) on which a soldier stood. Zimmerman intended for the platform to be maneuvered "kinesthetically", leaning his body in the desired direction of travel, which it was hoped would be not only effective but easy to learn. Construction of the first prototype, officially the Model 1031 Flying Platform, began in January 1954, and was delivered for testing in September under the designation YHO-1E. Flight testing began soon after, with the first untethered flight taking place in January or February 1955.

-Diagram for the Model 1031 from the original patent filing. | Illustration: Hiller Aircraft Company

The first prototype was almost 7 1/2 feet tall, with a diameter of 5 feet and a weight of approximately 440lbs. Two Nelon H-59 piston engines, rated at 44hp each, drove a pair of contra-rotating two-bladed aluminum propellers. On the ground the platform rested on four legs. The controller's platform provided a railing and attachment points for safety belts, as well as twist controls for the throttle and propeller torque, used to adjust the 1031's altitude.

-A test pilot flying the first Model 1031 prototype. | Photo: Hiller Aircraft Company

ONR and the Army were impressed enough with the results of the test program to order two more prototypes as the VZ-1 and VZ-1E Pawnee. The second prototype (s/n 56-6944), which first flew in 1958, was larger (8 feet in diameter, 7 3/4 feet tall) and heavier (460lbs empty, 660lbs max). This increased mass required larger propellers as well as a third H-56 engine to match the first model's performance. Like the early Model 1031, the VZ-1 could achieve a maximum speed of 16mph. The pegs of the 1st unit were replaced by casters to ease moving the platform while not under power. As the test program proceeded, Hiller engineers uncovered a limitation of the ducted fan design in that the vehicle could not climb out of its ground effect, limiting the Pawnee to an altitude roughly equal to twice its diameter. The first two platforms also proved to be stable and self-righting, but this was a double-edged sword, as the pilot was fighting to employ the kinesthetic maneuvering.

-A soldier aims his rifle from atop the second VZ-1 Pawnee. | Photo: Hiller Aircraft Company

Hiller attempted to address these issues with the third prototype, designated the VZ-1E (s/n 56-6945), which first flew in 1959. While maintaining the eight foot diameter of the second model, the -1E had a duct of greatly increased height, with the vehicle standing nearly nine and a half feet tall. The caster wheels of the earlier VZ-1 were gone, replaced by a single circular skid, and the pilot's pedestal was replaced by a seat with helicopter-style controls, the Pawnee having grown so large as to make the kinesthetic controls useless. The VZ-1E had the best performance of the series, achieving a maximum altitude of 33 feet, but it was still as slow as the others.

-The VZ-1E, last model of the Hiller Pawnee flying platform. | Photo: Hiller Aircraft Company

Six total examples of the Pawnee were built by Hiller, but by the end of the test program in 1963 the US Army decided that they were too slow, fragile and ultimately limited battlefield use.

Hiller continued to use the various Pawnees for research on ducted fan technologies, but the Army abandoned the VZ-1. Of the six completed, only two original VZ-1s remain. One is at the Hiller Aviation Museum in California and the other is at the Udvar-Hazy Center of the Smithsonian National Air & Space Museum. A replica of the first Model 1031 was built for the Evergreen Aviation and Space Museum in Oregon.

DE LACKNER HZ-1 AEROCYCLE Development of the Aerocycle, originally called the Heli-Vector, began at approximately the same time as the Pawnee, and also incorporated Charles Zimmerman's kinesthetic control concept, but instead of a ducted fan the Aerocycle the platform, given the company designation DH-4, used a somewhat more simple arrangement of a central pod, supported by outriggers, supported the engine and two counter-rotating, two bladed rotors, over which a platform for the pilot was placed. As with the ZV-1, the pilot simply leaned in the direction he wanted to go, while motorcycle style grips controlled the engine.

-An Aerocycle being flown by a soldier during the test phase. | Photo: US Army

Power for the DH-4 was provided by a Mercury Marine 20H outboard motor, which produced 40hp. The motor was connected to a chain reduction unit, and drove the two 15' diameter rotor blades via a belt drive. The first Aerocycles rested on one central airbag supported by four smaller outrigger bags which allowed landing on soft ground or water, but this was replaced later by helicopter-style skids. The DH-4 stood seven feet tall from the ground to the handlebars, which in addition to giving the pilot something to lean against to guide the Aerocycle also supported several basic flight instruments. The vehicle weighed 172lbs empty, while at max load that climbed to 454lbs, including the pilot and one gallon of gasoline, whith allowances for 120lbs of slung load cargo or a five gallon auxiliary tank, which increased the range to 50 miles. The pilot and engine were secured to this column by safety straps. The DH-4, which made its first tethered flight on 22 November 1954, followed by a free flight in January of 1955, attracted enough interest from the Army to result in a contract for a dozen production models, initially designated YHO-2, subsequently changed to HZ-1.

-Several revisions to the pedestal and airbags were made during the course of the program. | Photo: US Army

Extensive testing proved that the Aerocycle was as easy to learn (Zimmerman claimed 20 minutes of instruction were sufficient) as promised, and was quite stable despite appearances, but it was also a higher performance vehicle than the ZV-1, with a top speed of 75mph and a ceiling of 5,000 feet. Additionally, the low-mounted rotors kicked up enough dust, rocks and other debris to be a hazard. Two serious by non-fatal accidents occurred during testing, both involved the rotors inadvertently intermeshing and shattering, resulting in an immediate loss of altitude as well as control.

-The shattered remains of one of the HZ-1s after the rotors collided. | Photo: US Army

Flight tests were halted while the cause of the accidents was investigated, over the course of which several HZ-1s were tested in the full-scale wind tunnels at Langley Research Center. Although an uncontrollable pitching was observed at high speed, this was determined to not be the cause of the two crashes. With the cause undetermined, and with Army interest in the program waning, the Aerocycle was withdrawn by 1960. Out of the 12 HZ-1s produced, only one survives, on display at the US Army Transportation Museum at Fort Eustis, Newport News, Virginia. The DH-4 prototype has also been preserved, and is on display at the Evergreen Aviation and Space Museum.

-The last HZ-1 on display at the Army Transportation Museum. | Photo: Miles Lumbard 

-The DH-4 AeroCycle at the Evergreen Museum. | Photo: Daderot

[thegikitiki]

Watch Your Step!

   Lackner HZ-1 Aerocycle, 1954