#so like itll be cooler than ground level but i think the oxygen content should be roughly similar?

[svvitchfoot]

Science in the Sky: How do Hot Air Balloons work?

Hot air balloons are the simplest version of human flight. Invented in 1783, they really haven’t changed much over the years. All you really need to fly is the balloon (called an envelope), a means of burning fuel, and a basket.

Hot air balloons work on the scientific principal that warm air rises, compared to the cooler air around it. As the air inside the envelope is heated, it’s warmed up, and is warmer than the outside air. This is how the balloon is lifted off the ground, and stays in the air. As the balloon gets higher up in the atmosphere, the temperature of the surrounding air drops, so the hot air of the balloon is able to keep the balloon afloat.

In all cases, the hot air is warmed by a burner, usually fueled by propane (like the stuff you’d use for an outdoor or camping grill, or some kinds of lanterns). Propane is a hydrocarbon chain, that is, it’s three carbons bonded in a line with hydrogens bonding to the carbons. Hydrocarbons are really effective at storing and releasing energy, which the release of energy we call combustion. Propane burns at ~3,600F, which is really hot, but really good when you want to heat a large amount of air pretty quickly, as in the case of trying to get a hot air balloon off the ground. To release hot air, there’s a vent at the top of the envelope that the pilot can open and close to either slow down while going up, or if the vent is open for a long time, the balloon starts to sink.

So how do you steer a hot air balloon? Well, you kind of don’t. You’re at the mercy of the wind, but wind isn’t consistent in the atmosphere. Have you ever watched clouds pass by in the sky? The clouds move because of wind in the upper parts of the atmosphere, but there isn’t necessarily wind at ground level, or wind in the same direction, or wind of the same strength. The wind changes at different heights in the atmosphere (well, until the atmosphere is too thin to have air currents, but that’s a lot higher up than a hot air balloon with people in it is going to go, since humans kinda need air and warmth to survive), so to go in different directions, a balloon pilot would burn more fuel to catch a wind current above them, or vent air to drop down to a wind current below them. 

In short, hot air balloons are pretty cool if you want to go a short distance, or go no distance at all, or play a live show, but pretty terrible for long distance flight. Thank goodness we invented airplanes.