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A society lives on geostationary platforms at some vast height above the ground. The platforms themselves are not affected by gravity, wind, etc. Their technology has only just reached the point where they can construct biplanes about equivalent to a Sopwith Camel. Unfortunately, they do not have the knowledge or resources to expand their platform enough to build a suitable runway, so they resort to a different technique: steering the plane off of the edge of the platform.

Is this feasible? And if so, from how high would the plane have to fall to safely clear the ground and attain level flight? Would the pilot still be conscious by the time the plane reached this point in order to fly it?

On a side note, would such a plane be able to land again by stalling its engine and steering down like a glider? (again, because of the lack of a runway).

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    $\begingroup$ related questions on aviation.SE: aviation.stackexchange.com/q/16800/1467 aviation.stackexchange.com/q/8565/1467 $\endgroup$ – Federico Aug 11 '17 at 7:47
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    $\begingroup$ Note that "geostationary" typically implies an orbit (one where the orbital period exactly matches the rotation rate of the surface below, such that the point to nadir -- directly below -- remains geographically the same). If you mean remaining stationary in an atmosphere, then I believe the most common term would be hovering. $\endgroup$ – a CVn Aug 11 '17 at 8:36
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    $\begingroup$ Also, here's a term for you to look up: glide ratio. It specifies how far a given aircraft can glide while losing a given amount of altitude, usually expressed as a ratio (so you might see a jet airliner with a glide ratio of 10:1, meaning for every 1 km it drops vertically it'll glide 10 km horizontally; or a glider with a 100:1 ratio, meaning it drops 100 meters for a 10 km glide). $\endgroup$ – a CVn Aug 11 '17 at 8:39
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    $\begingroup$ How high? It makes a big difference not least because WW1 aircraft had a pretty limited ceiling. Their engines were not able to work at high altitudes. $\endgroup$ – James K Aug 11 '17 at 10:39
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    $\begingroup$ @JamesK, these engines would probably be built to work at the altitude where the platforms usually float. If the platforms are high enough, it would mean the engine would be overboosted and blow up if operated on full throttle near the ground, but they wouldn't, at least initially, intend to go that low anyway. $\endgroup$ – Jan Hudec Aug 11 '17 at 13:11
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Yes, they would fly. Once dropped, a plane would pitch nose down, and fall, once it got above stall speed, you could pull the stick back, and enter level flight.

Here is video of a similar idea, in this case a "parasite fighter" dropped from a blimp

https://youtu.be/DTGBFY82Gik?t=100

Here is a more modern one, of a plane actually pitching off of a cliff

https://youtu.be/uNCT9bnlBK4

Recovery would be more difficult, since you would have to kill your velocity somehow. Fortunately a WW1 biplane has a very slow stall speed. You could capture into a net, or an arresting cable, like on an air craft carrier. since you are on a high platform, the cable could be on the bottom of the platform, and the landing hook on the top of the plane. The plane could come in at under 50 MPH and hang itself on the cable. The cable stretching could absorb the rest of the plane's energy.

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    $\begingroup$ I forgot about parasite aircraft! Now that you've mentioned it, I'll have to look into them some more. $\endgroup$ – null_dynamic Aug 11 '17 at 5:46
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    $\begingroup$ The aircraft could also kill off more speed by going on a ballistic curve. The plane would come in below the platform and turn up. This would trade speed for height, but as long as the plane would use inertia and not wings to keep going, it would remain controllable. With a bit of practice, it could meet the arresting gear at the top with almost no speed. The result would look something like the hammerhead, except the plane would probably pitch nose down rather than to the side and meet the arrestor just below the top. $\endgroup$ – Jan Hudec Aug 11 '17 at 8:42
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    $\begingroup$ @JanHudec +1 to your comment because this is how birds do it, so the people would have observed the technique. $\endgroup$ – Whelkaholism Aug 11 '17 at 12:51
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    $\begingroup$ +1 but I would add one note for clarity: This civilization would need to have figured out the importance of putting center of gravity in front of the center of lift. Otherwise, it will not naturally pitch nose-down after dropping. If the CoG is aft of the CoL, a dropped aircraft would fall tail-first, which is not very conducive to flying. $\endgroup$ – reirab Aug 11 '17 at 15:13
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    $\begingroup$ @reirab. Granted, the poster did specify WW1 biplanes specifically, which are in the required configuration. However, the evolution of this civ's flight program would be a very interesting story, given that their brave pilots would need to cliff dive in untested hardware. $\endgroup$ – Nate White Aug 11 '17 at 15:38
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Yes. In fact, it has (essentially) already done in actual history. Granted, the "parasite aircraft" experiments of the 1910-1930 were launched from "rigid airships" rather than floating platform cities, but the concept is the same.

You will still have to work out a landing plan, however, as early "parasite aircraft" designs relied on a ground-based runway for the smaller planes to land, and later designs required the smaller plane to match speeds with the airship to latch back on.

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If those platforms are flying at an altitude where there is breathable air, and stationary over the ground, then the wind speed at the platform might well be enough to provide stall speed for the plane. Turn the platform into the wind and launch or recover your planes.

Aircraft carriers do the same at sea level, which could be a constraint on maneuvers. If your platform does not maneuver, you might have to wait for the right weather conditions.

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  • $\begingroup$ Using the wind to slow the planes is a pretty cool idea; I'll have to look into that sometime. $\endgroup$ – null_dynamic Aug 11 '17 at 5:42
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    $\begingroup$ Even aside from carriers, while we can't actually rotate the runway at an airport, we do try to pick the runway with the most headwind for both takeoff and landing. Maximum headwind allows flying with the least groundspeed, reducing the ground roll for both takeoff and landing. $\endgroup$ – reirab Aug 11 '17 at 15:16
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Re: landing - the "modern" Antonov AN-2 has no rated stall speed ... the pilot manual apparently says

"If the engine quits in instrument conditions or at night, the pilot should pull the control column full aft and keep the wings level. The leading-edge slats will snap out at about 64 km/h (40 mph) and when the airplane slows to a forward speed of about 40 km/h (25 mph), the airplane will sink at about a parachute descent rate until the aircraft hits the ground."

If there was a routine need for such landing characteristics, all aircraft would be designed that way.

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Geostationary platforms would be much to high, unless your planet has very high gravity or a huge atmosphere.

For example on earth, a geostationary orbit has a height of around 36,000 km (22,000 miles) above the surface. Compare that with the maximum operating height of most propeller-powered aircraft which is less than 4 miles. Most modern jet engine powered aircraft only have a maximum altitude of around 8 or 9 miles - i.e. only twice the height of Mount Everest. The "official" operating ceiling of a Sopwith Camel is a bit lower than the summit of Everest.

Even if you could launch the plane successfully (and it would have to be designed to withstand very high speeds while it was still in free fall, and then slow down as the atmosphere became denser) there is probably no way it could climb back to the altitude of the platform to land.

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The Sopwith Camel had a take off run of about 49 meters (length of the deck of HMS Furious, from which they took off during the Tondern raid).

If your platform doesn't have 50 meters to host a road, I wonder how can it host a society.

Nevertheless, if the plane does an incomplete run and then goes nose down, it can reach a sufficiently high velocity to sustain flight (I think it is normal advice for pilots to go nose down when the plane is about to stall).

Vice versa, landing by stalling is a tad more tricky. Said Sopwith Camel could take off from the 49 meters deck, but the landing on that deck was described "as safe as ditching into open water". What can be tried is to set the plane with 0 velocity with respect to the landing strip and then stall, so that the plane will "sit down" on the ground. You can do it with a ship (that's how Sopwith Camels attempted landing on those carriers), I don't know if you can do it with your platforms.

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    $\begingroup$ "Vice versa, landing by stalling is not generally feasible." It's very feasible in an old biplane, and in fact it's pretty much the only way to get onto the ground. The trick is to stall at as low an altitude as possible, of course (i.e. 10 feet or so!) With a head wind, some old planes can even fly backwards relative to the ground - stall speeds can be as low as 30 knots. $\endgroup$ – alephzero Aug 11 '17 at 7:30
  • $\begingroup$ @alephzero, edited my answer. $\endgroup$ – L.Dutch - Reinstate Monica Aug 11 '17 at 7:33
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    $\begingroup$ Definitely not true that "once the airplane stalls, it simply goes down like a stone". A stall just means that the wings generate less than their maximal lift at the current airspeed, not that you get zero lift. Recovering from a stall after it sets in is a basic piloting skill. $\endgroup$ – Henning Makholm Aug 11 '17 at 9:45
  • $\begingroup$ See Antonov AN-2 for a counterexample. $\endgroup$ – Brian Drummond Aug 11 '17 at 10:52
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    $\begingroup$ Counterexample to stalling "like a stone", sorry it was unclear. $\endgroup$ – Brian Drummond Aug 11 '17 at 11:04
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It's been done. The military had an airship aircraft carrier pre-WW2 which launched bi-planes by dropping them and recovered them by a hook under the airship. To 'land' the pilot had to fly up under the airship and hook the plane onto the carrier at the apex of a climb/stall via a loop on the wings. If he missed he could dive, recover speed and try again.

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If by "geostationary", you mean fixed position over ground, there could be problems with too much or too little wind. Under ideal conditions, it would be like the parasitic aircraft scenario described in other answers. WWI-era biplanes had relatively low stall speeds; they would't have to fall very far in still air to gain flying speed.

Consider a common airshow stunt: the tailslide. An aircraft pulls up into vertical flight and throttles back to idle. It momentarily comes to a complete stop in the air before sliding backwards; it very quickly acquires enough airspeed to flip around into a vertical dive and then recover. This clearly demonstrates how any aerobatically capable aircraft (like a WWI fighter) can be simply dropped and fly out of it. The only snags might be fuel delivery and oil containment. Early airplanes may have had problems with zero or negative G inducing fuel and/or oil starvation/flooding or oil going where it doesn't belong (or exit the engine entirely).

Not enough relative wind on landing can be a problem. Without any runway, the aircraft has to slow to zero airspeed, at which point it will fall and most certainly break when it contacts the landing surface. But, a very short runway may suffice. Aircraft carriers provide only short runways (relative to the flying speeds of the aircraft they host) for both takeoff and landing; suitably equipped aircraft are assisted by catapult to achieve flying speed in very short distances and are likewise stopped in short distances with the aid of arrestor gear.

If your floating platforms are geostationary in high-altitude winds, it may be too much for a WWI-era aircraft to handle, either taking off or landing.

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