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An electric, vertical takeoff drone lifts a manned glider 5 km in the air. The glider is then released from the drone, and glides 50 km to carry its passengers across a lake. The drone meanwhile simply descends vertically back to the ground to where it took off from, without passengers or a pilot on board.

Would this sort of “glide slide” be viable? Is it a way of realizing the advantages of electric flight (in niche situations, for very short flights across physical barriers like Great Lakes) while minimizing the problem of battery weight? And of realizing the benefits of gliding without needing a towplane (which in turn requires a second pilot, a runaway, etc.)?

[Or perhaps, alternatively, instead of having a vertical takeoff drone lift a glider, you could have an electric plane which takes off on a runway but then drops its batteries by parachute back down to earth once the plane reaches altitude, and then the plane glides the rest of the way...]

And what about pushing the concept to far more extreme lengths even? Instead of rising vertically 5 km and then gliding 50 km diagonally back down to earth, what about a (much smaller) glider being lifted 20 km vertically and then gliding 1000 km across?

I know nothing, so would love some feedback here.

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    $\begingroup$ All you suggest is feasible, getting certified for commercial carriage of passengers is another thing entirely. I'm pretty sure the FAA would frown on the lack of missed approach capability. $\endgroup$ Commented Nov 30, 2022 at 0:13

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With a cheap source of electricity the concept might be viable, if only for tourist flights.

Another approach might be with a balloon. Here the lift is free and great heights are possible.

Or, perhaps, a combination of the 2 using electric props, an aerodynamicly shaped dirigible, and solar cells as sustainers.

A realistic glide ratio for starters may be 1:15 to 1:20, so 20 km lift could be around 300 km glide, not 1000.

Using a battery pack to climb, and then dropping it?

Surprisingly, this will not affect the glide range. Reducing weight once you're up there only throws away potential energy that can be used for a faster glide. And, if you keep your batteries, the glide could be "stretched" quite a bit with some propulsion.

If the plane can lift all the weight to extreme altitude, with batteries, it may be better just to have a charger at the destination.

However, climbing to higher altitudes does have advantages on longer trips. Extra energy climbing to altitude must be weighed against energy savings at that altitude$^1$. Airliners these days take this approach all the time, with the added bonus of being able to fly over bad weather most of the time.

$^1$ true air speed is greater than indicated airspeed in thinner air

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  • $\begingroup$ That's great, thanks very much for the answer. I had considered the balloon idea, but wasn't sure it could be done safely or comfortably for passengers... what do you think? And I guess more importantly, how big might the aircraft be? If you were okay with a very low glide ratio, could you have a high passenger capacity? Hypothetically, could a high-passenger-capacity plane cross a Great Lake (40 km, say) from a 20 km-altitude balloon? $\endgroup$ Commented Nov 29, 2022 at 23:51
  • $\begingroup$ Look into the lifting capacities of the airships from the 1920s to 1930s. The $Hindenburg$ could lift over 200 tons, and modern swiveling electric motors with aerodynamic shaping would only add more, especially with a runway. $\endgroup$ Commented Nov 29, 2022 at 23:58
  • $\begingroup$ One might start at 12 km, with a very modest 10 to 1 glide ratio. Remember, from a balloon drop, an initial dive is needed to gain best gliding speed. From the altitude where this speed is attained with the plane stabilized on its glide path, apply the glide ratio to get your distance. $\endgroup$ Commented Nov 30, 2022 at 0:37
  • $\begingroup$ Would it be possible for the glider to take off vertically from the balloon, so as to give the passengers a more comfortable ride - in other words, to avoid the dive? And could a balloon that is only intended to move vertically for the most part (unlike the Hindenburg) be built in such a way as to have a much larger lift capacity? $\endgroup$ Commented Nov 30, 2022 at 1:57
  • $\begingroup$ A very large carrier could support a launch system, almost like an airborne "flat top". Bouyant lift could support the carrier, but the issue would be how to land it after dropping the glider. The combination of aerodynamic lift for the glider and bouyant lift for the carrier (hybrid airship) seems the most feasible approach for now. $\endgroup$ Commented Nov 30, 2022 at 5:02
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Making a glider gain altitude by lifting it up vertically using a drone or a crane does not make much sense. It's a bit like denying the fact that the glider has wings.

To make an analogy with the bicycle, it's like attaching a trailer to it, and deciding not to use the wheels on the trailer, i.e. using a drone to lift a glider vertically would be like loading both the trailer and the trailer's payload onto the bike's luggage rack.

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Boeing experimented with a strategy to launch a parachute via rocket, and then use that as a winch point in the sky. A rope would connect the falling parachute to a glider on the ground on one end, and a winch on the other. (To others at SE.Aviation: I forget the name of this program, so sadly cannot find references for it. Please drop it in a comment if you know it.)

Possibly a more viable strategy would be to have a parachute which is held aloft by a balloon. The same principle applies, which is that the winch point is in the sky and so launches wind up much, much higher. However, in this scenario after every launch the balloon returns the parachute to its maximum height, thus allowing repeated launches for (almost) no more energy than is required to satisfy the glider's potential and kinetic energy gains.

Modern gliders reach 60:1 glide ratios or better. Even a 787 has a 20:1 glide ratio. So 5km height would be amply sufficient to go 50km, with all but the strongest headwinds.

Michael Hall's excellent point that the FAA wouldn't appreciate the lack of go-rounds is arguably met by having a system which has just enough battery power to execute a go-round. There are plenty of motorgliders which can validate the concept.

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  • $\begingroup$ You need to subtract the kinetic energy to get the glider to best glide speed from the potential energy added by lifting the glider up. Say the best glide speed is 50m/s then this altitude is 130 m without conversion losses. I would at least double this for realistic figures. $\endgroup$ Commented May 1, 2023 at 8:35
  • $\begingroup$ @PeterKämpf I think this is what I was saying, but I added the word "glider's" to clarify that section. Let me know if this is different from what you meant. $\endgroup$ Commented May 2, 2023 at 12:03

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