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I know there are VTOL craft meant to take off and land with a vertical trajectory. But, under the perfect wind conditions, could a normal airplane ever land (safely) with a vertical or nearly vertical trajectory?

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    $\begingroup$ I don't have video, so I'll leave this as a comment - my father, Capt. Andy Alsop, landed a Loganair Britten Norman Islander at a ground speed that was slightly backwards. This is because the landing speed is about 52kts and the wind that day in Orkney had increased to nearly 60kts. $\endgroup$ – Rory Alsop Oct 10 '15 at 17:11
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    $\begingroup$ Well if it could take off... $\endgroup$ – fooot Oct 12 '15 at 14:49
  • $\begingroup$ Can it? Yes. Safely? No. $\endgroup$ – vasin1987 Oct 14 '15 at 3:45
  • $\begingroup$ Is there anything I can add to my answer for you? $\endgroup$ – Simon Oct 17 '15 at 9:08
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Yes.

I assume that you do not have a good understanding of aerodynamics. I apologise if that is not the case.

The way to think about these sort of questions is to ask "does the aircraft know that it's moving in relation to the Earth". The answer to this is "no".

The only thing that matters, and the only thing that the aircraft cares about is airflow (wind) over the wings.

Ignore all sorts of little side effects and imagine an aircraft needs 70 kph of wind over the wings to generate lift and stay afloat, straight and level.

Now, imagine the aircraft is flying along and you could somehow make the Earth disappear but leave behind gravity and the atmosphere. What would happen to the plane? Nothing! It still has 70 kph of wind over the wings and it keeps flying.

Now put the Earth back. It still keeps flying.

If the pilot reduces the power to 69 kph ("thrust X"), the force generated by lift pushing the aircraft up is a little less than that generated by gravity pulling the aircraft down and the craft will start to descend. Eventually, it will land (assuming that you remembered to put the Earth back!).

So two scenarios. First, one where the air is perfectly still and the thrust from the engine ("thrust Y") is pushing the aircraft forward at 70 kph. Second, where the wind is blowing at 70 kph and thrust Y is such that the aircraft is stationary with respect to the Earth. Again, the aircraft does not know, or care, that it is stationary with respect to the Earth, just that it has 70 kph of wind over the wings.

Modify the second scenario slightly so that the wind is now 69 kph. The aircraft moves forward at 1 kph. Again, the aircraft does not know, or care, that it is going fowards with respect to the Earth. The wind over the wings is still 70 kph (speed of wind, 69, plus speed of aircraft 1).

Reduce the thrust to X again and the aircraft will start to descend, and also become stationary. Eventually, it will land with no forward or backward speed.

In reality, this would be almost impossible since the wind is never of a constant speed from a constant direction so little movements would always be taking place.

I have seen a video, which I can no longer find, of a bi-plane which took off into a strong wind, flew backwards down the runway and landed on a spot before the one it took off from.

This comes very close. With just a little more wind, a vertical landing would have been possible.

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  • $\begingroup$ There was a great book on aviation history (forget the name - sorry) where a passenger plane took off into the famously strong winds of Patagonia and made no headway pretty much beyond the end of the runway where it flew until finally running low on fuel and (almost crash) landing. $\endgroup$ – GDB Oct 11 '15 at 2:35
  • $\begingroup$ Need to keep that video link handy. It's the perfect answer for every "fly backward", "take off from a treadmill" type question, ever. $\endgroup$ – FreeMan Oct 12 '15 at 14:49
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    $\begingroup$ I understand the aerodynamics; the two things I was really after with my question were (a) since fast wind near the ground is usually fairly turbulent (as a result of uneven land contours and man-made structures), if that might interfere with landing at speeds comparable to the wind's speed, and (b) what sort of wind conditions and what sort of plane would such a feat require. $\endgroup$ – AJMansfield Oct 12 '15 at 14:56
  • $\begingroup$ @AJMansfield Well, that's a different question (sort of wind and what plane) but you're right about the turbulence, which is why I said almost impossibe. The Highlander in the video gets awfully close and with a little more wind, if you're prepared to accept the odd kph plus or minus due to the turbulence, then it would have been vertical. With a really responsive engine, a very fine throttle control and a pilot with excellent reactions, it should always be doable. $\endgroup$ – Simon Oct 12 '15 at 15:50
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Under the perfect wind conditions, could a normal airplane ever land (safely) with a vertical or nearly vertical trajectory?

Yes, watch this video: Alaska Super Cub, 10 foot landing, 10 foot take off. Had the wind been a bit stronger the plane would have landed at a null horizontal speed.

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  • $\begingroup$ I suppose the question, then, is whether such a maneuver would ever be considered "safe". A headwind at or near the design takeoff/landing speeds would very likely exceed the maximum crosswind components by a fair margin, and so as soon as the airplane tried to turn off the runway, it would be blown over like a leaf. $\endgroup$ – KeithS Oct 13 '15 at 2:20
  • $\begingroup$ Even if the aircraft continued to face into the wind the whole time it was at an airstrip, it would need to maintain engine power on the ground sufficient to overcome drag from the wind on the leading edges (a little more than approach RPM given that the flaps would be retracted on touchdown), and let us not forget that while the ground speed may be zero, the wind speed definitely isn't, so anyone attempting to deplane is not going to have a very fun time of it. $\endgroup$ – KeithS Oct 13 '15 at 2:23
  • $\begingroup$ great video, @robert werner. In a 40HP J-3 cub it is also possible in a very strong headwind to fly slowly backwards. Not a good idea when close to the ground as the cub has no rear-view mirror ;-) $\endgroup$ – niels nielsen Feb 15 '18 at 5:28

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