If I fly close to stall speed with a STOL plane and gust of 20kts tailwind comes at me,it will cause sudden reduction in lift ,becuase plane has inertia so it can not accelerate instantly.
How dangerous is this situations?
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2 Answers
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No. Any airplane (big or small) flies relative to the air in which it is moving. So, if there's a 10 knot tailwind, the airspeed of the plane will remain the same, while the ground speed is increased by 10 knots. And since ground speed doesn't affect lift, then there is no change in lift produced.
Having said that, there are two situations where the wind speed is relevant:
When the wind speed changes rapidly (called wind shear), the airplane's inertia keeps it from changing speed instantly. If the shear is very severe, this might lead to a momentary loss of lift, which the passengers will experience as slight turbulence.
During takeoff and landing, the airplane is actually touching the ground, therefore, ground speed suddenly becomes relevant. This is why airplanes always take off and land into the wind whenever possible, to get as much lift as possible at a lower ground speed.
answered Dec 22, 2020 at 22:02
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$\begingroup$ Re passengers experiencing wind shear as "slight turbulence", note that it has been the cause of quite a number of crashes. $\endgroup$– jamesqfDec 23, 2020 at 5:04
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If the wind is constant, it doesn't matter. The aircraft move relative to the surrounding air, and doesn't care how the air moves relative to the ground. If the aircraft has an (true) airspeed of 100 knots, and a tailwind of 100 knots, it's flying 200 knots relative to the ground. If the aircraft turns into the wind it will stlil fly 100 knots relative to the air, but 0 knots with respect to the ground.
The danger comes with gusts. If the aircraft is flying 100 knots airspeed in a 10 knot tailwind, it is flying 110 knots relative to the ground. If there is a gust of wind increasing the tailwind to 50 knots in an instant, the groundspeed will still be 110 knots. The airspeed will thus suddenly drop to 60 knots. That's the kind of speed drop that can cause stalls and crash aircraft.
answered Dec 22, 2020 at 21:58
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$\begingroup$ Yes constant wind dont exist,at least where I live.. $\endgroup$– user52248Dec 22, 2020 at 22:28
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2$\begingroup$ @Aeolus That's because you live on the ground. Trees, buildings, etc. create a lot of turbulence, which you feel as changing wind. Up where airplanes fly, the wind is almost always pretty constant. $\endgroup$ Dec 22, 2020 at 22:33
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1$\begingroup$ @Aeolus that trimaran crash was nowhere near 40 knots of wind. I guess it was 15 knots wind. Gusts are more difficult to assess, but I'd be surprised if there was more than 25 knots. Incredible how the didn't release the main sheet or steered upwind... probably a jammed sheet and then taken by surprise. $\endgroup$– DeltaLima ♦Dec 22, 2020 at 23:11
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1$\begingroup$ @Aeolus Part of any student pilot's primary flight training is navigation by dead reckoning. If I'm flying at 100kts, it should take me 30min to reach an airport 50nm away. But if I have a 50kt tailwind, then my ground speed will actually be 150kts, so I'll reach the airport in 20min. The winds aloft are steady enough that this was the primary navigation method before radio navaids were invented, and still serves as a useful backup. Now, that's not to say that gusts that severe don't occasionally happen. But, unlike boats, planes aren't in contact with the water, so there's nothing to resist $\endgroup$ Dec 23, 2020 at 0:11
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1$\begingroup$ the change beyond the plane's own inertia. So, as I mentioned in my own answer, there's a momentary gain/loss of lift, i.e. turbulence, then the plane adjusts to the new airspeed and keeps flying. $\endgroup$ Dec 23, 2020 at 0:11
some validity????? Your problem is that you are stuck with constant wind speed and not give up.I know that you know what my question is,but your intetion from begginig is to devalue my question. $\endgroup$