# How dangerous are tailwind gusts for STOL aircraft?

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?

• It's only a problem when taking off. The rest of the time it's a plus. – John K Dec 22 '20 at 22:07
• Each time you have edited your question, you have actually made it worse. A car on a bridge has absolutely no commonality which an aircraft in flight. – Mike Sowsun Dec 22 '20 at 22:10
• Again your edit has further degraded your question. Ground speed has NOTHING to do with wind gusts or wind shear. – Mike Sowsun Dec 22 '20 at 23:51
• After many edits, your question has some validity. But now the previous answers also need to be edited to match your new question. – Mike Sowsun Dec 23 '20 at 10:32
• @MikeSowsun 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. – user52248 Dec 23 '20 at 10:46

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.

• Yes constant wind dont exist,at least where I live.. – user52248 Dec 22 '20 at 22:28
• @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. – HiddenWindshield Dec 22 '20 at 22:33
• @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. – DeltaLima Dec 22 '20 at 23:11
• @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 – HiddenWindshield Dec 23 '20 at 0:11
• 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. – HiddenWindshield Dec 23 '20 at 0:11

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:

1. 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.

2. 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.

• Re passengers experiencing wind shear as "slight turbulence", note that it has been the cause of quite a number of crashes. – jamesqf Dec 23 '20 at 5:04