“When an airplane is flying, it is in a mass of air which normally is moving. The airplane moves with that mass of air. So that if you have air going this way (gestures) and the airplane is going the same direction, then the speed of the aircraft is augmented by the speed of the wind. But if you are going 500 miles an hour with 50 mile an hour headwind, you’re doing 450.

 

This is the difference between air speed, the speed through the air, which takes into account the movement of the wind, and ground speed, which is your speed over the ground. If the wind is blowing from the side, your airplane moves with it.

 

If you line up with the runway ten miles back, and you stay lined up with the runway, you’re going to end up (gesturing) over here somewhere. So, you have to compensate for the wind. You compute how strong it is, what direction it is coming from, and then you allow for ‘drift’.

 

If I have strong wind coming from here (gesturing) and I want to stay lined up with the runway, I can head into wind so my new heading is over here (gesturing) and I am being blown that way (gesturing):  I compensate for the effect of the wind. If you over-compensate, you’ll err on either side, so you have to hit the right degree of compensation.

 

The other way is to stay lined up with the runway but to drop the wing, so that you are, in effect, saying ‘We are in a turn to the left’.

 

But because the air is blowing you continue to be lined up with the runway.

 

You have to compensate for the fact that your wings are turned by using a bit of rudder to stop from turning.

 

In the one instance you are coming in at an angle to the runway so when you cross the threshold of the runway you are on an angle. And if you land like that your wheels are going to be hitting sideways which is a terrible strain on the undercarriage. So just before touchdown you kick it straight.

 

The other way is similar; you’ve got your wings down but over the runway you put your wings level.

 

If you are subject to turbulence, airliners, by and large will use the yaw technique. Their wings are so large if they drop a wing, they are 75 feet in the air. They don’t normally drop a wing; they normally head into wind.

 

A lot of people would assume that on take off you’d want to have a tail wind. Zoom!  But it’s just the opposite - you want a head wind. You’re sitting at the end of the runway, before you even release the brakes you’ve got a 40 Knot airspeed; the wind over the wings produces lift. If take off speed is 110, with a 40 Knot wind, it only takes 70 Knots and you’re airborne.

 

The lift, the thing that keeps the airplane in the air, is not, as the song says, the wind beneath my wings; it is not pushed up from the bottom, it is sucked up from the top. The Bernoulli principle. When gas speeds up, pressure drops. The top of the wing is intentionally curved to make the air speed up to go around it.”

 

(All errors are the typist’s, not the speaker’s.)