Windshear

[Joey Jo Jo]

Help, not understanding something here. If the shear was instant instead of gradual like I'm told it usually is, why does the airspeed momentarily change.

Ex. Flying with a 30 kt tailwind, and it reduces to a 10 kt tailwind. Why does the airspeed show an increase of 20 kts for a short time?

Probably simple, but I thought I would ask anyways


Joey

[5x5]

Well, basically it's because you're not only flying through the air but also flying with the air. For example, at 100 kias you're going through the air at that speed. With a 30 knot tail wind, you're still only going through the air at 100kias. However, you are also going with the air at 30 knots. This makes for a ground speed of 130 knots.

Should the air abruptly/instantly slow from 30 knots to 10 knots, it takes a moment or two for the plane to lose the momentum it had moving with the wind at 30 knots. While the plane is losing this momentum it acts as though you are actually going through the air faster since the pocket of air that was surrounding you is now, in essence, falling behind until the plane slows down to move with the air at 10 knots.

This gives the temporary indication of an increase in air speed.

Hope that helps.[/i]

[Joey Jo Jo]

alright, that makes sense.

Thanks