Originally Posted by
autoflight
So what has windshear got to do with a simple downwind turn? In both cases the aircraft is flying into a reducing headwind and in the case of the downwind turn, we have set the circumstances to be eventually an equal tailwind.
In the downwind turn we are deliberately flying from an area with a headwind to an area with a tailwind. We are effectively creating our own windshear.
No, we're not. A Squared beat me to it. In wind shear, you're transitioning from one air mass to another, in a small enough timespan that the airplane's inertia temporarily preserves groundspeed, and thereby changing your airspeed. If given enough time after the transition to reach steady state, the plane would stabilize at the original airspeed.
In a turn within the same airmass, there is nothing affecting the airspeed other than drag (the same way that drag would affect your airspeed if the airmass were not moving, i.e., zero wind). Rate of turn does not matter for the ability to recover lost airspeed, because there is no airspeed loss to recover. If it was a function of a gradual enough rate of turn, as you claim, that implies that there is some rate of turn/wind combo for which the "graduality" safety effect would not work, and there would be a significant airspeed loss. How about when you are walking upwind at 1 knot at knots in an airliner, toward the tail, with a groundspeed of negative 499 knots. You turn around to face the nose (downwind) in one second, and keep walking at 1 knot airspeed, but now your groundspeed is 501 knots. You just walked through a one thousand knot self-created windshear in one second, according to your theory, which predicts that there should be some effect. But there is none. When should this effect start kicking in? Remember that your theory also has to account for the "groundspeeds" around the center of the Earth, around the Sun, around the center of the galaxy, etc.