Downwind turn Myth
Another thread contains a postulation that a model crashed due to the wind direction relative to the models flight path as it topped a loop. In other words, the model might not have crashed if the nose had been pointed into the wind over the top. (sigh)
Most of you learned better a long time ago, but this myth just keeps hanging in there. It's persists (sadly) even in the lower rungs of full scale aviation, and among pilots who have had enough training to know better. Lets set the record straight once and for all please.
It does seem counter-intuitive, but here is the truth:
Once an a/c has broken ground, steady state winds have no effect on airspeed (hence, lift) whatsoever, and airspeed does not change simply because one is flying upwind, downwind, crosswind, or even when alternating between any combinations of the above. Period. That is the beginning, middle, and end of the story.
As an aid to understanding this seemingly counter-intuitive fact, imagine yourself boating in a wide river with a 10 knot currrent. If you are putting along at 5 knots indicated speed, the water does not come crashing over the side simply because you are traveling from one bank to the other perpendicular to the current. It does not wash over the stern when headed down stream, as if you were suddenly traveling at a speed of five knots negative.
Or go for a swim in the ocean where the current is flowing parallel to the beach.
Or go scuba diving.
You will be carried along with the current, but not feel it, no matter which way you face or swim.
Or note that airliners don't fall out of the sky when making a 180 degree turn from a 150 kt headwind to a 150 tailwind, even though that net 300 kt difference in the wind is TEN TIMES the typical stall speed margin at the altitudes where such winds are encountered.
Birds fly just fine downwind, and don't suddenly crash into the trees when turning in that direction.
We could go on and on...but hopefully that's not necessary?
Don.