Downwind turn controversy explained

[PT20J]

I ran across this paper from a test pilot. It isn't all that well written and the math is a bit complex, but the idea is simple. If you fly a turn downwind by reference to to the instruments, the airplane doesn't care which way the air mass is moving. But if you fly the turn close to the ground with reference to the ground itself, you will lose airspeed and sink when turning downwind. The phenomenon is easily visualized considering a U-control model airplane flown in a steady wind. Turning upwind causes the airplane to climb; turning downwind causes it to sink. If the "pilot" were on a platform moving in the same direction and speed as the wind, the airplane would stay level. 

ADA368602.pdf

[Andy95W]

I found it interesting that 3 of the sources cited by the author were from Barry Schiff, who has been writing about this topic since the ‘70s.

[PeteMc]

3 hours ago, PT20J said:

But if you fly the turn close to the ground with reference to the ground itself, you will lose airspeed and sink when turning downwind.

Wouldn't it be wonderful if Primary "learners" had some exercise to show how that worked.  Maybe we should create some practice maneuver where they went and, I don't know, maybe kept turning around one point on the earth?  

 

[midlifeflyer]

Yes, the big controversy is about an illusion caused by physical and optiical sensations.

[Ibra]

Without complicating things  is this valid for left or right turns? valid in N-S or E-W? assuming flight in northern hemisphere, just making sure we are not missing anything from Coriolis effet and compass turn errors 

Maybe unrelated, I recall while circling thermals at lower levels in gliders, the upwind part feels strong where downwind part feels weak, I wonder if it’s a similar illusion, say lower part of thermals are  “attached to ground reference ”? or it’s a genuine effect, say the lower part of thermal “have an asymmetric shape” in windy days?

Edited September 13 by Ibra

[Fly Boomer]

11 minutes ago, Ibra said:

Without complicating things  is this valid for left or right turns? valid in N-S or E-W? assuming flight in northern hemisphere, just making sure we are not missing anything from Coriolis effet and compass turn errors

Same same.  Airplane only "knows" about the air mass it's moving with.  Airplane cannot "see" the ground.  As far as the airplane knows, there is no wind.  This assumes steady wind -- wind shear is different.

[midlifeflyer]

18 hours ago, Ibra said:

Without complicating things  is this valid for left or right turns? valid in N-S or E-W? assuming flight in northern hemisphere, just making sure we are not missing anything from Coriolis effet and compass turn errors 

Maybe unrelated, I recall while circling thermals at lower levels in gliders, the upwind part feels strong where downwind part feels weak, I wonder if it’s a similar illusion, say lower part of thermals are  “attached to ground reference ”? or it’s a genuine effect, say the lower part of thermal “have an asymmetric shape” in windy days?

You are definitely complicating things to find a reason for something aerodynamically nonexistent.

[N201MKTurbo]

I have been flying for 44 years. I have been reading about this for 44 years. The story hasn’t changed.

[Pinecone]

Now, how about an airplane on a treadmill.
 

[Andy95W]

4 hours ago, Pinecone said:

Now, how about an airplane on a treadmill.
 

https://mythresults.com/episode97