AA5BY you mention the condition that made me question everything that has ever been taught about the spiraling slipstream.
What is this spiral doing to the rest of the airplane In a vertical hover?
The spiral is always taught with one illustration from the side of the plane showing the spiral impinging on the vertical fin. Draw the same airplane from a top view and draw in the same spiral. No one ever shows that spiral doing the same thing to the wings and stabilizer. Where and why does this huge rolling force that is acting on the wings and tail plane go? No flight instruction manual OR engineering manual ever addresses it. It stops at stik and rudders simple explanaiton. Period.
If you do a complete free body diagram a plane should be rolling to the right, not just yawing to the left