Nick..
I have always maintained that the wind provides the force that provides the acceleration in a downwind turn. I thought it was you that said the wind had no effect.
Now if the force of the wind provides the acceleration during a downwind turn is it not possible that given the right(wrong) circumstances eg low airspeed steep turn, that the acceleration is not quick enough and you loose airspeed.
I know a lot of people here keep talking about loosing speed low due to ground references but who has ever been taught to fly ground references. Surely in visual flight we fly attitude.
And if you maintain attitude and don't increase power and we know from conservation of momentum theory that it is not just the force applied but how long it is applied, so in a quick turn the force of the wind doesn't have a lot of time to act and this may contribute to the problem ????