W.J. (Bill) Dean (U.K.). wrote:

I have been told two things:

1. That the Reynolds number applicable to a glider changes with altitude,

2. That the Reynolds number affects the stall/spin behaviour and recovery.

I can remember an anecdote (I am vague as to who or when) about a K21 at
Aboyne. The glider was at about 20,000 ft., and the crew wanted to get
down for the next pupil. They put it into a spin (which it entered without
difficulty), and then held the spin without moving the controls. It span
down to about 7,000 ft. and then self-recovered without any
change in control position. Heights are QNH.

I don't understand Reynolds numbers, but I know it matters; and it would
seem not only to designers. It might well be that some gliders more easily
spin and are harder to recover at height. I would expect this to apply at
altitudes above about 7,000 ft. QNH, above which height they are almost
certainly not test flown.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

So I'm a test pilot every time I fly from my home field at 7,500 ft MSL?