Dick,
Further to my last post (yes I know it was long enough already). Your figures for the Hunter show that the quoted Vy lapse rate of 1 Kt per 4000 ft is incorrect. It should be noted that this figure is not my invention, but was produced by (would you believe it) the CAA examiners.
At the CAA/FTO meeting to which I referred earlier, the PPSC representative was asked to come up with a definitive statement of how Vx and Vy behave as altitude increases. He invited me to contribute and after a day or so we came to the conclusion that Vx remains constant while Vy decreases to converge on Vx at the absolute ceiling. He then passed this on the CAA.
A couple of days later I asked him if there had been any further developments and he stated that. "Apparently there is an aerodynamics expert upstairs in the CAA building. He has stated that Vy only decreases by 1 Kt per 4000 ft altitude increase, so it is okay to say that it remains constant". At this point I realized that there was no hope of resolving the matter, so I threw my hand in with this particular discussion.
[ 20 January 2002: Message edited by: Keith Williams. ]</p>