Originally Posted by Rivet gun
Fly-sd, thanks for posting the link
http://www.flightlab.net/pdf/8_Maneuvering.pdf.
I had not seen that one before, but it gives a good explanation of your original question.
Worth pointing out though that this discussion concerns only the manouver envelope, and makes no mention of the gust envelope. In particular their use of the term "Vc" is misleading since it is quite different to the usage of the term Vc in FAR/CS 23.
In CS23 "Vc" means design cruising speed, and is the speed at which the aircraft will tolerate a 50 fps "design gust" up to 20000 ft.
Yes good point - in most cases people seem to refer Va with reference to gusts but as you point out they are different.