Hi Eagle1,
Yep, V
A varies with mass, and since it a speed related to angle-of-attack (alpha), it will vary like all other alpha-related speeds, e.g. V
S, V
L/D MAX and so forth - when massgoes down,so does the speed.
The easiest way I found to understand V
A is to think of how the stall-speed varies with G. When decelerating very slowly, i.e. for all purposes at 1G, the aircraft will stall at V
S. It you decelerate harde, e.g. at 1,5 G, stall will occur at a higher speed. And - if you decelerate at the "design loadfactor", e.g. 6 G, the aircraft will stall at an even higher speed - and this speed is known as V
A.
So V
A is the lowest speed where the aircraft can attain the design loadfactor - and the highest speed where a stall will prevent you from exceeding that loadfactor. Fly any slower, and you will stall before 6G, fly any higher, and you can overstress the aircraft. Therefore, if V
S is the stall speed for 1 G and V
A is the stallspeed for 6 G - you can see why V
A must vary with mass - if the mass goes down, the stallspeed goes down. The new V
A can be calculated using the same formula as you use to calculate a new V
S given a different mass.
Empty