Originally Posted by tmmorris
You may be right, Rivet_gun - it's certainly not my field of expertise - but I have seen (placarded) Va described as 'turbulent air penetration speed'...
Tim
Aircraft must be designed to meet both manouver envelope requriments and gust envelope requirements. For light aircraft, the manouver requirements tend to be the more limiting, at least at lower speeds.
Va is defined with reference to the manouver envelope. Where the manouver envelope is limiting it is generally the "top left corner" of the the v - n diagram.
Theoretically in that case Va would indeed be the speed at which the aircraft could sustain the maximum vertical gust without either stalling or being over stressed. We may not know how big that gust would be but it would be greater than the design gust requirements (since the manouver envelope is more limiting).
We do know that the aircraft will sustain at least the 50 fps "design gust" at Vc. In turbulent air speed control is not going to be accurate, so aiming for a speed somewhere between Va and Vc would seem a good compromise between the risks of stalling and overstressing.
Hope this makes sense?