Question on Va/manouvering speed
 

Hi all,

At the moment I'm studying to become a gliding instructor, and wrestling with a few questions. One of them has to do with the manouvering speed, Va:
is Va also dependent on the weight of the aircraft, and if so, in what way? I understood earlier that the lower the weight, the lower Va is as well; am I right?
If any of you airline-pilots is willing to shed some light on this, I'd be happy to hear. Thanks in advance.

Eagle

Hi Eagle1,

Yep, VA 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. VS, VL/D MAX and so forth - when massgoes down,so does the speed.

The easiest way I found to understand VA 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 VS. 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 VA.

So VA 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 VS is the stall speed for 1 G and VA is the stallspeed for 6 G - you can see why VA must vary with mass - if the mass goes down, the stallspeed goes down. The new VA can be calculated using the same formula as you use to calculate a new VS given a different mass. :cool:

Empty

I see Empty Cruise has beat me to it, but here's my 2 cents:

For jets, the maneuvering speed can be dictated by the weight, a lower IAS for a lower weight. This is to ensure the maximum G loading for the aircraft will not be exceeded. For example, the engine/pylon combination is designed for a certain G loading, so the maneouvring speed for the weight will ensure the aircraft stalls before the allowable load factor is exceeded.

For some jets, the speed is given without any reference to weight. As long as one doesn’t exceed the minimum flight weight, exceeding the G loading is not possible. But if you were to be in excess of the maximum allowable weight, and be at this published maneuvering speed, you could not exceed the strength limit of the wings by applying elevator, since the aircraft would stall first.

Maneuvering speed is also the highest speed that full aileron and rudder control can be applied without overstressing the aircraft. For rudder, that is one control input, slowly, to max deflection, and then slowly removed.

Hawk

But not in the direction of any established side slip.