Va question

[wessidemike]

ok we all know the definition of maneuvering speed. But does this include negative load factors. Since aircraft are not designed to pull the same negative g's as they are positive. Shouldn't the definition include it's for abrupt positive g maneuvers. if you look at a VG diagram what would be the Va for negative loads is different than the Va for possitive loads. I guess my question is how do you derive the airspeed for negative loads on a VG diagram. We tried using the formula for Va but does not work. Can Anyone clarify

 

[FN FAL]

ok we all know the definition of maneuvering speed.

Do we?

 

[Singlecoil]

ok we all know the definition of maneuvering speed. But does this include negative load factors. Since aircraft are not designed to pull the same negative g's as they are positive. Shouldn't the definition include it's for abrupt positive g maneuvers. if you look at a VG diagram what would be the Va for negative loads is different than the Va for possitive loads. I guess my question is how do you derive the airspeed for negative loads on a VG diagram. We tried using the formula for Va but does not work. Can Anyone clarify

You're right, Va is simply the speed at which the airplane will stall before exceeding the positive g load limit factor. It isn't the speed that you can "pull the yoke in any direction and you won't hurt the airplane" as some have said. I don't have a Vg diagram handy, but it should be simple to derive the slower speed at which the wing stalls before exceeding the negative g load factor.

 

[FN FAL]

ok we all know the definition of maneuvering speed. But does this include negative load factors?

If you are just below VA in level unaccelerated flight and push in on the yoke, asside from bumping your head on the ceiling of the airplane, risking breaking your neck, wouldn't you accelerate past VA speed?

 

[VNugget]

ok we all know the definition of maneuvering speed. But does this include negative load factors. Since aircraft are not designed to pull the same negative g's as they are positive. Shouldn't the definition include it's for abrupt positive g maneuvers.

You are right. It does, but it's implied, and you never hear anyone explicitly say it.

I guess my question is how do you derive the airspeed for negative loads on a VG diagram. We tried using the formula for Va but does not work. Can Anyone clarify

I'm not sure what formula you used, but it was probably the one that relates stall speed at a "new" G to a function of a known stall speed at a given G (usually 1), right?

Well for a cambered airfoil (meaning most scenarios) you can't use that for negative G or Va, since the limit G isn't the only thing that's changed... You have less Cl available, which means that it stalls at a higher speed for any given G. You'd need at least one given data point for the negative side of things. Most POHes, I suppose, don't give you an inverted stall speed.

If you're really bored, you CAN figure out the inverted stall speed yourself by getting the lift curve for the airfoil, and using the negative Cl max and plugging it into the basic lift equation. Then you can even start playing around with adjusting for errors due to the finite wingspan and the resultant change in the lift curve, etc. etc. etc.