G Limits in aerobatic aircraft
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Except in so far as saying "controls to the maximum inputs" - it's only one control.
Back to your "Can anyone point out a definition of Va from an accredited body that even mentions the word "stall"." The authority, had they wished, could have defined Va as "the maximum permissable stall speed when maneuvering".
just to add -assymetrical changes in spanwise normal incremental loading and a decrease in limit load on the due with aileron deflection is one reason why compound mauneuvers are not covered by Va
but physically Va is a function of stall speed and design limit load...it is the highest speed at which an accelerated stall will imapart a limit load as shown by the flight envelope get closer to Vne you have to be careful with as lift coefficients are available for ultimate loading well before a stall...but increased dynamic pressures offer some protection...one reason why stabilators are not seen in aerobatic aircraft is the low stick force/g which can lead to overstress
Va= Vs(nlimit)^.5 double stall speed you have 4 g triple it 9g due to high limit loads on some of these planes up to 20g Va could be set quite high especially if stall speed is high ...
but physically Va is a function of stall speed and design limit load...it is the highest speed at which an accelerated stall will imapart a limit load as shown by the flight envelope get closer to Vne you have to be careful with as lift coefficients are available for ultimate loading well before a stall...but increased dynamic pressures offer some protection...one reason why stabilators are not seen in aerobatic aircraft is the low stick force/g which can lead to overstress
Va= Vs(nlimit)^.5 double stall speed you have 4 g triple it 9g due to high limit loads on some of these planes up to 20g Va could be set quite high especially if stall speed is high ...
...also rudder deflection coupled with inertial input in other axes may be limiting because side loads generally are less than vertical loads so the factor is lesser but the same explanation with regard to change in normal incremental loading with high lift surface deflection including flaps...when compound maneuvers such as a snap roll are done the entry speed will be less than Va but the total load allowed is up to a limit load but unless you're professional well conditioned and well paid with many modern aerobatic plane with limit loads well above FAR23 requirements few of us really have to worry...you can't sell the plane either when you're done
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While the limit stall case normally is equivalent to Va, sometimes other control limits may be more restrictive. For instance, the early 125s had Va dependent on rudder input and consequent yawing dynamics - no idea whether that applied to the later versions or not.
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I don't recall any mention in the Pitts S2B flight manual about roll inputs at Va, although it is a valid point. I do however know (or did) that no factory manufactured Pitts had ever broken up in flight, which is a solid testament to Curtis's design.
Re the 125, I believe that no longer applies, and the 800 aileron rolls very nicely, provided the toilet is emptied first in case one gets a bit slow over the top. The 900 variant seems to lack the roll rate, and thus a bit more energy is required, probably due to the winglets. In the sim, of course!
Re the 125, I believe that no longer applies, and the 800 aileron rolls very nicely, provided the toilet is emptied first in case one gets a bit slow over the top. The 900 variant seems to lack the roll rate, and thus a bit more energy is required, probably due to the winglets. In the sim, of course!
Well, AC 23-19A has a different take on this.
48. What is the design maneuvering speed VA?
a. The design maneuvering speed is a value chosen by the applicant. It may not
be less than Vs√ n and need not be greater than Vc, but it could be greater if the applicant
chose the higher value. The loads resulting from full control surface deflections at VA are
used to design the empennage and ailerons in part 23, §§ 23.423, 23.441, and 23.455.
b. VA should not be interpreted as a speed that would permit the pilot
unrestricted flight-control movement without exceeding airplane structural limits, nor
should it be interpreted as a gust penetration speed. Only if VA = Vs √n will the airplane
stall in a nose-up pitching maneuver at, or near, limit load factor. For airplanes where
VA>VS√n, the pilot would have to check the maneuver; otherwise the airplane would
exceed the limit load factor.
c. Amendment 23-45 added the operating maneuvering speed, VO, in § 23.1507.
VO is established not greater than VS√n, and it is a speed where the airplane will stall in a
nose-up pitching maneuver before exceeding the airplane structural limits.
48. What is the design maneuvering speed VA?
a. The design maneuvering speed is a value chosen by the applicant. It may not
be less than Vs√ n and need not be greater than Vc, but it could be greater if the applicant
chose the higher value. The loads resulting from full control surface deflections at VA are
used to design the empennage and ailerons in part 23, §§ 23.423, 23.441, and 23.455.
b. VA should not be interpreted as a speed that would permit the pilot
unrestricted flight-control movement without exceeding airplane structural limits, nor
should it be interpreted as a gust penetration speed. Only if VA = Vs √n will the airplane
stall in a nose-up pitching maneuver at, or near, limit load factor. For airplanes where
VA>VS√n, the pilot would have to check the maneuver; otherwise the airplane would
exceed the limit load factor.
c. Amendment 23-45 added the operating maneuvering speed, VO, in § 23.1507.
VO is established not greater than VS√n, and it is a speed where the airplane will stall in a
nose-up pitching maneuver before exceeding the airplane structural limits.
