Va and full aileron deflection question

[Mdragon]

I'm hoping to get an answer to this more from an aeronautical engineer's perspective.

In researching this for awhile I have not found the answer.

When looking at manuevering speed, one of the definitions is the speed at which a maximum deflection of one of the control surfaces is still safe. But reading further, it seems it is to avoid a maximum deflection from exceeding the g tolerance of a particular aircraft.

Reading further, most are speaking about maximum Elevator deflection. For example, at X speed, you pull all the way back, and have now exceeded the G forces to which the airplane is rated/designed.

I'm wondering with respect to full aileron deflection if this is the case, as you are rolling the aircraft, but it is certainly not pulling much if any G's.

Will full deflection of the ailerons at speeds above Va potentially damage the ailerons, or is this not so much the case?

I notice many pilots roll their aircraft a margin above Va.

 

[DerekS]

Though we are not governed by part 23 they give us a good starting point for design loads.

FAR 23.335(c) tells us how to come up with Va:

Va - defined (typically limited by) the speed at which we won't pull the wings off the plane in a positive G pull at gross weight because the wing will stall first, hence all the references to elevators.

c. For design maneuvering speed, VA , the following applies:
(1) VA may not be less than Vs4n where
(a) Vs is a computed stalling speed with flaps retracted at the design weight,
normally based on the maximum airplane normal force coefficients, CNA,
and
(b) n is the limit maneuvering load factor used in design.

FAR 23.455 - Does the ailerons.

FAR 23.455 Ailerons.
a. The ailerons must be designed for the loads to which they are subjected:
(1) in the neutral position during symmetrical flight conditions and
(2) by the following deflections (except as limited by pilot effort) during
unsymmetrical flight conditions:
(a) sudden maximum displacement of the aileron control at VA, suitable
allowance may be made for control system deflections,
(b) sufficient deflection at Vc, where Vc is more than VA, to produce a rate of
roll not less than obtained in paragraph a.(2)(a) of this section, and
(c) sufficient deflection at VD to produce a rate of roll not less than one-third
of that obtained in paragraph a.(2)(a) of this section

So the (Part 23) plane is designed to roll between Va and Vc as long as you don't exceed the roll rate you can get at full deflection at Va, and up to Vd at 1/3rd that rate

Vc is required to be higher than Nno (23.1505), so you are good up to the yellow arc for a roll rate the same as you have at Va.

FAR 23.349 Adds one more condition:

b. The wing and wing bracing must be designed for the loads resulting from the aileron deflections and speeds specified in FAR 23.455, in combination with an airplane load factor of at least two thirds of the positive maneuvering load factor used for design. Unless the following values result in unrealistic loads, the effect of aileron displacement on wing torsion may be accounted for by adding the following increment to the basic airfoil moment coefficient over the aileron portion of the span in the critical condition determined in FAR 23.333(d):

So don't do it while pulling design G's

Aircraft that are not part 23 are not bound by these. YMMV (A very important and potentially life ending caveat)

Derek

 

[rsultzbach]

Avoid rolling pullouts as if your life depended on it, because it does. If your intent is to roll the airplane while pulling G’s you must be aware of asymmetric loads during rolling pullouts. If you pull loads near aircraft limits you may exceed the ability of one wing to withstand the G load your G meter is reading.