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Mass Balance of Ailerons

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Fenix

Well-Known Member
Supporting Member
Joined
Dec 25, 2020
Messages
90
I am in the final stages of construction of a pair of custom tapered wings for my RV-4. (To answer now what is likely to be inevitable questions: I contracted with a structural engineer to do a stress analysis/design but have not done any performance analysis - that will come in flight.) I just have to paint them, balance the painted ailerons, and then do the wing exchange from the original wings to the tapered wings.
My question relates to the mass balancing of the ailerons. The standard RV-4 (and 6,7 and 8) ailerons have a 1/2" galvanized water pipe attached to the leading edge of the ailerons that runs the length of the aileron so the mass balance is all along the the aileron length, not at the outboard end as is typical with "hammer type" balances (such as is used on the elevator of the RV's). This length of pipe gives an approximate balance of the aileron. (I'm sure Vans tried different diameters and wall thicknesses until one was about right). On my plane the trailing edge of an aileron (with the actuator rod disconnected) weighs about 4 ounces. So they are not 100% balanced.

My plan for the tapered aileron was to totally balance them so the trailing edge of the aileron, when hinged and with the airplane in the fight attitude, weighs zero or very near zero when painted.
I will accomplish this by having an "adjustable weight" balance instead of the galvanized pipe that weighs whatever it turns out to weigh. In place of the galvanized pipe, I have installed a hollow aluminum tube, which, like the original galvanized pipe design, also runs the entire length of the aileron. In this tube I will slide a solid mild steel round bar and fix it in place with some set screws. I can adjust the length of the solid bar to get the exact balance I want which, as stated above, is "neutral" (comments by any who suggest that I balance them at something other than neutral are welcome.)

My intent was to locate this "mass balance" near the root end of the aileron instead of near the tip end, as is common, because at the root the distance between the hinge point and the leading edge of the aileron, and therefore my aluminum tube, is greater. The arm (distance between the hinge point and center of the aluminum tube/mild steel bar) gets progressively less as you move toward the tip due to the tapered shape of the aileron of course. Putting the mass at the root of the aileron means the mass can be less, thus saving weight.

However, in watching Sonja Englert's video series on A/C design she states the weight can be along the entire length of the aileron (as in the standard RV 4) or it can be at the tip end (as is common on the aforementioned "hammer type" mass) but she seems to indicate a problem with the mass being at the root end of the aileron. She does not elaborate on this and I'm not clear even if in fact it is a problem to put the mass at the root, and if so, is this true in some arrangements but not in others. So I am seeking some input as to whether or not it is OK to put the mass at the root end of my aileron, or if I need to instead put it at the tip end, which will increase the mass required to balance the aileron. AND of course, being the curious type, WHY?

Thanks for any input!
 
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