Balancing flight controls

[PIN 37]

I am in the process of final assembly after paint. Balancing the elevators was not a problem and could be done accurately, however, when I put the rudder on the knife edges I found it was very much out of balance and would need a LOT of weight added to the counterbalance. What is the collective wisdom?

[bret]

I may be wrong, but what I have read on here is that the rudder will not balance out, ( if you are doing this horizontal ) like the elevators.

[Marc Bourget]

If you'd like to consult a reference, NACA Technical Note #609, Sept 2, 1937 discusses the considerations involved in adding weight to Ailerons.

Balancing these surfaces is intended to deal with dynamic issues, like how the surface responds to accelerations relative to the rest of the structure, like gust loading.

mjb

[lr172]

I discussed this with Van's when I built my 6A (with the later, counter-balanced rudder) and was told the counter-balance is engineered and not field set. I don't believe that it is designed to be neutral, like the elevators.

Larry

[BillL]

Originally Posted by PIN 37

I am in the process of final assembly after paint. Balancing the elevators was not a problem and could be done accurately, however, when I put the rudder on the knife edges I found it was very much out of balance and would need a LOT of weight added to the counterbalance. What is the collective wisdom?

The rudder is not fully balanced by design. I am interested in the cg limit, if any guidance is provided from Vans.

You have standing to ask Vans what limit you should use when painting.

[johnny stick]

I am a strong believer in balance control surfaces. I am glad you started this thread. It gives me time to think how I would balance these surfaces. In my view, flutter happens with a non stiff linkage on a non balanced surface. The least stiff control surface is the rudder, and not balance to me means flutter will happen here first. Just my opinion and is worth what you paid for it.

[Kevin Horton]

Originally Posted by johnny stick

I am a strong believer in balance control surfaces. I am glad you started this thread. It gives me time to think how I would balance these surfaces. In my view, flutter happens with a non stiff linkage on a non balanced surface. The least stiff control surface is the rudder, and not balance to me means flutter will happen here first. Just my opinion and is worth what you paid for it.

None of RV designs to date require a fully balanced rudder. There are many thousands of these things flying, with the rudder balance as designed by Van (which is no balance at all on some models), and the service history confirms that the design works as-is. Don't think you are smarter than the engineers at Vans, unless you are prepared to back up your changes with a full structural and flutter analysis and test program.

[johnny stick]

Kevin I agree with you that thousands of rvs Ae flying and most Cessnas too do not have mass balance control surfaces and they all fly fine. But there is one accident I remember that leads me to believe the flutter margin is fairly close to the vine limit. Maybe mass balancing the rudder is not the answer, I don't know.

But this brings up another question, what makes a gulf stream jet capable of 400 knots but the rv series only 200 or so? Is it better mass balanced control surfaces, structural stiffness, or just some extra special mojo?

[Kevin Horton]

Originally Posted by johnny stick

Kevin I agree with you that thousands of rvs Ae flying and most Cessnas too do not have mass balance control surfaces and they all fly fine. But there is one accident I remember that leads me to believe the flutter margin is fairly close to the vine limit. Maybe mass balancing the rudder is not the answer, I don't know.

But this brings up another question, what makes a gulf stream jet capable of 400 knots but the rv series only 200 or so? Is it better mass balanced control surfaces, structural stiffness, or just some extra special mojo?

There have certainly been quite a few inadvertent exceedences of VNE during aerobatics. I've heard anecdotal stories about more than 230 KIAS on a few occasions.

Aircraft designed for high airspeeds, like jets, have much stronger, stiffer, heavier structure. They also are subjected to a flutter analysis, which uses info on frequencies and modes from a ground vibration test program, and a full flutter flight test program.