Made the maiden flight on my new GP Super Stearman today and experienced some unexpected aileron flutter. Powewred by Zenoah G26, Zinger 16x8 prop.
After setting the trims and getting the first flight jitters calmed down, I decided to try some simple manuvers. Gained some altitude to try a big loop. A shallow dive followed by a quick pull-up. Throttle was at about 1/2 power. I was more concerned with keeping the wings level through the loop than throttle setting. Applied full power to get the Stearman over the top and on the backside was greeted with very violent flutter. At first, I thought the top wing was coming off! I quickly throttled back and levelled off. The Stearman returned to normal smooth flight. I promptly lined up for final approach and made a beautiful "float it in" landing.
Inspected linkages and hinges. Could find no slop or any other problems. Could just overspeeding on the down-side of a loop cause such violent flutter?
Anyone else experience this? I'm thinking I may need stronger servos on the ailerons. I'm running servos on the lower only with the rods connected to the upper ailerons. Great flying plane!

John

Any airplane should be throttled back any time you are going to pass through vertical on a down line. Too much speed causes flutter even if your linkages are tight and servos are powerful. If you are going to do these manuevers, go to stronger servos just to be safe and throttle back.

You also have to make sure your servos have the mechanical advantage to hold the aileron... and the aileron doesn't have the mechanical advantage to move the servo

A great follow up. Thanks.

Thanks guys. Would going to a hole closer to the control surface on the aileron control horn and a shorter servo arm help?

The Stearman is set-up using the outermost hole in both servo arm and control horn. The servos by the way are standard Futaba S3004's with 42 oz torque. The manual specifies a minimum of 54 oz. Guess I'm flirting with disaster! If I go to a 6 volt battery, that will boost the torque to 57 oz. I think this may be a wake-up call! Now the decision, bigger battery or bigger servos!

John

You can get Futaba S3305's at tower for $37... THey have 99 oz./in. torq at 4.8 volts. and 124 at 6.0 v.! Great Servo's...


BTW they ARE metal geared

With rods in both outermost holes you close to one to one which is risky with underpowered servos for the suggested application. Mechanical advantage is furtherest out on the control surface, closer in on the servo...it is really a leverage thing.

Forget the increase in battery power, although it helps. Go with stronger servos, it is safer and less likely to fail. Two good servos cost less than loosing the plane.

You did flirt with disaster and came away with your plane intact. Those servos might work for flying around in big circles, but put any pressure on them to perform in a 1.20 size plane and they just don't cut it. I use lots of the Futaba 3305's or Hitec 645's in my bigger planes. They are more expensive, but you'll save an expensive plane... it's the price we pay for going larger. I'm putting together an Air Wild 38% Giles... Over $900 for the servos on the control surfaces. Plus a cheap $54 servo on the throttle.... this becomes more like an obsession I'm afraid.

Dick T, Sounds like good advice to me. I think I'll go with the better servos, I would really hate to lose this plane.

If you haven't looked at the Great Planes Super Stearman, it is one really beautiful ARF!! And flies great too! I'm a long time kit-builder(20+ yrs) and I couldn't build a plane with the same quality for twice the price of the Stearman.

Regards,
John

Thanks p39, You are soooo! right! Will follow you guys advice.

I have seen the Super Stearman and it is a sweet airplane. I have the PT-17 version in the shop, planning on Hitec 645 MG servos and a G-23 for power.

Thanks and enjoy.

as another point of view, if it's truly high speed flutter, I seriously doubt that your "weak" servos are causing the problem, unless the out put gear is now stripped and missing some teeth..... even if the servo can't hold the aileron perfectly still, the torque applied will dampen the oscillations dramatically and reduce the frequency considerably.... no, I would bet your problem is loose, inadequately sized, or poorly installed linkages or bad hinges or big gaps or some other mechanical phenomenon....

[:-]

What? Nobody mentioned sealing hinge gaps? Stickman/vic

Well all I can tell you is that I have a ST 3250 with a 20x8 on it Yea I know a little overpowerd. I use HT 645s on mine and never had any flutter at all and it flys super I love this plane.

Start with stronger servos and seal all of your hinge lines. I've got a Saito 180 swinging an 18x8 in my Stearman and have never experienced flutter on any of the surfaces even on full throttle pull outs. Not exactly scale speed but that's what the throttle is for...