I have a great planes ultimate powered by an os fx.46. Love this plane, cannot say enough good about it, but, every once in a while, on a high speed pass or long spinning dive, there is a very loud flutter and i cannot figure out from where. It seems to come and go. It has done it maybe 5 or 6 times over about 200 flights. It is very loud and I always cut throttle and pull up right away and it stops right away. Control surfaces are tight, cowling is new fibreglass. Could it be the wheel pants as they are a little loose after several re builds? Could it be the monokote? Very loud and deep sounding.
Anyway to find out what is fluttering before I loose a great airplane?

Have you seald the hinge lines? If not, perhaps yo0u should. You can use monokote or clear tape. If it is flutter, the controls are tight, sealing hinge gaps should solve it.

Thanks.I have the hinge lines on the ailerons sealed but not the elevator.
Could be, I'll try it.

No Problem. I hope it works. Ivehad a GP Ultimate with a saito 91 in it. Great plane and never had a problem until a tree from hell stood up, grabbed the plane and toosed it right into the ground.

Your flutter is more likely caused by control slop rather than a gap between surfaces. Have the holes in the servo arms or horns worn some? If you have metal geared servos, have the gears worn? If you can grasp any surface and slightly move it without the servos moving, it is an invitation for flutter.

If all of the surfaces are tight as you say, I would loose the pants for a few flights and purposely try to cause the condition in flight. If it happens again, you'll know it's not the pants. 5 or 6 times out of 200 flights is not much, I doubt that it's surface flutter but you'll have to try eliminating one thing at a time to find the cause.

We had one sounding the same way at the field this weekend, and found out it was the cowling!! Everything seemed tight, but with the throttle up, it would sound like the thing was going to fall apart! They took the cowling off, ran it WOT, and everything was fine. The owner said he was going to put more bolts in the cowling to see if that helps.

Take Care!

Try this: put your plane in a flat line at full power straight & level make sure you are somewhat directly under the path of flight. have another person observe with you with binoculars observe all the flight controls on each pass. I tried this and found I had some violent aileron flutter. To fix the problem I used better control linkages (heavier wire). Your control linkage could actually be flexing. Use a good quality clevis system such as robart. Also check your servos you might need to replace them as well. Good quality digital servos are best.

Just to follow up, I put a little scitch tape on the gap between the elevator and stab and viola, no more flutter.
At least not on the last couple flights.....
Thanks for the input.

Scotch tape won't last very long. Monokote makes a clear covering that you can iron in to the gaps. 3M also makes a tape called "Blenderm" which is made to adhere to your skin well. Skin is somewhat oily. Blenderm is realy tough in an oily environment.

I prefer the monokote solution since it is easier to find but I have used blenderm as a field fix and it works extremely well. It has held up through thousands of laps around pylons.

Sealing the hinge gaps is always a good idea. I always seal mine top and bottom on high performance planes.

[:-]What is a good technique for sealing the hinge gaps?? I have never had to seal the gaps before, but I feel I'm going to have to with the Ultimate.[8D]

Thief,
Use regular covering material (or clear packing tape).
Dennis-

I have found, after you cut the strip of material, if you fold it length wise, it will lay down inside your hinge area while you are putting it on.

Good luck!