[Going Balistic]

Looking for some feedback on an issue I am experiencing with a new plan.

The plane is a custom designed .60 size which is a variation of a goldberg Tiger 2. The kit was designed by a friend in Texas and he had Sig cut a few hundred kits.

The structure is well hardend for the .60 size engine and is heavier than what you would expect froma .40 size model. The ws is approximately 15% larger than than of a .40 size plane.

I am essentially ready to maiden the plane, but have noticed a vibration / flutter in the tip of the left aileron (some also in the tip of the right as well).

The root and middle portion of the ailerons do not move at all. The vibration occurs a 1/2 throttle and above.

All of the linkages are tight and the servos are new and have no slop in them.

I ntoice the issue most when the plane is on a elvated starting stand that restrains the wings and holds the plane from moving forward.

The issue is reduced (but still present when the wings are not restrained.
Looking for ideas / suggestions.

the engine is new and has only been broken in on the bench and has a total of 1.5 - 2 tanks through it (OS .61 FS ring), prop is an APC 11 x 7 (well balanced). Will the problem subside when the engine has had a few flights?

Wondering if I need to put a hardwood strip on the aileron to stiffen it or maybe carbon fiber?

Will this be an issue in the air as it seems to calm down when it is not reatrained by the wings.

Is this commen in a really stiff structure?

Radio is not the problem.

Thanks,

GB

[JimMcIntyre]

Sounds like harmonic oscillation, likely caused by vibration transmitted through the restraints.

Does the vibration only occur at certain throttle settings?

If yes, is it possible to vary the control horn placement by placing it further out on the wing? This would change the natural harmonic frequency, hopefully to something out of range of the vibration.

Dual servo setup I presume?

OTOH, If you can't recreate the vibration with the plane unrestrained, I'd say it's a non-issue. Just beware of fatigue if you tend to run the engine while the plane is restrained often.

[Going Balistic]

Hi Jim,

Thanks for responding.

The vibration occurs once I have reached appoximately half throttle and above.

I have a dual ailerons servos (L & R).

Do you think it is possible that since the fuse and wings are very rigid that the vibration from the engine could jsut be translated to the aileron tips? Only the tips vibrate.

When I place my hand on the aileron (load) most, if not all of the vibration dissapears.

Could prop wash cause this?

I have not maiden the plane yet untill the issue is resolved, but I'm wondering if the plane does not react adversly in the air if there is much to be concerned about?

Thanks,

[Guest]

How much do the tips move roughly?

This is common to see on pattern models with large ailerons running 4-strokes. Playing with soft mounts helps, playing with linkage position helps, however there is almost always a throttle position that it will happen at.

As long as the vibration is not extreme it should not cause a problem while flying.

Also which orientation are your servos to the fuse (do the mounting screws point at the fuse, or in the direction of flight?).

[Going Balistic]

The movement is approximatey 1/8 in each direction, but the ailerone is vibrating rapidly, you really need to look close to see that it is actually moving.

The mounts I used as per the plans are glass filled nylon and are as short as will make the engine fit in the molded compartment. FYI the engine compartment is ply and balsa which has been carved to form a compartment which is open on the top and closed everywhere else. Because of the comparment there is no room for changing the mount without cutting the complete front of the compartment away - undesireable unless it is a last resort.

The engine is an OS .61 2 cycle.

The servos are flat in the wing with the control horn pointing toward the wing tip and the screws pointing toward the fuse.

[Guest]

Sounds like your servo is oriented properly to minimize flex.

I would not be that concerned about it and would for sure go flying. I would just take it easy on the speed the first flight and really listen and watch closely as you pick up the pace for signs of flutter or differences in control.

All of my larger pattern models do this at certain rpm ranges and I have thousands of flights on them without incident.

Go for it but just keep an eye on it for a while.

[Going Balistic]

Thanks Can773,

I don't think there is a huge issue here so I think that I will test fly the plane on the weekend and see.

I'm also thinking of changing the prop to a larger diameter and pitch and see if the reduction in RPM will eliminate the problem. A number of the guys over on RC Universe mentioned that the 11 x 7 currently installed is only reccomended for break in.

Will re-post following the test flight and let you know.

Thanks,

GB