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Thread: What causes "Flutter" Reply to Thread

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[QUOTE=Cougar429;711625]Flutter is the term used for self induced oscillation of a control surface and is not just on the horizontal stab. Most often it is caused by improperly designed, hinged or balanced control surfaces. On real ones you will see that a control surface will tend to require weight added so that it balances at the hinge point, something impossible with our hinges simply stuck at the leading edge of the aileron, elevator and rudder.

It can be exacerbated by loose linkages, so look to tightening them up if possible. Same thing with flexible control surfaces. You may be able to hold the input area of the surface rigidly, but the outboard sections can flex so much you would get that flutter isolated away from the control horn.

I suffered the loss of my Kougar from the same thing happening in the ailerons, growing so bad in a dive it tore the gears out of the servo. I found out from experimentation the easiest fix was to bolt on another control horn at least 1/2 surface span outboard of the input and add weight to the end of the horn. This increase in mass helps change the oscillation frequency of the control surface and dampen the flutter, but a better solution I use now with my foamies, (by nature flexible structures) is to add C/F rod along the span of the control surface to increase rigidity.[/QUOTE]

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Topic Review (Newest First)

06-09-2010 08:41 PM

Barnroof

Re: What causes "Flutter"

Gentlemen, we can bring this discussion to a close.

Tonight I did test fly the Cloud Dancer with the new servos as described above.

The plane flies perfect, no flutter!

Wow, what a difference, and it can dive at high speed without any strange stress sounds.

The character of this plane has certainly changed.

Thanks for the comments, explanations and support, it's a real pleasure being a member of RCC.

06-08-2010 08:10 PM

hifly2104

Re: What causes "Flutter"

Quote:

Originally Posted by SJrcflyer

Good post Cougar, lots of good advice but don't forget that a lot of flutter can be cause by too much of a gap between the control surface and the solid structure. Try to minimize this gap and also SEAL your hinge lines. Some clear covering works best and it is a simple and fast precaution to take.

Had a large profile Edge 540 from OMP and it litterally sheared off both servo shafts. New servos where installed and gap was sealed with covering. I have found that on most of my 50" electrics clear scotch tape works just as well

06-08-2010 07:37 PM

sclitheroe

Re: What causes "Flutter"

This has been a very informative thread - thanks everyone (even though none of my stuff flutters....yet)

06-08-2010 06:36 PM

Barnroof

Re: What causes "Flutter"

The new servos are a JR MN 48. 48 oz inch.

The wind is still crazy here, perhaps a flight tomorrow!

06-08-2010 12:32 PM

Max

Re: What causes "Flutter"

Quote:

Originally Posted by Barnroof

Gentlemen, I have purchased two upgraded servos, slightly larger , but much more torque, a JR servo, type and kind TBA later.

I took the time to install these in each wing about half way out. Made a nice frame, all went well. The new servos are absolutely tight, no free movement.

I re-worked the radio setup, centering , trim EPA, etc.

Looks very promising.

Next fine day we will see the results.

I expect this plane will become a hot item, not the unstable cripple it was before with the flutter effect.

I will keep you informed.

Excellent!!!

Thanks for the update....

06-06-2010 07:16 PM

Barnroof

Re: What causes "Flutter"

05-11-2010 07:43 PM

Max

Re: What causes "Flutter"

Quote:

Originally Posted by Barnroof

I surveyed the plane tonight.
I compared the feel of the ailerons to my other planes.
I can notice a very spongy, soft feel to the ailerons.
This spongy feel comes from the torque rod, it appears to be twisting . The servo is well locked in place, the aileron is full wing length, it can be easily deflected 3 mm , both up and down, a total of 6 mm deflection, with no servo movement.

If there is a strong oscillation about the trailing edge , then the ailerons must be moving, and easily making the noise.

All my other planes have tight, ridged ailerons, locked in place.

There is no easy fix for these weak torque rods.

I will consider mounting one servo in each wing and drive the aileron in this fashion.

Also, to address the possibility of the servos being too weak, we must consider the fact that I used two servos , one for each aileron, a typical flaperon arrangement.

Therefore the 38 oz in is totally for one aileron, dedicated to only one wing. This was my original consideration in decided this Micro Mini would do the job.

So compared to one standard servo of 44 oz in, driving both wings. I have provided 76 oz in for two wings.

Looks like I will be doing some wing modifications.

I look forward to your comments.

Regards......

Absolutely! the sponginess you feel in the aileron is a significant contributor to flutter. Putting one servo in each wing and bypassing the torque rod is the best solution- it will (should

) make your ailerons rock solid. As you mentioned, one of each of those micro servos in each wing should be adequate. I would imagine once you stiffen up the ailerons, the problem will be gone

05-11-2010 06:50 PM

Flypaper

Re: What causes "Flutter"

Looks like you have the fix figured out. Good for you.

05-11-2010 06:35 PM

Barnroof

Re: What causes "Flutter"

05-10-2010 07:07 PM

Barnroof

Re: What causes "Flutter"

Very interesting discussion.
When the weather becomes fine I will make a few test flights.
I will investigate stronger servos, this would be an easy fix.
Perhaps Hitec makes a stronger servo.
I really like the video of the fluid flow showing the oscillations, thats really easy to understand.
I will look the plane over very closely to see if I can find any evidence to support the suggestions.

We will continue this discussion

Thanks again

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