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help me understand aileron "flutter"

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Old 04-21-2008, 08:48 AM
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crashinator
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Default help me understand aileron "flutter"

I have a shrike 10, newly built, all the controls are tight, close tolerences on the surfaces blah blah blah, There is no "slop' from the servo arm out to the horn (almost)

During high speed passes it has a flutter that will go away during a turn. It seems that the aileron control wire I used is "torqing"

If the aileron is true to the trailing edge of the wing, no twists, nice taper,ect., shouldnt they not flutter?

It would be nice to make an aerodynamic adjustment instead of ripping the plane apart to replace the wires.

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Old 04-21-2008, 08:55 AM
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allans
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Default RE: help me understand aileron "flutter"

Can I also add to this discussion the causes of both rudder and elevator flutter and how the can be prevented and cured.
I have it on two planes an Aeroworks Yak os 120 FS and Aeroworks profile Extra with OS 120 FS. The extra has wires on the tail surfaces , but the rudder flutter is visable and audible from the ground. The Yak is not so apparent.
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Old 04-21-2008, 09:12 AM
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Default RE: help me understand aileron "flutter"

If everything is snug on the ground. Then there should be only 2 causes in the air.

The plane is flying too fast for the STIFFNESS of ALL the mechanical parts in that control.

The servo is being pushed off of your deflection in a turn or loop.

If it happens in level flight. You , believe it or not, need a stiffer pushrod & support tube. It can also be caused by guide tubes not glued down at enough places. I run a complete glue down of the entire guide tube.

Flutter can even come from 1/2 of a elevator. The connecting wire is not stiff enough & or not glued well enough.

You guys that take stock 40 mph ARF's & kits to 60 or 100 mph should have all kinds of flutter problems. You have to redesign everything for the greater forces.
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Old 04-21-2008, 09:26 AM
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Default RE: help me understand aileron "flutter"

You can also put balance tabs on the surfaces, where a tab is added forward of the hinge line with weight added to the tab that balances the weight of the surface. You'd need to unhook the pushrod at the surface, then add weight till the surface balances level on it's own. Take a look at a Mustang rudder and you can see the tab about halfway down the rudder hinge line. That's to prevent flutter.
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Old 04-21-2008, 09:52 AM
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Default RE: help me understand aileron "flutter"

Good answers all............

You can also lighten the ailerons by stripping them, then drilling lightening holes. The mass of the ailerons contributes to the flutter. So reducing the mass changes the speed at which flutter happens. The reduced mass also helps later if the balance horns are needed.

BTW, it is a joke told in aeronautics classes that even a bowling ball will flutter if flown fast enough. Everything has a flutter speed.

The "almost no slop" needs to be fixed if nothing else. But if you don't sort the problem, you will lose a servo or two sometime. And that is a bit of bother at any speed.
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Old 04-21-2008, 09:52 AM
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Default RE: help me understand aileron "flutter"


ORIGINAL: crashinator

If the aileron is true to the trailing edge of the wing, no twists, nice taper,ect., shouldnt they not flutter?

It would be nice to make an aerodynamic adjustment instead of ripping the plane apart to replace the wires.

If the aileron leading edge is thinner then the trailing edge of the wing or there is too much taper it may flutter. The fix on my 40 size Shrike was 1/64 ply over the hinge line.
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Old 04-21-2008, 11:23 AM
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Default RE: help me understand aileron "flutter"

........especially with full span ailerons made out of solid balsa sheet, if the torsional strength isn't there in the wood to resist resonating like a clarinets reed it doesn't matter how stout the control system is. The outboard tips of the ailerons can be either taped to the wing, or shortened with stationary outboard sections in place. Directly driving the flaps from center span [of each flap] is superior to torque rods from a control stand point.
Owning a numbered drill index helps with setting up control systems but you can also use a slightly heated piece of push rod wire to make custom fit, slop free holes in servo arms and nylon control horns.
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Old 04-21-2008, 11:29 AM
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Default RE: help me understand aileron "flutter"

Good stuff!

My shrike is all stock with a Magnum .15xls, It sounds like the only real fix is to remove the ailerons, and somehow increase the wire tubes and thus allowing larger, more stiff wires to be installed. Or find the same sized wire with less torqabilityness.

More fun than a barrel of monkeys!!!

FEAR NOT! a lesson has been learned!

thanks
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Old 04-21-2008, 11:38 AM
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Default RE: help me understand aileron "flutter"

Another option is putting smaller servos, half the thrust of the one you have now, out in the wings. Then you get a good solid drive out to the wing.
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Old 04-21-2008, 12:33 PM
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Default RE: help me understand aileron "flutter"

I had thought about that, using micro servos for each. Its probably about the same amount of work, hhhhmmmmm.... !
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Old 04-21-2008, 12:37 PM
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Tall Paul
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Default RE: help me understand aileron "flutter"


ORIGINAL: Flypaper 2

Another option is putting smaller servos, half the thrust of the one you have now, out in the wings. Then you get a good solid drive out to the wing.
.
With the Goldberg Tiger II, a notorious flutterer, the 2 servo fix is mandatory.
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Old 04-21-2008, 12:37 PM
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Default RE: help me understand aileron "flutter"


ORIGINAL: crashinator

I had thought about that, using micro servos for each. Its probably about the same amount of work, hhhhmmmmm.... !

It actually might be quite a bit less work. No dissassembly required.
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Old 04-21-2008, 12:47 PM
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Default RE: help me understand aileron "flutter"


ORIGINAL: Tall Paul


ORIGINAL: Flypaper 2

Another option is putting smaller servos, half the thrust of the one you have now, out in the wings. Then you get a good solid drive out to the wing.
.
With the Goldberg Tiger II, a notorious flutterer, the 2 servo fix is mandatory.
Is this in addition to the aileron servo, or are you suggesting to switch to dual aileron servos, each with less torque?
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Old 04-21-2008, 01:02 PM
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Default RE: help me understand aileron "flutter"

Torque rod style ailerons are even more prone to flutter thanks to driving the ailerons from one ende rather than somewhere in the middle. This style of control activation ensures that the ailerons out at the tips are quite flexy and that just adds to the possibility of flutter. They basically can never be stiff enough.
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Old 04-21-2008, 02:11 PM
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Default RE: help me understand aileron "flutter"

If the torque rods are 1/8" music wire and not too long, that will do the trick. A slop free torque rod bearing can be made by oiling the rods and burying them in puddles of 5 minute epoxy. That XLS .15 must be running pretty good?
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Old 04-21-2008, 02:21 PM
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Mike Connor
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Default RE: help me understand aileron "flutter"

Many racing airplanes use torque rods because it is clean and light. It just needs to be done right. With torque rods in my Shrike 40 and a Jett 50 I could do a terminal velocity dive without flutter after mods to correct issues. The larger control surface size does take some work.
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Old 04-21-2008, 02:37 PM
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Default RE: help me understand aileron "flutter"

The xls is on its 5th tank turning a M.A. 8x4 and revving 16,800

It was 1/8" piano wire I used with some brass tubing for sleeves, If I could find some other wire with less "torqabilityness" (Im starting to like this word!) it would be the easiest thing I guess. But I suppose the easiest way may not be the BEST way.
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Old 04-21-2008, 02:53 PM
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Default RE: help me understand aileron "flutter"

If your getting flutter at your current speeds in level flight there is something very wrong. Did you epoxy the torque rod into the aileron? Had to ask.
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Old 04-21-2008, 03:52 PM
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Default RE: help me understand aileron "flutter"



Thanks for the good laugh, Mike.

I do the control horn in the center of the surface if I do not get impatient.
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Old 04-21-2008, 04:13 PM
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Default RE: help me understand aileron "flutter"

If the plane is only doing 60-70 mph, there should be something very obvious. The stock Shrike 10 airframe with the single square balsa spar would allow the whole airframe to flutter at some point.
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Old 04-21-2008, 05:16 PM
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Default RE: help me understand aileron "flutter"

I did glue the rod into the aileron, with close inspection, its obvious the wire is just too giving.

The plane feels solid, responds well to commands.

Could a guy temporarily put some rubber bands around the wing fore and aft to apply pressure to the aileron and go for a test flight?
would this help prove it is an aileron, or would it result in scrap balsa !!!!
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Old 04-21-2008, 05:33 PM
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Default RE: help me understand aileron "flutter"

Another way to fix it is to bolt on a plastic Dubro horn about in the middle of the aileron as far as the length goes, and as near to the hinge line as possible. Figure out how to screw a piano wire to it so it hangs down and forward on about a 45 degree angle and add weight to the front till it balances the aileron without being hooked up. Take a look at the stab on the P38 Lightning to get a picture of what I'm talking about. It has two on it, top and bottom, but you only need one. The lightning needed it on a high speed dive. This would be good as an experiment.
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Old 04-21-2008, 05:37 PM
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Default RE: help me understand aileron "flutter"

You could just tape the hinge line to make it stiffer for a test flight. I wouldn't use rubber bands.
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Old 04-21-2008, 09:10 PM
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Default RE: help me understand aileron "flutter"


ORIGINAL: FatOrangeKat


ORIGINAL: Tall Paul


ORIGINAL: Flypaper 2

Another option is putting smaller servos, half the thrust of the one you have now, out in the wings. Then you get a good solid drive out to the wing.
.
With the Goldberg Tiger II, a notorious flutterer, the 2 servo fix is mandatory.
Is this in addition to the aileron servo, or are you suggesting to switch to dual aileron servos, each with less torque?
.
I use the first two servos that I pick out of the spares box. These don't necessarily have to match the single being replaced.
.
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Old 04-26-2008, 11:06 AM
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Default RE: help me understand aileron "flutter"

Have you sealed the hinge line?

If you are getting flutter, either your control rod has slop, or the wind going through the hinge line starts the control surface oscillating.

Sealing the hinge line can't do anything else but help the situation.

Regards,

Dennis
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