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help me understand aileron "flutter" - 4/21/2008 2:48:43 PM   
crashinator


 

Posts: 51
Joined: 8/27/2007
From: westport island, ME, USA
Status: offline 		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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RE: help me understand aileron "flutter" - 4/21/2008 2:55:10 PM   
allans


 

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From: Yorktown Hgts, NY, USA
Status: offline 		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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RE: help me understand aileron "flutter" - 4/21/2008 3:12:10 PM   
cyclops2


 

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From: Frenchtown, NJ, USA
Status: offline 		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.

< Message edited by cyclops2 -- 4/21/2008 3:13:11 PM >

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RE: help me understand aileron "flutter" - 4/21/2008 3:26:48 PM   
Flypaper 2



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From: Kingston, ON, CANADA
Status: offline 		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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RE: help me understand aileron "flutter" - 4/21/2008 3:52:11 PM   
da Rock



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Joined: 10/11/2005
From: western, NC, USA
Status: offline 		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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RE: help me understand aileron "flutter" - 4/21/2008 3:52:12 PM   
Mike Connor



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quote:

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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RE: help me understand aileron "flutter" - 4/21/2008 5:23:49 PM   
combatpigg



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Status: offline 		........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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RE: help me understand aileron "flutter" - 4/21/2008 5:29:57 PM   
crashinator


 

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From: westport island, ME, USA
Status: offline 		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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RE: help me understand aileron "flutter" - 4/21/2008 5:38:29 PM   
Flypaper 2



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Status: offline 		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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RE: help me understand aileron "flutter" - 4/21/2008 6:33:09 PM   
crashinator


 

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From: westport island, ME, USA
Status: offline 		I had thought about that, using micro servos for each. Its probably about the same amount of work, hhhhmmmmm.... !

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RE: help me understand aileron "flutter" - 4/21/2008 6:37:12 PM   
Tall Paul



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quote:

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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RE: help me understand aileron "flutter" - 4/21/2008 6:37:49 PM   
da Rock



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quote:

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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RE: help me understand aileron "flutter" - 4/21/2008 6:47:54 PM   
gaRCfield


 

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quote:

ORIGINAL: Tall Paul


quote:

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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RE: help me understand aileron "flutter" - 4/21/2008 7:02:15 PM   
BMatthews



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Status: offline 		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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RE: help me understand aileron "flutter" - 4/21/2008 8:11:56 PM   
combatpigg



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Status: offline 		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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RE: help me understand aileron "flutter" - 4/21/2008 8:21:59 PM   
Mike Connor



Posts: 1339
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From: Tulsa, OK, USA
Status: offline 		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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