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ACRO E-mail Archive Thread: [Acro] RE: Aileron Flutter Question

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ACRO E-mail Archive Thread: [Acro] RE: Aileron Flutter Question


Thread: [Acro] RE: Aileron Flutter Question

Message: [Acro] RE: Aileron Flutter Question

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From: "Peter Ashwood-Smith" <petera at>

Date: Fri, 01 Nov 2002 03:23:38 UTC


Presumably, unless the surface is REALLY stiff a mass at the end will
actually make things worse. The carbon fiber ailerons can get away with this
but a fabric/wood thing probably is not stiff enough. I guess the reason for
this is because a non stiff aileron can actually be thought of as two or
more independent ailerons which can move a bit with respect to each other.
Since the mass is associated with only the outer most one, it only really
counterbalances the outer 'aileron'. For that job it is too much mass and
hence the outer 'aileron' is now incorrectly balanced and will flutter ..
bringing the other pieces of aileron with it a few milliseconds behind.
Hence the reason why the mass is best evenly distributed the length of the

One really fascinating thing about aileron flutter is that an aileron (as it
deflects up or down) acts much like a trim tab or boost tab on your elevator
or rudder. It induces the thing it is attached to twist the other way with a
huge leverage due to its distance from the spar. This means your entire wing
will rotate about its main spar a little bit each time the aileron goes up
or down. This will eventually break the rear spar and then cause the wing to
depart the aircraft due to the now unrestricted twist up and down induced by
the aileron....unless the hinges let go first.


	-----Original Message-----
	From:	Klusmanp at [SMTP:Klusmanp at]
	Sent:	Thursday, October 31, 2002 9:22 PM
	To:	acro at
	Subject:	[Acro] RE: Aileron Flutter Question

	I've got an old IAC "Technical Tips Manual, Vol II" that has a good
	on flutter (see page 112). The article shows a ground vibration test
	determine flutter characteristics of a "Stephens-Type Monoplane"
after a 
	flutter induced crash/fatality of another of the same type airplane.

	The testing revealed that a counterbalance horn at the tip of the
	would actually be making the flutter situation worse! The article
goes on to 
	advise a very specific placement of a COMBINATION of counterweights
to avoid 
	the possibility of flutter for these airplanes.

	I've been invloved in flutter issues in my work at Cessna. I'm a
	engineer and I've learned just enough about flutter to know that I
don't know 
	anything about flutter. 

	Bottom line: Follow the advice of Peter's last paragraph below.

	Paul Klusman
	Pitts S-1S

	In a message dated 10/31/02 10:21:18 AM EST,
petera at writes:

	<< You  make both flutter resistant with proper static balance.
Normally you
	 would put weight in the leading edge ahead of the hinge point in a
Friese to
	 obtain the proper static balance. If the hinge point is not aft of
	 leading edge, you would add a counter balance in the form of a horn
(i.e the
	 surface is L shaped). Alternatively you can add mass under and
ahead of the
	 surface hinge line with a streamlined tube of some kind angled 45
degrees or
	 more forward, this is often combined with a spade.
	 Other tricks that can reduce flutter are reduced hinge gap. With an
	 hinge you can make a beautifully tight hinge gap. I.e. the cross
section of
	 the trailing edge '(', leading edge of the aileron '(' and hinge
axis 'o'
	 look like this: "((  o ". 
	 Anyway you don't want to be mucking with this stuff unless you know
what you
	 are doing because flutter can rip a plane apart in milliseconds.
Attachement 1: part2.html


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