Can Washout Cause Flutter??

[DonMorrisey]

A friend's homebuilt recently went down with an 8000 hour pilot at the
controls. No one was hurt and the plane was landed in a field. The
pilot reported hearing/feeling an extremely loud vibration from the
wing, he immediately killed power and landed. One of the wings was
visibly buckled. The airplane is all aluminum with a 36 ' wing span.
The NTSB showed up and after getting the plane to a hangar, the wing
was dismantled. The rear spar had failed and was twisted and buckled,
although the wing had held together. The NTSB guys said the very solid
structural design and construction of the wing was what saved the plane
from coming apart in the air, as well as the pilot's quick response.
The conclusion by the NTSB was aileron flutter, they found several
bolts in the aileron hinge bracket assemblies (which hold the aileron
to the rear spar) that were supposed to have been drilled 10 MM from
the top and bottom edge of the spar flange and these had been drilled
at 25 MM or so. That was it and they walked away. There was no
visible damage to the aileron, the aileron spar or the hinge bracket
assemblies. The pliot reported no vibration in the stick. My friend
is convinced it had something to do with the washout of the wing. The
wing is a NACA 4413 Airfoil, modified in that it has no undercamber on
the bottom, the bottom is flat. The washout, which is built into the
wing during construction, is a couple of degrees. The plane I am
building uses the same wing/washout. I have done research but can't
find anything specific linking washout to flutter.

Any thoughts on this??

Thanks. Don...

[Wayne Paul]

Don,

A common cause of flutter is unbalance control surfaces. Here is a link that
you might find helpful.
(http://www.soaridaho.com/Schreder/Construction/HBldr_Hall.html#flutter)

Wayne
HP-14 "6F"
http://www.soaridaho.com/Schreder


"DonMorrisey" > wrote in message
oups.com...
>A friend's homebuilt recently went down with an 8000 hour pilot at the
> controls. No one was hurt and the plane was landed in a field. The
> pilot reported hearing/feeling an extremely loud vibration from the
> wing, he immediately killed power and landed. One of the wings was
> visibly buckled. The airplane is all aluminum with a 36 ' wing span.
> The NTSB showed up and after getting the plane to a hangar, the wing
> was dismantled. The rear spar had failed and was twisted and buckled,
> although the wing had held together. The NTSB guys said the very solid
> structural design and construction of the wing was what saved the plane
> from coming apart in the air, as well as the pilot's quick response.
> The conclusion by the NTSB was aileron flutter, they found several
> bolts in the aileron hinge bracket assemblies (which hold the aileron
> to the rear spar) that were supposed to have been drilled 10 MM from
> the top and bottom edge of the spar flange and these had been drilled
> at 25 MM or so. That was it and they walked away. There was no
> visible damage to the aileron, the aileron spar or the hinge bracket
> assemblies. The pliot reported no vibration in the stick. My friend
> is convinced it had something to do with the washout of the wing. The
> wing is a NACA 4413 Airfoil, modified in that it has no undercamber on
> the bottom, the bottom is flat. The washout, which is built into the
> wing during construction, is a couple of degrees. The plane I am
> building uses the same wing/washout. I have done research but can't
> find anything specific linking washout to flutter.
>
> Any thoughts on this??
>
> Thanks. Don...
>

[Fortunat1[_2_]]

"DonMorrisey" > wrote in
oups.com:

> A friend's homebuilt recently went down with an 8000 hour pilot at the
> controls. No one was hurt and the plane was landed in a field. The
> pilot reported hearing/feeling an extremely loud vibration from the
> wing, he immediately killed power and landed. One of the wings was
> visibly buckled. The airplane is all aluminum with a 36 ' wing span.
> The NTSB showed up and after getting the plane to a hangar, the wing
> was dismantled. The rear spar had failed and was twisted and buckled,
> although the wing had held together. The NTSB guys said the very
> solid structural design and construction of the wing was what saved
> the plane from coming apart in the air, as well as the pilot's quick
> response. The conclusion by the NTSB was aileron flutter, they found
> several bolts in the aileron hinge bracket assemblies (which hold the
> aileron to the rear spar) that were supposed to have been drilled 10
> MM from the top and bottom edge of the spar flange and these had been
> drilled at 25 MM or so. That was it and they walked away. There was
> no visible damage to the aileron, the aileron spar or the hinge
> bracket assemblies. The pliot reported no vibration in the stick. My
> friend is convinced it had something to do with the washout of the
> wing. The wing is a NACA 4413 Airfoil, modified in that it has no
> undercamber on the bottom, the bottom is flat. The washout, which is
> built into the wing during construction, is a couple of degrees. The
> plane I am building uses the same wing/washout. I have done research
> but can't find anything specific linking washout to flutter.
>
> Any thoughts on this??
>

Umm, unlikely. Mostly flutter is caused by the surface itself deflecting
whatever it's been attached to and when that surface moves the related
control surface moves with it and inertial forces cuase it to deflect in
the opposite direction, loading up the surface. In one scenario, for
instance, the wing is deflected rapidly upwards by a gust. the aileron
is left behind because of inertia, i.e, the trailing edge of the
aileron's mass tends to deflect it downwards which of course now adds to
the wing's journey upwards. the wing loads up, bends, and eventualy
springs back in the other direction, down, thereby causing the aileron
to now deflect upwards and so on. the mass balance attached to a control
surface should eliminate this problem. Flutter can also be induced by an
aerodynamic cyclic where the flow covering the surface is cycled. I've
seen this and it's nowhere near as destructive as the previous example.
One thing worth remembering about flutter is that the tendency of a
surface to flutter is exacerbated by the load on the wing. That is to
say that a surface is more likely to flutter if it's loaded up with G
than it is if not. So, you screw up a maneuver and end up pointing
downhill and accelerating fast. Off comes the power and up comes the
nose and the G. This is a likely scenario for flutter.. Anything that
loads a susceptable surface up is going to induce it more quickly at a
given speed than the same scenario without the extra G, whether it be
caused by manueveing, turbulence or W.H.Y..

Needless to say, a control surface which has been incorrectly attached
to the airframe is significantly more likely to suffer.

Even if a control surface has been correctly balanced during building,
care must be exercised to ensure balance is maintained after painting.
Paint can add significantly to the weight and quite a few accidents have
been attributed to neglecting to do this..

[Morgans[_2_]]

"DonMorrisey" > wrote

> My friend
> is convinced it had something to do with the washout of the wing. The
> wing is a NACA 4413 Airfoil, modified in that it has no undercamber on
> the bottom, the bottom is flat. The washout, which is built into the
> wing during construction, is a couple of degrees. The plane I am
> building uses the same wing/washout. I have done research but can't
> find anything specific linking washout to flutter.
>
> Any thoughts on this??

Since we don't know the design of this plane, I have to ask if the aileron
goes all the way to the tip, or is there a small region at the tip where
there is a little plain wing.

I ask because the vortices peeling off the wingtip striking the aileron can
help to excite flutter. I don't have anything to site, but I have read this
before, and it does apply to model planes.

If balanced completely, and there is no slop, this might not be a problem,
but having it attached that far down no doubt left some play in the system.
--
Jim in NC

[[email protected]]

Just having washout or any other design feature incorporated in a wing
does not usually cause flutter. It is the total overall effect of all
design parameters that determines whether flutter will be an issue.
Adding washout to a wing could just as easily solve a flutter problem
as cause one. It just depends. That's why aerodynamics is such an easy
subject. ;).

Bud


DonMorrisey wrote:
> A friend's homebuilt recently went down with an 8000 hour pilot at the
> controls. No one was hurt and the plane was landed in a field. The
> pilot reported hearing/feeling an extremely loud vibration from the
> wing, he immediately killed power and landed. One of the wings was
> visibly buckled. The airplane is all aluminum with a 36 ' wing span.
> The NTSB showed up and after getting the plane to a hangar, the wing
> was dismantled. The rear spar had failed and was twisted and buckled,
> although the wing had held together. The NTSB guys said the very solid
> structural design and construction of the wing was what saved the plane
> from coming apart in the air, as well as the pilot's quick response.
> The conclusion by the NTSB was aileron flutter, they found several
> bolts in the aileron hinge bracket assemblies (which hold the aileron
> to the rear spar) that were supposed to have been drilled 10 MM from
> the top and bottom edge of the spar flange and these had been drilled
> at 25 MM or so. That was it and they walked away. There was no
> visible damage to the aileron, the aileron spar or the hinge bracket
> assemblies. The pliot reported no vibration in the stick. My friend
> is convinced it had something to do with the washout of the wing. The
> wing is a NACA 4413 Airfoil, modified in that it has no undercamber on
> the bottom, the bottom is flat. The washout, which is built into the
> wing during construction, is a couple of degrees. The plane I am
> building uses the same wing/washout. I have done research but can't
> find anything specific linking washout to flutter.
>
> Any thoughts on this??
>
> Thanks. Don...

[DonMorrisey]

>
> Since we don't know the design of this plane, I have to ask if the aileron
> goes all the way to the tip, or is there a small region at the tip where
> there is a little plain wing.
>
> --
> Jim in NC

Hi Jim, the aileron does not extend to the tip. There is perhaps a 12"
section of wing from the outboard side of the aileron to the tip of the
wing.

Don...

[cavelamb himself]

DonMorrisey wrote:
>>Since we don't know the design of this plane, I have to ask if the aileron
>>goes all the way to the tip, or is there a small region at the tip where
>>there is a little plain wing.
>>
>>--
>>Jim in NC
>
>
> Hi Jim, the aileron does not extend to the tip. There is perhaps a 12"
> section of wing from the outboard side of the aileron to the tip of the
> wing.
>
> Don...
>

WERE (because it's probably a moot point now) the hinges and alieron
actuation mechanism TIGHT (or maybe a little sloppy)?

[DonMorrisey]

> WERE (because it's probably a moot point now) the hinges and alieron
> actuation mechanism TIGHT (or maybe a little sloppy)?

Well, I actually never saw the airplane. My firiend says they were
tight but who knows, he also didn't realize the bolts in the brackets
were too far down from the bend in the spar flange, so I can't really
say.

He was surprised that the aileron and nothing associated with it had
any damage. That's what led him to his conclusion that the washout had
something to do with it.

Don...

[cavelamb himself]

DonMorrisey wrote:
>>WERE (because it's probably a moot point now) the hinges and alieron
>>actuation mechanism TIGHT (or maybe a little sloppy)?
>
>
> Well, I actually never saw the airplane. My firiend says they were
> tight but who knows, he also didn't realize the bolts in the brackets
> were too far down from the bend in the spar flange, so I can't really
> say.
>
> He was surprised that the aileron and nothing associated with it had
> any damage. That's what led him to his conclusion that the washout had
> something to do with it.
>
> Don...
>

As another poster pointed out, we don't know anything about the design
or construction of this plane.

But you _may_ have just answered your own question.

If the aileron brackets were supported by nothing more than the web of
the rear spar I wouldn't be surprised it it encountered flutter.

It's an Aero-Elastic phenomenon, remember?

If it can flex, it fer sure will...

Glad nobody was hurt.

[Stealth Pilot]

On 15 Jan 2007 19:48:55 -0800, "DonMorrisey" >
wrote:

>A friend's homebuilt recently went down with an 8000 hour pilot at the
>controls. No one was hurt and the plane was landed in a field. The
>pilot reported hearing/feeling an extremely loud vibration from the
>wing, he immediately killed power and landed. One of the wings was
>visibly buckled. The airplane is all aluminum with a 36 ' wing span.
>The NTSB showed up and after getting the plane to a hangar, the wing
>was dismantled. The rear spar had failed and was twisted and buckled,
>although the wing had held together. The NTSB guys said the very solid
>structural design and construction of the wing was what saved the plane
>from coming apart in the air, as well as the pilot's quick response.
>The conclusion by the NTSB was aileron flutter, they found several
>bolts in the aileron hinge bracket assemblies (which hold the aileron
>to the rear spar) that were supposed to have been drilled 10 MM from
>the top and bottom edge of the spar flange and these had been drilled
>at 25 MM or so. That was it and they walked away. There was no
>visible damage to the aileron, the aileron spar or the hinge bracket
>assemblies. The pliot reported no vibration in the stick. My friend
>is convinced it had something to do with the washout of the wing. The
>wing is a NACA 4413 Airfoil, modified in that it has no undercamber on
>the bottom, the bottom is flat. The washout, which is built into the
>wing during construction, is a couple of degrees. The plane I am
>building uses the same wing/washout. I have done research but can't
>find anything specific linking washout to flutter.
>
>Any thoughts on this??
>
>Thanks. Don...

flutter can be prevented by....

having the cg of the aerofoil section in front of the spar.

the aileron can be treated as an aerofoil section in the same way but
the entire overall wing cross section needs to follow the rule as
well.

the rear spar needs to be more flexible than the front or main spar.

the ailerons must not have the ability to move without the control
moving them.

the corollary is that if you get any or all of these in the opposite
sense then you can aid in the occurrence of flutter.

washout in itself cant cause flutter.

Stealth Pilot

[jls]

"cavelamb himself" > wrote in message
link.net...
> DonMorrisey wrote:
> >>WERE (because it's probably a moot point now) the hinges and
alieron
> >>actuation mechanism TIGHT (or maybe a little sloppy)?
> >
> >
> > Well, I actually never saw the airplane. My firiend says they
were
> > tight but who knows, he also didn't realize the bolts in the
brackets
> > were too far down from the bend in the spar flange, so I can't
really
> > say.
> >
> > He was surprised that the aileron and nothing associated with it
had
> > any damage. That's what led him to his conclusion that the
washout had
> > something to do with it.
> >
> > Don...
> >
>
> As another poster pointed out, we don't know anything about the
design
> or construction of this plane.
>
> But you _may_ have just answered your own question.
>
> If the aileron brackets were supported by nothing more than the web
of
> the rear spar I wouldn't be surprised it it encountered flutter.
>
> It's an Aero-Elastic phenomenon, remember?
>
> If it can flex, it fer sure will...
>
> Glad nobody was hurt.
>

A wing being built here at the moment has three steel channel aileron
hinge brackets supported by the rear spar. They are attached to the
web by AN 5-5 bolts. They are also attached to the false spar,
though. That must make all the difference in the world.

Here's something interesting, to me anyways. C. G. Taylor did some
interesting things when he broke away from Bill Piper and tooled up
for the Taylorcraft. He made extensive use of magnesium alloy, in the
wheels, yokes, and aileron hinge brackets. It's light and strong, but
woe unto you when it starts to corrode.

On my Taylorcraft I noticed that the false spar was tight against the
hinge brackets. I should have looked more closely. When the aircraft
was built in the '40's, the false spar holes for the magnesium hinge
brackets were hand-cut, and some of them allowed the aluminum false sp
ar to rub up against the hinge brackets. From the constant faying one
of the magnesium brackets developed a crack over decades of use, and
one day it broke. I noticed the aileron response was mushy.

Thankfully a friend preflighted the aircraft before I flew it again.

[Blueskies]

"DonMorrisey" > wrote in message ups.com...
:
: > WERE (because it's probably a moot point now) the hinges and alieron
: > actuation mechanism TIGHT (or maybe a little sloppy)?
:
: Well, I actually never saw the airplane. My firiend says they were
: tight but who knows, he also didn't realize the bolts in the brackets
: were too far down from the bend in the spar flange, so I can't really
: say.
:
: He was surprised that the aileron and nothing associated with it had
: any damage. That's what led him to his conclusion that the washout had
: something to do with it.
:
: Don...
:

the aileron & linkage could be stout and break the wing without any damage visible.

[J.Kahn]

Yeah washout has nothing to do with it.

Flutter is equivalent to when you boost yourself on a park swing to go
higher. Your body is the aileron, and the swing chains are the wing
structure, and you move the CG of your body in a harmonic relationship
to the swing to excite and then amplify its movements. The aileron is
doing the same thing if its CG is aft of its hinge line.

By balancing the aileron and putting its CG on the hinge line the
aileron is incapable of adding to the energy in the vibrating wing
structure so stiffness is less critical. Its like laying out horizontal
on the park swing so if someone moves the swing your body just goes
along and can't amplify its motion.

John