Wrinkly flat panels

I've seen a few homebuilts with part of the fuselage panel that are flat
aluminum that are quite wrinkly and tend to "oil can" and make noise in
various flight attitudes. I haven't seen cross breaks used to stop this,
although it is used in duct work to stiffen flat panels. (cross breaks are
slight bends in the metal, done diagonally from corner to corner)

Another thought to reduce this noise is to spray urethane foam on the panels.
I know that this foam is combustable, but I figure for it to get on fire would
mean the pilot and passenger cabin is already engulfed, so it wouldn't really
matter.

What do you think?

thanks,
tom pettit

On Wed, 25 Feb 2004 00:19:12 GMT, wrote:

:I've seen a few homebuilts with part of the fuselage panel that are flat
:aluminum that are quite wrinkly and tend to "oil can" and make noise in
:various flight attitudes. I haven't seen cross breaks used to stop this,
:although it is used in duct work to stiffen flat panels. (cross breaks are
:slight bends in the metal, done diagonally from corner to corner)
:
:Another thought to reduce this noise is to spray urethane foam on the panels.
:I know that this foam is combustable, but I figure for it to get on fire would
:mean the pilot and passenger cabin is already engulfed, so it wouldn't really
:matter.

Check out

http://www.eng.fiu.edu/pantherskin/

It's very interesting stuff. Especially the burn through test.

wrote in message
...
I've seen a few homebuilts with part of the fuselage panel that are flat
aluminum that are quite wrinkly and tend to "oil can" and make noise in
various flight attitudes. I haven't seen cross breaks used to stop this,
although it is used in duct work to stiffen flat panels. (cross breaks
are
slight bends in the metal, done diagonally from corner to corner)

Another thought to reduce this noise is to spray urethane foam on the
panels.
I know that this foam is combustable, but I figure for it to get on fire
would
mean the pilot and passenger cabin is already engulfed, so it wouldn't
really
matter.

What do you think?

thanks,
tom pettit

A stiffening bead pressed into the panel or aluminum channel or angle
riveted to the back of the panel. My old Taylorcraft has half-circle
pressed beads on the firewall to stiffen it, and I notice the old Cessna I
have the cowl off of has a flange running horizontally across the middle of
the firewall, plus a few other neat stiffening devices. That stiffens it
for you. You can countersink the rivets for appearance's sake if you wish.

Stiffening a panel of fiberglas is great fun: all you have to do is make a
sandwich with foam in between, the thicker the foam the stiffer. As a
matter of fact as the thickness increases the stiffness and strength go up
at a staggering rate. There are formulas for that and not being a
mathematician I'd best not delve into the theory of beams but if you double
the height of a beam you have increased the stiffness and strength of the
beam by exponents of the increase in height. Let Billy B. Badd explain it
to you in his most inimitable articulate way.

The solution is simple. Cut the panel from 0.090 2024. The panel will
never wrinkle. Then paint the panel with an epoxy based paint. It will look
great for years.

We have them CNC machined all the time and they look great. email me if you
need me to set you up with a place that can do that.

Thanks, Chris

wrote in message
...
I've seen a few homebuilts with part of the fuselage panel that are flat
aluminum that are quite wrinkly and tend to "oil can" and make noise in
various flight attitudes. I haven't seen cross breaks used to stop this,
although it is used in duct work to stiffen flat panels. (cross breaks
are
slight bends in the metal, done diagonally from corner to corner)

Another thought to reduce this noise is to spray urethane foam on the
panels.
I know that this foam is combustable, but I figure for it to get on fire
would
mean the pilot and passenger cabin is already engulfed, so it wouldn't
really
matter.

What do you think?

thanks,
tom pettit

Curiously enough, I've seen pannel wrinkling on the front end of a B-52!

Harry

The stiffness goes up by the third power if the thickness. Double the
thickness of a plate, and it's eight times as stiff.

--
Bob (Chief Pilot, White Knuckle Airways)


" jls" wrote in message
. ..

wrote in message
...
I've seen a few homebuilts with part of the fuselage panel that are flat
aluminum that are quite wrinkly and tend to "oil can" and make noise in
various flight attitudes. I haven't seen cross breaks used to stop
this,
although it is used in duct work to stiffen flat panels. (cross breaks
are
slight bends in the metal, done diagonally from corner to corner)

Another thought to reduce this noise is to spray urethane foam on the
panels.
I know that this foam is combustable, but I figure for it to get on fire
would
mean the pilot and passenger cabin is already engulfed, so it wouldn't
really
matter.

What do you think?

thanks,
tom pettit

A stiffening bead pressed into the panel or aluminum channel or angle
riveted to the back of the panel. My old Taylorcraft has half-circle
pressed beads on the firewall to stiffen it, and I notice the old Cessna I
have the cowl off of has a flange running horizontally across the middle
of
the firewall, plus a few other neat stiffening devices. That stiffens it
for you. You can countersink the rivets for appearance's sake if you
wish.

Stiffening a panel of fiberglas is great fun: all you have to do is make
a
sandwich with foam in between, the thicker the foam the stiffer. As a
matter of fact as the thickness increases the stiffness and strength go up
at a staggering rate. There are formulas for that and not being a
mathematician I'd best not delve into the theory of beams but if you
double
the height of a beam you have increased the stiffness and strength of the
beam by exponents of the increase in height. Let Billy B. Badd explain it
to you in his most inimitable articulate way.

Earlier, "Chris Batcheller" wrote:

The solution is simple. Cut the panel from 0.090 2024...

I think that the original poster was using the term "panel" in a
somewhat generic sense, and not necessarily to refer to an instrument
panel. But that was the way I first read it, too.

Thanks, and best regards to all

Bob K.

Howdy All,

Thanks for your thoutful replies. They seem to fall into three main ideas:

Thicker panels:
yeah. This will work, but for exterior fuselage panels, it would be
prohibitively heavy. I'll pass.

Building in some kind of "upset":
This will work. Breaks, as I described will make the panels stiffer. Another
poster suggested rolling in ridges that would stiffen the panel. These would
look kind of goofy, and have a small drag effect. I think I'll pass.

Spraying a urethane foam on the inside:
This will stiffen the panel and improve the noise level inside the aircraft.
It would require a fire rated foam such as "gator skin". Other are
available. I'm leaning this way.

Thanks to all,
tom pettit

wrote:
Howdy All,


Building in some kind of "upset":
This will work. Breaks, as I described will make the panels stiffer. Another
poster suggested rolling in ridges that would stiffen the panel. These would
look kind of goofy, and have a small drag effect. I think I'll pass.

tom pettit

Tom, your plane, and you'll do as you please, but I don't think it would
have to add a measurable amount of drag or look goofy. I'm thinking of
a WW2 Japanese rising sun motif, starting at the center or the front
edge and expanding toward the back.

Aaah, if there were only time to build every iteration of airplane that
I could dream up.

--
http://www.ernest.isa-geek.org/
"Ignorance is mankinds normal state,
alleviated by information and experience."
Veeduber

wrote:

Howdy All,

Thanks for your thoutful replies. They seem to fall into three main ideas:

Thicker panels:
yeah. This will work, but for exterior fuselage panels, it would be
prohibitively heavy. I'll pass.

Building in some kind of "upset":
This will work. Breaks, as I described will make the panels stiffer. Another
poster suggested rolling in ridges that would stiffen the panel. These would
look kind of goofy, and have a small drag effect. I think I'll pass.

Spraying a urethane foam on the inside:
This will stiffen the panel and improve the noise level inside the aircraft.
It would require a fire rated foam such as "gator skin". Other are
available. I'm leaning this way.

Thanks to all,
tom pettit

Lean back the other way some, Tom.
You are about to fall off of something here...

Filling large cavities with foam may be great for boats,
but don't do it to a metal airplane.

The lightest mix you'll get will be at least 3 pounds per cubic foot,
minimum.
And you'll need to pull a light vacuum to get that repeatably.

The foam will also continue to expand long after the skin has bulged way
outta shape.

Better solutions:

Deeply curved panels an not so susceptible to oil canning by nature of
their shape.
But that's a preliminary design issue, not an add on.

Better support inside will help reduce skin wrinkling and noise.
Closer spaced ribs, a cleverly placed stringer here or there?

I think the correct answer is thicker skin.

Increasing skin thickness a few thousandths will make a stiffer panel at
a fraction
of the weight of extra structure - or a fifty emergency flotation.


Now, may I suggest you contact the original designer with this question?

Because something as simple sounding as increasing skin thickness can
have snowball
effects on light structures.

In my book, that's considered a bad thing.

Richard