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.

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

In article , Richard Lamb wrote:


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.

Richard

Sorry I wasn't clearer on my intention. I'd only spray about an inch on the
panels. Not much weight, and still get significant damping.

tom

wrote:

In article , Richard Lamb wrote:


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.

Richard

Sorry I wasn't clearer on my intention. I'd only spray about an inch on the
panels. Not much weight, and still get significant damping.

tom

Balderdash, tom.

I think you are blowing in my ear.

First, just how do you expect to "spray on" a 1 inch thick layer
of foam INSIDE a wing? I can't do it, and I can do anything
(with Duct tape!).

Second, a 100 square foot wing is 14,400 square inches.
One inch thick is 14,400 CUBIC inches, or 8.3 cubic feet.
Top and bottom skins give 28,800 cubic inches or 16.6 cuft.

At the mythical 3 lb/ft^3, that's 50 pounds.

Sorry dude, that boat don't float...

ala TriMotor - corrugations

--
Dan D.



..
wrote in message ...
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

Blueskies wrote:

ala TriMotor - corrugations

--
Dan D.


Absolutely.

MUCH thicker skins

Rihcard

In article , "Blueskies" wrote:
ala TriMotor - corrugations

I kind of like the idea of corregations. Any ideas on how to accomplish them?

thanks,
tom