Wrinkly flat panels

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...

In article , Richard Lamb wrote:
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...

Yeah it will. 8^) I was talking about flat panels on the fuselage. The
Zenith CH701 I would like to build has about 60 square feet of fuselage area
behind the cabin. At one inch, that amounts to 5 cubic feet. One website I
visited that made fire retardant spray urethane foam says 1.75 pounds per
cubic foot, so the weight of this addition would be less than nine pounds.

By the way, I don't know you well enough to blow in your ear.

Regards,

tom

wrote:

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

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

Yeah it will. 8^) I was talking about flat panels on the fuselage. The
Zenith CH701 I would like to build has about 60 square feet of fuselage area
behind the cabin. At one inch, that amounts to 5 cubic feet. One website I
visited that made fire retardant spray urethane foam says 1.75 pounds per
cubic foot, so the weight of this addition would be less than nine pounds.

By the way, I don't know you well enough to blow in your ear.

Regards,

tom

No no no no no noooo.

Ok, a different offering?

Look around for some light weight sound deadening material.
It's right about 1/8" thick and either has a self stick backing
or can be stuck in place with probond.

(That's the way my neighbor did his 601-HDS anyway).

You really don't need to completely cover the area to reduce rattling.
A wide strip across the panel can be as effective.


Lastly, check that fire proof foam for "frangibility". (:^)

And how well it doesn't stick to bare aluminum?

You may find your fuselage is soon full of white fluff...



Richard

wrote in message
...
snip of misunderstanding

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...

Yeah it will. 8^) I was talking about flat panels on the fuselage. The
Zenith CH701 I would like to build has about 60 square feet of fuselage
area
behind the cabin. At one inch, that amounts to 5 cubic feet. One website
I
visited that made fire retardant spray urethane foam says 1.75 pounds per
cubic foot, so the weight of this addition would be less than nine pounds.

If the panels are really flat, then why spray it on? Low density foam is
available in sheets. I'll bet the consistency is better than you can get
from a can. Bond it on before you rivet. It shouldn't have to go all the
way to the edges to prevent the oilcanning.

It looks like for the 9 lb weight penalty you could increase the thickness
of just those panels by about .010 inches (.15 lbs/sq ft). That would make
it less likely to oilcan and stronger.

Does the foam really need to be continuous? Why not just bond some foam
stiffeners to the inside of the panel every six inches or so? The HP-18
sailplane wing is made from 1/2" foam on four inch centers. That technique
might be more anechoic than a smooth continuous foam surface, too. You
could taper the stiffeners to be thicker in the center of the panel, and get
more stiffness/unit weight that way.

An interesting way to bond the stiffeners might be to use 3M VHB (Very High
Bond) double stick tape. It's used to bond side panels on truck and trailer
bodies. Fast and no goop.

Tim Ward

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