Wrinkly flat panels

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

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

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

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

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

thanks,
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

In article , Richard Lamb wrote:

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

The stuff sticks amazingly well to almost anything. It is quite tough. I
guess if it started flaking off, I could cut a hole in the back and start sky
writing with the trail of white flakes.

Probably the premade dampening material would be most practical. I have used
them before. The better performing ones are almost as heavy as the foam,
though.

tom

wrote:

In article , Richard Lamb wrote:

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

The stuff sticks amazingly well to almost anything. It is quite tough. I
guess if it started flaking off, I could cut a hole in the back and start sky
writing with the trail of white flakes.

Probably the premade dampening material would be most practical. I have used
them before. The better performing ones are almost as heavy as the foam,
though.

tom

Certainly neater :^)

It really doesn't take that much material to damp the flat panel
rattling and oil canning.

If I'm not mistaken, this is the same kind of fire proof foam that was
used in the World Trade center to protect the steel structure from fire.
Too much was knocked loose during the impact.
The rest is history...

I'd expect the vibration (and expecially local vibratin (oil canning?))
would play hell with sprayed on foam...

So, have you started on the Zodiac yet?

Richard