Johnny C!

Hello gang!
I read here sometime ago about using panty hose
& epoxy over a plug for cowls, etc. I tried this
technique earlier tonight. The article that I read
said to invert a balloon over the part before the
epoxy has cured. This technique worked really
well, except for one thing. The shell that I made
seems to be really soft, when I began trimming
off the excess. I used some 30 minute 2 part
epoxy that I buy at Wally World. The part came
out really smooth. No sanding at all, other than
a slight sandable protrusion where I had an air
bubble in the balloon. This was really easy to do,
so I really want to figure this out.
I'm going to let it dry over night & check it in
the morning. Should I have used some other
epoxy or resin for a stiffer finished part, or
will it cure out better now that I have removed
the balloon?

Thanks for any input!

Johnny C!

khodges

My Feedback: (1)

I would have used finishing resin, and added some milled fiberglass. I think leaving it in the "mold" overnight to fully cure before taking it out would be better. Once you get the basic shell (the pantyhose) formed and cured, then place a couple of layers of 1/2 or 3/4 oz 'glass cloth on the inside to strengthen and stiffen it. Got any pics of your cowl?

js3

My Feedback: (3)

Johnny C,

You should post this in the Composite Construction forum. Those guys are really experienced and offer lots of good advice.

Johnny C!

I didn't know there was a composite
forum area! Can someone move this
thread?

Attached is a pic of the part. This one is
not a cowl. Its an add on to a model of
a vehicle that my buddy was commissioned
to build. I just figured it was good practice
for some cowls that I do need to make.
I have just finished wetting another plug.
This time I used Bondo resin, with three
layers of panty hose. I still need to cut
out some doors & windows so I think I'll
do that before I remove the plug. I intend
to melt the styrofoam out with mineral
spirits or gasoline.

I hope I can perfect this method. This
first part came out really smooth. This
will be an excellant way to make those
cowls!

Thanks!

Johnny C!

AlphaWhisky

I`ve done several cowlings in different sizes using this method and most impressed. Largest I`ve done so far is for an 80" span Spitfire. I used 3 layers of pantyhose and 'everyday' polyester resin scroungerd from a local glass boat-builder.

I used 4 layers of pantyhose and the result is very light but not very rigid. To stiffen it up I installed an oval shaped former flush with the rear and fixed the cowling to the firewall using button head screws accessed from the front - behind the 4" spinner hole. The former was initially held in place with Ca and then a glass ribbon and resin around the full inside perimeter.

I find this method a lot easier to do than using various weights of glass cloth - it clings to the former with no messy loose strands sticking up. I`ve only used the balloon method once - for the concave front of a cowling for a small Tigermoth. That worked well too.

Alan W

Campy

My Feedback: (1)

I have done some cowls using the lost foam method. What I have found is that once the cowl has been removed from the plug it takes 4 or 5 days for the fiberglass to harden up. until it hardens up the part will be soft and very mallable (great for final shaping if needed)

TexasAirBoss

My Feedback: (22)

Wow guys !!!! This is brilliant !!

BTW, I think UV light, or sunlight will help resin harden quicker.

Johnny C!

The part that I attempted to make with resin
on foam failed. The resin attacked the foam.
If I need to do a resin part, I will simply coat
the foam with epoxy, or better yet a balloon!
The epoxy part has stiffened up over time,
and will acceptable for the application.
When I do the rather large nose cone (it's
for the center pod an a twin I'm bashing, hence
"cone", not cowl), I think I will simply carve out
the foam as needed for the nose gear clearance
& leave the rest. It won't add much weight, but
it will add strength.

This is the most fun I've had trying something
new in a long time. But that's probably because
I good success with the first attempt. I can see
me adding cowls to all of my non scale, exposed
engines planes!

Later!

Johnny C!

da Rock

JohnnyC,
You hit the bullseye. If anyone is making a one-of-a-kind part, it's easiest to carve it out of foam, epoxy/glass that shape and use it as is. The foam adds a trememdous amount of strength and support to the glass. And provides crush/crash protection too.

saintcreed

My Feedback: (205)

The panty hose trick works great...as stated in all the above threads...I use four layers with epoxy letting it dry 12 hours or more before putting on the next layer...paint it with primer sand with 220 grit and repeat as needed to make it smooth....one thing I do that I didn't see mentioned is...after you get the foam shaped to your liking and before you install a panty hose over the foam form...cover the foam with saran wrap...it works like a releasing agent...when you're all done with the number of layers you want to cover with and everything is dried to your satisfaction just do your normal trimming and then pull your foam form out...as with any form don't forget to put in a little taper..in other words on a cowl...don't make the front larger than the back..

Phlip

AW,

I loved the article on the Tiger Moth in Flying Models! And the pantyhose cowling was one of the best parts ... I'd not seen this done before. I'm considering ordering your plans, but I definitely will use the pantyhose cowling idea.

Phil

andrew66

i have a question about this method:
how do you guys carve the shape out of the foam? do you use a heated foam cutter, or a very sharp razorblade? i would like to try this method on a plane i intend on upsizing. (sig smith miniplane)

jetpack

My Feedback: (1)

All foams sand different. If your using the pink or blue foam insulation then permagrit sanding blocks work well, or a sure-form plane the cheese grater type or just good old 80 grit open grain sandpaper. That's all I've had to use so far.

AlphaWhisky

Thanks Philp,

The cowling really is quite easy to produce. I forgot to mention above, but someone picked it up - use kitchen cling-film between the foam plug and the first layer of nylon.

I applied the four layers of nylon and then worked the resin through the lot in one operation, not per separate layers as someone mentioned.

Andrew - I used polyurethane foam for the plug- the sandy stuff they make surfboard blanks out of down here. It cuts easily with a handheld hacksaw blade and shapes up nicely with coarse sandpaper as jetpack mentioned. It would take maybe ten minutes to shape the whole plug to an acceptable standard.

Alan W

DaveMcFarlane

I decided to try making a cowl with pantyhose after reading the positive posts in this thread.

I have to say that it works awesome!! I used four layers of pantyhose and expoxy resin. After it had dried I brushed on another layer of expoxy to smooth it out. This is a much easier way than laying up fiberglass.

Give it a try!!

voyager_663rd

Q-->when you "invert the balloon" over it, do you mean like you were putting a condom on? I'm serious about this question so please don't laugh.

jetpack

My Feedback: (1)

no its a good question, you inflate it then push the plug into the balloon as you slowly let the air out.

digital_trucker

I've done similiar before, except that I've used thin CA instead of resin. Doesn't stiffen the cowl, but makes it much more resistant to cracking. I didn't use a balloon, but I thinned some of that lite filler stuff (I forget the brand) to fill in the weave.

voyager_663rd

Thanks[sm=thumbup.gif]

dbresky

I am a total beginner with this foam plug/ fiberglass stuff. Just finding out the white stuff from the craft store is expensive and messy. The blue or pink stuff looks like the way to go. Now I am reading about Panty Hose? Is the panty hose part the finished product that you paint and use as the cowl? or do you use the form for a female fiberglass layup.
Is there anyplace I can find start to finish series picks?

Thanks