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  #1  
Old 06-27-2007, 12:56 PM
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TMann TMann is offline
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Default N200LZ: Chapter 21 - Strakes

I'm planning on making my strake molds this weekend.
Yes, I know this isn't per plans but I'm planning on laying up my skins such that they are curved from the start vs. trying to curve them after the fact.

My plan is to stop by Home depot and get some 2" x 48" x 96" polystyrene, sandwich them together with 3M 77 adhesive and then hotwire them to shape.
I'm planning on building in the curve of the fuse into it and the whole bit.
Extra work .... I know but this has always been in-scope for my project.

Now, don't anyone panic ..... none of the foam will actually be part ov the build itself. It will only serve as a mold.
Another benefit is I can cut my hotwire teeth on cheap foam!

I'll post pics when I have them!
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Last edited by TMann : 06-27-2007 at 01:42 PM.
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  #2  
Old 06-27-2007, 01:21 PM
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Default Re: N200LZ: Chapter 21 - Strakes

sounds complex, i just mean 5 templets

root
section that bends
strake end
inside top
inside bottom

for top and bottom trace with a compass

cut away
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  #3  
Old 06-27-2007, 01:29 PM
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Default Re: N200LZ: Chapter 21 - Strakes

Sounds complex but in reality not so bad.
Once the skins are fabricated, I can slice and dice the mold to get the exact profile and alignment for the ribs and baffles to insure a precise fit when I seal it up. I really don't want to spend a lot of time fighting tank problems.

It's something to work on now that will help make all of my alignments more precise going forward.
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Old 06-27-2007, 02:31 PM
Phil Kriley Phil Kriley is offline
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Default Re: N200LZ: Chapter 21 - Strakes

Is polystyrene safe to hot-wire cut? What kind of styrofoam creates toxic fumes when cut with a wire? I know one of them is really toxic, but can't remember which kind...?
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Old 06-27-2007, 02:52 PM
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Default Re: N200LZ: Chapter 21 - Strakes

I think all polystyrene is safe to hot wire and so are some of the other foams, i think there is just 1 bad one that we use
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  #6  
Old 06-27-2007, 03:03 PM
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Default Re: N200LZ: Chapter 21 - Strakes

Polystyrene is wing foam.
POLYSTYRENE FOAM
POLYSTYRENE Blue Large Cell expanded 1.6 lb. density, with flame retardant additive. Cuts easily with hot wire for airfoil shapes. Can be dissolved with fuels, solvents, and thinners. Originally used on VE & LE designs. Do not use with polyester resin - use only epoxy. Can be glued with any type of adhesive.

You can also hotwire styrofoam.
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Old 06-27-2007, 04:47 PM
Ron Springer Ron Springer is offline
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Default Re: N200LZ: Chapter 21 - Strakes

I am fairly certain that 3M 77 spray adhesive will dissolve polystyrene (wing) foam. Now, how do I know this?

Well, the end of one of my copper foil antennas was not sticking down well to the foam anymore and I was about to skin the canard. So, I thought I would hold it with some spray adhesive (not sure if it was 77 or 90 though). I sprayed some on a stick and wiped it under the end of the antenna. Then, I watched the foam dissolve and leave an indentation! Then, it was time for dry micro.
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Old 06-27-2007, 04:53 PM
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Default Re: N200LZ: Chapter 21 - Strakes

That's good to know (ahead of time!)
I'll have to try a test piece before I get after this.
I believe the styrene they sell at Home Depot has a thin plastic film on it.
If this doesn't cause the hotwire any problems, I'll leave it on and spray the 77 on that.

If not ....... guess it's on to plan 'B'.
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Old 06-27-2007, 05:03 PM
Ron Springer Ron Springer is offline
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Default Re: N200LZ: Chapter 21 - Strakes

Quote:
Originally Posted by TMann View Post
That's good to know (ahead of time!)
I'll have to try a test piece before I get after this.
I believe the styrene they sell at Home Depot has a thin plastic film on it.
If this doesn't cause the hotwire any problems, I'll leave it on and spray the 77 on that.

If not ....... guess it's on to plan 'B'.
You can buy some "Great Stuff" spray foam at Home Depot and use a thin layer of it instead. It won't dissolve the foam. That should suit your purposes for making a mold.
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Old 06-27-2007, 05:07 PM
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Default Re: N200LZ: Chapter 21 - Strakes

Yeah ........ I just hate to have to do that. Great Stuff is the "BAD" foam that you don't want to hotwire through.
I'll just have to dink around with it some.
Thanks for the suggestions.
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  #11  
Old 06-27-2007, 05:34 PM
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Default Re: N200LZ: Chapter 21 - Strakes

Use a staplegun to hold the foil in place before you glass it.

Waiter
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Old 06-27-2007, 06:33 PM
chasingmars chasingmars is offline
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Default Re: N200LZ: Chapter 21 - Strakes

Quote:
Originally Posted by TMann View Post
Polystyrene is wing foam.
POLYSTYRENE FOAM
POLYSTYRENE Blue Large Cell expanded 1.6 lb. density
I think wing foam needs to be *extruded* polystyrene, not expanded. But as you say, in this application, it's not part of the plane.

Watch your vacuum strength if you are vac bagging, expanded polystyrene has a low enough compressive strength to be deformed under vacuum
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  #13  
Old 06-27-2007, 10:19 PM
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Default Re: N200LZ: Chapter 21 - Strakes

have you looked at my posting on cg/smp stakes ? there are lots of photos of how i jigged up foam to hold the skin-foam in place wile the micro dried. i then took the hole skin off and glassed the inside of the foam
if you also glass the out side lower skin, you can flip the plane one less time
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Old 06-27-2007, 10:23 PM
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Default Re: N200LZ: Chapter 21 - Strakes

Quote:
Originally Posted by TMann View Post
That's good to know (ahead of time!)
I'll have to try a test piece before I get after this.
I believe the styrene they sell at Home Depot has a thin plastic film on it.
If this doesn't cause the hotwire any problems, I'll leave it on and spray the 77 on that.

If not ....... guess it's on to plan 'B'.
use the hot sticks, 15.00 at ace, and get a big bag of glue sticks
you will become a believer
no more waiting for the flox to dry, just hot glue the corners then fill with flox/micro and move on...
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Old 06-27-2007, 10:26 PM
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Default Re: N200LZ: Chapter 21 - Strakes

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Originally Posted by Waiter View Post
Use a staplegun to hold the foil in place before you glass it.

Waiter
i used a staple gun once, but the next day i needed the gun back, so i had to cut the big bump and retreve it. it was no good anymore.
next time i'll try a staple.
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