Home made plastic cowl  
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Home made plastic cowl - 5/17/2008 11:11:54 AM   
Krener


 

Posts: 185
Joined: 11/5/2006
From: AS, AUSTRALIA
Status: offline 		Hey all.

Well I saw this method some time ago somewhere on the net and have given it a try as I needed a cowl for my Sig Somethin Extra.
Laying up fibreglass bores me to tears and making one from balsa wasn't likely to do me any favours either so I made a plastic one.
This is to cover my Saito 72 so it had to have a bit of length in it, but little weight.

Pic 1. This shows the balsa block I started with and roughly cut to shape
Pic 2. Same balsa block again but with prop shaft centre marked and outside of spinner back plate traced out.
Pic 3. After a bit of sanding your left with a nice plug the shape you need (sanding is made ALOT easier with a bench sander ). Also shows the top section of a drink bottle which will become the cowl.
Pic 4. Testing done on remaining section of bottle to check shrink rate, heat required, burn and melting points. A good thing to do as I tried it on another bottle and it shrunk slower, but burned alot faster.
Pic 5. Bottle in place over plug and shrinking started. Just using low heat on the heat gun and 'waving' it over the bottle worked extremely well. I started on the bottom to 'lock' the plug in place and heated opposite sides of the bottle each time so as not to 'pull' the plastic around to much on the plug.
Pic 6. Shrinking complete. I left the tip till last as this bit required very little shrinkage to snug down. The opening for the prop shaft on this one is large, but for a smaller opening just move the plug away from the bottle top a little.
Pic 7. Completed cowl removed from plug. To remove the plug from the cowl I just got the bottle top and place it on the front face of the plug, and hit it with a hammer.

Not bad for a first time but this one is a prototype. I'll make another for the final project.

One thing I would change is to make the plug longer at the rear so there is more plastic to trim away to get the perfect fit.

Well, a spot of paint on the inside and it would be finished but trying to find matching paint is gonna be a pain.
On the next one I'm going to try leaving the plug in the cowl and strecthing film over it with the heat gun. With the plug in place the plastic wont distort if it gets to hot and it will be alot sturdier so I can pull on the film without the cowl buckling.

The best thing is it cost me a total of $3.50 for the drink bottle (tasted good to ) plus some time (maybe 2 hours at the most), and is totally fuel proof AND I can reuse the plug should the cowl ever get damaged AND it's light, alot lighter than it would be if I made one from glass or balsa.

OK, off to modify the plug (length) and make another cowl.

Cheers



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I live in my own little world.................but it''s OK, they know me here.
       Post #: 1

RE: Home made plastic cowl - 5/17/2008 11:17:40 AM   
Krener


 

Posts: 185
Joined: 11/5/2006
From: AS, AUSTRALIA
Status: offline 		Had to make this a 2 part post as my pics are too big

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_____________________________

I live in my own little world.................but it''s OK, they know me here.

(in reply to Krener)
       Post #: 2

RE: Home made plastic cowl - 5/17/2008 1:43:30 PM   
Stripes


 

Posts: 638
Joined: 5/17/2003
From: Orchard Park, New York
Status: offline 		The top of the bottle can also be put back on and a small hole drilled so compressed air can be used to remove the new cowl from the plug.

I found I had to use three liter pop bottles to get enough size. Turns out the only ones available around here are from supermarket brand generic pop.

< Message edited by Stripes -- 5/17/2008 1:44:30 PM >

(in reply to Krener)
       Post #: 3

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