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Vacuum-forming Royal B-17 Cowls - 11/20/2012 11:44 PM   
Scratchie



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From: Mendota heights, MN, USA
Status: offline 		I wanted to build a Royal B-17 kit I had, but was concerned about their reputation for being heavy. To lighten the plane I decided to try making vacuum-formed cowls instead of using the aluminum ones from the kit. The vacuum-form uses a wood box base with peg board top, all edges sealed air tight. A shop vac hose goes into a hole in the base. Styrene plastic is stapled-gunned to a wood frame and heated in an oven. Because I didn’t want an open flame in the oven near the plastic, I pre-heated the oven to 400, put in the styrene, turned off the oven and baked the styrene like a pizza for about 90 seconds. Then I turned on the shop vac and quickly placed the styrene over the mold. That’s it, it was easy. Chad Veich was very helpful and answered some questions.

Chad Veich, www.cwvmodels.com - Scale Model Design & Construction

Pic 1 is the vacuum-form base with a pedestal I put the cowl on. I used the pedestal so that the bottom of the mold would have crisp edges. Pic 2 is the aluminum cowl ready to be molded. Pic 3 is a frame that I stapled 0.04” styrene plastic to – note the handles on the sides. Pic 4 is right after heating the styrene and putting it over the aluminum cowl mold. Pic 5 was my first attempt – oven way to hot. Pic 6 is a molded cowl before trimming. Pic 7 are the molded cowls before final trimming. Here’s the point of all this. The four aluminum cowls weigh 8.6 oz. The four molded cowls, before final trimming, weigh 2.2 oz. That’s a 6 oz. savings. Btw, 0.04” styrene is quite strong and not flimsy.

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RE: Vacuum-forming Royal B-17 Cowls - 11/21/2012 12:13 AM   
aymodeler



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Status: offline 		Looks great! I have always been afraid to take the "plunge" in vacuuforming, but you have made it look easy!

You said pic 4 was "...right after heating the styrene and putting it over the aluminum cowl mold". Can I assume that you turn on the shop-vac then pull the heated styrene down over the mold and let the vacuum draw it tight?


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RE: Vacuum-forming Royal B-17 Cowls - 11/21/2012 1:10 AM   
Scratchie



Posts: 409
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From: Mendota heights, MN, USA
Status: offline 		That's correct.  I watched the styrene in the oven until it sagged about 1 inch, then turned the vac on and quickly took out the styrene and put it over the mold.  There's a lot of youtube videos that help.  It took a few phone calls to find styrene sheets, but once I found a vendor I got it for $22.50 for a 4'x8' sheet.  A lot cheaper than from eBay.

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RE: Vacuum-forming Royal B-17 Cowls - 11/21/2012 1:21 AM   
buzzard bait


 

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From: Ithaca, NY, USA
Status: offline 		Nice work and good pictures and tips.

Usually the most important weight savings is in the tail of the plane. That is because many scale models naturally come out tail heavy. When you scale down, the engine is not proportionally as heavy as in the original. Then because of the leverage of the tail on the nose, you need a lot of nose weight to bring it into balance. That is very frequently the main cause of over weight.

But it all adds up, so good work cutting off 6 oz. Use the same idea and weigh your wood. Parts that are not structurally critical should be made of the lightest balsa you can get, or even foam. Wings can get heavy too, especially when sheeted. The spars provide the main strength. The sheet balsa often just adds unnecessary weight. Buy yourself some "contest grade" balsa and a scale. Get used to figuring out wood densities.

The smaller the scale the more critical weight becomes on a scale model. Multi-engined aircraft are usually built to small scales, like 1/12th or 1/14th or less, so they are the most difficult. Good work going after the weight!

Jim

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RE: Vacuum-forming Royal B-17 Cowls - 11/21/2012 1:36 AM   
Scratchie



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Status: offline 		Wood replacement and lightening holes are next, trying to acheive a low wing loading is my new hobby.

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RE: Vacuum-forming Royal B-17 Cowls - 11/21/2012 6:50 AM   
frets24


 

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Status: offline 		Who's the vendor for the polystyrene?

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RE: Vacuum-forming Royal B-17 Cowls - 11/21/2012 4:58 PM   
Scratchie



Posts: 409
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Status: offline 		I bought a 4'x8' sheet of 0.040" white styrene for $22.52 from Laird Plastics, 4300 Round Lake Road, Arden Hills, MN 55112.  Tel. 763/535-2118  very easy to work with.

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RE: Vacuum-forming Royal B-17 Cowls - 11/22/2012 4:20 PM   
frets24


 

Posts: 1176
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From: charlotte, NC, USA
Status: offline 		Thanks for the info.

Like you, I have Chad V's tutorials to thank for opening up the world of vaccuforming to me. Now, I don't know how I went for so long without this invaluable building resource/tool.

BTW, nice job on the cowls.

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RE: Vacuum-forming Royal B-17 Cowls - 4/22/2013 10:30 PM   
I-fly-any-and-all


 

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Status: offline 		Very nice, but I thought with the b-17, you would want the excess nose weight?

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RE: Vacuum-forming Royal B-17 Cowls - 4/23/2013 3:40 PM   
LesUyeda



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Status: offline 		"Very nice, but I thought with the b-17, you would want the excess nose weight?'


I would expect that those are too far back to help much.

Les

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RE: Vacuum-forming Royal B-17 Cowls - 4/24/2013 3:25 AM   
acdii


 

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Status: offline 		What is the scale of it?


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