Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

Demon cowl, take 2

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Old 10-16-2009, 07:34 AM
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Default Demon cowl, take 2

I finally got over the mental anguish of trashing my first cowl plug, and got to work on #2.. One cannot imagine the care with which I will prep the plug for molding this time.

I raised the tank area deck height a bit, though it might hamper rear exhaust efforts a bit. I intend to have another cowl for fully enclosing RE pipes, but this guy could serve to cowl the engine and part of the header and clean things up quite a bit.

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Old 10-16-2009, 10:07 AM
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Default RE: Demon cowl, take 2

I can see how the point in back would be the toughest area to get released. One thing I read recently was how the heat of the cure homogenized the parting wax into the resin. Imagine having a full size sail boat mold glue itself to the lay up............
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Old 10-16-2009, 10:58 AM
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Default RE: Demon cowl, take 2

Last time I went to the fiberglass shop near Toronto, I waited at the counter behind a fellow placing an order for delivery to his shop. His list went something like "better give me 6 drums of resin, 1 drum gelcoat, 2 cases catalyst - yeah, the 250ml size - 8 rolls of.." etc. I said jeezy petes, are you doin', building a catamaran? Turns out that was exactly what he was doing, 46 footer or something like that, and he was going to ship the materials down to St. Maarten or somewhere like that. The materials bill at that transaction was up in the 15k range. Yeah.. I would not want to stick one of those!

I am using room temp cure laminating epoxy. The problem was the stuff I used for the surface finish on the plug. Turns out the wax layer was messed up as a result of what I think was simply compatibility, and having skipped the PVA because (a) I thought I had done bang-up job waxing it, and (b) my air brush was screwed up, I got a nice bond over about half the plug as a result.

Duh. My impatience got the better of me again. Had I waited until I got to the shop to buy a new airbrush which I badly needed anyway.. had I then PVA'ed the plug.. had I not made a stunned decision in my eagerness to move forward.. I would not be repeating the effort. Live and learn and even then.. no guarantees.

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Old 10-16-2009, 11:16 AM
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Default RE: Demon cowl, take 2

I've always brushed the PVA on and it flows out almost as good as sprayed on. I'll have to try spraying sometime.
The boat factory I worked at in High School just used 6 coats of paste wax for prep. Back then the molds were valued at about $50,000 a set. You could take a rag, barely push it and watch it glide 10 times farther than what looked possible. I don't remember how the cross hatch non skid deck surface [looked like it was knurled] was prepped, but that is where they had problems. Their highly skilled mold repaiman made about $6.50 an hour and was one of the highest paid out there.
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Old 10-16-2009, 11:50 AM
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Default RE: Demon cowl, take 2

Yeah I needed to spray it, for a production mold the surface finish has to be glass smooth or as close to that as you can get. I never got a finish I was happy with by brushing.

I believe the residual solvents in the plug finish affected the wax, and when I thought I was building successive layers I was probably removing most of the wax again. So in other words, I was asking for trouble. If I had a working air brush at the time I would have sprayed a proper finish on the plug itself not to mention the release coats. Then I would not have had that problem or so the theory goes. But as it was I decided to have a go with aerosols. Duh. Just get the right tools silly..

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