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Old Jun 10, 2012, 01:15 PM
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Joined Dec 2007
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Dummy radial instalation in 1/4 scale round cowl

Hi all,
Looking for some building-technique advice. Have a round 1/4 scale cowl and a plastic dummy radial that I'm planing on gluing the area of the cylinder heads to the inside of the cowl. I was going to make a plywood backing to add structure and support. What I don't know how to do is to get it perfectly centered around the prop nut and how far out to bring the radial. Any suggestions, advice and/or pictures would be great.

Thanks
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Old Jun 11, 2012, 06:29 AM
Too windy to fly? Lets surf
w1nd6urfa's Avatar
Athens, Greece
Joined Oct 2008
534 Posts
Hi
You should first install the engine on the mount, then dry fit the cowl on its mounts.

Position the cowl so it looks straight with the fuse and the prop nut is at the centre of the cowl, the prop backplate should protrude about 1/4". Mark the cowl position and drill the mount screws

Assuming your engine has right-thrust, the next step is to look at the cowl from the top: you should be able to judge if the dummy engine will be "true" parallel to the cowl or it needs some right thrust too to align with the engine. You can dry fit the dummy engine in the cowl (cowl is attached to fuse) and experiment with various positions until you find the right place. Mark the position and then remove cowl and dummy engine and glue in place.

Measure twice - cut once applies here a lot more than in other stages of the build!
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Old Jun 13, 2012, 12:24 PM
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Thanks all, any advice on what to use to "fill" in the back of the hallow plastic (fragile) radial? I didn't want to use epoxy because of weight. I want a silicone like (flexible) material but light. Any ideas?
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Old Jun 16, 2012, 10:47 PM
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Keller, TX
Joined Aug 2005
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Quote:
Originally Posted by greggk View Post
Thanks all, any advice on what to use to "fill" in the back of the hallow plastic (fragile) radial? I didn't want to use epoxy because of weight. I want a silicone like (flexible) material but light. Any ideas?
You might consider epoxy with micro balloons mixed in. It will give you sufficient rigidity with little weight. The more micro balloons, the less weight, compared to straight epoxy. I use it for shaping, where strength is not a requirement.
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Old Jun 17, 2012, 08:19 AM
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Joined Dec 2007
410 Posts
Hi all,
I was trying to detail the dummy 1/4 scale Pratt & Whitney 985 Wasp radial. I'm want to find something to make up the spark plugs and wires, also I want to use small hex bolts around the hub (I think around 2/56-4/40 in size) Any suggestions on where to find this stuff and what to use? Any other input would welcomed, I have never done this before! The installation is going well.
Thanks
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Old Jun 18, 2012, 05:06 AM
Too windy to fly? Lets surf
w1nd6urfa's Avatar
Athens, Greece
Joined Oct 2008
534 Posts
This is a great article I have referenced many times:

http://bestpilots.typepad.com/my_web...-insignia.html
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