greggK

Hello to 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

Dash7ATP

My limited experience saysx you definitely need to put lite ply behind the dummy plastic cylinders, expecially if they are of the vacuum formed type. Typically, you will probably be limited to how far back into the cowl you can place the dummy due to your engine. If your dummy engine has a domed front gear case, the front of that will usually be set back slightly (full scale) due to the prop shaft and back of the propellor. After you cut out the hole to allow your engine shaft to extend through it, you may not have much left of the front dome.

Basically, it's about trying to make it look right and that may be difficult depending on your engine; two cycle, four cycle, gas. etc?. Type and location of your carb will also be an issue here.

As for locating it all and keeping it centered on the engine, that just takes patience. Measure twice and cut once, I laways heard. ASSUMING your engine is properly mounted and
CENTERED, you can make a plywood disc the diameter of the front of your cowl. Mount the enigne and then mount the cowl to keep the disc centered. If the dummy radial is centered in the cowl, it should look OK.

Dash

John Baligrodzki

Greg,

Before you cut a ply back make a template out of a chipboard from a cereal box or soda case. Takes a bit of time to get it to size and located at the correct distance so the real engine will fit behind it and everything works and has clearance. Then when you cut the real one out cut it slightly oversize. Then sand to fit. Thie process of doing this project involves a lot of cutting fitting but well worth it.

John B.

Boomerang1

The plywood plate does two things, supports the dummy engine & baffles the airflow to your engine.
I usually get the cowl mounted first with the crankshaft in the desired position then mount a plywood
disc on the crankshaft of the motor.

The disc is then supported to the cowl with some scrap balsa, the cowl removed & the ply disc then
becomes a reference to position the ply baffle plate, dummy engine, needle valve, ducting etc.

Once everything is secured in the correct position you remove the disc leaving everything in the right
place relative to the engine & cowl. - John.

greggK

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?

vasek

My Feedback: (4)

If it's any kind of warbird or similar, I wouldn't worry about the weight upfront

BobH

My Feedback: (2)

You might try that expandable foam that's for sale at Lowes and home Depot. Spray it in and then sand back until it's flush.