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Old Jul 21, 2014, 08:57 PM
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Help!
So what do I do now, shorter DLE standoffs?

So this is my first 1/4 scale gasser...a lot of firsts...please see supporting pictures.

The cowl has a former that is supposed to butt up to a former on front of fuselage.

I cut the cowl until it slipped past engine and the two formers butted together.

But now it appears as if I have way to much prop shaft sticking through front of cowling. I might end up with a 5/16" gap between cowl ring and back of prop spinner. That can't be right, can it?

So I guess I ditch the stock DLE35RA 60mm standoffs and start shopping for shorter ones, assuming there are shorter ones to be bought. Is there?

Shorter standoffs would probably mean cutting a larger hole in firewall for carburetor to plunge partially through firewall, right?

I have no idea what I am doing and no friends that fly or build this sort of plane so any and all help that the group can provide is appreciated.
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Old Jul 21, 2014, 11:31 PM
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At 200 feet you'll never notice it. Prop it up and burn some gas! ;-)
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Old Jul 22, 2014, 06:26 AM
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Another possibility is to move the firewall back the amount you need. Yes, there are shorter standoffs out there, or you can get custom ones made, but you will have to cut a larger hole into the firewall to allow the carb to set back into. It shouldnt be too difficult to cut off the firewall & move it rearward. You can install tristock behind the firewall & pin the firewall with dowels. Reinforce everything with glass & it will be stronger than new. .Gene
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Old Jul 22, 2014, 07:14 AM
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If you are not experienced in building I don't suggest messing with your firewall. From your pics I think you should get shorter standoff. It looks like you have enough rearward movement to lesson the 5/16 th gap.
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Old Jul 22, 2014, 07:23 AM
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How about spacers for the cowl. Move it forward a bit. A few wood blocks at the screw points should work.
Edwin
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Old Jul 22, 2014, 08:02 AM
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If you do decide to cut a hole in the firewall (as I did for a recent install) I recommend rounding off the edges to keep chafing of fuel lines and wires to a minimum.

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Old Jul 22, 2014, 08:09 AM
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I say fly it there's an inch and a half on my 40% Sukhoi it looks ok.
If you go shorter standoffs you'll have to cut open the firewall. If you try and move the cowl forward you'll a big space.
What I don't see is a good airflow path for cooling the engine. I see the clyender sticking in the airflow but I don't see the exit out of the cowling to let the air flow around and exit.
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Old Jul 22, 2014, 06:50 PM
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Jetmech makes a good point about " airflow ". Maybe the smart thing would be to slide the cowl fwd a bit and leave a slight gap for Airflow . With a bit of thought you could make it look OK and maybe save yourself some problems with engine overheating. ENJOY !!! RED
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Old Jul 23, 2014, 01:15 PM
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Quote:
Originally Posted by edwin1 View Post
How about spacers for the cowl. Move it forward a bit. A few wood blocks at the screw points should work.
Edwin
My thought as well, looks like 1/4 all around would do the trick.
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Old Jul 24, 2014, 07:01 PM
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Thank you

I wanted to stop in and say thanks for all the replies.

Today I stopped at the local airport and looked at a full scale Pitts. All the cooling air that enters the cowl exists around the exhaust under and towards the back of the cowl. To get my cowling on after muffler is on is going to require a pretty fair sized oval hole so I think I will have enough air flow.

I also found a set of 50mm standoffs and a single fender washer under each allowed the engine to pull back towards the firewall which just made everything come together...looks sweet!

I really appreciate all the input. This group is really where the only guidance I get comes from as no one in my club flies anything like this build. They are mostly nitro, electric, or sail planes.

Thank you!
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Old Aug 23, 2014, 05:21 PM
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Generally, you want twice the size of air exit hole as the size of the air entrance hole. A lot of people don't have the exit holes big enough.

Don't worry about the prop shaft sticking out a little more than scale.

What's more important is to expect more shaking with the gas engine, than with a nitro engine. Make sure that you have triangle stock strengthening the firewall to the rest of the plane.
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