Pusher cowling ideas

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Eugene

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There is various information that may be useful in this article:

Yes, pretty good article, thank you! But, still trying to determine which shape will work the best for me A or B?

"A" = Will give you smaller frontal area and better in floor into the propeller, but will increase interference drag.

"B" = Will do better on interference drag, but frontal area will be bigger and definitely separation in front of the prop

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Eugene

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Eugene

Perhaps this will help!

What the Americans thought in WW2

Take your pick....

Cheers,

Kevin

Thank you! Very interesting. Very informative. However from what I understand slightly different situation.

Both Americans and Germans were talking about dressing the shaft. I am talking about correct way to dress fat engine very close to propeller.

Also surprisingly huge angle between wing cord line and shaft. My engine tilted down by 3° in reference to chord line.

Looks like there is clear message to avoid large radius fillets.

I guess my engine cowling will be combination of shape "A" and "B"

B = should be in the middle of the cowling

A = should be used close to propeller

Picture below is best arrangement they found with least amount of drag

Screen Shot 2021-07-29 at 21.38.50.pngScreen Shot 2021-07-29 at 21.35.10.png
 

WINGITIS

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You will need to take into account the size of the aircraft and the speed they are representing.

The Reynolds number is 6,000,000 for those tests but yours may only be 3,000,000 or so.

Calculate it from my REFLEX AIRFOILS THREAD free spreadsheet.

Have a look at both the B35 and B36 Pushers as well for the variations between the two.

You will have to use your intuition for the rest, those documents just expand the knowledge base as input to that.
 

WINGITIS

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Eugene

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Found a pretty good way to get up and work on engine cowling. General shape from up above looks pretty promising to me. I think. Probably next smart step is to remove all wood planks and wrap engine around with plastic wrap. This way I can continue without worrying about anything get into engine.

With spinner to get it perfect I had to get professional assistance. $200 machine was wobbling side to side. That’s OK, I learn my lesson again. Hopefully one of these days I will stop learning and making mistakes and my life will become much more productive. Hopefully…


04FE0CD9-B78F-4FD4-82DB-D78D84AD2134.jpegD276BE93-9FD0-4798-A8FC-33AC3D69A735.jpegF4501A76-C397-4CCC-8A95-FC3936B7ACD3.jpeg75ECBAF2-773D-4012-8402-851FC8639FE3.jpeg
 

Vigilant1

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Cosmetically, that looks a lot better than the stock situation (IMO). I do wonder if the flow will stay attached at that aft section, but the prop inflow pressure gradient should help (and I'm not sure there's a practical way to improve things anyway. Maybe VGs are in your future back there).
Any guess on how the effective (net of obstructions, etc) exit area of the proposed nacelle compares to the intake area?
You'll probably want to do something to protect your rear cowl and top of wing surface from the heat of the muffler and exhaust. A radiant barrier at least, but possibly a thin layer of insulation to reduce conductive heat transfer (in flight and after shutdown).
 

Pops

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As long as you are doing something you will be learning and hopefully learning from your mistakes. The only way to stop making mistakes is not do anything. We may not make as many mistakes as we learn but we will still make them.
 

Eugene

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reduce conductive heat transfer (in flight and after shutdown).
I know that exhaust pipes can be insulated with high temp wrap. I don't know if muffler itself could be insulated as well. Didn't think that residual heat on muffler could be that substantial after shut down. I know that muffler would get pretty high temperature wise, but there is really no mass. Just the thin metal. And should be dropping temperature pretty quickly after shut down. But, what do I know?

Inlet is pretty solid and predictable. Except for the fact that I have to find away for that whole thing fly away with a parachute during deployment.

Outlet for sure will be much larger than it needs to be. And there is nothing I can do about it. Engine is shaking substantially and they need to provide enough clearance. 912 engines shaking pretty hard during shut down because of that gearbox. I figure that inch and a half clearance I will need there.
 

Vigilant1

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I know that exhaust pipes can be insulated with high temp wrap. I don't know if muffler itself could be insulated as well. Didn't think that residual heat on muffler could be that substantial after shut down. I know that muffler would get pretty high temperature wise, but there is really no mass. Just the thin metal.
Some folks like the exhaust wrap, others say it reduces the life of exhaust pipes and they hide crack and breaks that would otherwise be found early. In the case of your setup, I'd probably first see if this is even an issue (does radiant heat get the cowling too hot), and if so, see if just a bit of shielding or reflective film on the inside of your cowling does the trick. Insulating the pipes and muffler would be a last resort.
 
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Eugene

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Some folks like the exhaust wrap, others say it reduces the life of exhaust pipes and they hide crack and breaks that would otherwise be fofon
I completely agree. I fixed already some cracks, because I found them visually. If you have engine cowling, that already representing high risk of missing on something during preflight inspection. I don't know. Everything is compromise. I will try to find my own comfort zone. And if I get in trouble, I can always ask my wife for advice. She is normally willing to tell me what to do without hesitation.
 
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Pops

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Picture of the stainless steel radiant heat shield for the front cylinders of the JMR.
About 3/4" away from the exhaust pipe.
 

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Eugene

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Picture of the stainless steel radiant heat shield for the front cylinders of the JMR.
About 3/4" away from the exhaust pipe.

"If its not there, it cost nothing, weighs nothing, and is 100% reliable???"

Yes, I should be able to fabricate something like that for my own situation. Thank you. But, not sure if I can make it 100% reliable
 

WINGITIS

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Found a pretty good way to get up and work on engine cowling. General shape from up above looks pretty promising to me. I think. Probably next smart step is to remove all wood planks and wrap engine around with plastic wrap. This way I can continue without worrying about anything get into engine.

With spinner to get it perfect I had to get professional assistance. $200 machine was wobbling side to side. That’s OK, I learn my lesson again. Hopefully one of these days I will stop learning and making mistakes and my life will become much more productive. Hopefully…


View attachment 113681View attachment 113682View attachment 113683View attachment 113684
What is this plane/kit?

Also you may want to lookup the "Meredith Effect" before you finalize your cowling, just to complicate things....!

K
 
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