Pusher cowling ideas

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Vigilant1

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Another idea: If you tip the radiator 45 degrees (actually, 44.43 degrees 😀) the radiator's 5" height will have 3.5" toward the incoming air (just the size you want for your scoop's height). The longitudinal distance it would cover is 3.5", so it would still fit behind the BRS box.

If the radiator fins run vertically, tipping it shouldn't cause much/any impedance to the airflow. This arrangement would result in a sharp angle at one edge of the duct/radiator junction, I don't know how that would affect things. But, this does result in a very compact installation and a duct that can be absolutely straight (no dreaded divergence angles) and it keeps everything clear of the BRS. The rocket would need to be mounted to one side (would still be inside the nacelle).
There could be great reasons not to do it this way, I haven't read K & Weber and am no expert in ductollogy.


Mark
 
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Eugene

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Well it is like trying to watch someone pound a square peg into a round hole, so maybe move the peg over a different hole and try for a while.
Sometimes I feel this way while watching my wife trying to accomplish things around the farm. But it is only obvious to us if we have knowledge about the subject. Knowledge is what this guy is trying to get
 

Eugene

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Is there room inside the landing gear fairings for duct?
Not really. There is two unused empty spaces under pilot and the passenger legs divided in the middle with main 120 mm tail boom. Sometime in the future I was planning to convert them into openable glove compartment for snack during flight.

This was just an example of how idea from outside of the box is not necessarily good idea or practical idea. To keep everything up above is much smarter in my opinion. One box that will serve purpose of engine cowling on outside and cooling duct on the inside is better way to go.

IMG_0296.JPGIMG_0298.JPGIMG_0850.jpeg
 

blane.c

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Looks like room for a differently shaped radiator were the pink bottle is of course then you need a new place for pink bottle.

A split radiator could fit on each side of the narrowed area at rear of gearbox ahead of propeller flange with possibly a heat shield above the muffler.
 

WonderousMountain

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So what I sketched out here is a proposal to relocate the BRS up where the intak lip goes, I gave it some down angle, not sure how much. Then aligned rocket, & dual radiator setup under it. Also shown is an intake ramp, matched to the canopy transition. Top peaks earlier than your mold modelling, not sure that was on purpose. Opening after the radiator is maybe overzelous. I do not love it and wonder is a horizontal oil tank would do any good.

IMG_20210808_105548.jpg
 

Eugene

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So what I sketched out here is a proposal to relocate the BRS up where the intak lip goes, I gave it some down angle, not sure how much. Then aligned rocket, & dual radiator setup under it. Also shown is an intake ramp, matched to the canopy transition. Top peaks earlier than your mold modelling, not sure that was on purpose. Opening after the radiator is maybe overzelous. I do not love it and wonder is a horizontal oil tank would do any good.

View attachment 114060
Thank you! I will try to rearrange this way on paper and using real world dimensions. It should work. We are using essentially same components without adding anything. We will see.
 

Eugene

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So what I sketched out here is a proposal to relocate the BRS up where the intak lip goes, I gave it some down angle, not sure how much. Then aligned rocket, & dual radiator setup under it. Also shown is an intake ramp, matched to the canopy transition. Top peaks earlier than your mold modelling, not sure that was on purpose. Opening after the radiator is maybe overzelous. I do not love it and wonder is a horizontal oil tank would do any good.

View attachment 114060
This is what I got

IMG_6167.jpegIMG_6168.jpeg
 

wsimpso1

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One thing to know. There is nothing magic about 7 degree divergence. That angle is what you generally need to stay with if you want to keep attached flow without help. On internal ducts there are many examples of more steeply diverging ducts - some carefully done tuft testing and development of a few guide vanes might be needed to "wet" the whole radiator face. Somewhat steeper angles may allow you to shorten the nose enough to get into a simple duct instead of one that must eject ahead of the recovery parachute.

Sticking it on the belly... cool, but it looks like a nightmare to service/purge, and it puts water at boiling point where it could fill the cabin with steam. More failure modes to manage. And, you will still need to put some air through the cowling to cool all that incidental under-cowl stuff, that you were already getting for free after passing through the radiators.
 

Eugene

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There is nothing magic about 7 degree divergence.
OK, so nothing is magical about 7° divergence. I was struggling this morning to imagine how I supposed to organize the flow into propeller around the muffler. Seems like no matter how I do it I will end up with pretty sharp corners. I know that propeller suction will fix separation to certain degree. How much will it fix? Can my angle be 15°?


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wsimpso1

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Another idea: If you tip the radiator 45 degrees (actually, 44.43 degrees 😀) the radiator's 5" height will have 3.5" toward the incoming air (just the size you want for your scoop's height). The longitudinal distance it would cover is 3.5", so it would still fit behind the BRS box.

If the radiator fins run vertically, tipping it shouldn't cause much/any impedance to the airflow. This arrangement would result in a sharp angle at one edge of the duct/radiator junction, I don't know how that would affect things. But, this does result in a very compact installation and a duct that can be absolutely straight (no dreaded divergence angles) and it keeps everything clear of the BRS. The rocket would need to be mounted to one side (would still be inside the nacelle).
There could be great reasons not to do it this way, I haven't read K & Weber and am no expert in ductollogy.
Mark
This is an oblique diffuser setup - they can work, but usually require more radiator weight, bigger inlets, and more drag than a more conventionally aligned system.

Billski
 

Vigilant1

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This is an oblique diffuser setup - they can work, but usually require more radiator weight, bigger inlets, and more drag than a more conventionally aligned system.

Billski
Thanks. In this case at least the radiator weight won't be going up (he's using what he's got, which works fine with zero ducting so should be plenty big here). Airflow and internal duct drag not ideal, but sure to be better than the present system and easier to fabricate and lighter than the "move the parachute above the duct" approach.
Getting a smooth covering over all the engine bits and bobs will achieve most of any drag reduction from this project, IMO.
Again, thanks for the info.
 

blane.c

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2 Cents.

Initially I like the raising of the parachute above the duct idea and the air coming in on the bottom, but after reading about some of the pressure issues a lot more pertinent information is needed. If there is essentially a pressure dam at the intersection of the lower portion of the cowling and the cabin, you have a serious physics problem to overcome if the air inlet is place there. Time spent finding some diagrams that show how air flows around typical pusher cowlings similar to your own would be time well spent (if there are any to find of course) but big internet lots of braggarts likely there is something to look at that makes it less a simple guess and more a swag (scientific wild as* guess).
 

Eugene

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some diagrams that show how air flows around typical pusher cowlings similar to your own

I was told by Peter Garrison to simply copy this cowling. He was telling me that this guys spend quite a bit of time testing it out. And apparently with very good results. There is really not much out there for comparison

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