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  #11  
Old 03-04-2021, 07:07 AM
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DanH DanH is offline
 
Join Date: Oct 2005
Location: 08A
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Larry, here's a graphical presentation borrowed from a textbook:

https://www.danhorton.net/VAF/Oil%20...er%20Flows.pdf

I've attached a sketch below. I'm pushing my pay grade here (so Steve, please confirm/correct/expand), but when length constraints result in included angles more than 15 degrees or so, the cheat is to shape the diffuser like the example on the right.

The examples are proportional, and applied to the same problem, a 4" inlet required to expand to 8" in a distance of 6". With straight walls, the included angle is more than 36 degrees, and the result will be the jet flow Steve described.
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  #12  
Old 03-04-2021, 07:40 AM
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bjdecker bjdecker is offline
 
Join Date: Jun 2005
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I'll be the first to admit that a whole lot of TLAR went into the design of my diffuser.

I mounted a 10599R to the firewall behind and below the #4 jug and slightly above the gear tower (I have a tail dragger, so my motor mount includes a brace each side of the firewall between the top and bottom corner mount bolts -- makes for a tight installation) which necessitated an angle of about 20 from the horizontal for the oil cooler.

For the mold, I did the exact same things as Larry, used pink-foam sheets to make the plug, etc. Once I had the inlet angle set to allow the SCEET to transition as smoothly as possible to the #4 back baffle, I rolled in some modeling clay to build up the shape to look as much like the bell on a Trombone, Clarinet, etc. - no sharp angles for transitions, no "lips" or edges to trip up the flow.

This "system" gets me a ~185 F OT on my IO-360-A1B6 at 75% power, 6500FT MSL, OAT 15C.

Improvements/do betters:

1. Change to 4" duct -- currently 3" SCEET.
2. Extend the "neck" and eliminate as much SCEET as possible. There's a small pucker in the SCEET that I don't like.
3. Add a butterfly valve at the exit of the #4 baffle to regulate OT
4. Add a more pronounced bell transition on the baffle the inlet. It's a 1/8" radius currently -- 1/4" might be better.
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2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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  #13  
Old 03-04-2021, 08:25 AM
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Default Butterfly valve

Anyone know how this could be attached to the baffle?
https://www.aircraftspruce.com/catal...xoC9xMQAvD_BwE
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Larry Larson
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Donated 01/01/2021, plus a little extra.
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  #14  
Old 03-04-2021, 08:27 AM
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bjdecker bjdecker is offline
 
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Quote:
Originally Posted by wirejock View Post
Anyone know how this could be attached to the baffle?
https://www.aircraftspruce.com/catal...xoC9xMQAvD_BwE
IIRC It slips over the flange on the baffle ... at least the 3" version did.
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Brian Decker
Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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  #15  
Old 03-04-2021, 09:06 AM
David Paule David Paule is offline
 
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You could make a fiberglass flange for it.

Dave
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  #16  
Old 03-04-2021, 09:18 AM
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wirejock wirejock is offline
 
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Default Butterfly valve

Ok. Getting closer. I will order one and try it.

This is a facinating disccussion but it seems we are missing a point.
What is the air doing inside the baffles while it fights to get through a flat hole in the baffle.
The best diffuser isn't going to help the tornado going on inside.
Am I missing something?
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Larry Larson
Estes Park, CO
http://wirejockrv7a.blogspot.com
wirejock at yahoo dot com
Donated 01/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (2,000+ hours)
Empennage, wings, fuse, finishing kit, now FWF
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
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  #17  
Old 03-04-2021, 09:59 AM
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I could be wrong but I really feel like this being looked at with way too close of a microscope. Larry you are using the bigger oil cooler to cool the parallel valve 180 hp motor. I sincerely doubt that this thing wouldn't cool properly using a simple scat tube. I'm not saying that's how you should do it, I'm merely saying that I wouldn't over analyze this and I think your original plan will more than suffice. Just my 0.02.
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  #18  
Old 03-04-2021, 10:54 AM
scsmith scsmith is offline
 
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Quote:
Originally Posted by jcarne View Post
I could be wrong but I really feel like this being looked at with way too close of a microscope. Larry you are using the bigger oil cooler to cool the parallel valve 180 hp motor. I sincerely doubt that this thing wouldn't cool properly using a simple scat tube. I'm not saying that's how you should do it, I'm merely saying that I wouldn't over analyze this and I think your original plan will more than suffice. Just my 0.02.
Larry, If you have a parallel valve engine without piston oil squirters, then Jereme is probably right. If you do a good job with the cooler air supply, you will probably have way too much cooling. That's ok, just close off the throttle valve as needed. But he is right, the shutter and the abrupt adapter to the cooler will serve you well.

BUT! if you want to get serious about closing down the cowl cooling exit to get lower cooling drag, that reduces the available pressure differential across the oil cooler, and once again, a well-designed installation will pay dividends.

Also, on the question of what the flow is like in the upper cowl plenum above the cylinders and making its way back to the rear baffle -- the pressure is very high in there, almost full pitot pressure, so the velocities are very slow, blobs of air just milling around waiting for their chance to go rushing through the cooling fins. Not much pressure loss or frictional loss associated with that. So there is a ready supply of air that wants to flow through that 4" hole and through to the cooler.
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RV-8 N825RV
IO-360 A1A
WW 200RV
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Hobbs 635
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bought my old LS6-A back!!
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  #19  
Old 03-04-2021, 11:07 AM
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wirejock wirejock is offline
 
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Default Air supply

Thanks Steve.
I really am enjoying this discussion and your insight.
Since the engine and baffles are not installed, I have lots opportunity to play.
Latest iteration is going to be a Vans 4" flange to the Aircraft Spruce 4" butterfly valve then flexible duct to the oil cooler.
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Larry Larson
Estes Park, CO
http://wirejockrv7a.blogspot.com
wirejock at yahoo dot com
Donated 01/01/2021, plus a little extra.
RV-7A #73391, N511RV reserved (2,000+ hours)
Empennage, wings, fuse, finishing kit, now FWF
Disclaimer
I cannot be, nor will I be, held responsible if you try to do the same things I do and it does not work and/or causes you loss, injury, or even death in the process.
Reply With Quote
  #20  
Old 03-04-2021, 11:32 AM
scsmith scsmith is offline
 
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Location: Ashland, OR
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Quote:
Originally Posted by wirejock View Post
Thanks Steve.
I really am enjoying this discussion and your insight.
Since the engine and baffles are not installed, I have lots opportunity to play.
Latest iteration is going to be a Vans 4" flange to the Aircraft Spruce 4" butterfly valve then flexible duct to the oil cooler.
Let us know how the flange and valve body fit together. I assumed they were the same diameter, not one a slip fit over the other. But I am curious.

You could trim the butterfly valve tube back fairly close to the shaft bushings, and have the flange welded to it. (take the bushings out first so they don't get cooked).

I made my own from a 4" flange, a length of 1/4" stainless rod, two brass bolts drilled through to act as bushings, and had a shop mill a flat on the shaft for the round butterfly.

I did find it is a pretty tight fit to get a 4" round flange on the back of my #3 rear baffle. That is party why I went with 3.5" the first time.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 635
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
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