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  #11  
Old 01-11-2010, 07:18 AM
RV8R999 RV8R999 is offline
 
Join Date: Dec 2008
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I've Conducted numerous wind tunnel and CFD studies during my grad school experience using all shapes and sizes of NACA inlets. Sized, shaped and located appropriately a NACA inlet will allow plenty of airflow for an oil cooler. The size and hence shape isn't the hard part, its correct location on the cowl that will make all the difference and without a full cowl CFD this will be more intuition than science..thats the fun of it.

Ultimately my goal will be to throttle down the exit area as well as inlets and will most likely provide a dedicated oil cooler outlet to the slip stream.

I did something similar in my BD4 and actually had to reduce the size of the NACA inlet as oil temps were in the 170's even in the summer.

Another fun experiment I did for the BD4 was making an exit venturi which really was just a glass shroud over the exit cowl flap. The slip stream was accelerated through the venturi creating a low pressure area at the cowl exit. This dropped my CHTs from the 390's to 340's and increased top speed from 168 to 174 mph (indicated at 1000 ft standard day). The speed increase however wasn't due to a cooling drag reduction as much as it was covering the firewall flat plate area that was exposed (due to the design of the exit hole being forward of the firewall).
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  #12  
Old 01-11-2010, 12:35 PM
RV8RIVETER's Avatar
RV8RIVETER RV8RIVETER is offline
 
Join Date: Sep 2005
Location: 1T7, Kestrel Airpark , Texas
Posts: 773
Default Sounds good.

Ken

In my research and studies, I have come to a similar conclusion. I think the most efficient way to supply a cooler is it's own dedicated duct. As you can see from Alan's posts, beside his awesome glass work, is that a NACA duct will work fine when properly executed.

I am working on my cowling right now. I mounted my cooler to the firewall and will supply it with a dedicated inlet. The outlet will also be ducted to the single round exhaust pumped exit.

There many ways to "skin a cat", just as long as they are done well.
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  #13  
Old 01-11-2010, 05:02 PM
SHIPCHIEF SHIPCHIEF is offline
 
Join Date: Mar 2008
Location: Seattle
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The side of the cowling is probably one of the lower pressure areas on the airframe.
I'm using the cowl side for my oil cooler air exit. I'm just ground running now, but it seems to be working fine.
Although I'm an 'alternate engine builder' I'm using a stock cowl, with a few mods.
Just my 2 cents, but if you experience a need for more oil cooler air flow...after trying the stock set up, you might try ducting the cooler exit air out the side thru a reverse facing scoop (extractor). IF you must, otherwise I'd advise you to duct the oil cooler exhaust air out the bottom as already mentioned.
One thing is for sure. If you change anything, build time gets a LOT longer. Ask me how I know this, or just check my link.
Build it stock, change it later.
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RV-8 N89SE first flight 12/26/2013
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  #14  
Old 01-11-2010, 06:51 PM
David-aviator David-aviator is offline
 
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Location: Chesterfield, Missouri
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Quote:
Originally Posted by SHIPCHIEF View Post
The side of the cowling is probably one of the lower pressure areas on the airframe. ......
I agree.

The attached image depicts the side Bonanza vents I copied and built and they are a reason the IO360 cht's and oil run cool, too cool in fact. Beech invented them about 50 years ago and they work.

The vents were installed to facilitate cooling with the Subby H6 and were almost removed when the Lycoming was installed. But one test flight changed my mind. I taped them shut with duct tape wanting to observe temperatures just using the stock cowl exit. There was no change and I thought coming in to land, they will be removed.

But after shut down I saw why there was no change. The internal lower cowl pressure had blown the duct tape off the cowl and they were taped tight. With that I decided to leave well enough alone. I don't think there is any drag with them as the airplane goes as fast as Vans numbers and somedays a bit faster. The max CHT observed so far is 405 and that was a WOT climb to 10,000' last summer to see how long it would take to get up there. (8 minutes, 26 seconds ) Oil temp with that climb was 185 or 190.

I believe you get good cooling by running air across the engine, lots of it, and one way to do that is having a copious amount of exit area. The standard Vans inlet is about 45.5 inches square and the exit 49 which equals 107%. That works for many guys.

My cowl was modified at least 4 times trying to cool the H6. I undid some of it going to the IO360 but I still have the Bonanza vents and a 5X16 bottom exit. Total area is 108 inches which computes to an exit ratio of about 237%.

Now I know that much exit area is not suppose to work in terms of drag and there is no science to qualify why the engine runs cool and airplane flies like it does, but it does. I suppose I could make some changes to perhaps see an improvement in performance. But I spent about 4 years trying to cool that H6 (never did conquer the beast) and flying around with a Lycoming that never over heats is such a pleasure, I think I will leave it all alone.

At present the side vents are taped shut on the inside to facilitate getting the oil temp up a bit. Even with the air shut off, oil temp still runs around 160. This is with the SW8432R mounted like in the RV-10 with a 4" scat tube from aft of #4 baffle.

I also believe another reason this thing is running like it is, is because it is not a 200+HP engine. (it turned up 187 on the Barrett dyno) There is a lot more heat generated with engines like what Alan Judy and others are running. And of course the faster you go, the more drag becomes an issue.

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  #15  
Old 08-25-2011, 03:21 PM
Conifer Conifer is offline
 
Join Date: Mar 2010
Location: Colorado
Posts: 10
Default Oil cooler cooling

Have you read my thread "Oil cooler cooling". I was thinking to install a "Advanced Aero Components " Naca Scoop large on the left side of the lower cowling and connect it directly the the SW oil cooler through a " scat tubing.
This naca scoop seems to be the best I have found around but its price is a big deterent ($ 225). Teh advantage of doing this will be to entirely devote the air going through the SJ plenum to the 4 cylinders equally. Cylinder # 4 is presently with a CHT 40F higher than # 1, 2 and 3 due the air going to theoil cooler mounted on the firewall through a 3" scat tubing.
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  #16  
Old 08-25-2011, 06:55 PM
RV8R999 RV8R999 is offline
 
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I've concluded after 1 year of flying my -8, a an oil cooler air source seperate from cyl cooling air isn't warranted. My oil cooler is mounted low in the cowl on the engine mount and fed cooling air via 3" scat from the #4 cyl baffle. As it is now, I have the inlet covered 50% and still do not see OT above 190, even during extended climb in the Florida Summer heat. I experimented with blocking the OC inlet in varying degrees to observe changes in CHT (particularly #4) and have determined it doesn't vary much at all if any as a function of OC inlet area.
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  #17  
Old 08-26-2011, 04:39 PM
SHIPCHIEF SHIPCHIEF is offline
 
Join Date: Mar 2008
Location: Seattle
Posts: 1,412
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Thanks for the follow up.
Our hangar nieghbor has an RV-4 with a custom oil cooler arrangement.
He mounted the cooler dead center on top of the crankcase on the front side of the rear baffle. The air flows right straight thru it and he controls the air flow seasonally with a partial blocking plate at the back.
He claims more even cylinder temp as well.
It is strong and simple.
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Scott Emery
http://gallery.eaa326.org/v/members/semery/
EAA 668340, chapter 326 & IAC chapter 67
RV-8 N89SE first flight 12/26/2013
Yak55M, and the wife has an RV-4
There is nothing-absolute nothing-half so much worth doing as simply messing around with Aeroplanes
(with apologies to Ratty)
2019
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