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  #1  
Old 06-01-2010, 08:47 PM
elippse elippse is offline
 
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Location: Arroyo Grande, CA
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Default Engine cooling

Guys, I have to tell you! These airplanes we build are gorgeous creations, and give us lots of bang for the buck! Way back when, Bellanca used to crow about how it got 135 mph on 135 horsepower, and now here are -6s doing 193 mph on 150 HP; Augustus would be mightily impressed! But for all of that, with the go-fast streamlining on these planes, the cooling systems are reminiscent of something the Red Baron would have had on his Fokker! After going to all of the trouble to build this to-kill-for plane, and then totally ignoring the air flow in and out of the cowling is montstrous, to say the least. So many take the output of their oil cooler and just dump it in front of the firewall and hope it will find its way out. Basically the same can be said of the engine cooling air; just have an inlet and place some baffles so that most of the air will find its way through the fins on the cylinders, and then let it find its way out the back! Why bother putting fairings on the gear struts and pants on the wheels? Just use the same thing the venerable old J-3 did and don't even bother with a cowling. Just let the cylinders hang out in the air! If you're going to go to all of the work and time and effort to build this thing of beauty, please at least take the time to put in a low drag cooling system.
Do you know how a jet engine works? It takes in air at its inlet, heats the air up, and then takes this increased volume of air and exhausts it out the back. When you heat the cooling air with your engine and oil, you've created a jet engine, not a very efficient one, but one just the same. When you allow the cooling air to find its way out the back through struts and wires, you take a lot of energy out of it that increases your overall drag. Have you noticed those dropped, streamlined sections on the bottom of the cowling of the Malibu and Cessna Corvallis, nee Columbia 400, nee Lancair ES? That's a duct that takes the air right from the bottom of the cylinders and conducts it smoothly out into the airstream. Each 1% extra speed you get, say 2 mph, is like having 3% more power, 4.5-5 HP! So please, do some experimenting with your inlet and outlet ducting. Make youselves nice expander ducts on the inlet-side to take the air, slow it down to increase its pressure, and then guide it into the cylinders.
And also do some experimenting with the use of your exhaust with an augmenter to help propel the air out the back. I've come up with some very short augmenters that use the Coanda principle to get the air on its way, and I'd be happy to share the drawings with any of you for free. I'd like to see you guys come all the way into the 21st century with your planes. When one or more of you more-daring individuals puts one of these together, you're going to say "This thing will never work!" and then you'll be amazed when you see it, cause everyone who's ever made one had to put the output of the Shop-Vac into it to see if it would work or if they wasted their time.
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  #2  
Old 06-01-2010, 08:59 PM
SteinAir SteinAir is offline
 
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Calling Bob Axsom!
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  #3  
Old 06-01-2010, 10:03 PM
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Bill Wightman Bill Wightman is offline
 
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Location: OKC, OK
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Hey Paul - I must admit being "guilty as charged" in terms of my very stock RV cooling system.

Problem is, I don't have any good ideas on how to get the exit flow routed better. I ran a simple compressible duct flow analysis to see how much momentum flow energy might be available and it wasn't much, by my numbers. But a few of my assumptions may have been off.

Other than doing things like running a plenum; annular inlets; inlet diffusers; good sealing everywhere - what can we do other than maybe variable exit area to help? You have me considering a nozzle to help direct oil cooler exit flow, but that's all I can conjure up... thanks.
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  #4  
Old 06-01-2010, 10:46 PM
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flyboy1963 flyboy1963 is offline
 
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Location: West Kelowna, B.C. Canada
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Default losing my cool

also guilty of a stock J3 system, and wishing the air found a much smoother path out of the cowl, at least I wish for Vetterman exhaust bumperizer.

Once I've totally encased my engine in a cold air pressure intake plenum, and covered the outlets and exhaust with carbon fibre ducting, how the heck do I inspect, service, or preflight my engine?
I won't be able to see or get to a thing, so when something starts leaking a little, I won't know about it...until it's too late.

sounds good, but for now, I like to see my engine, and will put up with the drag.
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  #5  
Old 06-02-2010, 01:41 AM
gasman gasman is offline
 
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Dave Anders did this to his RV4 from 1992 to 2000. And increased his speed to 261 mph. Or econo cruse of 190 mph on 4.5 gph. Here are his notes...................

http://sacrvators.com/Aircraft%20Efficiency%20N230A.pdf
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  #6  
Old 06-02-2010, 06:52 AM
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Mel Mel is offline
 
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Paul, Have you considered communicating with Larry Vetterman on this matter? He has some experience with testing cooling airflow on RVs.
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  #7  
Old 06-02-2010, 01:33 PM
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DanH DanH is offline
 
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Workin' on it Paul.....or at least building the cowl exit zone to accomodate experiments later.

http://www.vansairforce.com/communit...&postcount=278
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  #8  
Old 06-02-2010, 03:10 PM
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rv7boy rv7boy is offline
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Quote:
Originally Posted by gasman View Post
Dave Anders did this to his RV4 from 1992 to 2000. And increased his speed to 261 mph. Or econo cruse of 190 mph on 4.5 gph. Here are his notes...................

http://sacrvators.com/Aircraft%20Efficiency%20N230A.pdf
I talked to Dave Anders at Oshkosh several years ago, and I made some photos of his exhaust augmentor. I wish now I had made notes. I'll see if I can find those photos.

Paul, I'm not far enough along to take you up on your offer, but this area has been of interest to me ever since I read how much drag the cooling airflow contributed to the total drag of the typical single engine airplane. I think a lot of Dave Anders's improvements came from Professor Raspet's work at Mississippi State. However, I do remember Dave saying some of his findings ran counter to some of the published literature on the subject. For example, he found that the exit area for his highly modified RV-4 should be about 75-80% of the inlet area, rather than >100% as some had published before. But remember he was at that time running an augmentor (not to be confused with a Piper or Cessna "Augmentor" of different design and purpose).

I like what DanH is showing us. It reminds me a lot of what Dave Anders did. Dan's workmanship is impressive and his exhaust system just looks like it should work!

I have read that Dave has recently altered his exhaust system to compete in the Sound Abatement contest sponsored by NASA. So I don't know what condition his exhaust system is in now.

Interesting stuff. I believe there is lots of potential drag reduction in improvinig the RV cooling airflow; maybe you should write an article for publication with your thoughts.
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  #9  
Old 06-02-2010, 03:54 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by rv7boy View Post
I talked to Dave Anders at Oshkosh several years ago, and I made some photos of his exhaust augmenter....
My arrangement is not currently an augmenter, but you never can tell where things may lead.

Quote:
75-80% of the inlet area, rather than >100% as some had published before.
Novice studies of theory say there is no golden number....it varies with several factors. And on the practical front, consider that the average RV cowl is a leaky sieve, ie it has "exit area" all over the place, most of it wrong.

Quote:
.....exhaust system just looks like it should work!
I only picked the 4 into 1 because its shape compliments efforts to increase cooling exit velocity....the tubes are mostly parallel to airflow.
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  #10  
Old 06-02-2010, 04:35 PM
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BSwayze BSwayze is offline
 
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Quote:
Originally Posted by elippse View Post
I've come up with some very short augmenters that use the Coanda principle to get the air on its way, and I'd be happy to share the drawings with any of you for free.
Paul,

I'm a ways off yet from this part of the build, but I'm very interested in your thoughts and your drawings. Send them to me, please!

I have already talked about this subject with a couple of local builders. I think the awareness is rising a little bit.

Please keep your thoughts coming to this forum, too! Thank you.
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