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  #1  
Old 12-08-2005, 03:21 PM
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Default powerflow exhaust surprise

Talked to a guy today, the tube bender/flight instructor, who is now flying a powerflow 172. He is impressed with the increased performance and decreased fuel flow.

Good to hear equel length actually works - hope my headers have some small impact
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  #2  
Old 12-08-2005, 04:01 PM
wvshoem wvshoem is offline
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I’m doing away with the Brock exhaust that came with my long EZ project and going to run four pipes out the back. I’m building plenums around the cylinders and will use the exhaust to help draw cooling air through them. Several others have done this with good success. I need to look for a tube bender when the time comes because Hal Hunt’s exhaust pipes are a little more than I would like to pay.

This is the stuff I really enjoy about experimental aviation. I could get so much more out of the O540 in my Cherokee, but… well, we all know about the certified world.

William
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  #3  
Old 12-08-2005, 04:10 PM
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Make your own exhaust out of mandrel bends - a guy in Wisconsin sells the flanges
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Old 12-08-2005, 04:19 PM
wvshoem wvshoem is offline
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Cool.............. what are Mandrel Bends???
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  #5  
Old 12-08-2005, 04:21 PM
Wayne Hicks Wayne Hicks is offline
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The "powerflow" exhaust system and "why no canards fly with them" come up every year. Short answer is, the power flow exhaust still robs power and still adds weight. It just robs less power and reduces the weight from the muffler it is made to replace.

We aren't required to have mufflers (not yet anyway). And as far as I know, straight pipes are far better than powerflow or mufflers.
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  #6  
Old 12-08-2005, 04:24 PM
Wayne Hicks Wayne Hicks is offline
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Google man, google! ("What is a mandrel bend?")

Definition of mandrel bend" as it applies to this discussion:
http://en.wikipedia.org/wiki/Mandrel

For a picture of a mandrel bend in an exhaust pipe:
http://www.roadraceengineering.com/mandrelbends.htm
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Old 12-08-2005, 04:35 PM
wvshoem wvshoem is offline
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To Wayne from TLTG (too lazy to google) - Thanks.
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  #8  
Old 12-08-2005, 05:30 PM
Wayne Hicks Wayne Hicks is offline
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Be glad I had too much time on my hands today I'm leaving work now to flip the plane over and start thinking about finishing off that bottom before Santa gets here!
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  #9  
Old 12-08-2005, 07:52 PM
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mmmm - know that no back preasure is the best, but we have to have a pipe on to keep hot exhaust from under the cowl. wonder if there is an optimum length, besides short as possible.
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  #10  
Old 12-08-2005, 10:57 PM
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Hey wayne - don't tell em that they should google - newbies are sensitive. ask away EVERYONE

go, here to see samples
http://www.magnumforce.com/ubend.asp

when items are mandrel the tube or pipe is kept at the sam internal and external diameter throughout the bend. other forming techniques don't do that and air flow suffers
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dust

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  #11  
Old 12-09-2005, 12:07 AM
Don P-Factor Don P-Factor is offline
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Default Back pressure

Dust, I disagree that "No backpressure is best" I have had some experience tuning engines and can tell you that some backpressure is desireable. Thats what all the hullabaloo is over tuned exhaust. Also intake runner length may create uneven flow using equal length exhaust systems. You must design what is best for your application and not get too Anal about it. Most of the race cars use different rocker ratios for the longest intake runners to even out the flow. Unfortunately this is not possible on aircraft engines, unless you are willing to spend a loooong time figuring out custom camshaft profiles. Every engine that I have run with open exhaust and with restrictiors has performed better with some restriction. This includes 2 and 4 stroke engines. There was an article a few years ago regarding using a automotive muffler on an aircraft in Kit Planes mag and they also increased the power of that unit. Happy testing. Don.
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  #12  
Old 12-09-2005, 12:38 PM
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Well, the tuned exhaust thingy - i thought it was that the power pulses arrived at the merge collector in a timed manner, one after another, after another and created a sucking force in the other tubes, effectively creating negative back pressure or suction

just a newbie trying to understand
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dust

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  #13  
Old 12-09-2005, 02:04 PM
Lynn Erickson Lynn Erickson is offline
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Default Just a few exhaust things

Just thought I would try and post some of the exhaust systems that I have built for Eze type aircraft. I saw that Dust is starting his system and some pictures might help or confuse him even more.
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  #14  
Old 12-09-2005, 02:13 PM
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Well - you went the tuned route - any info on before and after on hp, etc? were ther 4 straight or 2 - 2 into 1's?

As for me - my system will look quite different as i have a 6 cylinder continental and am installing twin turbos.

I opened up this topic as a matter for all in the normally aspirated (almost everyone here) to consider and learn about exhaust.
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dust

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  #15  
Old 12-09-2005, 02:47 PM
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Okay, here's a newbie question. What is the reason for having exhaust going out the back at the prop? It seem we could design the cowl to pipe the exhaust straight out the sides keeping heat away from the engine. Why not like some of the WWII fighters?
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