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  #41  
Old 03-14-2012, 02:47 AM
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rvmills rvmills is offline
 
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Mike,

Can you e-mail me the pdf? I can try to repost it as a link or just try to post it as picture file here.

On the discussion of trimming the exhaust pipes: In one talk with Paul Lipps, I asked about straightening my pipes along the belly, but expressed my concern about the drumming on the belly. He told me that I could straighten them out, then cut them off at an angle so the opening is oblique to the pipe (top longer than bottom...basically like a turned down pipe, but with no bend...if that makes sense). Paul said that the exhaust plume would still be more aligned with the fuselage (less plume pointing down), but the sound would travel down, and not drum on the belly. Haven't gotten to that mod yet, so I have no field experience with it, but just passing it along, FYI.

Jason Rovey is watching this thread, and sent me a couple pics of his latest mod tonight. He extended the collector on his 4 into 1 exhaust quite a bit, and says he gained 2 KTAS on his already fast RV-8, as shown in multiple tests. He's having trouble posting pics, so I'll post them here, and hopefully he'll jump in with the data from Cafe and the info on powerflow exhausts he used (per his e-mail). Looks interesting, and he's considering a cowl extension to enclose it now, based on this thread. Good for more discussion!

Cheers,
Bob

Jason's pics:


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  #42  
Old 03-14-2012, 10:04 AM
gereed75 gereed75 is offline
 
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Location: pittsburgh pa
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Quote:
Originally Posted by Bob Axsom View Post
Gary the air coming through my cylinder cooling fins never sees the firewall because of my baffle configuration in the lower cowl. I think your fairing does what you describe and more. I don't know if you have ever met Alan Carroll but he is one smart dude also (like you) with a fast RV-8. You may recall earlier he mentioned he extended the cowl at the bottom of the outlet which is the other thing your fairing does. If you think about it the air mass in the lower cowl has some downward force in the stock configuration and the outlet being chopped off at the firewall does not eliminate that. I can imagine an inverted rooster tail of air or a burbling directionless mass coming out of there but your and Alan's fairing's turn it and give it some direction aft. in addition to your side barriers. It will be interesting to see what Dan and Brian report when they get to fly their fairings.

Bob Axsom
As I was typing late last night, I was trying to recall your internal baffle configuration and thought that it did direct the airflow directly to the outlet.

My fairing will still do as you say, further turning, aligning and streamlining that relatively turbulent air before it gets ripped by the freestream flow.

And if your talking about modifying exhausts, see Bob's notes above. This is exactly what I was considering - turnback, extend and cut at an angle. Then fair it all in.

It has to be all good!!
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Last edited by gereed75 : 03-14-2012 at 10:19 AM.
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  #43  
Old 03-14-2012, 10:15 AM
gereed75 gereed75 is offline
 
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Default Oh great

Quote:
Originally Posted by rvmills View Post

On the discussion of trimming the exhaust pipes: In one talk with Paul Lipps, I asked about straightening my pipes along the belly, but expressed my concern about the drumming on the belly. He told me that I could straighten them out, then cut them off at an angle so the opening is oblique to the pipe (top longer than bottom...basically like a turned down pipe, but with no bend...if that makes sense). Paul said that the exhaust plume would still be more aligned with the fuselage (less plume pointing down), but the sound would travel down, and not drum on the belly. Haven't gotten to that mod yet, so I have no field experience with it, but just passing it along, FYI.

Jason Rovey is watching this thread, and sent me a couple pics of his latest mod tonight. He extended the collector on his 4 into 1 exhaust quite a bit, and says he gained 2 KTAS on his already fast RV-8, as shown in multiple tests. He's having trouble posting pics, so I'll post them here, and hopefully he'll jump in with the data from Cafe and the info on powerflow exhausts he used (per his e-mail). Looks interesting, and he's considering a cowl extension to enclose it now, based on this thread.
Just when I thought I would shelve my ideas to transition and extend my exhausts straight back until next winter, along comes this info!!

Back to the drawing boards.... Call Larry for some angled couplings ......and now no chance of ever catching Jason!!.

Thanks Bob, you are a real pal!
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  #44  
Old 03-14-2012, 10:30 AM
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Mike S Mike S is online now
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Quote:
Originally Posted by rvmills View Post
Mike,

Can you e-mail me the pdf? I can try to repost it as a link or just try to post it as picture file here.


Cheers,
Bob
Will do.

BTW, one of the things mentioned in the CAFE stuff is to extend the exhaust pipe out past the cooling exit shroud.
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  #45  
Old 03-14-2012, 10:43 AM
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hydroguy2 hydroguy2 is offline
 
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Quote:
Originally Posted by rvmills View Post
......then cut them off at an angle so the opening is oblique to the pipe .....

Jason Rovey .....gained 2 KTAS on his already fast RV-8, ..........he's considering a cowl extension to enclose it ......
Angle cut on my exhaust is my plan.

NO Jason, that'll never work you new exhaust should angle turn and extend straight down about 12"...it'll add lift...honest. I'll never catch you guys if you keep making mods.
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  #46  
Old 03-14-2012, 11:13 AM
David-aviator David-aviator is offline
 
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The Vetterman 4 pipe exhaust on the airplane Jerry Cockran now owns extended below the cowl opening considerably, so I trimmed each pipe as per a template Larry included in the kit.

The result was a better looking set of pipes but it did not improve performance so far as I could tell and whereas the fuselage bottom remained clean of exhaust stains before, after the trim job it showed a typical exhaust trail of grime.

The cooling outlet fairing, does it affect cooling? Seems like it may restrict the exit area just a bit which in turn could affect cooling.
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  #47  
Old 03-14-2012, 01:41 PM
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NovaBandit NovaBandit is offline
 
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Quote:
Originally Posted by Mike S View Post
I put it up the only way I know how to do it.

You could try searching for "CAFE Foundation" in Google or some such, then click on the "Research" button, then in the drop down menu, go to "CAFE Reports" and then to "Local Flow 2" in the list of reports.

It is a PDF, maybe that is why you can not see it???
Here is the picture Mike is talking about:


Source: http://cafefoundation.org/v2/research_reports.php > Local Flow II (they must have a direct link policy on their files)
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  #48  
Old 03-14-2012, 02:00 PM
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Thanks Ed, I knew someone out there in VAF land would be able to do this.

I have no idea what a direct link policy is, but glad you understand how to deal with it.

Note the rear part of the upper exit ramp is hinged, and moves the ramp up and down to adjust flow.
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VAF 909

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Flying as of 12/4/2010

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"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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  #49  
Old 03-14-2012, 06:40 PM
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Quote:
Here is the picture Mike is talking about:

Note the identified features.

"External flow provides suction".....which translates as "the external flow provides the energy to accelerate the cooling outflow". Put another way, suction = drag. In return you get increased mass flow, i.e. improved cooling.

"internal flow guide, green".....simple enough, no square corners please.

and

"rounded door leading edge"....a nice radius on the bottom of the firewall, again the no square corners rule.

"aft hinged door...to smooth the exit flow".....aka an exit throttle. This feature does accelerate exit mass and reduce both drag and turbulence.

The reference does not attribute anything to the shape of the body shell beyond the suction due to its airfoil shape (the front half). There's no mention of the slashed form afterbody. Seems like if you expect goodness you'll need to incorporate the referenced features.

I'm just sayin'
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  #50  
Old 03-14-2012, 09:04 PM
Bob Axsom Bob Axsom is offline
 
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Default A little different thought

To my way of thinking the shroud or outlet fairing is a must for me to try. What the CAFE drawing shows is essentially what I had been thinking of but without lowering the exhaust there is not enough room to make it work B-u-u-u-u-t What if you mounted an inverted airfoil with an undercamber in the outlet and adjusted the angle of attack to optimize the speed? You could possibly rig it to get the blown flap effect of the YC-15 and and the coanda effect of the YC-14. With a little work you would be able to tune it from the cockpit.

Bob Axsom
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