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  #31  
Old 03-13-2012, 08:58 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by hydroguy2 View Post
.. you can see the PAX side hangs down more than the pilot side.
Yeah, yeah, a lot of guys have that problem
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  #32  
Old 03-13-2012, 09:29 PM
gereed75 gereed75 is offline
 
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Yikes, As I read I was expecting something real bad!! Sorry for hanger owner, glad for you!
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  #33  
Old 03-13-2012, 09:55 PM
Bob Axsom Bob Axsom is offline
 
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Default That is the right way to apply the curves for the desired effect

Quote:
Originally Posted by Mike S View Post
Airfoil shaped (flat on top, curved on bottom) after fairing on the bottom of the fuse-----fit it between the sides of your cowl extensions, depending on size and how far forward, you get to choke off the outlet, but at the same time give it a smooth ramp for the air to follow. Coanda stuff that Paul Lipps talked about, I seem to remember him posting a drawing of something like this.

You can also research stuff like it on the CAFE website------as I recall the guy who runs the CAFE foundation did this to a Mooney with good results. http://cafefoundation.org/v2/aboutca...oard.php#brien

More info for you techie types here. http://cafefoundation.org/v2/tech_en...greduction.php
That is what I was planning to do but when I went out to the hangar to visualize where I was going to mount things I decided it will not work unless I move the exhaust pipes down and then it is questionable. I did implement a version of that with the curve going the wrong way and it did look slick but slowed the airplane down. I'm doing OK right now and I haven't had a chance to work on the outlet fairing yet but i'm sure it will work if I alter the exhaust pipe position.



Bob Axsom
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  #34  
Old 03-13-2012, 09:57 PM
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Jerry Cochran Jerry Cochran is offline
 
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Default Adjust?

Quote:
Originally Posted by hydroguy2 View Post
Thanks Bruce. Your pipe set up is different. I see you "A" model folks are dealing with a clogged outlet also, but looks like you have a lot more exit area.

I am trying to streamline the exit flow So thought trimming the pipes a bit might actually help and be less turbulence.

Here's a pic looking aft, you can see the PAX side hangs down more than the pilot side. Thought I could even them out a touch.
I have a 4 pipe with ball joints aft. If yours are the same, can't you adjust them to line up?


.
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RV-7a 707DD Bot from David Domeier 12/01/11
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  #35  
Old 03-13-2012, 10:03 PM
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I haven't tried lately, but recall when I was initially installing them, this is where they want to be. I figured it was better to support them in that position than to induce a stress problem. I'm pulling the lower cowl tomorrow, so I'll look again.
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  #36  
Old 03-13-2012, 11:02 PM
gereed75 gereed75 is offline
 
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Bob, Glad you put that picture in. I worked with it in paint to try to show where I think the fairing really does it's work.





The fairing gives the very slow, low energy, undirected air coming out of the sharp intersection corners a chance to get straightened out before the free stream airflow coming off the bottom and sides of the cowling mixes with it turbulently (is that a word??)

Not sure I described it right, but I'm sure you will get the message. The air coming out of the baffles under the cylinders flowing aft bangs into the firewall and is trying to find it's way out of that sharp corner and needs time to straighten itself. The simple corner fairing gives it that time.

My center body, bottom of firewall fairing and underbelly fairing probably all contribute a little, but this simple corner fairing gave me the bulk of my results.

That's what I think anyway.
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Last edited by gereed75 : 03-13-2012 at 11:25 PM.
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  #37  
Old 03-13-2012, 11:37 PM
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Quote:
Originally Posted by gereed75 View Post
Mike, Can you get me to that link another way?? I'm getting the "forbidden 403" message. Thanks
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???
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  #38  
Old 03-13-2012, 11:41 PM
RVnoob RVnoob 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???
try this link:

http://www.cafefoundation.org/v2/pdf...localflow2.pdf



(somehow you need the www in the front of the URL)
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  #39  
Old 03-13-2012, 11:51 PM
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Quote:
Originally Posted by RVnoob View Post
try this link:

http://www.cafefoundation.org/v2/pdf...localflow2.pdf



(somehow you need the www in the front of the URL)
That gave me the forbidden message.
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Flying as of 12/4/2010

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  #40  
Old 03-14-2012, 01:44 AM
Bob Axsom Bob Axsom is offline
 
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Default I got the forbidden message as well

Coanda effect is a pretty simple concept and if you just want the general idea of what it is a Google search will do it for you. Does anyone remember the Boeing YC-14? It was in a STOL cargo aircraft competition with the McDonnell Douglas YC-15 It had its two engines mounted high to exhaust over the upper surface of the wing and follow the deployed flaps and generate lift. The MDC entry directed the exhaust from its four engines under the wings directly against the deployed flaps to generate lift.

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
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