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  #11  
Old 02-05-2009, 02:14 PM
DeltaRomeo DeltaRomeo is offline
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Quote:
Originally Posted by DickF View Post
Somehow I'm not finding the article that is being discussed. Can someone provide a link?

Thanks..
Front page of www.VansAirForce.net (2/5/9).

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d
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  #12  
Old 02-06-2009, 07:52 AM
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Alan Carroll Alan Carroll is offline
 
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Default RV-8 cooling exit experiment

Quote:
Originally Posted by Ironflight View Post
I am also interested to see how this might apply to the -8's, as we have a built-in exit ramp which changes the shape of the belly at that point - it is not flat all the way across as in the side-by-sides. Larry's comments make me wonder if van was experimenting with similar ideas when he did the -8 design - I have read that initially, the ramp was supposed to be variable (I think for cooling), but ended up fixed.
A couple of months ago I did an experiment to test exactly this idea. I installed a new temporary exit ramp below the existing one. This new ramp had a large-radius hemispherical lip at the front end where it meets the firewall (that covered the existing lip), and was attached to the same aft location as the existing ramp. It was positioned so that it blocked about 40% of the cooling exit. The exhaust (Larry Vetterman's crossover system, two 1.75" pipes) was repositioned as low as possible to avoid interference.

Before and after flights made on the same day under the same conditions showed that I was successful in raising CHTs about 20°F (this on cold day, around 20°F OAT). I measured 0.5 knot increase in speed (4-way GPS, Horton/NTPS spreadsheet calculation), but this could well be due to measurement error (I generally don't trust any measurement differences of less than one knot). Certainly it was not a big change. My original intent was to make the cooling ramp position adjustable in flight, but based on this experiment I probably won't do it. I think this was also Van's conclusion (see 12/93 issue of RVator).

I suspect that the sharp bottom edge of the cowl cooling exit produces a lot of drag-inducing secondary flow, perhaps because its nearly impossible to exactly match the exit air velocity to the free stream velocity. The earlier-reported tuft testing seems to show this. I also know based on breakage of the inward cowl attachment hinge eyes and on paint cracks that this area experiences a lot of vibration, and I can easily believe Larry's idea that its the source of some of the vibration felt through the cockpit floor. I think his modification is a great experiment to smooth out the flow in this area, provided its possible to get adequate cooling in warmer weather.
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Last edited by Alan Carroll : 02-06-2009 at 07:55 AM.
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  #13  
Old 02-06-2009, 08:11 AM
n38139 n38139 is offline
 
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Default Photos?

I just logged in today (6th) and don't see the info. Is there another site or thread?
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  #14  
Old 02-06-2009, 08:18 AM
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LifeofReiley LifeofReiley is offline
 
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You need to pull down the main page a little to see it.
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  #15  
Old 02-06-2009, 08:25 AM
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RVbySDI RVbySDI is offline
 
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Quote:
Originally Posted by n38139 View Post
I just logged in today (6th) and don't see the info. Is there another site or thread?
The original post was on the front page for Thursday, February 5, 2009. You will have to go back to that day's front page to read it.

Doug,
Perhaps the original post can be added to this thread. Since previous front pages are now out of site without clicking on the "Past Day. . ." links, maybe it will not confuse everyone.
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  #16  
Old 02-06-2009, 08:52 AM
DeltaRomeo DeltaRomeo is offline
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Originally Posted by RVbySDI View Post
snip...Doug,
Perhaps the original post can be added to this thread. Since previous front pages are now out of site without clicking on the "Past Day. . ." links, maybe it will not confuse everyone.
I plan to create its own article in 'Builder Mods' sometime over the weekend.

b,
d
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  #17  
Old 02-06-2009, 09:21 AM
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DanH DanH is online now
 
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<<I suspect that the sharp bottom edge of the cowl cooling exit produces a lot of drag-inducing secondary flow>>

Specific to the unique configuration of the -8, at some point I intend to try the "mirror" of Alan's experiment; leave the fuselage ramp standard, but remove (or reduce) the lower cowl air exit box. Not possible on the 6 and 7 (no ramp inset in the fuselage), thus Larry's experiment.

I'm building a flange with nutplates into the belly of the cowl just to make it easy to swap out different cowl exit sections. There are some companion mods (cowl inlets, baffles, a bit of internal duct) and I hope to wind up with a rather small fixed exit. However, there is still a cruise penalty for a fixed exit; an after-fairing like Larry's would make practical installation of a variable exit a lot easier.
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  #18  
Old 02-06-2009, 02:37 PM
BD4Guy BD4Guy is offline
 
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Pardon the intrusion, but do a a username search under "bryanflood" for his version of this mod- he has inflight video!
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  #19  
Old 02-06-2009, 03:09 PM
Danny7 Danny7 is offline
 
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Originally Posted by BD4Guy View Post
Pardon the intrusion, but do a a username search under "bryanflood" for his version of this mod- he has inflight video!
here' ya go

http://www.vansairforce.com/communit...ad.php?t=31275
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  #20  
Old 02-06-2009, 03:38 PM
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Mike S Mike S is offline
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Default 'nother idea

Looking at the above mods, makes me wonder if this would work well in conjunction with augmenter tube type exhaust/cooling air exits???

It should be possible to increase the air flow velocity---and therefore CFM, while reducing the area.
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