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02-05-2009, 02:14 PM
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unqualified unfluencer
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Join Date: Jan 2005
Location: Highland Village, TX
Posts: 4,088
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Quote:
Originally Posted by DickF
Somehow I'm not finding the article that is being discussed. Can someone provide a link?
Thanks..
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Front page of www.VansAirForce.net (2/5/9).
b,
d
__________________
Doug Reeves (your host) - Full time: VansAirForce.net since '07 (started it in '96).
- Part time: Supporting Crew Member CAE Embraer Phenom 300 (E55P) @ KDFW.
- Occasionally: Contract pilot (resume).
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02-06-2009, 07:52 AM
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Join Date: Jul 2007
Location: Madison, Wisconsin
Posts: 778
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RV-8 cooling exit experiment
Quote:
Originally Posted by Ironflight
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.
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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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Alan Carroll
RV-8 N12AC
Last edited by Alan Carroll : 02-06-2009 at 07:55 AM.
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02-06-2009, 08:11 AM
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Join Date: Jun 2005
Posts: 678
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Photos?
I just logged in today (6th) and don't see the info. Is there another site or thread?
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Steve
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02-06-2009, 08:18 AM
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Join Date: Jan 2005
Location: Round Rock, TX
Posts: 3,778
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You need to pull down the main page a little to see it.
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Reiley
Retired N622DR - Serial #V7A1467
VAF# 671
Repeat Offender / Race 007
Friend of the RV-1
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02-06-2009, 08:25 AM
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Join Date: May 2005
Location: Tuttle, Oklahoma
Posts: 2,563
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Quote:
Originally Posted by n38139
I just logged in today (6th) and don't see the info. Is there another site or thread?
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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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02-06-2009, 08:52 AM
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unqualified unfluencer
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Join Date: Jan 2005
Location: Highland Village, TX
Posts: 4,088
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Quote:
Originally Posted by RVbySDI
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.
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I plan to create its own article in 'Builder Mods' sometime over the weekend.
b,
d
__________________
Doug Reeves (your host) - Full time: VansAirForce.net since '07 (started it in '96).
- Part time: Supporting Crew Member CAE Embraer Phenom 300 (E55P) @ KDFW.
- Occasionally: Contract pilot (resume).
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02-06-2009, 09:21 AM
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Join Date: Oct 2005
Location: 08A
Posts: 9,500
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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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Dan Horton
RV-8 SS
Barrett IO-390
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02-06-2009, 02:37 PM
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Join Date: Sep 2007
Location: Los Angeles CA
Posts: 25
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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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02-06-2009, 03:09 PM
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Join Date: May 2008
Location: central oregon
Posts: 1,089
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Quote:
Originally Posted by BD4Guy
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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here' ya go
http://www.vansairforce.com/communit...ad.php?t=31275
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nothing special here...
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02-06-2009, 03:38 PM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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'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.
__________________
Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"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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