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06-05-2009, 12:10 PM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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Easy wind tunnel...
...for you guys wanting to reduce drag.
Years ago, I put drops of black, used oil on the leading edges of my homemade brake fairings on my Cassutt and I wondered if I'd shaped them correctly. I flew around the pattern and went wide open and then landed. Low and behold.....beautiful streaks all the way to the rear....good, laminar airflow.
So today while I was refueling my dirty Air Tractor for another load, I looked at the leading edges and saw the turbulence behind the round-head rivets and remembered reading in an EAA publication years ago that the first rivet causes as much drag as the next seven..well here it is...the leading edge is on the right side and the chemical streaks show airflow.

I'm gonna do the fuel drains and aileron hinges of my -6 with a few drops of black oil and go fly....a cheap wind tunnel.
Regards,
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga
It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132
Dues gladly paid!
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06-05-2009, 09:02 PM
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Join Date: Mar 2009
Location: Massapequa,NY
Posts: 115
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That might just be the first rivet taking all the hit. 
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06-05-2009, 09:28 PM
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Join Date: Sep 2005
Location: Maple Grove, MN
Posts: 2,334
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Pierre, excellent photo! That is how I found out that some of the cooling air exit area has reverse flow - I put drops of oil on the belly and noted some went forward!
I guess some of the air gets scared and climbs back into the cowl.
__________________
Alex Peterson
RV6A N66AP 1700+ hours
KADC, Wadena, MN
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06-05-2009, 11:52 PM
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Join Date: Feb 2007
Location: San Diego, CA
Posts: 1,670
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Messy
Well, YEAH, but whatta ya use for cleanup? 
__________________
Pete Hunt, [San Diego] VAF #1069
RV-6, RV-6A, T-6G
ATP, CFII, A&P
2020 Donation+, Gladly Sent
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06-06-2009, 05:07 AM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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This.....
Quote:
Originally Posted by PCHunt
Well, YEAH, but whatta ya use for cleanup? 
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Purple cleaner from NAPA...daily.
Regards,
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga
It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132
Dues gladly paid!
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06-06-2009, 09:01 AM
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Join Date: Aug 2008
Location: North Central TX, via Taylorsville, GA
Posts: 87
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Big ol' protruding head rivets...
Pierre, we use those great big headed rivets for noise abatement. We don't want you guys breaking the sound barrier going to and from the field!  It keeps the sonic booms to a minimum (happy neighbors) and also keeps the Thrush guys from getting too jealous!
CDE
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06-06-2009, 10:24 AM
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Join Date: Dec 2008
Location: Los Angeles, CA
Posts: 301
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Secret is out
So the secret is out; what every glider-guider knows. The oil tells the whole story. If anyone can get there hands on some of the glider flight test reports from Soaring magizine, oil testing is a big part of performance maximizing. The biggest gain is to look at the transition from laminar to turbulent flow and reducing the drag from this transition. Most gliders have a step in the finish to trip this laminar flow to prevent a drag-inducing bubble, or reverse flow region. Besides keeping everything clean and dealing with the cowl exit, I believe tripping the flow results in the biggest reduction in drag. So if someone can minimize the drag from the cowl exit and trip the laminar flows properly, the airplane will have maximum performance. I suspect the only laminar flow is outside of the prop wash, but not sure. Good luck and hope to see a lot of oily planes out there.
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06-06-2009, 12:10 PM
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Join Date: Jan 2005
Location: 57AZ - NW Tucson area
Posts: 10,011
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And it can also be done in color...
I believe this is oil with food coloring added. Spots (dabs?) placed on the ground and flying then makes the streaks along the flow lines...

__________________
Gil Alexander
EAA Technical Counselor, Airframe Mechanic
Half completed RV-10 QB purchased
RV-6A N61GX - finally flying
Grumman Tiger N12GA - flying
La Cholla Airpark (57AZ) Tucson AZ
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06-06-2009, 01:01 PM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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Gil, I wonder...
....if oil paints would stay wet long enough for a takeoff and flight to WOT.
I think we're leaving a bunch of speed on the table, as Dave Anders has already proven...a 265 MPH -4, even with 230HP he has really cleaned her up.
Bob Axsom(sp?) has already picked up around 20 MPH and there's more to be had.
I'm also gonna oil up the surfaces around the gaps between the ailerons and flaps and wingtips to see what's going on there as well.
Thanks,
__________________
Pierre Smith
RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15 Sold
Air Tractor 402 PT-6-20 Sold
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga
It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132
Dues gladly paid!
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06-08-2009, 12:23 PM
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Join Date: Oct 2008
Location: Lake Country, B.C. Canada
Posts: 2,416
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wind tunnel
...anyone ever rigged up a wind tunnel that they mounted on the back of their pickup?
I'd like to try an airfoil with flaps to figure out the best place for VG's on the -9 airfoil, among other things.
Even a 1/4 scale chunk of wing bolted to the side mirror would be interesting, no?
I guess the ulitmate rolling wind tunnel was the rig hung off the front of a truck so customers could 'fly' a BD-5 down the runway without loss of life or significant aluminum! (hard to find pics...here's one in Bud Davisson's article circa 1974!)
http://www.airbum.com/pireps/PirepBD-5.html
__________________
Perry Y.
RV-9a - SOLD!....
Lake Country, BC
Last edited by flyboy1963 : 06-08-2009 at 12:41 PM.
Reason: add link
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