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POSTING RULES

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04-08-2010, 08:52 AM
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Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
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Bob,
Thanks, though I won't claim the speed is real till it gets confirmed in a race or the side by side testing (great idea Mark!) The flat plate idea sounds like it may be the best of all the tip projects...good luck with that when time permits. What will you use to plug the aileron? I'm still considering the aileron plug along with covering that riblet in the back of the flat tips, but having the plug come loose and bind with the tip is a concern. Terminating the tip at the wing trailing edge and then plugging the aileron alleviates that, so is appealing. Looking forward to seeing the development. Sorry I'll not get to meet you in Taylor Bob...was looking forward to that. But I understand the home front, and thoughts are with you and your bride! Good luck with the fixes and the projects as well, and good luck in the next couple races. Mike will be looking forward to the rivalry as well, I'm sure!
Mark,
Launching early tomorrow, and hope to get to Taylor with a little light left. Will need to swap the tips, but we could make a quick run with the normal (X-C) tips on Friday, then do it again on Saturday am before the race. My cell is 775-544-3511. If ya can, plz call so I can grab your cell to call you inbound. I'm going conservative and planning 3 fuel stops this time, the last one being at E30, 150 miles west. If you'd like, we could meet there (or in between) and fly side-by-side to Taylor and give it a whirl for round 1 with normal tips. Airnav sez cheap gas there. Just watch for the TFR for the airshow to the west.
In the race, let's hope the radome doesn't jam our GPS's again. This time I get to follow you, but I promise to call you if I see you turning too far or too short...I promise!
Cheers,
Bob
Last edited by rvmills : 04-08-2010 at 08:57 AM.
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04-08-2010, 02:50 PM
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Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
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Speed increase
Nice to see your work is paying off, Bob. On my Lancair the flaps can be reflexed up to 8 degrees. I've done some experimenting with them and I found that down low with higher speeds and more dense air where my required CL is lower, that I can use all of my reflex. But at density altitudes of 12k-15k and higher weight, I found that my speed would go up 3 mph in going from 8 deg. to 6 deg., then I lost 3 mph going to 4 deg., then 4 mph more at 2 deg. I think it has to do with the CD vs CL at reduced camber. I've noticed that RVs seem to fly nose low at low altitude and higher speed. I'd guess the wing incidence was designed for slower speeds. But reflexing the flaps makes the nose rise due to the higher AOA needed with less camber, so I was wondering if any of you have tried making it possible to reflex your flaps and seeing what that does to your speed.
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04-08-2010, 08:26 PM
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Join Date: Jan 2008
Location: Ashland, OR
Posts: 2,573
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reflex might help a little
Hi,
The airfoil on the RV- 3,4,6,7,8 is a very low CM_o airfoil, with very short laminar run, so reflex generally should not help, but just a degree or two might help a small amount. I would encourage someone to try, but I would be somewhat surprised.
Your experience in the difference in reflex that is best at different altitude reinforces my comments on another thread that at high altitude, induced drag is a bit more important than people might think, because the CL is higher. The Lancair airfoil (NLF-0215) (perhaps modified) was originally designed to be used with substantial reflex for cruise. Keep it clean and it will achieve significant laminar flow in the 'bucket'. The reflex shifts the bucket to lower CL.
The RV-10 airfoil was designed to benefit from a modest amount of reflex at cruise, and I would encourage people to experiment with that too. (how do I know this? send me a PM and I'll tell you) 
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet"
Hobbs 625
LS6-15/18W sailplane SOLD
bought my old LS6-A back!! 
VAF donation Jan 2020
Last edited by scsmith : 04-08-2010 at 08:30 PM.
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04-09-2010, 09:48 AM
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Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
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[quote=scsmith;422207]Hi,
Your experience in the difference in reflex that is best at different altitude reinforces my comments on another thread that at high altitude, induced drag is a bit more important than people might think, because the CL is higher. QUOTE]
Hi, SS! When I had Jim Smith do some testing with my prop on his RV-6, I noted how his speed drop-off with altitude was much greater than mine. I calculated the induced drag for his 4.8:1 AR and saw that it was much greater than mine with its 8.1:1. I commented that he must see much higher nose-up angle at high altitude and he cincurred. I designed some triangular tips for his wings to increase AR without a big area increase, he made and installed them, and it seems to be working well. His area went from 110 to 116, and span from 23' to 26'. His takeoff and landing speeds are lower, his climb is better, and above 6000'-7000' his speed is better. He photographed tufts on the wing-tips close to stall and they were straight back!
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04-09-2010, 11:29 AM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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You have one..
Quote:
Originally Posted by scsmith
The RV-10 airfoil was designed to benefit from a modest amount of reflex at cruise, and I would encourage people to experiment with that too. (how do I know this? send me a PM and I'll tell you) 
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PM sent, Steve,
Best,
__________________
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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04-10-2010, 09:22 AM
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Join Date: Mar 2005
Posts: 5,685
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How's that working out?
How are things working out at Taylor, TX?
Bob Axsom
Quote:
Originally Posted by rvmills
Bob,
Thanks, though I won't claim the speed is real till it gets confirmed in a race or the side by side testing (great idea Mark!) The flat plate idea sounds like it may be the best of all the tip projects...good luck with that when time permits. What will you use to plug the aileron? I'm still considering the aileron plug along with covering that riblet in the back of the flat tips, but having the plug come loose and bind with the tip is a concern. Terminating the tip at the wing trailing edge and then plugging the aileron alleviates that, so is appealing. Looking forward to seeing the development. Sorry I'll not get to meet you in Taylor Bob...was looking forward to that. But I understand the home front, and thoughts are with you and your bride! Good luck with the fixes and the projects as well, and good luck in the next couple races. Mike will be looking forward to the rivalry as well, I'm sure!
Mark,
Launching early tomorrow, and hope to get to Taylor with a little light left. Will need to swap the tips, but we could make a quick run with the normal (X-C) tips on Friday, then do it again on Saturday am before the race. My cell is 775-544-3511. If ya can, plz call so I can grab your cell to call you inbound. I'm going conservative and planning 3 fuel stops this time, the last one being at E30, 150 miles west. If you'd like, we could meet there (or in between) and fly side-by-side to Taylor and give it a whirl for round 1 with normal tips. Airnav sez cheap gas there. Just watch for the TFR for the airshow to the west.
In the race, let's hope the radome doesn't jam our GPS's again. This time I get to follow you, but I promise to call you if I see you turning too far or too short...I promise!
Cheers,
Bob
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04-16-2010, 01:50 AM
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Join Date: Mar 2005
Posts: 5,685
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More levels of testing
I now have eight wing tips for our RV-6A and materials for four more. I have tried to make all of my test results comparable by conducting them at 6,000 ft density altitude. Most of the time when flying in cross country air races I fly at 500 ft AGL and the performance (speed) is different there. I am somewhat limited by the surrounding Ozarks on how low I can go but I think it would be interesting to fly test triangles at 3,000, 4,000, 5,000 and 6,000 feet then tabulate and graph the results for each wingtip configuration.
Bob Axsom
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04-16-2010, 05:33 AM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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I saw the 'Scimitar' wingtips...
...on an NXT at Sun 'n Fun, that was so sharp at the trailing edge, it had a slit tennis ball protecting passersby.
Do they know something most of us don't? Sorry, no pic,
Best,
__________________
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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04-16-2010, 06:30 AM
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Join Date: Sep 2006
Location: Defiance, MO
Posts: 1,674
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Quote:
Originally Posted by pierre smith
...on an NXT at Sun 'n Fun, that was so sharp at the trailing edge, it had a slit tennis ball protecting passersby.
Do they know something most of us don't? Sorry, no pic,
Best,
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Yes, NXT and Jon Sharp have access to Lockheed wind tunnel and CFD therefore I am positive they know more then most of us. They get a lot better data then Bob building 8 wings tips and trying to get flight test data on the differences. (Bob's way is much more fun and in the spirirt of good old American grass roots innovation and I would much rather see Bob's data then NXT data (although NXT data would be cool too, I'm an engineer, the more data the better))
__________________
Philip
RV-6A - 14+ years, 950+ hours
Based at 1H0 (Creve Coeur)
Paid dues yearly since 2007
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04-16-2010, 09:30 AM
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Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
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Bob,
I think that lower altitude testing is definitely a benefit. Building and testing with our race altitudes as a target is key. The lowest I can get near to home plate is 4200' MSL, and I'll do my testing there from now on. If I can get over to the central valley or the coast, I will add some testing there.
Bruce Hammer had some new wingtips in Taylor as well. They were somewhat symmetrical (top to bottom) and radiused (for to aft) at the leading edge, and narrowed to a flat edge at the trailing edge. Bruce said the angle (slightly outward) from the LE to the TE was part of the design, and the aft edge was a continuation from the aileron/flap plane. They were not unlike my X-C tips and your 3" racing tips Bob. There is likely more engineering behind it, but Bob, you may want to shoot Bruce a note to get more info...Bruce is the man. We had a discussion on tips, and he said tons of work has been done by many, and that speed advantages are hard to attain. Guess it depends on the starting point, but little gains may yet be out there.
Just thought I'd pass it along. Given the winds and the bumps, and the fact that Mark F and I flew slightly different profiles, I didn't get a read on what my flat tips really did. I think there was something there, but will need to test and race more to see. Funner than a wind tunnel though, as plehrke said! 
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