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10-19-2007, 05:15 AM
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Join Date: Jan 2005
Location: Ontario, Canada
Posts: 1,544
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I have the evo wing and when it came with a flat tip I thought I could make something more attractive. I spent a lot of time and came up with a very nice looking tip that complemented the tapered wing. After a couple of months I took one tip off and replaced it with the stock flap tip. There was no doubt which wing was fastest as my nice rounded tip was dragging the aircraft noticeably on that side.
This year I thought, if it worked for the wing, it should work for the tail. So I cut off those nice rounded tips on the tail and made some flat tips by filling the end with foam and glass. I could not measure any speed advantage. However the tail now matches the wings and it has given the plane a whole new beasty look.
Keep in mind that my flat wing tips were done on the EVO wing. Tony Blair, a rocket owner in Austrailia, flew with flat tips on a standard wing. He reported a faster roll rate, reduced weight, a 5 knot increase in stall speed an NO improvement in cruise speed. From this limited comparison you could speculate that the standard wing has a higher induced drag at the tip than does the samller EVO tip. There is a relationship between the removal of the parasitic drag of the tip that is balanced with any benefits that the tip plays in reducing induced drag. Older Mooney aircraft had flat tips which have been replaced on newer offerings, I wonder what testing they did and which tips worked better with their tapered wing?
__________________
Tom Martin RV1 pilot 4.6hours!
CPL & IFR rated
EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
RV14 Tail dragger
Fairlea Field
St.Thomas, Ontario Canada, CYQS
fairleafield@gmail.com
Last edited by Tom Martin : 10-19-2007 at 05:21 AM.
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10-19-2007, 07:53 AM
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Join Date: Feb 2006
Location: Pagosa Springs, CO
Posts: 130
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Quote:
Originally Posted by Tom Martin
Older Mooney aircraft had flat tips which have been replaced on newer offerings, I wonder what testing they did and which tips worked better with their tapered wing?
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Last summer we toured the Mooney factory and I asked the guide about the new wingtips...he said they were pure marketing/cosmetics and did nothing for speed.
The hershey bar wings may have a bigger wingtip vortex than the tapered wings, and so respond differently. The aero case for tapered wings (and props) involves reducing the tip vortex.
John
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10-19-2007, 04:44 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Bob - Congrats on the nice speed increase. If you can stop tinkering with the aircraft for more than a few days, it would be interesting to see the results from some speed runs on additional flights. How consistent are the results from flight to flight?
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10-19-2007, 08:55 PM
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Join Date: Mar 2005
Posts: 5,685
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The runs seem coherent
The wind seemed fairly light and steady even though I did not maintain the 1 kt margin over the five 20 sec. interval recordings on each leg. it was close. This test seems to fall in place with the other tests that I have run and I believe additional tests would confirm that. Sometimes I have an uneasy feeling about the validity of test results but I believe these results are accurate and the plane is actually faster.
I have pulled the tips and laid on 8 strips of cross stacked fiberglass at the nose already to get a better fit between the mounting surface of the tip and the inside of the wing skin at the front end. The stacks have cured and I started sanding the right tip. The shape is pretty good now but I need to remove some material to allow the whole tip to move forward slightly and center, as much as possible, the platenuts under the wing skin dimpled holes - I can shove it there but it's not quite right. I have to do the whole front end fit thing with the left tip yet. Then I have to smooth the exposed surface of the the stacked fiberglass and bend it into the basic tip fiberglass so there are no iregularities. After that I want to sand and fill and sand the tips until thy are free of visible fiberglass weave pattern and resin excesses and try to paint them before next Saturday's (10-27) race at Memphis. I do not believe any of this work will have any effect on speed but it will probably a couple of weeks before I can do it. Something could happen to invalidate the comparative test but I don't really think so. I will try to do that and report the results.
Bob Axsom
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10-20-2007, 07:54 PM
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Join Date: Jan 2005
Posts: 4,285
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What about NO wing tip
Quote:
Originally Posted by Tom Martin
Tony Blair, a rocket owner in Australia (I thought he was British  ) , flew with flat tips on a standard wing. He reported a faster roll rate, reduced weight, a 5 knot increase in stall speed an NO improvement in cruise speed. Older Mooney aircraft had flat tips which have been replaced on newer offerings, I wonder what testing they did and which tips worked better with their tapered wing?
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Yea my thought exactly. How a bout a flat "end plate", with or with out some flange extending like a winglet? Hummmm further reducing wing span, frontal area, wetted area.
If designed properly might be cool.
Bob, did I miss if you checked stall speed? Rate of Climb? Roll Rate? The no free lunch rule may be. However 3 ka-not's ain't bad.
Any way nice experiment Bob.
__________________
George
Raleigh, NC Area
RV-4, RV-7, ATP, CFII, MEI, 737/757/767
2020 Dues Paid
Last edited by gmcjetpilot : 10-20-2007 at 07:59 PM.
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10-28-2007, 08:41 AM
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Join Date: Mar 2005
Posts: 5,685
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Memphis Check
Flew to Memphis, participated in the Memphis 100 and returned. No formal speed check was made but the plane is faster than it has ever been with the change to this configuration. It is slightly more demanding to fly with a higher sink rate and roll rate but it seems more "solid" in turbulance. We won the RV Blue Class in the Memphis 100 Air Race beating Mike Thompson in his fast RV-6 for the first time ever. We averaged 203.52 mph which was run at 1,000 MSL except for the finish which was at 1,200 MSL.
Bob Axsom
Last edited by Bob Axsom : 10-28-2007 at 10:19 AM.
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10-28-2007, 09:02 AM
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Join Date: Jan 2005
Location: MN
Posts: 2,269
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Way to Go Bob!
I follow your experiments here on the forums and am happy to see your work paid off! Good show!
__________________
Cheers,
Pete
Amateur Plane - RV-9A N789PH - 2350+ Hrs
Amateur Radio - KD0CVN
Doggies Delivered - 25+
St. Paul, MN
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10-28-2007, 05:47 PM
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Join Date: Jan 2005
Location: Ottawa, Canada
Posts: 2,357
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Quote:
Originally Posted by Bob Axsom
Flew to Memphis, participated in the Memphis 100 and returned. No formal speed check was made but the plane is faster than it has ever been with the change to this configuration. It is slightly more demanding to fly with a higher sink rate and roll rate but it seems more "solid" in turbulance. We won the RV Blue Class in the Memphis 100 Air Race beating Mike Thompson in his fast RV-6 for the first time ever.
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Congrats Bob. It is good to learn that all your hard work has paid off. Of course the other guys will be working hard to catch up, so you need to keep improving too.
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10-29-2007, 01:33 PM
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Join Date: Jan 2005
Posts: 17
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New Wingtips
Congrats Bob. It is good to learn that all your hard work has paid off. Of course the other guys will be working hard to catch up, so you need to keep improving too.
Boy, you got that right.
As the beatee, I have some ideas for a Winter project and race season 2008!
Your next project should be rear-view mirrors, Bob, cause here I come!
- Mike
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10-29-2007, 08:27 PM
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Join Date: Feb 2005
Location: Minneapolis
Posts: 2,473
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Hi Bob,
You've been so good to let all of us see your testing over time...so thanks!
But, since Dan had to point out your draggy antenna - I felt it my duty to aky why you haven't thought of removing that large carbunkle hanging off the front of your plane...you know...that "land-o-matic" thingy under the front cowl! I don't see one of those on Huft's or Martin's plane?!?!?!
You realize Van's does make a "low drag" version, and even a fairing to match!
All in fun I promise!
Cheers,
Stein
PS, I am serious about thanking you for posting your trials. I truly like to see real world testing and since I'm too lazy and stupid to do it myself, I appreciate you putting up with ribbing from people like me!
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