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05-26-2011, 08:05 PM
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Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
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Wing-tip comparison
The triangular wing-tips Jim Smith has mounted to his RV-6 have not only increased his speed above 8000' dalt, but also down to at least 4000' dalt. He's getting 2 mph more at 4000' dalt, 3 mph more at 8000' dalt, 5 mph at 10,000', and 7 mph at 11,000'. To demonstrate in a significant manner to all of you folks how dramatic this is, I would propose the following demonstration. I would like one or more of you with 150HP RV-6s, as is Jim's, with no engine enhancements, (he runs on mogas), or even 160 HP, to volunteer to do some side-by-side runs with Jim on at least two separate two-way, GPS-measured runs at 8000' dalt, where Van's gives his speeds, calling out your ground speeds along the way. We might even get some higher speed planes to accompany them and verify their ground-speeds to keep it on the up-and-up. Since the 160 has a 2.2% speed advantage over a 150HP at the same rpm, we can adjust the speed of the one of the planes for HP and RPM to normalize the results. If we can get some planes within 400 miles of Jim's home in Wichita, then each of them could fly a little over and hour to a meeting place.
I'm sure many of you have heard of the Oswald efficiency factor which gives the percentage of a wing span that is truly effctive. On a typical rectangular or tapered wing with a square tip and a well-shpaed tip it can get to 82%; a rounded tip like a Cub drops it to 75%. However, an elliptical wing is 100%. If you can reshape the end of the wing to bring it closer to the elliptical ideal, you can go beyond the 82% and approach the 100%. In my number-crunching of why Jim's tips performed better than I predicted, I found that his wings are running 91%! That's why he's even seeing an improvement below 7000' where I told him that hiis speed would drop slightly due to more wing area. Not only is his speed better, but he lands slower and takes-off and climbs faster, due to the reduced induced drag!
I sure hope we can get some takers in the months before Oshkosh.
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05-28-2011, 03:10 PM
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Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
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C'mon! Aren't there any of you interested in finding out more about the speed improvement by use of different tip designs? We need to get some volunteers to step up!
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05-28-2011, 03:42 PM
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Join Date: Aug 2005
Location: Pasadena CA
Posts: 2,484
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Well, this is essentially the same thing that was done on the Wittman Tailwinds back in the day. The problem is the W-8 was twitchy and had a decently high wing loading. It also suffered from Steve's lack of any dihedral in the design. The later W-8 and W-10 wing use an tapered elliptical style tip which increases wing area, top speed, and stability...
The RV's already have enough wing though, so the way to make this truly effective is to clip the wing a little before adding a longer wingtip... not an option on a built airplane for most folks.
The tapered wing design that was used on the F1 rocket decreased the effective CG range, weighed more, and was only marginally faster.
The racing guys have found that down low, flat cap or shorty tips have been more effective because the ratio between induced drag and parasite drag is weighted differently down low.
So the main benefit for these would be people who do lots of high cross country work... Many of those folks aren't so concerned in a couple knots here and there, which might explain the lack of resounding interest. I don't have a built RV yet. But if I was truly that concerned about high altitude performance, I'd probably have bought or built a different airplane.
__________________
Stephen Samuelian, CFII, A&P IA, CTO
RV4 wing in Jig @ KPOC
RV7 emp built
Last edited by osxuser : 05-28-2011 at 03:43 PM.
Reason: Spelling
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05-28-2011, 06:40 PM
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Join Date: Sep 2006
Location: Townsend, Montana
Posts: 3,179
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could be that the 150hp RV-6 guys with their FP props are perfectly happy with the setup they are running....or 5mph isn't worth the extra work.
If he was closer I'd race him.....I mean.... run along side for comparison. But not likely a fair comparison. 180+hp, RV-7 C/S prop.
__________________
Retired Dam guy. Life is good.
Brian, N155BKsold but bought back.
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05-29-2011, 05:19 AM
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Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
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I'll be cruelly honest.
Paul, I'm sorry to have to say so, but those tips are ugly! I'd rather have a couple MPH slower airplane that's purty!!
Kinda like the guy who's married to a trophy wife who's a biatch.
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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05-29-2011, 09:56 AM
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Join Date: Dec 2006
Location: Paso Robles, CA
Posts: 1,177
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Ahhh the wisdom of the Elders..
Quote:
Originally Posted by pierre smith
Paul, I'm sorry to have to say so, but those tips are ugly! I'd rather have a couple MPH slower airplane that's purty!!
Kinda like the guy who's married to a trophy wife who's a biatch.
Best,
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I appreciate your posts Pierre, there is always truth and practicality in your advice. But better yet, us lister's also get some humor 
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05-29-2011, 10:20 AM
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Join Date: Aug 2007
Location: Wichita Falls, TX
Posts: 2,182
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I've always wondered why nobody has come up a set of fiberglass elliptical shaped wingtips for the RV wings. They'd look pretty good and I'd reckon you could probably sell quite a few sets.
__________________
Neal Howard
Airplaneless once again...
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05-29-2011, 11:42 AM
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Join Date: Jan 2005
Location: Kansas
Posts: 384
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Paul, I fly over to Jim's strip often and would not mind going flying with Jim. I'll get a hold of Jim and set up a time to go fly (I look for any excuse to fly). I have a O-320-H2AD with a Fred Felix prop, with a max RPM of approx 2680 at 8k.
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05-29-2011, 11:44 AM
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Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
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Hey Paul,
Just MHO, but I'm not sure a side-by-side test using two different airplanes is a very effective test (too many variables). Carefully controlled before and after tests (same airplane, swap tips) would seem a much more effective measure of effectiveness and performance for the "tri-tips" (sorry, couldn't resist...it is BBQ season after all!  ) (Edit, just saw Curtis's post above, and was not commenting on it...will be interested to see what kind of data it yields).
Interesting note from Steve about clipping the wing to start...hmmm...I just happen to have clipped wings. They were built shorter to decrease the bending moment of the wing, to allow standard g limits at the higher gross weight associated with the big engine...or so the theory goes. I recall a post in an earlier thread discussing these tri-tips, that more or less stated that adding these tips would be the quickest way to turn your RV-6, 7 or 8 into an RV-9. That is not to disparage the wonderful RV-9, but the additional wing area would likely reduce the g limits and perhaps remove the ability (or recommendability) to do acro.
For me and many others, that becomes a deal-breaker. These tips may be awesome for X-C, and may even have an applicability for racing AirVenture Cup when its west to east and run high; but methinks mainstream "Total Performance" RV flyers probably don't want to swap tips for various missions. Heck, ya never know when your going to be jumped by someone and have to fight your way back to friendly country!
All that being said, with those clipped wings of mine, and an interest in AVC, if ya wanna build me a set, I'll come down to SMX and test them at all altitudes, SL to wherever you want. I'll even buy the famous Santa Maria BBQ when we're done. Bet we could get a couple other stock 6, 7, and/or 8 builders that would be willing beta testers too. We could post the results, and those tri-tips might start to look purtier, if the results are that significant! I know that you are not trying to sell these, but rather want to advance knowledge and effeciency among the community, so I doubt that is something on the table...but I'm a willing tester if you ever want to go that route!
And Pierre...I think the guy with the pretty, but slightly slower RV is much happer than the guy with the TW/B that you speak of...eh amigo!
Cheers,
Bob
Last edited by rvmills : 05-29-2011 at 11:49 AM.
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05-29-2011, 01:13 PM
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Join Date: Jan 2005
Location: Ontario, Canada
Posts: 1,544
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Quote:
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The tapered wing design that was used on the F1 rocket decreased the effective CG range, weighed more, and was only marginally faster.
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Well I do have quite a bit of time in this wing and so I will comment on the above "facts"
I can carry the same load with my tapered wing as I did with the standard wing. The stick does have a lighter feeling fully loaded but that it has not affected how I use the aircraft. I have often carry 250 pound + passengers in the aircraft.
Yes the wings are heavier, about 60 pounds, that is a negative, but the increased lift has negated any performance decrease due to the extra weight.
I can still carry a full load with a gross of 2050 lbs
As for speed I will let the SARL results speak to that issue. In the last race of 2010 I was close to 15 mph,12.75knots, faster then the next closest rocket. At the slow end the stall speed is 5 to 10 knots slower.
PLUS, and this is a big plus; My wife, who suffers from motion sickness, has for the first time in 25 years been able to share my love of flight. We have travelled from coast to coast with this wing. The added stability of the tapered wing has made all the difference in the world for her.
I guess it is easy to see that I am a Big fan of the EVO wing and I hope that Mark Fredrick will be able to get his new wing into production so that more people can share the rewards that I have received from this design.
As for the wing tips I would like to try a set with my plane. I think that the tapered wing could benefit from a properly designed elliptical tip. I would give up a bit of lower speed for an increased altitude speed AND an even lower stall speed that would result from an increased wing area. I am in agreement with Pierre in that esthetically I to not care for the triangular shaped tips. However I must say that it is easy to say that you are not interested in two or three knots until your buddy slides past you by two or three knots!
__________________
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 : 05-29-2011 at 01:22 PM.
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