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05-29-2011, 10:30 PM
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Join Date: Feb 2007
Location: San Diego, CA
Posts: 1,670
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Quote:
Originally Posted by Tom Martin
........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. .......
Not being an aerodynamicist (hope I spelt that right!), I am very curious why a tapered wing would work better in turbulence? What would Barnaby Wainfan say???
..... 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!
Ain't THAT the truth! 
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Always looking to learn something new.......
__________________
Pete Hunt, [San Diego] VAF #1069
RV-6, RV-6A, T-6G
ATP, CFII, A&P
2020 Donation+, Gladly Sent
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05-30-2011, 12:11 PM
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Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
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I guess I'm somewhat puzzled by the tag that these tips are ugly; I always thought beauty was in the eye of the beholder. Just becuase someone holds that OPINION it doesn't mean it's true, just an opinion. If true, I guess that means that my Lancair with its similar tips, or Peter Garrison's Melmoth, or the Katana, or the Xenos are all delegated to the stack of planes with improved performance that shouldn't be seen in company with more orthodox planes. 'Course they won't be, because they are faster and leave the orthodox behind.
Really, I'm not trying to sell anything here. I just thought that some of you who will spend thousand$ to get a little more speed might want to see a demonstration of a different technology that really produces results. 'Seems to me wing-tip experimentation is something that a lot of you do!
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05-30-2011, 06:15 PM
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Join Date: Aug 2008
Location: Sun city, Ca.
Posts: 255
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Slightly elliptical tips
These are kind of elliptical. Need a view from overhead to show a little better. I don't know what, if any, performance affect they'll have, but I like the look a lot more then the stock tips. At the very least though they took off about 10 lbs.

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05-31-2011, 03:19 AM
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Join Date: Sep 2008
Location: Auckland, New Zealand
Posts: 80
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Quote:
Originally Posted by elippse
I guess I'm somewhat puzzled by the tag that these tips are ugly; I always thought beauty was in the eye of the beholder.
Really, I'm not trying to sell anything here. I just thought that some of you who will spend thousand$ to get a little more speed might want to see a demonstration of a different technology that really produces results. 'Seems to me wing-tip experimentation is something that a lot of you do!
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Can you post some pictures (from different angles) of the plane with these tips on, or direct us to some place on the web that pictures are. I can't figure out if they are ugly or not just from people saying they are ugly. 
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05-31-2011, 01:55 PM
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Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
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I spoke with Jim yesterday and he said that the tips come off with 17 screws each and he can put the old tips on the same. He thinks he can change out the tips in less than an hour so it would be no problem doing the test by changing the tips as someone suggested. For this the test would need someone with at least a 180 HP to fly alongside and verify the two GPS ground-speed runs. 160 HP would not keep up at the two higher density altitudes. By doing the test at 7000', 9000', and 11,000' density altitudes this should cover the typical range of density altitudes covered in the summer when the density altitude is about 1500' to 2500' higher than the baro altiudes of 5000', 7000', and 9000'. The shape of the tips is not important as long as it brings the lift distribution close to the elliptical ideal. The Wittman design with the LE coming back to the 25% chord and the TE going forward to the same point is just as good as Jim's swept LE triangular.
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06-01-2011, 12:19 AM
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Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
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Quote:
Originally Posted by elippse
I spoke with Jim yesterday and he said that the tips come off with 17 screws each and he can put the old tips on the same. He thinks he can change out the tips in less than an hour so it would be no problem doing the test by changing the tips as someone suggested. For this the test would need someone with at least a 180 HP to fly alongside and verify the two GPS ground-speed runs. 160 HP would not keep up at the two higher density altitudes. By doing the test at 7000', 9000', and 11,000' density altitudes this should cover the typical range of density altitudes covered in the summer when the density altitude is about 1500' to 2500' higher than the baro altiudes of 5000', 7000', and 9000'. The shape of the tips is not important as long as it brings the lift distribution close to the elliptical ideal. The Wittman design with the LE coming back to the 25% chord and the TE going forward to the same point is just as good as Jim's swept LE triangular.
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Paul,
Since I'm the one that suggested the before and after tests, I'd be happy to chase Jim, if we can find a good location to meet, if a closer candidate is not available.
I'd also like to get your take on Chris's tips. Pls see pic above and comments below.
Quote:
Originally Posted by Cfrisella
These are kind of elliptical. Need a view from overhead to show a little better. I don't know what, if any, performance affect they'll have, but I like the look a lot more then the stock tips. At the very least though they took off about 10 lbs.
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Chris,
At the risk of thread creep, I'd really like to see more pics of those tips installed, from different angles. They kind of look like my flat tips, but with the center portion pushed (or bulbed) out to a pseudo-elliptical shape.
I'm also interested in your treatment of the aileron outboard ends. Do you have more pics of that, from various angles? They kinda look like EVO tips (just the aileron covers...but that is a potentially draggy area on an RV. Have these tips flown yet? Wondering if any handling anomalies have been noted.
Pretty neat stuff...I saw your posts when you were fabbing them, but hadn't seen them installed. Very cool look!
Paul,
Whattya think of those? Could sharp edges on the outer part (near the wing connection), combined with the elliptical center portion be a performance-enhancing combo of high Oswald Factor and increased elliptical wing area? I'd pull the lights for a racing tip, but wondering about the overall design. Thoughts?
Cheers,
Bob
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06-01-2011, 02:08 AM
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Join Date: Oct 2007
Location: Belvidere, IL
Posts: 169
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Removable Tips
It seems like some people want to optimize the wing for one thing OR another. Rather than play with trade-offs, removable wingtips would allow the wing to be optimized for multiple missions. For example, one could build a drastically shorter wing (as high a wing loading as they felt comfortable with) that's optimized for racing. Between races, they could use a different wingtip that returns the wing to stock area and tip.
Most new sailplanes have removable wingtips that allow the pilot to race in both 15m and 18m classes (nearly a 10ft difference in span!). Winglets may usually be added or removed depending on the weather conditions. It only takes a minute to swap the tips.

__________________
David Shelton, Aerospace Engineer and Soaring Nut.
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06-01-2011, 08:58 AM
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Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
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Bob, from what I've read, in order to get even the 82% span efficiency with a square tip, the tip needs a sharp edge along the top surface in order to trip the tip vortex as far out on the tip as possible. What I'm mainly referring to is an elliptical or semi-elliptical planform to get as close as possible to the elliptical lift-distribution. What is looked for is to bring the lift gradually to zero at the tip so that the upper-lower pressure gradient disappears with no vortex. The typical wing tries to generate lift almost to the tip with its resultant high top-bottom pressure gradient which causes flow from the bottom to the top around the tip, which is the vortex. That's why with a sharp edge you try to tip the flow, whereas with a rounded edge the flow around the tip is actually enhanced by Coanda effect.
That's exactly what my propeller design with its elliptical lift distribution does which is why my props generate no noise as proven in an anechoic chamber by Northwest UAV. No tip vortex, no turbulence, no noise, no energy loss, high efficiency.
'Appreciate your offer, Bob, but Jim is in Wichita which is about 1300 statute away from Reno.
Smith, Jim
planehouse@hotmail.com
316 776 9912
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06-01-2011, 04:25 PM
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Join Date: Aug 2008
Location: Sun city, Ca.
Posts: 255
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As Bob reguested
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06-02-2011, 02:08 AM
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Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
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Thanks Chris...they sure look sharp! I'm gonna ask Paul, you and others following this thread a few questions...but please don't take them as criticism...its all geared towards tip development and educational discussion.
Here goes:
In looking at Chris's tips, I believe I see the following:
1. An edge around the circumference of the tip, that is somewhat sharp, but slightly rounded.
If Chris had made these tips flat, they would look very much like my flat racing tips (just way nicer!), shown here:
2. An elliptical-ish extension from the middle of the tip, almost like an extrusion, or a bulbous (not the best word to use) push-out of the tip. The shape is biased towards the leading edge a bit, especially if the aileron is included in the tip chord calculations.
3. An aileron end-cap of sorts. It looks as though there is still a space between the aileron and the cap, as there is at the trailing edge of my tip. However, Chris's aileron cap obviously moves with the aileron, as opposed to my fixed trailing edge (of the tip).
Questions:
- In a true elliptical tip, would it be better to not have that edge lip? In other words, have the top and bottom of the wing and the top and bottom of the tip be flush...then perhaps taper slowly to the outer edge of the elliptical tip.
- Or is this a beneficial combination of a sharp-edged tip (higher Oswald Factor, longer attachment of the vortex) plus an increased wing area in an elliptical shape to reduce the overall vortex that remains?
From Paul's earlier statements, these two characteristics may be in opposition, but ya never know...it might be a little "discovery". (Chris, did you engineer any of this with these things in mind?)
Would the elliptical shape be better if it was centered along the chord line, and included the aileron portion as well? That would be harder to fabricate with enough strength to extend alongside the aileron, since there is no support back there. Just mulling over the difference in a full-chord elliptical tip versus one that only covers the wing chord, and not the aileron (like Chris's).
Chris, does the aileron cap have a gap between it and the aileron, and if so, how is it attached? (Just hard to see that part.)
Any controllability issues with capping the aileron like this that anyone can think of? I've heard reports of winglet-like end plates loading up ailerons and making the contols stiff, but nothing about caps like this. The EVO wing looks a lot like this in the aileron area (just smaller), but this may be a different aileron design, so just wonderin'.
Along those lines, any concerns of aileron flutter when adding a cap to the outer edge of the ailerons? I know some folks have filled the tip rib outboard of the aileron, but I don't know if anyone has filled the gap in the aileron, or has capped it. These look very lightweight, but just thinking about all issues, since its a departure from plans (not a bash there!). Thoughts?
Chris, they really look sharp...just beautiful work sir, so these are just experimentin' questions. I'd love to hear Paul and others' thoughts about these versus Jim's tri-tips, and other designs (and don't use too many 5 syllable words on me now Paul!  )
If Jim heads anywhere near my way, I'll meet him Paul. Or maybe do it en route to a race later this year if we don't get another taker (I think one stepped up earlier).
Fun discussion!
Cheers,
Bob
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