David Shelton
Well Known Member
Jim Smith's tips:
Van's Air Force
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Smaller Wing Tips for Speed
- Thread starter Bob Axsom
- Start date
Christopher Murphy
Well Known Member
too ugly for my plane
Sorry Jim Smith, That is too ugly to be on an RV. Those tips and the spars and attachment weight surely has to offset any performance gain. Can you say double tapered wing?
Chris M
Sorry Jim Smith, That is too ugly to be on an RV. Those tips and the spars and attachment weight surely has to offset any performance gain. Can you say double tapered wing?
Chris M
Maybe tried later
This would be fairly simple to implement with sheet metal, angle brackets and floating platenuts. I am thinking about it but not now - schedule crunch.
Bob Axsom
This would be fairly simple to implement with sheet metal, angle brackets and floating platenuts. I am thinking about it but not now - schedule crunch.
Bob Axsom
hevansrv7a
Well Known Member
Easier yet?
Wouldn't it be easier to just attach with fixed platenuts inside the new, flat tips? I don't see what the angle brackets would do.
Wouldn't it be easier to just attach with fixed platenuts inside the new, flat tips? I don't see what the angle brackets would do.
More on wingtips
Let me give you a few equations so you can play around with the numbers to see what performance increase you can see at different weights and density altitudes.
Parasite drag, lb., = Q X AP; Induced drag = W^2/ Q X S^2 X PI X e, where:
Q=rho X V^2 / 2, AP=equivalent parasite drag area, sq. ft. W=weight, lb., S=span, ft., PI=3.1416, e=Oswald efficiency factor, V=TAS,mph X 22/15, rho=.00237689(1-6.88E-6 X dalt)^4.256.
Add the two drags, multiply by V, and divide by 550. That will give you the total drag power required.
Now let me show you the resulting HP required from increasing the span by 13% to 26' and reducing the area by 13% to 97 sq. ft., using 200 mph TAS at 1400 lb and 1600 lb at three different density altitudes. It also shows the HP difference and the speed increase that could be seen.
1400 lb 1600 lb
dalt 23/110 26/97 23/110 29/97
1000' 130.7 124.9 4.7% 203.1 133.1 126.7 5.0% 203.3
7500' 110.5 105.0 5.2% 203.4 113.4 107.3 5.7% 203.7
14,000' 93.9 88.6 6.0% 203.9 97.5 91.4 6.7% 204.3
You can use these values to check your own calculations and a spreadsheet program to see if you've set it up right.
Let me give you a few equations so you can play around with the numbers to see what performance increase you can see at different weights and density altitudes.
Parasite drag, lb., = Q X AP; Induced drag = W^2/ Q X S^2 X PI X e, where:
Q=rho X V^2 / 2, AP=equivalent parasite drag area, sq. ft. W=weight, lb., S=span, ft., PI=3.1416, e=Oswald efficiency factor, V=TAS,mph X 22/15, rho=.00237689(1-6.88E-6 X dalt)^4.256.
Add the two drags, multiply by V, and divide by 550. That will give you the total drag power required.
Now let me show you the resulting HP required from increasing the span by 13% to 26' and reducing the area by 13% to 97 sq. ft., using 200 mph TAS at 1400 lb and 1600 lb at three different density altitudes. It also shows the HP difference and the speed increase that could be seen.
1400 lb 1600 lb
dalt 23/110 26/97 23/110 29/97
1000' 130.7 124.9 4.7% 203.1 133.1 126.7 5.0% 203.3
7500' 110.5 105.0 5.2% 203.4 113.4 107.3 5.7% 203.7
14,000' 93.9 88.6 6.0% 203.9 97.5 91.4 6.7% 204.3
You can use these values to check your own calculations and a spreadsheet program to see if you've set it up right.
Not Really
The old semi-flat tips with the rounded edges are considered offerings to the God of Speed - N_G. If I do this I will start with a flat 0.016" aluminum tip plate butted right up against the end of the wing skin. The angle brackets will be riveted to the inside of the tip plates and will extend inside the wing skin aligned with the existing tip mounting holes. The floating platenuts will be riveted to the angle brackets and pick up the #8 flathead tip mounting screws. After I have the 3/32" platenut mounting holes drilled in the angle brackets using a non-floating platenut as a drill guide I will open the center hole to 3/8" to clear the wing skin dimples. I hope that clarifies the approach. I may start with an oversized tip plate (anyone remember Ron St Jean's Ram Rod 750?) then test and trim and test and trim ... until the edge of the tip plate conforms exactly to the size of the end of the wing.
Bob Axsom
The old semi-flat tips with the rounded edges are considered offerings to the God of Speed - N_G. If I do this I will start with a flat 0.016" aluminum tip plate butted right up against the end of the wing skin. The angle brackets will be riveted to the inside of the tip plates and will extend inside the wing skin aligned with the existing tip mounting holes. The floating platenuts will be riveted to the angle brackets and pick up the #8 flathead tip mounting screws. After I have the 3/32" platenut mounting holes drilled in the angle brackets using a non-floating platenut as a drill guide I will open the center hole to 3/8" to clear the wing skin dimples. I hope that clarifies the approach. I may start with an oversized tip plate (anyone remember Ron St Jean's Ram Rod 750?) then test and trim and test and trim ... until the edge of the tip plate conforms exactly to the size of the end of the wing.
Bob Axsom
C-FAH Q
Well Known Member
Bob,
did you guys get that space camera going on my hanger? I was sure the lead sheild would prevent it !!
You are thinking what i have started to do. quick and easy and no fibreglass.
Christopher Murphy
Well Known Member
Mike S
Senior Curmudgeon
I saw that prop too, on a race plane at Reno-------kicked but t on the rest of the field big time----like 30 mph IIRC
Wing tips and prop tips!
It sure did! That's one of the ones I designed for Tom Aberle and JeFF Lo. If you think those tips were rad, you should see the ones I designed for Tony Higa's racing Pitts, my new three-blade, and the way-out tips on two Reno T-6 racers. And no patented T-6 noise. With these props a T-6 is no longer the most efficient way to convert av fuel to noise!
The new Boeing designs now feature a longer triangular extension. I think the 737-800 or -900 as well as the 787 have them. No more turned up tips.
It sure did! That's one of the ones I designed for Tom Aberle and JeFF Lo. If you think those tips were rad, you should see the ones I designed for Tony Higa's racing Pitts, my new three-blade, and the way-out tips on two Reno T-6 racers. And no patented T-6 noise. With these props a T-6 is no longer the most efficient way to convert av fuel to noise!
The new Boeing designs now feature a longer triangular extension. I think the 737-800 or -900 as well as the 787 have them. No more turned up tips.
Here are some pics of my designs. http://tinypic.com/4dukursz
Last edited by a moderator:
Flyfalcons
Well Known Member
Go to where you uploaded your image and right click on the image itself. Click "Properties", then copy the address. On the posting box, click on the mountain picture and paste the address for your image. Result will link directly to the image:
WhiskeyMike
Well Known Member
Paul,
Are these high performance prop designs suitable and/or appropriate for use in everyday flying, and if so, are they going to be available at some point to the retail marketplace? Thanks.
Are these high performance prop designs suitable and/or appropriate for use in everyday flying, and if so, are they going to be available at some point to the retail marketplace? Thanks.
Props
Hi, Mike! We're getting a little off-subject here, but I design props for experimentals. Please contact me at [email protected]. Thanks! Paul
rvmills
Well Known Member
Bob, Gary and the gang:
Two-topic post...rad props and wingtips...sorry in advance for the length...
The discussion on props has generated some thoughts on prop options (hmmm, wonder how much a custom "rad" prop would cost and achieve, relative to the Hartzell BA upgrade I'm contemplating...got any ideas for an IO-540 RV-6 Paul?)
As for wingtips, first the quotes:
First, for Gary...I told ya we'd find out (and Wayne didn't give it up when we talked). We'll never tell if it was good intel, or a total stumbling onto it. I'm midway through glass tips, but flat caps are on the drawing board too. Bob, for those, do you think .016 caps will be thick enough? Any concern about oil canning? What are you using Gary? We're also batting around the idea of 1/4" plywood caps covered in glass and attached to angle brackets as you've described. One could even experiment with various fences/mini-winglets fabbed into the plywood or AL endcaps (is that what you meant by an oversized plate Bob?)
Made an interesting discovery about my plane that may require some effort to make things work. More on that below.
I've been working (slowly) on some flat tips. After seeing your results Bob, comparing pics of your tips to those of Wayne, and reading the discussion in this thread on rounded vs sharp edges, I formed a plan. Wayne's tips fit outside his wings, and appear to have a flatter/sharper edge. Your tips and mine fit inside the wing, making it a bit harder to square the edge and fit the tip flush to the wing skin, and perhaps that made a difference in the resuts seen. Bob, its hard to tell from the pics, but it looks like there may also be a little drop-off from the wing skin to the flat tips' surface, so perhaps there is a seam of sorts all around the edge of the wing. That may not be correct at all, but just in case, I want to make the edge of my tips fit very flush to my wing skin, rather than have the skin edge sit on top of the tip material (not sure if that makes sense).
I used 2" foam trimmed to the shape of the wing, and cut/sanded it to just fit into the end of the wing. Then we placed 3 layers of glass on the foam, and will sand-fill-sand the tip so it matches the profile of the wing skin.
Next we'll clean out the foam, and cut the tips down to about 1/2" to 3/4" deep, and then glass in flanges to the inside, that will fit inside the wing and have aluminum backing on the flanges to hold the nutplates for attaching.
Pic below is the foam molds with glass and super-fill in pretty rough form, ready to begin the sand-fill-sand process, and the strips of glass for the flanges prepped.
But here's where we made the interesting discovery...
Placing the tips back to back, and expecting them to be pretty close to identical, we were surprised at a 1/2" divergence at the trailing edge. A litttle off would be no big deal, but 1/2" seemed like a lot.
My plane has always (since I've owned it anyway) had a bit of rolling tendency (fully trimable), but flies straight and level with slight (approx) 1/4" aileron deflection. In the past I've measured wingsweep, angle of insidence and tail surface symmetry, and things checked out pretty well. This year we squeezed an aileron a bit and fixed a bit of a heavy wing, but the aileron deflection remained. That 1/4" is not much, and I've read many posts about things not ever being perfect, but I don't know how that 1/4" stacks up. Thoughts?
After seeing the tip differences, we grabbed a friend's wooden RV wing template, and checked both wings, ailerons and flaps. Turns out the right flap has almost 1/2" of twist at the trailing edge, and the ailerons appear to have been rigged to match the flaps. Then the wingtips must've also made to match the ailerons, and thus the 1/2" from the flap twist was carried out to the tip.
I know no aircraft is perfect, but I'm not sure if that is a large delta or nothing to be concerned about. The airplane flies fine, and my "mentor" and I are deciding whether to just build flat tips to match, or build one new flap, take out the twist, re-rig the ailerons, then build flat tips to match true(er) wings. I'd then have to work my current wingtips a bit to make them match the newly trued flaps/ailerons. Lots of work, but truing the twisted flap and getting rid of that aileron deflection may actually net more speed than doing a wingtip mod...hmmm.
As a non-builder who's getting an education via upgrades and mods, I'm going to check into the cost of the parts to build a flap, and then consider which course of action to take. Plane is still very flyable/raceable until we replace the flap, and I've got multiple RV builders, some repeat offenders, to help build/paint the flap, rig the aileron and fab the tips.
Just gotta decide whether to accept the flap twist and finish these tips I've started, or to replace the bad flap, and see how fast this puppy will go when straight and true. Ah decisions!
Any thoughts from the gang?
Cheers,
Bob
Two-topic post...rad props and wingtips...sorry in advance for the length...
The discussion on props has generated some thoughts on prop options (hmmm, wonder how much a custom "rad" prop would cost and achieve, relative to the Hartzell BA upgrade I'm contemplating...got any ideas for an IO-540 RV-6 Paul?)
As for wingtips, first the quotes:
First, for Gary...I told ya we'd find out (and Wayne didn't give it up when we talked). We'll never tell if it was good intel, or a total stumbling onto it. I'm midway through glass tips, but flat caps are on the drawing board too. Bob, for those, do you think .016 caps will be thick enough? Any concern about oil canning? What are you using Gary? We're also batting around the idea of 1/4" plywood caps covered in glass and attached to angle brackets as you've described. One could even experiment with various fences/mini-winglets fabbed into the plywood or AL endcaps (is that what you meant by an oversized plate Bob?)
Made an interesting discovery about my plane that may require some effort to make things work. More on that below.
I've been working (slowly) on some flat tips. After seeing your results Bob, comparing pics of your tips to those of Wayne, and reading the discussion in this thread on rounded vs sharp edges, I formed a plan. Wayne's tips fit outside his wings, and appear to have a flatter/sharper edge. Your tips and mine fit inside the wing, making it a bit harder to square the edge and fit the tip flush to the wing skin, and perhaps that made a difference in the resuts seen. Bob, its hard to tell from the pics, but it looks like there may also be a little drop-off from the wing skin to the flat tips' surface, so perhaps there is a seam of sorts all around the edge of the wing. That may not be correct at all, but just in case, I want to make the edge of my tips fit very flush to my wing skin, rather than have the skin edge sit on top of the tip material (not sure if that makes sense).
I used 2" foam trimmed to the shape of the wing, and cut/sanded it to just fit into the end of the wing. Then we placed 3 layers of glass on the foam, and will sand-fill-sand the tip so it matches the profile of the wing skin.
Next we'll clean out the foam, and cut the tips down to about 1/2" to 3/4" deep, and then glass in flanges to the inside, that will fit inside the wing and have aluminum backing on the flanges to hold the nutplates for attaching.
Pic below is the foam molds with glass and super-fill in pretty rough form, ready to begin the sand-fill-sand process, and the strips of glass for the flanges prepped.
But here's where we made the interesting discovery...
Placing the tips back to back, and expecting them to be pretty close to identical, we were surprised at a 1/2" divergence at the trailing edge. A litttle off would be no big deal, but 1/2" seemed like a lot.
My plane has always (since I've owned it anyway) had a bit of rolling tendency (fully trimable), but flies straight and level with slight (approx) 1/4" aileron deflection. In the past I've measured wingsweep, angle of insidence and tail surface symmetry, and things checked out pretty well. This year we squeezed an aileron a bit and fixed a bit of a heavy wing, but the aileron deflection remained. That 1/4" is not much, and I've read many posts about things not ever being perfect, but I don't know how that 1/4" stacks up. Thoughts?
After seeing the tip differences, we grabbed a friend's wooden RV wing template, and checked both wings, ailerons and flaps. Turns out the right flap has almost 1/2" of twist at the trailing edge, and the ailerons appear to have been rigged to match the flaps. Then the wingtips must've also made to match the ailerons, and thus the 1/2" from the flap twist was carried out to the tip.
I know no aircraft is perfect, but I'm not sure if that is a large delta or nothing to be concerned about. The airplane flies fine, and my "mentor" and I are deciding whether to just build flat tips to match, or build one new flap, take out the twist, re-rig the ailerons, then build flat tips to match true(er) wings. I'd then have to work my current wingtips a bit to make them match the newly trued flaps/ailerons. Lots of work, but truing the twisted flap and getting rid of that aileron deflection may actually net more speed than doing a wingtip mod...hmmm.
As a non-builder who's getting an education via upgrades and mods, I'm going to check into the cost of the parts to build a flap, and then consider which course of action to take. Plane is still very flyable/raceable until we replace the flap, and I've got multiple RV builders, some repeat offenders, to help build/paint the flap, rig the aileron and fab the tips.
Just gotta decide whether to accept the flap twist and finish these tips I've started, or to replace the bad flap, and see how fast this puppy will go when straight and true. Ah decisions!
Any thoughts from the gang?
Cheers,
Bob
I think 0.016 will work fine
I have a lot of things on my plate that take priority right now but I had thought of starting with flat 0.016" tip plates maybe 2" larger than the airfoil - I do not think there will be any oil canning if the fitting is right and floating platnuts are used to allow no stress alignment. Test fly, record the results, then cut down 1/4" test fly record and repeat until there is no extension beyond the airfoil. That may not happen but that was the way I was planning to approach it. My semi-flat tips were a tremendous waste of time except for educational value.
Bob Axsom
I have a lot of things on my plate that take priority right now but I had thought of starting with flat 0.016" tip plates maybe 2" larger than the airfoil - I do not think there will be any oil canning if the fitting is right and floating platnuts are used to allow no stress alignment. Test fly, record the results, then cut down 1/4" test fly record and repeat until there is no extension beyond the airfoil. That may not happen but that was the way I was planning to approach it. My semi-flat tips were a tremendous waste of time except for educational value.
Bob Axsom
pierre smith
Well Known Member
Have either of you guys considered upswept tips...
..like a lot of the really fast F-1 guys run?
Best,
..like a lot of the really fast F-1 guys run?
Best,
F1Boss
Well Known Member
Whatsis?
Hey Pierre:
Pictures please! I'm aware of the sheared tips, but no upswept versions -- yet. The Evo uses a flat tip, and tufting shows very little upper surface diagonal flow, but than again the airfoil at the tip is only 4" thick and 36" long. I kinda doubt any sort of tip would improve level flight speeds, but I would think a NXT sort of tip might help if any sort of G is put into the equation.
Mike Thompson tried a flat plate tip (clear plexi) -- might ask him for his results.
For Bob Mills:
I see a new flap in your future....might as well get started now.
Carry on!
Mark
Hey Pierre:
Pictures please! I'm aware of the sheared tips, but no upswept versions -- yet. The Evo uses a flat tip, and tufting shows very little upper surface diagonal flow, but than again the airfoil at the tip is only 4" thick and 36" long. I kinda doubt any sort of tip would improve level flight speeds, but I would think a NXT sort of tip might help if any sort of G is put into the equation.
Mike Thompson tried a flat plate tip (clear plexi) -- might ask him for his results.
For Bob Mills:
I see a new flap in your future....might as well get started now.
Carry on!
Mark
L.Adamson
Well Known Member
For Bob Mills:
I see a new flap in your future....might as well get started now.
I second that motion............since he asked...
Otherwise, it's a bit of drag, opposing some other drag, which didn't
need to be there in the first place.
L.Adamson --- RV6A
rvmills
Well Known Member
I'll second the request for pics. And Mark, what is a sheared tip? I've thought about Lancair IV looking tips, and even winglets, but the aerodynamic and stress analysis that due diligence would require (IMHO) is a big challenge...and not resident in my personal skunk works. But I'm game to look at things that may work. Turned up tips would look really cool...maybe not so cool on a hershey bar wing as on a tapered wing...however, to pull a page from Bob Axsom's book...looking cool aint what this is about...its all about the speed! Mark, got an extra set of EVO wings to bolt onto a super-six?
Mike told me that when he tried a fence that went back along the aileron, it made the ailerons very stiff at speed...uncomfotably so. The thought was that the prevention of span-wise flow over the aileron (spilling over or under the outer end, so to speak) was causing the stiffness. That might be a good thing in the ultra-low speed regime (good aileron effectiveness right to the stall), but if the airplane is hard to turn or control at race speeds, that would be in the "bad" column, I reckon.
I've considered making a fence that tapers down from the thick part of the chord down to nothing just ahead of the aileron, but developing the shape of that is totally shooting in the dark without extensive tufting tests. Anybody know if wingtip tufting has been viewed on a standard Van's wing before, and if spanwise flow is big consideration out there?
Mark, that's an interesting observation on the EVO wing, and why I asked the question above. Let me ask you and the gang this...
Mike T's flat tip is all one piece, and that's the way my current design is heading. But, if I make a flat plate tip cover, and end it at the rear spar, then do a flat plate aileron cover, how do you think that would do? It was suggested in an earlier post, and I think Bob Ax may have tried filling the aileron voids (can't remember if it was boom or bust though Bob). I would think this might be a good way to go, especially if ya made the two covers blend/fit the way the EVO wing tips do it. Any aerodynamic or structural gotchas to this approach? Gary, is that how you are doing it (remember, I can find out...just a little satellite redirection...
)For Bob Mills:
I see a new flap in your future....might as well get started now.
Carry on!
Mark
I second that motion............since he asked...
Otherwise, it's a bit of drag, opposing some other drag, which didn't
need to be there in the first place.
L.Adamson --- RV6A
Been talking with Speedy Tom about this as well. It likely is more drag, and may yield some top-end, but its tough to say. He's had some similar experience, and the reward could be undewhelming. Guess it all depends on how bad that apparent 1/2" twist really is. Tom hada good suggestion to measure the wings more closely to see if there is also some wing twist contributing to the problem. Good idea that I will follow. In this case, the fix is a bit complex, more-so for the realingment of my stock tips that will have to take place after I redo the flap and realign the aileron, than for actually building a flap. That will take building up the top face of the tip trailing edge, and sanding down the bottom face of the tip, and adjusting the trailing edge rib stiffener (that sits next to the aileron). Got the glass and the paint...just need to weigh the time-cost/benefit. Then again, I picture the Marine DI standing over me saying, "well boy, do ya wanna go fast...well, do ya?"
Thanks for the feedback...I did ask, and it's much appreciated. Now to mull it over a bit and talk to Van's about a flap "kit".
Keep it comin'!
Cheers,
Bob
pierre smith
Well Known Member
Hey Pierre:
Pictures please! I'm aware of the sheared tips, but no upswept versions -- yet.
Mike Thompson tried a flat plate tip (clear plexi) -- might ask him for his results.
For Bob Mills:
I see a new flap in your future....might as well get started now.
Carry on!
Mark
Here ya go:
They supposedly reduce the vortex to a tighter horizontal "tornado" with an accompanying drag reduction....but hey, what do I know?
Best,
rvmills
Well Known Member
Hey Pierre, you know a lot! Mark and I weren't questioning the existence or your assertion of speed...pilots are just visual beasts...as you know!
What is that tip in the pic from? Almost looks like a Lancair 360, but the tip in your pic looks like it may be a bit more turned up.
Heck, now I'm gonna be googling wingtip design all night. Anybody know a wingtip design engineer? Anybody have a wind tunnel?
Could be a fun experiment. However, there is that edgy area where building and testing fancy wingtips could possibly generate negative flying characteristics and perhaps even flutter. Maybe not control surface flutter or airframe flutter, but who needs a fancy wingtip to go "buzz" and depart the pattern either. An area I want to stay clear of. Is there any body of knowledge of experiments such as this that have gone well...or poorly? Always good to learn from who has gone before.
Kinda thinkin' KISS is a good thing here, though there have been some incradible advances in wingtip design that make one ponder, as Pierre has postulated.
Found out its $100 for a right flap kit...not too bad...still pondering that piece too...
Cheers,
Bob
What is that tip in the pic from? Almost looks like a Lancair 360, but the tip in your pic looks like it may be a bit more turned up.
Heck, now I'm gonna be googling wingtip design all night. Anybody know a wingtip design engineer? Anybody have a wind tunnel?
Could be a fun experiment. However, there is that edgy area where building and testing fancy wingtips could possibly generate negative flying characteristics and perhaps even flutter. Maybe not control surface flutter or airframe flutter, but who needs a fancy wingtip to go "buzz" and depart the pattern either. An area I want to stay clear of. Is there any body of knowledge of experiments such as this that have gone well...or poorly? Always good to learn from who has gone before.
Kinda thinkin' KISS is a good thing here, though there have been some incradible advances in wingtip design that make one ponder, as Pierre has postulated.
Found out its $100 for a right flap kit...not too bad...still pondering that piece too...
Cheers,
Bob
I did try the aileron & flap end void fill
It was a bust but I still have the plugs and I intend to reinstall them when I get a chance to work out the hole closure around the aileron supports - especially on the bottom of the wing at the tip and between the flat and aileron. Like other things I have tried, sometimes you have to stick with what appears to be a good idea until you refine it to a successful configuration. I'm still noodling that one.
Bob Axsom
P.S. I don't care for tip plates but the capability to test is so easy with the configuration I'm thinking of, I may as well do it. Many non aviation issues prevent me from doing that now though. I'm very interested in you efforts and results.
It was a bust but I still have the plugs and I intend to reinstall them when I get a chance to work out the hole closure around the aileron supports - especially on the bottom of the wing at the tip and between the flat and aileron. Like other things I have tried, sometimes you have to stick with what appears to be a good idea until you refine it to a successful configuration. I'm still noodling that one.
Bob Axsom
P.S. I don't care for tip plates but the capability to test is so easy with the configuration I'm thinking of, I may as well do it. Many non aviation issues prevent me from doing that now though. I'm very interested in you efforts and results.
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Wing tips
Hi, all! If you've seen pix of my plane, you'll know I have turned-up tips that are a truncated triangle in planform. The reason they are turned up at 30 deg is to give me more lateral stability, as the Lancair has very little dihedral. At 30 deg, they only contribute cos(60) to the lift, 87%, so if I was going only for speed I would not have turned them up. The leading edge slants back at a 55 deg angle based on a NACA report. Peter Garrison's Melmoth and the Katanas have somewhat similar tips. When I asked Peter why he chose his sweep-back angle, he said that it just looked right on his aero program. The triangular tips I designed for Jim Smiths RV-6 were to reduce his high altitude, high gross weight drag by considerably reducing his induced drag, as I have written about before. As with my prop designs, I would recommend reducing the tip to a point so that there would be no bottom-top pressure differential, and so no tip vortex; what you can get is a straight-line approximation to an ellipse, which planform Prandtl said was about the most efficient. I think that might be what Steve Whitman was attempting on the Tailwinds and Buttercup. Bringing the tip to a point at the 25% point allows you to carry the spar through to the tip. If you'd like to see a low pass I made at Hanford last September with a two-blade prop that I modified by curving the leading edge to a point at the trailing edge over the last 7.5" and see how quiet the prop is, go to www.youtube.com/watch?v=tArjwNyTGQO.
Hi, all! If you've seen pix of my plane, you'll know I have turned-up tips that are a truncated triangle in planform. The reason they are turned up at 30 deg is to give me more lateral stability, as the Lancair has very little dihedral. At 30 deg, they only contribute cos(60) to the lift, 87%, so if I was going only for speed I would not have turned them up. The leading edge slants back at a 55 deg angle based on a NACA report. Peter Garrison's Melmoth and the Katanas have somewhat similar tips. When I asked Peter why he chose his sweep-back angle, he said that it just looked right on his aero program. The triangular tips I designed for Jim Smiths RV-6 were to reduce his high altitude, high gross weight drag by considerably reducing his induced drag, as I have written about before. As with my prop designs, I would recommend reducing the tip to a point so that there would be no bottom-top pressure differential, and so no tip vortex; what you can get is a straight-line approximation to an ellipse, which planform Prandtl said was about the most efficient. I think that might be what Steve Whitman was attempting on the Tailwinds and Buttercup. Bringing the tip to a point at the 25% point allows you to carry the spar through to the tip. If you'd like to see a low pass I made at Hanford last September with a two-blade prop that I modified by curving the leading edge to a point at the trailing edge over the last 7.5" and see how quiet the prop is, go to www.youtube.com/watch?v=tArjwNyTGQO.
pierre smith
Well Known Member
Paul, the video says it's not available...
...when I clicked on your link,
Regards,
...when I clicked on your link,
Regards,
F1Boss
Well Known Member
it LOOKS zoomy
Hey Pierre:
You've seen this on a Rocket? I did not hear about that one. One of our builders did make up a similar tip for his Evo (heck, that could be a picture of it?) but he said it slowed him down a bit at lower altitudes. I think he went back to the flat tip -- I'll check to make sure.
One thing: I sure wish I was talented enough to make parts like that!
Carry on!
Mark
Here ya go:
They supposedly reduce the vortex to a tighter horizontal "tornado" with an accompanying drag reduction....but hey, what do I know?
Best,
Hey Pierre:
You've seen this on a Rocket? I did not hear about that one. One of our builders did make up a similar tip for his Evo (heck, that could be a picture of it?) but he said it slowed him down a bit at lower altitudes. I think he went back to the flat tip -- I'll check to make sure.
One thing: I sure wish I was talented enough to make parts like that!
Carry on!
Mark
Christopher Murphy
Well Known Member
nice looking tip
That's a nice looking tip. When we started adding the winglet tips on our 757s the claim was that they cut fuel burn by about 7%. They add 10 foot to the span not counting the verticle portion of the tip.
I suspect the effiecency comes from the added span that increases the optimun altitude at a higher weight vs. any effect of the winglet itself.
Chris M.
That's a nice looking tip. When we started adding the winglet tips on our 757s the claim was that they cut fuel burn by about 7%. They add 10 foot to the span not counting the verticle portion of the tip.
I suspect the effiecency comes from the added span that increases the optimun altitude at a higher weight vs. any effect of the winglet itself.
Chris M.
pierre smith
Well Known Member
Just start carving, Mark...
...on a piece of foam glued to the last rib and make it the shape you want. Dan H. has some great pointers on 'glass work as well.
I didn't see that tip on a Rocket...it was on an ad for Piper wingtips
Wingtip aerodynamics is a bit of voodoo science and there's no real definitive.."This is the absolute be-all, end-all superfast wingtip" that you just gotta have.
Like Bob Axsom (sp?) does, it really takes a lot of time, trials and testing on days with the same temps, DA and a lot of record-keeping. Tips are probably one area that won't yield much more speed, other than chopping them off.
The sheared wingtips like the -7 and -8 seem to give great results as long as the edge is kept pretty sharp, not rounded off.
From what I've seen over the years, the biggest gains can be had by modified intakes, exits and coolling, since that's where 30%+ of the total drag is. That said, it only makes sense to address that area. Think "Alan Judy'.
At Reno, I've seen a lot of very thin, very sticky tape used to tape up the upper/lower cowl parting surface, the cowl/firewall intersection and any other area where air from inside the airplane can come 'squirting' out into the airstream, often perpendicular to it, creating an effective barrier to oncoming air...say 'drag'.
Best,
...on a piece of foam glued to the last rib and make it the shape you want. Dan H. has some great pointers on 'glass work as well.
I didn't see that tip on a Rocket...it was on an ad for Piper wingtips
Wingtip aerodynamics is a bit of voodoo science and there's no real definitive.."This is the absolute be-all, end-all superfast wingtip" that you just gotta have.
Like Bob Axsom (sp?) does, it really takes a lot of time, trials and testing on days with the same temps, DA and a lot of record-keeping. Tips are probably one area that won't yield much more speed, other than chopping them off.
The sheared wingtips like the -7 and -8 seem to give great results as long as the edge is kept pretty sharp, not rounded off.
From what I've seen over the years, the biggest gains can be had by modified intakes, exits and coolling, since that's where 30%+ of the total drag is. That said, it only makes sense to address that area. Think "Alan Judy'.
At Reno, I've seen a lot of very thin, very sticky tape used to tape up the upper/lower cowl parting surface, the cowl/firewall intersection and any other area where air from inside the airplane can come 'squirting' out into the airstream, often perpendicular to it, creating an effective barrier to oncoming air...say 'drag'.
Best,
Just type "Paul Lipps" in the youtube search bar, I think it's the first video that comes up
Earlier post about tip plate experiments
I'm just not going to do it. The tips I make will be flat 0.016" 2024 T3 and they will exactly match the airfoil at the tip (butt up against the wing skins). There is no way the tip plates can increase speed unless you cut off some wingspan and use tip plates to compensate for the loss of lift. I will end the tips forward of the ailerons and put the plugs back in the recess. Those will be tips number 9 and 10 and that will be the end of my wing tip experimentation. I an going for some benefit from the sharp edge feature mentioned by Paul Lipps earlier. It will be some time before I get this done.
Bob Axsom
I'm just not going to do it. The tips I make will be flat 0.016" 2024 T3 and they will exactly match the airfoil at the tip (butt up against the wing skins). There is no way the tip plates can increase speed unless you cut off some wingspan and use tip plates to compensate for the loss of lift. I will end the tips forward of the ailerons and put the plugs back in the recess. Those will be tips number 9 and 10 and that will be the end of my wing tip experimentation. I an going for some benefit from the sharp edge feature mentioned by Paul Lipps earlier. It will be some time before I get this done.
Bob Axsom
rvmills
Well Known Member
Finished up some testing on my flat wingtips this week and last, in preps for the Taylor 150 race. Thought I'd share the preliminary results, which may show a slight increase in speed over my normal tips. I say "preliminary" and "may" because my three test runs are really just scratching the surface, showed mixed resluts, and I have done a few other items during the tip build that may impact the overall picture. Some explanation of that follows, so the test results can be viewed in the proper light (Bob Ax, I know you're watching! )
Here's a couple pics on the table in the hangar. We went with flat tips with fairly sharp edges, per Paul's posts earlier (and thanks for the diagrams with Oswald Factor notes Paul...someday maybe I'll even figure out what it all means!). We made ribs to strengthen the trailing edges, but did not cover them (another project for later!). The inner flange is 3 layers of glass with an AL backplate to help hold the nutplates.
I do admit that my testing purity (from a one-mod-at-a-time perspective) was not superb this time. Mostly due to schedule constraints (working between trips and with the race looming). I've been working on sealing all plenum leaks and re-routing my heater air source, in preparation for some cowl inlet/exit experimentation, but the inlet/exit work is stll pending, so the plenum work is unlikely to effect speed...might make things run cooler (I hope), but no speed gains expected till the cowl work begins...and even then its a long shot!
The biggest additional aerodynamic change I made during the tip build was to rebuild my right flap, which we discovered had a nearly 3/4" twist in the trailing edge. After installing the new flap, the flap, aileron and tip on the right wing were in great alignment, and the ailerons were in good rig (outer rib tooling holes lined up). However, with the right wing looking good, we then discovered the left flap had a more insideous twist, of about 3/8". No time to fix that, so we extended the flap push rod a couple turns on the rod-end bearing to make the flap-aileron disparity a bit smaller (by about 1/2, or about 3/16' to 1/4". I didn't really like that idea, as extending the flap at all would, to my simple mind, invite more drag. But we figured we'd test it and then perhaps raise it and retest...which is how it played out.
I learned more about testing through the next few flights, as in the devil really is in the details, and no one flight does a result truly show.
I flew a test flight with the new flap and the new tips, as the old tips had been originally matched to the twisted flap, but I know the new tips are true, so I elected to test in that configuration first. From Wayne Hadath's tests of similar tips, I expected about a 4-5 knot increase in stall speed, and hoped for the same 4-5 knot increase in top speed that he saw.
To my surprise, the stall speeds I saw were identical to my previous stall testing, when calibrating my Dynon AOA pitot. 58 clean, 53 full flaps. Hmmm, that's odd, I thunk.
Then I ran a 4 way GPS run down as low as I could go over the Black Rock Desert, in this case at 4500' MSL. Plugged the numbers in, and the result was...no change! This run was 207.6 kts, and was nearly identical to my last run (+0.1 knot...so insignificant), before flaps and wingtips. That has been a pretty consistent speed in the 8500-9500 msl range that I do testing at here in Reno. I've moved out over the desert and found a great test range, and now do the runs down as low as I can get...similar to race conditions. Even down low (4500') the runs have been consistently in the 207kt range. I ran 208+ in Taylor last year at sea level (wind/turns included), so it seems like a good baseline.
Between the flap and the tips, I was really hoping to see a some change, but these mods can be a mystery, as Tom Martin and Bob Ax and others have said many times. But the local gang was really scratching its head on this one over the weekend. The stall speed similarity was more surprising than the top-speed similarity, until I realized that the early testing/calibrating was done at full fuel, and once with a pax (that was at 550+ hours TTAF, not in phase I) to give good max gross stall testing, and the recent test was done at my (now) standard test fuel load of 24 gallons.
So on Tuesday, I shortened that flap push rod-end bearing to put the flap flush at the fueselage, and accept the slight reflex next to the aileron. I flew back to back runs with flat tips and then normal tips (the only difference between the two runs was the tips). Two identical profiles...stalls then high speed runs, in very similar conditions, an hour apart.
The stalls with the flat tips were again 58 kts clean, 53 dirty, while the stalls with the normal tips (and thus longer span) were 54 clean, and 48 dirty. OK, there is the 5 or so knots Wayne saw, and the 48 is the original Vso from the builder's Phase I testing. This makes more sense!
On the 4-way GPS runs, I saw some interesting results. I flew the runs very carefully, and although it was a bit bumpy, it was the same on each run. This time the runs showed the flat tips faster by 1.7 knots. Perhaps a positive result, but no claim yet, as it needs more testing...and no place better to test it than at the Taylor 150 race this weekend!
The real interesting result was the actual speed. These were the fastest runs I've ever had, and were 212.8 (flat tips) to 211.1 (normal tips).
In reviewing the data, and trying to poke holes in it or determine what might add that speed, I came up with the following thoughts:
- The left flap droop on last week's test may have masked improvements from the right flap rebuild and the flat tips. I hope that is the case!!
- The temps at 4500' were within two degrees, but the altimeter setting during the tests was 29.88 last week, and 30.33 this week. I saw more than a 1" increase in MP during the test this week over that of last week.
- The bumps could be a factor as well, and the std dev from the NTPS spreadsheets were less than 1 last week, and just over 1 this week.
So did I get a 1.7 kt increase from flat tips, or a 4-5 kt overall increase from all the recent work...I dunno (I'm not betting on it yet!). We'll see what shows in Taylor (man, I guess I better fly that course well!)
But its fun work, and I'll keep playing and testing to see what might be there.
And Bob, the flat tips and aileron plugs you mentioned in your previous post sound very interesting. They soud a lot like the EVO Rocket wingtip, so it may be a very productive project.
As Tom has said...the proof is in the races, so let the season begin!
Cheers,
Bob
)Here's a couple pics on the table in the hangar. We went with flat tips with fairly sharp edges, per Paul's posts earlier (and thanks for the diagrams with Oswald Factor notes Paul...someday maybe I'll even figure out what it all means!
). We made ribs to strengthen the trailing edges, but did not cover them (another project for later!). The inner flange is 3 layers of glass with an AL backplate to help hold the nutplates.
I do admit that my testing purity (from a one-mod-at-a-time perspective) was not superb this time. Mostly due to schedule constraints (working between trips and with the race looming). I've been working on sealing all plenum leaks and re-routing my heater air source, in preparation for some cowl inlet/exit experimentation, but the inlet/exit work is stll pending, so the plenum work is unlikely to effect speed...might make things run cooler (I hope), but no speed gains expected till the cowl work begins...and even then its a long shot!
The biggest additional aerodynamic change I made during the tip build was to rebuild my right flap, which we discovered had a nearly 3/4" twist in the trailing edge. After installing the new flap, the flap, aileron and tip on the right wing were in great alignment, and the ailerons were in good rig (outer rib tooling holes lined up). However, with the right wing looking good, we then discovered the left flap had a more insideous twist, of about 3/8". No time to fix that, so we extended the flap push rod a couple turns on the rod-end bearing to make the flap-aileron disparity a bit smaller (by about 1/2, or about 3/16' to 1/4". I didn't really like that idea, as extending the flap at all would, to my simple mind, invite more drag. But we figured we'd test it and then perhaps raise it and retest...which is how it played out.
I learned more about testing through the next few flights, as in the devil really is in the details, and no one flight does a result truly show.
I flew a test flight with the new flap and the new tips, as the old tips had been originally matched to the twisted flap, but I know the new tips are true, so I elected to test in that configuration first. From Wayne Hadath's tests of similar tips, I expected about a 4-5 knot increase in stall speed, and hoped for the same 4-5 knot increase in top speed that he saw.
To my surprise, the stall speeds I saw were identical to my previous stall testing, when calibrating my Dynon AOA pitot. 58 clean, 53 full flaps. Hmmm, that's odd, I thunk.
Then I ran a 4 way GPS run down as low as I could go over the Black Rock Desert, in this case at 4500' MSL. Plugged the numbers in, and the result was...no change! This run was 207.6 kts, and was nearly identical to my last run (+0.1 knot...so insignificant), before flaps and wingtips. That has been a pretty consistent speed in the 8500-9500 msl range that I do testing at here in Reno. I've moved out over the desert and found a great test range, and now do the runs down as low as I can get...similar to race conditions. Even down low (4500') the runs have been consistently in the 207kt range. I ran 208+ in Taylor last year at sea level (wind/turns included), so it seems like a good baseline.
Between the flap and the tips, I was really hoping to see a some change, but these mods can be a mystery, as Tom Martin and Bob Ax and others have said many times. But the local gang was really scratching its head on this one over the weekend. The stall speed similarity was more surprising than the top-speed similarity, until I realized that the early testing/calibrating was done at full fuel, and once with a pax (that was at 550+ hours TTAF, not in phase I) to give good max gross stall testing, and the recent test was done at my (now) standard test fuel load of 24 gallons.
So on Tuesday, I shortened that flap push rod-end bearing to put the flap flush at the fueselage, and accept the slight reflex next to the aileron. I flew back to back runs with flat tips and then normal tips (the only difference between the two runs was the tips). Two identical profiles...stalls then high speed runs, in very similar conditions, an hour apart.
The stalls with the flat tips were again 58 kts clean, 53 dirty, while the stalls with the normal tips (and thus longer span) were 54 clean, and 48 dirty. OK, there is the 5 or so knots Wayne saw, and the 48 is the original Vso from the builder's Phase I testing. This makes more sense!
On the 4-way GPS runs, I saw some interesting results. I flew the runs very carefully, and although it was a bit bumpy, it was the same on each run. This time the runs showed the flat tips faster by 1.7 knots. Perhaps a positive result, but no claim yet, as it needs more testing...and no place better to test it than at the Taylor 150 race this weekend!
The real interesting result was the actual speed. These were the fastest runs I've ever had, and were 212.8 (flat tips) to 211.1 (normal tips).
In reviewing the data, and trying to poke holes in it or determine what might add that speed, I came up with the following thoughts:
- The left flap droop on last week's test may have masked improvements from the right flap rebuild and the flat tips. I hope that is the case!!
- The temps at 4500' were within two degrees, but the altimeter setting during the tests was 29.88 last week, and 30.33 this week. I saw more than a 1" increase in MP during the test this week over that of last week.
- The bumps could be a factor as well, and the std dev from the NTPS spreadsheets were less than 1 last week, and just over 1 this week.
So did I get a 1.7 kt increase from flat tips, or a 4-5 kt overall increase from all the recent work...I dunno (I'm not betting on it yet!). We'll see what shows in Taylor (man, I guess I better fly that course well!)
But its fun work, and I'll keep playing and testing to see what might be there.
And Bob, the flat tips and aileron plugs you mentioned in your previous post sound very interesting. They soud a lot like the EVO Rocket wingtip, so it may be a very productive project.
As Tom has said...the proof is in the races, so let the season begin!
Cheers,
Bob
Good news Bob Mills
I have all of the material for my next flat tip configuration but circumstances here at home have my time and flexibility limited. I bought a 4'x6' sheet of 0.016 2024T3 aluminum from Aircraft Spruce along with 12' of 3/4"x3/4"x1/16" 6061T6 aluminum angle and 200 #8 floating platenuts for the job.
During the annual condition inspection (on going) I found the FAB mounting plate broken almost in two and had to make a new one out of 0.090" stock to replace the original 0.063" plate. That was installed yesterday but as you say the races are getting closer and I have to spend what time I have on getting the inspection done. I had to cancel out of Taylor because I just can't be away long enough to go down there and stay overnight and the inspection is not complete. Hopes for the races at Sherman (Texoma) and Dyess AFB (BCAF) are still alive but fragile.
All of the delay gives time for the mind to refine the new flat tip implementation details. The large number of floating platenuts is intended to allow me to precisely align the top and bottom edges of the very thin aluminum tip (0.016") with the top and bottom surface of the wing skin in an effort to get the razor sharp edge mentioned by Paul Lipps. I could reduce the weight and expense by riveting the angles inside the tip instead of screw mounting but the precision requirements would be much greater - still thinking that one even though I already have the nuts and screws. Since I want nothing sticking out beyond the end of my 21' wingspan the tips will end at the front of the ailerons. the ends of the ailerons will be plugged. I will have a friction fitting inside the tip at the leading edge to hold it tight against the end of the wing skin to prevent the 200+ mph wind from rolling it back like a sardine can lid.
Good luck at Taylor against Mark Frederick's Continental 550 powered EVO Rocket. He was still working with fairings and other things I'm sure when I saw his plane at Courtland, Alabama last year. He was dealing with his mother's health needs then and his available time was limited but he has it fully refined by now I'm sure. Both of you seem intensely interested in performance improvement while being good sportsmen - competition doesn't get any better than that.
Congratulations on your tip development results.
Bob Axsom
I have all of the material for my next flat tip configuration but circumstances here at home have my time and flexibility limited. I bought a 4'x6' sheet of 0.016 2024T3 aluminum from Aircraft Spruce along with 12' of 3/4"x3/4"x1/16" 6061T6 aluminum angle and 200 #8 floating platenuts for the job.
During the annual condition inspection (on going) I found the FAB mounting plate broken almost in two and had to make a new one out of 0.090" stock to replace the original 0.063" plate. That was installed yesterday but as you say the races are getting closer and I have to spend what time I have on getting the inspection done. I had to cancel out of Taylor because I just can't be away long enough to go down there and stay overnight and the inspection is not complete. Hopes for the races at Sherman (Texoma) and Dyess AFB (BCAF) are still alive but fragile.
All of the delay gives time for the mind to refine the new flat tip implementation details. The large number of floating platenuts is intended to allow me to precisely align the top and bottom edges of the very thin aluminum tip (0.016") with the top and bottom surface of the wing skin in an effort to get the razor sharp edge mentioned by Paul Lipps. I could reduce the weight and expense by riveting the angles inside the tip instead of screw mounting but the precision requirements would be much greater - still thinking that one even though I already have the nuts and screws. Since I want nothing sticking out beyond the end of my 21' wingspan the tips will end at the front of the ailerons. the ends of the ailerons will be plugged. I will have a friction fitting inside the tip at the leading edge to hold it tight against the end of the wing skin to prevent the 200+ mph wind from rolling it back like a sardine can lid.
Good luck at Taylor against Mark Frederick's Continental 550 powered EVO Rocket. He was still working with fairings and other things I'm sure when I saw his plane at Courtland, Alabama last year. He was dealing with his mother's health needs then and his available time was limited but he has it fully refined by now I'm sure. Both of you seem intensely interested in performance improvement while being good sportsmen - competition doesn't get any better than that.
Congratulations on your tip development results.
Bob Axsom
F1Boss
Well Known Member
A meeting with the Bobs...
Hey Bobs:
1st, no real refinements since the final race last year, so Col. Mills, if you picked up any speed, it's gonna be a race!
2nd, I guess #1 covers #2 also!
Bob Mills: let's do some air-to-air testing on Fri if you get here early enough. Less wing area benefits show up better at low altitudes. I'll be happy to see you again, unless you are faster then me!
Se ya then!
Mark
Hey Bobs:
1st, no real refinements since the final race last year, so Col. Mills, if you picked up any speed, it's gonna be a race!
2nd, I guess #1 covers #2 also!
Bob Mills: let's do some air-to-air testing on Fri if you get here early enough. Less wing area benefits show up better at low altitudes. I'll be happy to see you again, unless you are faster then me!
Se ya then!
Mark
rvmills
Well Known Member
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
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:
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.
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.
scsmith
Well Known Member
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)
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)
Last edited:
pierre smith
Well Known Member
You have one..
PM sent, Steve,
Best,
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)
PM sent, Steve,
Best,
How's that working out?
How are things working out at Taylor, TX?
Bob Axsom
How are things working out at Taylor, TX?
Bob Axsom
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
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
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
pierre smith
Well Known Member
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,
...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,
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))
rvmills
Well Known Member
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!
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!
