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  #81  
Old 03-03-2010, 07:53 PM
elippse elippse is offline
 
Join Date: Dec 2006
Location: Arroyo Grande, CA
Posts: 938
Default 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.
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  #82  
Old 03-04-2010, 07:03 AM
pierre smith's Avatar
pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
Default Paul, the video says it's not available...

...when I clicked on your link,

Regards,
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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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  #83  
Old 03-04-2010, 07:03 AM
F1Boss's Avatar
F1Boss F1Boss is offline
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 811
Default it LOOKS zoomy

Quote:
Originally Posted by pierre smith View Post
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
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  #84  
Old 03-04-2010, 07:45 AM
Christopher Murphy Christopher Murphy is offline
 
Join Date: Feb 2007
Location: colorado
Posts: 873
Default 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.
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  #85  
Old 03-04-2010, 08:40 AM
pierre smith's Avatar
pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
Default Just start carving, Mark...

Quote:
Originally Posted by F1Boss View Post
Hey Pierre:

. 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
...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,
__________________
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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  #86  
Old 03-04-2010, 10:17 AM
1:1 Scale 1:1 Scale is offline
 
Join Date: Aug 2007
Location: S21, Oregon
Posts: 161
Default

Quote:
Originally Posted by pierre smith View Post
...when I clicked on your link,
Just type "Paul Lipps" in the youtube search bar, I think it's the first video that comes up
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Kelly
RV-7 empennage done, wings done, fuselage to QB stage.
1973 Maule M4-220C flying
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  #87  
Old 03-04-2010, 09:28 PM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default 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
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  #88  
Old 04-08-2010, 01:42 AM
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rvmills rvmills is offline
 
Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
Default

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
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Bob Mills
RV-6 "Rocket Six" N49VM
Reno-Stead, NV (KRTS)
President/Sport 47/49, Sport Class Air Racing
President, Formation Flying Inc (FFI)
Flight Lead, Lightning Formation Airshows
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  #89  
Old 04-08-2010, 05:06 AM
Bob Axsom Bob Axsom is offline
 
Join Date: Mar 2005
Posts: 5,685
Default 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
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  #90  
Old 04-08-2010, 07:21 AM
F1Boss's Avatar
F1Boss F1Boss is offline
 
Join Date: Aug 2006
Location: Taylor Texas
Posts: 811
Default 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
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