|
-
POSTING RULES

-
Donate yearly (please).
-
Advertise in here!
-
Today's Posts
|
Insert Pics
|

03-02-2010, 01:18 AM
|
 |
|
|
Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
|
|
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:
Quote:
Originally Posted by 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
|
Quote:
Originally Posted by C-FAH Q
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.
|
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
|

03-02-2010, 07:11 PM
|
|
|
|
Join Date: Mar 2005
Posts: 5,685
|
|
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
|

03-03-2010, 05:58 AM
|
 |
|
|
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
|
|
Have either of you guys considered upswept tips...
..like a lot of the really fast F-1 guys run?
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!
|

03-03-2010, 07:58 AM
|
 |
|
|
Join Date: Aug 2006
Location: Taylor Texas
Posts: 811
|
|
Whatsis?
Quote:
Originally Posted by pierre smith
..like a lot of the really fast F-1 guys run?
Best,
|
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
|

03-03-2010, 08:22 AM
|
 |
|
|
Join Date: Apr 2005
Location: KSLC
Posts: 4,021
|
|
Quote:
Originally Posted by F1Boss
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
|

03-03-2010, 12:05 PM
|
 |
|
|
Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
|
|
Quote:
Originally Posted by pierre smith
..like a lot of the really fast F-1 guys run?
|
Quote:
Originally Posted by F1Boss
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.
|
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?
Quote:
Originally Posted by F1Boss
Mike Thompson tried a flat plate tip (clear plexi) -- might ask him for his results.
|
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...  )
Quote:
Originally Posted by F1Boss
For Bob Mills:
I see a new flap in your future....might as well get started now.
Carry on!
Mark
|
Quote:
Originally Posted by L.Adamson
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
|

03-03-2010, 12:56 PM
|
 |
|
|
Join Date: Jan 2005
Location: Louisville, Ga
Posts: 7,840
|
|
Quote:
Originally Posted by F1Boss
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,
__________________
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!
|

03-03-2010, 05:48 PM
|
 |
|
|
Join Date: Nov 2007
Location: Reno, NV
Posts: 2,125
|
|
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
|

03-03-2010, 06:44 PM
|
|
|
|
Join Date: Mar 2005
Posts: 5,685
|
|
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.
Last edited by Bob Axsom : 03-03-2010 at 06:48 PM.
Reason: Added P. S.
|

03-03-2010, 07:50 PM
|
|
|
|
Join Date: Feb 2005
Posts: 592
|
|
I believe I saw here that someone made a custom set of wingtips like the one Pierre posted for Randy Lervold. But I was never able to find anything out about the builder or the tips.
Maybe he is lurking around and will chime in.
Glenn Wilkinson
|
Posting Rules
|
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts
HTML code is Off
|
|
|
All times are GMT -6. The time now is 02:35 AM.
|