Van's Air Force
Don't miss anything! Register now for full access to the definitive RV support community.
BatWing tips on RV-6.
- Thread starter Mel
- Start date
Kyle Boatright
Well Known Member
Back in the day, early adopters claimed better climb at altitude and higher TAS at altitude. The claimed improvements were of a magnitude that would be very hard to *prove* without some pretty thorough testing, but theory would tell you that the slight increase in span would give those results.
I usually look at "new mod = performance gain" claims with a critical eye, because few of us (myself included) like to 'fess up that we just spent a thousand bucks and 50 man hours (or whatever) making a modification that didn't help things.
Actually in theory, I believe that the original "hoerner" style tips should be more efficient. I was just thinking that maybe the extra span and area might help on the low end. I acquired a set at a pretty reasonable cost and I was thinking about putting them on my -6 just to be different. If I can show some kind of justification, it would help. Of course for night flight, I would have to add a tail strobe.
pierre smith
Well Known Member
We have them as well.....
.....Mel. The airplane never flew with anything but these 'bat-wing' tips but we can make 203 MPH solo at 2700 revs, so I'm not sure if it's the Catto or the tips or some of both. Very few F-1 racers use Hoerner tips, closer to the batwings and those guys really get into nano-improvements in speed.
We wanted the flush lights and no antenna approach for speed purposes and it all ended very well.
Regards,
.....Mel. The airplane never flew with anything but these 'bat-wing' tips but we can make 203 MPH solo at 2700 revs, so I'm not sure if it's the Catto or the tips or some of both. Very few F-1 racers use Hoerner tips, closer to the batwings and those guys really get into nano-improvements in speed.
We wanted the flush lights and no antenna approach for speed purposes and it all ended very well.
Regards,
Bob Martin
Well Known Member
Robbie's RV-6 has them
Mel,
Robbie Attaway's RV-6 has them.
and he raced his with a TAS of 226.
or course he also did a "few" other things as well.
Go for it! then you can tell us for sure.
Mel,
Robbie Attaway's RV-6 has them.
and he raced his with a TAS of 226.
or course he also did a "few" other things as well.
Go for it! then you can tell us for sure.
Bill Wightman
Well Known Member
Mel,
Adding the Batmobile tips will add span and area. This will definitely help the low end, if that's what you want. As you know, induced drag increases with reduced airspeed (or more specifically, higher AOA). And induced drag is tightly tied to aspect ratio - increasing AR will drive the induced drag numbers down, especially when slow. Adding AR and span will also shift the best L/D speed downward, if that's what you want.
The Bat tips also rake outward a little, forcing the tip vortex to separate at a discreet point - helping to reduce induced drag.
But, there are a few things that will be adversely affected too: Top speed at lower altitudes probably will go down a little; max roll rate will decrease slightly, and you might have a slightly heavier empty weight.
If these items don't worry you then I'd go ahead with the new tips. The 6's wing span is a bit short for good efficiency at the altitudes most of like to cruise at, so the added span and area will do much more to help than hurt across the envelope.
Adding the Batmobile tips will add span and area. This will definitely help the low end, if that's what you want. As you know, induced drag increases with reduced airspeed (or more specifically, higher AOA). And induced drag is tightly tied to aspect ratio - increasing AR will drive the induced drag numbers down, especially when slow. Adding AR and span will also shift the best L/D speed downward, if that's what you want.
The Bat tips also rake outward a little, forcing the tip vortex to separate at a discreet point - helping to reduce induced drag.
But, there are a few things that will be adversely affected too: Top speed at lower altitudes probably will go down a little; max roll rate will decrease slightly, and you might have a slightly heavier empty weight.
If these items don't worry you then I'd go ahead with the new tips. The 6's wing span is a bit short for good efficiency at the altitudes most of like to cruise at, so the added span and area will do much more to help than hurt across the envelope.
Last edited:
az_gila
Well Known Member
But... the Hoerner tips...
...are designed to increase the "effective" wing span by altering the induced drag at the tips.
So it might end up as a wash... real span vs. effective span, and a reduced wetted area with the Hoerner tips.
IIRC, Vans conclusion was that it was a wash (and he didn't like the top surface "sagging" of the original tips?)....
Page 282 of this aerodynamic book has some details....
http://books.google.com/books?id=C8...X&oi=book_result&resnum=9&ct=result#PPA282,M1
...are designed to increase the "effective" wing span by altering the induced drag at the tips.
So it might end up as a wash... real span vs. effective span, and a reduced wetted area with the Hoerner tips.
IIRC, Vans conclusion was that it was a wash (and he didn't like the top surface "sagging" of the original tips?)....
Page 282 of this aerodynamic book has some details....
http://books.google.com/books?id=C8...X&oi=book_result&resnum=9&ct=result#PPA282,M1
Bill Wightman
Well Known Member
Gil,
Yes the Hoerners are an improvement over a simple rounded tip like many older aircraft used. And they'd probably perform better than Vans old standard tip. However, they're still not as good as adding real span. The Bat tip's raked planform is an improvement over the old stock tip whether it has a Hoerner cross section or not. As an engineer, if you give me a choice of altering wing tip planform -vs- cross section, I'll choose to alter planform nearly every time. Its far more influential than changing cross section.
I do agree the difference would be small, at least on the top end. But Mel wanted low speed performance, and adding real physical wing span will produce pretty substantial results on that end of the spectrum.
BTW, that's not a bad book either...
Yes the Hoerners are an improvement over a simple rounded tip like many older aircraft used. And they'd probably perform better than Vans old standard tip. However, they're still not as good as adding real span. The Bat tip's raked planform is an improvement over the old stock tip whether it has a Hoerner cross section or not. As an engineer, if you give me a choice of altering wing tip planform -vs- cross section, I'll choose to alter planform nearly every time. Its far more influential than changing cross section.
I do agree the difference would be small, at least on the top end. But Mel wanted low speed performance, and adding real physical wing span will produce pretty substantial results on that end of the spectrum.
BTW, that's not a bad book either...
Mel, don't you have a biplane you should be finishing?
I do have the engine and prop hung!
Don't distract me!
Right now I'm working on the house. Patching and painting.
And the -6 is scattered all over the hangar getting it's annual once-over. It needs 'tenshion.
Don't distract me!
Right now I'm working on the house. Patching and painting.
And the -6 is scattered all over the hangar getting it's annual once-over. It needs 'tenshion.
rv9aviator
Well Known Member
I feel better now. My 9 has been sitting alone for about three months while I re-trim the whole house with new baseboards cove molding, and door casings. I finished the last of the project today.
pierre smith
Well Known Member
Say Bill...
......Our batwing tips cave in in the rear one third, on the top surface, during cruise. Is this a result of the vortex coming over the top? Or what?
Thanks,
......Our batwing tips cave in in the rear one third, on the top surface, during cruise. Is this a result of the vortex coming over the top? Or what?
Thanks,
Bill Wightman
Well Known Member
Hey Pierre - really? I've not seen that. It's definitely due to loads applied but the question is from where?
Two possibilities come to mind: 1) Its what you said. There's some vortex wrapping around the tip, and impinging on the upper surface. or.... 2) the larger overall surface area of the tip puts more load on it. The bat tips' planform gets wider toward the trailing edge of the wing, so there's more chance for loads to build on that part of the structure. Those lift loads then can bend the entire tip upward just a bit, resulting in the upper surface sagging.
You could check out (1) above with a simple tuft test in flight. Just tuft the upper surface of the tip with some yarn and go fly. Take a look... maybe some pics... and you'll see if the vortex is wrapping over the tip. I'd guess it isn't due to the raked outboard shape. But this would be a good way to eliminate one variable.
You could check out (2) simply enough: Using your hands, lift up on the outboard edge of the tip (simulate lift loads). Put some decent force on it and see if the upper surface sags. If so, I think that might be the culprit.
To fix it, I'd think some light internal structure could be installed to stiffen the upper surface.
Two possibilities come to mind: 1) Its what you said. There's some vortex wrapping around the tip, and impinging on the upper surface. or.... 2) the larger overall surface area of the tip puts more load on it. The bat tips' planform gets wider toward the trailing edge of the wing, so there's more chance for loads to build on that part of the structure. Those lift loads then can bend the entire tip upward just a bit, resulting in the upper surface sagging.
You could check out (1) above with a simple tuft test in flight. Just tuft the upper surface of the tip with some yarn and go fly. Take a look... maybe some pics... and you'll see if the vortex is wrapping over the tip. I'd guess it isn't due to the raked outboard shape. But this would be a good way to eliminate one variable.
You could check out (2) simply enough: Using your hands, lift up on the outboard edge of the tip (simulate lift loads). Put some decent force on it and see if the upper surface sags. If so, I think that might be the culprit.
To fix it, I'd think some light internal structure could be installed to stiffen the upper surface.
My guess would be #2. Vortex generation is usually greatest at lower speeds and higher AOA, not at cruise.
BTW, If I install the bat-wing tips, I intend to add one internal span-wise rib because these particular tips have not been stored properly and have a large deformity.
Last edited:
pierre smith
Well Known Member
They don't sag...
......when I lift the tip as much as I dare. I'll tuft test soon and reply....good idea, one I've always wanted to try. BTW, the tips are 17" wide next to the aileron leading edge/rear end of the top skin and very limber with no internal reinforcement. Does Van recommend foam/glass or other stiffeners for these tips?
Regards,
......when I lift the tip as much as I dare. I'll tuft test soon and reply....good idea, one I've always wanted to try. BTW, the tips are 17" wide next to the aileron leading edge/rear end of the top skin and very limber with no internal reinforcement. Does Van recommend foam/glass or other stiffeners for these tips?
Regards,
The only stiffener specified is the closeout rib at the trailing edge beside the aileron.
The RV-9 tips do use a span wise rib. Because of the different airfoil profile they are very thin at the aft end.
