Van's Air Force
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Wing tips
- Thread starter Got2Fly
- Start date
Bob Kuykendall
Well Known Member
Well, no. You are correct that winglets wouldn't do much for an RV-type airplane.
However, there is still plenty of spanwise flow on straight-wing airplanes. Think of it as if the higher pressure air under the wing is trying to sneak around the wingtip to get to the lower-pressure area over the wing. As a result, there are substantial wingtip vortices on straight wing aircraft, and even on aircraft with forward swept wings.
Consider that sailplanes often if not usually have winglets, and their wings tend to be about as unswept as wings get. Sailplane winglets improve the lift to drag ratio in certain flight regimes, and in some cases yield improved handling while circling.
Note that a winglet is never as effective at increasing the lift to drag ratio as would a span extension equivalent to the winglet height. However, the winglet does not increase the span (which is good for span-limited situations such as racing classes and facilities constraints), and also adds less root bending moment, which is good if wing stiffness or strength are constraining factors.
Maybe Steve Smith will chip in on this. I know that he has designed several winglet installations, including the set on my sailplane project. Steve also designed the wing profile on your RV-10
Thanks, Bob K.
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Has anyone tried droopy winglets on RVs?
They used to use them on agricultural aircraft and others as well. I was wondering if anyone had experience with them before and after installation.
It would seem that the droopy winglets would contain the spanwise flow and convert it to lift.
They used to use them on agricultural aircraft and others as well. I was wondering if anyone had experience with them before and after installation.
It would seem that the droopy winglets would contain the spanwise flow and convert it to lift.
wing tips
There are lots of wing tip shapes that "contain the flow" or reduce the vortex creating tendency of the higher pressure air underneath the wing and the lower pressure above the wing. One way is to have a sharp edge at the intersection. Mooney tips do this, actually they have two sharp edges, on on the top intersection and one on the bottom intersection. Hoerner tips as used on earlier RVs do this as well as the "sheared" tips on later RVs. The latter, although they have a rounded profile, have a tapered planform that helps "contain the flow".
There are lots of wing tip shapes that "contain the flow" or reduce the vortex creating tendency of the higher pressure air underneath the wing and the lower pressure above the wing. One way is to have a sharp edge at the intersection. Mooney tips do this, actually they have two sharp edges, on on the top intersection and one on the bottom intersection. Hoerner tips as used on earlier RVs do this as well as the "sheared" tips on later RVs. The latter, although they have a rounded profile, have a tapered planform that helps "contain the flow".
MauleDriver
Well Known Member
Fashion statement
I have a limited understanding of the aerodynamics, but it's interesting to note how drooped, Hoerner inspired wing tips were in style back in the 70s, along with STOL capabilities in general, but seem to have fell out of favor since. That may suggest that the desired benefits weren't there even if they were attractive at some level.
At least that's what I'm thinking each time I watch a local 'STOL' C172 with drooped tips and a run-out engine depart... standing still it looks dowdy, in flight it looks tired, but that's just me.
Given how well the basic design works it would be a waste to do it without committing to some testing. Like putting together a drooped set and a standard set for comparision tests.
Bill
I have a limited understanding of the aerodynamics, but it's interesting to note how drooped, Hoerner inspired wing tips were in style back in the 70s, along with STOL capabilities in general, but seem to have fell out of favor since. That may suggest that the desired benefits weren't there even if they were attractive at some level.
At least that's what I'm thinking each time I watch a local 'STOL' C172 with drooped tips and a run-out engine depart... standing still it looks dowdy, in flight it looks tired, but that's just me.
Given how well the basic design works it would be a waste to do it without committing to some testing. Like putting together a drooped set and a standard set for comparision tests.
Bill
David Shelton
Well Known Member
Bob pretty much covered everything. The stock raked wingtip isn't too bad and there really isn't much performance to be gained from a winglet on an RV-10. In fact, if the design isn't perfectly optimized, there will likely be a net performance loss.
Performance aside, there are still a couple reasons to consider a winglet: 1) They look cool. 2) They often improve the low-speed aileron authority.
I used to fly an ASW-15b that had been modified with ASW-20 winglets. I didn't notice any measurable performance gain but I generally liked the aileron feel for thermal flights. For ridge running, I always removed them because they likely hurt performance at higher speeds.
Performance aside, there are still a couple reasons to consider a winglet: 1) They look cool. 2) They often improve the low-speed aileron authority.
I used to fly an ASW-15b that had been modified with ASW-20 winglets. I didn't notice any measurable performance gain but I generally liked the aileron feel for thermal flights. For ridge running, I always removed them because they likely hurt performance at higher speeds.
The vortex up and over the wing tip tends to reduce the lift, by increasing the pressure on top, so the plane flies at a higher angle of attack to compensate; so the vortex contributes to induced drag.
You'll notice that sailplanes and 737's tend to operate in regions where induced drag is an important consideration. (Sailplanes near best L/D, 737's at high altitudes and hence relatively low indicated airspeeds).
RV-10's tend to operate at altitudes where parasitic drag is much greater than induced drag. So in principle winglets help, but in practice their design has to be "just right" or else they cause more parasitic drag than the gain from reducing the induced drag.
You'll notice that sailplanes and 737's tend to operate in regions where induced drag is an important consideration. (Sailplanes near best L/D, 737's at high altitudes and hence relatively low indicated airspeeds).
RV-10's tend to operate at altitudes where parasitic drag is much greater than induced drag. So in principle winglets help, but in practice their design has to be "just right" or else they cause more parasitic drag than the gain from reducing the induced drag.
David Shelton
Well Known Member
To be honest, wingtips, swept tails and other features are often selected for aesthetic reasons. These things fall in and out of style like clothing and car bodies. In the most high performance aircraft (sailplanes, airliners, fighters, record setters), they actually invest in trade studies and testing to optimize the tip. In most other cases, they simply select any reasonable tip that looks sexy.
MauleDriver
Well Known Member
Fashion statement
True enough about esthetics... but I haven't seen a low aspect ratio 'hersey bar' wing with sexy looking winglets yet.
Nothing more beautiful or functional than a high performance sailplane though.
Bill "always a glider guider in my heart" Watson
PIK20b, LS6b
True enough about esthetics... but I haven't seen a low aspect ratio 'hersey bar' wing with sexy looking winglets yet.
Nothing more beautiful or functional than a high performance sailplane though.
Bill "always a glider guider in my heart" Watson
PIK20b, LS6b
One tip on your wing tips
Configure your wing/wing tip interface with forethought so you can easily remove them. Wing tips are fairly easy to develop and the differences in performance (speed is all I care about) of any reasonable design is small. So far my fastest design is a straight streamlined design with the plan view shape defined by the shape of the lower surface of the wing. The span of each tip is 3". Stock on my RV-6A is 12". I also built and flown it with tips of 0", 3/4" and 21" span.
Bob Axsom
Configure your wing/wing tip interface with forethought so you can easily remove them. Wing tips are fairly easy to develop and the differences in performance (speed is all I care about) of any reasonable design is small. So far my fastest design is a straight streamlined design with the plan view shape defined by the shape of the lower surface of the wing. The span of each tip is 3". Stock on my RV-6A is 12". I also built and flown it with tips of 0", 3/4" and 21" span.
Bob Axsom
Cfrisella
Well Known Member
Hey bob,
I followed all your work before making mine. In the end I just did something that made me say "Yeah", I like that. I've only flown for 7 hours so far. I don't think their slowing me down so I'm cool with them. Your efforts in my design are most appreciated though. I'll make you a set if you want for whatever reason if you like. I really did follow your trials. Thanks, Chris.
I followed all your work before making mine. In the end I just did something that made me say "Yeah", I like that. I've only flown for 7 hours so far. I don't think their slowing me down so I'm cool with them. Your efforts in my design are most appreciated though. I'll make you a set if you want for whatever reason if you like. I really did follow your trials. Thanks, Chris.
No more tips exactly
I think I have found the best for the stock wing. We in the Axsom household are dealing with a major problem that prevents me from doing anything about the airplane right now but the mind never stops thinking about it. Should we survive God's latest challenge I am planning to reduce the stock wingspan by one rib bay on each side. It is not as risky as it sounds since my tip tanks add 9" inches back on each side (1.5 feet total). The idea is to have three configurations (1) tip tanks and stock tips with lights, etc. for travel and 55 gallons of fuel, (2) Long range racing tip tanks & 3" racing tips, (3) short range racing 3" tips only. I still have the flat tips that I may experimentally try with tip plates of decremental size to find the best size. This last one would be to confine the flow over the greatly reduced wing and reduce the angle of attack (induced drag) by more than the parasitic drag of the tip plates.
Bob Axsom
I think I have found the best for the stock wing. We in the Axsom household are dealing with a major problem that prevents me from doing anything about the airplane right now but the mind never stops thinking about it. Should we survive God's latest challenge I am planning to reduce the stock wingspan by one rib bay on each side. It is not as risky as it sounds since my tip tanks add 9" inches back on each side (1.5 feet total). The idea is to have three configurations (1) tip tanks and stock tips with lights, etc. for travel and 55 gallons of fuel, (2) Long range racing tip tanks & 3" racing tips, (3) short range racing 3" tips only. I still have the flat tips that I may experimentally try with tip plates of decremental size to find the best size. This last one would be to confine the flow over the greatly reduced wing and reduce the angle of attack (induced drag) by more than the parasitic drag of the tip plates.
Bob Axsom
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