Winglets
 

I have a question concerning the use of winglets in models. I am aware of there use in full scale aircraft but was wondering if they as useful to same extent in models like make a 48 inch wing fly and glide like a 55 inch wing. I am considering modifying a combat armadillo wing with winglets to see what results I get and was wondering if anyone has tried this before. It is currently on a homeade SPAD aircraft that flies rather quickly and laterally is very touchy. The plane is set up well and trimmed will fly hands off. Will winglets slow down roll rates? The plane lands beautifully with no bad stall characteristics that I have found. I was wondering what shapes might be the best to try. Thanks in advance

RE: Winglets
 

Winglets only work on a positively loaded wing. They have a minimal effect on any aircraft with a light wing loading, say under 50lbs/sq ft. What they do is control the losses at the wingtip created by the vortex, and harness the spiralling flow in such a way that dramatically reduces drag. Some actually claim they produce thrust, like a sail on a boat. Wind tunnel model testing has shown that even on small corporate jets, their benefit is negligable when considering the cost to manufacture. On the Rutan design Vari-Eze and Long -Eze, the winglets are actually vertical fins that are needed for yaw stability and control. Any additional benefit in performance on those designs is just a bonus. On a model, the best you can hope for is the use of a tip plate. They will effectively lengthen the span of the wing, but be aware that their effect on performance depends on the sum of the overall design. They will also help in inverted flight, where a winglet only works right side up.

RE: Winglets
 

I'd imagine that they slow your roll rate simply because they're extra weight at the end of your wing (which the ailerons then have to accelerate in order to create a roll). So keep them light [8D]

RE: Winglets
 

Winglets are a thing about which many have misconceptions. Often a person produces a poor winglet design and finds that his performance is even less, hence they are very sensitive to design. The idea that winglets only work on high wing loadings is not true. If one were to only look at full size competition gliders, he would come to see the error of that notion. These gliders are very lightly loaded (6.24-10.58 lb/ft² for a Discus 2a which uses winglets) and still use winglets to improve performance. It is true that there is more to be gained from a higher loaded plane due to the fact that the tip vortice of these aircraft consumes more energy when compared to a similar airplane that is lighter. Nonetheless, even models with small wingspans (around 12!QUOT!) can benefit from winglets. I currently do not have the link, but researchers at Arizona State University showed that winglets on a small wing did improve performance over the baseline, but also showed that performance degradation with a non-optimized design. End plates were mentioned as a solution, this might be true if your plane is operating in a range were parasite drag is much greater than induced drag (ie crop dusters) but where induced drag is greater than parasite, winglets are a better solution. In effect, the winglet (also the end plate) are ways to make it so that the wing behaves more like a wing of infinite span. Finite span wings have losses (like those associated with vorticies, span-wise flow, and other things) and the addition of a winglet only helps to reduce those losses. In effect a winglet is to the wing what the tuned exhaust is to the engine. Neither increases performance, but both help reduce the losses and help the device come closer to its optimal efficiency.

As for manufactures not finding them design and manufacture, This might not be true. There is a group that currently has designed a STC'ed kit for the 757. Boeing has installed them, or intends to, on their 737-800 and 900ER, 787, 747-400, and other models. There are other wingtips that are also employed on the 767, 777 and 787 models which is a raked design which is similar in concept to what the winglet does. Winglet mods are also available for some earlier Learjet and Gulfstream models. Winglets have also been successfully applied to Cessna 400 series airplanes, Beech Barons, and Piper Navajo series. These being prop jobs. One must note that the !QUOT!gains!QUOT! are around 2-5% in better economy. This is not much, but over the years will result in lower operating costs. I hope not to offend anyone, just clarify a cloudy subject. If all els fails, winglets look great!

Adam

RE: Winglets
 

Tip plates are the way to go. They will usually increase the roll rate because they eliminate tip losses that degrade the effectiveness of the ailerons at the most important end of the lever arm. You will also notice better aileron authority at low speeds, like on approach. I had a set of plates on a Mark's Wanderer, and a flying buddy had the same plane, but with the standard tips. He flew both and was moved to comment that mine handled much better than his and was much steadier on approach & landing. I now routinely add them to just about all my non-scale planes.

RE: Winglets
 

One thing to bear in mind with winglets is that they produce the same effect as additional dihedral, unless they extend equally above, and below, the wing. This can be good, or bad. The chief value of winglets, in my view, is their ability to reduce induced drag within the confines of a given wingspan. Wind tunnel tests revealed that the optimum angle for winglets was pointing straight out - in other words, simply adding to wingspan. Winglets, of course, would produce less additional bending moment in the wing structure than a wingtip extension.

An old NACA report is available on the NASA website, of wing tip plates. These were found to considerably reduce induced drag at high lift coefficients, but total drag was increased up to a lift coefficient of around 0.5 because of the profile drag of the tip plates. I found that tip plates tightened up the loop radius of a competition fun-fly model, and - a bonus - they improved overall handling, since they greatly increase yaw resistance.

RE: Winglets
 

Wing caps are probably thr easiest for my application and I'll give it a whirl and see how it performs. The beauty of using coro is I can start large and square and trim into a different shape and see how it goes. What I'm looking for is taming it's lateral touchiness during slow flight. Get it to fly like it has a bigger wing without using a bigger wing. Thanks for all the input.

RE: Winglets
 

Just one more note on winglets. Yes, they work, and there are measurable reductions in drag with their use. The design of the winglets for heavy aircraft has still not yet been optimized. I'm sure the basics in planform and rigging angles have been fairly well established, but there is one more reason as to their use on jets. It has to do with the shock wave interraction with the winglet at high subsonic cruise flight. The McDonnell Douglas C-17 is currently wearing winglets. Over the past 20 years, my company has built several pairs of winglets for the model C-17 that our company also built. This model runs or has run in the Nasa Langley National Transonic Facility, or NTF. Some of the design changes are so subtle that you can't see them by comparing, while others are a radical departure to what would be considered normal. Usually, the test engineer is not only a test engineer for models, but also an aeronautical engineer that plays a major role in the final design of the aircraft. It is through conversations with these people that I learned about winglet design vs. benefit to performance. The guys from one company told the big boss that the winglets produce only a small amount of drag reduction on a certain new clean sheet design. He said, "I don't care! All my airplanes will have these winglets! End of discussion." It's kind of neat being in that loop of initial aircraft design and testing of the first models. The F-22 Raptor has done well by me over the last 18 years, when that design got going. Now I can occasionally see one fly over.

RE: Winglets
 

Be carefull with tip-plate alignment. A small "toe-out" error results in a violent roll into the toed-out wing.

RE: Winglets
 

Adam.......Winglets already installed on many new generation 737-700,800,900.....Southwest, Continental,Westjet , also Continental using Winglets on their 757's as well, just to name afew........biggest consideration is fuel efficiency...as price of Jet-A nears $1.50/gallon.....average fuel consumption drops an average of 3%........sounds minimal, but over lifespan of an aircraft that can save alot of money......I added winglets to a Great Planes Patriot some years ago, using the same dimenesions and angles as a 747-400......certainly looked neat but the biggest thing I got out of it was how straight it flew........all maneuvers just were more crisp.....seemed to fly on "Rails", no matter what I did with it.........also it wqas quite fast, but no way to really tell if winglets had anything to do with the speed...............but still was tons-of-fun................Bill

RE: Winglets
 

Can someone kindly explain the difference between wing: ...lets, ....caps, and ...plates. I have a .60 glow powered 3D plane that has what I consider a poor wing tip design because the iron on covering of the wing tip formers (which parallel the main wing spar) leaves several very deep depressions between the formers which cannot possibly have smooth airflow. I was thinking of cutting off the wing tips and replacing with plank balsa glued to outer rib with an angle of about 30 degrees from front to back, maybe 1 to 1.5 inches above and below the wing at the trailing edge. This is a square wing, symetrical airfoil, 100% span ailerons.

I have to buy a ticket to get anywhere close to a 747, and then they won't let me try to put winglets on it.

RE: Winglets
 

Maybe shrink the covering with the heat gun to get out those depressions would be better than chopping up the wing tips???

I'm not sure about winglets adding enough mass to have any effect on rolling moments past the wingtip vertices improvements. Maybe mass would help rolls instead of resisting them.

I'm not sure that winglet designs will help controllabillity during slow flight.

RE: Winglets
 

Due to the expansive empty spaces in my mind, I have no clue what you mean by ... "rolling moments past the wing tip vertices" ... Are you refering to the aerodynamic effects of the vortex rolling off the wing tip affecting the roll of the plane? I was wondering if winglets as I described above would smooth out the airflow enough to be worth the trouble. Maybe reduce wing rocking at high angles of attack near stall speed?

RE: Winglets
 

A tip plate...This is a semisymetrical airfoil, so the shape also extends below the wing, to about half the distance lower than the wing surface as the upper.

And oh yeah, they'll increase the roll rate. They'll also allow slower approach speeds with better aileron authority near the stall.

RE: Winglets
 

SST,
Have you ever experimented with a tip plate that is a constant overhang all the way around, including the leading edge? I was,(am), going to try some tip plates on my two planes, an F90 and a Harrier 46 to see what effect they have on knife edge flight. I like your design. It looks good, and I guess the reason for not having them forward of the leading edge is to keep them from snagging in the grass should you drag one.

RE: Winglets
 

The reason for that particular shape, I must admit, is purely aesthetic. However, I believe the majority of losses occur at the midpoint-to-trailing edge area. I didn't think the possible benefits of a forward overhang outweighed the aesthetic drawbacks, as life's too short to fly ugly planes! ;) I also have a similar set of plates on a Sig Ninja, that I've powered with a Norvel .074, and My flying buddies thought enough of them to add them to their Combat Gremlins...

RE: Winglets
 

I just added a pair of tip plates to my F90. They are flush back to the spar, then taper up and are cut like yours. I will fly it tomorrow and see if there are any performance changes. I also moved my cg forward a little to keep it from ballooning on landing. Hopefully, I will be able to tell how much the plates do with the cg shift happening at the same time. I agree on the ugly. My tips actually look very nice.

RE: Winglets
 

Very nice. My TE shape is pretty much the same as yours. I think you'll see a noticeable change in roll & low-speed handling.

RE: Winglets
 

i don't need the plane to fly any slower, and the roll rate is too fast already. What I am after is the high alpha flight in both pitch and yaw. High alpha knife edge and harriers to be specific. We shall see.

RE: Winglets
 

No, what I meant to say was it should not help past the subject of helping reduce vortices. However, maybe roll rates will improve, especially if ailerons run close to the wing tips. It would seem that tip plates and winglets would give ailerons more undisturbed air to work with.

I've wondered what tip plates would do to a Somethin Extra. I may tack some on tomorrow if the weather cooperates.

RE: Winglets
 

Thanks for the pictures. I am still in the flight test and set up phase. After I get it all set up, adding the tip plates will be the last thing I do. At least they do look better than the ugly wing tips it came with.

RE: Winglets
 

Okay, here's the flight report. Basically, they worked! The knife edge is much improved as it locks in now and doesn't hunt like it used to. The coupling has mysteriously vanished as well. As for the roll rate, I fly on low rates most of the time, but when I switched to high rates to try some rolling harriers, I couldn't use full aileron. It was simply too fast. Landing speed is the same. I did make a cg change at the same time, so I think that may have helped in the KE as well.

RE: Winglets
 

Cool! [8D]

RE: Winglets
 

I ran coro tip planes / winglets (not sure which they were technically-speaking) for a couple years on my B class combat planes. I found they had a couple of effects:

- delayed the onset of tip stall, so I could turn tighter. Noticeably tighter.

- decreased (eliminated) aileron flutter problems

- increased over all aileron effectiveness.

- (RC Combat specific) sometimes helped keep streamers from sliding off the wing. (note, due to combat rules, mine didn't extend forward of the LE)

If I recall, they extended up 2" above the wing at the TE and 1" below the wing. At just past the LE, they were about 1/2" above and below the wing

http://www.wheek.org/airplanes/1fsa2.jpg

RE: Winglets
 

Montague,

Always liked your icon.....

I think those would qualify as tip plates. I think you need a lifting effect airfoil to be classified as winglets. Winglets have mostly lateral lift vectors with some vertical component, but not much.