Winglets

[NewbieX]

So if winglets make a flying wing more efficient, do they also work on a more conventional plane as well?

I've noticed that some commercial airliners and business jets have them as well as Zagis and hand-gliders.

So when I get busy building some new model should I consider winglets or is it a negligable difference in actual performance?

[RD Blakeslee]

On airliners the winglet interupts the tip vortex and slightly decreases induced drag (important in that application).

At the wing loadings and speeds we fly, they probably aren't worthwhile for that prpose.

In typical model flying wings, where the wingtips are well aft of the center of pressure, they work as vertical fins and increase stability about the yaw axis - a little help - not much.

They can also be used to firmly hold washout angle steady , if you add that to decrease tip-stalling. Cut off the outer couple of inches of elevon, angle it upwardly five degrees or so, and glue the outbard end to the inside of the winglet. You get increased stability at the expense of roll rate.

For me, winglets mainly work to take the beating my typical "landing" gives the wingtip and outboard end of the elevon.

[Andy W]

Winglets on full-scale aircraft are extremely precise aerodynamic devices that improve the efficiency of the wing by a few percent (but a few percent can make all the difference in competition, or a large savings in fuel, for example). The ones on flying wings are strictly there for yaw stability.. these models fly just fine without them in calm conditions..
..a

[Slope Nut]

I dont know if they actually add any performance enhancements, but they sure look cool :) My CL-415 is going to get a set to round off its look

[DeaninMilwaukee]

My friend Bruce added winglets to a faster sport plane of his with very positive results. The plane was obviously faster with them than without, and had better duration as well.

It seemed like his total drag was reduced a fair amount.

The downside came in rough air where they seemed to give the wind something to push against, and made the plane seem slightly unstable, hunting around.

I calmer air though, they definately worked.

This was a non tapered constant chord wing BTW.


Dean in Milwaukee

[Sail 'n Soar]

Last year I attended a lecture on winglets by one of the full scale German sailplane designers/builders. For sailplane racing they are trying to improve performance even a small fraction of a percent for a competitive edge. Winglets are primarily limited to the 15 meter designs, where they cannot increase wing span due to sailplane class restrictions. There conclusion was that winglet design is critical. Winglets may decrease drag in one part of the operating envelope, but at the expense of another. It was a very tough task developing a design which did improve overall performance.

I don't think anything in our model work is that precise.

[Sail 'n Soar]

My friend Bruce added winglets to a faster sport plane of his with very positive results. The plane was obviously faster with them than without, and had better duration as well.

Because they are added to reduce induced drag, which reduces with speed by the square of the lift coefficient, the drag from the added area and corders, etc., will probably offset the slightly reduced induced drag at top speed for a faster sport plane. The benefits might be retained in high G turns, but not straight and level flight.

Dean in Milwaukee: Can you provide more detail on how the plane was faster?

[DeaninMilwaukee]

Here goes:

We, ( Bruce and I) were having out own informal " power wars " last year, trying to make faster sp500 powered planes to race against each other. :D

I had the advantage in raw power and was using motocalc to come up with geared systems to gain advantage for my ugly pink foam jobs through brute thrust, where Bruce on the other hand was striving to be as sleek as possible, to allow his cheaper DD setups to fly fast.

The week he showed up with his tiplets added, I was ahead in the power race, and could fairly easily pull away from him to about 10% faster.

That week, with only the adding of the tiplets, ( big ones BTW, 1/2 vert stab area, and swept well behind the TE.), he could suddenly stay with me, and was staying up as long as me as well, even though he was running 1500 cells instead of the 2400's I was.

It convinced me. :eek:

[Sail 'n Soar]

OK, you've convinced me they worked in Bruce's case. Was his wing without the tiplets a relatively low aspect ratio short and stubby thing? Would sure like to know what's happening.

[DeaninMilwaukee]

It was as constant chord, somewhat thick ( 12% therebout's) full sym wing of about 40 span and 10 chord. Wing tips were slightly rounded before, and then flat with the tiplets.

The plane weighed about 45 oz I belive.

It really flew very well considering it was only pulling around 20 amps on 8 cells.


Dean in Milwaukee

[Sail 'n Soar]

Dean,

Another way of looking at the affect of winglets is they increase the effective span and aspect ratio of a wing. Normally increasing the span and aspect ratio provides a better balanced solution to winglets if you are not wing span constrained. Winglets also provide a structural weight savings advantage by adding a smaller wing bending load compared to what increasing the span would add.

I am thinking about building a plane with a similar wing geometry to your friend, Bruce's, (40" span, 386 sq in.) with a geared AF 020 sensorless but at around 33 oz AOW and without winglets. In my what-if's I've tried increasing the design span and aspect ratio, which would simulate the induced drag reduction benifits of winglets. While there are some improvements, I can't come up with the sort of top speed and indurance advantages your friend is seeing.

Only thing I can figure is that his form drag must be much lower than what I'm assuming. Can you send a picture?

'tis a mystery.:confused: :confused:

Gerry

[DeaninMilwaukee]

I could'nt find a pic of that plane, but I was able to find a pic of his smaller sp400 powered version that came first. The bigger one was essentially a scaled up version of the one in the pic.

http://www.rcgroups.com/forums/showthread.php?s=&threadid=20994

This smaller one is actually a Lanier dominator 200 that Bruce modified by stretching out the fuse to accomodate a sp480 and 8 600ae's. The dominator needs the nose extended to balance too.

Bruce ahd also modified this one by stretching the span 1 extra bay. It really was an amazing flyer, way better than the sum of its parts.

Dean in Milwaukee

[Sail 'n Soar]

Thanks for the pic. That's one serious air ship. Nothing much to slow it down. It's definitely beyond my presents flying skills.