Winglets, and their effects or not..

[Sparky Paul]

I just completed a couple of tests looking for the drag effects of winglets, based on a question from a guy that wanted to reduce the tip vortex, so he fly faster than his buddy with the same plane.
I don't have a plane in his speed range, 140 mph, but I do have a ZAGI™ lying around with tipplates on the top side.
Based on Dr. Eppler's demonstration that a down-going tiplet has more drag than one going up, I added down-going tips on both sides, and flew the plane in 4 configurations:
With everything, to get a base-line feel and value for the lateral trim.
Then removed the down-going tiplet on the left side, and flew again.
Then removed the up-going tiplet on the left side. and flew again.
Both power on and power off the trim kept coming back to the same value.
As there MUST be some effect, I intuit the effect is 1) very small, and 2) is discernible only over a longer period of time than the test plane permits... (goes out of sight)
Martin Simons says the effect of a winglet is so small anyway it's difficult to detect.
I think a value of less than 1% for these test conditions, based on the lack of obvious trim change for the airplane tested is a good number.

[watnsee]

your winglets will have more affectif they had a semi semetricle air foil . they will act as a venturi over the tips thus speeding up and holding the air on the wing.

[Sparky Paul]

The test wasn't to find a "better" shape. just a way to see what is the most basic effect.
The down-turned tip "adds drag", according to Dr. Eppler. The turned-up tip also "adds drag", just less. Drag + more drag=?
Adding drag that needn't be there....
The limited range which tiplets work best isn't found on a racing plane, which goes fast... AND turns tightly..

[DaveGherardini]

I have been searching for valid test data on windtunnel data for different shaped winglets . I havent had much luck. Paul your tests seem to line up with what i figured it would be. So small in visual performance thats its to hard to tell. Ive seen major claims on improved performance in winglet shape for wings but have yet to find any valid windtunnel testing on all of the claims to sell me on. I have found that my wings seem to fly faster with out them. but slow speed handling gets less stable. But that make sense to me because its just more drag at higher speeds.(lift is drag thing). with your knowledge i wish you had some way to do drag annalisys in a tunnel, To cut the fine line on the last 1% or so of the best shape for flying wings....thanks for sharing this info..dave

[DaveGherardini]

watness,

dont take this in a mean way please. im just curious

"act as a venturi over the tips "

could you explain this to me. I think your saying that your winglet has a cambered foil shape with the lifting side toward the center. If so then i would think that it would disturb the boundry layer creating more drag or turbulance on the tips. Am i thinking correct? This is a good discussion...thanks ..dave g

[steve wenban]

guys I work in the field we you are talking about and the wing fence are more effective than the winglet their is just no real hard evidence that any great benfit has been gained by using winglets
747/400 used them I worked under them for 2 years Airbus fitted them to the A330/340 because the 747 had them and it was a selling point . Small improvements have been made in fuel ecomony which is a bit of an advantage when your burning it by the ton 737/700 start to use them and even retrofitted them to -400 ,-500 -600 models butthe aircraft can still be ordered with the lets. and now to top the whole lot of Airbus has put them on the new A380 but heres the catch on the A380 they have gone back to fences that happen to look like winglets hope this didnt bore anyone

[Purdue Aero Man]

The whole point of winglets is to control the tip vortex, as you all probably well know. A very well designed winglet can reduce the induce drag of the wing greatly enough to overcome the drawbacks such as increased wetted area and structural requirements for the winglet. A poorly designed winglet won't help you as much or may not even help you at all. For a little better explanation of their affect, try this link http://aero.stanford.edu/reports/nonplanarwings/CWingTheory.html

[DaveGherardini]

"genetic algorithm " from the stanford link

what is that. that page looks good but i dont understand it. I agree that a winglet can reduce the magnitude of a vorticy because ive seen it with my own eyes. However the tunnel i verified it in only had constant flow. It didnt max out the envelope of the test wing, But on a flying wing the visibility with winglets help when its away on it edges from you. A big advantage.
"Control tip vorticies"
well, yes , that would be cool. I wish somebody could show how they acheived proof. Dont take this in a mean way there Purdue aero man. Im just looking for tunnel testing proof. Heck maybe these guys at S were using a tunnel. I dont see there comparison to a non-tiped wing in the artistry renditions . good stuff here you guys...dave

[Sparky Paul]

The tunnel test would be a definitive method of determining the effects, but if the effect is truly 1% or less, the tunnel has to be a very good one! :)
Blowing a kitchen fan thru a box with a dietary scale for a balance may be a few orders of magnitude too gross. :)
A side effect of this is my interest in reducing the "head-shaking" my sloper ZAGI™ planes exhibit. The powered plane somewhat less so, but it does shake.
Yesterday with all tiplets off the shake was more noticeable but it has the central vertical area of the motor/battery cover.
.
I have a sloper ready to try when the wind decides to cooperate, but for this observing the head-shake changes will be more important than any drag change.
The sloper flies much slower the powered version.. same size wing.
And I think this phenomena is speed related.. the faster the plane the smaller the effect of a tiplet.

[Sparky Paul]

Flew the powered ZAGI™ today, sans the tips.
The head-shake is most evident at the turn-around in a 1/2 pipe. Less pronounced when the speed is higher.
Odd rolling behavior.
Axially, at times it would hesitate at about 200° around, then continue.
And there is a distinct "hang-time" 1/2 way thru the roll in an Immelmann.
Appears to be a lot of yaw then.
I think I'll put a few feet of cassette tape on each tip and try it again tomorrow.

[Sparky Paul]

Originally posted by DaveGherardini
watness,

dont take this in a mean way please. im just curious

"act as a venturi over the tips "

could you explain this to me. I think your saying that your winglet has a cambered foil shape with the lifting side toward the center. If so then i would think that it would disturb the boundry layer creating more drag or turbulance on the tips. Am i thinking correct? This is a good discussion...thanks ..dave g
.
There's a mod to the home-built RV-4, which uses a chordwise tube at each tip to "eliminate" the tip vortex.
Done in France, with a claim of wind-tunnel verifcation at Dassault.
Seems to be one-off so far as I've encountered.

[Ollie]

I'd sure like to know how to eliminate the tip vortices without eliminating the lift at the same time. That is a goal that all sorts of people have pursued without much success for close to 100 years. The birds have been at it for a lot more that 100 years and they haven't had much success either.

[Sparky Paul]

I made a flight late yesterday (another beauuuutiful day in the Antelope Valley, couldn't not fly! :) ) with audio cassette tape streamers on each tip.
Photos didn't show much of anything, but the streamers did provide a reference for heading/yaw.
I noted that the plane would yaw -into- a turn.. towards the upgoing elevon, then straighten out.
I added a stick to the bottom to give a long FRL and flew again today.. (another etc..)
and by anticipating the effect fooled the camera into taking photos at the right time.
(I hate auto-focus! )
Here's one of the better ones..

[Sparky Paul]

I reinstalled the standard ZAGI™ tip plates, with extensions below the wing on the powered plane.
Found 3 things... the roll response was "crisper"... faster rate.
The proverse yaw was still present, but much less obvious..
But most interesting the cassette tape streamers, which had shortened by about 50% on the tipless flight hardly changed length at all, although starting at the same 4' more or less..
Attached at the chord line on the plate, not the top or bottom

[Dax]

All I know is this, my PCW flies great with winglets, and wont fly further than I can throw it without them.

[vintage1]

On machines with virtually no side area, wingletes are more like ridders, controlling yaw rather than tip vorices.

[Sparky Paul]

Something relative to the tip activity is going on there.
Lots of tape erosion without the plate, very little with it.
The effect on yaw is undeniable of course, plate on or off.

[vintage1]

Oh. I didn't understand what you menat. You mean there are more vortices ripping up the tapes without winglets. That figures.

You could also try what birds do - have the wing tip broken into a lot of little 'feathers' with a gap between each. That is supposed to reduce drag on birds that have to have short spans to manouver in trees etc. As opposed to gulls, which have long thin wings instead.

[Sparky Paul]

Earlier today I put one of the tapes at the tip of the right plate and flew the same sort of stuff.
The tape didn't get shorter, and neither side shows the burbles along their length the tapes on the no-tipplate tests indicated.
There may very well be a benefit to a tip-plate versus none at all.
I expect any benefit would be too small for any but the best tunnel to find, though..

[Sparky Paul]

I'm thinking that maybe the milli-ounces of tip vortex drag a winglet decreases might be of no use to a manuvering plane, but for TD or XC, milliounces less drag per second can be ounces over the long term.
Another thought is the plate at the end of the moving surface can eliminate the excitation of the tip vortex when the surface moves. I've seen mighty waves go down our trailing cone hoses from rudder motions showing there's a lot of energy being used there..

[tjr]

Sparky Paul,
That last picture looks a little familiar and your location tells me why; I used to work on the B-2's at Whiteman AFB. The April issue of RCM has an article on wingtip design and the bottom of pg. 114 has a picture of the land "bird" slotted tips.

[watnsee]

I have a large glow powered aircraft designed to produce large amuonts of lift for a local cargo contest. Power is limitted to a .40glow. 132" span. Testing winglets now . the tape is a great idea!!!!so for ,22lbs with a seven pound plane.

[Sparky Paul]

Originally posted by watnsee
I have a large glow powered aircraft designed to produce large amuonts of lift for a local cargo contest. Power is limitted to a .40glow. 132" span. Testing winglets now . the tape is a great idea!!!!so for ,22lbs with a seven pound plane.
.
We GOTS to see pictures of that!
Please?????

[watnsee]

here are the pics I have.

[watnsee]

another one.

[watnsee]

and lastly.

[Sparky Paul]

Looks very good!
Lots of lightness inside, where it counts. :)

[Bob Reynolds]

Go to Jets, Tucson Jet rally Photos and take a look at my Probe. My son says that the plane is very groovy and thinks the tips help,

[Sparky Paul]

Originally posted by Bob Reynolds
Go to Jets, Tucson Jet rally Photos and take a look at my Probe. My son says that the plane is very groovy and thinks the tips help,
.
Although "thinks" and "feels" and "seems" are commonly used to describe the effects of changes, in essence these are not quantifable terms.
That's why I chose the test procedures I used. If there was an effect which would affect the trim of the plane, it should have shown up on the trim indication.
As nothing was noted, the effect, which must be there, is too small to be identified using that procedure.
And at a probable value of less than 1%, of little importance relative to all the other things which can change performance by much larger percentages.
I did note the roll response was "crisper", another non-quantifiable term, without any meaningful basis except I preferred the response with the tip plates.
Someone else may not care to notice.
A test for this new parameter would involve using equipment which could quantify the roll response... say a video camera to measure the roll rate with and without the additions.
Picking out the effect of any single change to an item requires choosing how to measure the change.
And change -only- the item being tested.
It can be a rigorous task to isolate all the variables which could affect the situation and narrow in on the item of interest.
The non-shortening effect on the tape streamers was completely unexpected.
The streamers I've flown on various airplane-always- erode.
The non-shortening effect was noted only after the flight with the tip plates; it wasn't expected at all.

[MartinL]

My experience..it reduces stall speed on a 1/4 scale glider.
It is more effiecient, less drag..that is why most modern
gliders have them.

[green66]

Here are four winglet articles Winglets (scroll down) (http://www.mandhsoaring.com/winglets.html) by the designer of several winglet config's used on some well-known FS gliders, I believe several Schleicher ships and the Ventus.

[Majortomski]

Back in my younger days when the 1:1 world was going winglet crazy we had a project to put winglets on the good ole KC-135 and save gazillions of gallons of jet fuel so we could pay for the CFM-56 engine conversion. In fact the winglets would make the fuel guzzling, smokey, waterburnin J-57 powered KC-135A so efficient that we wouldn't need the CFM-56s.

End result. On a very very very instrumented stock tanker, with variable sweep, incidence and dihedral angle on the winglets to obtain the absolute best performance. Fuel saving amounted to less than 3% at only the OPTIMUM cruise. In some cases they raised the fuel burn.
AND
The increased air loads were too much for the lower skin on the outboard wing.

End of that program, on with the CFM-56's on the KC-135R
Which by the way was a purely political designations so that the powers in charge could understand that we were talking about the KC-135RE-Engine program
Tom

[deh6]

Nickel & Wohlfahrt, Tailless Aircraft in Theory and Practice, talk about the “pendulum dive,” which they think only occurs with swept-back flying wings that have winglets. As they describe it, under some conditions when the wing stalls, rather than spin, it goes vertical and oscillates yaw-wise. What makes it bad is apparently, it is almost impossible to break the oscillation (except when it hits the ground!). They observed this in several models.

One model that had rudders on the winglets coupled to the ailerons did not have this problem. The most reliable way to break the oscillation was to apply full aileron to make the wing rotate, thus breaking the side-to-side oscillation and converting it into a spin where the usual recover method will work.

BTW, I just received my copy of the book. It became available in March. AIAA has had it reprinted. A great book for understanding and designing flying wings.

[Sparky Paul]

I've heard of and experienced the ZAGI™ "death spiral"™ which is an artifact of an aft c.g., but not this yaw thing.

[DaveGherardini]

Sparky Paul, did you try any different shapes of winglets on that wing? just curious, i wonder if there is an optimum shape for a flyin wing of that configuration and what it would be.. i should find a cassette and try myself.....good stuff

[Terry I]

Fwiw, my experience with winglets were quite dramatic...the IFO on the left loses it after about 8mph winds, the RocketBird flies happily in 18, gusts to 23 :)
..they also created a stability akin to feeling like you're riding on rails...with nice crisp rolls as well

Off Topic: Sparky, I'm trying to work out balanced elevons on this thing, as I've hit a speed/servo wall...Dave Hederich mentioned you did a thread on them. Can't seem to search it out of hiding...Wondering if you could provide the link and/or stop by and put in your 2 cents? Tia
http://www.rcgroups.com/forums/showthread.php?postid=2026412#post2026412

[Sparky Paul]

Originally posted by Terry I
...
Off Topic: Sparky, I'm trying to work out balanced elevons on this thing, as I've hit a speed/servo wall...Dave Hederich mentioned you did a thread on them. Can't seem to search it out of hiding...Wondering if you could provide the link and/or stop by and put in your 2 cents? Tia
http://www.rcgroups.com/forums/showthread.php?postid=2026412#post2026412
.
I must be having a senior moment.. I don't recall anything like this..
But to aerodynamically balance the surface, put the hinge line at 25% of the mac.
To statically balance it regardless of hinge line, add weight ahead of the hinge line so the surface floats level, when not connected to the servo.
The streamlined things seen on some planes that look like small bombs, usually dangling off the bottom of the surface..

[Sparky Paul]

Originally posted by DaveGherardini
Sparky Paul, did you try any different shapes of winglets on that wing? just curious, i wonder if there is an optimum shape for a flyin wing of that configuration and what it would be.. i should find a cassette and try myself.....good stuff
.
Dave, I've used only the ones you see. Theory says a true tip plate should be about 2 chords long and high. Ugolee!!!
I was interested in first seeing if there was a detectable effect on the plane, and second to get rid of the head shaking of the wing.
At the speeds the things fly at, there's almost no way to detect a change in performance, other than that something does happen, and the head shaking is diminished.

[Terry I]

Sparky..I'll tell Dave HE'S having a senior moment :D

Thanks...that balancing act was the missing link I
was looking for:)

[Dave Hederich]

Gentlemen, we are all growing older together. ;)

Terry I, I was talking about control surfaces in general, not elevons specifically.

Sparky Paul, I'm sure you'll remember this thread:

http://www.rcgroups.com/forums/showthread.php?s=&threadid=124489

[Terry I]

Hail Seniors! :D