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Author Topic: Winglets  (Read 1127 times)

Online Dave_Trible

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Winglets
« on: April 13, 2022, 10:14:21 AM »
So I was just reading about how most newer airliners and some older ones are being fitted with winglets.  The benefit for the airlines is improved fuel economy,  around 5% which is very meaningful in the long haul.  For our purpose I’m not interested in that.  However they say another real benefit is how much smoother the winglets make the airplane fly through turbulence.  I could see benefit in that for stunt.  I may retrofit an old airplane and try it.  Has anyone tried this in our application?

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Online Ken Culbertson

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Re: Winglets
« Reply #1 on: April 13, 2022, 01:05:45 PM »
So I was just reading about how most newer airliners and some older ones are being fitted with winglets.  The benefit for the airlines is improved fuel economy,  around 5% which is very meaningful in the long haul.  For our purpose I’m not interested in that.  However they say another real benefit is how much smoother the winglets make the airplane fly through turbulence.  I could see benefit in that for stunt.  I may retrofit an old airplane and try it.  Has anyone tried this in our application?

Dave
I put something similar to winglets on a Jetco Dolphin back in the mid 60's.  It consisted of tip plates about 1" above and below the wing.  I don't think they did much or I would have remembered.  There were some planes I saw with what they called a "skyhook" on just the outboard wing.  Don't think that worked either!

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Offline Trostle

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Re: Winglets
« Reply #2 on: April 13, 2022, 01:12:35 PM »
I can understand how those winglets on the airliners help fuel efficiency.  This means those winglets help reduce drag.  Those are on wings of the airliners with high aspect ratios and a lot of taper compared to our stunt ships.

Drag is not a primary concern with our stunt ships.  Otherwise, we would not be flying our stunt ships with their 15% to 20% wing sections, comparatively much lower aspect ratio, and a very small amount of taper.

I wonder how they could benefit our stunt ships doing inside and out side maneuvers.  Will it be necessary to put "winglets" on the bottom of the wing as well as the top?

Keith

Online Dave_Trible

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Re: Winglets
« Reply #3 on: April 13, 2022, 01:15:24 PM »
That article spoke about tip plates- sort of what you are talking about- and said they helped but weren’t as effective as tips that rolled or curved up.  Some 737s have winglets that roll both up and down which is the way I’d fashion a trial airplane.  The principal is to prevent the topside and bottom airflow from rolling around the tip and joining into a real drag inducing tip vortex.....

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Re: Winglets
« Reply #4 on: April 13, 2022, 02:03:57 PM »
The airspeed difference is so huge that I wonder what, if anything really applies. 
550-650mph for an airliner at 30,000 ft vs 50-60mph for a stunt ship at ground('ish) level.
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Online Dave_Trible

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Re: Winglets
« Reply #5 on: April 13, 2022, 02:38:10 PM »
Yeah that’s what we wouldn’t really know till we tried it.  The principal is still valid.  I think if we can get those tips through the air cleaner in turbulence the airplane should remain more stable and perhaps not accelerate and decelerate side to side as the airplane goes around the circle continuously reorienting to the wind-  maybe.

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Offline Dave Hull

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Re: Winglets
« Reply #6 on: April 13, 2022, 11:03:28 PM »
I'm more than a little skeptical--for numerous reasons.

First, go read about the original Whitcomb winglet design. It has both upper and lower surfaces, each with very specific yaw "incidence" angles. Of course, all optimized for upright flight. While current industry designs have moved on, you can begin to understand what the engineers were trying to do. (Lower winglet projections are not very damage tolerant. It doesn't matter if you gain another .01% efficiency if you can't taxi out due to damage sustained in the gate area....)

Essentially what you have is a wingtip flow control device. It fools the airflow into thinking the wing aspect ratio is much higher. The same thing could be accomplished by simply making the wing longer, but hanger sizes are fixed, and gate separations etc. are what they are.

An interesting plane to consider is the Stits Junior--at one time the smallest manned plane in the world. Practically a square wing. With tip plates to fool the air into thinking it was a larger wing. There is a CL model design by D.B. Matthews (MA Oct. 1978) that I was reminded of just the other day. Always wanted to make one of those....

As far as "behaving better in turbulence" my first thought is this:  military aircraft are designed with something called "ride quality" or how harsh the vertical accelerations due to turbulence are. If you have a plane with a lighter wing loading, the ride quality suffers. If you take an airliner and keep the projected wing area constant, but add winglets to fool it into behaving like a higher aspect ratio wing with more area, you might keep the original ride quality but gain in efficiency, most easily measure in glide ratio. Hence, on business jets and Rutanian objects, winglets are de rigueur...

If you want to get a modeler's take on this at relevant airspeeds (although admittedly it is based on testing of R/C glider wings) go find the old article in Model Aviation. As I recall, it was actually a pretty good technical article which had an extensive test program.

Dave

Offline Dave Hull

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Re: Winglets
« Reply #7 on: April 13, 2022, 11:19:38 PM »
Ok, just found the MA article by C. Anderson on winglets. May 1980---back when modelers tolerated more technical articles in their publications....

One paragraph of perhaps some relevance to note:
"As might be expected, the large side area of the winglets makes the model more sensitive to gusty crosswinds. This same sensitivity to lateral disturbances also causes the wings to rock when flying in the vicinity of lift."

Now these were large winglets intended to increase glide ratio within a fixed wingspan rule. No such constraint would be on a stunt model. Still, I think you would find that a highly tapered wingtip or tapered overall wing might provide a similar intended benefit?

A take-apart plane would be an ideal testbed. If the new wing was terrible, it could be replaced without abandoning (or reworking) the model.

D
« Last Edit: April 14, 2022, 01:16:07 AM by Dave Hull »

Online Dave_Trible

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Re: Winglets
« Reply #8 on: April 14, 2022, 07:41:30 AM »
Interesting points Dave.  I can see some awkward handling of an airplane with winglets in and out of the car, house etc., and would likely break something at least once.   Also size- wouldn't know where to start.  The smaller the better due to weight if nothing else.  Construction?  Not easy if truly curved.   I think I would keep them under four inches above and three inches below the wing surface.  At that there wouldn't be much ground clearance.
Not sure I want to invest the time in a whole new airplane until I convinced myself it was worthwhile unless maybe a profile I could build in a couple weeks.  The other thing is you would like a base line to compare it to.  If I used an old airplane with known flying qualities I think I could tell what differences there are.......more questions than answers..

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Offline Dave Hull

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Re: Winglets
« Reply #9 on: April 14, 2022, 08:31:05 PM »
Ty, Ty, Ty,.....   The only place you should be using bait anymore is on the end of your fishing line....

Dave,
I think the easy way to get some practical testing done is to use something like a Twister with squared-off wingtips. Put a couple of threaded inserts in it. Maybe consider some pins to ensure alignment. Then make however many bolt-on tips that you'd like to try--or have the patience to build. Could be a lot of fun flying them back to back. And maybe you'd find one set good for still air and one set good for gusty winds? Who knows?

Were it me, I'd also embed some kind of incidence adjustment into the tip. From the prior MA article, flight characteristics seemed to be sensitive to that. No point in gluing that setting in and missing the sweet spot....

The fins could even be made to plug in to different tip blocks using some 1/16" music wire joiners in brass tube sockets. The forward socket could be your pivot for the aforementioned incidence adjustment. Lots of ways to do this. I would also note that in order to compensate for moving the center of lateral area forward, that you might need to retrim by adding a tab on the vertical stab to get back where it was. As usual, changing one thing may unknowingly change others that affect the results.

One thing I would watch out for, or maybe even expect, is that you might end up with a yaw oscillation as the inner and outer winglets try to establish some kind of constant loading. I've seen this on slope soaring flying wings. It that configuration, you can easily end up with a dutch roll tendency where the toe-in tip fins couple with the dihedral of the wing. I have seen the oscillation on flat wings, too. But there the dynamics seem to be a pure yaw jiggle, not dutch roll. So getting the yaw incidence just right, and maybe tripping the boundary layer so it is more consistent seems like something to try in this experiment.

Dave

Offline Mark wood

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Re: Winglets
« Reply #10 on: April 16, 2022, 09:12:55 AM »
Only one way to find out. One or two of you engineer types, do this, report back with all the formulae and dazzle us. We wait with baited breath, honest. H^^ y1 #^

Ok, I'll bite. Winglets are a point design type of device and would likely prove ineffective for a CLPA airplane which requires symmetry in performance. Winglets on airliners are designed for cruise operations at some narrow range of operating conditions. Their function is to balance the pressure top and bottom of the wing to reduce the roll up of vortices' and associated induced drag. As such they would not work equally well both upright and inverted. Pretty much makes them a non starter. End plates on the other hand would perform quite well as they fence off the end of the wing. Trouble is twofold. First is the susceptibility to damage. Second is they have inherent parasitic drag and achieving a balance of improved reduction in induced drag vs parasitic drag is a challenge. Oh, there's a third trouble with end plates which in engineering terms is known as fugliness extremedness maximus which also makes them a non starter. I have experimented with both on FF models and they do work but the susceptibility to operational damage reduces their desirability. 
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Online Ken Culbertson

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Re: Winglets
« Reply #11 on: April 16, 2022, 11:15:07 AM »
I have experimented with both on FF models and they do work but the susceptibility to operational damage reduces their desirability.
Most of my A-2 and 1/2A gas planes had upside down winglets.  Can't remember what we called them way back then but the word fuggy never came up, except at parties. LL~

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Offline Mark wood

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Re: Winglets
« Reply #12 on: April 16, 2022, 12:14:07 PM »
Most of my A-2 and 1/2A gas planes had upside down winglets.  Can't remember what we called them way back then but the word fuggy never came up, except at parties. LL~

Ken

Back in my earlier days, a little damage wasn't such a big deal but as the performance of he models improved to a level that the number of maxes increased to a level that flight cycle rate became the biggest challenge, having to stop and facilitate repairs became more of an issue. Hoerner style droop tips work pretty good for slow speed gliders STOL aircrafts but pay a drag penalty on faster moving aircraft. The early Boeing style wingtips are a very good general purpose option. We call them swept or Flight Streak style wing tips.
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Online Dave_Trible

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Re: Winglets
« Reply #13 on: April 16, 2022, 12:59:13 PM »
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Re: Winglets
« Reply #14 on: April 16, 2022, 01:00:07 PM »
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Re: Winglets
« Reply #15 on: April 17, 2022, 01:50:12 PM »
I think I would try something like these Boeing-style winglets.  They would be of a wider chord simply because we don't use real highly tapered wings.  I think getting them aligned will be quite important.  I can't think of why I would want them adjustable as long as I got them set straight-away the first time.  If they proved themselves worthwhile, I could see making them from carbon down the road for weight and durability.  Heck maybe even a single wheel gear with tiny drag wheels in the lower winglets.......

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Offline Tim Wescott

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Re: Winglets
« Reply #16 on: April 17, 2022, 02:54:06 PM »
Mentioned already, but winglets basically reduced induced drag in a similar manner to more span.  In fact, with winglets, you have to cant them so the "lift" is inward, and you end up loading the spar the same as if you'd just made them stick out horizontally -- but also already mentioned, winglets mean that the plane fits in more hangers, terminals, etc.

I think that you'd find that winglets have roughly the same effect as high-aspect ratio wings -- less induced drag, so more windup in maneuvers.  You may not have more sensitivity to asymmetric turbulence trying to roll the plane, but you may have more sensitivity to cross wind.  To really get all the benefits, you'd need to extend the flap out to the wingtip, with an articulated mechanical nightmare joint, and you might need a degree in aerospace to get the correct relationship between the tip flap and the 'real' flap.

I'm with building a test plane that allows bolt-on wingtips.  Then make sure to fly it in bad conditions as well as good.  You may need to start with something that flies better than a Twister, like your backup plane's backup plane, or an Imitation, or a known-good ARF from Brodak, or whatever.
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Offline Dave Hull

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Re: Winglets
« Reply #17 on: April 17, 2022, 05:41:07 PM »
Dave,

Well, if you know you can hit the magic angles for your particular installation...then I can't think of why you'd want them adjustable either. Same as with adjustable tip weight, and adjustable elevator horns, or for that matter, adjustable pushrods for elevator droop (aka stab incidence). Hit it right out of the gate and don't look back....

But I guarantee you that the winglets on anything that says "Boeing" on the outside of it had both a ton of CFD analysis and wind tunnel tests. Iteratively. All flight regimes. Because they needed to find the sweet spot, too.

Dave

Online Dave_Trible

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Re: Winglets
« Reply #18 on: April 18, 2022, 08:00:21 AM »
I guess I don't have a clue what sort of a sweet spot I'd be looking for.  I'm not after glide endurance.  I'm looking to see if the airplane will cleave the "corn turbulence" at the flying field any better.  Under those conditions I doubt VERY subtle adjustments could be felt anyway.  I do know it will have to act the same upright and inverted, inside and outside so they couldn't be anything other than symmetrical in angular adjustment unless they were correcting some other fault like a warp or misalignment.  At that these are turned nearly vertical and so I can't see how a moving flap (if you could make it work without a concentration of weight at the tips) would accomplish anything I'm looking for.  This reminds me of something we say at work:  A giraffe is a horse designed by a committee.......:--)).

Dave
« Last Edit: April 18, 2022, 08:45:55 AM by Dave_Trible »
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Re: Winglets
« Reply #19 on: April 18, 2022, 02:06:51 PM »
Though tempted, I think I'll wait until I finish what I'm already working on at the worktable before I do much with this.  I just finished a new profile design that flies very well and I'm thinking I will build another like it but with winglets to compare.  Maybe could try them on a Shameless instead.  The swept tips would make that transition pretty easy. That one is quite good in turbulence as is so I may not learn much from it. What technical data I can find to read on the subject seems only to be interested in drag reduction for fuel economy or slow speed for glider endurance.  What I'm interested in is a noted side effect which is commented on but not studied much.  There may be something to learn about this for our application. 

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Offline Dave Hull

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Re: Winglets
« Reply #20 on: April 19, 2022, 02:13:29 AM »
Dave,

For your purposes, I would agree on the upper and lower strake being identical. But the point I have tried to make is that there may be an oscillatory yaw effect due to these winglets. I have seen it on gliders and it seems to vary with the speed of the plane. In other words, at the slowest speed it might be steady (no yaw oscillation) but if you put the nose down and pick up speed it starts hunting. And that tendency is affected/mitigated by changing the angle of the surface relative to the local flow. Before we all decide that this would simply not apply to a control line plane, we might consider the tribal knowledge of stunt wherein there is a benefit to a slight amount of positive incidence in the horizontal stab for a plane of conventional layout. Because people have empirically determined that doing this can be a preventative trim adjustment for conditions of pitch oscillations.

And we still ask the question: for a given wingtip shape, wing planform, and airfoil, what does the local flow near the tip do? And how do you place a winglet so that it does not simply deflect more flow than it needs to, potentially making a lot more disturbance which might vary with maneuver and flight condition? Ie. give you unexpected trim changes?

I think the Shameless is a great design. I also think that the unusual wing planform is part of the reason for it. And, as you say, that might make it a poor candidate for a winglet test bed. Better I think to use a fat wing with both LE and TE taper. Square tips that you can bolt different winglet systems onto. But, it's your experiment. And I do wish you the best....

Dave H

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Re: Winglets
« Reply #21 on: April 19, 2022, 06:28:40 AM »
Thank You Dave.  We won't know what to fix until we've made a few mistakes.  In this case it's a lot of guess work to start with.  I did sketch winglets onto the side view drawing of the new profile-looks strange from that angle!

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Re: Winglets
« Reply #22 on: April 28, 2022, 08:42:12 PM »


or whacking off the ' fins ' would get a 'V' in the ends of the wing , dual Horneor ? tips .  :(

works in the tangental plane , to aircraft . Dunno how much of a gimick it is ?

A TUBULAR wingtip isnt exactly a ' winglet ' , but as far as PURPOSE goes , it could do the trick .

Vortice & wake control .



Youd basically be using it to do this at the ends of the wing . But as its not there to cool / slow airflow , the internals are merely a duct . ( you could put WINGLETS inside it .  ;D  VD~ )



Maybe just half a one'd do .  ???

Square vertical tip plate with semi circle ' capture ' duct .



Theres Circular  wing planes & paper gliders , if the aerodynamics are of intrest .

Or if youd like a real headache . https://www.sciencedirect.com/topics/engineering/bound-vortex A full summary , in thirty minutes , and we'll be happy .  :-X ( Not to sure wot theyreon about , at a glance . )

 S?P




Offline phil c

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Re: Winglets
« Reply #23 on: July 28, 2022, 09:00:22 PM »
So I was just reading about how most newer airliners and some older ones are being fitted with winglets.  The benefit for the airlines is improved fuel economy,  around 5% which is very meaningful in the long haul.  For our purpose I’m not interested in that.  However they say another real benefit is how much smoother the winglets make the airplane fly through turbulence.  I could see benefit in that for stunt.  I may retrofit an old airplane and try it.  Has anyone tried this in our application?

Dave
A number of years back I came across a book, Aeronautic Engineering for  NAVY Pilots, or something similar.  It's a fairly easy read.  It does help to know at least some algebra.

The best part is most of the heavy duty math is already taken care of and reduced to various graphs.  The one I found most helpful was a graph of wing efficiency vs. aspect ratio, span loading, and airfoils.  The most curious part was that a tip chord in the range of 50-60% of the root chord was the most efficient wing layout.  It worked from the first good foam wing combat plane I built, the BumbleBeeII to the latest Psycho with a 14.125in. root chord and a 6.25in. tip chord.  After a lot of trimming I figured it out.  With a straight, un-twisted wing the Psycho could do a figure 8 within about 15 ft. and didn't appear to lose any speed.  It probably was slowing, but with an OS FP40 and a 9/6n prop it took barely a second.  We'll see if I can make it work in a match!
phil Cartier


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