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why are wing tips UP , Down , or flat ?

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Old 08-09-2012, 10:49 AM
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Default why are wing tips UP , Down , or flat ?

I have many planes that are just flat at the ends , maybe the underneath is taper up. I also have some that have the ends of the wings hung or bent down. Then I have some that the tips or ends are turned upward.

The reason I asked is because my new millenium is supposed to be flat yet it came damaged with both tips bent UP. I'm wondering what adverse affect this may have on it.

Thanks for the lesson.
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Old 08-09-2012, 04:40 PM
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Default RE: why are wing tips UP , Down , or flat ?

All depends on what the designer thought looked good. Wing tips on our models do very little. Different story on full scale as tip shape can be used for stall control and effeciency increases, not so much for our models. I'm sure all the full scale theorists will come in and argue my point of veiw. If anyone is willing to test some different tips on a telemetry equipped airplane and report the results, it would be interesting.
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Old 08-09-2012, 04:52 PM
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Default RE: why are wing tips UP , Down , or flat ?

I'm very surprised at the answer. I figured it was VERY important as the end of the wing was most important. Not too worried about my tips being bent up then. They don't even look too bad. The plane flies nice enough.
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Old 08-09-2012, 05:15 PM
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Default RE: why are wing tips UP , Down , or flat ?

Thye fact that the airplane flys well as is pretty much sums it up. Maybe posting pics of the bent tips may worth some giggles.
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Old 08-09-2012, 05:45 PM
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Default RE: why are wing tips UP , Down , or flat ?

sorry about the blurry. The millenium is the 3rd plane up from bottom and is upsidedown.
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Old 08-09-2012, 06:26 PM
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Default RE: why are wing tips UP , Down , or flat ?

Looks like they made a change and the tips are made this way imtentional. BTW I counted at least 5 different wing tip designs in your pictures.
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Old 08-10-2012, 08:49 AM
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Default RE: why are wing tips UP , Down , or flat ?

I don't think so. My bad pics are to blame. Some packer or UPS modified them. I'm sure they are to be straight. http://www.flyzoneplanes.com/airplan...602/index.html One was bent , the other one was broke so I just glued it to match. Hey, at least they are the same.

You must have a better eye for it than me. IDK much about designs. Thanks for your help.

ps. I have another millenium for parts , but guess what part is missing? The wing. I have another on the way and will double chech the tips.
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Old 08-10-2012, 09:13 AM
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Default RE: why are wing tips UP , Down , or flat ?

Tip shape DOES make a difference, sometimes quite markedly. A tip that is tipped up tends to act like increased dihedral and does give some righting ability just as dihedral does. On high performance models like some gliders, tip shape and form can make a great difference.
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Old 08-10-2012, 10:47 AM
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Default RE: why are wing tips UP , Down , or flat ?

Wing tips can make a difference you can notice, especially if you like to experiment or make a plane fly better.

Several years ago a buddy of mine constructed a pseudo wind tunnel and tested wing tips. He had seen me flying a plane with end plates and decided to test tips. His wing was constructed so he could attach several different kind of tips. He had thread attached to the leading edge so you could watch the flow. His idea was to note the formation of and the amount of the wing vortex. His best tip was an end plate. Second best was just a flat rib on the end, followed by a rounded block, the Stick, swept tip and finally, the rounded, 1930's style was the worst.

I reported this when I wrote a column for the old, print edition of R/C Report magazine. I also mentioned that my flight test with end plates indicated that they would lower the stall speed, make spins harder to enter and lower the landing speed. Some of my readers emailed me that after reading my column, they tried plates and confirmed my results.

A variation of end plates can be used to help increase or decrease dihedral effect. It is a known fact that dihedral will cause a plane to roll in the direction of applied rudder. Conversely, anhedral will cause the plane to roll opposite to the rudder. I used a flat wing (do dihedral), .32 powered Little Stick I had at the time for the test. In the air, it would roll with rudder due to the high wing location. My test was to see if a downward only plate would cure the roll coupling.

I cut 2 plates from 1/8" lite ply. The top of the plate was flush with the top of the airfoil and the bottom was 1-1/2" below the wing. I figured that 1-1/2" was more than enough. I also marked off 1/4" lines so I could trim the plate an equal amount on each side at the field. The plates were attached with screws.

At the field, I cranked up, took off and trimmed. I then did a flat turn and knife edge. In both maneuvers, the plane rolled opposite to the rudder, indication that 1. the plates were acting like anhedral and 2. the plates extended too far below the wing tip. After a few trims and flights, I recall that at about 3/4" below the wing, the roll coupling was pretty much eliminated, making knife edge and flat turns easier.

The photos show the Little Stick with and without the plates. The plates are the original size which was much too large.


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Old 08-10-2012, 11:02 AM
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Default RE: why are wing tips UP , Down , or flat ?

plates done right really do add to low speed performance .and assist knife maneuvers

been there
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Old 08-10-2012, 01:28 PM
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Default RE: why are wing tips UP , Down , or flat ?


Quote:
ORIGINAL: Rodney

Tip shape DOES make a difference, sometimes quite markedly. A tip that is tipped up tends to act like increased dihedral and does give some righting ability just as dihedral does. On high performance models like some gliders, tip shape and form can make a great difference.

Like I said, in theory yes. Practice is another thing all together. lets take your sailplane example. Look at some high performance sailplanes. It's been a good number of years that I have been out of sailplanes so my examples may be a bit outdated but these were all cream of the crop when I competed for a spot on the US Soaring team.

Mueller Elipse, Elliptical tips

R&R Mellinium, Tapered, curved tip that met at trailing edge.

R&R Synergy 91 3 taper wing. tips are fairly squared off and cut at a bevel.

V Ultra, Pretty much the same as the Synergy 91

Lots of different tip designs yet none really superior over the other as all these differnt models were flown in the 1996 team selection finals and a few more not listed. I doubt the air has changed much from 1996.

Tip plates are a different story as they increase side area and will make the ailerons a little faster but this is well beyond the OP's original question.

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Old 08-10-2012, 03:22 PM
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Default RE: why are wing tips UP , Down , or flat ?

Trixie has it right. Wing tips that are fixed are pretty much all the same. Especially once one addresses the needs of multiple velocities and flight profiles.

Winglets on the other hand can dramatically decrease induced drag and likewise stop tip stalling in a dramatic fashion. They are particularly good at a single speed such as low speed flight. High speed flight they once again become a hinderance. Note on commercial airlines they are pretty small because of this fact. They still negate about 3% of the drag of the airplane. A not insignificant reduction! Likewise on sailplanes they can be useful and at the same time are a hinderance. On high aspect ratio wings they are minimally useful and require a wind tunnel to get them right and even then are pretty much useless. On a low aspect ratio wing such as a trainer, 2m sailplane, etc they become highly desireable not just for reduction of drag, but in regards to tip stalling, turning, and stability. For such an airplane a winglet with a cant angle of 3 degrees outward, 10-15 degrees back angle, clark Y airfoil with its "top" pointed inwards, a twist of 3-5 degrees where the twist if looking "down" on the wing in question on the left wing tip will be clockwise(toe in), and a height of about the tip chord will give results that don't need a wind tunnel and can be applied to every airframe out there. Effectively decreasing induced drag by about 10-25%. For more drastic reductions in drag, a wider tip chord is desired, a larger height, a greater cl winglet airfoil, and a bit more twist. Think piper cub here.

Depending on the rules of The SAE weight lifting plane competition, winglets can improve total lift from effectively 0% to near 30%. The year I won, our winglets allowed us to pick up another 3lbs. If I knew what I know now, a different wing shape along with winglets would have allowed the additional lift of over 10lbs or an additional 33% more weight lifted. Easily.

I have also added twist winglets to a COZY full sized airplane. As you might already know a cozy has flat winglets as used for a "rudder". Said "rudder" is effectively a joke on said canard. By going with far more aggressive winglets both up and a bit of down where one reverses what I wrote above, top speed increased by 5% as recorded by GPS going with and against the wind. Take off distance decreased by 10-15% depending on how one takes headwind into consideration.

Full sized sailplanes with their super high aspect ratio wings have not seen any benefit to winglets as their induced drag is already minimal. They do benefit in that tip stalling is given a bereavment. Honestly I am flabbergasted that all the UAV's flying around today don't have these on their wings. Just goes to show they were more interested in getting a product out the door and into real world testing and obtaining said government contract over a perfect platform. A smart decision as high aspect ratio wings require a bit of finesse to get the desired results. IE pick a load flight profile to adhere to and then adjust the twist,cl, and height of said winglet.
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Old 08-11-2012, 04:23 PM
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Default RE: why are wing tips UP , Down , or flat ?

hi there from Toledo

I think Gallagher (the guy with the sledge hammer and produce) summed it up perfectly, "STYLE".

ciao -rjf
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Old 11-13-2012, 08:59 PM
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Default RE: why are wing tips UP , Down , or flat ?

there are different schools of thought on this topic.. with a flat wing, the higher pressure from underneath (or the lower pressure from up top) causes the air under neath to get sucked over the tips (this is where wing vortices come from). those vortices significantly increse induced drag. now, the downgoing tips eliminate this problem by forcing that air down. back to newton laws now, for every action there is an equal and opposite reaction. hence. more lift. but still very little reduction in induced drag. the up going ones are a bit different. they block the air from coming up altogether. since it cant get on top, it cant create vortices and hey! little to no induced drag!
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Old 11-14-2012, 06:35 AM
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Default RE: why are wing tips UP , Down , or flat ?

Actually, that's not altogether accurate. First, every wing that is able to actually make a plane fly has a pressure differential between top and bottom. Airfoil shape simply determines what speed and angle of attack will be needed for those pressures to be there. You have it right about the vortices, but the problem with them is not induced drag (at least not directly) but rather the loss of lift caused by losing the pressure differential between top and bottom. When the pressure is lost, you're still dragging the wing through the air but not getting as much lift benefit for doing so. Up or down tips do the same thing- keep the pressures from leaking around the wing tips by giving them a longer and more difficult path to flow through. It still leaks anyway (to totally eliminate it requires tips that are too big to be practical) but not as much.
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Old 11-14-2012, 05:18 PM
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Default RE: why are wing tips UP , Down , or flat ?

The most important thing about wingtips is the distance between them.

But for lowest drag you want the wingtip rounder at the front, but sharp edged at the rear,

AND you want the wingspan to increase as you move from the leading edge to the trailing edge. This is known as an "advancing tip". Sweeping up or down is style only.
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Old 11-14-2012, 06:53 PM
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Default RE: why are wing tips UP , Down , or flat ?

I saw that when Dr (or professor) Eppler was testing wing tips he had a glider with one tip plate that went up and on the other wing it went down.
It always turned towards the down tip indicating more drag than the upwards plate.
Well I found it interesting, lol.
Jim

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Old 01-03-2013, 02:39 PM
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Default RE: why are wing tips UP , Down , or flat ?

I'm building a Tiger60 sport plane and I'm trying to improve the performance, dihedral has been reduced to 1% or 1/2" at each wing tip. Question, if I put end plates from spar to 3/4" high at trailing edge top side of tip will it perform better by directing the air stream over the aileron rather than flowing off the tip. Does it help reduce tip stalling. Is there a better shaped tip over the rounded up tapered block they give you to make tips from.

I want to learn to do knife edge, hover and the many things this plane is capable of, actually I have bashed it trying to enhance performance and wing tips are the last thing yet to do. There is alot of experience out there and I hope to gain some of it.

Thanks, Leroy
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Old 01-03-2013, 03:22 PM
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Default RE: why are wing tips UP , Down , or flat ?


Quote:
ORIGINAL: Leroy Gardner

I'm building a Tiger60 sport plane and I'm trying to improve the performance, dihedral has been reduced to 1% or 1/2'' at each wing tip. Question, if I put end plates from spar to 3/4'' high at trailing edge top side of tip will it perform better by directing the air stream over the aileron rather than flowing off the tip. Does it help reduce tip stalling. Is there a better shaped tip over the rounded up tapered block they give you to make tips from.

I want to learn to do knife edge, hover and the many things this plane is capable of, actually I have bashed it trying to enhance performance and wing tips are the last thing yet to do. There is alot of experience out there and I hope to gain some of it.

Thanks, Leroy

I've had a number of Tigers. They are straight wing planforms. That wing shape stalls naturally from the center out. I've never had a tip stall with any of them. In fact, they were difficult to stall. Snaps weren't automatic off the building board with the suggested CG, in other words.

They have strip ailerons. Those are the last choice a designer would put on a 3D model. Hovering wasn't something mine did without rolling.

Another problem with Tigers is the elevator is a strip elevator. There isn't any area in the elevator to speak of. I modified my last Tiger in hopes it would actually stall in level flight in order to get into an IMAC described spin. I doubled the elevator chord. It didn't help significantly. The horizontal tail is proportioned on the powerful side. It has more than enough area in the stab and not very much in the elevator. It's not ever going to be a sensitive animal without some major help.

The model was supposed to have been designed as a low wing trainer. It is an excellent model for smooth, flowing maneuvers. It lands itself. It's rather hard to get it into trouble. It's not going to be a very successful 3D, hovering devil.

what I would do about those tips..........
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Old 01-03-2013, 03:26 PM
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Default RE: why are wing tips UP , Down , or flat ?

About the Tiger's tips..........

I often considered reducing the wingspan. I very often considered building a new tapered wing. The design is so strongly stable in roll and pitch.
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Old 01-03-2013, 03:29 PM
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Default RE: why are wing tips UP , Down , or flat ?

BTW, all of mine did knife edge well. I chose to put rudder-elevator and rudder-aileron mix into the last couple simply to learn how to program the radio and see how they flew. They did hammerheads better. That was about all that was noticable.
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Old 01-03-2013, 10:45 PM
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Default RE: why are wing tips UP , Down , or flat ?

daRock are you saying an end plate will not aid the performance. I have added to the cord of elevators 1 1/2" from the V and tapered it to the tipand it now has balance tabs, did the same to veritcle stab. and rudder. Thrust line is raised 1" for sake of 20cc engine and weight needed up front, I know I don't need all the power. Wings have also been raised 3/4" and are now slip on plus it's a tail drager. Strip ailerons are now built up 15" X 2 1/2" cord and flaps 15" X 2 1/4 cord plus wings are sheeted. Thats the bulk of the changes I made.

Much that I have learned about this plane is about lack of authority in the stableizers and I'm hoping to improve on that, wing tips are the only other matter and I dont like the ones suggested for the plane. I would like some input about the changes I made, are they good, enough and are they going to work for me.

You can see the build here www.rcuniverse.com/forum/m_11326847/tm.htm

Here is a pict of what I have so far. Won't upload this time of night, please check out my build I'm really intrested in a professional opinion, thanks Leroy

I tried again, it worked. Buy the way, don't the tabs also add to the area of rudder and elevators ?
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Old 01-04-2013, 12:10 AM
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Default RE: why are wing tips UP , Down , or flat ?

Quote:
I've had a number of Tigers. They are straight wing planforms. That wing shape stalls naturally from the center out. I've never had a tip stall with any of them. In fact, they were difficult to stall. Snaps weren't automatic off the building board with the suggested CG, in other words............................................. ......................

It's rather hard to get it into trouble.
Yeah, that's what I thought too. It seemed very stable, and I could not get it to spin upright. However when I tried an inverted spin, it fell right into a normal spin. But unfortunately when I put it into a flat inverted spin it did not want to revert back to a normal inverted spin to recover and took so many extra turns to get out that when it finally broke into a normal spin I was too low to recover.

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Old 01-04-2013, 12:25 PM
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Default RE: why are wing tips UP , Down , or flat ?

Some times getting an answer has more to do with where you ask the question ( post it ) in order to get it to those that actually have an answer and those that actually read the question as they are actually related.

I will ask again, do vertical end plates aid in wing tip performance on a straight semi-symmetrical? wing foil. Hope I spelled that right. Some times It can be asked in such a way others don't know what your talking about, I hope thats not the case here as I want to get this done as soon as possible.

Thanks for your help.
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Old 01-04-2013, 01:09 PM
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Default RE: why are wing tips UP , Down , or flat ?

OK, lots to talk about............

I increased my elevator area more than yours. Your balance tabs do add area. And your increases in the vertical tail will help too. It's a shame I did not notice your build thread, as I think we could have discussed a couple of things before you built them. The horizontal tail as designed has always struck me as having way too much of the area in the stab. I have wanted to build or modified a Tiger60 with 2 things ever since my 2nd one. (BTW, my 2nd one was a Calmato 46. see attached)

Since day one, I've wanted to move the elevator hinge line forward. OK, that's not exactly correct. I've wanted to take 10% -20% of the area of the stab and give it to the elevator, maybe more. I've never taken the time to do the math, but the idea is to keep the horizontal tail area, just divide it up better. Just adding elevator area ignores just how big the stab is. I figured to increase the aspect ratio while knocking out the new parts. That stab is simply too much to overcome. Better to work on it. Your balance tabs are a good step along that path. Wish I'd thought of them when I redid my elevators. I'd do it now except I sold the airplane.
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