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Tip Plates? - 1/27/2003 11:20:02 AM   
Ralph Morris



Posts: 194
Joined: 11/29/2002
From: Glendale, AZ, USA
Status: offline 		How many have tried wing-tip plates, and did you think they were worthwhile?

Some years ago I flew a Midwest "Sweet Stick" with "tipletts," as I called them, which were made of 1/8-inch balsa. They were attached with two machine screws (2-56 size), into blind nuts in the outer-most rib, which was double thickness. The plate had only one hole near the leading edge, but three different holes for the second screw. This allowed the plates to be attached so that the area of the plate was totally above, totally below, and half-and-half (half above and half below).

As you might expect, they were most effective when positioned below the wing. Above the wing probably reduced the vortex somewhat, but the increased efficiency of the ailerons was most apparent with the plates all below the wing. Roll-rate was obviously increased.

Attached is a photo of my newest design for electric power, with tip plates.

These add to the efficiency of a wing (improving lift/drag ratio), especially at low airspeeds, by reducing the wing-tip vortex. It does this by restricting the flow of high-pressure air from the underside of the wing, which wants to roll up to the top of the wing where there is a nice low-pressure area. The circular flow that results is called a vortex, and it spoils the lift near the wing tip as well as creating additional drag.

Try 'em; you'll like 'em.


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Here's that photo... - 1/27/2003 11:24:36 AM   
Ralph Morris



Posts: 194
Joined: 11/29/2002
From: Glendale, AZ, USA
Status: offline 		Sorry, I guess my photo was too large. Here's a link where you can view the "tipletts."

http://www.rcuniverse.com/gallery/showphoto.php?photo=6773


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Tip Plates? - 1/27/2003 12:41:45 PM   
Selcuk


 

Posts: 37
Joined: 12/3/2002
From: ankara, TURKEY
Status: offline 		I tried winglets on my learjet which has its cg at leading edge of the wing. I put the up winglets with an angle of 30 degree angle with the up surface of the wing but it did not prevent to stall at low speed. As I understand you said down winglet is more effective. I can change it. Do you advise me to do that? And do you have any size recommendation?

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Tip Plates? - 1/27/2003 2:10:24 PM   
BMatthews



Posts: 9052
Joined: 10/4/2002
From: Burnaby, BC, CANADA
Status: offline 		Tiplets or tip plates are a different animal from winglets. Winglets have a specific size in relation to the tip chord that they must be or you won't see the advertised benifits. And on models they seem to need to be a little larger by about 10% all around then the full size airliner types to get the max benifit. The small ones I've seen on the full size Learjets won't do diddly on a model size Lear.... Or at least nothing that you can really feel.

The tip plates are pretty much accepted to do some good but not much. They are just too small. Ralph, in your case I suspect what's happening is that the plate is acting as an end plate for the ailerons to help prevent the spillage over the very narrow chord of the aileron. In that function they would work quite well I suspect. More so for the down moving aileron than the upward moving one that would still have a gap.

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Tipplets - 1/28/2003 6:37:42 AM   
Ralph Morris



Posts: 194
Joined: 11/29/2002
From: Glendale, AZ, USA
Status: offline 		Selcuk; They don't have to be very big to be effective, and my tests indicate that low-speed lift is improved more with the plates below the wing. I know that several current commercial jets use turned-up winglets, which are useful at high speed, probably not very effective at model speeds.

Bruce; what you said is true. The down aileron is operating in a high-pressure area, and its effeciency is greatly improved with an end plate. Remember that the high-pressure air is trying to roll up from under the wing, so the plate would not be effective on the up aileron, even if it extended above the wing to "close the gap," as you mentioned.

Low-speed lift is improved in the same manner. Any time you can keep the high pressure air from moving to the "wrong" side of the airfoil, lift will be improved. This is especially true during ground effect.


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Tip Plates? - 1/28/2003 7:06:19 AM   
Ben Lanterman



Posts: 1296
Joined: 10/27/2002
From: St. Charles, MO, USA
Status: offline 		The upturned winglets on commercial airliners and that type of airplane are there to get a little drag reduction. It is optimized for cruise speed and would never be seen by the pilot except in a reduction in gallons consumed at the end of a long trip. Remember that a drag count ends up being dollars out of the pocket in fuel cost.

In the RC world the effects we notice are in airplane control response and will the airplane fly on a certain size motor. The winglet would never be noticed one way or the other.

Tip plates and large downturned wing tips will show up in control response if the aileron is close to them and perhaps be noticed in a stall pattern change. Since it requires that we notice a visual difference in the way the airplane flies it needs a fairly large plate to effect the aerodynamics.


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Tip Plates? - 1/28/2003 8:44:20 AM   
Ralph Morris



Posts: 194
Joined: 11/29/2002
From: Glendale, AZ, USA
Status: offline 		[QUOTE]Originally posted by Ben Lanterman
... perhaps be noticed in a stall pattern change. [/QUOTE]

Hi Ben;

With plates extending below the wing, the increase in lift at ground-effect level would lower the stall speed at flare-out, which is what I observed with the adjustable plates on my "stick" back in the 1980's.

Other than that, I wouldn't expect any change in the stall characteristics, since that is something that occurs on the top side of the wing.

If this image isn't too large to attach, check the tipplets on this gargantuan Russian surface-effect mobile missile launcher. Maximum altitude: 10 meters. Speed? Fast. See, we're not the only ones who build fantastic weapons systems that are never deployed.

Attachments
Click to see fullsize image.
Click for fullsize



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Tip Plates? - 1/28/2003 9:00:53 AM   
bentgear


 

Posts: 2754
Joined: 3/25/2002
From: Brandon, MS, USA
Status: offline 		FWIW:
Have played with plates on the end of two planes wings. A Magic and a Dazzler. Both were made to be about 1/2 inch larger than the end of the wing all the way around. All low speed performance was increased. I love to fly them around just above idle. Did not notice a big change in roll rate, however both planes roll rather quickly stock. Both planes did exhibit one negative characteristic, at least to me, both lost the ability to get really flat in a spin.
Ed M.

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Tip Plates? - 1/28/2003 9:06:40 AM   
Ralph Morris



Posts: 194
Joined: 11/29/2002
From: Glendale, AZ, USA
Status: offline 		I just remembered, there is a photo of my "stick," complete with tipplets, in my gallery. It's an old photo, since the stick fell out of the sky back in the '80s because someone turned on their transmitter without checking.

This photo shows the plates in the center position, half above the wing and half below. These are quite large when fully above or below the wing. Later, on another plane, I found that smaller ones are still quite effective, especially when they are positioned below the wing.

The ones in this photo would still be effective if the part above the wing were removed.

Here's the link, for your viewing pleasure:

http://www.rcuniverse.com/gallery/showphoto.php?photo=5334&papass=&sort=1&thecat=500


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tipplets - 1/28/2003 9:17:06 AM   
Ralph Morris



Posts: 194
Joined: 11/29/2002
From: Glendale, AZ, USA
Status: offline 		[QUOTE]Originally posted by bentgear
FWIW:...
[/QUOTE]

Hi Ed; Your post is worth a lot. So far, you're the only respondent to this thread who has actually experimented with tip plates on model airplanes. Interesting, your observation about tipplets preventing flat spins.

My experience indicates that symmetrical airfoils will flat spin better than non-symmetrical ones, but I'd never considered the effect of tipplets.


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Tip Plates? - 1/28/2003 11:02:54 AM   
bentgear


 

Posts: 2754
Joined: 3/25/2002
From: Brandon, MS, USA
Status: offline 		Ralph, Ed Moorman of RC Report had an article last year I think that got me started on them, maybe he will join in on this.
As I said, I have this thing about flying slow at times, but don't care about the park flyers. With the plates in place either plane could be made to almost stand still in the slightest breeze and with a slight wind fly backwards.
Both are comfortable to fly 6" off the ground all around the field at about 2 clicks above idle. While both planes, stock, are capable of very slooooooooow landing speeds, with the plates it is just float them in like a silk scarf falling.
I need to add that both were built with small servos and powered with OS 32SX with small battery packs.
I wanted to try the plates on an Ultra Stick 60 but put it in and busted up the fuse. Guess this may encourage me to get it back flying again and make the mod.
Ed M.

Just to add, both planes would hover and then pull verticle althought the dazzler was no rocket ship. Lighter and balanced sure does fly good. Not sure why so many folks think mega (heavy) motor is needed.

< Message edited by bentgear -- Jan 28 2003 6:09AM >

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Tip Plates? - 1/28/2003 1:35:53 PM   
Selcuk


 

Posts: 37
Joined: 12/3/2002
From: ankara, TURKEY
Status: offline 		Thanks all for your explanatinions. So I decided to change winglets with down tip plates on my learjet, however I am not sure about the size and shape of it. In the first picture it is more rhomboid while in the second one more triangular. Do you have any suggestion?
Thanks again.

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Them Plates - 1/28/2003 10:56:55 PM   
Ralph Morris



Posts: 194
Joined: 11/29/2002
From: Glendale, AZ, USA
Status: offline 		Bentgear; Light is right, for flying. It sounds like your planes are lots of fun to fly.

My electric planes aren't real light, at 20 and 19 ounces per square foot of wing area, but they can "hang" real well in stall turns and still roll and snap quickly.

I'm still learning how to build light. When I showed my 8-ounce wing to a friend who builds free flight, he said "Man, that's heavy."

My M2-E must be overbuilt, 'cause I dumped it recently when a guy stepped out on the runway as I was landing (club pres, wouldn't you know).

I was just ready to flare out, too slow for a touch 'n go, when I see this large shape moving towards the spot where I'll be landing. So I plulled up, opened the throttle and applied too much left rudder.

The wingtip hit first, and the forward half of the fuselage (with the weight of the battery) kept going. There were no marks on the spinner or prop, which indicates that the fuse snapped off purely from the wingtip impact, neatly in half at the back of the wing saddle. The wing and tail stayed together, undamaged.

It was really easy to glue it back together. The wingtip required only a patch of fabric, and I added a 1/64 ply skin to the inside of the saddle bay to reinforce it. The fuselage sides are 1/8 balsa with a 1/64 ply skin on the outside, with triangular cut-outs aft of the saddle.

The wing that transferred that impact with sufficient force to snap the fuselage has only 1/4-square balsa spars, but they have 1/16-inch balsa shear webs and 1/4-inch carbon-fiber tape on top and bottom. I think I could stand on the wing between two chairs.

Selcuk; Shape isn't that important. Bentgear reported above that his tipplets extend all the way around the wing. I've seen some like that on a full-scale crop-duster.

The ones on my old stick were made triangular because they could be positioned above, below, or centered on the wingtip. The way I designed those on my M3-E was to lay a straight-edge tangent to the curve of the bottom leading edge, and angle it downward so that the distance from the trailing edge to the tip of the plate (vertically) is slightly more than the maximum thickness of the wing.

There's an old saying among boat designers that if it looks right, it probably is. Don't worry, just cut 'em out and stick 'em on there. If you make them of 1/8-inch balsa, they're sacrifical anyway. Just be sure they line up fore 'n aft. You don't want any side loads on them.

Don't expect too much improvement, especially with a tapered wing, where the chord at the tip is small. The wings on bentgear's and my planes have straight wings so the tip chord is the same as the root. If the wing on your Learjet is scale, it was not designed with model speeds in mind.


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Tip Plates? - 1/28/2003 11:50:17 PM   
Ben Lanterman



Posts: 1296
Joined: 10/27/2002
From: St. Charles, MO, USA
Status: offline 		Although wing tip plates are fun to experiment with and I have played with them in the past (I put them on a Ken Willard .09 powered pylon racer design in 1964, kick up escapements for elevator) it is a real problem determining the effects in a model world.

We spent several days in a wind tunnel once and as we were looking at gross effects our devices were big, if there was an effect we would refine them later. Large fences were put on top of the wing and we varied the lateral position out to the wingtip. It is surprising how little effect was seen.

On a typical model to get the same lift just reduce the weight a few percent, increase the angle of attack or increase the control throw a little. A small decrease in taper ratio will give the same effect. Since most aero forces and moments are a function of V^2 it is easy to get the same effect as tip plates on the high velocity side, just a little more throttle. Putting tip plates on a rectangular wing is helping something that is good to start with.

On the low side is becomes a problem of placebo effect. If you think they are helping then they will appear to help. We are all human and that is just the way we work. Other than having them for the fun of it to really be sure they are working do this test.

Determine a setting of a low engine throttle that can be duplicated each flight by counting the engine stick clicks or by putting some sort of repeatable stop to assure the same engine speed. Do the same thing for the elevator control.

Set the engine and throttle for low speed level flight. Do this with and without wingtip plates. Make every effort to keep the stick settings the same. Do a long level pass the length of the runway.

Since the tip plates will increase the lift coefficient of the wing by stopping the loss at the tip if they are working as expected the airplane should climb with them and not climb without them. If you can't tell the difference then the differences are buried in the experimental error and you wouldn't be able to determine the difference by just flying the airplane around.

< Message edited by Ben Lanterman -- Jan 28 2003 7:13PM >


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