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Jan 07, 2012, 04:08 AM
Balsa + glue + bluesky= fun
leaktech's Avatar
Discussion

wing tips


I'm almost ready to carve some wing tips for a 3 meter flat bottom woody. The plan shows anti vortex tips which look cool. I like unfancy diminishing tips because they're easier to carve. Question is, do anti vortex tips improve thermaling and/or thermal hunting? What is the ideal tip for thermal hunting? I've looked for a anti vortex tip carving thread and can't find one, does anyone know where to look or have a link? Thanks.

James
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Jan 07, 2012, 09:55 AM
Registered User
James:

Years ago, Cessna did a study. They compared (in their wind tunnel, devoted to 100 mph Cessnas) a variety of tips, and used as a base line a simple, angled tip. I make the same tips on my woodies, glueing a piece of triangle stock to the end rib, then contouring it to the rib profile: easy, simple, light (very important), easy-to-cover.

For Cessna, the simple angle proved to be the best, providing the best overall wing efficiency. The other tips included rounded tips, flat end plates, "Hoerner" tips and several variations.

The translation of their results to our models is not direct - there are things that happen at full-scale speeds and sizes that do not happen with our models, and vice-versa.

But, I have ever since favored the simple triangle-stock tip, for the reasons I gave above. At the same time, if your model is a relatively successful one (lots of them built, perhaps) then you can probably assume that the design tips work just fine. Just be sure to make them light weight.

I'd love the chance to compare tips on a common airplane, but DLGs are taking up my time these days. Perhaps one of those smart guys like G_T can do one of their simulations.

Yours, Greg
Jan 07, 2012, 10:10 AM
Envies his own avatar
rockyabq's Avatar
James,

I've read about "scimitar-shaped" wingtips being the cat's meow for lowest drag, but I can't personally confirm or deny. (Below is a Stork II.) I just think they'd be the antithesis of Greg's idea--nearly impossible to shape correctly, keeping the airfoil accurate in three dimensions, and then hugely difficult to cover. (The Stork II is fully molded.)

Take care,
Rocky

Jan 07, 2012, 10:26 AM
Just call me crash for short
Quick61's Avatar
If anyone is looking for a shiny idea in wing tips, look no further - http://www.automotto.com/entry/minix...ficiency-by-6/

Mark (now, where did I put my molding supplies )
Jan 07, 2012, 10:32 AM
Registered User
Horner, in his Fluid Dynamic Drag, reports that the tip with the least drag is a full sharp tip that simply tapers to a knife edge. He also states in that book that he did not design "the Horner tip" and did not recieve any monitary compensation. Forty years ago, I spent a lot of time studying Fluid Dynamic Drag for a V/STOL project I was working on.
Jan 07, 2012, 12:29 PM
Registered User
Quick61:

Pretty cool, but I'd have a heck of a time trying to sand that one out of balsa.

Yours, Greg
Jan 07, 2012, 12:53 PM
It's gonna be YUGE!!!
LVsoaring's Avatar
Cessnas (and any other full-scale aircraft for that matter) have a much higher wing loading than model sailplanes, and therefore a much higher pressure gradient between the top and the bottom of the wing. It is for this reason the winglets on passenger jets result in noticeable improvements in efficiencies. As I recall, the improvement in fuel efficiency on 757's with winglets added was so great that in 18 months of service,the fuel saving alone covered the cost of the winglet mod.

But sailplanes, being high aspect and relatively low wing loading aircraft to begin with, are already very efficient. Of course the full-scale sailplane manufacturers want to eke out every possible bit of performance, so they are now designed with winglets. But for modeling purposes, it's doubtful you'd notice any improvement in performance with winglets as opposed to a simple triangle-stock type of wingtip.
Jan 07, 2012, 01:15 PM
Balsa + glue + bluesky= fun
leaktech's Avatar
Wow Quick that's some tip there. I'm bailing on the plan tips and going with G Man's method. KISS. Will reserve the notion to change it again while I shape the leading edges with a razor plane and sanding block. Image is from Ray's Craft Air Viking kit.
Jan 07, 2012, 03:56 PM
Just call me crash for short
Quick61's Avatar
LVsoaring, good point. On the slower / lighter ships it would be more of a WoW factor than any real benefit. The faster / heaver DS ships might see some noticeable difference approaching 400mph and around 40oz /sq ft load. Might be an interesting experiment. Not for me mind you, I had just seen those tips a while back and thought I'd share while on the topic.

leaktech, keeping it simple is far more often than not the better way to go. The less time you have to put into building it, the less pain you feel when you smack it up, right?

Mark
Jan 07, 2012, 04:09 PM
Balsa breaks better
Thermaler's Avatar
Quote:
Originally Posted by leaktech
Wow Quick that's some tip there. I'm bailing on the plan tips and going with G Man's method. KISS. Will reserve the notion to change it again while I shape the leading edges with a razor plane and sanding block. Image is from Ray's Craft Air Viking kit.
I carved the tips on my first Viking MKI, the next five got the KISS treatment. I did not notice any difference but then I was to busy trying not to break another one back then!!
Is that a MKI or MKII your building?

Joe
Jan 07, 2012, 05:32 PM
Balsa + glue + bluesky= fun
leaktech's Avatar
MK I with turbs. All the other woodies here have faster airfoils. This will be a little different.

James
Jan 07, 2012, 08:35 PM
Play loud, Fly high
Gil Gauger's Avatar

Tips


On these types of planes, especially builtup wings, an important consideration is pitching moment at the tips in high speed/high lift conditions ie: launch. We have all seen planes fold when overstressed, but personally I have had more failures tucking the tips when getting too fast.
I have experimented several times with a semi-circular tip planform with a swept back trailing edge on sheeted foam wings and have been pleased. The aero guys will trash me for the kink in the trailing edge, but subjectively I see an advantage. I am currently constructing a self designed 110" woody RES and will incorporate this tip. It will be constructed with reinforced sheet stock shaped to the tip planform, stuck on the chord line of the last rib, and the covering providing the airfoil transition from airfoil thickness to flat at the very tip. In this case it will also provide an additional poly break. This will closely approximate what I did on the foam versions. I will see how it works. What I am after is higher Reynolds number and no camber at the tip.
Jan 09, 2012, 07:55 AM
Hot Dawg Glider Pilot
schrederman's Avatar
These are relatively easy to carve and cover. I believe I covered how in my Houston Hawk and Yardbird build threads. Shape the curve bottom first, after marking the curve on the trailing edge side. Then use a sharp chisel to gouge out the upper curve, followed by coarse sandpaper wrapped around a piece of PVC pipe of the proper diameter.

They probably don't help as much as I'd like to think they do, but I sure get a lot of looks and compliments at the field...

Darth Winglet
Jan 09, 2012, 08:28 AM
Kurt Zimmerman ≡LSF 4461≡
kzimmerm's Avatar
Quote:
Originally Posted by schrederman
These are relatively easy to carve and cover. I believe I covered how in my Houston Hawk and Yardbird build threads. Shape the curve bottom first, after marking the curve on the trailing edge side. Then use a sharp chisel to gouge out the upper curve, followed by coarse sandpaper wrapped around a piece of PVC pipe of the proper diameter.

They probably don't help as much as I'd like to think they do, but I sure get a lot of looks and compliments at the field...

Darth Winglet
I agree with Mr. DW that they are not difficult to make. I have had a loop blade for my exacto which works great. A curved chisel works just as well.

Covering them is as simple as heat/stretch and repeat.

Kurt
Jan 09, 2012, 02:02 PM
Balsa + glue + bluesky= fun
leaktech's Avatar

Darth Tips


Darth tips start at post #39
https://www.rcgroups.com/forums/show...=3#post6631856

I made the simple tips like Greg's. I'll make the fancy ones next woody.


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