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Old Oct 09, 2011, 11:22 AM
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Wing Tip Design

NB Formerly titled Droop or Drooped Wing Tip Design

Howdy Folks:

I would like to use the drooped tip design. From what I've found out so far it gives the wing/airplane a lower stall speed. Its use on the A-10 ground support airplane is said to give it very good loiter ability. The drooped tip is mentioned in the Wingtip device Wikipedia article where it is called a "Hoerner Tip", but I believe that is a misnomer. There is a drawing of the drooped tip lower down in this "Anatomy of a STOL Aircraft" article:

Unfortunatly I can not find the design parameters. Would any of you in RCG land know where this information is?

Thanks
- Jim
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Last edited by JimHSoars; Oct 12, 2011 at 02:45 PM. Reason: Change thread title.
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Old Oct 09, 2011, 03:33 PM
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could this be the original report? http://oai.dtic.mil/oai/oai?verb=get...fier=ADA800374

this might help a little http://www.sigmfg.com/BuildManuals/SIGRC66WonderP1.html
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Old Oct 09, 2011, 03:47 PM
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I've used them on several designs, and they do haelp a great deal with vortex control and lift at lower speeds.
I've compared my Super Sportwin with Denny Sumners, which used a tapered tip, and it does seem that mine has a good bit longer approach, especially in ground effect.
The A10 uses a similar design....
Tip plates, which are much easier to make and cover, do the same thing , just to a slightly less efficient level.
Mark
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Old Oct 09, 2011, 04:31 PM
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As an aside it's literally been decades since I looked at the wingtips of an A-10 so I'm a bit curious about what they've added as far as equipment. Any idea what the equipment bays are used for? I assume they're some kind of AWS or CM pods but I honestly have zero idea.
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Old Oct 09, 2011, 05:13 PM
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alphamax, how on earth did you find the old military document?

Thanks for the post.

Mark those are great pictures of the A10 wing tip. I have been trying to work my way through your Super Sportwin thread and missed the drooped tips. Thanks

- Jim
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Old Oct 09, 2011, 08:05 PM
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Quote:
Originally Posted by Lacquerhead View Post
As an aside it's literally been decades since I looked at the wingtips of an A-10 so I'm a bit curious about what they've added as far as equipment. Any idea what the equipment bays are used for? I assume they're some kind of AWS or CM pods but I honestly have zero idea.
I believe the fairings are for Chaff and Flare dispensers
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Old Oct 10, 2011, 01:44 AM
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Hoerner actually recommended a tip where the top surface was flat and the underside curved up to meet it, along with a straight TE with a 90 deg corner formed where the tip intersected. He tested downswept tips and found them to be less efficient than a simple square cut tip.

I'm not sure where the A-10 type tip originated from? I believe they were available as aftermarket fitments for light aircraft and sold under the name 'Hoerner tip' but I'm not sure that Hoerner had any part in their development? Also I'm unaware of any actual scientific testing by anyone that indicates they have any advantage?

As for the A-10's long loiter capability. I think you may find that's mainly due to it's high efficiency turbofan engines, plus it's big wing with it's high lift airfoil, and not least it's good fuel capacity.

Steve
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Old Oct 10, 2011, 10:14 AM
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The Wikipedia article on Wingtip Devices says that Dr. Hoerner published a paper in 1952 where he talked about drooped wingtips. Another article I read said he was a principle designer of the Feisler Storch which obviously placed huge emphasis on low speed flight. Yet another article cites him as the originator of the 45 degree bevel we know as Hoerner tips and see on many, many light aircraft such as Piper Senecas, Cherokees, etc. I don't think you'd be remiss in calling either of them a Hoerner design but the Hoerner tip is usually thought of to be the beveled tip we see frequently.

BTW, those drooped tips look absolutely dead sexy on Mark's Super Sporttwin.
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Old Oct 10, 2011, 01:39 PM
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Quote:
Originally Posted by JetPlaneFlyer View Post
As for the A-10's long loiter capability. I think you may find that's mainly due to it's high efficiency turbofan engines, plus it's big wing with it's high lift airfoil, and not least it's good fuel capacity.
Those tips do what the drawing in the original post of this thread shows ie push the tip vortex down and outboard. This doesn't do very much in cruise but i does increase ground effect which is very helpful to an overloaded plane.

--Norm`
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Old Oct 10, 2011, 02:06 PM
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They must have some form of noticeable effect, I guess. The A10 was designed with the minimum possible amount of complex curves, so that it could be easily repaired on the field using sheet metal. The wingtips are a pretty complex shape when compared to the rest of the plane.
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Old Oct 10, 2011, 02:30 PM
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Quote:
Originally Posted by Lacquerhead View Post
The Wikipedia article on Wingtip Devices says that Dr. Hoerner published a paper in 1952 where he talked about drooped wingtips.
The article was linked earlier: http://www.dtic.mil/cgi-bin/GetTRDoc...c=GetTRDoc.pdf

It makes no mention that i can find of drooped tips. The recommendation is tips with a up-swept lower surface, similar to the 45 deg beveled tips you mention.

The only mention I can find of drooped tips is in reference to a lecture given by Eppler in 1987. According to the document i have Epper said that in terms of induced drag drooped tips were 10.2% worse than simple square cut tips and 11.3% worse than up-swept tips... Which makes drooped tips look pretty bad
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Old Oct 10, 2011, 03:57 PM
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As above, I consider a Hoerner wingtip to be one with a curved, upswept lower surface, the idea being, as I understand it, to minimise the tip vortices by reducing the thickness of the tip to virtually nothing.

http://metcoaire.com/technical/tech_...r_design.shtml

I wonder if the notion behind the downward curving tips is to have a similar effect to winglets, but without the dihedral effect?
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Old Oct 10, 2011, 04:12 PM
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First let me say I'm not an aerodynamicist though I pretended to play one once in front of the TV. As I understand it, the drooped tips help contain high pressure at high alpha. I believe the idea is to contain high pressure and keep it from spilling over the tips to improve stall behavior.
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Old Oct 10, 2011, 05:07 PM
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Mark Rittinger's anecdotal report above supports either lower drag at low speeds or greater ground effect mentioned by Norm. Mark also mentions using droop tips in his Super Sportwin build thread in post #161 and post #765 where he states he once researched them.

In Model Aircraft Aerodynamics by Simons there is a photo of Dr. Eppler launching a little balsa glider with one up and down winglet in a classroom. Because it swerves toward the down winglet he states that proves it has has more drag than the up winglet.

(The balls in your research court now Mark.)

Jim
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Old Oct 10, 2011, 05:19 PM
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If anyone has a reference for Hoerner suggesting to droop the wingtips, I would like to see it. This is what I found with a quick google search for a Hoerner wing tip
http://images.rcuniverse.com/forum/u...90/Us54843.gif

In his 1965 book "Fluid-Dynamic Drag" he talks about how there are two separate vortex sheets that leave the tip, one from the top surface and one from the bottom. They "roll up" and merge as they leave the wing tip. He presents several different wing tip shapes that were experimentally tested, and it seems as though the sharp tips do the best.
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