Is this a wing-tip device on the A-10 "Warthog"?

Question

^{Source: Flickr courtesy of: U.S. Air Forces Central Public Affairs, photo by Master Sgt. William Greer}

Notice at the side edges, the wing peels down and back around towards the fuselage. (The airplane is upside-down in this photo.)

Never noticed this before. Is this a wing-tip device producing more lift? If so, what kind is it? I would like to read more about it.

Thank you for the gorgeous photo. The detail behind the Warthog, especially the snow line, is absolutely phenomenal. — dotancohen, Oct 21 '15 at 13:52
Looks like this might be the source: https://www.flickr.com/photos/dvids/5510306058 *> An A-10 Thunderbolt II from the 23rd Fighter Group, Moody Air Force Base, Ga., peels away after being refueled from a KC-135 Stratotanker, assigned to the 340th Expeditionary Air Refueling Squadron, while flying over Afghanistan in support of Operation Enduring Freedom, Feb. 26, 2011.
U.S. Air Forces Central Public Affairs

Photo by Master Sgt. William Greer

Date Taken:02.26.2011

Location:SOUTHWEST ASIA, AF* — Bob, Oct 22 '15 at 08:38
Reference a Civilian (737) question here: http://aviation.stackexchange.com/questions/21122/what-are-some-differences-that-make-the-new-737-max-winglets-more-efficient-than/21127#21127
Civ. aircraft look much harder at fuel economy, etc. but it seems the primary benefit is low-speed performance and better overall performance. — blaughw, Oct 22 '15 at 16:26

aeroalias · Answer 1 · 2015-10-21T17:04:08.150

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The wingtip devices used in A-10 Warthogs are called drooped wingtips (also called Hoerner wingtips in some cases), which essentially increase the aspect ratio of the wing by forcing the vortices further out.

Source: zenithair.com

There are a few reasons for having this wingtip device:

The drooped wingtips act in a manner similar to the winglets and reduce the induced drag. As a result, the loiter capability of the aicraft, an important one for Close Air Support (CAS) aircraft, is improved. The A-X competition, that lead to the A-10 develpment, required the aircraft to have Two hour mission loiter time at max mission radius with 9,500 lbs payload
The drooped wingtip increases the local span loading near the wingtip, due to which the aileron response is improved, increasing the manuverability at low altitudes. The A-X competition required the aircraft to be Highly maneuverable below 1,000 ft
The drooped wingtips also improve the takeoff performance, an advantage as the aircraft is expected to be operated from short, forward fields. Infact, drooped wingtips are found in STOL kit of some aircraft, like DC-2 Beaver. One of the requiremens of the A-X competition was that the aircraft should have 4,000 ft takeoff distance at MTOW.

As can be seen, the drooped (down) wingtips wingtips serves these purposes.

There seems to be some confusion regarding the reason for these wingtip devices. One theory (@Peter Kämpf) is that they are there to protect the ailerons from ground contact. However, I think this is unlikely, given the ailerons, when extended, go well beyond the wingtips, as shown below:

Source: scienceforums.net

Dropped down wingtips do serve that purpose (sometimes) in gliders. However, there is no reason to believe that is the case here, considering the height above the ground and the aspect ratio. The drooped wingtips, on the other hand serve to hold the countermeasure system.

Source: rcgroups.net

edited Oct 21 '15 at 17:04

answered Oct 21 '15 at 10:13

aeroalias

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The improved take-off performance isn't really a reason to install drooped tips, other types of winglets would also improven the take-off performance. – ROIMaison Oct 21 '15 at 11:24
@ROIMaison - The drooped wingtip, unlike other winglet styles, acts as somewhat of a pressure barrier, keeping air under the wing in addition to modifying the tip vortex. This improves lift at high AOA such as during takeoff rotation. – KeithS Oct 21 '15 at 19:17
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This comes at the cost of reduced reduction of vortex wake compared to an upward-swept winglet, which for the A-10 was a secondary concern as range, speed and ceiling requirements didn't require ultra-low-drag (the thing can carry over a dozen Maverick missiles; wingtip vortex drag is not the first item on the list for drag reduction) – KeithS Oct 21 '15 at 19:28
A reduced reduction of vortex wake? Does that mean it makes more votrex wake, @KeithS? :) – FreeMan Oct 21 '15 at 20:16
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@FreeMan I read that as "more vortex wake than an upward-swept winglet, but less vortex wake than no winglet at all" – raptortech97 Oct 21 '15 at 22:36
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The picture you're using to show the reach of the ailerons has them split and fully deflected to be used as speed brakes (something Peter Kämpf also mentioned), and they are possibly well beyond the angle of deflection achieved when they are closed and being used as an aileron. The actual deflection required for the aileron for maneuvering when in a bank (which is the suggested usage case) seems to be covered by that wing tip bend, so Peter's idea still holds up. I'm not saying you are necessarily wrong...but the evidence you are using doesn't actually support your argument. – Jae Carr Oct 22 '15 at 13:01
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@JayCarr If you're in risk of your ailerons contacting ground while in a bank in normal flight, there's plenty of other things hanging off the bottom of an A-10 which will contact first. – Schwern Oct 26 '15 at 17:57
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I just read on the Wikipedia page for the Cessna 172: "The wings can be modified using a number of STOL modification kits, some improving high speed/cruise performance but most concentrating on STOL performance. Horton's STOL kit is one of the better-known of the latter. It involves fitting a more cambered leading edge cuff to increase the maximum coefficient of lift, fitting fences at the aileron/flap intersection and fitting drooped wingtips." – Steve Oct 30 '15 at 01:00
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On the Horton's page, they claim this: Conical Cambered Wing Tips -
Low speed aileron effectiveness is improved by special wing tips. Induced drag is further reduced since the HORTON STOL-CRAFT tips reduce wing tip vortex strength. They also increase the wing area and decrease the stall speed.
– Steve Oct 30 '15 at 01:03

score 11 · Answer 2 · answered Oct 21 '15 at 07:45

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It's called a drooped wingtip.

The general idea is to move the vortex away from the wing, reducing it's influence. As with all the winglet variants, opinions vary about whether or not it generates more lift than other variants.

Source

There are more aircraft that employ this type of wingtip device:

Source

answered Oct 21 '15 at 07:45

ROIMaison

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That is odd. I thought moving the vortex to a spot above the wing surface was ideal, because that low pressure vortex can add lift that way. Moving it farther away from the wing (spanwise) doesn't seem to change anything that I can see. – DrZ214 Oct 21 '15 at 09:48
See this answer http://aviation.stackexchange.com/questions/21799/why-does-the-vortex-created-by-wing-affects-its-own-angle-of-attack/21803?noredirect=1#comment49685_21803. Moving it further away reduces its strength and effects. – ROIMaison Oct 21 '15 at 09:54
I'm guessing they don't work as well as a winglet. – Ethan Oct 21 '15 at 11:38
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@DrZ214: Moving it away from the actual wingtips have the effect of reducing the vortex size. Up or down doesn't seem to matter much. – slebetman Oct 22 '15 at 09:21
@slebetman, why would up or down be any different from sideways? The velocity is only a function of distance from the center: https://en.wikipedia.org/wiki/Vortex – ROIMaison Oct 22 '15 at 09:28
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@ROIMaison: Yup. Increasing span also works. In fact, it's the best option. However, if you're span limited, winglets or winglet-like devices makes sense. It's just that up or down doesn't matter much. – slebetman Oct 22 '15 at 14:49

score 10 · Answer 3 · edited Oct 26 '15 at 16:37

If I add raised wingtips to one of my RC planes they significantly decrease the aileron authority, meanwhile improving the dihedral effect and the self-stabilizing tendency. But for maneuverability, it's not as good. If I add an autopilot, like Ardupilot, the raised wingtips will make harder for the autopilot to instantly correct the leveling when passing through turbulence, because the effect of the ailerons is dampened by the self-leveling tendency. Basically, the ailerons have to fight not only to change the attitude of the wing, but against it's tendency to rotate by itself, that might not act in the right direction when flying through turbulent air.

If I add dropped wingtips, they improve lift (the same wing is capable to carry more weight) and they increase greatly aileron authority, while decreasing passive auto-leveling.

The plane becomes harder to fly manually, but for the autopilot the effect is good, because the smallest deflection of the ailerons will have a big effect. The autopilot is capable to correct instantly the horizontal attitude of the wing, by moving the ailerons very fast, and in minute increments. The plane will look like it's flying on rails, even when it passes through turbulence. And the lower the altitude, the greater the turbulence, because the wind is moving over ground obstacles and it's not flowing laminarly. When the wind is strong and there are bushes and trees on the terrain, the turbulence can be so great, that a RC model can become impossible to fly low if it doesn't have some sort of electronic self-leveling device.

The conclusion is that, for a plane that has to fly low, dropped wingtips and an active self-leveling device are the best combination. If the plane was low wing - high CG, I would have used raised wingtips.

Interesting answer from another perspective, welcome to Aviation.SE :) — ROIMaison, Oct 23 '15 at 10:08
Indeed! Excellent answer with practical experience that directly applies to the A10's flight profile. — FreeMan, Oct 23 '15 at 13:00
Can you post a picture of your RC plane? Or at least tell us it's basic shape? Are the wings high-aspect ratio rectangles like the A-10? I'm interested because there are plenty of raised wingtips on modern large commercial jets, which have swept wings around 30 degrees. Never heard of any poor handling characteristics this incurs at low speed low altitude, so it could be the swept wings. — DrZ214, Oct 24 '15 at 02:48
Commercial jets have very different needs. They fly high and have to be very fuel efficient. They have a low wing, which by default has an anhedral effect, and raised wingtips annihilate that and make the plane neutral, that's why they have good aileron authority. The situation of the commercial jets is more complex. their wings are aerodynamically very elaborate, with a lot of slates, flaps, spoilers etc that can change the configuration of the wing for every needed speed and attitude. So it's not fair to compare such complicated monsters with simpler wings. — mr2day, Oct 25 '15 at 18:29

Peter Kämpf · Answer 4 · 2015-10-21T14:01:10.460

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Oh boy, you guys are obsessed with that wingtip vortex, seemingly the source of all drag. No, the reason for this wingtip shape is much simpler.

It's about the protection of the ailerons from ground contact at low level flight. This is especially important for gliders with their central wheel, but also for aircraft which maneuver a lot at low altitude. They will benefit from something that takes the impact forces and keeps the control surface intact and working, especially when this surface will be deflected downwards at the time of ground contact.

Honestly, this is the reason, not some esoteric vortex shifting.

edited Oct 21 '15 at 14:01

answered Oct 21 '15 at 11:13

Peter Kämpf

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The right wing of this image http://www.foodman123.com/cut42.jpg, shows that the ailerons stick out quite a lot further downwards than these tips do, so then the ailerons (if deflected by a reasonable angle) would still hit the ground ealier than the tips?For the gliders it makes sense, but for the A10, it's a bit out of scale. If they wanted to protect the ailerons, to me it would have made more sense to place a larger protecting tip. – ROIMaison Oct 21 '15 at 11:26
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@ROIMaison: The ailerons of the A-10 split when used as a drag device. What the drawing you linked to shows is the deflection when used as a speed brake, and yes, with that it will touch the ground before the wing tip does. Better read this. Also, the aileron doesn't quite reach out to the tip and with some bank the wingtips give sufficient protection. – Peter Kämpf Oct 21 '15 at 12:05
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Thanks for the link, it is an interesting read! In this document (p43) I found the following phrase: "The wings have Hoerner wingtips that reduce induced drag and wingtip vortices. They also improve aileron effectiveness at low speeds." so it seems they also agree on the vortex reduction effect. – ROIMaison Oct 21 '15 at 12:22
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Also, consider this image. The hardpoints on the wings provide plenty protection for control surfaces, it seems. I'm afraid this answer just doesn't apply to an A-10. – Sanchises Oct 21 '15 at 12:56
@sanchises: For one, this A-10 is clearly at rest, so aileron deflections will not help. Also, it is not banking. Why would you think this picture applies here? – Peter Kämpf Oct 21 '15 at 13:55
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@ROIMaison: This is not the official manual. It is a fan product (citation: The manual for Eagle Dynamic's DCS: Warthog). But it contains a lot of details in one place. The fans, however, should not be trusted with the details behind the engineering decisions. What did you expect? The sentence you quoted will never be uttered by the engineers - maybe by marketing, but not by engineering. – Peter Kämpf Oct 21 '15 at 13:57
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I don't think it makes sense to only trust the part of a source that supports your statement. Why should the 'fans' have a lot of knowledge concerning the usage of the wing tips to protect the aileron, but be completely wrong about the usage of wing tips to reduce the effect of tip vortices? – ROIMaison Oct 21 '15 at 14:03
@ROIMaison Where do the fans say it is about ground contact protection? No, this document only illustrates nicely that the ailerons double as air brakes (pages 44 and 46). Also, it contains a lot of photos. There is nothing in it which discusses the engineering decisions. – Peter Kämpf Oct 21 '15 at 14:08
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@PeterKämpf I'm sorry, I thought you brought up this source to support your statement about the protecting of ailerons, my bad. – ROIMaison Oct 21 '15 at 14:14
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Is this answer suggesting you want to protect the aileron when the wing hits the ground in flight? Isn't that called a "crash" ? When you hit the ground, protecting the ailerons seems to be the least of your problems. The sudden deceleration will cause quite some yaw, and hitting your wingtip means the plane was also rolled (A10 has dihedral) which means the yawing also causes a pitch down. Pitching down at 1 ft above ground is NOT a good thing. – MSalters Oct 21 '15 at 14:53
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@MSalters: There are different levels of hitting the ground, and the more benign ones would end in a crash if you lose aileron control. A lot of real world experience went into the A-10 (and not the kind of experience you get when watching Hollywood movies). If the wingtip only touches the ground, protecting the ailerons should actually be very high up on your list. – Peter Kämpf Oct 21 '15 at 15:13
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[citation needed] – Russell Borogove Oct 21 '15 at 15:20
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@MSalters I would think grazing a wingtip would be a very good reason to want aileron authority (i.e. in order to stop grazing said wingtip as quickly as possible.) – reirab Oct 21 '15 at 15:52
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@PeterKämpf "The sentence you quoted will never be uttered by the engineers - maybe by marketing, but not by engineering." I wish I had a dollar for every time I've read or heard such a sentence. – reirab Oct 21 '15 at 15:55
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I like the answer, and have no reason to doubt it, but I think it would be wise to provide some amount of citation for what you are saying. If for no other reason than not everyone is familiar with your level of experience... – Jae Carr Oct 21 '15 at 19:30
Hey, we never said the wingtip vortex was the source of all drag. I thought that you can never completely get rid of the vortex, so the best thing to do is to move it somewhere best, such as above the wing so its low pressure (and relatively higher pressure under the wing) cause additional lift. So a drooped wingtip is very strange to me, seemingly doing the exact opposite! But looking at your pictures, they seem to do neither, and instead shift the vortex horizontally away and not so much vertically in ether direction. Which is still strange. – DrZ214 Oct 21 '15 at 22:20
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Very very strange answer. Where is the data to confirm such a claim aside from glider mentioning (but notice gliders do have single centered wheel and can roll to the sides once slowed down enough.) – Alexus Oct 21 '15 at 23:51
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Drooped wing tips can be found on the Cessna 172 - a high wing aircraft not generally associated with extreme low-level maneuvering of a nature that wingtip to ground contact would demand engineering consideration. I can't imagine that the Cessna engineers considered protection of the ailerons in their motivation to fit the 172 with drooped wingtips. However, I can certainly understand such a design choice for its aerodynamic/efficiency benefits. – Anthony X Oct 22 '15 at 03:50
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GVG's Air Vectors (what I would consider a solid, well-researched source) indicates that they are in fact wingtip devices: the wingtips are slightly turned down to improve aileron response and reduce wingtip vortexes that would impair flight efficiency. – egid Oct 26 '15 at 16:41
I hate to ask it, Peter, but do you have a source from the Athens development where the OEM (Fairchild Republic) designed that wingtip shape for the reasons you stated? – Romeo_4808N Aug 22 '23 at 18:18
@CarloFelicione No, but the shape can only serve that function. The turned-down part is too small to do anything substantial to the airflow. But it is just big enough to protect the deflected aileron (but not the airbrakes). – Peter Kämpf Aug 22 '23 at 20:32
@PeterKämpf could you link to theory/tests which show that the turned-down part is too small for substantial beneficial aerodynamic effects? – Kenn Sebesta Aug 23 '23 at 18:08
Partially supporting your answer there's the fact that "the wheels of the main landing gear partially protrude from their nacelles when retracted, making gear-up belly landings easier to control and less damaging". So it was actually designed to land/touch down like a glider – sophit Aug 23 '23 at 18:18
@KennSebesta Size does matter! The effect is proportional to size, so while a small change in the flow will be observed, it will be far too small to show up in performance charts. There are countless reports which will confirm this. – Peter Kämpf Aug 23 '23 at 18:45
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@KennSebesta to complete the comment of Peter: the reduction in induced drag is for sure negligible (a full winglets may reduce drag of some 3% so that small thing might reduce induced drag of some 0.x%) plus there is obviously the relevant increase in the friction drag to be considered. At the end I also suppose that the real job is as explained by Peter plus as a protection for the chaff and flare (which would actually be a job of paramount importance for this kind of airplane). If you want something to read I'd suggest this pdf – sophit Aug 23 '23 at 20:47
@PeterKämpf: what abou this picture? – sophit Aug 23 '23 at 21:20
@sophit Thank you for the link to the McLean article! Figures 4.1 and 4.2 should be required reading for all winglet cult members. The picture shows only that in level flight the turned-down wingtip is not needed. It really is meant for the banked, flying airplane close to the ground. – Peter Kämpf Aug 25 '23 at 05:08

score 2 · Answer 5 · answered Apr 13 '16 at 15:10

I thought of another one; if you're installing wingtips and it doesn't matter whether they point up or down, the latter will be less of an obstruction to the view from the cockpit, which is convenient for an aircraft also used for forward observation.

It's an interesting question! I think my answer wasn't mentioned yet?

Is this a wing-tip device on the A-10 "Warthog"?

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