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View of A-10 underside in flight
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.

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    $\begingroup$ Thank you for the gorgeous photo. The detail behind the Warthog, especially the snow line, is absolutely phenomenal. $\endgroup$ – dotancohen Oct 21 '15 at 13:52
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    $\begingroup$ It is a great photo. Could you add attribution? $\endgroup$ – Jeffrey Bosboom Oct 21 '15 at 19:40
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    $\begingroup$ Looks like this might be the source: 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 $\endgroup$ – Bob Oct 22 '15 at 8:38
  • $\begingroup$ Reference a Civilian (737) question here: aviation.stackexchange.com/questions/21122/… Civ. aircraft look much harder at fuel economy, etc. but it seems the primary benefit is low-speed performance and better overall performance. $\endgroup$ – blaughw Oct 22 '15 at 16:26
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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.

Drooped wing tip

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:

Aileron extended

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.

CMDS wingtip

Source: rcgroups.net

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    $\begingroup$ 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. $\endgroup$ – ROIMaison Oct 21 '15 at 11:24
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    $\begingroup$ 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) $\endgroup$ – KeithS Oct 21 '15 at 19:28
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    $\begingroup$ @FreeMan I read that as "more vortex wake than an upward-swept winglet, but less vortex wake than no winglet at all" $\endgroup$ – raptortech97 Oct 21 '15 at 22:36
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    $\begingroup$ 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. $\endgroup$ – Jay Carr Oct 22 '15 at 13:01
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    $\begingroup$ @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. $\endgroup$ – Schwern Oct 26 '15 at 17:57
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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.

enter image description here

Source

There are more aircraft that employ this type of wingtip device: Glider with drooped tips

Source

enter image description here

Source

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  • $\begingroup$ 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. $\endgroup$ – DrZ214 Oct 21 '15 at 9:48
  • $\begingroup$ See this answer aviation.stackexchange.com/questions/21799/…. Moving it further away reduces its strength and effects. $\endgroup$ – ROIMaison Oct 21 '15 at 9:54
  • $\begingroup$ I'm guessing they don't work as well as a winglet. $\endgroup$ – Ethan Oct 21 '15 at 11:38
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    $\begingroup$ @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. $\endgroup$ – slebetman Oct 22 '15 at 9:21
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    $\begingroup$ @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. $\endgroup$ – slebetman Oct 22 '15 at 14:49
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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. my plane

wingtip

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.

enter image description here

enter image description here

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    $\begingroup$ Interesting answer from another perspective, welcome to Aviation.SE :) $\endgroup$ – ROIMaison Oct 23 '15 at 10:08
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    $\begingroup$ Indeed! Excellent answer with practical experience that directly applies to the A10's flight profile. $\endgroup$ – FreeMan Oct 23 '15 at 13:00
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    $\begingroup$ 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. $\endgroup$ – DrZ214 Oct 24 '15 at 2:48
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    $\begingroup$ 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. $\endgroup$ – mr2day Oct 25 '15 at 18:29
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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.

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    $\begingroup$ 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. $\endgroup$ – ROIMaison Oct 21 '15 at 12:22
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    $\begingroup$ 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. $\endgroup$ – Sanchises Oct 21 '15 at 12:56
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    $\begingroup$ @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. $\endgroup$ – Peter Kämpf Oct 21 '15 at 13:57
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    $\begingroup$ [citation needed] $\endgroup$ – Russell Borogove Oct 21 '15 at 15:20
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    $\begingroup$ 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. $\endgroup$ – Anthony X Oct 22 '15 at 3:50
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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?

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