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In some parts of the flying envelope of the F/A-18 Hornet and MiG-29 the ailerons from the external parts of the wings go up in sync. They're made to go one up one down in order to get rolls, not up/up .

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https://m.facebook.com/story.php?story_fbid=548605942390983&id=148530445855064

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    $\begingroup$ It is wrong to assume any flight control surface on a modern fighter jet would have a simple traditional function. (They're made for swing up /down in order to get rolls, not up /up). The flight control computer can use any surface for any desired effect if it is programmed to do so. $\endgroup$ – Jpe61 Feb 2 at 19:05
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    $\begingroup$ Mig 29 is not fly by wire jet $\endgroup$ – George Geo Feb 2 at 19:07
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    $\begingroup$ Doesn't have to be fly-by-wire to have a flight control computer that can add the sort of other-that-traditional inputs that Jpe61 mentions into a mix that directs hydraulic controls. Lots of non-FBW aircraft have inputs (stick pusher, speed trim, yaw damper, etc) into their flight controls from sources other than the pilot. $\endgroup$ – Ralph J Feb 2 at 19:21
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    $\begingroup$ BTW I don't see why this question would deserve minus points? It is a valid question, and I'm sure someone (not me though) will be able to give at least a theoretical reason for the fcs movements. $\endgroup$ – Jpe61 Feb 2 at 19:26
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    $\begingroup$ Are we sure this isn't just an optical illusion due to a slight flap deflection downward during maneuvering? $\endgroup$ – Bryson S. Feb 3 at 8:23
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The pictures in the question show the normal position of the MiG-29 ailerons. That's how they are unless a roll is commanded.

According to Mikoyan Mig-29 Fulcrum Pilot's Flight Operating Manual (google books) the slight upward position is set to improve yaw stability during roll meneuvers:

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As for whether this angle (neutral position of ailerons) changes in accordance with flight envelope: it does not. Check out this and this Youtube video for an example. Climb, dive, straight and level, no change. The position of the ailerons is not affected by load factor either, as you can see below, 1g (straight & level flight):

1G

... and a pull of 3g's:

3G

(Source: the second Youtube video posted above)

Whenever you see the ailerons move, it is always accompanied by roll.

As for the F-18, I'll investigate and be back later. (edit: as a preliminary claim I'd say the F-18 drops flaps a few degrees on high g maneuvers to increase camber, but the flaperons only move when roll is comanded or flaps are lowered. So no flaperon up with high g)

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  • $\begingroup$ But in my video presented here the Mig29 is in level turn not rolling $\endgroup$ – George Geo Feb 4 at 17:16
  • $\begingroup$ @GeorgeGeo ...and in the video the ailerons are in the same position as they are in the picures in my answer aren't they? Just as they are supposed to be. $\endgroup$ – Jpe61 Feb 4 at 19:22
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    $\begingroup$ When a roll is not being commanded, both of the MiG-29 ailerons are in a slight up position. $\endgroup$ – Jpe61 Feb 4 at 19:24
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    $\begingroup$ @GeorgeGeo I found a source explaining the slight upward tilt of the ailerons, I edited my answer to include this information. $\endgroup$ – Jpe61 Feb 5 at 18:35
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On these modern aircraft, there is a thing called flaperons - meaning ailerons and flaps combined, which both move down and up when more lift is needed (TO, LDG and also during some aggressive maneuvers), and are used in order to roll the aircraft.

Also- traditionally- you would assume that the plane uses his tail elevators for pitch, but the contrary is correct- watch rolling F-15 or F-16 and you will see the tail elevators compensating for the wing's inability to roll in various occasions.

I would say that the best and shortest answer would be: Don't try to extrapolate from the basic aerodynamics of a Cessna or a simple aircraft with old school steering surfaces to these jets as they are very different in design and function.

Every plane has it's own very specific characteristic in order to cope with its design problems. For example, in an F-15 when you roll a full stick aside during a very high angle of attack maneuver, the ailerons don't move in order to maintain stability (otherwise there would be a spin due to aileron drag and other factors).

Try to look at these planes as really fly-by-wire (although some of them achieve the same results of stability using plain mechanical devices and not computers), so elevons, flaperons, and such.

Maybe what you see is actually a momentary roll to the left, resulting in an aileron that is above the profile of the left wing. And another note regarding your question- there is no really such a thing as a "dive" which you can see on the wings. These are very momentary positions of the control surfaces to induce movement and acceleration in some direction. Look at an F-16 taxiing and you will see it's tail dancing in order to compensate for the instability of the G sensor on rough ground.

Regarding your assumption, There are no such loads on such short wings of the combat jets so this is not the reason really. These are just rockets with people strapped to them basically, so they try to be as slick as possible, with just the minimum drag by their control surfaces, using the little lift made by their body and wings with the high speed they fly in.

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  • $\begingroup$ Stav Nemirovsky The Mig 29 has flaps inboard and ailerons outboard .The F16 uses flaps and ailerons single command surface called flaperons for rolling but is not the case for MIGs. The elevators differential is used for rolling in this aircraft too , but that is not the question here .The F15 use rudders at higher AoA for roll s by ARI system $\endgroup$ – George Geo Feb 3 at 8:45
  • $\begingroup$ Stav Nemirovsky ,I like your thinking about the aircraft complexity but the Mig 29 have only analogue available systems incorporated and some boosted for help pilot with fatigue. $\endgroup$ – George Geo Feb 3 at 8:57
  • $\begingroup$ All correct. So show me the movie and i wll explain what he does. Probably- it's just a moentary roll command. And also- i dont really know what goes on inside the mig 29's control computer (such we both understand the F15), but i would guess something there is quite the same. What i can say for sure is that these anes don't use the ailerons to reduce loads on the wingtips. So next- lets see the movie! $\endgroup$ – Stan Feb 3 at 9:13
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    $\begingroup$ The video does indeed seem to show the outer and inner control surfaces to be in differing agles, outers more upright than the inner ones. $\endgroup$ – Jpe61 Feb 3 at 20:58
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    $\begingroup$ well, no idea then :) I will attend my professional help now! My guess would be some kind of stabilization as maybe the wings in a neutral position give a natural pitch up tendency. $\endgroup$ – Stan Feb 4 at 19:28

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