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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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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:
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):
... and a pull of 3g's:
(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)
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.
I found the right answer to the question. Maneuver load alleviation device is this function on some jets. These implementations actually schedule symmetric trailing edge (inboard) flaps down while scheduling the ailerons (outboard) trailing edges up. The total lift stays about the same, but more of the lift is generated closer to the fuselage, in an attempt to reduce that total bending moment.
