1. When you are pulling g, the wing must produce more lift. For example at 5 g, the wing produces five times as much lift as in level flight. This increases induced drag (drag due to lift) dramatically – especially if you approach maximum lift. If you want to sustain this load factor, you cannot allow the airspeed to bleed off from the best airspeed for sustained load. To compensate this increased drag you need more thrust. The load factor at which total drag (including this big induced drag component) equals total thrust in level flight is the sustained load factor. More engine thrust = higher sustained load factor. Lower induced drag = higher sustained load.
Another type of load factor is instantaneous load factor. This one cannot be sustained because your airspeed is bleeding off rapidly, you do not have enough thrust to compensate the high induced drag. Instantaneous load factor is a function of speed and wing aerodynamic characteristic.
The limit load factor is what the pilot is allowed to pull before damaging the airframe – with some safety margin.
The ultimate load factor is that safety margin applied to limit load, it is where permanent deformation of the structure can occur, or some other type of failure.
2. The sustained load at sea level is higher than at 15,000 ft because the engine produces more thrust at sea level. It is quite possible that the M346 engines have enough thrust to sustain more than 8.0 g at sea level, but it cannot be more than the limit load of 8.0 g which is a structural limit.
3. Sustained load is not meaningless, it is a key air combat capability parameter. It is useful to know if you want to realistically train for air combat.
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