The speed in landing pattern is not fixed one due to the weight/drag of the aircraft at the moment(loads of bombs and fuel). But if you speed up then you're going to go upwards don't you(if you keep the11 AOA) ? Because any changes in pitch increases the amount of the lifting force. See my point of view? If change one must alter the other. So if you're not happy with the glide slope (to steep or to shallow adjust the throttle (for F16 only) but automatically within that case the AOA will decrease or increase.
Using AoA as reference gives a simple way to maintain a safe stall margin. If approach speed was used as reference, there would have been multiple speeds to memorize, as the weight is not the same from mission to mission.
Remember, wings basically always stall a certain AoA, not certain speed. Specifying a AoA to maintain, the weight of the plane is automatically compensated for.
The pilot does not need to worry about speed. If he/she wants to go higher, add throttle, maintain AoA -> plane goes up. If one is too high, decrease throttle, maintain AoA -> plane descents. The airspeed is out of the equation, so simple. Just remember to keep AoA at 11 degrees.
As you stated, depending on mission, military aircraft have huge variation in takeoff and landing weights. They also have very reliable AoA metering, so it' s best to go this way.
Correct that changes to one performance parameter will affect others, but it isn't totally clear what you are asking.
If you are in the pattern at 11 deg AOA and level flight you are in equilibrium. 11 deg AOA correlates to a certain airspeed at a given weight.
That airspeed will vary depending in weight, and the correct indicated airspeed must be for each landing weight and cross checked against the AOA gauge for accuracy.
If you “speed up”, you won't be at 11 deg any longer. If you just pitch up, you will increase AOA, climb, and decelerate unless you add power.
If you are light, your airspeed will be lower at 11 degrees AOA than if you are heavy. So, “multiple airspeeds to memorize” is partly true, but generally there are basic rules of thumb that make it easier: For example, if you know your 11 deg airspeed at your base weight, you simply add fuel and stores weight, multiply by some factor, (in my case 1.5 Kias per 1000 lbs) then add this to the base approach speed.
The reality is that your “on-speed” approach and landing speed will typically only vary +/- 10 knots from “normal”, and the quick calculation plus fuel gauge accuracy probably has a tolerance of a few knots as well, so as long as airspeed is in the ball park enough to trust your AOA gauge, then that is what you use.
The original question states:
The speed in landing pattern is not fixed one due to the weight/drag of the aircraft at the moment(loads of bombs and fuel). But if you speed up then you're going to go upwards don't you(if you keep the11 AOA) ? Because any changes in pitch increases the amount of the lifting force.
This is a flawed premise.
Any time that the aircraft is travelling at a nearly horizontal trajectory with a constant airspeed and vertical speed, lift is very nearly equal to weight.
Given these conditions, if we prescribe a target angle-of-attack, then we are essentially prescribing that the airspeed should vary according to the square root of any change in wing loading. Any variation from this target speed will cause in imbalance between (the vertical component of) of lift and weight, which will cause the flight path to curve upwards or downwards.
If we are holding 11 degrees angle-of-attack, and our weight suddenly increases by a factor of 2 for some mysterious reason, and our airspeed increases by a factor of 1.4 for the same mysterious reason, no, we will not "go up". As long as the airspeed varies according to the square root of the change in wing loading, the forces on the aircraft can remain in balance.