The lift coefficient (CL) is not constant, as Ikarus appeared to be suggesting even though it probably was not what he meant. However, it does not vary with airspeed (except for slightly, through the changed Reynolds number) but only with angle of attack.
If the angle of attack, and thus CL
, is kept constant, lift is indeed proportional to the (total) airspeed squared. However, as you generally want just the right amount of lift to compensate for the weight of the aircraft (in level flight only, if you want to be strict about it), you’ll typically find yourself reducing the angle of attack and thus CL
to keep the same amount of lift as speed increases. Thus, the lift coefficient will decrease with increasing airspeed. Perhaps this is what your instructor was talking about?
L = CL
* q_a * S = CL
* 1/2 * rho * V^2 * S
where L is lift, q_a is the ambient dynamic pressure, S is the wing area, rho is the air density and V is TAS.
Extending flaps does change the CL
(AoA) curve. The main purpose of flaps is (typically) to increase the maximum CL
, allowing flight (i e lift equals weight) at a lower airspeed.
I thought I was doing good trying to avoid those airport hotels... and look at me now.