During a stall or spin, which flight control is the least effective?

During a stall or spin, the ailerons are the least effective flight control. This is primarily due to the aerodynamic conditions that prevail during these phases of flight. In a stall, airflow over the wings is disrupted, reducing overall lift and increasing drag. Since ailerons function by altering the airflow around the wings to create differential lift, their effectiveness is significantly diminished when the wings are not generating sufficient lift due to the stall condition.

In a spin, ailerons can actually exacerbate the situation. Attempting to roll out of a spin using ailerons can induce further yaw, leading to increased spin rates or delaying the recovery from the spin. The aerodynamic stall results in a loss of aileron authority because the wings are already flowing in a stalled condition. Hence, applying ailerons has little to no impact on changing the aircraft's roll attitude effectively.

In contrast, the other flight controls, such as the elevator and rudder, still maintain some level of effectiveness during stalls or spins. The elevator can be used to pitch the nose down to break a stall, while the rudder is crucial for controlling yaw during spins for recovery. Flaps, although not typically effective in stalls and spins, do not interfere with the basic recovery mechanisms