Time response of quadcopter attitude closed-loop system with cascade PID controller operating in-ground-effect (a1) regulation with different initial conditions and desired roll, pitch, yaw to 0; (a2) settling time at z = 0.47 m; (a3) settling time at z = 0.02 m; (b1) regulation with zero initial conditions and different desired attitude; (b2) settling time at z = 0.47 m; and (b3) settling time at z = 0.02 m