The aim of this paper is to compare between different control techniques for the aircraft longitudinal motion. It deals specifically with poorly damped flight conditions. Three types of longitudinal autopilots are presented; rate of climb, altitude hold, and velocity hold autopilots. Some continuous-time control techniques are presented for the rate of climb autopilot; optimal control using state feedback, pole placement, and lag control. Finally, the Model Reference Adaptive Control (MRAC) technique is presented. The MRAC is selected to be the appropriate control technique for the autopilots of such types of aircrafts. Then It is used in designing an appropriate control system for the rate of climb autopilot, and also used in designing the control system for the rest autopilots; altitude hold and velocity hold. Due to
the complexity of the velocity hold system for these types of aircrafts in some flight conditions, an online system parameter estimation algorithm is used along with an online design and implementation algorithms for MRAC.