Optimal takeoff procedures for a transport category tiltrotor

Abstract

TILTROTOR aircraft are capable of performing running takeoffs similar to an airplane, whereas they use vertical and short takeoffs when operating as a helicopter. A method is presented to determine optimal takeoff procedures according to the available field length such that the takeoff weight is maximized while also complying with the transport category regulations. Contents Commercial tiltrotors are expected to be certificated in the powered-lift transport category,1 one which requires that the aircraft can continue takeoff in one-engine-inoperative (OEI) conditions once the critical decision point (CDP) has been passed (continued takeoff, CTO), and also be safely landed when power failure occurs during takeoff before reaching the CDP (rejected takeoff, RTO). These requirements impose a significant limitation on the takeoff weight, and accordingly, research has been directed at investigating optimal takeoff procedures to realize efficient tiltrotor operation.2-3 Our previous work developed a method to analyze helicopter takeoff procedures for transport category operations by applying nonlinear optimal control theory to a theoretical helicopter model.4 This led to the present article which extends this method to include a tiltrotor configuration. The following state variables are considered: forward speed u, rate of descent w, pitch rate q, pitch attitude ®, rotor rotational speed f), nacell angle /„, height above the takeoff surface /i, and flight distance from the takeoff point jc, while the column and collective lever positions and nacelle angle rate are the control variables. Vertical Takeoff Optimization