Longitudinal control system design and handling qualities assessment of a Blended Wing Body aircraft

Design of a longitudinal flight control system for a Blended Wing Body (BWB) tailless aircraft is presented. The BWB aircraft is assumed to be operating with a reduced static margin and is marginally stable. After trimming, the linear model is obtained by evaluating the dimensional derivatives for a low speed terminal flight condition. The linear model is then augmented with actuator dynamics. The longitudinal short period and phugoid dynamics are initially analyzed for the open loop case. The short period mode was restored artificially to nominal values by incidence and pitch rate feedback. Once the conventional short period is restored a pitch rate command attitude-hold (RCAH) flight control system was designed to improve the handling qualities of the aircraft. The Gibson Dropback handling qualities assessment criteria was applied to evaluate the pilot opinion rating. The handling qualities were assessed for both the augmented and un-augmented case. For this tailless configuration, the handling qualities improved from Level 2 to Level 1 when the rate command attitude hold longitudinal flight control system was engaged.