System Identification and Stitched Modeling of the ADAPT™ Winged Compound Helicopter Scaled Demonstrator

Frequency-domain system identification was performed for the ADAPT™ Winged Compound Helicopter Scaled Demonstrator, a 10% scale version of the Piasecki X-49A, at four flight conditions spanning its flight envelope. Since the aircraft has eight redundant control effectors – lateral cyclic, longitudinal cyclic, collective, Vectored Thrust Ducted Propeller (VTDP) RPM, rudder, differential flaperon, symmetric flaperon, and elevator – and exhibits a large amount of inter-axis coupling, the Joint Input-Output (JIO) Method was used for system identification in addition to the Direct Method. Based on the identified frequency responses, a hybrid model structure, which explicitly includes the coupled fuselage-rotor flapping dynamics and a first-order model for VTDP RPM lag, was used. State-space models were identified at each flight condition, and combined with trim data to form a full flight envelope stitched simulation model. A detailed analysis of the trends of the stitched model trim, stability and control derivatives, eigenvalues, and frequency responses was performed.