An aeroelastic model structure investigation for a manned real-time rotorcraft simulation

Historically, rotorcraft simulations have assumed a model structure incorporating rigid blades and uniform inflow. Advances in computational techniques and rotorcraft theory has enabled the inclusion of higher order models elements into the real-time simulation. This research addresses a model structure assessment of a flexible rotary wing manned flight simulation. The model is a UH-60 blade element simulation. The model possesses a unique capability to provide a variable model structure with consistent matching between structural and aerodynamic theory. The structural model is a representation of the flexible blade based on apriori data. The dynamic inflow model is an adaptation of the Peters and He theory. The investigation methodology consisted of a piloted assessment, frequency domain and time domain criteria evaluations. Real-time operation permitted a piloted evaluation with rapid alterations to the model structure in question. Frequency response testing permitted an evaluation of the mid to high frequency range. The Comprehensive Identification from FrEquency Response (CIFER) program was used for determining the frequency responses. Time domain response was obtained by driving the simulator controls, recording the resultant response and comparing it to flight test data. This testing methodology was a comprehensive approach which investigated the full range of operation including objective and perceptual fidelity. The CIFER program was invaluable as a frequency response tool. Results indicated that an increase in dynamic wake complexity increased the damping of the heave, pitch and roll channels. Inclusion of blade elasticity reduced the control sensitivity and increased the excitation of existing system modes. The real-time, coupled, simultaneous solution methodology for rotorcraft modeling was superior to previous techniques for off-axis and modal predictions. The previous used model assumptions of rigid blades and uniform inflow resulted in dramatic errors in off-axis response and predictability. The inclusion of second harmonic blade dynamics and dynamic wake is essential for a simulation used in analysis, design, flight test training and modal prediction.