An Integrated Methodology for Flight Vehicle Sizing Subject to Stability and Control Constraints

Abstract

This dissertation focuses on incorporating stability and control into the conceptual sizing of novel flight vehicle concepts based on flying qualities guidelines defined for both rotor-borne and wing-borne flight conditions. The nonlinear model of the bare airframe is numerically linearized at discretized segment points during sizing iterations and the dynamic modes are evaluated using eigenvalues of the linear time-invariant system. Aircraft dynamic stability and flying qualities guidelines for both fixed-wing and rotary-wing vehicles are included as constraints for respective flight modes and the vehicle sizing rules are defined to size respective control effectors while satisfying the constraints at all the trim points throughout the mission profile, including possible off-nominal flight conditions. Control requirements are posed for nominal and off-nominal flight conditions, and a control effector sizing method is developed to meet those requirements in the conceptual sizing. Two different methods are presented in this study: (i) nonlinear time domain simulation is used to evaluate flight dynamic performance and control effectors are sized to meet the enforced constraints at each sizing iteration, and (ii) maneuverability requirements are defined in terms of desired moment requirements and the attainable moment subset approach is used to size the respective control effectors to meet desired moments. For an overactuated system with multiple control effectors, this dissertation presents an approach to determine the control allocation to meet desired controllability requirements for both nominal and off-nominal flight conditions, including possible failure scenarios. In addition to incorporating flight dynamics constraints into the sizing process, this dissertation also demonstrates a robust design approach to account for aleatory and epistemic uncertainties in the conceptual design stage by using Monte-Carlo simulations to assess the probability of achieving certain performance targets in the presence of such uncertainties. An electrified general aviation aircraft is proposed, and a comparative study is presented against the conventional baseline aircraft, where block fuel and range performances are compared against the baseline, subject to the uncertainties in the assumed technology and operational variables.