Handling Qualities Requirements and Control Design for High-Speed Rotorcraft
Open Access
- Author:
- Berger, Tom
- Graduate Program:
- Aerospace Engineering
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- October 01, 2019
- Committee Members:
- Joseph Francis Horn, Dissertation Advisor/Co-Advisor
Joseph Francis Horn, Committee Chair/Co-Chair
Eric Norman Johnson, Committee Member
Edward Smith, Committee Member
Christopher D. Rahn, Outside Member
Mark B. Tischler, Special Member
Amy Ruth Pritchett, Program Head/Chair - Keywords:
- Rotorcraft
Handling Qualities
Flight Control System
Control Laws
Tiltrotor
Compound Helicopter - Abstract:
- The U.S. Department of Defense has established the Future Vertical Lift initiative to develop a family of next-generation vertical lift aircraft that will fly farther, faster, and more efficiently than the current fleet of rotorcraft. To accomplish these goals, advanced rotorcraft configurations beyond the single main rotor/tail rotor design must be considered. Two advanced configurations currently being flight tested in a technology demonstrator program are a lift offset coaxial rotorcraft with a pusher propeller and a tiltrotor. The U.S. Army Aviation Development Directorate has developed generic, high-fidelity flight-dynamics models of these two configurations to provide the government with independent control-system design, handling-qualities analysis, and simulation research capabilities for these types of aircraft in support of the Future Vertical Lift initiative. In an effort to begin defining high-speed handling qualities requirements for these types of advanced rotorcraft configurations, full flight envelope inner-loop explicit model following control systems were designed for both configurations using a multi-objective optimization approach to meet a comprehensive set of stability, handling qualities, and performance requirements. The requirements were chosen from both helicopter and fixed-wing criteria. The control laws for both aircraft were evaluated in a piloted simulation experiment at the NASA Ames Vertical Motion Simulator using a series of high-speed handling qualities demonstration maneuvers. The results from the simulation experiment show overall assigned Level 1 handling qualities for both aircraft which correlates well with the predicted Level 1 handling qualities they were designed to, thus supporting the choice of handling qualities requirements selected during the design process. In addition, outer-loop control laws were also developed for both aircraft in an effort to improve handling qualities and reduce pilot workload. A dynamic inversion control law architecture was used for the outer loops, and again a comprehensive set of stability, handling qualities, and performance requirements was used to optimize the parameters of the control laws. The outer-loop control laws for both aircraft were evaluated in a piloted simulation experiment at the Pennsylvania State University Flight Simulator facility using a subset of the high-speed handling qualities demonstration maneuvers used in the first evaluation. Overall, the outer-loop control laws provided Level 1 handling qualities for the Break Turn and High-Speed Acceleration/Deceleration maneuvers, with improvements seen over the inner-loop control laws. In addition, the outer-loop control laws improved performance and reduced workload during a formation flying task that was developed for this project. However, for pitch attitude capture and tracking tasks, the outer-loop control laws degraded handling qualities as compared to the inner-loop control laws. This was due to the pitch attitude dropback behavior of the outer-loops, even though they were tuned to meet the dropback specification. The results suggest that the amount of allowable dropback should be decreased for high-speed rotorcraft and the outer-loop functionality might be provided as a selectable mode. The set of handling qualities criteria used to optimize the inner- and outer-loop control systems presented here are proposed as a set of requirements to tune high-speed rotorcraft control systems to achieve Level 1 handling qualities.