Masters Theses

Date of Award

12-1999

Degree Type

Thesis

Degree Name

Master of Science

Major

Aviation Systems

Major Professor

W. D. Lewis

Committee Members

U. P. Solies, Fred Stellar

Abstract

Since the 1950's, several nations have attempted to build Vertical and Short Takeoff and Landing (V/STOL) jet fighter aircraft in a variety of configurations. One of the greatest challenges of each design team was in designing and implementing a flight control system that reduced pilot workload to an acceptable level during the transition from conventional flight to fully jetborne flight. Not all the ideas worked, and even the more successful aircraft were difficult and dangerous to fly. Pilot workload of the only currently operated V/STOL attack fighter design, the Harrier, was reduced by installing limited authority augmented flight controls to increase aircraft stability, but still it remains more difficult to fly than conventional aircraft. The United States Marine Corps (USMC) and the United Kingdom's Royal Air Force (RAF) and Royal Navy (RN) have decided to replace their aging Harrier fleet of aircraft with an affordable next generation Short Takeoff and Vertical Landing (STOVL) strike fighter. All three services require the new STOVL aircraft to possess vast improvements in handling qualities over the Harrier. This thesis examines the solutions to reduce the excessive workload associated with V/STOL flight. In this thesis, specific comments on individual evaluated mode effects on handling qualities will be addressed, while deficiencies due to individual inceptor mechanical characteristics will be minimized. The analysis and solutions are based on the author's research, extensive Harrier flight time, and recent V/STOL flight test experience. The coupling of a highly augmented digital flight control system with STOVL task optimized, blended control response types controlled by an intuitive flight control inceptor scheme would greatly improve the handling qualities of an advanced STOVL strike fighter. The preferred inceptor scheme includes a left inceptor, a right center inceptor with an attitude trim switch and a thumbwheel, and control pedals. During STOVL operations, the recommended response type blended flight control design includes: sideslip command blended into yaw rate command on the control pedals, flightpath command blended into height rate command on the left inceptor, roll rate command with attitude hold blended into roll attitude command with natural ground referenced lateral acceleration coupling on the right inceptor lateral axis with crosswind compensation, flightpath command blended into pitch attitude command with augmented natural ground referenced longitudinal acceleration coupling on the right inceptor longitudinal axis, pitch and roll attitude right inceptor trim switch for use in the slow speed flight region, Translational Rate Command sub-mode option with the right inceptor, and flightpath referenced acceleration command blended into ground referenced acceleration command on the right inceptor located thumbwheel with speed hold detent. Implementation of the above concepts would greatly improve handling qualities in the STOVL flight regime. It has been decided that there is an advantage for the next generation of strike fighter to have a STOVL flight capability, but without increased operational cost or risk. To insure these requirements are satisfied, the aircraft contractors and military must use the existing technologies available to vastly reduce the pilot workload over past and current V/STOL aircraft designs.

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