Dynamics Control And Flying Qualities Of V Stol Aircraft

Annotation This text presents the principles of dynamics and control for vertical, short take-off landing (V/STOL) aircraft. It is the first book of its kind. It is intended for graduate students and professionals in aeronautics who have knowledge of linear systems analysis, aircraft static, dynamic stability, and control. The text begins with a discussion of V/STOL aircraft operations. Control strategies, equations of motion, longitudinal and lateral-directional flying qualities in both hover and forward flight, wind and turbulence responses, and control augmentation and cockpit displays are covered. Specific examples of the YAV-8B Harrier and XV-15 Tilt Rotor aircraft are used to illustrate actual V/STOL dynamic and control characteristics.

This publication presents materials that constituted the lectures presented by the author as part of Course AA 234 Dynamics, Control, and Flying Qualities of V/STOL Aircraft that was taught in the Department of Aeronautics and Astronautics at Stanford University. It covers representative operations of vertical and short takeoff and landing (V/STOL) aircraft, a discussion of the pilot's strategy in controlling these aircraft, the equations of motion pertinent to V/STOL tasks, and their application in the analysis of longitudinal and lateral-directional control in hover and forward flight. Following that development, which applies to the characteristics of the basic airframe and propulsion system, the text concludes with a discussion of the contributions of control augmentation in specific flight tasks and of the integration of modern electronic displays with these controls.

A study has been undertaken to define hand-ling qualities criteria for V/STOL aircraft. With the current military requirements for helicopters and airplanes as a framework, modifications and additions were made for conversion to a preliminary set of V/STOL requirements using a broad background of flight experience and pilots' comments from VTOL and STOL aircraft, BLC (boundary-layer-control) equipped aircraft, variable stability aircraft, flight simulators and landing approach studies. The report contains a discussion of the reasoning behind and the sources of information leading to suggested requirements. The results of the study indicate that the majority of V/STOL requirements can be defined by modifications to the helicopter and/or airplane requirements by appropriate definition of reference speeds. Areas where a requirement is included but where the information is felt to be inadequate to establish a firm quantitative requirement include the following: Control power and damping relationships about all axes for various sizes and types of aircraft; control power, sensitivity, d-amping and response for height control; dynamic longitudinal and dynamic lateral- directional stability in the transition region, including emergency operation; hovering steadiness; acceleration and deceleration in transition; descent rates and flight-path angles in steep approaches, and thrust margin for approach.

An investigation to determine the ranges of various lateral directional characteristics required to provide adequate flying qualities for turning maneuvers at low speed was undertaken using an airborne V/STOL aircraft simulator. Five parameters were varied in a systematic manner: the damping ratio, the frequency, and the ratio and the frequency of the numerator of the roll-angle to aileron-control-input transfer function. The pilots performed a low speed, visual maneuvering task and documented their assessment of the characteristics through extensive comments and a numerical rating. The report presents all the data categorized with respect to the test parameters. (Author).

The hover analysis considers pilot attitude and position control tasks in the presence of horizontal gusts. The effects of each of the stability derivatives on the difficulty of the control tasks and on the closed-loop gust responses are determined. It is clearly shown that the handling qualities studies of control sensitivity and angular damping must consider the influences of M sub u (or L sub v) and should include gust inputs. These conclusions are substantiated by previous variable-stability-helicopter experiments. The effects of vehicle size and geometry are investigated by several approaches. The key result of increasing size is found to be a reduction in M sub u and L sub v which can, in turn, lower the requirements for control power and damping. The handling qualities during transition of two vehicles, a tilt duct and a tilt wing, which were previously tested on a simulator are analyzed. It is shown that both trim control and perturbations about the trim conditions must be considered. In fact, part of the increased difficulty in landing transitions, in comparison with takeoff transitions, is due to more difficult trim control; the much more stringent position control requirements in landing are also a contributing factor.

Proceedings are reported of a symposium held in Dayton, sponsored by the Flight Dynamics Laboratory during 2-5 March 1982. The symposium was planned and ran by the Flight Control Division, specifically the Flying Qualities Group and the Control Techniques Group as part of an ongoing effort to revise and upgrade both MIL-F-8785C, Military Specification, Flying Qualities of Piloted Airplanes, and MIL-F-9490D, Flight Control System-Design, Installation and Test of Piloted Aircraft, General Specification For. Specialists from both the flying qualities and flight control system disciplines were gathered in Dayton from both industry and government agencies. Formal and informal presentations, plus workshop discussions, were structured around proposed draft versions of the new Flying Qualities MIL-Standard and Handbook and the new Flight Control Systems MIL-Specification and Handbook. This report contains a record of the presentations and discussions as submitted by the individual authors.