V Stol Dynamics Control And Flying Qualities

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.

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.

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.

"This report presents a series of discussions on selected topics related to the development of VTOL flying qualities criteria. The topics were chosen on the basis of their importance to flying qualities and the potential significance to the Air Force VTOL Integrated Flight Control System (VIFCS) program. The treatment given to the selected topics was aimed at identifying those areas that require further study and research within the scope of the VIFCS program. -- page iii.

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.