Handling Qualities Criteria

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.

In-fl ight simulation experiments performed in 1967 with a variable-stabil ity aircraft during the author's stay at Princeton University, motivated the study of handl ing characteristics of future transport aircraft with closed-loop fl ight control systems. In 1972, the first experiment took place at the National Aerospace Laboratory NLR, using one of its research aircraft. In anticipation of expected developments in (digital) fl ight control technology, the research programme following the first experiments was aimed at the establ ishment of quantitative handl ing qual ities criteria. An appreciable part of that programme has been sponsored by the Netherlands Agency for Aerospace Programs (Nederlands Instituut voor VI iegtuigontwikkel ing en Ruimtevaart) and the Department of Civil Aviation of the Netherlands (Rijksluchtvaartdienst). In 1981, a thorough review of the extensive and valuable data gathered was started. The result, presented in this book, was also included in the author's thesis for a Ph.D. degree of the Delft University of Technology. To introduce the reader to the multi-discipl inary field of handl ing qual ities research, introductory chapters are presented on longitudinal aircraft dynamics, closed-loop fl ight control systems using non-mechanical signal transmission, human pilot dynamics, hand I ing qual ities assessment techniques, and the present status of handl ing qual ity criteria.

"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 report uses as a point of departure the concept that control of bank angle is the primary piloting task in maintaining or changing heading. Regulation of the bank angle to maintain heading is a close-loop tracking task in which the pilot applies aileron control as a function of observed bank angle error. For large heading changes, the steady-state bank angle consistent with available or desired load factor is attained in an open-loop fashion; it is then regulated in a closed-loop fashion throughout the remainder of the turn. For the transient entry and exit from the turn, the pilot is not concerned with bank angle per se, but rather with attaining a mentally commanded bank angle with tolerable accuracy in a reasonable time, and with an easily learned and comfortable program of aileron movements.

This report is a codification in two parts of conventional aircraft handling qualities criteria. The results of this effort are to serve as an intermediate design guide in the areas of lateral-directional oscillatory and roll control. The roll handling qualities portion of this report uses as a point of departure the concept that control of bank angle is the primary piloting task in maintaining or changing heading. In the lateral oscillatory portion of this effort, in defining requirements for satisfactory Dutch roll characteristics, a fundamental consideration is the fact that the motions characterizing this mode are ordinarily not the pilot's chief objective. That is, he is not deliberately inducing Dutch roll motions in the sense that he induces rolling and longitudinal short-period motions. A worthwhile approach to establishment of Dutch roll damping requirements is to first establish the basic level, and then to study the varied influences of the disturbance parameters. This approach provides the basis for the material contained in this report.