Techniques to improve maneuver stability characteristics of a nonlinear wide-body transport airplane in cruise flight

The maneuver control stability characteristics of an aircraft are a flying qualities parameter of critical importance, to ensure structural protection as well as adequate predictability to the pilot. Currently, however, maneuver stability characteristics are not uniquely addressed in the Federal Aviation Regulations (FAR) Part 25, for transport aircraft. In past transport category certification programs, the Federal Aviation Administration (FAA) has used a combination of requirements (longitudinal control, vibration and buffeting, high-speed characteristics, and out-of-trim characteristics) to ensure safe and controllable maneuver stability characteristics over a range of flight conditions and airplane configurations. Controversies exist regarding each of these regulations, however, and considerable expenditures in terms of design studies and testing time have resulted from the requirements. It is also recognized that additional engineering guidance is needed for identifying acceptable nonlinear maneuver stability characteristics, particularly as they relate to relaxed stability, highly augmented transport configurations. The current trend in large aircraft design is toward relaxed, or even negative, static margins for improved fuel efficiency. The advanced flight control systems developed for these aircraft, in many instances, have rendered current aforementioned maneuver stability criteria either too stringent or of little practical use. Current design requirements do not account for these advanced designs. The objective was to evaluate a broad spectrum of linear and nonlinear longitudinal stability characteristics to generate data for defining satisfactory and unacceptable maneuver characteristics, as defined by pilot opinion. Primary emphasis was placed on two techniques of varying column force per normal acceleration. This study was a joint venture with four pilots participating; one from NASA, one from the FAA, and two from industry

Techniques To Improve Maneuver Stability Characteristics of a Nonlinear Wide-Body Transport Airplane in Cruise Flight

Lockheed L-1011 aircraft used for in-flight research. The PACS provided acceptable flying qualities for negative static margins to 5 percent. As the aircraft center of gravity moved aft and the static margin changed from positive to negative, the maneuver stability characteristics were modified through systematic variations of PACS, pitch-rate damper gain, control loading (column force per column deflection (F c =ffi c )), and control gearing (horizontal-tail deflection per control force (ffi H =ffi c )). The evaluation tasks consisted of performing (l) small pitch-attitude changes, (2) standard operational turns, and (3) wind-up turns at an altitude of 33 000 ft at a Mach number of 0.83, and in calm atmospheric conditions. Nonlinear maneuver stability is defined as a nonincremental change in stick force required to effect an incremental change in normal acceleration. The results of this experiment verify current mi