Closed Loop System Identification Experience For Flight Control Law And Flying Qualities Evaluation Of A High Performance Fighter Aircraft

This paper highlights some of the results and issues associated with estimating models to evaluate control law design methods and design criteria for advanced high performance aircraft. Experimental fighter aircraft such as the NASA-High Alpha Research Vehicle (HARV) have the capability to maneuver at very high angles of attack where nonlinear aerodynamics often predominate. HARV is an experimental F/A-18, configured with thrust vectoring and conformal actuated nose strakes. Identifying closed-loop models for this type of aircraft can be made difficult by nonlinearities and high order characteristics of the system. In this paper, only lateral-directional axes are considered since the lateral-directional control law was specifically designed to produce classical airplane responses normally expected with low-order, rigid-body systems. Evaluation of the control design methodology was made using low-order equivalent systems determined from flight and simulation. This allowed comparison of the closed-loop rigid-body dynamics achieved in flight with that designed in simulation. In flight, the On Board Excitation System was used to apply optimal inputs to lateral stick and pedals at five angles at attack : 5, 20, 30, 45, and 60 degrees. Data analysis and closed-loop model identification were done using frequency domain maximum likelihood. The structure of identified models was a linear state-space model reflecting classical 4th-order airplane dynamics. Input time delays associated with the high-order controller and aircraft system were accounted for in data preprocessing. A comparison of flight estimated models with small perturbation linear design models highlighted nonlinearities in the system and indicated that the closed-loop rigid-body dynamics were sensitive to input amplitudes at 20 and 30 degrees angle of attack. Murphy, Patrick C. Langley Research Center NASA/TM-1998-207995, NAS 1.15:207995 ...

Adverse aircraft-pilot coupling (APC) events include a broad set of undesirable and sometimes hazardous phenomena that originate in anomalous interactions between pilots and aircraft. As civil and military aircraft technologies advance, interactions between pilots and aircraft are becoming more complex. Recent accidents and other incidents have been attributed to adverse APC in military aircraft. In addition, APC has been implicated in some civilian incidents. This book evaluates the current state of knowledge about adverse APC and processes that may be used to eliminate it from military and commercial aircraft. It was written for technical, government, and administrative decisionmakers and their technical and administrative support staffs; key technical managers in the aircraft manufacturing and operational industries; stability and control engineers; aircraft flight control system designers; research specialists in flight control, flying qualities, human factors; and technically knowledgeable lay readers.