An Approac e Determination of Aircraft Handling Qualities Using Pilot Transfer Functions

Abstract

It is shown that a correlation exists between pilot-aircraft system closed-loop characteristics, determined hy using analytical expressions for pilot response along with the analytical expression for the aircraft response, and pilot ratings obtained in many previous flight and simulation studies. Two different levels of preferred pilot response are used. These levels are 1) a static gain and a second-order lag function with a lag time constant of 0.2 sec and 2) a static gain, a lead time constant of 1 sec, and a 0.2-sec lag time constant. If a system response with a pitch-angle time constant of 2.6 sec and a stable oscillatory mode of motion with a period of 2.5 sec can be achieved with the first level pilot model, it is shown that the pilot rating will be satisfactory for that vehicle. Further, if an altitude response with a stable oscillatory mode of motion with a period of 5 sec can be achieved, the vehicle will be rated satisfactory. If the second level pilot model is required to achieve these system response characteristics, the aircraft will be rated acceptable-unsatisfactory. Nomenclatureh = altitude, ft (m) K\ -pilot model static gain La. = normalized lift-force derivative, per sec L& e = normalized control-lift derivative, per sec M q = normalized damping-moment derivative in pitch, per sec M a = normalized pitching-moment derivative, per sec 2 Ms e = normalized pitching control-moment derivative, per sec 2 P h = closed-loop period of the altitude mode of motion, sec P a -closed-loop period of the angle-of-attack mode of motion, sec s = Laplace operator, per sec T -closed-loop time constant, sec TI = pilot model lead time constant, sec TI -pilot mo'del lag time constant, sec T$z -open-loop aircraft lead time constant, sec V = velocity, ft/sec (m/sec) x = displacement, ft (m) a. = angle of attack, rad 7 = flight-path angle, rad 8 = control deflection, rad e = displayed error, rad f = damping ratio £h -damping ratio of the altitude mode of motion £a = damping ratio of the angle-of-attack mode of motion B = pitch angle, rad wn = open-loop aircraft undamped natural frequency, rad/sec ojf = control actuator undamped natural frequency, rad/sec Subscripts c = command h = altitude = error = pitch