Higher-order control system dynamics and longitudinal handling qualities

Abstract

An experimental investigation of the effects of higher-order control system dynamics on the longitudinal handling qualities of a fighter airplane are discussed. This research was undertaken using the USAF/CAL variable stability T-33 airplane as an in-flight simulator. Different higher-order responses were simulated by altering the elevator feel system, elevator actuator, and airplane short-period characteristics. Essentially the same configurations were evaluated by two pilots using a revised pilot rating scale. One pilot also rated the configurations for their pilot-induced oscillations (PIO) tendencies. Comments and ratings were related to a response delay parameter. Many of the higher-order control systems investigated produced pronounced PIO tendencies in flight, and some were considered unflyable with certain higher-order characteristics. A comparison of fixed-base and in-flight evaluations indicated that configurations with significant PIO tendencies were rated poorer in flight, and configurations with little or no PIO tendencies were rated better in flight.