Evaluation of Longitudinal Control Feel System Modifications Proposed for USAF F/RF-4 Aircraft.

摘要

This report presents the results of a 13-flight evaluation of modifications proposed for USAF F/RF-4 longitudinal control feel systems. The modified system (phase II) consisted of a mechanical stop in place of the viscous damper, revised damper links and replacement of the production 5 pound per g bobweights with 3 pound per g bobweights. The phase II system was designed to decouple the aircraft/flight control natural frequencies, and thereby eliminate aircraft residual oscillations. The stability and control characteristics of the F-4C with the phase II system were acceptable, and the longitudinal handling qualities were greatly improved. Residual oscillations were eliminated with the phase II system. Subsonic maneuvering forces were essentially the same with both systems. Caution should be used when maneuvering in the transonic speed region near limit load factors because a noseup pitching tendency exists at approximately 10 units angle of attack which could lead to aircraft overstress or loss of control. With the phase II installation, the airplane exhibited on 'unstable' variation of stick force with Mach number during low altitude supersonic flight conditions. This was considered objectionable but acceptable since the longitudinal forces could be easily trimmed out. The most significant deficiency of both the phase I and phase II systems was poor stick centering at low speeds in the power approach configuration. The phase II control system should be installed in USAF F/RF-4 aircraft.