C-17 engine-out compensation system testing

Abstract

The C-17A Engine-Out Compensation System (EOCS) developmental test and evaluation program was conducted at the Air Force Flight Test Center, Edwards AFB, California, during December 1997 and February 1998 by the C-17 Test Team. The purpose of EOCS is to improve C-17A takeoff performance, particularly on wet runways, by reducing the minimum control groundspeed (Vmcg). The Vmcg is the minimum speed during the takeoff run at which the pilot can maintain control of the airplane on the runway surface following sudden loss of thrust by the most critical engine (in the case of the C-17A aircraft, an outboard engine). This speed has to account for a 1-second delay in pilot reaction time from engine failure. Analyses have shown that a reduction in the reaction time translates into a significant reduction in Vmcg, leading to reduced runway lengths required for takeoff. The EOCS was designed to reduce the yaw and lateral deviation of the aircraft following failure of an outboard engine by scheduling rudder inputs opposite to the expected yaw from asymmetric thrust before the pilot begins corrective action. The prototype version of EOCS software tested used a 16-degree fixed rudder input (12 degrees for initial test points) for all engine failures. However, the final production EOCS configuration will use variable rudder input based on the speed at which the en,sine failure occurs and the takeoff thrust setting used. The EOCS software was resident in Electronic Flight Control Software (EFCS) version 5.2, and was tested using the C-17A Change-A-Gain system for maximum flexibility. The objectives of the testing were to evaluate the function of the EOCS, determine its effect on C-17A takeoff performance on dry and wet runways, acquire additional data for model development and validation, and refine the system configuration as necessary. Engine failures were simulated by performing a fuel cut to an outboard engine and pilot reaction time was targeted to be within 0.8 to 1.2 seconds. After the EOCS configuration was set, additional takeoff performance testing was accomplished to acquire additional Vmcg data for EOCS model development and validation at varying weights, and thrust levels on both dry and wet runways. Overall performance of the prototype C-17 EOCS was satisfactory and significant improvement in C-17A Vmcg was obtained on both dry and wet runways. Average improvement of dry runway Vmcg was 18 knots, with wet runway improvement averaging 12 knots.