2.
Pressing the autothrottle disconnect switch on the throttle
3.
Lowering the AFS override switch on FCC 1
4.
Moving the left or right throttle more than the preselected (2° ) allowable limit
5.
Depressing any of the ALT FADEC switches (which disallowed any data bus inputs to the engine control logic)
The PCA system would also disengage if any of several software error .ags were set or avionics unit failures occurred. When disengaged, standard normal MD-11 operation was immediately restored.
PCA DEVELOPMENT AND TEST
Throttles-only control was .rst investigated on the MD-11 engineering simulator in August 1991. This simulator did not properly model the lateral control available with differential thrust and gave a pessimistic impression of the controllability with thrust. Later, the higher .delity FDS was used, and a much better lateral control capability was evident. Although the task was highly dif.cult at .rst, there was a rapid learning curve, and with some experience and a very high workload, gross control using manual throttle manipulation could be achieved. Bank angle, heading, and .ightpath could be controlled to within a few degrees. Because of the low-mounted wing engines, a pilot using only the wing engines could simply increase thrust slightly to increase .ightpath angle and could reduce thrust slightly to decrease .ightpath angle. Phugoid damping could also be achieved using this same technique (i.e., add thrust during the descent and reduce thrust during the climb). The size and timing of these inputs, however, are critical. The center engine could be used as a trimming device to control speed; increasing center engine thrust has a strong nose-down pitch effect and increased the trim speed.
Differential thrust was effective in inducing sideslip, which resulted in the aircraft rolling. At speeds greater than 170 kn, the dutch-roll mode was adequately damped and bank angle could be controlled reasonably well. At speeds less than 170 kn, dutch-roll damping decreased, and bank angle control was more dif.cult. At speeds less than 150 kn, using the throttles to attempt to damp the dutch roll was very dif.cult, and even experienced test pilots had little success. This situation is because exact timing is required to successfully damp the dutch roll.
MDA did an in-house study of a PCA system for the MD-11 based on their work on the F-15 PCA system. This study showed that the bare airframe dutch-roll damping could be increased from 0.05 to 0.45, while the bare airframe phugoid damping could be increased from 0.02 to 0.55.
In September 1992, a manual throttles-only .ight test was conducted. MD-11 ship 506 was .own out of Yuma, Arizona. For these tests, the LSAS and yaw dampers were turned off, the speed protect feature of the AFS was disabled, landing gear was lowered, and fuel transfer was selected to manual. The pilots then released the controls and .ew with throttles-only control. Nearly 4 hr of small throttle step tests, phugoid damping tests, dutch-roll damping tests, and low approaches were .own. Although gross control was certainly possible and improved with practice, a manual throttles-only landing on a runway would have been very dif.cult. The third of four low approaches was the only one that might have been suitable for a runway landing. Data collected on this test .ight were used to validate the FDS results for throttles-only control investigations.
Based on the success of the F-15 PCA development, the gross control capability of manual throttles-only-control in the FDS and in .ight, and the internal MDA study results, NASA contracted with MDA to perform a study of a PCA system for the MD-11. A linear model based on the FDS was developed and used to design a PCA control law. This control law worked well on the linear simulation, but when tried on the FDS, performance was poor. The problems were primarily because of the nonlinear engine response characteristics. Later, a nonlinear model was developed for control law analysis and development. Initially, the center engine was used along with the wing engines; however, to simplify the initial control design and to demonstrate the concept for aircraft without centerline engines, only the wing engines were used.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：Development and Flight Test of an Emergency Flight Control System Using Only Engine Thrust on an MD-11 Transport Airplane(21)
