Time, sec
Hyd 3 on
970613
This test veri.ed that the PCA system can control the MD-11 with no hydraulic pressure, and that the .oating surfaces make little or no change in the PCA system response or stability. The test also showed that simulator predictions of the effects of .oating surfaces were not correct. The simulation predicted that the outboard ailerons would .oat to 17° , whereas the .ight data aileron position was approximately 12° .
PCA System and Rudder Mode
A partial-failure PCA test was conducted at ~12,000 ft at an airspeed of 175 kn, with gear down and Flaps 28. The test consisted of using only the longitudinal mode of PCA (FPA) in conjunction with the rudder for achieving lateral control. This test would simulate a failure mode that is possible in some aircraft that have an all .y-by-wire .ight control system except for the rudder. The wing-engine PCA roll gains were zeroed to preclude any PCA differential thrust inputs. PCA system pitch control was normal, and after becoming familiar with the aircraft response to rudder, the pilot could effectively control bank angle and heading. With the yaw dampers off, rudder inputs excited the dutch roll, but at 175 kn, it was reasonably well damped. Pilot A commented that this con.guration was controllable with a 2° to 3° roll oscillation, which is satisfactory for .ying at altitude but another evaluation would have to be made for .ying this con.guration in a lineup to a runway. In a later test, this same mode was selected at low altitude in light-to-moderate turbulence. Pilot A .ew a descent and turn to downwind and was pleasantly surprised with the controllability.
Rudder With Wing Engine Failed, PCA System Control
This test was con.gured as the earlier test except that a wing-engine failure was simulated by retarding engine 3 to .ight idle. In this case, the pitch thrust gain on the remaining engine was doubled to increase the authority for pitch response and control. The pilot controlled bank angle with rudder, and the PCA system controlled pitch with the wing engine. The center-engine thrust was manually set by the pilot to provide an acceptable average thrust setting for the wing engine. Because of the lateral thrust asymmetry, every pitch input generated a large rolling input as well. The results were that PCA vertical control was much more loose, the dutch roll was more pronounced, and the aircraft control was much poorer than in the earlier test. Minimum simulator development had been done on this mode (it had been successfully .own on the F-15 (ref. 1)), and more development would be required for acceptable performance.
Sustained PCA Operation
In addition to the PCA system testing, PCA operation as an autopilot was suf.ciently good that the .ight crew used it routinely. At times, the PCA system was left engaged for an hour or more. The crew did not need to disengage PCA to change .ight conditions or set up for the next approach. Overall, in the 30-hr .ight program, over 25 hr of PCA operation were logged. No unplanned PCA disengagements occurred.
Simulation-to-Flight Comparison
In general, the .ight results have compared well with the .ight deck simulation. The pitch control in .ight is somewhat less damped than in the simulator, possibly because the vertical CG in the test airplane is lower than in the simulation. The somewhat sluggish and dif.cult lateral control effects on approach are well modeled. Anticipated lateral control instability at higher altitudes, based on simulation, was not found in .ight. The trim speed change caused by turning off all hydraulics was of the right magnitude but in the opposite direction.
Pilot Comments
Pilot comments were recorded on the cockpit video immediately after each approach. Pilot A, the project pilot, reported that pitch control was excellent and that all of the workload was in the lateral task. He reported that, in turbulent air, it was dif.cult to anticipate the lead needed for track changes, and that it was necessary to get established on the extended centerline well out and use only small inputs. After the PCA landings, he commented that he was really impressed that control was so good that not only a survivable landing but a normal landing could be made using PCA control. Pilot C reported that he would not have believed that such precise control could be achieved using only the wing engines. Other pilots also found that the lateral control was suf.ciently sluggish that considerable experience was needed before learning how to maintain runway lineup.
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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(32)
