F light
C ommand Simulatio n
Simulation
Fl ight
Simulation
Flight
Time, sec
970598
Figure 16. MD-11 airplane and .ight deck simulator response to PCA .ightpath thumbwheel step commands, gear down, Flaps 28, 10,000 ft, center engine idle.
86
84
Magnetic
track,
deg
82
80
6
4
Bank
angle, 2
deg
0
–2
1.40
1.35
Left 1.30
EPR 1.25
1.20
1.40
1.35
Right 1.30
EPR 1.25
1.20
5 deg track step
Com mand
Improved
Original
Improved
Orig inal
Origi nal
Improved
Original
Improved
Figure 17. MD-11 PCA small track change response; original and improved gains, 12,000 ft, airspeed = 170 kn, gear down, Flaps 28, center engine idle.
0 5 10 15 20 25 Time, sec
970599
Runway Approaches
Following veri.cation of the improved track response, approaches were made to the runway. After establishing the airplane con.guration with gear down, Flaps 28, and the stabilizer trimmed for an airspeed of approximately 170 kn, the .ight controls were released and not touched, thus simulating a .ight control failure that could occur immediately after takeoff. The PCA system was engaged. Once on .nal approach, the pilots usually set the PCA .ightpath command to the desired glideslope, and then spent most of their attention making track corrections to achieve and maintain runway alignment. In the summer turbulence at Yuma, Arizona, it was dif.cult to judge on their .rst few approaches, the inputs required to maintain runway alignment. However, control seemed adequate to consider actual PCA landings. Sink rate is not shown on the time history plots; however, it is a function of FPA and airspeed. At 200 kn, FPA = –1° for example, is equivalent to a 5.9 ft/sec sink rate.
Track, deg
Altitude, ft
Flightpath angle, deg
Airspeed, kn
Bank angle, deg
Roll rate, deg/sec
EPR
180
130
80 5000
4800 1
0
–1 175
170
165 20 15 10 5 0
–5 4
2 0
–2
1.4
1.3
1.2
1.1
Time, sec
970600
Figure 18. Time history of MD-11 PCA track change of 80° , gear down, Flaps 28, center engine at idle.
PCA System Landings
PCA system landings were practiced in the FDS using the .ight FCC and .ight software load. The technique was found to produce consistently safe landings (.g. 19). The simulator pilot shallowed the .ightpath to –1° at 200 ft AGL. At 50 ft AGL, the ground effect caused a slight pitchdown, and the PCA system added thrust, which reduced the sink rate and resulted in a touchdown at a sink rate of 5 ft/sec. This technique was planned for the .rst attempts to make actual PCA landings.
The MD-11 was .own to Edwards AFB, where a 15,000-ft long, 300-ft wide runway was used for initial PCA landing attempts. Pilot A .ew three PCA low approaches to gradually lower altitude PCA system go-arounds.
400
Radar altitude, 200 ft AGL
400
0
–1 Flightpath angle, deg –2
– 3
5
Angle of attack, deg 4
3
175
Airspeed, 170
kn 165
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