–
1.0
.4
.2
0
–
.2
–
.4
3.1
3.0
2.9
2.8
2.7 176
175
174 .5
0
– .5
1.35
1.30
1.25
1.20
1.15
Mea sured
Command
Center
Right
Left
0 10 20 30 40 50 Time, sec
970609
Figure 27. Time history of MD-11 .ightpath steps, three-engine dynamic longitudinal mode, 17,000 ft, gear down, Flaps 28.
12.5
Altitude, ft MSL x10–3 12.0
11.5
260
250
Airspeed, kn 240
230
220
Flightpath, deg
– 10
– 10
Bank angle, deg – 2– 30 0
– 40
– 50
EPR
Figure 28. Time history of PCA system recovery from a 7° dive/45° bank upset condition, gear and .aps up, no .ight control movement.
5 0
–5
0
1.4
1.2
1.0
.8
970610
4
Altitude,
ft
3
2
20
0
Bank – 20
angle,
deg –40
–
60
–
80
20
0
Flightpath angle, deg
–
20
–
40
300
250 Airspeed, kn 200
150
3
RPM
2
1
5 x 103 PCA engaged at 80° bank and 5° climb Recovered to level flight
Co mmand
Measure d
C ommand
M easured
4 x 103
Left
Ri ght
Figure 29. FDS time history of MD-11 PCA upset and recovery, 200 kn, 4800 ft AGL, gear and .aps up, center engine idle.
–20 –10 0 10 20 30 40 50 60 70 Time, sec
970611
Flightpath angle, deg
Bank angle, deg
Magnetic heading, deg
Control surface position, deg
EPR 1.0
.5
0
– .5
0
– 10
60
40
20
0 15
10
5
0
–5
1.3
1.2
1.1
1.0
.9
–
1.0 20 10
Measured
Command
Measured
Command
Both outboard ailerons
Right inboard aileron
Left and right outboard elevator, right inboard elevator
Left inboard elevator and rudder, left i nboard aileron
Left
Center
Right
0 20 40 60 80 100 Time, sec
970612
Figure 30. Time history of MD-11 PCA operation with hydraulic systems 2 and 3 off, three of four ailerons .oating, 220 kn, 10,000 ft, gear up, .aps up, CG = 31 percent, speed control mode on.
PCA System Operation in the Enhanced Mode
As discussed earlier, the MD-11 and DC-10 aircraft incorporate hydraulic fuses in hydraulic system 3 so that control can be maintained in case an uncontained failure in the tail engine severs all three hydraulic systems in the tail. With this control capability, a landing may be accomplished, although the lack of phugoid damping makes .ightpath control very dif.cult.
For the .ight test, this con.guration was made available by installing a switch to activate the tail hydraulic shutoff valve. Activating this switch, coupled with turning off hydraulic systems 1 and 2, effectively left the aircraft in the enhanced con.guration with no hydraulics to the elevators and rudders, and hydraulics to one-half of the stabilizer trim actuator, only one of the four ailerons, and the leading edge slats. The PCA system test in the enhanced mode was performed to see whether .ying qualities were substantially improved.
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