Split Piloting Tasks
In the MD-11 PCA .ight test, one pilot controlled PCA while the other pilot acted as safety pilot. In the FDS, it was found very helpful for pilots to split the task, with the left-seat pilot .ying the lateral control knob, while the right-seat pilot would .y the FPA thumbwheel. This task splitting greatly reduced the workload and improved performance, and would likely be the preferred mode for an operational PCA system. Task splitting would also improve the likelihood of a successful approach on the .rst try that was very dif.cult for a single pilot.
MD-11 Speed Control Example
With .ight controls failed, the MD-11 has several indirect means of changing the trim speed, as discussed earlier. The degree of speed adjustment available is a function of the initial speed, initial payload, fuel quantity, and CG position. Except right after takeoff, the likely problem is to slow to an appropriate landing speed. Effective ways to reduce the trim speed (assuming a total hydraulic failure) include the following:
1.
Reduce weight
2.
Move the CG aft
3.
Lower the landing gear
4.
Reduce center engine thrust
The condition with the least amount of speed-reduction capability would be late in the .ight when the CG is still aft but not much fuel is available.
Using analytical techniques with the data of .gure 10, supplemented with .ight data on the effects of gear extension and loss of all hydraulics, trim speed variation was determined. Two examples are presented: one is at a high-speed climb condition at high weight with a mid CG, and the other is at the mid weight aft CG cruise condition.
Figure 42 shows the speed change for the heavyweight 550,000-lb climb at 330 kn case with the CG at 25 percent. Loss of all hydraulics is assumed at the initial condition, resulting in 25 kn of slowing. Then fuel burning/dumping to a GW of 400,000 lb is used to reduce the speed to 262 kn. A small CG shift to 27 percent reduces the speed further to 248 kn. Once near the landing site, the gear is lowered with the alternate gear extension system, slowing another 15 kn to 233 kn. When the center-engine thrust is reduced to idle, the trim speed is reduced to 200 kn, just right for a no-.aps approach and landing.
Desired,
slats/flaps 0
Effect of center engine thrust
Effect
of gear
Effect
of CG
Idle 12% 21% 25% 30% CG = 34% MAC Down Up Equal Maximum Plan to shift CG to 27% GW = 400,000 lb
Stabilizer angle, deg
Airspeed, kn
970625
Figure 43 shows the speed situation for an initial condition of cruise .ight at a CG of 31 percent, 285 kn at 450,000 lb. At hydraulic failure, the .oating surfaces reduce the airspeed from 285 to 260 kn. Burning or dumping fuel to 400,000 lb reduces speed to 252 kn. The CG is maintained at 31 percent by inhibiting the forward transfer of tail fuel, which would normally occur when the airplane descends below 20,000 ft. Lowering the gear with the alternate system reduces speed to 238 kn, and reducing the center engine to near idle lowers speed another 38 kn to 200 kn, appropriate for a no-.aps landing.
Desired,
slats/flaps 0
Effect of center engine thrust
Effect
of gear
Effect
of CG
1
0
–1
–2
Stabilizer – 3 Effect of angle,
gross deg –4
weight
–5
–6
–7
–8
Airspeed, kn
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本文鏈接地址：Development and Flight Test of an Emergency Flight Control System Using Only Engine Thrust on an MD-11 Transport Airplane(39)
