Development and Flight Test of an Emergency Flight Control System Using Only Engine Thrust on an MD-11 Transport Airplane(17)

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Figures 10(a) through 10(i) show the MD-11 trim airspeed as a function of stabilizer setting, gross weight (GW), and longitudinal CG position. These data were obtained from the nonlinear simulation. Figures 10(j) and 10(k) are crossplots for the variation in trim speed with CG at .xed GW. With these data, determining the stabilizer-.xed speed range available as a function of GW and CG is possible. Fuel transfer, either to or from the tail tank, or between the main tanks, could shift the CG as much as 10 percent, which would change speed as much as 100 kn. At the forward CGs such as 12 percent, the airplane has strong speed stability (steep slope of stabilizer vs. speed), whereas at aft CGs such as 34 percent, speed stability is reduced by at least 50 percent. Also note the effects of decreasing weight at constant CG and stabilizer position on trim speed. Flying at approximately 220 kn, trim speed is reduced by approximately 1 kn for every 3000 lb of fuel consumed (approximately every 12 to 15 min).

Airspeed, kn
970582
(a) CG = 12 percent, gear down, altitude = 4800 ft.

Airspeed, kn
970583
(b) CG = 21 percent, gear down, altitude = 4800 ft. Figure 10. Effect of airspeed, gross weight (GW), and CG on stabilizer position, zero .aps/slats.
Stabilizer angle, deg
2 1 0
–1
–2
–3
–4
–5
–6
–7
–8

160  180  200  220  240  260  280  300  320  340  360 
Airspeed, kn  970584 
(c) CG = 25 percent, gear down, altitude = 4800 ft. 

Airspeed, kn
(d) CG = 30 percent, gear down, altitude = 4800 ft.

Airspeed, kn
(e) CG = 34 percent, gear down, altitude = 4800 ft. Figure 10. Continued.
Stabilizer angle, deg
2 1 0
–1
–2
–3
–4
–5
–6
–7
–8

160  180  200  220  240  260  280  300  320  340  360 
Airspeed, kn  970587 
(f) CG = 21 percent, gear up, altitude = 4800 ft. 

Stabilizer angle, deg
2 1 0
–1
–2
–3
–4
–5
–6
–7
–8

160  180  200  220  240  260  280  300  320  340  360 
Airspeed, kn  970588 
(g) CG = 25 percent, gear up, altitude = 4800 ft. 
Figure 10. Continued. 

Stabilizer angle, deg
2 1 0
–1
–2
–3
–4
–5
–6
–7
–8

160  180  200  220  240  260  280  300  320  340  360 
Airspeed, kn  970589 
(h) CG = 30 percent, gear up, altitude = 4800 ft. 

Stabilizer angle, deg
2 1 0
–1
–2
–3
–4
–5
–6
–7
–8 2

160  180  200  220  240  260  280  300  320  340  360 
Airspeed, kn  970590 
(i) CG = 30 percent, gear up, altitude = 20,000 ft. 
Figure 10. Continued. 

1
0
–1
–2
Stabilizer angle, – 3 deg
–4
–5
–6
–7
–8

CG  = 34 percent MA C 
30 perc ent  . 
25 perc ent 

21 perc ent 

12 perc ent 

160  180 200 220 240 260 280 300 320 340 360 Airspeed, kn
970591
(j) Crossplot, GW = 400,000 lb.

 

 

　
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