mech 6091 flight control systems final course project f-16
TRANSCRIPT
1 MECH-6091 – FLIGHT CONTROL SYSTEMS
F-16 AUTOPILOT DESIGN
MECH 6091 – Flight Control Systems Final Course Project
F-16 Autopilot Design
Lizeth Buendia Rodrigo Lezama Daniel Delgado December 16, 2011
AGENDA
2 MECH-6091 – FLIGHT CONTROL SYSTEMS
F-16 AUTOPILOT DESIGN
• Theoretical Background • F-16 Model and Linearization • Controller Design
• Results and Conclusions • Q&A
Theoretical Background
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• Reference Frames
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• Aircraft Variables Assumptions:
1. The aircraft is a rigid-body. 2. The earth is flat and non-rotating. 3. The mass is constant during the time interval over which the motion is
considered. 4. The mass distribution is symmetric relative to the longitudinal plane.
Theoretical Background
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• Equations of Motions EOM Force: Moment:
Theoretical Background
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• Stability Requirements
< 0 • Longitudinal EOM
Theoretical Background
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• Linearized Longitudinal EOM
Theoretical Background
F-16 Nonlinear Model
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• F-16 Russell Model: • 12 State Variables • 4 Input Variables
• F-16 Longitudinal Linear Model:
• 5 State Variables • 1 Input Variables
• MATLAB linmod command used for linearization
• Low-Fidelity model
Longitudinal EOM in State Space Form
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Control Input Limits
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Nonlinear vs. Linear Model
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15
k ft
@ 6
00
ft/
s 5
deg
Ele
vato
r D
istu
rban
ce
Pit
ch r
ate
Nonlinear Model
Linear Model
Controller Design
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F-16 AUTOPILOT DESIGN
FLIGHT QUALITY REQUIREMENTS – MIL-F-8785C • Flight Category B – Cruise • Level 1 – Clearly adequate for mission flight phase
Parameter Current MIL Target Desired
SP – ζ 0.464 [0.3, 2] ≥ 0.7
SP – ωn 1.63 rad/s [1.1, 7] rad/s ≥ 3 rad/s
SP – τ 1.32 s --
P – ζ 0.057 > 0.04 ≥ 0.3
P – ωn 0.066 NA ≥ 0.5 rad/s
P – τ 262 s -- ≤ 7s (ts≤30s)
Controller Design – SAS
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• Full-Feedback State (All states are available)
• Pole Placement Method
• Necessary and Sufficient Condition for Arbitrary Pole Placement
Controller Design – SAS
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F-16 AUTOPILOT DESIGN
25
k ft
@ 7
00
ft/
s 1
deg
Ele
vato
r D
istu
rban
ce
Controller Design – SAS
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• Stability improvement achieved
• Excellent disturbance rejection
• New characteristics:
Parameter Desired Achieved
SP – ζ ≥ 0.7 0.7
SP – ωn ≥ 3 rad/s 3 rad/s
P – ζ ≥ 0.3 0.287
P – ωn ≥ 0.5 rad/s 0.522
P – τ ≤ 7s (ts≤30s) 6.67 s
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Controller Design – Autopilot
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F-16 AUTOPILOT DESIGN
• Altitude Reference Trajectory o Up to 5k ft increase/decrease tracking
• Augmented A/C TF
• Desired Response Characteristics: oSettling time < 30s oOvershoot <= 5%
oSteady-State error = 0 oMinimize oscillations
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Controller Design – Autopilot
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• PID Controller Design
• SISO tool + Manual Tuning • Attention to Actuator Saturation!
Anti-Windup included
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F-16 AUTOPILOT DESIGN
Controller Design – Autopilot
18 MECH-6091 – FLIGHT CONTROL SYSTEMS
F-16 AUTOPILOT DESIGN
1k
ft in
crea
se @
70
0 f
t/s
No
Ele
vato
r D
istu
rban
ce
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F-16 AUTOPILOT DESIGN
Controller Design – Autopilot
19 MECH-6091 – FLIGHT CONTROL SYSTEMS
F-16 AUTOPILOT DESIGN
5k
ft in
crea
se @
70
0 f
t/s
No
Ele
vato
r D
istu
rban
ce
20 MECH-6091 – FLIGHT CONTROL SYSTEMS
F-16 AUTOPILOT DESIGN
Controller Design – Autopilot
20 MECH-6091 – FLIGHT CONTROL SYSTEMS
F-16 AUTOPILOT DESIGN
5k
ft in
crea
se @
70
0 f
t/s
No
Ele
vato
r D
istu
rban
ce
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F-16 AUTOPILOT DESIGN
Controller Design – SAS + Autopilot
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Scenario: 1. 1000 ft altitude increase, followed by 2. +5deg perturbation, followed by 3. -5deg perturbation
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Controller Design – SAS + Autopilot
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Scen
ario
1
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Controller Design – SAS + Autopilot
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Scen
ario
1
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Controller Design – Nonlinear Model
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Compare: • Linearized Model + LTI Controller • Nonlinear Model + LTI Controller
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Controller Design – Nonlinear Model
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Scen
ario
1 –
Alt
itu
de
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Controller Design – Nonlinear Model
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Scen
ario
1 –
Th
eta
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Controller Design – Nonlinear Model
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Scen
ario
1 –
Pit
ch R
ate
Conclusions
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• A good linearization method is extremely important
• FFS eases SAS design -> In real life, not all states are available (estimators required)
• Nonlinear model shows longitudinal/lateral coupling
• Satisfactory overall results
• Future work: Scheduled PID and Lateral Motion
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Q&A