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AEM 668 Lecture 21 Control Augmentation Systems (CAS) Dr. Jinwei Shen University of Alabama April 9, 2015
AEM 668 Lecture 21ControlAugmentationSystems(CAS)
Dr. Jinwei Shen
University of Alabama
April 9, 2015
Roadmap
▶ Chap. 1: Kinematics, Dynamics, EOM▶ Chap. 2: Modeling the Aircraft▶ Chap. 3: Modeling, Design, and Simulation Tools▶ Chap. 4: Aircraft Dynamics/Classical Control
▶ Introduction and Handling-Qualities▶ Stability Augmentation System▶ Control Augmentation System▶ Autopilots▶ Simulating the System
▶ Chap. 5: Modern Control Theory
AEM 668 Lecture 21 J.Shen 2/11
Control Augmentation Systems (CAS)
▶ CAS add pilot command input into flight control▶ CAS eliminate SAS problem of pilot inputs being
opposed by feedback loop▶ CAS provide dramatic improvement in handling
qualities: both stability and control response couldbe optimized
AEM 668 Lecture 21 J.Shen 3/11
Pitch-Rate Control Augmentation
▶ Short-Period Mode Approximation⎡⎢⎣Δ�̇�Δ ̇𝑞
⎤⎥⎦
= ⎡⎢⎣
𝑍𝑤 𝑢0𝑀𝑤 + 𝑀�̇�𝑍𝑤 𝑀𝑞 + 𝑀�̇�𝑢0
⎤⎥⎦
⎡⎢⎣Δ𝑤Δ𝑞
⎤⎥⎦
▶ Natural Frequency: 𝜔𝑛 = √𝑍𝛼𝑀𝑞𝑢0 − 𝑀𝛼
▶ Damping Ratio: 𝜁 = 𝑀𝑞+𝑀�̇�+ 𝑍𝛼𝑢02𝜔𝑛
AEM 668 Lecture 21 J.Shen 4/11
Pitch-Rate Control Augmentation203.18 (s+10) (s+1.029)
------------------------------------------(s+20.17) (s+10.16) (s^2 + 1.969s + 1.077)
−15 −10 −5 0−8
−6
−4
−2
0
2
4
6
8
Pitch−Axis CAS
Real (seconds−1
)
Ima
g (
se
co
nd
s−
1)
−15 −10 −5 0−8
−6
−4
−2
0
2
4
6
8
Pitch−Axis CAS
Real (seconds−1
)
Ima
g (
se
co
nd
s−
1)
AEM 668 Lecture 21 J.Shen 5/11
Pitch-Rate Control Augmentation
101.59 (s+10) (s+3) (s+1.029)---------------------------------------------------(s+13.67) (s+10.75) (s+1.018) (s^2 + 6.86s + 20.96)
0 0.5 1 1.5 2 2.5 30
0.2
0.4
0.6
0.8
1
1.2
1.4
Step Response
Time (seconds)
Am
plit
ud
e
AEM 668 Lecture 21 J.Shen 6/11
Lateral-Directional CAS
AEM 668 Lecture 21 J.Shen 7/11
Roll-rate Loop
−30 −20 −10 0 10−30
−20
−10
0
10
20
30
Root Locus
Real (seconds−1
)
Imag (
seconds
−1)
AEM 668 Lecture 21 J.Shen 8/11
Yaw-rate Loop
−30 −20 −10 0 10−15
−10
−5
0
5
10
15
Root Locus
Real (seconds−1
)
Imag (
seconds
−1)
AEM 668 Lecture 21 J.Shen 9/11
Lateral Acceleration Loop
−20 −15 −10 −5 0
−10
−5
0
5
10
Root Locus
Real (seconds−1
)
Ima
g (
se
co
nd
s−
1)
AEM 668 Lecture 21 J.Shen 10/11
Next lecture (SL 4.6)
▶ Autopilots
0“Aircraft Control and Simulation, 2ed” by B.L. Stevens and F.L.Lewis, Wiley, 2003
0“Performance, Stability, Dynamics, and Control of Airplanes,2ed” by B. Pamadi, AIAA, 2004
0“Introduction to Aircraft Flight Mechanics: Performance, StaticStability, Dynamic Stability, Classical Feedback Control, andState-space Foundations” by T.R Yechout et al, AIAA , 2014
AEM 668 Lecture 21 J.Shen 11/11
