AEM 668 Lecture 22Autopilots

Dr. Jinwei Shen

University of Alabama

April 14, 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 22 J.Shen 2/13

Autopilots

▶ Most airplanes are equipped with pilot-relief orautopilot functions

▶ Outer-loop systems to control aircraft and performholding or navigation functions

▶ Example (holding): pitch hold, altitude hold, bankangle hold

▶ Example (navigation): heading hold, VOR-hold,automatic landing

AEM 668 Lecture 22 J.Shen 3/13

Aeroflot Flight 593 Accident

▶ 23 March 1994▶ Airbus A310-304▶ Fatalities 75 (all)

AEM 668 Lecture 22 J.Shen 4/13

Pitch-Attitude Hold

-1.1334 (s+0.5567) (s+0.01897) (s+0.0001666)-----------------------------------------------------------------(s+0.0001892) (s^2 + 0.004943s + 0.008084) (s^2 + 1.047s + 1.756)

AEM 668 Lecture 22 J.Shen 5/13

Pitch-Attitude Hold

−12 −10 −8 −6 −4 −2 0−6

−4

−2

0

2

4

6

Pitch−rate feedback

Real (seconds−1

)

Imag (

seconds

−1)

0 10 20 30 40 500

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

Pitch−attitude autopilot

Time (seconds)

Am

plit

ud

e

45.335 (s+0.5567) (s+0.01897) (s+0.0001666)---------------------------------------------------------------------(s+6.646) (s+0.3815) (s+0.02522) (s+0.0001718) (s^2 + 3.999s + 9.704)

AEM 668 Lecture 22 J.Shen 6/13

Pitch Hold with Dynamic Compensation

6.298 (s+0.07305) (s+0.6112)-----------------------------------------------------------(s+9.288) (s^2 + 0.03672s + 0.01796) (s^2 + 1.888s + 1.644)

−150

−100

−50

0

50

100

Magnitude (

dB

)

10−2

100

102

−270

−180

−90

0

Phase (

deg)

Bode DiagramGm = 18.6 dB (at 3.29 rad/s) , Pm = 64.8 deg (at 0.797 rad/s)

Frequency (rad/s)

AEM 668 Lecture 22 J.Shen 7/13

Pitch Hold with Dynamic Compensation

−150

−100

−50

0

50

100

Ma

gn

itu

de

(d

B)

10−2

100

102

−270

−180

−90

0

Ph

ase

(d

eg

)

Bode DiagramGm = 21 dB (at 11 rad/s) , Pm = 66.8 deg (at 2.14 rad/s)

Frequency (rad/s)

AEM 668 Lecture 22 J.Shen 8/13

Pitch Hold with Dynamic Compensation

0 10 20 30 40 500

0.2

0.4

0.6

0.8

1

1.2

1.4

Pitch−attitude autopilot with Dynamic Compensator

Time (seconds)

Am

plit

ud

e

AEM 668 Lecture 22 J.Shen 9/13

Pitch Hold with Dynamic Compensation

−50 0 50 100

−100

−80

−60

−40

−20

0

20

40

60

80

Nyquist Diagram

Real Axis

Ima

gin

ary

Axis

Nyquist Diagram

Real Axis

Ima

gin

ary

Axis

−2 −1.5 −1 −0.5 0 0.5 1 1.5

−1.5

−1

−0.5

0

0.5

1

1.5

2

System: sysGain Margin (dB): 21At frequency (rad/s): 11Closed loop stable? Yes

System: sysPhase Margin (deg): 66.8Delay Margin (sec): 0.544At frequency (rad/s): 2.14Closed loop stable? Yes

AEM 668 Lecture 22 J.Shen 10/13

Autopilot Navigation Modes

▶ Heading hold: hold the aircraft on a given compassheading

AEM 668 Lecture 22 J.Shen 11/13

Autopilot Navigation Modes

▶ VOR (VHF Omni Range) hold: home on anomni-directional radio beacon

AEM 668 Lecture 22 J.Shen 12/13

Next lecture (SL 4.7)• Nonlinear Simulation

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 22 J.Shen 13/13