smart icing systems review, june 19-20, 2001 3-1 aircraft autopilot studies petros voulgaris vikrant...

3-1

Smart Icing Systems Review, June 19-20, 2001

Aircraft Autopilot Studies

Petros Voulgaris

Vikrant Sharma

University of Illinois

3-2


Objectives

Investigate the A/P & FCS

behavior under icing conditions.

Develop methods to enhance the

A/P behavior :

- Envelope Protection - Adaptation of the current A/P

- Robust redesign

3-3


Overview of the Talk

• Autopilot Modes

• Autopilot structures

• A few simulations

• Current and Future work

3-4


Autopilots

Longitudinal Modes

– Pitch Attitude Hold (PAH)– Altitude Hold (ALH)

Lateral Modes

– Roll Attitude Hold (RAH)– Heading Hold (HH)

3-5


Block Diagram for PAH

Ki/s

K

Kq

ActuatorDynamics&CompDelay

A/C Dynamics

q

PAH

integrator

refref

--++

++

++--

ee

3-6


Block Diagram for ALH

Ki/s

Kh

Kq

Actuator Dynamics&Comp

Delay

A/C Dynamics

q

Hr

integratorH

dKs

s

K

Washout filter

++

--

++

++--

++--

ALHALH

ee

3-7


Block Diagram for RAH

A/C

Turn CoordinationLoop gains

ref

K

Ki/s

ActuatorDynamics

&Comp Delay

a

r

r

RAH

+-

+

++

3-8


Heading Hold

A/CDyn.

Turn CoordinationLoop gains

K

Ki/s

ActuatorDynamics

&Comp Delay

a

r

r

K

ref

HH

+

++

+

-+-

3-9


A/P Performance

• Local designs exhibit good performance and stability margin properties

• Gains are scheduled on A/C speed

• Overall A/P performs well over the operational envelope of Twin Otter for clean conditions

3-10


Simulation results : Case 1c

• Aircraft State : Initially trimmed at V = 76 m/s and H = 2300 m • No icing• Autopilots engaged : Altitude Hold till T = 370 s and then Pitch

Hold is engaged.

• Maneuver made : pitch up by 11.5 degrees at T = 370 s and the pitch back at T = 420 s.

0 50 100 150 200 250 300 350 400 450 50040

45

50

55

60

65

70

75

80

Velocity response

Time (s)

Vel

oci

ty (

m/s

)

0 50 100 150 200 250 300 350 400 450 5000

1

2

3

4

5

6

7

8

9

10

Angle of Attack Vs Time

Time (s)

Ang

le o

f A

ttac

k (d

eg)

3-11


Case 1c : Pitch Up

• Case 1 continued :

0 50 100 150 200 250 300 350 400 450 5002250

2300

2350

2400

2450

2500

2550

2600 Height Vs Time

Time (s)

Hei

ght (

m)

0 50 100 150 200 250 300 350 400 450 500-2

0

2

4

6

8

10

12

14Pitch Angle vs Time

Time (s)

Pitc

h A

ngle

(de

g)

0 50 100 150 200 250 300 350 400 450 500-10

-8

-6

-4

-2

0

2 Elevator Deflection Vs Time

Time (s)

Ele

vato

r D

ef (

deg)

3-12


Case 1i

• Aircraft State : Initially trimmed at V = 76 m/s and H = 2300 m.• Icing : Gets fully iced in 100 seconds Starting at T = 0.• Autopilots engaged : Altitude Hold engaged till T = 370 s and then

Pitch Hold is engaged.• Maneuver made : Pitch up to 17 degrees at T = 370 s and the

pitch back at T = 420 s to its trim condition at T = 370 s.

0 50 100 150 200 250 300 350 400 450 50030

35

40

45

50

55

60

65

70

75

80Velocity Vs Time

Time (s)

Vel

oci

ty (

m/s

)

0 50 100 150 200 250 300 350 400 450 5000

5

10

15

20

25Angle of attack Vs Time

Time (s)

Ang

le o

f A

ttac

k (d

eg)

3-13


Case 1i : Pitch Up

0 50 100 150 200 250 300 350 400 450 5002220

2240

2260

2280

2300

2320

2340

2360

2380Height Vs Time

Time (s)

He

igh

t (m

)

0 50 100 150 200 250 300 350 400 450 500-5

0

5

10

15

20

25Pitch angle vs Time

Time (s)

Pitc

h a

ng

le (

de

g))

0 50 100 150 200 250 300 350 400 450 500-20

-15

-10

-5

0

5Elevator deflection vs Time

Time (s)

Ele

vato

r d

efle

ctio

n (

de

g))

3-14


Comparison

Case 1c Case 1i

350 360 370 380 390 400 410 420 430 440-5

0

5

10

15

20

Blow up of the pitch response

Time (s)

Pitc

h a

ng

le (

de

gre

es)

350 360 370 380 390 400 410 420 430 440-20

-15

-10

-5

0

5Blow up of the elevator response

Time (s)

Ele

vato

r d

ef

(de

g)

350 360 370 380 390 400 410 420 430 440-5

0

5

10

15

20

Blow up of the pitch response

Time (s)

Pitc

h a

ng

le (

de

g)

350 360 370 380 390 400 410 420 430 440-20

-15

-10

-5

0

5

Blow up of the elevator response

Time (s)

Ele

vato

r d

ef

(de

g)

3-15


Case 2c

• Aircraft State : Aircraft initially trimmed at V = 76 m/s and H=2300m • No icing• Autopilots engaged : Altitude Hold engaged till T = 370 s and then

Pitch Hold is engaged. • Maneuver made : Pitch up by 2 degrees at T = 370 s and the pitch

back to the initial trim at T = 420 s.

0 50 100 150 200 250 300 350 400 450 50069

70

71

72

73

74

75

76

77

78Velocity vs Time

Time (s)

Vel

oci

ty (

m/s

)

0 50 100 150 200 250 300 350 400 450 5000

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8Angle of Attack vs Time

Time (s)

Ang

le o

f at

tack

(de

gre

es)

3-16


Case 2c : Pitch Up

0 50 100 150 200 250 300 350 400 450 5002280

2300

2320

2340

2360

2380

2400Height vs Time

Time (s)

Hei

ght

(m)

0 50 100 150 200 250 300 350 400 450 500-0.5

0

0.5

1

1.5

2

2.5

3

3.5Pitch angle vs Time

Time (s)

Pitc

h an

gle

(deg

rees

)

0 50 100 150 200 250 300 350 400 450 500-5

-4

-3

-2

-1

0

1

2

3

4


Time (s)

Ele

vato

r de

flect

ion

(deg

)

3-17


Case 2i

• Aircraft State : Initially trimmed at V = 76 m/s and H = 2300 m.• Icing : The aircraft is allowed to get fully iced in 100 seconds.• Autopilots Engaged : Altitude Hold engaged till T = 370 s and then

Pitch Hold is engaged.• Maneuver made : Pitch up by 2 degrees at T = 370 s and then pitch

back to the trim state just before pitching up at T = 420 s.

0 50 100 150 200 250 300 350 400 450 50045

50

55

60

65

70

75

80 Velocity vs Time

Time (s)

Vel

oci

ty (

m/s

)

0 50 100 150 200 250 300 350 400 450 5000

1

2

3

4

5

6

7

8

9 Angle of Attack vs Time

Time (s)

Ang

le o

f at

tack

(de

gre

es)

3-18


Case 2i : Pitch Up

0 50 100 150 200 250 300 350 400 450 5002280

2290

2300

2310

2320

2330

2340

2350Height vs Time

Time (s)

Hei

ght

(m)

0 50 100 150 200 250 300 350 400 450 5000

2

4

6

8

10

12

14Pitch angle vs Time

Time (s)

Pitc

h an

gle

(deg

rees

)

0 50 100 150 200 250 300 350 400 450 500-10

-8

-6

-4

-2

0


Time (s)

Ele

vato

r de

flect

ion

(deg

)

3-19


Comparison

Case 2c Case 2i

350 360 370 380 390 400 410 420 430 440-0.5

0

0.5

1

1.5

2

2.5

3

3.5

Blown up pitch angle response

Time (s)

Pitc

h an

gle

(deg

rees

)

350 360 370 380 390 400 410 420 430 4404

5

6

7

8

9

10

11

12

13Blow up of the pitch angle response

Time (s)

Pitc

h an

gle

(deg

rees

)

3-20


Case 3c

• Aircraft State : Initially trimmed at V = 60 m/s and H = 2300 m.• No icing• Autopilots Engaged : Altitude Hold engaged throughout and RAH

is engaged after T = 370 s.• Maneuver made : Roll by 10 degrees at T = 370 s and then roll

back at T = 420 s.

0 100 200 300 400 500 60058

59

60

61

62

63

64 Velocity vs Time

Time (s)

Vel

oci

ty (

m/s

)

0 100 200 300 400 500 6002.4

2.6

2.8

3

3.2

3.4

3.6

3.8

4Angle of Attack vs Time

Time (s)

Ang

le o

f A

ttac

k (d

egre

es)

3-21


Case 3c : Roll

0 100 200 300 400 500 6002295

2296

2297

2298

2299

2300

2301

2302

2303

2304 Height vs Time

Time (s)

He

igh

t (m

)

0 100 200 300 400 500 600-2

0

2

4

6

8

10

12 Roll angle vs Time

Time (s)

Ro

ll a

ng

le (

de

gre

es)

0 100 200 300 400 500 600-10

0

10

20

30

40

50

60

70

80

90 Yaw Angle vs Time

Time (s)

Ya

w a

ng

le (

de

gre

es)

0 100 200 300 400 500 6001.5

2

2.5

3

3.5

4

4.5

5 Pitch Angle vs Time

Time (s)

Pitc

h A

ng

le (

de

gre

es)

3-22


Case 3c : Control deflections

0 100 200 300 400 500 600-2.6

-2.4

-2.2

-2

-1.8

-1.6

-1.4

-1.2Elevator deflection vs Time

Time(s)

Ele

vato

r de

flect

ion

(deg

)

0 100 200 300 400 500 600-1.5

-1

-0.5

0

0.5

1

1.5Rudder deflection vs Time

Time (s)

Rud

der

defle

ctio

n (d

eg)

0 100 200 300 400 500 600-6

-4

-2

0

2

4

6Aileron Deflection vs Time

Time (s)

Aile

ron

defle

ctio

n (d

eg)

3-23


Case 3i

• Aircraft State : Initially trimmed at V = 60 m/s and H = 2300 m.• Icing : Aircraft gets fully iced in the first 300 s.• Autopilots Engaged : Altitude Hold engaged throughout and RAH

is engaged after T = 370 s.• Maneuver made : Roll by 10 degrees at T = 370 s and then roll

back at T = 420 s.

0 100 200 300 400 500 60025

30

35

40

45

50

55

60

65 Velocity vs Time

Time (s)

Vel

oci

ty (

m/s

)

0 100 200 300 400 500 6000

5

10

15

20

25

30 Angle of attack vs Time

Time (s)

Ang

le o

f A

ttac

k (d

egre

es)

3-24


Case 3i : Roll

0 100 200 300 400 500 600600

800

1000

1200

1400

1600

1800

2000

2200

2400 Height vs Time

Time (s)

He

igh

t (m

)

0 100 200 300 400 500 6002

4

6

8

10

12

14

16

18

20

22 Pitch angle vs Time

Time (s)

Pitc

h a

ng

le (

de

gre

es)

0 100 200 300 400 500 600-40

-20

0

20

40

60

80

100

120

140Yaw angle vs Time

Time (s)

Ya

w a

ng

le (

de

gre

es)

0 100 200 300 400 500 600-6

-4

-2

0

2

4

6

8

10

12

14Roll angle vs Time

Time (s)

Ro

ll a

ng

le (

de

gre

es)

3-25


Case 3i : Control deflections

0 100 200 300 400 500 600-22

-20

-18

-16

-14

-12

-10

-8

-6

-4

-2 Elevator deflection vs Time

Time (s)

Ele

vato

r d

efle

ctio

n (

de

g)

0 100 200 300 400 500 600-1.5

-1

-0.5

0

0.5

1 Rudder deflection vs Time

Time (s)

Ru

dd

er

de

flect

ion

(d

eg

)

0 100 200 300 400 500 600-3

-2

-1

0

1

2

3 Aileron deflection vs Time

Time (s)

Aile

ron

de

flect

ion

(d

eg

)

3-26


Comparison

Case 3c Case 3i

350 400 450 500 550-2

0

2

4

6

8

10

12Blowup of the Roll response for the clean case

Time (s)

Ro

ll a

ng

le (

de

gre

es)

350 400 450 500 550-6

-4

-2

0

2

4

6

8

10

12

14Blowup of the roll response for the Iced case

Time (s)

Ro

ll a

ng

le (

de

gre

es)

3-27


Some Conclusions

• Icing can cause saturation of control surfaces

• Icing can cause severe degradation in A/P performance

• Altitude cannot be held with elevator only

• There is a need to adapt overall A/P structure

3-28


Adaptation

• Three levels

- Level 1 : Envelope Protection

- Level 2 : Adapt current FCS gains

- Level 3 : Augment with new FCS design

3-29


Level 1 : Pilot Command Module Adaptation

A/C Dynamics

IcingCharacterization

A/P & SASK=K(V)

EnvelopeProtection

ModulePilot

Control

Inputs

Ref.

Comm.Inputs

Aircraft Icing Parameters

Sensor

Meas.

ice

3-30


Level 2 : Pilot Command Module & A/P Adaptation

A/C Dynamics


A/P & SASK=K(V, )

EnvelopeProtection

ModulePilot

Ref.

Comm.Inputs


Control

Inputs

Sensor

Meas.

ice

ice

3-31


Level 3 : Augment with New A/P Design

A/C Dynamics


A/P & SASK=K(V, )

EnvelopeProtection

ModulePilot

Ref.Comm.

Inputs


Control

Inputs

NewA/P

Design SensorMeas.

++

ice

ice

3-32


Envelope protection module

• Account for peak transient values• Use of robust control methods

Want for all t

What is the maximum allowable ?

Ytyp )(

)(tr

A/C&

A/P

ypr

Pilot inputs Variables to be limited

3-33


Our Approach to EP

• A Fact

for all t iff for all t

where : L1 norm

• A simple bound on pilot stick commands

Ytyp )(Y

sGtr 1

),()(

1),( sG

G(s, )r yp

Pilot inputs Variables to be limited

A/C & A/P linearized dynamics

3-34


Concepts for new design

• Use robust control methods

• G(s,) depends on A/P• Can find limits of A/P performance :

want for

What is maximum allowable Overall possible A/P’s ?

• Leads to guidelines for new A/P design

A/C&

A/P

yp

Variables to be limited

r

Pilot inputs

Ytyp )( Wtw )()(tr

}

G(s,)

w Disturbances

3-35


Current and future work

Use a nonlinear model for Cm, Cl

and Cd curves.

Performance characterization.

Adaptation : Three levels

Incorporate throttle control

smart icing systems review, june 19-20, 2001 3-1 aircraft autopilot studies petros voulgaris vikrant...

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