1. Smart Icing Systems Review, June 19-20, 2001 3-1 Aircraft Autopilot Studies Petros Voulgaris Vikrant Sharma University of Illinois

2. Smart Icing Systems Review, June 19-20, 2001 3-2 Objectives

3. Smart Icing Systems Review, June 19-20, 2001 3-3 Overview of the Talk Autopilot Modes Autopilot structures A few simulations Current and Future work

4. Smart Icing Systems Review, June 19-20, 2001 3-4 Autopilots  Longitudinal Modes – Pitch Attitude Hold (PAH) – Altitude Hold (ALH)  Lateral Modes – Roll Attitude Hold (RAH) – Heading Hold (HH)

5. Smart Icing Systems Review, June 19-20, 2001 3-5 Block Diagram for PAH K i /s KK KqKq Actuator Dynamics &Comp Delay A/C Dynamics  q PAH integrator  ref - + + + - eeee

6. Smart Icing Systems Review, June 19-20, 2001 3-6 Block Diagram for ALH K i /s KhKh KqKq Actuator Dynamics &Comp Delay A/C Dynamics  q HrHr integrator H KK Washout filter + - + + - + - ALH eeee

7. Smart Icing Systems Review, June 19-20, 2001 3-7 Block Diagram for RAH A/C Turn Coordination Loop gains  ref KK K i /s Actuator Dynamics & Comp Delay aa rr r  RAH + - + + +

8. Smart Icing Systems Review, June 19-20, 2001 3-8 Heading Hold A/C Dyn. Turn Coordination Loop gains KK K i /s Actuator Dynamics & Comp Delay aa rr r   KK  ref HH + + + + - + -

9. Smart Icing Systems Review, June 19-20, 2001 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

10. Smart Icing Systems Review, June 19-20, 2001 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. 050100150200250300350400450500 40 45 50 55 60 65 70 75 80 Velocity response Time (s) Velocity (m/s) 050100150200250300350400450500 0 1 2 3 4 5 6 7 8 9 10 Angle of Attack Vs Time Time (s) Angle of Attack (deg)

11. Smart Icing Systems Review, June 19-20, 2001 3-11 Case 1c : Pitch Up Case 1 continued : 050100150200250300350400450500 2250 2300 2350 2400 2450 2500 2550 2600 Height Vs Time Time (s) Height (m) 050100150200250300350400450500 -2 0 2 4 6 8 10 12 14 Pitch Angle vs Time Time (s) Pitch Angle (deg) 050100150200250300350400450500 -10 -8 -6 -4 -2 0 2 Elevator Deflection Vs Time Time (s) Elevator Def (deg)

12. Smart Icing Systems Review, June 19-20, 2001 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. 050100150200250300350400450500 30 35 40 45 50 55 60 65 70 75 80 Velocity Vs Time Time (s) Velocity (m/s) 050100150200250300350400450500 0 5 10 15 20 25 Angle of attack Vs Time Time (s) Angle of Attack (deg)

13. Smart Icing Systems Review, June 19-20, 2001 3-13 Case 1i : Pitch Up 050100150200250300350400450500 2220 2240 2260 2280 2300 2320 2340 2360 2380 Height Vs Time Time (s) Height (m) 050100150200250300350400450500 -5 0 5 10 15 20 25 Pitch angle vs Time Time (s) Pitch angle (deg)) 050100150200250300350400450500 -20 -15 -10 -5 0 5 Elevator deflection vs Time Time (s) Elevator deflection (deg))

14. Smart Icing Systems Review, June 19-20, 2001 3-14 Comparison Case 1c Case 1i 350360370380390400410420430440 -5 0 5 10 15 20 Blow up of the pitch response Time (s ) Pitch angle (degrees) 350360370380390400410420430440 -20 -15 -10 -5 0 5 Blow up of the elevator response Time (s) Elevator def (deg) 350360370380390400410420430440 -5 0 5 10 15 20 Blow up of the pitch response Time (s) Pitch angle (deg) 350360370380390400410420430440 -20 -15 -10 -5 0 5 Blow up of the elevator response Time (s) Elevator def (deg)

15. Smart Icing Systems Review, June 19-20, 2001 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. 050100150200250300350400450500 69 70 71 72 73 74 75 76 77 78 Velocity vs Time Time (s) Velocity (m/s) 050100150200250300350400450500 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 Angle of Attack vs Time Time (s) Angle of attack (degrees)

16. Smart Icing Systems Review, June 19-20, 2001 3-16 Case 2c : Pitch Up 050100150200250300350400450500 2280 2300 2320 2340 2360 2380 2400 Height vs Time Time (s) Height (m) 050100150200250300350400450500 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 Pitch angle vs Time Time (s) Pitch angle (degrees) 050100150200250300350400450500 -5 -4 -3 -2 0 1 2 3 4 5 Elevator deflection vs Time Time (s) Elevator deflection (deg)

17. Smart Icing Systems Review, June 19-20, 2001 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. 050100150200250300350400450500 45 50 55 60 65 70 75 80 Velocity vs Time Time (s) Velocity (m/s) 050100150200250300350400450500 0 1 2 3 4 5 6 7 8 9 Angle of Attack vs Time Time (s) Angle of attack (degrees )

18. Smart Icing Systems Review, June 19-20, 2001 3-18 Case 2i : Pitch Up 050100150200250300350400450500 2280 2290 2300 2310 2320 2330 2340 2350 Height vs Time Time (s) Height (m) 050100150200250300350400450500 0 2 4 6 8 10 12 14 Pitch angle vs Time Time (s) Pitch angle (degrees) 050100150200250300350400450500 -10 -8 -6 -4 -2 0 2 Elevator deflection vs Time Time (s) Elevator deflection (deg)

19. Smart Icing Systems Review, June 19-20, 2001 3-19 Comparison Case 2c Case 2i 350360370380390400410420430440 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 Blown up pitch angle response Time (s) Pitch angle (degrees) 350360370380390400410420430440 4 5 6 7 8 9 10 11 12 13 Blow up of the pitch angle response Time (s) Pitch angle (degrees)

20. Smart Icing Systems Review, June 19-20, 2001 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. 0100200300400500600 58 59 60 61 62 63 64 Velocity vs Time Time (s) Velocity (m/s) 0100200300400500600 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 Angle of Attack vs Time Time (s) Angle of Attack (degrees)

21. Smart Icing Systems Review, June 19-20, 2001 3-21 Case 3c : Roll 0100200300400500600 2295 2296 2297 2298 2299 2300 2301 2302 2303 2304 Height vs Time Time (s) Height (m) 0100200300400500600 -2 0 2 4 6 8 10 12 Roll angle vs Time Time (s) Roll angle (degrees) 0100200300400500600 -10 0 10 20 30 40 50 60 70 80 90 Yaw Angle vs Time Time (s) Yaw angle (degrees) 0100200300400500600 1.5 2 2.5 3 3.5 4 4.5 5 Pitch Angle vs Time Time (s) Pitch Angle (degrees)

22. Smart Icing Systems Review, June 19-20, 2001 3-22 Case 3c : Control deflections 0100200300400500600 -2.6 -2.4 -2.2 -2 -1.8 -1.6 -1.4 -1.2 Elevator deflection vs Time Time(s) Elevator deflection (deg) 0100200300400500600 -1.5 -0.5 0 0.5 1 1.5 Rudder deflection vs Time Time (s) Rudder deflection (deg) 0100200300400500600 -6 -4 -2 0 2 4 6 Aileron Deflection vs Time Time (s) Aileron deflection (deg)

23. Smart Icing Systems Review, June 19-20, 2001 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. 0100200300400500600 25 30 35 40 45 50 55 60 65 Velocity vs Time Time (s) Velocity (m/s) 0100200300400500600 0 5 10 15 20 25 30 Angle of attack vs Time Time (s) Angle of Attack (degrees)

24. Smart Icing Systems Review, June 19-20, 2001 3-24 Case 3i : Roll 0100200300400500600 800 1000 1200 1400 1600 1800 2000 2200 2400 Height vs Time Time (s) Height (m) 0100200300400500600 2 4 6 8 10 12 14 16 18 20 22 Pitch angle vs Time Time (s) Pitch angle (degrees) 0100200300400500600 -40 -20 0 20 40 60 80 100 120 140 Yaw angle vs Time Time (s) Yaw angle (degrees) 0100200300400500600 -6 -4 -2 0 2 4 6 8 10 12 14 Roll angle vs Time Time (s) Roll angle (degrees)

25. Smart Icing Systems Review, June 19-20, 2001 3-25 Case 3i : Control deflections 0100200300400500600 -22 -20 -18 -16 -14 -12 -10 -8 -6 -4 -2 Elevator deflection vs Time Time (s) Elevator deflection (deg) 0100200300400500600 -1.5 -0.5 0 0.5 1 Rudder deflection vs Time Time (s) Rudder deflection (deg) 0100200300400500600 -3 -2 0 1 2 3 Aileron deflection vs Time Time (s) Aileron deflection (deg)

26. Smart Icing Systems Review, June 19-20, 2001 3-26 Comparison Case 3cCase 3i 350400450500550 -2 0 2 4 6 8 10 12 Blowup of the Roll response for the clean case Time (s) Roll angle (degrees) 350400450500550 -6 -4 -2 0 2 4 6 8 10 12 14 Blowup of the roll response for the Iced case Time (s) Roll angle (degrees)

27. Smart Icing Systems Review, June 19-20, 2001 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

28. Smart Icing Systems Review, June 19-20, 2001 3-28 Adaptation Three levels - Level 1 : Envelope Protection - Level 2 : Adapt current FCS gains - Level 3 : Augment with new FCS design

29. Smart Icing Systems Review, June 19-20, 2001 3-29 Level 1 : Pilot Command Module Adaptation A/C Dynamics Icing Characterization A/P & SAS K=K(V) Envelope Protection Module Pilot Control Inputs Ref. Comm. Inputs Aircraft Icing Parameters Sensor Meas.

30. Smart Icing Systems Review, June 19-20, 2001 3-30 Level 2 : Pilot Command Module & A/P Adaptation A/C Dynamics Icing Characterization A/P & SAS K=K(V, ) Envelope Protection Module Pilot Ref. Comm. Inputs Aircraft Icing Parameters Control Inputs Sensor Meas.

31. Smart Icing Systems Review, June 19-20, 2001 3-31 Level 3 : Augment with New A/P Design A/C Dynamics Icing Characterization A/P & SAS K=K(V, ) Envelope Protection Module Pilot Ref. Comm. Inputs Aircraft Icing Parameters Control Inputs New A/P Design Sensor Meas. + +

32. Smart Icing Systems Review, June 19-20, 2001 3-32 Envelope protection module Account for peak transient values Use of robust control methods Want for all t What is the maximum allowable ? A/C & A/P ypyp r Pilot inputs Variables to be limited

33. Smart Icing Systems Review, June 19-20, 2001 3-33 Our Approach to EP A Fact for all t iff for all t where : L 1 norm A simple bound on pilot stick commands G(s,  ) r ypyp Pilot inputs Variables to be limited A/C & A/P linearized dynamics

34. Smart Icing Systems Review, June 19-20, 2001 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 ypyp Variables to be limited r Pilot inputs } G(s,  ) w Disturbances

35. Smart Icing Systems Review, June 19-20, 2001 3-35 Current and future work