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• Thrust-vectored control, next generation short-range missile.
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• Being developed with Greece, Italy, Norway and Sweden.
• Extreme maneuverability.
• m-synthesis robust control technique used to design lateral and roll
controllers.
– Scheduled on dynamic pressure
• Successful flight test in May 2000.
Italy
Eurofighter
• Germany, United Kingdom, Italy, Spain.
• Quad redudant, full authority DFCS.
Alenia responsible for basic autopilot
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• Longitudinal axis controls attitude or pitch angle, lateral axis controls bank
angle and heading.
• Autopilot designed using classical control tools.
– Control structure defined, Nicholas/Bode plots, linear time responses.
– Large amplitude, nonlinear closed-loop simulations.
– Modified control structure with nonlinear elements.
– Mode logic increased nonlinear elements to satisfy mode schedules.
Sweden
Saab/BAE JAS 39 Gripen
• Contract awarded in 1982
• Lightweight, multi-role combat aircraft
• All moving, delta canard configuration
• Hungary (2003) orders 14, 232 ordered
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SAAB
SHARC
Sweden
• Pilot-induced Oscillation (PIO)
• First test aircraft crashed after 6th flight (1989), first operational aircraft
crashed in 1993.
• Partial cause: PIO related to control surface servo rate limits.
– Reduced phase margin or extra delay in feedback loop.
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Sweden
Controller modification based on PIOs
• Feedback phase compensation based on anti-windup methods.
• Increased or advanced phase around nonlinearity.
• Low pass filters used to eliminate biases and high frequency roll off issues
• Flight tested and verified.
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• Phase compensation technique (frequency domain) used in place of rate
limiters in Gripen production flight control system.
United Kingdom
Commercial
• Airbus
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Military
• Harrier
• Saab/BAE JAS 39 Gripen
• Eurofighter
• Lockheed Martin/BAE F-35 JSF
UK - Jaguar and EAP Programs
• FBW Jaguar program (1980s) precursor to VAAC
• Prove principles of active
control technology, establish
design and flight clearance
techniques for DFCS.
• First UK airplane equipped
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with full authority DFCS.
UK - Jaguar and EAP (Eurofighter) Programs
• Experimental Aircraft Program (EAP, 1983-1995)
– Follow on from Jaguar program.
– Control design process:
• Linear low frequency: PI scheduled as function control
• Nonlinear: trim distribution, nonlinear control power, nonlinear
variations of stability
• Linear high frequency: avoid structural coupling
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– Lessons learned: separate regulator and command path designs.
• FBW Jaguar and EAP shaped Eurofighter flight controller
United Kingdom
Vectored thrust Aircraft Advanced Control (VAAC) program
• Inception in 1984.
• Handling, control and display requirements for future short takeoff/vertical
landing (STOVL) aircraft.
• Experimental FBW VAAC Harrier.
• Development and testing of advanced aircraft flight control algorithms.
– Longitudinal axis, integrated management of thrust vectoring and
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aerodynamic forces for decoupled control.
UK - VAAC Control Strategies
• Classical control, loop-at-a-time
– Frequency shaping, gain-scheduling, significant nonlinearities
linearized with inverse functions, iterative design.
– Anti-windup scheme and control allocation (“alocação de polos”).
• Nonlinear static inverse
– Nonlinear inverse of the aircraft to determine control effectors to trim.
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aircraft at a given maneuvering state.
– Constrained design process used to define unique solution to nonlinear
inverse problem (trim map).
– Nonlinear inverse feed-forward combined with low gain, classical
feedback design for stability.
UK - VAAC Control Strategies
• Nonlinear Dynamic Inversion (NDI) (trajectory ècontroller)
– Nonlinear dynamic model of aircraft used to invert nonlinearities and a
classical PI controller designed to track desired pitch rate command.
– Pilot commands filtered prior to input to NDI controller.
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UK - VAAC Control Strategies
• Hµ loop shaping
– Multivariable linear controllers at 4 points: hover-to-forward flight.
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