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Flight Control Law Design:
An Industry Perspective
Technological Institute of Aeronautics – ITA
São José dos Campos – SP - Brazil
Prof. Bento S. de Mattos
Based on Presentation of
balas@aem.umn.edu
Aerospace Engineering and Mechanics
University of Minnesota
V5-Out 2008
Presentation Overview
Historical Progress and Survey of the control
techniques being used by industry in Brazil, Europe,
Russia and the United States of America to design
flight control laws for fixed-wing aircraft.
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Modern FCS - Outline
ØIntroduction
ØBackground
ØCountries
• Brazil
• Europe
• France
• Israel
•Russia
•United States of America
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• Germany
• Italy
• Sweden
• United Kingdom
•Boeing
•Honeywell
•Lockheed Martin
ØSummary
Control Theory - Terminology
Robust control is a branch of control theory that explicitly deals with uncertainty in its approach to controller design. Controllers
designed using robust control methods tend to be able to cope with small differences between the true system and the nominal model
used for design. The early methods of Bode and others were fairly robust; the state-space methods invented in the 1960's and 1970's
were sometimes found to lack robustness. Amodern example of a robust control technique is H-infinity loop-shaping developed by
Duncan McFarlane and Keith Glover of Cambridge University. Robust methods aim to achieve robust performance and/or stability in
the presence of small modeling errors.
Robust Control
H∞ (i.e. "H-infinity") methods are used in control theory to synthesize controllers achieving robust performance or stabilization. To use
H∞ methods, a control designer expresses the control problem as a mathematical optimization problem and then finds the controller that
solves this. H∞ techniques have the advantage over classical control techniques in that they are readily applicable to problems involving
H-infinity methods in control theory
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multivariable systems with cross-coupling between channels; disadvantages of H∞ techniques include the level of mathematical
understanding needed to apply them successfully and the need for a reasonably good model of the system to be controlled. Problem
formulation is important, since any controller synthesized will only be 'optimal' in the formulated sense: optimizing the wrong thing often
makes things worse rather than better! Also, non-linear constraints such as saturation are generally not well-handled.
The term H∞ comes from the name of the mathematical space over which the optimization takes place: H∞ is the space of matrix-valued
functions that are analytic and bounded in the open right-half of the complex plane defined by Re(s) > 0; the H∞ norm is the maximum
singular value of the function over that space. (This can be interpreted as a maximum gain in any direction and at any frequency; for SISO
systems, this is effectively the maximum magnitude of the frequency response.) H∞ techniques can be used to minimize the closed loop
impact of a perturbation: depending on the problem formulation, the impact will either be measured in terms of stabilization or
performance.
Simultaneously optimizing robust performance and robust stabilization is difficult. One method that comes close to achieving this is H∞
loop-shaping, which allows the control designer to apply classical loop-shaping concepts to the multivariable frequency response to get
good robust performance, and then optimizes the response near the system bandwidth to achieve good robust stabilization.
History of Flight Control
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History of Flight Control
In the early 1900s, Dr. Elmer Sperry pioneered an electromechanical autopilot to augment
aircraft stability. Sperry had extensive experience in developing large gyros for ship
stabilization. In 1909 he proposed , a similar gyroscope-based design to the Wright Brothers.
His design used a stabilized four-gyro configuration to send error signals to electrical,
mechanical, and pneumatic mechanisms that positioned aircraft control surfaces.
Demonstration of the Sperry gyro-stabilizer by his son over Paris in 1914 caused a great
sensation. In a superb publicity stunt, son Lawrence stood upright in the cockpit with his
arms folded while his mechanic walked out onto the wing. The aircraft maintained a straight
and level flight. His gyro-stabilizer was a forerunner of today’s autopilots. The French War
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