Flight control system

1. Introduction
Flight Control Systems

2. AAE – 342 Flight Control Systems
First Automatic Flight

3.  What is a Flight Control System?
 The system that is used to control the flight of an aircraft is
called flight control system (FCS).
 Modern aircraft include a variety of automatic flight control
systems that aid the flight crew in:
Augmenting the stability characteristics of the airplane
Flight Management
AAE – 342 Flight Control Systems

4. AAE – 342 Flight Control Systems
Early Days of Flying

5. AAE – 342 Flight Control Systems
Fly by Wire

6. AAE – 342 Flight Control Systems
Components of an AFCS
 In general, Automatic Flight Control System (AFCS)
can be sub-divided into three distinct groups
Computers
Sensors
Output Devices (servomechanisms etc.)

7. AAE – 342 Flight Control Systems

8. AAE – 342 Flight Control Systems
AFCS Sensors

9. AAE – 342 Flight Control Systems
AFCS Sensors

10. AAE – 342 Flight Control Systems
AFCS Computer(s)
 A computer
 has a much higher reaction velocity than a pilot.
 isn't subject to concentration losses and fatigue.
 can more accurately know the state the aircraft is in. (Computers
can handle huge amounts of data better and also don't need to
read a small indicator to know, for example, the velocity or the
height of the aircraft).
 The computation performed in this part of an AFCS
may be very simple or extremely complex,
depending upon the type of system and the
functions to be performed.

11. AAE – 342 Flight Control Systems
AFCS Output Devices/Actuators
 The output signals from the computer must be
converted to produce physical movement of the
control surfaces; this is normally effected through
some form of actuator, utilising either electro-
mechanical, electro-hydraulic. or pneumatic
principles. Not only are there different types of
actuators, but they can also be used in different
configurations, i.e. in series with the flying controls,
parallel to them or a combination of both.

12. AAE – 342 Flight Control Systems
AFCS Output Devices/Actuators
 The design of an actuator depends upon:
Authority or percentage of control surface movement
effected;
Size and accuracy of movement for stability and/or
control

13. Types of Automatic Flight Control
Systems
 Stability Augmentation Systems
 If an airplane is marginally stable or unstable, automatic
control systems can provide desired handling qualities
 e.g. pitch or yaw damper
 Autopilots
 To reduce pilot workload
 e.g. Attitude, Altitude, Velocity hold control systems
 Navigation e.g. Landing Aids
AAE – 342 Flight Control Systems

14. Typical Flight Control System
AAE – 342 Flight Control Systems

15. AAE – 342 Flight Control Systems
Books
 Text Books
 “Introduction to Aircraft Flight Mechanics: Performance,
Static Stability, Dynamic Stability, and Classical Feedback
Control” by Thomas R. Yechout
 “Flight Dynamics Principles” by M.V. Cook
 Reference Books
 “Feedback Control of Dynamic Systems” by Gene F.
Franklin
 “Flight Stability and Automatic Control” by Robert C. Nelson

16. Inner Loop Stability
and Control

17. Three Broad Categories
 Stability Augmentation Systems
 Control Augmentation Systems
 Fly-By-Wire Systems
AAE – 342 Flight Control Systems

18. AAE – 342 Flight Control Systems
Stability Augmentation Systems
 These were generally the first feedback control system
designs used to improve dynamic stability characteristics.
They were also referred to as dampers, stabilizers, and
stability augmenters. F-104, T-37, T-38, and F-4 had SAS
T-38

19. AAE – 342 Flight Control Systems
Simplified Stability Augmentation System

20. AAE – 342 Flight Control Systems
Typical Stability Augmentation System

21. AAE – 342 Flight Control Systems
Control Augmentation System
 The next step in the evolution of aircraft feedback control
was control augmentation systems (CAS).
 Aircraft such as the A-7, F-111,F-14, and F-15 have CAS.
F-111

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Simplified Control Augmentation System

23. AAE – 342 Flight Control Systems
A-7D
A-7D Digital Multimode Flight Control System Program

24. AAE – 342 Flight Control Systems
Typical Control Augmentation System

25. AAE – 342 Flight Control Systems
Fly by Wire System
 Aircraft such as the F-16, C-17, and F-22 have FBW
systems.
Boeing C-17 Globemaster

26. Simplified Fly by Wire System
AAE – 342 Flight Control Systems

27. Simplified F-16 Longitudinal FBW System
AAE – 342 Flight Control Systems