Introduction to the theory of basic flight control systems.

1. INTRODUCTION TO
FLIGHT CONTROL
SYSTEMS

2. INTRODUCTION TO FCS
• Scope of the Presentation
• History
• Introduction to flight control systems
• Conventional Vs Fly by Wire (FBW) Control Systems
• Importance of Indigenization of FCS
• Safety Implications

3. History
• The Architecture of flight control
system, essential for all flight
operations, has changed
significantly over the years.
• Soon after the first flights,
articulated surfaces were
introduced for basic controls.

4. Introduction
• Purpose of Flight Control System
• To regulate or guide the motion of an aerial machine or vehicle
• How it is done ?
• By transmitting the forces of the flight deck controls to the control
surfaces

5. Introduction
Basic Terminologies
• Centre of Gravity (C.G)
• Axes System
• Longitudinal Axis
• Lateral Axis
• Vertical Axis
x-axis
z-axis
y-axis

6. Introduction
• Aircraft Rotations
• Aircraft rotates about C.G about axis
• Roll
• Rotation about x-axis
• Pitch
• Rotation about y-axis
• Yaw
• Rotation about z-axis

7. Introduction
• Aircraft Flight Control Systems
• Primary Flight Control Systems
• Secondary Flight Control Systems

8. Introduction
• Primary Flight Control Systems
Required for three basic controls (Roll, Pitch and Yaw)
• Sub-systems
• Aileron Control System
• Elevator Control System
• Rudder Control System

9. Introduction
• Secondary Flight Control Systems
Required for finer control over aircraft by pilot and ease of workload
• Sub-systems
• Elevator Trim System
• Rudder Trim System
• High Lift Devices

10. Types of Flight Control Systems
• Mechanical
• Collection of mechanical components such as cables, pulleys and rods
• Hydro-Mechanical
• Hydraulically powered control surfaces
• Fly by Wire (FBW)
• Manual flight controls are replaced with electronic interface

11. Types of Flight Control Systems
• Mechanical Flight Control Systems
• Common on General Aviation Aircraft
• Gives pilot a lot of “feel” as he is directly connected to the control
surfaces on the aircraft
• Generally is made up of cables, pulleys, rods, and sometimes even
chains
• Routing these kind of systems throughout the aircraft requires a lot of
thought and creativity at times
• Generally not very good when there are large stick forces. The pilots
strength becomes the limiting factor.

12. Types of Flight Control Systems
• Mechanical Flight Control Systems

13. Types of Flight Control Systems
• Hydro-Mechanical Flight Control Systems
• Analogous to power steering on a car, easier physically to make control
inputs but loss of “feel” can be a problem
• Sometimes referred to as “boosted”
• Adds complexity to an already complex system
• Added weight
• Has to include hydraulic lines, actuators, pumps, and a linkage
between the hydraulic system and the mechanical cockpit controls
• Makes flying the aircraft less demanding and allows for high loads on
control surfaces and much physically larger control surfaces
• Sometimes makes use of “Artificial Feel Devices”

14. Types of Flight Control Systems
• Hydro-Mechanical Flight Control Systems

15. Types of Flight Control Systems
• Fly by Wire (FBW)
• Really more of a subset of Hydraulic Controls
• Commonly uses a hydraulic control circuit to physically move the
control surfaces and a computer controlled (digital) circuit that takes
pilot input and actuates the hydraulic system
• Common on newer commercial and military aircraft
• Computer “interpretation” of pilot input allows for better stability of the
aircraft allowing much more “on the edge” designs to be capable of
flying
• Has to be redundant because the computer is the only path between
the pilot and the controls

16. Types of Flight Control Systems
• Fly by Wire (FBW)

17. Types of Flight Control Systems
• Fly by Wire (FBW)
• This architecture is based on computer signal processing
• The pilot’s demand is first of all transduced into electrical signal in the
cabin and sent to a group of independent computers, the computers
sample data concerning the flight conditions and servo-valves and
actuators positions
• The pilot’s demand is then processed and sent to the actuator, properly
tailored to the actual flight status
• The full system has high redundancy to restore the level of reliability of
a mechanical or hydraulic system, in the form of multiple (triplex or
quadruplex) parallel and independent lanes to generate and transmit
the signals, and independent computers that process them.

18. Flight Safety Implications by Use of FBW
• Flight envelope protection
• Increase of stability and handling qualities
• Stability during release of weapons
• Interfacing of auto-pilot and other AFCS (Automatic FCS)
• Weight reduction

19. Q & A ?