UNIVERSITY INSTITUTE OF
EGINEERING
AEROSPACE ENGINEERING
Bachelor of Engineering ( Aerospace Engineering)
22AST-257 Aircraft Systems and Instruments
Unit 1 DISCOVER . LEARN . EMPOWER
By: Er. Sukumar Dhanapalan/AP/CU
22AST-257 Aircraft Systems and Instruments
Airplane Systems
And
Flight Control System
By: Er. Sukumar Dhanapalan/AP/CU
By: Er. Sukumar Dhanapalan/AP/CU
By: Er. Sukumar Dhanapalan/AP/CU
Fly –By –Wire System (FBW)
• The term "fly-by-wire" implies a purely electrically-signalled
control system
• It is a computer-configured controls, where a computer system
is interposed between the operator and the final control
actuators or surfaces
• It modifies the manual inputs of the pilot in accordance with
control parameters
• These are carefully developed and validated in order to
produce maximum operational effect without compromising
safety
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Introduction
• The FBW architecture was developed in 1970’s
• Initially starting as an analogue technique and later on
transformed into digital.
• It was first developed for military aviation, where it is
now a common solution
• The supersonic Concorde can be considered a first and
isolated civil aircraft equipped with a (analogue) fly-by-wire
system By: Er. Sukumar Dhanapalan/AP/CU
FBW – Introduction
• In the 80’s the digital technique was imported from military
into civil aviation by Airbus, first with the A320, then
followed by A319, A321, A330, A340, Boeing 777 and
A380 (scheduled for 2005).
• This architecture is based on computer signal processing
By: Er. Sukumar Dhanapalan/AP/CU
By: Er. Sukumar Dhanapalan/AP/CU
Operation
• The pilot’s demand is first of all transduced into electrical
signal in the cabin and sent to a group of independent
computers (Airbus architecture substitute the cabin control
column with a side stick)
• The computers sample also 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.
By: Er. Sukumar Dhanapalan/AP/CU
Operation
• The flight data used by the system mainly depend on the
aircraft category; in general the following data are sampled
and processed:
➢ Pitch, roll, yaw rate and linear accelerations
➢ Angle of attack and sideslip
➢ Airspeed/Mach number, Pressure, Altitude and radio
altimeter indications
➢ Stick and pedal demands
➢ Other cabin commands such as landing gear condition,
thrust lever position, etc.
By: Er. Sukumar Dhanapalan/AP/CU
Operation
• 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
By: Er. Sukumar Dhanapalan/AP/CU
Fly-By-Wire System
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Basic Operation
• When a pilot moves the control, a signal is sent to a computer,
this is analogous to moving a game controller, the signal is
sent through multiple wires (channels) to ensure that the
signal reaches the computer.
• When there are three channels being used this is known as
'Triplex'.
• The computer receives the signals, performs a calculation
(adds the signal voltages and divides by the number of signals
received to find the mean average voltage) and adds another
channel.
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Basic Operation
• These four 'Quadruplex' signals are then sent to the control
surface actuator and the surface begins to move.
• Potentiometers in the actuator send a signal back to the
computer (usually a negative voltage) reporting the position
of the actuator.
• When the actuator reaches the desired position the two
signals (incoming and outgoing) cancel each other out and
the actuator stops moving (completing a feedback loop).
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Basic Operation
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Stability
• Three gyroscopes fitted with sensors are fitted in the aircraft
to sense movement changes in the pitch, roll and yaw axes.
• Any movement (from straight and level flight for example)
results in signals being sent to the computer which again
moves the relevant control actuators, however, the input is
done without the pilot's knowledge; the cockpit controls do
not move
By: Er. Sukumar Dhanapalan/AP/CU
By: Er. Sukumar Dhanapalan/AP/CU
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Safety and Redundancy
• Aircraft systems may be quadruplexed (four independent
channels) in order to prevent loss of signals in the case of
failure of one or even two channels.
• High performance aircraft that have FBW controls (also
called CCVs or Control- Configured Vehicles) may be
deliberately designed to have low or even negative
aerodynamic stability in some flight regimes, the rapid-
reacting CCV controls compensating for the lack of natural
stability
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Safety and Redundancy
• Pre-flight safety checks of a fly-by-wire system are often
performed using Built-In Test Equipment (BITE).
• On programming the system, either by the pilot or ground
crew, a number of control movement steps are automatically
performed.
• Any failure will be indicated to the crews
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Advantages
• Flight envelope protection (the computers will reject and tune
pilot’s demands that might exceed the airframe load factors)
• Increase of stability and handling qualities across the full
flight envelope, including the possibility of flying unstable
vehicles
• Turbulence suppression and consequent decrease of
fatigue loads and increase of passenger comfort
• Use of thrust vectoring to augment or replace lift
aerodynamic control, then extending the aircraft flight
envelope
By: Er. Sukumar Dhanapalan/AP/CU
FBW – Advantages
• Drag reduction by an optimised trim setting
• Higher stability during release of tanks and weapons
• Easier interfacing to auto-pilot and other automatic flight
control systems
• Weight reduction (mechanical linkages are substituted by
wirings)
• Maintenance reduction
• Reduction of airlines’ pilot training costs (flight handling
becomes very similar in an whole aircraft family)
By: Er. Sukumar Dhanapalan/AP/CU
F-8C Crusader Digital fly-by- The Airbus A320, First airliner with
Digital fly-by-wire controls
wire test bed (1972)
(1984)
A Dassault Falcon 7X,
The first business jet with Digital fly-by-
wire controls
(2005)
By: Er. Sukumar Dhanapalan/AP/CU
Digital Fly-By-Wire (DFBW)
• A digital fly-by-wire flight control system is similar to analog
system. However, the signal processing is done by digital
computers and the pilot literally can "fly-via-computer".
• Increases in flexibility of the flight control system, since the
digital computers can receive input from any aircraft sensor
(such as the altimeters and the pitot tubes).
• Increase in electronic stability - system is less dependent on
the values of critical electrical components in an analog
controller
By: Er. Sukumar Dhanapalan/AP/CU
Digital Fly-By-Wire (DFBW)
• The computers "read" position and force inputs from the
pilot's controls and aircraft sensors.
• They solve differential equations to determine the appropriate
command signals that move the flight controls in order to
carry out the intentions of the pilot
• The programming of the digital computers enable flight
envelope protection.
By: Er. Sukumar Dhanapalan/AP/CU
Digital Fly-By-Wire (DFBW)
• Aircraft designers precisely tailor an aircraft's handling
characteristics, to stay within the overall limits of what is
possible given the aerodynamics and structure of the aircraft.
• Flight-control computers continuously "fly" the aircraft,
pilot's workloads can be reduced
• In military and naval applications, it is now possible to fly
military aircraft that have relaxed stability.
By: Er. Sukumar Dhanapalan/AP/CU
Digital Fly-By-Wire (DFBW)
• Better maneuverability during combat and training flights and
" carefree handling" because stalling, spinning. and other
undesirable performances are prevented automatically by the
computers
• Enable inherently unstable combat aircraft, such as the F-117
Nighthawk and the B-2 Spirit flying wing to fly in usable and
safe manners
By: Er. Sukumar Dhanapalan/AP/CU
DFBW - Redundancy
• If one of the flight-control computers crashes - or is damaged
in combat; or suffers from "insanity" caused by
electromagnetic pulses - the others overrule the faulty one (or
even two of them), they continue flying the aircraft safely, and
they can either turn off or re-boot the faulty computers.
• Any flight-control computer whose results disagree with the
others is ruled to be faulty, and it is either ignored or re-
booted.
By: Er. Sukumar Dhanapalan/AP/CU
DFBW - Redundancy
• Most of the early digital fly-by-wire aircraft also had an
analog electrical, a mechanical, or a hydraulic back-up flight
control system
• The Space Shuttle has, in addition to its redundant set of four
digital computers running its primary flight-control software, a
fifth back-up computer running a separately developed,
reduced-function, software flight- control system - one that
can be commanded to take over in the event that a fault ever
affects all of the computers in the other four.
By: Er. Sukumar Dhanapalan/AP/CU
DFBW - Redundancy
• This back-up system serves to reduce the risk of total flight-
control-system failure ever happening because of a general-
purpose flight software fault has escaped notice in the other
four computers.
• For airliners, flight-control redundancy improves their
safety
• Fly-by-wire control systems also improve economy in flight
because they are lighter, and they eliminate the need for many
mechanical, and heavy, flight-control mechanisms
By: Er. Sukumar Dhanapalan/AP/CU
DFBW - Redundancy
• Most modern airliners have computerized systems that
control their jet engine throttles, air inlets, fuel storage and
distribution system, in such a way to minimize their
consumption of jet fuel. Thus, digital control systems do
their best to reduce the cost of flights.
By: Er. Sukumar Dhanapalan/AP/CU
Text Books
Sr No Title of the Book Author Name Volume/Edition Publish Hours Years
1 Aircraft Systems Ian Moir and Allan Seabridge 2nd Edition PEP 2001
2 Aircraft Flight Instruments and Guidance David Wyatt 1st Edition Taylor and Francis 2015
systems
3 Civil Avionics Systems Ian Moir, Allan Seabridge and Second Edition Wiley 2013
Malcolm Jukes.
Reference Books
Sr No Title of the Book Author Name Volume/Edition Publish Hours Years
1 Aircraft Instruments – Principles and E. H. J. Pallett Second Edition Longman House 1981
Applications
2 General Hand Book of Airframe and Federal Aviation First English Book Store, 1995
Powerplant Mechanics Administration, New Delhi
U.S. Dept. of Tra
3 Automatic Flight Control E. H. J. Pallett and S. Coyle Fourth Edition Blackwell Science 1993
Ltd
By: Er. Sukumar Dhanapalan/AP/CU
By: Er. Sukumar Dhanapalan/AP/CU
