The Fly-by-Wire (FBW) System


Fly-by-wire (FBW) system is how a result is obtained or an end is achieved in aircraft control through the aid of a computer. Jack G. Ganssle and Michael Barr noted that the fly-by-wire system is the substitute of the previous conventional system or process by which an aircraft’s flight is controlled manually using electronic programming that controls a display for the user and allows the user to interact with the system1. In line with this, the fly-by-wire is the process whereby electronic quantity (voltage, current, or field strength) whose modulation represents coded information about the source from which it comes are transmitted by wire for movements in the control of the flight.

However, the digital computer that controls the flight of the aircraft decides how to move the mechanism that puts the aircraft into automatic action at each surface that controls the aircraft thereby accomplishing the expected result.

In addition to this, the Signal going into the electronic system which is performed through the line of code written as part of the digital computer program is achieved without the cognition of the pilot for the stabilization of the aircraft to execute additional undertakings.

Analysis of installation of a fly-by-wire system in small size aircraft with weight estimation

The installation of a complex or intricate flight control system is a Stimulating task that requires the effort and skill of various engineering disciplines in turn to accomplish a productive system design. Accordingly, the installation of fly-by-wire in the control system of an aircraft is not just by merely adding together wires. The process is a complicated one in that it alters the way intended performance of an aircraft and the technique at which it flies.

In the modern aircraft’s flight control system the use of fly by wire has been implemented with the aid of a digital computer. However, in the installation of fire-by-wire as noted by Collinson R.P.G “the electrical transmission of signals and instructions is a most important component” 2. Consecutively, electrical operational aircraft is the new technology introduced for the control of electric power of the aircraft and this process is gradually replacing the hydraulic circuit.

Furthermore, in the installation of fly by wire the electrical data bus is connected with wires which are then connected to the classical servo-control that is necessary for the flight control actuator which in turn is connected to a hydraulic circuit. The electro-hydrostatic actuator is then connected to an electric circuit. The installation of an electrical backup hydraulic actuator which is connected to multiple categories of power sources. There is also the installation of servo-controlled systems which broadens the possible mobility of the aircraft, also the system is designed to duplicate the other components or provide alternatives in case one component fails is required to increase, the reliability of the flight control system.

However, the fly-by-wire has to determine the essential quality of each actuator and the associated digital computer to provide control signals and failure of flight operation. In addition to this, in the installation of fire-by-wire, the rods are interchanged by uncomplicated and light wiring, and there is an increment in weight due to the installation of hydraulic or electrical actuators and power sources in conjunction with the source of power. Also, the installation of a data bus system that is recognized, furthermore, the data bus uses a screened twisted pair of wires which connects to the bus using dividing transformers. There is an embedment of the bus controller in the flight control computers.

How to wire fly-by-wire system

Michael H. Tooley, Mike Tooley, and David Wyatt stated that with the digital computerized age of aircraft operation harsh atmospheric condition is experienced on electrical wiring, the yearning and need for acceptable service, and comprehensive check-ups to ensure smooth flow of the gadget.3

Fly-by-wire generally uses the well-established Mil std 1553 data bus system. The links and bus use a screened twisted pair of wires with connection to the bus through isolating transformers. This is a command/response system with the bus controller function embedded in the flight control computers. It has a data rate of 1 Mbit/s and a word length of 20 bits to encode clock, data, and address can receive or transmit up to 50 000 data words a second.

However, some aircraft use the new ARINC 629 data bus system. This is an autonomous system and operates at 2Mbit/s. The links and bus use an unscreened twisted pair of wires with connection to the bus through demountable current transformer couplers. Additionally, the electronic complexity required in these systems to code the data and transmit it, or to receive data and decode it, is encapsulated in one or two integrated microcircuits.4

Furthermore, in the wiring of a fly-by-wire, as noted by Campagna Palmiro, the rods and cables of the aircraft are substituted with electrical wires. In this process, an electrical indication is sent through the control column of the pilot to the electro-hydraulic actuator. This hydraulic actuator moves the control surface, hence the reduction of weight because the previous wiring system of wires and rods, pulleys, and bell cranks are of more weight than the electrical wiring installation.5

Given this, Williams Siuru stated that with the modern drastic and far-reaching change in the fly-by-wire system of wiring, the electrical signals are being transmitted through the wires and there is an electromechanical device that is used in the conversion of sticks and rudder pedal motions into electrical voltages.6

In turn, these voltages are measured and the derived values are inputted into the digital computer which is a highly coordinated network of wires. In addition, the aircraft travels through the air or is airborne with the aid of some certain input program which the digital computer passed into the system and controls the aircraft. Accordingly, the output of the digital computer is processed and sent out in the form of electrical signals, which are fed by wires to the actuators, which then move the control surfaces. In conclusion, the wiring of the fly-by-wire installation involves

Electrically command control system which is implemented through the computer.

In essence, fly-by-wire is installed by an electrical wire. All the wirings are connected using the flight control computer (FCC). Then it is connected to the computer which sends electronic signals to the actuators, in this specific case flaperons and slats. The FCC bridges the gap between measurement signals (from the inertial measurement unit and the air data transducers) and pilot inputs (such as the pilot’s stick, pedal, and throttle displacements) on hand, and controls surface actuators (such as flaperons, rudder, and canards) on the other. Based upon the pilot control inputs and available measured signals, the computer is then installed for the calculation of the independently required surface deflections and also gives the appropriate commands to the servos.

Weight estimation of components

By using a quadruplex digital flight control system and using fly-by-wire instead of mechanical flight controls, a weight saving of 6 percent is feasible. This saves 1,665 Ibs. The illustrated diagram shows the weight estimation in detail.7

Weight Kg

Weight Ibs

Forward Limit % MAC

Aft Limit % MAC

Minimum flight – Aft

14 696

32 400


Minimum flight – Forward

15 694

34 600


Maximum zero fuel

18 597

41 000



Maximum landing

28 304

62 400



Maximum for aft CG at 38,5 %

25 890

57 076



Maximum takeoff

31 751

70 000



Maximum ramp

31 842

70 200



Works cited

Campagna, P, Storms of controversy: The secret Avro Arrow files Revealed, Dundun press, ltd, Ontario, 2010, p.72.

Collinson, R.P.G, Introduction to avionics systems, Springer, 2003, P.161.

Ganssle, JG & Barr, M, Embedded systems dictionary, Focal Press, Lawrence, KS, 2003, page 107.

Roskam, J, Airplane Design: Component Weight Estimation, DARcorporation, Kansas, 1999, P.55.

Siuru, WD., Future Flight: The Next Generation of Aircraft Technology, 2nd edn, McGraw-Hill Professional, U.S.A, 1993, p.51.

Tooley, MH, Tooley, M & Wyatt, D, Aircraft electrical and electronic systems: principles, operation and maintenance: Aircraft engineering principles and practice, Butterworth-Heinemann Burlington, MA, 2009, p. 5.