The Role Of Computers In Fly By

Wire Aircraft Essay, Research Paper

THE ROLE OF COMPUTERS IN FLY BY WIRE AIRCRAFT.

AN INTRODUCTION TO FLY BY WIRE(FBW):

Traditionally pilots use an inceptor (a wheel, control column, or sidestick) to manipulate cables that control pumps and hydraulic actuators. The actuators in turn operate surfaces such as flaps, ailerons and rudders to provide the necessary effect (e.g. roll left, yaw right etc).

The FBW inceptor is usually a sidestick (so called because it is mounted on the pilot s side). Moving the stick generates electrical signals that are processed by the onboard Flight Control Computer (henceforth called FCC) and relayed as control signals to energise pumps, move actuators and position control surfaces. The set-up, inceptor to Relayer to Actuators constitutes a Flight Control System (henceforth called FCS).

The fundamental difference between conventional- mechanical FCS and FBW FCS is the relayers. Whereas conventional FCS connect inceptor to actuators mechanically via cables and mechanical linkages etc, FBW FCS use electrical signals sent down wires (hence FBW) from inceptor to actuators to achieve the desired effect. The FCC therefore is central to a FBW FCS and acts as a nerve centre where mechanical inputs from the inceptor are interpreted into electrical signals to be relayed to actuators. Here the electrical signals in turn cause mechanical movement of actuators and thus the flight control surfaces and ultimately the aircraft.

EXPLANATION OF TECHNICAL TERMS:

Inceptor: Joystick, control column or sidestick where command input is made.

Actuator: A device imparting mechanical motion.

Flap: An auxiliary wing surface basically designed to increase lift or drag as necessary located on trailing edge or wings.

Ailerons: Horizontal control surfaces on trailing edge of wings.

Rudder: Vertical control surface on trailing edge of vertical tail.

Angle of attack (AOA): Angle at which the cord of an aircraft wing meets the relative airflow.

Roll: Movement of an aircraft about the horizontal axis.

Bank angle: The angle of the aircraft wing measured from the horizontal during a roll.

Yaw: The rotation of an aircraft about its vertical axis.

Yaw angle: The angle between the longitudinal axis of the aircraft and its initial, undisturbed direction of flight.

WHY A FLY BY WIRE FLIGHT CONTROL SYSTEM.

Efficiency

The major advantage of computer-controlled flight is greater efficiency. The computer precisely controls all the flight control surfaces on the plane and in the process tailors the performance of these control surfaces to flying conditions for maximum efficiency. This improves handling significantly and cuts fuel consumption as compared to conventional aircraft. This advantage is even more marked in long haul, commercial aircraft like the Airbus A320, A340 and the Boeing 777 where operating efficiency is key to the survival of an airline.

A FBW FCS is also simple and confers a weight advantage over a conventional FCS since it has fewer parts and all the mechanical cables, linkages are eliminated and are replaced by lightweight wires and a FCC this in turn also saves further fuel. A lightweight is also critical to the performance of a combat aircraft, the lower the weight of the airframe etc. the faster the plane can go for the same thrust from the engines. Also more weapons can be carried.

The inherent simplicity of a FBW aircraft also renders it much easier to maintain. In-flight malfunctions and anomalies can be identified by the Central Maintenance Computer, which both identifies a failed component and assesses the integrity of repairs. A record is kept of such instances available for study by an on-ground engineer on landing, this makes a FBW FCS even more efficient as it improves troubleshooting capability, further simplifying maintenance and producing quicker turnarounds.

Reliability

FBW FCS is also considered by most to be more reliable than a conventional FCS. Because the FCC is so critical to the stability of the aircraft a malfunction would have catastrophic consequences. For this reason the primary FCC has independent backup computers which kick in in case of a total primary systems failure. This is known as Multiple Redundancy. A majority of FBW aircraft have quadruple redundancy (four backup computers). The Lockheed Martin F-16 Fighting Falcon, the Eurofighter Typhoon, the Airbus Industrie A340 fall in this category. But the more recent Boeing 777 incorporates 5 backup FCC s, as does the Airbus A320. Multiple redundancy drastically reduces chances of a total systems failure (in the case of the A320 it is equivalent to only a 1 in 10 chance of failure in a fleet of 1000 A320 s throughout their 30 year service life). Multiple redundancy confers failsafe/fail operative features to a FBW aircraft and thus increases reliability.

Safety

The FCC acts a the pilots eyes, ears and generally, a best friend keeping him/her out of sticky situations and keeping him/her informed about flight conditions at other times. This serves to alleviate the workload on the pilot considerably. The FCC also automatically damps out /trims turbulence or gusts allowing for a more comfortable flight. FBW also eliminates the danger of stall and overspeeding (an aircraf

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