In order to ensure that the high integrity levels of earlier mechanical systems are achieved in FBW planes, numerous lanes of computing and multiple signal sources are required to offer redundancy. The response of the aircraft to signals is feedback to both the flight control and auto-pilot computers through specific sensors and then sent for display to the aircraft crew through dedicated screens (Gibson, 1999). Flight control computers in FBW planes not only control operations but they also monitor them. When the plane is in auto-pilot mode, the flight control computers receive flight signals from the auto-pilot computers. The flight control computers in the planes interpret the pilot’s inputs and consequently move the surfaces as required to accomplish the desired flight path. In FBW planes, the side sticks are used to control the plane in pitch and roll as well as indirect control through turn coordination in yaw (Gibson, 1999). The early mechanical means of control had very high levels of integrity, in terms of the probability of the loss of aircraft control. The rudder and the Trimmable Horizontal Stabilizers in these airplanes can also be manually controlled. However in fly-by-wire airplanes, flight control surfaces are all digitally controlled and activated by means of a hydraulic system.
In standard airplanes, computers within the plane constantly modify the pilot feel on controls while the auto-pilot computers can be able to control the actuators (Lloyd & Tye, 1992). On a standard airplane, control signals from the pilot are transmitted to the actuators by a system of mechanical components as shown in Figure 2.įigure 2: Mechanical control system retrieved from Stephens & Lewis (1992, p.26)ĭirect mechanical connections between the cockpit controls (rudder pedals and pitch/roll sticks) and the control surfaces that maneuver the plane were used in mechanical flight controls. The Flight Control System is designed to achieve this through the aircraft’s flight control surfaces that include the rudder, edge flaps, trailing and foreplane (Pratt, 2000).įlight control system also needs to control the thrust provided by the engines, since they also produce the forces and moments acting on the plane. If we can control the forces and moments, then by default we can control the accelerations and hence velocities, rotations and translations. In order to achieve flight control, the capability to control the forces and moments acting on the plane is imperative. This model allows modeling of all forces and moments acting on the plane (Stephens & Lewis, 1992).įigure 1: Body axis aircraft co-ordinate system retrieved from Stephens and Lewis (1992, p.24) The rigid body dynamics therefore has six degrees of freedom, given by three rotations about, and three translations along the axes. In the study of mechanics of flight, we can assume that an aircraft can be represented as a rigid body, designed by a set body of axis as shown in figure 1. This means that the link between the operator and the control actuators is interposed by a computer system hence modifying the operator’s inputs with regards to the control parameters. The controls are configured to control computers in the aircraft. In fly-by-wire, the control of the aircraft is only achieved through the use of electrical signals. Mechanical flight controls are prone to several dangerous issues such as spinning, stalling and pilot-induced oscillation (Pratt, 2000). The control systems and cables need redundant backup that guard against failures and as such further increases the weight of the aircraft and the work of the crew.
#Redundant flight control system manual#
Manual flight control systems are very bulky and the control cables need to be carefully laid through the relevant sections of the airplane. The Airbus fly-by-wire system was certified in 1988 and was used the same year during the launch of the first A320 (McRuer & Graham, 1981).
The Airbus Company was the first airplane manufacturer to introduce this system in their A320. Fly-by-wire is an innovation that replaces an aircraft’s manual controls with an electronic interface.įly-by-wire is a digital flight control system that enables signals from manual controls to be converted into electrical signals after which control computers determine the appropriate response (Droste &Walker, 2003).
Before the introduction of the fly-by-wire system in civil aviation, pilots had to rely only on manual controls during flight.
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