![]() In the event of a total electrical failure, the pilot can control the aircraft manually using the trim wheel for lateral control and rudder pedals for longitudinal control.To summarise, the elevators and ailerons have access to 5 computers in total and only one is needed for operation.There are 3 hydraulic systems out of which only 1 or 2 are needed for operation, it shows that the system has electrical and hydraulic redundancy built into it. ![]() The stabiliser trim can be mechanically controlled by the pilots trim control wheel.The rudder is controlled through hydro-mechanical pedals by the pilot, however there are 2 Flight Augmentation Computers (FAC) that operate the rudder to keep the aircraft balanced in a roll.There are 3 Spoiler Elevator Computer (SEC) to control the spoilers ( more on the functioning of spoilers in a separate post) and elevators.In the event of the ELAC failing, the SEC will control the elevators and stabiliser.There are 2 Elevator and Aileron Computer (ELAC) to control the elevators, ailerons and stabliser.Each primary control has 2 hydraulic actuators, each fed from one of the three independent hydraulic systems.In the Airbus 320, there are 7 flight control computers and 3 hydraulic systems to take care of the primary flight controls (elevator, aileron, rudder).The actuators are still hydraulically operated that are similar to the hydro-mechanical system.The computer monitors the aircraft’s response to the flight control movement and modifies its output accordingly to the actuators.The pilots command are converted into electronic signals that are interpreted by the flight control computers.The computers interpret the pilot input and determine how to move the actuators connected to the flight control surfaces,as necessary, to follow their orders. The fly by wire system adds in an electronic interface to control the aircraft.As discussed above, flight controls could be handled mechanically or hydro-mechanically.However, a fly wire system is an electrical way of controlling the flight controls in an aircraft.Hence, hydraulic actuators (cylinders) are placed in the link to assist the pilot in moving the control surface. However in a high performance aircraft, the control surfaces have great pressure exerted on them and hence it is physically impossible for the pilot to manually move the controls.In a conventional light weight trainer type aircraft, cables are connected to the controls in the cockpit through a bell crank and the other side of the bell crank is connected to the control surface.Movement of the cockpit controls transfers force through the cable to the bell crank, which moves the control surface.The Wright Brothers used combinations of their body movements to deflect the portions of their FLYER, causing it to move in the desired directions.Conventional Flight Control Mechanism Picture Credits: Slideshare It not only controls the path of the aircraft but provides a flight protection envelope as well. The fly by wire system makes flying much more easier by being that system. Hence it could be so much easier if there was a system which could control the path of the airplane without the pilot constantly trying to adjust the controls and just obtain the desired pitch attitude and leave the yoke/side-stick without trimming or adjusting the power setting (with the help of the auto thrust – more on this later). Once you get more comfortable and experienced as a pilot, you start your instrument flying journey where you notice how important those initial lessons were on pitch and power as the margin of error is limited and your workload is at it’s peak. One of the first lessons that student pilots are taught in their training is the relationship between the pitch attitude and power settings required to control the aircraft.
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