For the earliest aircraft, flight control systems were solely mechanical (using rods, cables and pulleys). The pilot in the cockpit made use of a control stick and pedals to carry out the three basic aerodynamic movements - roll, pitch and yaw. As aircraft got bigger, systems became hydraulic (using pumps, pipes, valves and actuators), so that pilots could move the important control surfaces without having to rely on the own strength. The development of these hydraulic systems was also an important way for the engineers to keep the wetght of the aircraft down. As aircraft continued to grow in size and with the development of large passenger jets, this requirement to keep weight down led to the development of fly-by-wire systems. Fly-by-wire means that the aircraft is controlled by an electrical system. Nowadays fly-by-wire systems are digital and large aircraft are controlled by a computerized command system. The world's first digital fly-by-wire aircraft was the Airbus A320, which made its flight in 1987. The greatest innovation was the in-built safety feature in which the computerized system prevented pilots making what would normally be considered unsafe manoeuvres (taking the aircraft outside the flight envelope( capabilities of a design in terms of airspeed and load factor or altitude. )). While this was the subject of much debate at the time, it is now a standard feature of all new Airbus aircraft. Boeing was also developing digital fty-by-wire systems, but their systems allowed the pilots to take the airplane outside the flight envelope in an emergency situation. Thus there was a fundamental difference in philosophy between the two major constructors, Airbus and Boeing, which still exists to some extent today.
An obvious question is what happens when the computer fails (instrument blackout). The pilot then has no control over the aircraft (a back-up hydraulic system would increase weight significantly). Large aircraft usually have at least four parallel computerized control systems to deal with situations where one or even two computers might be down.
With sophisticated computer controls in place, there is no longer any need for a control stick in the cockpit. Yet even the newest aircraft (the Airbus A380 or the Boeing 787) have something which resembles a control sick in the cockpit. Research conducted amongst pilots has shown that this should remain for reasons which have nothing to do with technology and everything to do with human psychology.
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