pilots at all, but will be pre-programmed to fly a particular route unaided. Systemfailure is largely prevented by having several back-up systems, and as a last resortthe aircraft could be flown from the ground to complete a flight safely. The mainproblem with this would not be a technical one; it would be passenger resistance toa pilot-less aircraft. However, once it can be shown that automatic systems aresafer than human pilots, this means of flying will be available.33.4.10-5CHAPTER 10Look - no pilot
AUTO-PILOT AND RELATED SYSTEMS33.4.10-6Self Assessment Questions1. What does ILS mean?Do not mark the paper inany way - write youranswers on a separatepiece of paper, in the formof a sentence.
33.4.11-1CHAPTER 11CHAPTER 11AIRCRAFT SYSTEMSHYDRAULIC SYSTEMS1.Hydraulic systems are a convenient way of providing the force required toretract and extend undercarriages, and to operate flaps and wheel brakes. Theyare also widely used to move control surfaces, such as ailerons and elevators, inpower-assisted and power-operated control systems. Although the pumps andpipework needed to supply pressurised hydraulic fluid around the aircraft mightseem to be quite heavy, the system can be much lighter than an electrical ormechanical system. This is because of the high pressures used, which lead tosmall units of high power.2.Hydraulic systems use a special type of oil to transmit pressure. A pumppressurises the oil to about 210 kilogrammes force per square centimetre. Thismeans that a hydraulic jack capable of lifting a one-tonne family car might only beabout 25mm diameter. The hydraulic jack that is used to create this movementlooks like Figure 11-1.3.The flow of oil into the jack is controlled by a valve, and it is designed so thatoil can flow into one side of the jack to make it extend, and into the other to make itshorten or retract. By controlling the speed that the oil flows into the jack, the speedof its extension or retraction can also be controlled. When oil is fed into the rightside of the jack, the pressure acting on the face of the piston creates a force whichpushes the piston to the left. This causes the jack to extend. The movement of thepiston pushes oil out of the left chamber. In a similar way, pumping oil into the leftchamber retracts the jack, pulling control surface or undercarriage leg with it.4.The hydraulic oil needed for this movement is passed around the aircraft inpipes. Some are pressure lines, taking the oil from the pump to the control valves.Other pipes connect each control valve to its jack, or actuator. When the jack retracts,the oil that is expelled to allow the jack to move passes into low-pressure returnpipes, which take the oil back to the reservoir, where it is stored until it is neededagain.How hydraulic systemswork
AIRCRAFT SYSTEMS33.4.11-25.An aircraft hydraulic system is quite complicated, but is made up of a lot ofvery simple circuits. The system is similar in many ways to a set of electrical circuits,although of course a flow of oil is being used rather than a flow of electricity.
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