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Airframes and systems - part 2

Chiếc máy bay đối xứng cứng nhắc nối khung 1234567, thể hiện trong hình. P.12.4, là cố định hỗ trợ cứng nhắc 1 và 5 và được hỗ trợ bởi các con lăn nghiêng 45 "so với chiều ngang tại các nút 3 và 7. Nó mang một điểm P tải thẳng đứng tại nút 4 và tải một w thống nhất phân phối cho mỗi đơn vị chiều dài trên khoảng 26 G | HYDRAULICS BASIC HYDRAULICS ACTUATOR ACTUATOR Figure 1.5 Open Centre System 1.7 OPEN-CENTRE SYSTEM The main advantage of this system is that it is simple the main disadvantage is that only one service can be operated at a time. As shown in Figure. 1.5 fluid is passed directly to the reservoir when no services are being operated this allows the engine driven pump to run in an offloaded condition as little pressure is generated but there is still a flow of oil through the pump to cool and lubricate it. On selection of a user system the fluid is directed to the actuator which will move. When the actuator reaches the end of its travel pressure will build up to a value when the selector is returned to neutral in order to offload the pump and allow alternative selections to be made the relief valve will relieve excess pressure if the selector does not return to its neutral position. This type of system is popular in many light aircraft which do not require a constant pressure to be maintained all the time as only items like landing gear and flaps will be powered for short periods of time each flight. Light aircraft may alternatively be fitted with a self contained power pack the pack may operate the landing gear retraction system they are also be used on large aircraft as emergency systems or to operate freight doors etc. 2. 1 - 8 Oxford Aviation Services Limited HYDRAULICS BASIC HYDRAULICS RESERVOIR PUMP ACCUMULATOR RELIEF VALVE NON-RETURN VALVE PRESSURE FILTER ACTUATOR ACTUATOR Figure 1.6 Closed System 1.8 CLOSED SYSTEM With this type of system operating pressure is maintained in that part of the system which leads to the selector valves and some method is used to prevent over-loading the pump. In systems which employ a fixed volume pump constant delivery an automatic cut-out valve is fitted to divert pump output to the reservoir when pressure has built up to normal operating pressure. In other systems a variable volume pump constant pressure is used delivery being .