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Aviation History
1946
1946 - 1257.PDF
JUNE 27TH, 1946 FLIGHT 653 Messier Hydraulics Survey of the High- pressure Hydraulic System Installed in the Handley Page Hermes I Hastings Main undercarriageleg showing neat design of mag-nesium - alloy bridge casting, andmounting points. Tailwheel as- '• sembly relationponents robust showing ; of com- |and ! design, j THE development of aircraft in past years, particu-larly in the larger categories, has brought in itstrain so many ancillary services of diverse character that means for power operation had to be devised ; this led to the inclusion of hydraulic and electric power sys- tems to aid human muscles. Although there is still some sort of rivalry between the protagonists of the two basic power systems, it is now generally recognized that there are certain advantages inherent in each, and that, obviously, the sane thing is to combine the best features of both. For this reason, among others, Messier Aircraft Equipment, Ltd., the well-known hydraulic and undercarriage manufacturers, have changed their name to Electro-Hydraulics (Messier), Ltd., and in- tend to concentrate on wedding electrics and hydraulics together to produce the best form of power service pos- sible for any given application. The hydraulic system used on the Hermes and Hastings is, however, a slightly modified version of that employed on the Halifax, and, consequently, the "electro" part is quite small. " Power is supplied by the main inboard engines, each of which drives a Lockheed Mk VI positive- displacement piston-type pump, the delivery being to an automatic cut-out valve and thence into the main system. The cut-out valve is a " pressure-gate " which maintains a static pressure of 2,500 lb/sq in in the system. This is done through the agency of a hydraulic accumulator con- sisting of a cylinder divided into two compartments by a free-floating piston, on one side of which is compressed air and on the other side hydraulic fluid from the system. When a service is selected, e.g., undercarriage retrac- tion, the static pressure stored in the accumulator is opened to the undercarriage actuating jacks, which thereupon start to move, and the pressure in the accumulator begins to fall. Immediately the pressure has dropped to 2,000 lb/sq in, the cut-out valve automatically opens the pump delivery back into the system until the 2,500 lb value is again reached, when the cut-out once more operates and diverts the pump delivery back into the fluid supply tank. "Supercharging-" for Altitude Since the pumps are working all the time the inboard engines are running, and, obviously, their delivery is not required except at odd intervals when a service is selected, the diversion of delivery back to the supply reser- voir can be regarded as an idling circuit. As the instal- lation is a high-pressure system, an electric booster pump is fitted to the reservoir tank, '' supercharging '' the suction line to each engine-driven pump so that cavitation does not occur at high altitudes. Both the main and tail undercarriages are raised and lowered by double-acting jacks, and the selector by means of which their operation is initiated comprises a casing in which are four poppet valves operated by a rocker- arm moved by the selector TANK handle, one pair of valves being1 opened for each selection. One of the pair admits pressure fluid to RELEASE VALVE PUMP OIL UP AIR DOWN Fig. 1 (above). Detail section through main undercarriage jack showing oil andemergency-air actuation principle together with ingenious locking arrangements. Fig. 2 (right!. Diagram of hydraulic and emergency-air system for undercarriageoperation. JJ_ J_L AIR EMERGENCY
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