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Aviation History
1962
1962 - 0143.PDF
FLIGHT International, 25 January 1962 143 Control system Following separation of the boost motors, the control system is brought into action, initially to stabilize the missile to a roll datum followed by initiation of the control and guidance loops. An unusual feature of the lateral control is that the only sensing devices are two accelerometers, one in the nose and the other in the tail, one of which provides the basic feedback while the combined signals provide weathercock informa tion. During flight the parameters of the roll and lateral loops are varied by an aerodynamic stiffness unit, to compensate for changes it. velocity and altitude. The rear control surfaces are driven by h "draulic actuators pressurized by a gas-driven reciprocating pump. The gas generator, which also drives the turbo-alternator, was originally a cigarette-burning cordite charge. In 1957 this was abandoned in favour of iso-propyl nitrate, which produces a very clean gas, initially at about 1,100°C but cooled by the injection of water/methanol. Sustainer The solid sustainer motor employs cast double-base material, and at the time of its development was the largest long- duration motor with such propellant produced in the UK or USA. The case is wrapped and welded chrome molybdenum steel, and the presence inside of the large forged light-alloy ring carrying the wings and rear boost attachments means that the charges have to be loaded from each end through detachable closures. The subsonic blast pipe is of light alloy and asbestos phenolic resin, with a carbon insert at the nozzle throat. There has been only one recorded case of sustainer failure in more than 500 missile flight trials. Liquid propellant prototype P(L) Seaslug Mk I, complete with boost motors Development Problems The remainder of the paper is devoted principally to a discussion of flight-development problems and the extensive test and simulation programmes carried out to ensure the supreme reliability needed in any missile (and particularly in one for shipboard use, where only a limited number of rounds can be carried). One of the most elusive problems was the "g-pulse pheno menon," which led to repeated catastrophic structural failures before or during boost separation. It was finally found that these stemmed from the severe asymmetric loading on the missile after body arising from the strong Shockwave at the afterburning front of the boost flame. RPE Westcott finally supressed afterburning by introducing a potassium salt into each boost charge. Other problems concerned beam loop oscillation, roll torsional oscillation and anti-symmetric flutter. That these and other difficul ties have been overcome is evident from the following sentence, taken from the closing paragraphs of the paper: "The enviable reputation both for reliability and for high- and low-level accuracy which has been built up by Seaslug during its acceptance trials is second to no other weapon in this country, and possibly even in the United States." A or S Below, Seaslug Mk I
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