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Aviation History
1957
1957 - 0083.PDF
18 January 1957 The Rocket-boost Skeeter 83 SOLENOID-OPERATEDON-OFF VALVE Auxiliary Propulsive System Described and Illustrated By C. FAULKNER, D.CAe, VISITORS to last year's Faraborough Show will recall the startlingperformance of the Mk 5 Saunders-Roe Skeeter equipped with blade-tip rocket boost to supplement the take-off power of the Cirrus Bombardier(the production Mk 6 has the 200 h.p. Gipsy Major). In this brief article the system is described and its performance reviewed in relation to latermarks of Skeeter. The author is chief project engineer of the makers' helicopter division.T HERE are strong arguments in favour of the use in helicop-ters of "mixed power" systems, so that the primary power unit, which gives adequate power in forward flight, can besupplemented by a booster system during take-off and landing, when substantially more power is required for short periods. Intropical conditions particularly, the power outputs of both piston- engines and gas-turbines drop sufficiently to penalize severelymany helicopters operations, especially those involving flying from very restricted areas, such as jungle clearings. As a result, theneed for auxiliary power boosting was very evident both in Korea and, more recently, in Malaya, where helicopters have been usedextensively in military and rescue work. The new booster system for the Skeeter has been developed incollaboration with the rocket-engine manufacturers, D. Napier and Son, Ltd. It gives the machine greatly enhanced vertical flightand climb performances, and permits operation with higher pay- loads in more severe climatic/altitude conditions than would nor-mally be possible. In addition, in the event of failure of the main powerplant, the booster power is always available as a stand-by.Although insufficient by itself to maintain level flight, it can never- theless greatly decrease the glide angle and so give the pilot morelatitude in the selection of his emergency landing site. The system is simple and can be fitted to the standard Skeeterwith only minor modifications. Furthermore, although it was designed originally for the Mk 6 version, it is equally applicableto the later, more powerful, marks of Skeeter which are now going into production. TANK VENT VALVE VENT IPE ON-OFF VALVE Diagrammat i c layout of propel- lant system and control circuit. MASTERARMING SWITCH4—' The liquid monopropellant used in the Napier rocket motors isH.T.P. (hydrogen peroxide diluted with not more than 20 per cent by weight of water). This fuel is stored in a removable dome-shaped tank mounted above the rotor hub and is pumped to the rocket motors at the blade tips by the centrifugal action of the rotor. Feed pipes are housed inside the main spar tubes of the rotorblades, being supported at intervals by plastic spacers which locate the pipes centrally in the tubes. The rocket motors are attachedto the ends of these spar tubes by bolts through flanged fittings on both the motors and the tubes. They are, therefore, easilyremovable for inspection or replacement; and the feed pipes and spacers can also be extracted from the blades without difficulty.On entering the motors, the H.T.P. is decomposed into super- heated steam and oxygen. The generated gases then pass to anozzle and are ejected at high velocity to provide thrust reaction. As the booster power is supplied by thrust at the rotor tips, noadditional torques are imposed on the existing transmission system and, hence, no modifications are required to either the transmissionor the tail-rotor system. The boost is controlled by a solenoid- operated ON/OFF valve, actuated by the pilot via a firing triggerswitch mounted on the cyclic-pitch stick, the switch being con- nected to the solenoid through slip rings at the rotor hub. Inparallel, a vent pipe admits air to displace the hydrogen peroxide in the pipelines to the motors when the main supply is shut off.The control panel, situated on the cockpit dashboard sill, includes a car-type, key-operated master switch, a "firing ON" warninglamp, a timer giving fuel gone/available and a tell-tale safety meter which indicates the condition of the firing circuitry. The present system allows for substantially constant thrust,although a degree of control is possible by varying the rotor speed, which, in turn, varies fuel pressure at the blade tip and hencebooster thrust. However, a throttle control can easily be provided if required. This would consist of a valve operated by an electricactuator and, in this case, control would probably be achieved most effectively by adding a boost override in the normal twist-gripthrottle on the collective-pitch lever. The dry weight of the entire system is 36 lb and the dome tankcan carry up to 86 lb of H.T.P. fuel. As the system is so designed that all major items are readily removed, the weight penaltyinvolved when operating in regions where boosting is unnecessary is small, being of the order of 5 lb. The present system is designed to give a thrust of up to 22 lbat each blade-tip unit, which is equivalent to a total of 67 h.p. STEAMGENERATOR MOUNTING BOLTS THROUGH FLAPPING HINGE TIP FAIRING (Above) Arrangement of rotor-head tank, solenoid-operated yalve, and slip-ring electrical connection to pilot's control. (Right) Method of conveying fuel to the blade-tip boosters.
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