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Aviation History
1956
1956 - 1719.PDF
FLIGHT, 7 December 1956 MISSILES THAT THINK ... Stored air or other gas is held, at a pressure which may begreater than 5,000 lb/sq in, in any of a variety of forms of bottle. It has frequently been found that toroidal (ring-shaped) pressurevessels have to be adopted, not on the grounds of efficiency but because it may be impossible to fit a sphere into a missile. Thefeed-line leads through a pressure-reducing valve which regulates the delivery to a moderate pressure suitable for various services.This pressure can be held constant as the pressure in the bottle falls, and the circuit is so designed that the pressure remainingin the bottle does not fall below the level from the reducing valve within the flight-endurance of the weapon. Several missilesemploy pneumatic shaft power. Bendix, for example, produce a pneumatic-vane motor driving an alternator and hydraulic pumpfor the control system: data are 1.5 lb, 2.75 h.p. at 100 lb/sq in and limits of -20/ + 120 deg F and 60g. Slow-burning charges are widely used in missiles as sources ofhigh-pressure gas. The charge, of any suitable material such as a solid rocket propellant, is housed in a cylinder and ignited elec-trically at the firing of the missile. The combustion is stabilized automatically by the balance of gas pressure and rate of com-bustion, and the resulting gas-output is filtered and controlled for useful purposes. The British K.P.4 rocket motor is fed withliquid fuel under pressure from such a system and English Electric have developed complete accessory power packs energizedby such combustion. Ram-air systems can provide appreciable power for a lowinstalled weight, irrespective of the duration required. They are therefore suitable for weapons designed to fly at high super-sonic speed for an appreciable period at a height not greater than about 90,000ft. Such requirements are appropriate to ramjetmissiles and it is quite common to find a ram-air turbine driving a ramjet fuel pump and providing accessory power. As the fuelpump normally absorbs most of the shaft-power generated, it is fortunate that the fuel-flow required falls off in the same pro-portion as the ram-pressure as altitude is gained. A disadvantage is that systems powered by ram-air may have to be initiallyenergized by some different means immediately before launching. Among self-contained power sources the most widely used arethose in which a tiny turbine is spun by what is actually a rocket motor; the latter can burn any of the fuels normally employedin rocketry. Today it is possible to draw as much as 50 s.h.p. from a unit which, even with tanks, valves, control system andother appurtanences, is smaller than a typewriter. No information has been released on British equipment of thistype, but many varieties have been reported from America. Whirlajet, Inc., make solid-rocket units arranged like Hero's tur-bine in sizes from | h.p. to 20 h.p. A typical unit, running at 12,000 r.p.m., drives a hydraulic gear pump and a 2,500-Wattd.c. generator with commutator. AiResearch make a variety of missile A.P.Us, running on solid or liquid fuel. A typical 29 lbunit has a single shaft running at 24,000 r.p.m. with a single- stage turbine at one end and, at the other, a 2.5 h.p. hydraulicpump and/or an induction generator rated at 650 W (overload 1,600). A.M.F.'s turbo engineering department have also evolvedenvironment-free power packages based on turbines driven by hot air or controlled rocket combustion. Several patterns are available,rated at up to 35 h.p. with electrical or hydraulic output. Adel also make self-contained electro-hydraulic packages for use in missiles. Several firms have developed hydraulic systems for operationat 450 to 480 deg F and other companies—notably G.E.—are in •production with complete electronic systems (valves, trans-formers, capacitors, resistors and motors) capable of use at the remarkable temperature of 500 deg C. It is sometimes possible to use the energy from controlledmono-propellant combustion directly. An example of available equipment is an American missile-surface pulser for step func-tions. Power is drawn from fifty 0.22in cartridges driving opposed pistons, swash plates and an output shaft. At a surfacedeflection of 20 deg the torque generated is 250 lb-in, and higher values are achieved with longer cartridges. It is possible to adjust Taken last July, this photograph depicts a Boeing QB-17 drone about to be killed by a GAR-1 Falcon fired from an F-102A intercepter. The Falcon caught the drone in the fin (foot of page). the amplitude, duration and spacing of successive square-wavepulses. In short-duration weapons recourse is frequently made to"run-down" mechanisms. Gyros may be spun up before launch- ing and left without-energization during flight. It is also worthnoting that various types of stored mechanical energy, both from conventional springs and other systems, are finding missileapplications. Miscellaneous: The following are some of the many factors inwhich problems are being found in the development of missile equipment:— De-icing. Curiously, many missiles require to be de-iced. Inseveral, provision is made to heat the interior by hot air before launching in sub-zero conditions. This is perhaps the easiestmethod with a 70ft ballistic weapon or a large SAM elevated to a high angle. One American artillery-type missile is completelyshrouded by a G.E. electric blanket before firing. AAMs are, of course, invariably cold-soaked at high altitudebefore being called upon to perform their life's work with absolute reliability. It is difficult to cosset such a weapon inthe manner of Honest John but airframe de-icing can be carried out by such a system as Napier's Spraymat—which has alreadybeen successfully evaluated on RTVs. Furthermore, it is often necessary to feed the missile with hot air—to keep an infra-redphotocell at the correct temperature, for example—and with cold air, which may be needed to cool the electronics (which have tobe operating before the missile is fired). Filters. In several missiles there is a need for extreme purityin the working fluids, and a complete absence of foreign matter is essential where tiny bearings or metering orifices are involved.An example is the porous stainless-steel filter (Poroloy) used in the 3,000 Ib/sq in air-line to Corporal's air tank. Bearings. Present bearings are hard-put to withstand ambienttemperatures exceeding 250 deg F. Although thermal lag and clever insulation is staving off the evil day, there is no doubt thatthis limit must eventually be pushed to at least 1,000 deg F. Possible solutions are the employment of new bearing materials,like graphite or various ceramics, and the introduction of com- pletely new lubricants like molten sodium, powdered graphite,steam or even air. This is one of the major problems in the development of the intercontinental ballistic missile. FOOTNOTE: The two illustrations on the first page of this article(p. 876) are Crown copyright, reproduced by permission of the Con- troller, H.M. Stationery Office.
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