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Aviation History
1957
1957 - 1139.PDF
227 FLIGHT,16 August 1957 The prototype Swift 7 with a Fireflash under each wing. A Swift squadron is being equipped with these missiles. FIREFLASH . . . booths. Vibration equipment includes a 5 kW moving-coil exciter,many 1 kW exciters, scanning and control equipment, calibrators, and vibration transducers of various patterns. Bump machines,impact testers and centrifuges are also available in various capa- cities. These facilities supplement the usual structural, pneumaticand hydraulic test equipment at Heston as well as the more specialized test equipment used by the department. The Fireflash missile consists of a central unmotored cruciformwinged dart which is boosted to maximum speed by two solid-fuel rocket motors attached externally to its forward end. During theboost phase the unguided missile is spun by offset Venturis to minimize dispersion caused by asymmetric thrust. When themotors are "all burnt" an explosive separation device throws off the spent motor cases laterally, leaving the dart to coast towardsthe target. The four "rudders," indexed at 45 deg to the wings, unlock at separation and the missile is roll-stabilized by aileron-wise rudder deflections to a datum established at launching. As soon as the roll error is reduced to within specified limits guidancecommands are switched to the control blocks. The missile posi- tion relative to the axis of the radar beam, measured in polarco-ordinates, is interpreted as Cartesian linear errors resolved in the two control planes. The pneumatic actuators, served by electro-pneumatic relay valves, apply rudder deflections which tend to reduce the linear errors and to return the missile towards the'beam-axis. During this gathering phase the maximum lateral acceleration is limited by clamping diodes. The missile then ridesalong the beam axis, following any beam motion which may occur. The accuracy of the weapon then depends upon the accuracywith which the beam is laid on to the target. In the daylight fair-weather role the pilot of the firing aircraft tracks the targetby keeping its image at the centre of his gun-sight graticule. The radar beam axis is accurately harmonized relative to the gun-sight,so that the only significant guidance error introduced is that due to aim-wander of the pilot-aircraft combination in tracking thetarget, which may be taking evasive action. Development trials were carried out by the Fairey AviationCompany from installations on suitably modified Meteor 7 and Meteor N.F.I 1 aircraft, and successful beam-riding has beendemonstrated from a two-weapon installation in a Hunter. Royal Air Force trials are being made with further installations in asquadron of Swift 7s. Installation in other aircraft is stated to be "practicable and simple." The mechanical design is such that the weapon convenientlybreaks down into the rear cylindrical portion of the dart—on which the wings and rudders are mounted—containing all thecontrol, guidance and power supply equipment, and an explosive assembly comprising the two motors, their separation gear, thewarhead and its fuze. This forward assembly is offered up to the rear dart after the latter has been fully tested on an O.A.T.S.—operational airfield test set. Structurally the rear body consists of an extruded and forgedmagnesium-zirconium alloy tube, into which slides a two-rail chassis carrying the internal equipment. The wings and ruddersare aluminium forgings machined only over their bosses. The cruciform wings are swept back on their leading edges, havesquare-cut tips and are mounted to the_ tubular shell by flanges and countersunk bolts. Small controlling rudders are screwedand spigotted to cylindrical output shafts mounted on ball races in the actuator assembly block. Air, controlled by four electro-pneumatic relay valves (giving proportional position control), and ducted from the high-pressure storage bottle, is fed to either ofa pair of pistons running in cylinders formed in the block. The rams of the selected piston of the pair actuate the rudder eitherto the right or to the left through links, after the control surfaces nave been unlocked; there is a solenoid-operated release valvecontrolling—through a central operating piston and spring-loaded iocking linkage—locks on the rudder drive shafts. The two booster motors are attached to each other by a"U"-shaped separation unit, and location fittings on the motors mate with holes in the warhead case. The fuze is located forwardof the warhead to which it is attached, and forward of this, in the extreme nose, is a spacer device which pre-tensions the assemblyto make it rigid. The separation gear comprises a twin piston-cylinder breech-block containing 0.06 lb of cordite. The pistons, attached to one motor, are held by shear pins in the cylinders attached to the othermotor. A single igniter in the base of the unit flashes to the two separate charges in the two cylinders. A pressure switch, whicharms on build-up of pressure in the rocket tube and fires when the pressure subsequently falls to 250 lb/sq in, is located in the noseof each rocket motor; these are series-connected so that when both motors are "all burnt" a firing pulse is passed to the igniter. Thepressure in the cylinders builds up until the shear pins fail and the motors then separate relative to each other and to the dart.The motors are fitted with stabilizing fins to prevent their toppling after separation and so decelerating fast enough to endanger thefiring aircraft. Forward of the front bulkhead is the warhead, into which isfitted, when test rounds are fired, a compact telemetry unit. All the equipment behind the bulkhead is concerned with guid-ance and control and is installed between chassis rails to which covers are fixed to sheathe the telemetry wiring, fuzing and firingcircuits. At the front is a forged light alloy air bottle containing air at 3,000 lb/sq in for all the pneumatic supplies (in particularthe aerodynamic controls), an internal reducing valve and an electro-pneumatic stopcock.Behind this source of stored energy are the lateral accelerometers measuring in the two control planes, and the air-blown gyros inanother small assembly. The gyros derive their continuous power source from air piped from the aircraft by which they are carried;after the missile has been released and during the glide the gyros coast on their inertia. Mounted transversely in the gyro assemblyare two speed-monitored rate gyros--governing the "x" and "y" control axes and a gimbal-suspended roll-displacement gyrorotating in the fore-and-aft plane. The electronic heart of die weapon, also concerned with itsguidance, forms the remainder of the block of components. These are carried in an electronic sub-chassis. The electronic powersupply pack is mounted adjacent to the electronic gear. Behind the electronic section is the servo motor comprising—asdescribed earlier—the actuator and its four pairs of piston-cylinder units and, at the extreme rear, the receiver aerial assembly and rearbulkhead. All of the components and systems are designed and developed by Fairey, with "significant" help which they receivedfrom the Plessey Company (who contributed to the production of the receivers) and E. K. Cole, Ltd., who were responsible for theradar beam set installed in the carrier aircraft. As Fireflash is a coasting missile, propelled only during its acceleration period,guidance problems are eased by the lack of rocket-flame ioniza- tion, and the aerial system can be advantageously located in thetail of the dart. The aircraft industry—and the taxpayer—were forced to recog-nize long ago that the development of a guided missile was no quick and easy business; and Fairey's weapon division will beremembered for their success in producing die first missile to go into R.A.F. service. Fireflash was developed under a Ministryof Supply contract, and the credit accorded to Fairey's design and production teams must be extended to include Gloster, A.W.A.,Hawker, Air Service Training and Vickers Supermarine who, as aircraft contractors, co-operated willingly to expedite the installa-tion of the weapon system in aircraft for trials and operational use. The Ministry's technical establishments—R.A.E. at Farnboroughand at Westcott, R.R.E. at Malvern and A.R.D.E. at Fort Halstead and at its firing ranges—also gave valuable help and technicalsupport in the painstaking research and development needed to create a production weapon system. . ......
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