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Aviation History
1956
1956 - 1328.PDF
POWERED CONTROLS THE past year has seen increasingunification of the efforts of the powered control and electronic equipment manu-facturers to produce integrated flying con- trol systems in which the autostabilizer,autopilot, feel simulator and flying control form parts of a common whole. Once thenecessity of a "black box" to mix and amplify the various electrical informationfor transmission to the powered control valve has been accepted, signalling of thepilot's intentions to the surface actuator can also best be done electrically; andother advantages follow in turn—such as the avoidance of feed-back (caused bystructural distortion) to the powered con- trol, and the possibility of varying thecontrol-circuit gearing. Three newcomers to the field showed flying controls thisyear, and further information about some more familiar equipment has beenreleased. The Bolton Paul Aircraft stand wasconfined to static exhibits and did not include their electrically signalled controlsystem—which, they say, is now nearing the stage for flight trials (with a manualstand-by). Among the exhibits on the stand was a tandem piston-jack with adifferential input link to accommodate an autostabilizer. Designed for a medium-heavy fighter, it has duplicated rotary valves which, fed from separate hydraulicpressure sources, pass a maximum flow of slightly under 4 gal/min to the tandempistons. The valve follow-up is performed by a mechanical link from the output ramand four blow-off valves are incorporated to shed excess pressures into the returnline. This same valve block is shown with Elliott torque motors attached for elec-trically-signalled operation, but com- ponents of other makes can be used. The two other flying controls exhibited—the larger of which is fully-sectioned— incorporate the familiar Boulton Paulswashplate-operated variable delivery pump. One of these controls is designedfor a bomber with split control surfaces (four hydraulic controls would be requiredon an elevator) and incorporates an integral D.G motor, while the other is fullyduplicated and may also be operated manually. A small powered flying control, dupli- 480 . ' FLIGHT, 14 September 1956 SHOWGROUND Round the Static Exhibits at Farnborough "Farnborough . ..." We say it with bated breath; everybody says it and thinks it and talks and looks forward and expects. The word becomes magic, and it means British and best and sometimes new. In eager expectancy we hurry for the first time this year into the great static exhibition tent, thirsting for new gadgets. And as we jostle and stumble we see all that remarkable gear. There are engines and models of aircraft, but we delve further back and find electrical, hydraulic and pneumatic systems, instruments, seats, clothes and research equipment; it is laid out in rigs, rows, piles, racks and cases—and there are cases for carrying it in complete safety through tropical heat and Arctic cold. We march on through lane after lane of stands, through the buzz of technical voices and under the drumming of the rain on the vast canvas roof. We marvel, we congratulate and we retire. . . . Wonderful, wizard, bang on, excellent show .... Outside the "static," with the Martin-Baker ejector-seat trainer rig being demonstrated in the foreground. To the left is Napier's RJ.T.V.29 and beyond are the Deccer and Cossor radars and fagade of the great marquee. cated hydraulically by tandem pistons andtwo valves, was shown on the Electro- Hydraulics stand. Intended for generalrather than specific applications, it has an output load of 8,000 lb and an operatingstroke of 4.2 in. A ram rate of 12 in/sec was demonstrated when an equivalentinertia of 336 lb—provided by two bob- weights at the ends of cranked levers—was being accelerated. The two valves are of the spool type and are each suppliedfrom an independent source at a pressure of 3,000 lb/sq in; failure of one sourcehalves the jack operating power. The pressure feed on the demonstration unitwas passed through pipes incorporating swivel couplings of Electro-Hydraulicsdesign. Electrical signalling figured prominentlyon the Fairey Aviation stand, where signalling between a control-column hand-grip and an elevator surface operated by a small piston jack was demonstrated. Inthe arrangement shown, the jack body was the earthed member. The Fairey rotary-type valve was operated by a Newmark torque motor, and an additional miniaturecontrol column was used to enable the light operating loads and very small effectof load-relay hysterisis and valve overlap on positional repeatability to be assessed—the elevator surface is fitted with a dial gauge for this purpose. A feature of thesystem is the use of Ferranti-developed A.C. pick-offs at the stick and for feed-back at the elevator. Incorporated in the circuit is a Fairey-designed feel simulator. The basis of this unit is a coiled leaf spring, the rate ofwhich can be adjusted by re-positioning the pivot to change the effective length.This is accomplished by an actuator which accepts speed or Mach number variationsin the form of electrical signals which are pre-supposed to exist within the aircraft inwhich the flying control and artificial feel unit are installed. Among the otherpowered flying control equipment shown on the Fairey stand was the Type 779tandem-piston jack, which has a theoreti- cal output effort of over 44,000 lb at4,000 lb/sq in operating pressure. A device manufactured by the recentlyformed Technical Developments Division of the Gloster Aircraft Co., Ltd., is appliedto a feel simulator system, and is designed to modify the feel at a pre-determinedMach number. It consists of two entirely separate but identical units, consisting ofone evacuated capsule and one open to pitot pressure, the movements of whichare arranged to open a bleed-off valve in the pitot pressure line. Another electrical signalling system, inthis case in triplicated form for "majority- rule" reliability was shown by H. M.Hobson, Ltd. In this equipment, the out- put of a Type 251 tandem-piston jack iscontrolled by single-stage valves of the sliding-spool type operated by torquemotor. A feature of the system is that the electronics which are used to com-pare the signals from the stick and the position feed-back from the surface maybe used to vary the relative gearing between them. The Hobson standgained much from the large number of working exhibits. Among these was a modelaeroplane operated from a control column through a Type 203 piston jack. To demon-strate the effect of autostabilization, the model, which had little natural rolldamping, was fitted with a rate gyro from which information was fed via anamplifier unit to a Hobson autostabilizer servo actuator Type 214, which wasdifferentially connected to the powered control mechanical input. Autostabiliza-tion was switch-controlled for demonstra- tion purposes. An integrated system which controlsthe aircraft in both pitch and roll axes (as with elevons) was also displayed. Theessential components are two Type 157 double-acting tandem piston jacks withtwo separate controlling relay valves arranged to operate in unison and twoType 263 autopilot servo actuators which are self-centralizing in the event of elec-tric or hydraulic failure and limited in stroke to reduce the autopilot authority athigh speeds in the event of an actuator runaway. In the circuit shown, the actua-tors and flying controls were paired by links which were coupled to a stick-operated link (for roll actuation) and could be operated in parallel by switchmechanism through a Newmark autopilot. The remaining working exhibit con-sisted of a Type 173 Mk 4 screw-jack- type flying control powered by duplicatedmotors and supply systems—the control is capable of independent operation fromone hydraulic system—and a feel simula- tor control which provides the pilot with"q"-varied stick-rate up to a pre- determined E.A.S. and constant ratethereafter. The Lockheed Hydraulic Brake Co.,Ltd., again showed a wide variety of their
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