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Aviation History
1962
1962 - 2053.PDF
44* FLIGHT International, 13 September 1962 fed"?: £=t -QQ—HO JZ1 -LB SJ SPRING BOX n=fc: -=£ IZF > D OF 7 =CD^ •^ > £] IE Top, H./V1. Hobson's proposed method of avoiding runaway in one direction when a two-channel control system is employed (A, amplifier; G, sensing gyros). Lower drawing, a complex mechanical system for balancing the output of three jacks without a dead zone or step input in the failure case ROUND THE STANDS approach situation from a source of information independent of the automatic flight control. A roller-blind instrument with a narrow screen display for coaming mounting, the indicator utilizes an inverted white triangle, the apex of which represents the point of ground contact, to give an analogue presentation of height. Prior to contacting the glide slope, the base segment of the triangle fills the screen, but as height is reduced the triangle moves through the screen aperture at any gain so that a progressively narrower segment appears in the slot. Quantified height information (probably obtained from a monitored radio altimeter) is displayed on a moving ribbon, which is also displaced horizontally as the aircraft departs from the localizer centre line in a manner analogous to the cross-pointer of an ILS indicator. Centred on the ribbon is a model aeroplane, and the width of white segment displayed represents the manceuvre-limit capability of the autopilot. Once the model aircraft crosses from the white segment into the black surround, the autopilot is in capable of returning it to centre before touchdown is reached. Glide path information may be displayed by a horizontal line on the black surround, and parafocal lines, moving at a rate and showing width proportional to the magnitude of deviation from glide slope, will also be incorporated as attention-getters. If all is well the lines thin out and close up, and will normally blink open and closed to indicate that the autopilot is working correctly. Three of these instruments have so far been made, and the system is likely to be specified for the VC10. Developed units will incorporate shutters to provide indications of autopilot malfunction, the idea being to provide a simple "soft" display which hardens if failures occur. For the VC10, Elliotts have developed the monitored duplicated autopilot system, but fcr the SST, reference to which was made by diagram, and components employing micro-miniature techniques they are thinking in terms of a four-channel system with full electrical signalling between stick and powered flying control. Little can yet be said about the company's work in this field, which is in preparation for a Ministry design competition, but comprehen sive proposals have been made to both BAC and Sud. It is at Elliotts, more perhaps than anywhere else, that alternatives to multiplexing are being sought. In connection with large VTOL aircraft in the transition and hover modes, Elliotts are designing a series of high-reliability amplifier and computer installations in corporating integral and multiple redundancy techniques. Briefly (a more detailed appraisal appears in the preceding section) the intention is to improve autopilot reliability at component and circuit rather than system level, and to provide built-in failure indication by means of electroluminescent panels. Other units emanating from this company include a miniature autostabilizer for VTOL aircraft (referred to later) and an autothrottle control for military aircraft. In this system airspeed and pitch altitude information is amplified and used to operate a throttle actuator coupled to the throttle linkage through an electromagnetic clutch. Speed may either be maintained automatically at the correct thrust setting or the throttle set at an engine speed related to, but below, that necessary to main tain the desired speed before the clutch is engaged. In the latter case, the aircraft will reduce speed, and thrust be adjusted until the datum speed is reached. As the system provides safety of operation at VOID speed it has obvious naval applications. System weight is 91b. Shown on the Dowry Group stand was another VC10 unit—the Boulton Paul rudder p.f.c.—and the powered spoiler actuator for the Belfast. Interest in the latter unit centres around its electrical signalling; the control itself is the familiar Boulton Paul duplex arrangement employing variable-delivery pumps driven by 24V d.c. motors. A good deal of electrical-signalling experience has now been gained by this company, through the experimental system installed in the Tay Viscount, the system now in use in the Buccaneer, and that being manufactured for the VC10 autopilot system. There are four spoiler surfaces on the Belfast, each driven by one of the packaged electro-hydraulic control units. The system is the familiar one utilizing potentiometer units linked to the control column to provide input signals which are compared with a position feedback to obtain an error signal. This is amplified and applied to a torque motor on the servo control valve to supply an accelerating ratio of flow to the hydraulic ram. A continuous comparison be tween the pilot's input signal and ram position is made, and if the error exceeds 20" of spoiler position for more than 0.4sec a solenoid on the control box is de-energized and the spoiler closes under the influence of a spring box. Electrical signalling is also under practical investigation by Fairey Engineering, who have supplied the system now being test flown by the RAE in the Avro 707C. A second, mechanical con trol circuit in this aircraft is linked to the second pilot's stick and provides a manual override should there be a supply failure in the single-channel electrical supply. Among a wide range of powered controls shown by Fairey were systems for the Trident, P. 1127 (with autopilot and autostabilizer operation), Hindustan H.F.24 supersonic fighter and the Hunting H.126. Titanium jack bodies, obviously for a supersonic aircraft, were shown on the H. M. Hobson stand. These folio w up the research bodies in this material shown last year. The jacks operate on DP47 silicone fluid, and have a short-term temperature capability of up to 200°C. This company is currently discussing proposals for duplex servo applications in which runaway can be tolerated in one direction Concluded on page 458 *ER TAIL 10 Functional diagram of the Newmark helicopter autopilot Ferranti fight-control instrument system for helicopters
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