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Aviation History
1950
1950 - 2091.PDF
7 December 1950 525 Farnborough in September, the Ashton gives the appear- ance of being a modern multi-jet passenger aircraft. Powered by four Rolls-Royce Nenes, paired in twin nacelles, and with a roomy fuselage of lift diameter, the prototype Ashton is, in fact, the first of a series of six high-altitude research aircraft, each of which will be equipped (and modified as necessary) for application to individual fields of investigation. The fuselage is a semi-monocoque of circular section and entirely orthodox construction, but on the pressurized nose is carried a faired false-nose which, in that it merely accommodates the nosewheel when retracted, is unpres- surized—an entirely satisfactory and simple solution to the problem of pressure-sealing the awkward shapes of retrac- tion wells. Crescent diaphragm-ribs and top-hat stringers carry the skin of the false nose, the fore-part of which is extended to a needle-like proboscis incorporating a pitot head and yawmeter. These, however, comprise a test installation for the prototype flight trials, and will not be embodied as a permanent feature. In order to provide comfortable working conditions for the research personnel—as well as, ipso facto, to glean data on the subject—the fuselage is pressurized to a differential of 8.2 lb/sq in, whereby an 8,000ft altitude pressure- equivalent is given at an actual altitude of 40,000ft. This differential is provided by two-stage supercharging. Each pair of Nenes jointly drive a Rolls-Royce auxiliaries gear- box, and on each gearbox is mounted a 30 lb and a 15 lb Roots-type Godfrey cabin-blower. Each 30 lb unit runs at 0.544 engine speed, and delivers its output to its associated 15 lb unit, which runs at 0.696 engine speed. Below 7,000ft, however, the full two-stage delivery is not required and, therefore, by-passes are fitted so that die output of the 15 lb blowers is not used until 7,000ft is exceeded. With so much compression energy available, the inherent heating is ample to keep the cabin at a comfortable temperature even when the "aircraft is flying at its operational ceiling. For work in unwontedly low ambient conditions, however, the blowers are throttled so that the increased back-pressure amplifies the inherent heat generation. The fuselage interior is lagged with a double layer of insulating glass-wool blanket, each layer being of jin nominal thickness. One of the structural design details attendant upon the use of so high a pressure differential is that no Perspex glazing used in the Ashton is drilled or rebated. As no sudden changes of section exist, the known mechanical properties of the panels can be relied upon. The window panels of Perspex are held in rubber channel-section sur- rounds, and retained by curved clamps of flat-section spring steel, through-bolted to the window-frame structure. In the case of the pilots' glazing, a somewhat different system is used. The framework is an assembly of light alloy castings, and was designed originally for panels of curved glass; difficulties in the manufacture of curved panels of toughened glass, however, have led Avros to employ Jin- thick curved Perspex for the centre panel, this being flanked by flat glass panels to provide undistorted view and permit the use of windscreen wipers. The next panels port and starboard can be opened to provide direct vision, and rear- ward of these are curved panels, of fin-thick Perspex. The flat glass panels are Triplex three-ply units, the outer lamination being annealed plate glass, which is separated from the inner lamination of toughened glass by an inter- layer of Vinal, 0.12in thick. This interlayer has a lin selvedge, which is bonded to a light alloy reinforcing strip, through-bolted with a clamping ring and rubber seal to an adaptor frame, whereby the flat panel of glass can be accommodated within the contours of the main framing. There is nothing out of the ordinary about the flight- deck layout beyond, perhaps, a certain spaciousness which is apparent rather more in the accommodation of the flight engineer, navigator and radio officer than in the cockpit proper. Although, in practice, they may well use the main entry door on the port side of the rear fuselage, the crew are provided with a separate door which opens from a " vestibule " at the starboard side of the flight-deck, abaft the engineer's station. In the floor of the vestibule is a circular tampion hatch—or "manhole"—beneath which is a 24in- diameter escape tunnel for baling out. A small deflector around the leading edge of the tunnel outlet gives transient protection from airflow, and the hatch itself seats on a rubber inflatable seal for pressure-retention. The main volume of the fuselage is free space, in which all sorts of combinations and permutations of research equipment may be installed, according to the particular needs of a given line of investigation. In the prototype Ashton, at the time of our inspection, there were simply two automatic observers set up in the fore part of the cabin (Continued after double-page drawing of Ashton) This schematic diagram illustrates the relationship of the control system for the all-important cabin pressurization and conditioning. MASS-FLOWINDICATOR Pi •CONTROLLER AMPLIFIER ANO SETTWCSWITCH TRANSMITTER (P« $ . ANO N-R VMVE TYPE 1S BLOWER COOLER UNSHROUDED DUCTSTAT SHROUDED DUCTSTAT CABWSTAT DUCTSTAT t CABINSTAT ELECTRICAL SIGNALS CONTROL CIRCUIT TO ACTUATORS SIGNALS FROM METERMG DUCTS CONTROL CIRCUIT TO ACTUATORS (Above) A parachute exit in the form of a 24w-diametcr tunnel is embodied. Below) The cockpit is neat and uncomplicated. The captain's controls on the prototype incorporate a|" stick-force " uijft.,
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