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Aviation History
1955
1955 - 1381.PDF
16 September 1955 495 ON SHOW S.BA.C. Exhibition Tent even eliminate the air bottle and drawcompressed air from a ground supply. In a single-engined aircraft the entiresystem (less fuel and electrical con- nections) would weigh about 123 lb filled,of which the fuel in the i.p.n. tank accounts for half. This size of installa-tion would be capable of accelerating an engine of 680 to 700 lb/sq ft from rest to2,000 r.p.m. in from five to seven seconds, the capacity of the system beingsufficient for six consecutive starts. Joseph Lucas (Gas Turbine Equip-ment). Attention is now being increas- ingly drawn to the high rate of fueldelivery which could be achieved for a very modest weight by an air-turbinedriven centrifugal pump working on compressor-bleed air. The small unitdeveloped for the supply of afterburner fuel (weight 25 lb, delivery 3,000 gal/hr)was again exhibited, and it is likely that equivalent pumps will be developed forthe main supply to large turbojets. Such installations would not be tied toany particular engine, and the control problem at altitude is eased (throttling isbetter with an air turbine than with a mechanical drive). The governor con-trols a servo throttle and, although there is some difference of opinion on mis sub-ject, it seems to be generally held that the throttle should be in the fuel deliveryline and not in the air-supply pipe, since possibly instability may occur with thelatter system, owing to the compressible nature of air. For starting, a ground-supply of air could be employed (although, owing to the square-law delivery charact-eristics of centrifugal pumps the provision of full-flow at starting r.p.m. wouldimply a pump with a top-speed delivery grossly in excess of requirements). Plessey. To an M.o.S. requirement anaircraft starting system has been developed in which the combustion of iso-propylnitrate is initiated by a small cordite cartridge. A development of the com-pany's existing monofuel starting system, the new development dispenses with themotor, pumping unit, air blower, electrical igniter and spark plugs. A standardcordite cartridge is fitted in a remote and accessible breech, and is used to pressurizeone side of a differential piston. Move- ment of this piston expels i.p.n. fuel froma fixed-capacity injector to the piston chamber where it meets a cartridge-induced ambient temperature and pressure suitable for ignition. Fuel from the maintank then continues to decompose in the conventional manner. Communication ismaintained between the decomposing fuel and the differential piston to pre- **rtynwtrc77 one-shot stop vo/ve. pressurize the iso-propyl nitrate; at theend of the start a spring returns the piston to the bottom of its stroke, so rechargingthe cylinder for the next start. Piston-chamber characteristics in suchturbines depend upon the characteristic length L*, as in rocket motors. Originally,the piston chamber had to be large to relieve the pumping load, but the corditecartridge can produce about 1,000 lb/ sq in, making possible a much smallercombustion chamber. On the debit side is the high temperature of the corditegas and the fact that two separate stores are required to supply the system. Ultra Electric. Following closely uponthe highly developed B.A.P.3 electronic control equipment for the Proteus hascome a neater equipment providing a direct control of turbine speed and in-direct control of jetpipe temperature. The main unit comprises an amplifier,Type AN 390, and an altitude-compensat- ing unit, Type ZB 390. The formerweighs 8 lb and the latter 1| lb, and the two together provide a precise speeddatum, irrespective of fuel density or ambient conditions, and also permit theuse of maximum power at all altitudes without exceeding the limiting turbineentry temperature. UNDERCARRIAGES British Messier. More than any otherBritish firm, this company have experi- ence in designing undercarriages forhelicopters. Units chosen for display this year were the revised type of short leg for de Havilland airscrew for Rolls-Royce RB. 109. the stub-winged Bristol 173 and the newundercarriage for the wingless Bristol 191. The latter, which is designed to meetNaval rate-of-descent requirements, has a stroke of some 16in. Whereas the 173leg has suspension springs in compression the 191 has oleo-pneumatic units, con-ventional except for the fact that they can be inflated to H g when the helicopter isparked on a carrier to prevent roll of the aircraft with the deck. A castor-lock comes into action whenparked, and the brakes are actuated by a coil pipe running up the inside of the leg.Each leg is connected to the airframe by a pair of freely hinged wishbones, but thelegs are connected across the aircraft by ad hoc beams to which are attached rolldampers on the aircraft centre-line. The latter determine the magnitude of roll.As described on September 2nd, The Palmer Tyre, Ltd. provide brake snubberswhich determine the fore-and-aft stiffness. Dowty Equipment. Cleared for publicdisplay at this year's Show was the run- way brake—a device which appears radicaland highly unconventional, yet which is eminently logical and may well supplantwheel brakes entirely in some forms of air- craft. The reasoning is obvious. In a machinelike the Vulcan—for which Dowty supply an eight-tyre bogie main unit—the kineticenergy to be absorbed upon landing is of the order of 107 ft-lb. Nearly all of thishas to be absorbed by a heavy metal heat sink (the discs of the brakes) which stayswith the aircraft at all times. The heat sink of the runway brake is the runwayitself. Under the bogie (that for the Vulcanwas on show) is mounted a large shoe made of S.99 steel, to which are securedlight-alloy plates on which are mechanic- ally moulded a number of pads of a special
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