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Aviation History
1948
1948 - 1295.PDF
AUGUST 19TH, 1948 FLIGHT 201 SEAR The main cartridge is housed against a light ejecting spring in the head of the "bullet" beneath a threaded plug incorporating the firing body. This is simply a heavily spring-loaded firing pin, which is released by withdrawing a sear. Conventional piston-type gas control rings are fitted to the skirt of the " bullet " and effect a seal between •the "bullet" and the barrel. Ten inches up the barrel are vent holes to the diaphragm of the auxiliary cartridge and, when the " bullet " uncovers these holes, gas pressure bursts the diaphragm, and ignites the second cartridge. The propellant used, both in the main and secondary cartridges, is nitrocellulose and, for the main cart- ridge, a conventional detonator cap is employed. Two I-section beams form the chassis, or seat frame. At their base are four wheels of about 3J in diameter which engage the guide-rail. Laterally spanning the base of the frame beams is a cross-tube from which project two horn levers which carry the seat pan. At the top of the seat back-rest are small runner blocks which engage trackways in the frame members. By this means, vertical adjustment of the seat is obtained to accommodate varying lengths of back, the head position being fixed according to the aircraft's designed " constant sight line." A neat detail point is that the seat adjustment handle normally lies snugly against the seat side, but can be pulled away from the side against a light spring when adjustment is required. Protection The seat pan has peaked thigh-valances to prevent the legs from side movement and the pilot sits in the seat. On the star- board valance is a knob controlling the seat harness, which accordingly can be loosened to permit the pilot 10 in of forward move- ment with spring return against a ratchet. Z type harness is fitted which, in common with the seat, is stressed for accelerations up to 25 g. We have referred to the fact that the pilot might have to leave his aircraft whilst an overall acceleration is present. In these circumstances, it might well be difficult for him to lift his feet from the rudder pedals against g in order to tuck them back into the seat foot rests. To overcome the necessity for this, the seat foot rests are pivoted on the same cross tube as the seat itself so that they always . remain iu contact with the cockpit floor, irrespective of seat position. Telescopic struts between seat and foot rests provide limit stops. All that the pilot has to do prior to taking ejection action is to draw up his legs, allowing his feet to slide back along tronghs from the rudder pedals to -the seat foot rests. At the head of the seat frames is a trapezoidal box, on the forward face of which is fitted the padded leather head- rest. Immediately behind the head-rest is stowed the. face blind, and inside the box itself is housed the drogue. This is a miniature linen parachute of 24 in diameter and is attached to the seat by twelve 1,200-lb.nylon shroud lines which are gathered into threes and plaited to form a four- strand cable. The purpose of the drogue is to act as an " air-anchor " and slow down the speed of the seat so that the pilot can leave it merely by undoing his harness and rolling forward. To ensure that the drogue is not pulled out until the seat is well clear of the aircraft, a 20 ft static line is employed. This is packed into a small canister, bolted to the cockpit floor close to the base of the port main frame. The line 's led through a fairtead tube up to a toggle linkage in- corporating a spring-loaded sear. When withdrawn, this FIRINGPtN —PBOPELLANTX. - CARTRIDGE - ATTACHMENT-BASE BLOCK Cut-away section through seat- gun, showing twin cartridges and details of firing, release and attachment mechanisms. fires a small cartridge in the drogue-gun to expel a " bullet " in the shape of a small heavy tube which is attached by 2 ft of line to the crown of the drogue. Thus, when the seat has travelled the first 20 ft of its ejection course, the drogue- gun is fired, the drogue is pulled out and the seat is slowed down. The drogue-gun is mounted in quick-release clamps on the port main frame immediately behind the drogue box. The face blind is an essential feature of the Martin-Baker seat and is so shaped as to ensure that the pilot's head is not only pressed firmly against the head-rest but is also restrained from sideways movement. The pilot's ejection drill is to jettison the hood, draw back his feet into the rests, and reach up w^th both hands, firmly grasp the handle above the head-rest and pull down the blind over his face. The blind is cable- cennected to the sear of the gun firing pin ; the final inch of blind travel withdraws the sear, the gun is fired and the seat ejected. Holding the blind down over his face ensures that the pilot's hands and arms are in the most convenient position for the ejection operation. On the score of breaking ancillary con- nections the pilot has nothing to worry about. His intercomm. plug is arranged on the port side of the seat near the floor so that it readily pulls free when the seat leaves the aircraft, and the oxygen trunk from his face mask is carried to a quick- break connection on the starboard side valence of the seat. Since, however, ejec- tion may well have to take place at 40,000 ft and above, a small emergency bottle of oxygen is carried behind the drogue box, on the starboard main frame, with a small- bore pipe to the pilot's face mask. A static line to the cockpit floor automatically turns on the emergency bottle as the seat leaves the aircraft. • Standard Equipment After a considerable period of painstaking development the Martin-Baker seat has been established by an extensive pro- gramme of factual tests to be far in ad- vance of anything else of its kind existing. During the recent war the Germans devoted a certain amount of attention to the problem, but either they were hard- pressed or discouraged, for their efforts in seat ejection have been carefully tested and found to be wanting in several respects. Production Meteor IV's and all future high-speed aircraft for our Services are to have the Martin-Baker seat as standard equipment. Many foreign governments, not least among them that of the United States, have evinced considerable interest in this development. AUSTER A.2/45 FOLLOWING the Auster A.O.P. Mk. 6, as used by GreatBritain, Canada and other countries, and the Auster T.Mk. 7 Trainer (described in Flight, of July 8th, 1948), comes the A.2/45, the prototype of which is expected to appear atthe S.B.A.C. Display next month. Features of the design, which, considering the nature and duties of the aircraft iscommendably clean, are a wide-track undercarriage, designed to allow a very high rate of descent, and a good all-round field ofview. Performance figures may not.yet be quoted, but it is obvious that, with a crew of only two, the 250 h.p. GipsyQneen engine should give a very useful Speed and rate o'f clirnb. It is understood that the possibility of maintenance in thefield has been borne in mind, and that the aircraft has therefore been made unusuallv simple and accessible for servicing. Thespan is .43ft 6in, length 30ft lin and wing area 278 sq. ft.
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