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Aviation History
1949
1949 - 0583.PDF
„«*.' ? . The rear main leg unit, In addition to the twin Goodrich brakes on each wheel, a tail parachute is fitted. Stratojet Undercarriage Tandem Main Wheels Simplify Stowage in American Jet Bomber A"N unorthodox undercarriage is one of the numerousnovelties incorporated in the Boeing XB-47 Strato-jet six-jet bomber. The two main legs, each withtwin wheels, are arranged in tandem under the fuselage, instead of under the wings, and two small outrigger wheels are provided to hold the aircraft upright when at rest. This arrangement eases the undercarriage stowage problem —always a headache to designers. The weight and size of aircraft wheels are steadily increasing, while engine nacelles and wings tend to become smaller and thinner. On the XB-47 the nacelles required to house a normal-type undercarriage would have been disproportionately large ; by adopting the existing scheme, the designers appear to have Effected a considerable reduction in both weight and complication. Development was less involved than is normally required and the task of stressing the acutely swept-back wing was eased. The undercarriage has so far proved satisfactory under all take-off and landing conditions. To avoid the possi- bility of skidding—particularly on the snow- and ice- covered runways from which many of the initial flights have been made—an effective tail-parachute brake is at present fitted. Although no decision has yet been taken, this might well be a permanent feature on production air- craft. Provision of an emergency wheel-lowering device should also be comparatively easy and, in the event of this failing also, the fault should be accessible from inside the fuselage. The tandem undercarriage is not new, such a scheme having been used on an experimental Messier monopla"he built in 1933; but the XB-47 is the first modern aircraft to incorporate the idea. An interesting comparison is afforded with the novel four-legged undercarriage of the Vickers Windsor bomber of the late war years. The eighteen built-in A.T.O. rockets, nine of which are seen to advantage in the uppermost view, deliver a com- bined thrust of 18,000 lb. Each of the six General Electric TG-190 axial-flow turbojets has a designed rating of 5,000 1b static thrust, and more powerful units are pro- posed to permit operation at weights far greater than the 125,000 lb announced for the first prototype. The outrigger wheels are fully castoring and retract forwards into the nacelles.
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