Science: Stainless-Steel Airplanes

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A revolutionary trend in airplane production got off the ground last week: stainless steel. Aluminum, which has hitherto been aircraft metal No. 1, had a challenger on the production lines and battlefronts, and in the post-war future.

> In Philadelphia, for Budd Manufacturing Co.—biggest U.S. builder of stainless-steel trains—the Government began to run up a vast plant which by next spring will be turning out all-steel air freighters, big-bellied and wide-hatched to carry troops, tanks, guns to the war's four quarters.

> In Cleveland, metallurgists of Union Carbide & Carbon—biggest U.S. maker of ferrochrome, vital ingredient of stainless steel (usual formula: 18% chromium, 8% nickel)—announced that at last the behavior and strength of stainless steel under aerial conditions can be predicted with scientific exactitude.

Inability to predict such behavior, plane builders have claimed, has long made them wary of stainless steel, which for aviation purposes must often be used in sheets as thin as .004 in. So they have stuck to aluminum, whose behavior under flight conditions is tried & tested.

Some good reasons for preferring stainless steel:

— Stainless steel construction is as light as aluminum, because, though the steel is nearly three times as heavy, it is also a good deal stronger, so less metal—perhaps only one-third or one-fourth as much—need be used.

> Stainless steel can be fabricated faster and cheaper because, unlike aluminum, it can easily be spot-welded. A thousand steel spot welds cost less than 10¢. A like number of aluminum rivets may cost $30.* And Union Carbide & Carbon's engineers estimated last week that stainless-steel wings can sometimes be built four times as fast as aluminum wings.

> Stainless steel is more durable, stands up four times better than aluminum under the incessant vibrations and strains which can "fatigue" a plane's metal structure to the breaking point. Result : longtime maintenance of steel planes is easier. Hitherto this factor has not been important, but engineers think that after the war air transports will be built (like railroad cars) to stand the strain of at least ten years of heavy duty.

It is unlikely that stainless-steel planes will supersede aluminum planes during this war. But if Budd's all-steel transports are a wartime success, the whole peacetime future of aviation may be changed.

*Spot welding of aluminum is possible but tricky because the welded metal becomes brittle.