Transport: i-Line In Line

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Few years ago U. S. Army planes were the best in the world, and a Russian modification of its Boeing P-26, already obsolescent in this country, was the fanciest thing in the air in the early days of Spain's civil war.

But if U. S. plane designers and engine builders expected a pat on the back from the Army Air Corps for their performance as of 1939, they were disappointed last week when Major General Henry H. Arnold, baldish Chief of Air Corps, sat down before the House Military Affairs Committee to sketch the needs of the nation's air defenses.

"We don't know about speeds above 400 miles an hour," ruefully admitted the Army's greying Early-Bird pilot. "We are told that engines in the wings will deliver 30% more power at speeds over 300 miles an hour, and we ought to find that out, because we could use that added horsepower in more speed."

One nation that does know about speeds above 400 miles an hour, and well the Air Corps chief knows it, is Germany. Germany knows the advantages of streamlining engines into wings, and has the engines to do it. German designers already have their eyes set and their designing tools working for a speed of 500 miles an hour. Already its sleek Heinkel 112-U has hit 440 m.p.h. in level flight, and its Messerschmitt log is only a little slower.

While American engine builders have plugged away for years on the development of the air-cooled radial engine, now close to perfection, German designers have worked at the liquid-cooled, in-line power plant. Result for the U. S.: the radial engine, with cylinders ranged like the spokes of a wheel around a short crankshaft, has grown to such size that its drag on the high-speed airplane is now of alarming proportions. (Head resistance increases as the square of the speed, e.g., if speed is tripled, drag becomes nine times as great.) Results for German designers: the in-line engine, now cooled with ethylene glycol (Prestone) instead of water, has been made more compact, as light as the radial, much more adaptable to streamlining, since its cylinders extend back on a long crankshaft instead of spreading out like a fan. It can be tucked as neatly into airplane design as a sword into a scabbard.

The one U. S. builder of high-output motors to stick to the development of the liquid-cooled straight-line engine is Allison Engineering Co. In its little plant close by Indianapolis' famed motor speedway, its engineers and craftsmen, working on small orders for the U. S. Army, have kept the spark of in-line design firing, are now ready to go places. Already powered by Allison V-12's is the Army's twin-motored fighter, the Airacuda. More recently, the 1,000-horsepower Allison was built into a modification of the Army's snub-nosed Curtiss P-36. The ship has a speed of 280 miles an hour with a 1,100-horsepower radial. Powered with an Allison engine with 100 less horsepower, the lancelike P37 gained 75 m.p.h.