Packard-Diesel Motor

Packard Motor Car Co.'s President Alvan Macauley last week said that by the end of March he would be manufacturing the new Packard-Diesel airplane motor. That will be a milestone, the first Diesel-type (oil-burning) airplane motor developed in the U. S.

When an internal combustion motor operates it generates heat. In practically all automobile motors the heat is diffused by circulating water. Water takes up room and has weight. Weight and bulk have little importance in ground motoring but in flying they form a great handicap. Air-cooled motors are lighter and preferable for the air.

Hence the development of the radial air-cooled airplane engine. In this type 3, 4, 5, 6, 7 or 9 cylinders radiate like spokes from a common centre. Each cylinder bristles with thin metal fins which absorb the engine's heat and spread it to the cooler air.

The great designer of radial air-cooled engines is Charles L. Lawrence, now president of Wright Aeronautical Corp. There are no patents on the basic design, so more than a dozen U. S. motormakers are producing them. Most famed are the Wright Whirlwind* and Cyclone, Pratt & Whitney Wasp and Hornet, Warner Scarab.

The great handicap of the radial engine is that its spreading cylinders create wind resistance and so slow an airplane's speed.

The ordinary motorcar engine, with its 4, 6 or 8 cylinders set in a line, or its 6, 8 or 12 cylinders arranged in a deep V. has much less wind resistance than the radial airplane motor. Cooling by water requires bulk and weight, yet many a large and powerful plane uses Packard and Curtiss water-cooled models.

The only large air-cooled "inline" airplane motor is the remodeled Liberty, now made by the Allison Engineering Co., Indianapolis.

However, small 4-cylinder air-cooled "in-lines" are beginning to be manufactured in the U. S. Small gadabouts demand them. Among those already tried out satisfactorily are the Dayton Bear, American Cirrus, Aeronautical Products Scorpion, De Havilland Gipsy, National Aero Cameron.

All these motors use gasoline for fuel. It must be a high-grade gasoline. And it is expensive. A cheaper fuel, such as fuel oil, is desirable. So research has been going on. Diesel engines burn fuel oil. But Diesel engines are ponderous. Packard's triumph is that its engineers have designed a light-weight Diesel-type motor that burns cheap fuel oil efficiently, and is air-cooled. Although it is a radial, its invention gives promise of an "in-line" air-cooled successor.

*Wright aeronautical stock has been selling for $275 a share. Directors last week declared a 100% dividend.