Recognition: Army Air Forces Ground Observer Corps - Identification of Aircraft - IV: Engines

CHAPTER IV: ENGINES

SECTION I THE NUMBER OF ENGINES

60. Given a front or underneath view, it is not difficult to count the engines. Once the number is established, the field of choice narrows considerably, for one can be sure that a four-engine plane is no fighter, that a single-engine plane is no transport.

61. In all likelihood the observer will see only single-engine (single-motor), twin-engine (bimotor), or four-engine (multimotor) planes. A few three-engine types exist; they belong to the enemy.

SECTION II THE POSITION OF ENGINES

62. In single-engine planes, the engine is usually located in the nose. In twin- and multi-engine planes, the engines are usually housed in nacelles protruding from the leading edges of the wings. More rarely, the nacelles also protrude from the trailing edge. This is the case with the three medium bombers, the A-20, B-25, and B-26, in order to provide room for the landing wheels to be folded up, or "retracted," into the nacelles. It is also the case in the unusual "pusher," or rear-propeller, type of engine.

63. In addition it may be helpful, when a profile or front view is obtained, to observe the extent to which the nacelles hang below the wings, in "underslung" fashion, as distinct from being more or less centered with, or even above, the wing.

SECTION III THE SHAPE OF ENGINES

64. Radial engines (air cooled) lend blunt, stubby lines to the part of the plane which houses them. "In-line" engines (mostly liquid-cooled) produce slender, pointed lines. Note, for example, the radial engines in the B–17 pictured in the preceding paragraph. Compare the following "in-line" engines.

65. On some planes, the Buffalo for instance, a spinner of consider-able size is placed in front of the propeller on a radial, air-cooled motor, thereby reducing the resistance of the blunt nose.