If the projectile and steering qualities of Langley’s machine surpassed those of its predecessors, the propelling mechanism was a still greater advance in the art of aviation. The gasoline engine was a marvel of lightness, power, endurance and smoothness of running. It weighed, without accessories, 125 pounds, and developed 52.4 horse power in actual test at a speed of 930 revolutions a minute. With all accessories, including radiator, cooling water, pump, tanks, carburetor, spark coil and batteries, it weighed 200 pounds, or scarcely five pounds per horse power—a great achievement for that time. It could run many hours continuously under full load, consuming about one pound of gasoline per horse power per hour. Its five cylinders, arranged radially round a single crank shaft, were made of steel lined with cast iron, and measured 5 inches in diameter by 5.5 inches in stroke. Its running balance was excellent. By means of bevel gears it drove the twin screws at 700 revolutions per minute, giving a thrust of 480 pounds, the screws being very nearly true helices of unit pitch ratio and 30° width of blade, carefully formed of three radial arms covered with canvas. The whole machine weighed 830 pounds, including the pilot; spread 1,040 square feet of wing surface; measured 48 feet from tip to tip, and 52 feet from the point of its bowsprit to the end of its tail; soared at a speed of about 33 feet a second and a ten-degree angle of flight, the wings arching one in eighteen at one fourth the distance from their front edge. The double rudder, at the extreme rear, measured 95 square feet in each of its component surfaces.