364 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1961 



description of the motor by Wilbur Wright dated February 28, 1903, 

 he had this to say : 



We recently built a four-cylinder gasoline engine with 4" piston and 4" stroke, 

 to see how powerful it would be, and what it would weigh. At 670 revolutions 

 per min. it developed 8i/^ horsepower, brake test. By speeding it up to 1,000 rev. 

 we will easily get 11 horsepower and possibly a little more at still higher speed, 

 though the increase is not in exact proportion to the increase in number of revo- 

 lutions. The weight including the 30-pound flywheel is 140 lbs. 



A description of the rebuilt motor by Orville Wright dated June 28, 

 1903, follows : "Since putting in heavier springs to actuate the valves 

 on our engine we have increased its pov/er to nearly 16 horsepower, 

 and at the same time reduced the amount of gasoline consumed per 

 hour to about one half of what it was before." 



By November 5, 1903, the engine had been tested in the Wrights' 

 first powered airplane, the "Kitty Hawk Flyer." Considerable trouble 

 was experienced with the propeller shafts. Finally, new ones had to 

 be made, and so the engine did not become successfully airborne until 

 December 17, 1903. 



A detailed description of the motor follows. It consists of quota- 

 tions from "The Papers of Wilbur and Orville Wright," edited by 

 Marvin W. McFarland. 



This historic motor is described by Orville Wright in an undated typewritten 

 memorandum among the Wright papers in the Library of Congress: The motor 

 used in the first flights at Kitty Hawk, N.C., on December 17, 1903, had (four) 

 horizontal cylinders of 4-inch bore and 4-inch stroke. The ignition was by low- 

 tension magneto with make-and-break spark. The boxes inclosing the intake and 

 exhaust valves had neither water jackets nor radiating fins, so that after a few 

 minutes' run the valves and valve boxes became red hot. There was no float-feed 

 carburetor. The gasoline was fed to the motor by gravity in a constant stream 

 and was vaporized by running over a large heated siirface of the water jacket of 

 the cylinders. Due to the preheating of the air by the water jacket and the red- 

 hot valves and boxes, the air was greatly expanded before entering the cylinders. 

 As a result, in a few minutes' time, the power dropped to less than 75 percent of 

 what it was on cranking the motor. 



The motor was worn in by driving a flat-bladed fan, of approximately five-foot 

 diameter, mounted on the crankshaft. From measurements made in many tests 

 with a stop watch and revolutions counter the speed at which the motor could 

 turn this fan was known. The highest speed ever measured was 300 turns 

 (1,200 r.p.m.) in the first fifteen seconds after starting the cold motor. The 

 revolutions dropped rapidly and were down to 1,090 r.p.m. after several minutes' 

 run. 



The crankcase and water jacket were cast in a single block of aluminum alloy. 

 The crankshaft was made from a block of machine steel 1% inches thick and 

 had five babbitted main bearings. A 15-inoh, 26-pound flywheel was attached to 

 the rear end of the shaft. A chain drive on the front end drove the camshaft, 

 which operated the breaker arms and exhaust valves. A boxwood idler, 1^4 

 inches in diameter, without flanges, created tension on the chain. 



