220 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1950 



The instrumentation provided was solely for the purpose of obtain- 

 ing flight records. A Veeder counter on the engine recorded total 

 revolutions from its start until starvation took place after closing the 

 fuel valve. A Richards anemometer, with interconnected stop watch 

 actuated by a cord from the fuel valve, measured the air traversed in 

 meters. 



It may be interesting to note that by the old ALAM formula, 



horsepower = -— — 



where D is the diameter of the cylinders in inches, and N the number 

 of cylinders, the engine's power is 25.6 horsepower. 



The Wrights always said that their most difficult design problem 

 on the first airplane was that of the propeller. Since the empirical 

 formulas of marine propellers seemed not readily adaptable to air per- 

 formance, they worked out a practical solution of their own, which 

 was quite adequate and commendable. By taking scattered bits of 

 formulae and notes throughout their diaries, one can reconstruct their 

 theory and can best explain it by working out a sample computation 

 of power required. 



DEVELOPMENT WORK IN 1904 AND 1905 



A second airplane was built in 1904 and tested at Dayton through- 

 out the summers of 1904 and 1905. This airplane is of particular in- 

 terest in that it was really the development step between the 1903 

 prototype and the "practical flyer," as Wilbur put it. 



There were very few basic changes in the new wing cellule. The 

 front elevators were made larger and moved forward 1 foot. The 

 elevator support and skid structure was improved upon, and the 

 rudder was raised for more ground clearance. Also, fixed vertical fins 

 were added at the front elevators. All changes made on this machine 

 resulted in a 105-pound weight increase over the prototype. 



The engine for this airplane was basically the same except for certain 

 improvements : 



1. Bore was increased to 4^,^ from 4 inches. 



2. A gear-type oil pump, driven from the camshaft, was added. 



3. The fuel tank was made to hold a full gallon. 



4. A compression release was added to stop the engine without wait- 

 ing for the fuel to exhaust. This release was in the form of a rod which 

 pulled four small spring clips into place to hold all exhaust valves 

 open. 



Several notebook notations indicated that the engine was now de- 

 veloping 14.1 horsepower at 1,070 revolutions per minute and 19.8 

 horsepower at 1,300 revolutions per minute. 



