286 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1962 



^///////.','// A//^/w/////, ' 



Figure 18. — Farman planetary bevel gear. 



The plain spur gears used by the Eolls-Royce Merlin carried 2,200 

 takeoff horsepower satisfactorily on a 2-inch face width, a remark- 

 able achievement in gear design. 



SECONDARY PROBLEMS 



Only brief mention can be made here of the numerous secondary, 

 though often very important, problems encountered and solved in the 

 development of reciprocating aircraft engines. Among these should 

 be mentioned the following : 



Starting. — Hand starting by the propeller was standard before 

 1920. Subsequent development included hand cranks, hand cranks 

 with inertia flywheel, cartridge starters, air starters, and finally the 

 present electric starter with storage battery. 



Spark plugs. — Ceramic plugs were generally used in the U.S.A. be- 

 fore 1921. Both mica and ceramic plugs were used in Europe. From 

 about 1921 to 1935 mica plugs were generally used. The development 

 of new ceramic materials about 1935 caused a universal change to this 

 material. 



C arhuretion. — At the time of the Wright brothers' first flight, little 

 was known about carburetion, and various devices were used to intro- 

 duce fuel to air. As mentioned earlier, the Wright brothers used 

 gravity fuel feed from a small can to a heated surface in the inlet pipe. 

 Manly used a large sheet-metal box filled with porous wooden blocks. 

 These blocks were saturated with fuel, and the engine air was drawn 

 past them, in the hope that a combustible mixture would result. The 

 Antoinette engine apparently used a small pump to inject fuel into 

 the air-inlet pipe. The carburetion system used for the Gnome rotary 

 engine has already been described. All these systems required experi- 

 mental adjustment, good for only one speed of the engine. 



