A New Air Propeller of Steel and Enamel 



The framework is made of one piece of thin 

 steel over which the glossy coating is baked 



THE screw propeller of an aero- 

 plane or airship is made like a pair 

 of blades on an ordinary electric 

 fan. They are, however, about a dozen 

 times larger, and capable of throwing 

 back a column of air several thousand 

 times more powerful. When such a 

 propeller is revolved at high speed, it 

 will push with tremendous force against 

 the air; and with equal force will the 

 aeroplane be pushed ahead. Its opera- 

 tion is just like a propeller pushing a 

 ship, only that the aeroplane propeller 

 works against a very much lighter 

 substance. 



The first aeroplane propellers were 

 copies of windmills. Their blades 

 were of canvas stretched on a wooden 

 framework. They were, however, 

 very inefficient. The next step in 

 advance was made when aluminum 

 blades were riveted to steel arms 

 which projected from the driving- 

 shaft from the motor. But the 

 great defect in both of , 



them was their lack of 

 clean-cut outline. 

 Unless a propeller blade 

 is made rigid and 

 in one unbroken 

 piece, the slightest 

 projection or un- 

 evenness serves 

 only to churn the 

 air. At the high 

 speed at which 

 the propeller re- 

 volves, the vio- 

 lent churning 

 will hinder 

 rather than help 

 the aeroplane 

 in its progress. 

 The solid one- 

 piece wooden 

 propeller, in- 

 vented by Hi- 

 ram Maxim over 

 tw-enty-three years ago, practically elimi- 

 nated this defect. Its outline is unbroken 

 and its surface is polished as smooth as 

 glass. Nothing in the world is given so 

 high a finish, and its clean-cut blades churn 



The lacquered steel is as light 

 as wood and will withstand 

 any variety of weather 



The die wherein the inner framework of the 

 propeller is pressed into shape from thin sheet steel 



the air ver>- little. It has one great draw- 

 back, nevertheless, in that it is 

 affected by the weather. Changes in 

 degrees of moisture, heat and cold warp 

 the propeller in time. As a matter of 

 fact, the wooden propeller of one of 

 our military aeroplanes which ran the 

 risks of the Mexican climate 

 was warped suddenly while 

 the aeroplane was high in 

 the air, and came to grief. 

 The weather-proof pro- 

 peller, the next step, 

 has only recently 

 been developed. It 

 consists of a thin 

 one-piece steel 

 framework upon 

 which a glossy coating 

 of lacquer is baked. 

 The steel is pressed into 

 just the right form by a. 

 huge steel die. The sur- 

 face of the steel is treated 

 with chemicals. This 

 makes the steel spot- 

 lessly clean so that 

 it can "take" the 

 lacquer. A heavy 

 coating of the un- 

 baked lacquer is then 

 spread evenly o\er 

 the entire surface of 

 the steel. The tvvo substances 

 are forced together under great 

 pressure and are then brought 

 to a high temperature. The 

 steel and the lacquer amalga- 

 mate and one rigid piece 

 is formed. The light 

 lacquer strengthens 

 the inner framework, 

 and the propeller 

 itself is considerably 

 lighter on account of it 

 than if it were of solid 

 steel. When the pro- 

 peller is cooled and 

 polished, it forms a surface as smooth as a 

 lacquered Japanese box. This spells effic- 

 iency. The weather-proof quality of the 

 lacquer also enables the propeller to with- 

 stand all climates indefinitelv. 



671 



