NO. 3 LANGI.KY MEMOIK ON MECHANICAL PLIG] 17!) 



In November, L897, in order to obtain by actual test some data on pro 

 pellers, such as it was planned to use on the Large aerodrome in case it was 

 later built, it was decided to eonstrucl one propeller 2.5 metres in diameter and 

 1.25-pitch ratio with two blades, each covering the sector of 36 degrees on the 

 projected circle. About this same time an engine builder, who some years be- 

 fore had made some experimental model engines in the Institution shops, pro- 

 posed to construct a gasoline engine for the proposed large aerodrome. As 

 past experience, not only with such engines but with all other forms of ex- 

 plosive motors, had not been very reassuring it was thought best to make brake 

 tests of one of the heavier engines which he was ai this time building, and at 

 the same time make tests with one of these large propellers. A first series of 

 tests was made at several different speeds, and then a second series was made 

 with the engine driving the propeller at the same speeds. The engine varied 

 so much, however, in the power developed at any speed that the data obtained 

 were of little value. As it was also desired to learn just how much thrust 

 could be obtained from these propellers, when driven by a given horse-power, a 

 special hand car was fitted up to carry the engine, which was connected to a 

 shaft on which the propeller was mounted. The propeller was raised above 

 the floor of the car and projected over the rear end of it so as to lie as little 

 disturbed as possible by the deflection of the air currents caused by the car. 

 This car, with the engine and propeller, was tested on a track near Mount Holly, 

 N. J., in November, 1897, but the results were very unsatisfactory. In the first 

 place, the car with the engine mounted on it was so very heavy and offered 

 such a strong tractive resistance that very little speed of propulsion could be 

 obtained. In the second place, the engine, which was said to have furnished 

 over six horse-power on Prony-brake tests, evidently did not furnish anything 

 like this amount of power at this time. And in the third place, the propeller 

 was evidently far too large to permit the engine to run at the speed at which 

 it would develop a reasonable amount of power unless some reduction gearing 

 were interposed between it and the propeller. As the tests, for various reasons, 

 had to be made at a great distance from Washington, and the supervision of 

 them had to be entrusted by Mr. Langley to others, who either did not under- 

 stand or appreciate the value of obtaining accurate data, it was found imprac- 

 ticable to continue them. 



The large propeller used in these tests was built without special regard to 

 weight, since it was expected that il would be subjected to rather rough usage 

 under the very sudden strains produced by the irregular working of the gas 

 engine. Its hub was made of brass tubing, the horns being brazed to rings 

 which were slid over a central tube, the rings being finally soldered to the tube 

 after the arms had been adjusted to the positions which would give the blade 

 the correct shape and dimensions. The wooden arms were 1..") inches in diam- 



