NO. 



LANGLEY MEMOIR ON MECHANICAL PLIGHT 223 



and the necessity for keeping the weight a minimum, was a most difficult piece 

 of work. The work was rendered still more difficult by the fact that the water 

 jackets had to lie made in halves which were brazed together after they had 

 heen fitted over the head of the cylinder. Even when the work was done in 

 the most careful way this method of construction gave a great deal of trouble 

 from the leaking of the stuffing boxes or the jackets themselves. Eowever, 

 after much delay, the water jackets were finally completed, and upon test the 

 engine was found to develop 21.5 horse-power at 825 R. P.M., the engine itself 

 weighing 120 pounds. 



Further changes were made in this engine, especially in the pistons, a new 

 set of which were constructed which weighed 15 pounds less than the original 

 set. On account of the difficulty with the leakage of the water around the 

 stuffing boxes of the water jackets, and also from imperfections in the brazed 

 joints of the jackets themselves, it was found impossible to rely on the power 

 that the engine would develop at any particular time, as the water leaking 

 from the jackets and running down on the spark plugs of the lower cylinders 

 caused these cylinders to work erratically, and this not only materially reduced 

 the power but also caused jerky impulses in the absence of fly wheels. 



It seemed so desirable to obtain as soon as possible a first test in actual 

 flight of the large machine that the writer offered to put this engine in the 

 aerodrome frame and make a test with it if the machine were launched over 

 the water, but with the launching track mounted directly on the river bank. 

 However, Mr. Langley felt it so necessary to make the initial test from the 

 top of the house-boat and at an elevation of 30 feet or more that he would not 

 consent to this, and as the engine at its best did not develop quite 24 horse- 

 power, which had been calculated as the minimum which should be provided, 

 it was thought unwise to attempt to make the first test from the top of the 

 house-boat until the aerodrome had been provided with engines that could be 

 depended on to develop continuously not less than 24 horse-power. 



It then became necessary either to build a duplicate engine and use both 

 of them in the aerodrome, the original plan as already explained having been 

 to have two engines developing the 24 horse-power together; or, second, to con- 

 struct an entirely new engine large enough to furnish a minimum of 24 horse- 

 power and use this single engine. 



As the construction and tests of this experimental engine had shown many 

 places in which the weight might be safely reduced, the writer decided to con- 

 struct an entirely new and larger single engine, and thereby avoid the extra 

 weight and difficulties which would be introduced by bavin- to use synchroniz- 

 ing gears where two engines were used, it being impossible, of course, to run 

 the two propellers from the two engines independently without risk of serious 

 disaster. 



