176 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



formed by the use of sheet metal and tubing properly brazed together, and 

 noue of them ever gave any trouble. 



In the early photographs of the aerodrome frame, especially that of Jan- 

 uary 31, 1900, Plate 45, it will be noted that the two transmission shafts, which 

 extend from the propeller-shaft bed plates towards the center, are not in line, 

 the port transmission shaft being at the center of the transverse frame, while 

 the starboard one is three inches to one side. This arrangement was neces- 

 sary in order to connect the shafts to the rotary cylinder engine which was 

 being constructed under contract, and which was almost momentarily expected 

 for more than a year after its original promise of delivery on February 28, 

 1899. Later, when this engine was finally found to be a failure, and the writer 

 constructed the engine in the Institution shops, the starboard transmission shaft 

 was moved over to the center line and the crank shaft of the engine, which was 

 carried through on the center line of the transverse frame, was then connected 

 directly to the inner ends of the transmission shafts. 



These shafts, as well as the propeller shafts, were originally constructed 

 of steel tubing 1.5 inches in diameter and 1 16 of an inch thick, but on account 

 of the increased power of the large engine it was found necessary to increase 

 the thickness of the shafts to J of an inch. Difficulty was also found with the 

 tubing of which the shafts were made. This, though not exactly straight when 

 received from the factory, could be pretty accurately straightened in the lathe 

 li\ exercising proper care, but the moment any real strain was put upon it in 

 the transmission of power, it again went out of shape and caused serious dam- 

 age to the bearings by whirling, buckling, and so forth. As the skin of the tub 

 ing is really the strongest part, owing to the cold-drawing process to which it 

 has been subjected, great care was taken to secure shafts which were suffi- 

 ciently straight for use without machining, but it was finally found impossible 

 to rely on the unniachined shafts, and all the later shafts for the aerodrome 

 were made by getting tubing a sixty-fourth of an inch thicker than was cal- 

 culated to be necessary and turning oil' this extra metal in a lathe. 



Suitable flanges and collars were brazed to the propeller shafts; but, for 

 convenience in assembling, the flanges by which the main transmission shafts 

 were connected to the crank shaft of the engine were at firs! fastened to the 

 shafts by screw-threads, the threads being in the proper direction to cause Ihe 

 flanges to jam against the shoulders of the shafts when the engine turned in 

 iis normal direction. This method of fastening, however, caused serious trouble, 

 owing to the flanges jamming so tight that it became impossible to unscrew 

 them after they had once been used in driving the propellers. The usual pro- 

 visions of keys and key-ways adopted in general engineering practice, where 

 solid shafts are employed, were, of course, out of the question, since the shaft 

 would have to lie greatly increased in thickness throughout its entire length 



