NO. 



IA.NCLEV MEMOIR OX MECHANICAL FLIGHT 229 



the engine caused so much trouble on account of the inertia of the rotating 

 plates of the dynamometer that the time lost in keeping the universal joinl in 

 working order during the tests more than counterbalanced the extra time which 

 would have been required to construct a special wooden frame on which the 

 dynamometer and engine could have been mounted in line with each other so 

 that the crank shaft of the engine could have been directly connected to the 

 shaft of the dynamometer. 



Much time was also lost in the effort to construct an apparatus by which 

 a record could be obtained of the power actually used in propelling the aero- 

 drome. Various methods were in use by which the thrust of the propellers 

 could be more or less satisfactorily measured while the aerodrome was al rest, 

 but it was desired to know just how much power the aerodrome consumed while 

 in actual free flight. Such a record it was hoped to obtain from a device in- 

 corporated in the propeller shafts. This thrust-measuring device consisted es- 

 sentially of a propeller shaft made in two sections, one section telescoping the 

 other for a short distance. On the section of the shaft to which the propeller 

 was attached there was mounted a drum, having in its circumference two long 

 slots diametrically opposite. To the other section of the shaft a disc was fast- 

 ened with two diametrically opposite rollers mounted on its periphery, which 

 fitted the slots in the drum of the other section. A compression spring was inter- 

 posed between the disc and the drum, and the outside of the drum was so arranged 

 that a strip of paper could be wound around and fastened to it which would serve 

 as a chronograph sheet. A pencil was fastened to the frame, and, since the drum 

 was connected to the section of the shaft to which the propeller was attached and 

 which therefore moved to and from the frame under the action of the propeller 

 thrust, a record of the actual thrust of the propeller at any particular moment 

 could be obtained by simply pressing the pencil up against the paper on the drum 

 and calculating the thrust from the calibration of the compression spring. Since 

 the thrust would naturally be greater when the propellers were revolving in 

 a moored condition, during the few moments after the engine was started up 

 and before the aerodrome was launched, it was necessary to provide means for 

 having the pencil point held away from the chronograph sheet until the aero- 

 drome was launched, and then have the point come to bear on the sheet. This 

 was accomplished by having the point held off by a small trigger arrangemenl 

 which was to be released just at the moment that the aerodrome left the launch 

 ing car. A set of propeller shafts embodying this thrust-recording device was 

 constructed, but when they were actually tested on the aerodrome many diffi- 

 culties were encountered which had not been anticipated. In the first place 

 the gasoline engine for the model was started up (or " cranked over ") by 

 turning the propellers by hand. A gasoline engine never starts slowly, and on 

 account of this suddenness of starting causes a very great strain in any shaft- 



