NO. 3 LANGLE"S MEMOIR ON MECHANICAL FLIGHT 177 



merely to provide the extra metal at the small place in which the key way:; 

 were formed. Taper pins either sheared off or very soon stretched the holes 

 so badly as to leave the parts loose, and were otherwise verj unsatisfactory. 

 The method finally adopted, which proved very successful, was thai of forming 

 integral with the couplings shallow internal tongues and grooves which fitted 

 corresponding tongues and grooves either in the exterior surface of the shafts 

 or in collars brazed to them at the proper point. The form of flange coupling, 

 in which bolts draw the two flanges tightly together, was also a source of con 

 siderable trouble and delay, which was finally overcome by forming shallow 

 tongues and grooves in the faces of the flanges, the tongues taking up the tor- 

 sion and relieving the bolts which held the flanges together of all strain ex- 

 cept one of slight tension. The same difficulties experienced in mounting the 

 couplings on the shafts were met with in connection with the gears, both on 

 the propeller and transmission shafts, and were finally obviated in a manner 

 similar to that described above. 



The bevel gears originally constructed for transmitting the power from 

 the transmissidh shafts to the propeller shafts, were made of case-hardened 

 steel and were eight-pitch, twenty-five teeth, with three-quarter inch width of 

 face. The gears were very accurately planed to give as perfect a form of 

 tooth as possible, in order to avoid loss of power in transmission, and although 

 the manufacturer who cut the teeth on them asserted at the time they were 

 made that they would not be capable of transmitting more than five horse- 

 power, yet they actually did transmit considerably more than twelve horse- 

 power on each set; but they were not strong enough to transmit the full power 

 of the large engine which was finally used. The gears that were finally used 

 were similarly constructed of mild steel which was case hardened 1 64 of an 

 inch deep after they were finished, there being thirty-one teeth in the near on 

 the transmission shaft and forty teeth in the one on the propeller shaft, the 

 teeth being eight-pitch, three-quarters of an inch face. These fight gears proved 

 amply strong, and several times stood the strain which they accidentally re- 

 ceived when one of the propellers broke while the engine was under full power, 

 and thus threw the entire fifty horse-power over on the other propeller, which 

 was consequently driven at a greatly increased speed. 



Plain bronze bearings had been used throughout on the model aerodromes, 

 but in the construction of the large aerodrome ball-bearings were used on all 

 of the propeller and transmission shafts, not only on account of the decreased 

 loss through friction, but also because ball-bearings can be built much lighter 

 than solid bronze ones, and, furthermore, do no1 present such greal difficulties 

 in lubrication. However, owing to the limited size which it was possible to se- 

 cure for these bearings, because of their having been originally designed for only 

 twenty-four horse-power, and without any margin for a later increase of the 



