NO. 3 LANGLEY MEMOIR ON MECHANICAL FLIGHT 121 



In No. 5, as described above, a single engine mounted at the front end of the 

 hull communicated its power through transmission shafts and gearing to the 

 propellers, which were necessarily in the same plane. This brought the line of 

 thrust very nearly in the same plane as the center of gravity of the aerodrome, 

 a condition tending to promote instability of Longitudinal equilibrium. In No. 

 6, however, the use of two engines situated on the transverse frame and com- 

 municating their power directly to the propellers, made it possible to raise the 

 transverse frame 12cm. above the hull, and thus raise the line of thrust to a 

 position intermediate between the center of pressure and the center of gravity, 

 without materially affecting the latter. As a result of this change Aerodrome 

 No. 6 was rendered much more stable and made steadier flights with fewer un- 

 dulations than No. 5. 



The engines in use on No. 6 were the small engines described above in con- 

 nection with No. 4. The cylinders were of steel tubing 2.8 cm. in diameter, with 

 a 5-cm. stroke, each cylinder thus having a capacity of 30.8 cc. They were lined 

 with a thin cast-iron bushing and cast-iron rings were sprung in the piston head 

 so as to give as smooth a rubbing surface and as perfect action as possible. As 

 in the engine of No. 5 a plain sliding valve of the piston type was used, cut-off 

 being approximately at one-half, though the ports were so small that it was diffi- 

 cult to determine it with any great accuracy. No packing was used, but the 

 parts were carefully ground so as to give a perfect fit. 



These engines, as is most clearly shown in Plate 30, were mounted sym- 

 metrically on either side of the cross-frame and were connected directly to the 

 propeller shafts. In order to insure that the propellers would run at the same 

 rate, there was provided a synchronizing shaft, T, in Plate 30, having on each 

 end a bevel gear, which intermeshed with similar gears on the propeller shafts. 

 Steam for the cylinders was conveyed from the separator through the pipes LL. 



The steam-generating apparatus for No. 6 was exactly like that already de- 

 scribed in connection with No. 5, the only difference being in the more compact 

 arrangement in the case of No. (>. The relative location of the apparatus in the 

 two models is clearly shown in Plates 28, 29B, and 30, the corresponding parts be- 

 ing similarly labeled, so that a separate description for No. 6 is superfluous. 



The wings used on No. 6 were somewhat smaller than those of No. 5, and 

 differed from them in having the front mainrib bent to a quadrant at its outer 

 extremity and continued as the outer rib of the wing. The degree of curvature 

 of the wings was also somewhat less, being one-eighteenth for No. 6 and one- 

 twelfth for No. 5. The four wings were of the same size and had a total area 

 of 54 sq. ft. On account of the shortened hull of No. (! they were allowed a 

 much greater range of adjustment, which rendered it much easier to bring the 

 CP into the proper relative position to the CG than was the case with No. 5. 



