These engines, as is most clearly shown in Plate 30, were mounted symmetrically 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 described in connection with No. 5, the only difference being in the more compact arrangement in the case of No. 6. The relative location of the apparatus in the two models is clearly shown in Plates 28, 29B, and 30, the corresponding parts being 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. 6 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 ease with No. 5. [p122] The Pénaud rudder for No. 6 was similar to that for No. 5, the two in fact being interchangeable, and was similarly attached to the frame. The reel, float, counter, and all other accessories were identical for the two machines. To sum up the comparative features of these two successful steam-driven models: Aerodrome No. 6 was both lighter and frailer than No. 5, and required much more delicate adjustment, but when the correct adjustments had been made its flying qualities were superior, as regards both speed and stability. [Illustration: PL. 29A PLAN VIEW OF AERODROME NO. 6. OCTOBER 23, 1896] [Illustration: PL. 29B SIDE ELEVATION OF AERODROME NO. 6. OCTOBER 23, 1896.] [Illustration: PL. 30 PLAN VIEW OF STEEL FRAMES AND POWER PLANTS OF AERODROMES NOS. 5, 6] [Illustration: PL. 31 DETAILS OF AERODROME NO. 5] FOOTNOTES. [2] “Experiments in Aerodynamics,” ‹Smithsonian Contributions to Knowledge›, Vol. 27, 1891. [3] This chapter was written almost entirely by Mr. Langley in 1897. [4] 1897. [5] In this statement, of course, no account is taken of the “internal work of the wind.” [6] Ten years prior to 1897. [7] Communication to the French Academy. Extract from the Comptes Rendus of the Sessions of the Academy of Sciences, Vol. 122, Session of May 26, 1896. (Translation.) A Description of Mechanical Flight. By S. P. Langley.