118 SMITHSONIAN CONTRIBUTIONS TO KNOWLEDGE VOL. 27 



This, then, comprises the motive power equipment of the aerodrome, and, 

 to recapitulate, it includes the storage, automatic feeding and regulation of the 

 fuel; llic storage, circulation and evaporation of the water; the engine to con- 

 vert the expansive power of the steam into mechanical work; and the shafting 

 for the transmission of the energy developed by the engine to the propellers. 



The propellers were made with the greatest care. Those used in the suc- 

 cessful trials were 1 metre in diameter, with an actual axial pitch of 1.25 metres. 

 They were made of white pine, glued together in strips 7 mm. thick. The hub 

 had a length of 45 mm. and a thickness or diameter of 25 mm. At the outer edge 

 the blade had a width of 315mm. and a thickness of 2mm. These propellers 

 were most accurately balanced and tested in every particular; each propeller 

 blade was balanced in weight with its mate and the pitch measured at every 

 point along the radius to insure its constancy; finally the two propellers of the 

 pair to be used together were balanced with each other so that there would be 

 no disturbance in the equilibrium of the machine. As will be noted from the 

 foregoing description of the machinery, the propellers ran in opposite direc- 

 tions, as they were made right- and left-hand screws. The weight of each pro- 

 peller was 362 grammes. 



We now turn again to take up the details of the construction of the frame- 

 work by which this propelling machinery is carried. The whole aerodrome, as 

 clearly shown in the photographs, Plates 27A and 27B, is built about and depend- 

 ent from one main backbone or midrod, which extends well forward of all of the 

 machinery and aft beyond all other parts. This rod, as well as all other por- 

 tions of the framework, is of steel tubing. The midrod, being largest, is 20 mm 

 outside diameter, with a thickness of 0.5 mm. It is to this midrod that the 

 wings are directly attached, and from it the hull containing the machinery is 

 suspended. 



The plan outline of the hull skeleton is similar to that of the deck of a ves- 

 sel. The steel tubing, 0.5 mm. thick, of which it is formed, has an outside diam- 

 eter of 15 mm. from the front end to the cross-framing used to carry the pro- 

 pellers, hack of which the diameter is decreased to 10mm. 



The midrod makes a slight angle with this frame, the vertical distance be- 

 tween the centers of the tubing being 73mm. at the front and 67mm. at the 

 back. The tube, corresponding to the keel of a vessel, is braced to the upper 

 tidies by light U shaped ribs and by two S-mni. tubes forming a V brace on a 

 line with the back end of the guides of the engine. At the extreme front and 

 back there is a direct vertical connection pi the midrod. 



The propeller shafts are 1.23m. from center to center, and are carried on 



a special cross framing, partaking, as already stated, of the character of an out- 

 er mi a row boat. (See Plate 27B.) The rear rods, which are of 10 mm. steel 

 tubing, start from the front end of the rear bearings of the propeller shaft and 



