Langley Memoir on Mechanical Flight, Parts I and II / Smithsonian Contributions to Knowledge, Volume 27 Number 3, Publication 1948, 1911

by S. P. Langley; Charles M. Manly

These weights are those determined in December, 1896, when some slight changes had been made from the conditions existing at the time of the flight by this aerodrome on May 6. Previous to that time, with a pressure of 130 pounds, between 1.1 and 1.25 horse-power was given on the Prony brake. At the actual time of flight the pressure was about 115 pounds, and the actual power very near 1 horse-power.

The valve stem was pivoted to the center of the valve partly because this was the lightest connection that could be made, and partly to allow the valve perfect freedom of adjustment upon the seat. Many parts, such as guides, braces, crank-pins, wrist-pin and shafts are hollow. The steam is taken in at the front end of the steam chest, and the exhaust taken out of the center, whence it is led back to the stack and by means of a forked exhaust pipe discharged in such a way as to assist the draught of each coil of the boilers. Like the cylinder the steam chest is made of a piece of steel tubing, 20 mm. diameter on the outside, with an inside diameter of 19 mm., and is fitted with a cast-iron bushing 0.5 mm. thick, making the inside diameter of the steam chest 18 mm. It, too, has flanges brazed to the ends, to which the heads are held by small machine screws.

The shaft for conveying the power to the propeller shafts extends across the machine from side to side; it is hollow, being 8 mm. outside diameter, with a hole 5 mm. diameter through the center.

It is formed of five sections: the middle section, containing the crank, has a length of 110 mm. and is connected at either end, by flanged couplings, to lengths 320 mm. long, which are in turn extended by the end sections having a length of 230 mm. In addition to the four main bearings that are bolted to the pressed-steel bed-plate already mentioned, there are two bearings on the outer framework on each side. At the outer end of each shaft there is keyed thereto a bevel gear with an outside diameter of 27 mm. and having 28 teeth. This gear meshes with one of 35 teeth upon a shaft at right angles to the main shaft and parallel to the axis of the aerodrome. These two shafts, one on either arm, serve to carry and transmit the power to the propellers. They are 192 mm. long, 8 mm. in diameter, and are provided with three bearings that are brazed to a corrugated steel plate forming the end of the outrigger portion of the frame. These shafts are also hollow, having an axial hole 4 mm. in diameter drilled through them. The propeller seat has a length of 43 mm. and the propeller is held in position by a collar 25 mm. in diameter at the front end, from which there project two dowel-pins that fit into corresponding holes in the hubs of the propellers, which are held up against the collar by a smaller one screwed into the back end of the shaft. The thrust of the collar is taken up by a pin screwed into the end of the forward box and acting as a step against which the shaft bears, the arrangement being clearly shown by the accompanying drawing, Plate [26A]. [p118]

This, then, comprises the motive power equipment of the aerodrome, and, to recapitulate, it includes the storage, automatic feeding and regulation of the fuel; the storage, circulation and evaporation of the water; the engine to convert 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 successful 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 315 mm. and a thickness of 2 mm. 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 directions, as they were made right- and left-hand screws. The weight of each propeller was 362 grammes.

We now turn again to take up the details of the construction of the framework by which this propelling machinery is carried. The whole aerodrome, as clearly shown in the photographs, Plates [27A] and [27B], is built about and dependent 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 portions 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 vessel. The steel tubing, 0.5 mm. thick, of which it is formed, has an outside diameter of 15 mm. from the front end to the cross-framing used to carry the propellers, back of which the diameter is decreased to 10 mm.

The midrod makes a slight angle with this frame, the vertical distance between the centers of the tubing being 73 mm. at the front and 67 mm. at the back. The tube, corresponding to the keel of a vessel, is braced to the upper tubes by light U-shaped ribs and by two 8-mm. 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 to the midrod.

The propeller shafts are 1.23 m. from center to center, and are carried on a special cross-framing, partaking, as already stated, of the character of an outrigger on 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 [p119] extend across from side to side. The top rod is brazed to the side pieces of the hull and the bottom rod to the keel. They are connected by a vertical strut of 8-mm. tubing at a distance of 265 mm. inside of each propeller shaft. At the front end of the propeller shaft two more rods run across the frame. The lower is similar and parallel to the back rod already described, while the upper is bowed to the front, as shown in the plan view of the frame (Plate [30]). In order to take the forward thrust of the propeller a second cross-brace is inserted, which runs from the rear bearing of the propeller shaft to a point just in advance of the front head of the cylinder, and is brazed to the two upper tubes of the cross-frame as well as to the upper tubes of the main framing of the hull. The outer ends of the tubes of the cross-framing are brazed to a thin, stamped steel plate which firmly binds them together, while at the same time it forms a base for attaching the bearings of the propeller shaft. This end plate has a thickness of one millimetre.