This completes the description of the various parts of a model horizontal engine. A glance at [Figs. 1] and [2] will show the relative position of each.
V.—The Oscillating Engine.
Herewith are drawings of an engine with an oscillating cylinder. This form of construction economises space and weight; it is also more simple than slide-valve cylinders. In all oscillating engines the cylinder is mounted on trunnions or gudgeons, so that it may swing to and fro through a small arc, and allow the piston-rod to follow the motion of the crank. No connecting-rod is required in this engine, the piston-rod being attached direct to the crank-pin.
The [illustration] shows an engine specially adapted for propelling a model boat. The entire machine is kept low down, which is generally necessary for small boats. The fly-wheel is shown much heavier than are those attached to toyshop engines, but it is not unnecessarily large. Experiments show that a weighty fly-wheel is required on an engine which has the constant drag of a screw propeller to overcome. This fact is ignored by some makers of engines, and I have known cases where a useless engine has been made effective by the substitution of a much heavier fly-wheel. (See [page 132].)
The framework on which the cylinder is mounted, and which also generally serves to carry the bearings for the driving shaft, may be of almost any design. There is no set pattern for this purpose, and it rests with the designer to fashion his pattern according to fancy. The [form shown] possesses the essential characteristics. It is strong, yet light; there is a good base by which to secure the engine to the hull of the boat. Suitable provisions are made for the bearings of the crank-shaft, also for the valve-face and the cylinder trunnion. So long as these are provided for, the mere contour is of little importance.
[Fig. 1] gives a side elevation, and [Fig. 2] an end view of the same engine. The cylinder is 1 in. bore and 1 in. stroke. The length without covers is 11⁄2 in., that allows 1⁄4 in. for thickness of piston, 1⁄16 in. for each of the projections of the two covers, and the same distance left vacant at each end. The diameter of the cylinder across the flanges is 11⁄2 in., and a semicircular rib is shown in the middle. Each cover is held on by six hexagon-headed bolts, placed equidistant round it, tapped into the flange. These bolts are not shown in the lower cover.
The piston-rod is shown out from the cylinder to its fullest extent. The rod is of round steel 1⁄8 in. diameter. The crank-pin head is of brass screwed on to the end of the rod. Though shown as a solid piece, it would be better if this head was cut across horizontally at the diameter of the crank-pin, and the cap secured by two screws. The crank-pin is marked E. It is steel riveted into the disc which forms the crank. A crank-arm would do equally well, and the disc is shown simply as illustrating a different plan. The disc F is fixed on the crank-shaft either by screwing, by a transverse pin, or by a key.
Fig. 1.
