Fig. 47.—The seven-cylinder
50-h.p. Gnome motor.
The difficulty with air-cooling—although it had obvious advantages over water-cooling—was to bring enough air to play upon the surfaces of the cylinders; and it was here that the Gnome won so complete a success. In other engines the cylinders were stationary, and their pistons, moving up and down in the cylinders, turned a crank-shaft to the end of which the propeller was fixed. Therefore the only air the cylinders obtained was what rushed upon them through the speed of the machine in flight. But in the Gnome, instead of the cylinders remaining stationary and the crank-shaft revolving, the cylinders themselves spun round, and the crank-shaft did not move. An illustration of this motor with one end of the crank-chamber removed, so that the piston-rods can be seen, is given in [Fig. 47]. It will be noted that there are seven cylinders, set in the form of a star, and that the seven piston-rods projecting from them come together upon a single crank-pin, which is attached to the stationary crank-shaft and turns round it. The propeller, instead of being fitted to the crank-shaft, as was the case with other motors, was bolted to a plate upon the engine itself, so that when this turned around its crank-shaft, it carried the propeller with it.
A difficulty in this engine lay in feeding its cylinders with their petrol and air. We showed, in [Fig. 32], how this mixture is delivered to an ordinary motor, which has its cylinder stationary. But with the Gnome the mixture could not be supplied from a pipe to the cylinder-head, for the reason that the cylinder was revolving. The problem was solved by making the stationary crank-shaft hollow, and by delivering the mixture through this to the interior in the engine; thence it was sucked into the cylinder-heads through a valve in the pistons. There were other complications, inevitable to this ingenious motor, which led critics to declare it would prove unreliable. But their judgment was wrong, for by making every working part with scrupulous care, and sparing no expense in the quality of the materials used, the builders of the Gnome did render it reliable. They achieved another triumph as well; they eliminated overheating. Revolving more than 1000 times a minute, the cylinders of the Gnome cooled themselves automatically, and the engine proved that it would run for hours without becoming too hot, or the pistons seizing in the cylinders. Furthermore, seeing that the weight of water and of radiators was avoided, the Gnome was remarkably light. The 50-h.p. engine weighed no more than 165 lbs., which meant that it gave one h.p. of energy for each 3.3 lbs. of its weight. A photograph of the Gnome, as fitted to a Farman biplane, is seen on [Plate VIII].
The Gnome, when first built, was regarded with scepticism. Farman, however, showed the acuteness of his judgment. He obtained a Gnome and fitted it to the biplane which he flew at Rheims; and the wisdom of this choice was soon made clear. The chief prize at Rheims was for the longest flight, and this Farman won easily, remaining in the air for 3 hrs. 4 mins. and covering a distance of about 112 miles. The flight represented a world’s record; and by this feat alone Farman made his biplane famous, and demonstrated the reliability of the Gnome. Those who watched the flight will not forget it. Farman started rather late in the afternoon and flew low round the great aerodrome, his landing-wheels appearing sometimes to be a few feet only above the grass. He sat leaning forward in his seat and circled close to the wooden towers marking the course, losing no ground and steering his machine with perfect accuracy. So he flew for lap after lap, never rising higher or flying lower, and with the Gnome behind him emitting a booming hum as it whirled the propeller without falter or flag. Only the approach of darkness, in fact, caused the airman to descend.
A. Elevating-planes; B. Pilot’s seat and control-wheel; C.C. Main-planes; D. Ailerons; E. Motor and propeller; F. Tail-plane and rudder.
