across the Channel was accomplished by means of an Anzani
engine, and the Gnome engine, because it was used in the aeroplane
with which Paulhan flew from London to Manchester.
Fig. 7 shows transverse and longitudinal sections through the Anzani motor. Looking at the longitudinal section it will be observed that the cylinders are of the air-cooled type; the exhaust valves alone are positively operated, and the inlet valves are of the automatic lift kind. The transverse section shows that three radially arranged cylinders are used and three pistons act upon one crank-pin. The Otto cycle is followed, so that two impulses are obtained for
Fig. 7.
every three revolutions. The cylinders are spaced apart 60° and project from the upper side of the crank chamber. Although not shown in the drawing, the pistons overrun a row of holes at the out end of the stroke and the exhaust first discharges through these holes. This is a very common device in aeroplane engines, and it greatly increases the rapidity of the exhaust discharged and reduces the work falling upon the exhaust valve. The pistons and cylinders are of cast iron; the rings are of cast iron; the ignition is electric, and the petrol is fed by gravity. The engine used by Blérot in his Cross-Channel flight was 25 H.P., cylinders 105 mm. bore X 130 mm. stroke; revolutions, 1600 per minute; total weight, 145 ft. The engine, it will be seen, is exceedingly simple, although air-cooling seems somewhat primitive for anything except short flights. The larger Anzani motors are water-cooled.
A diagrammatic transverse section of the Gnome motor is shown at fig. 8. In this interesting engine there are seven cylinders disposed radially round a fixed crank-shaft. The seven pistons are all connected to the same crank-shaft, one piston being rigidly connected to a big end of peculiar construction by a connecting-rod, while the other connecting-rods are linked on to the same big end by pins; that is, a hollow fixed crank-shaft has a single throw to which only one connecting-rod is attached; all the other connecting-rods work on pins let into the big end of that connecting-rod. The cylinders revolve round the fixed crank in the manner of the well known engines first introduced to practice by Mr John Rigg. The explosive mixture is led from the carburettor through the hollow crank-shaft into the crank-case, and it is admitted into the cylinders by means of automatic inlet valves placed in the heads of the pistons. The exhaust valves are arranged on the cylinder heads. Dual ignition is provided by high tension magneto and storage battery and coil. The cylinders are ribbed outside like the Anzani, and are very effectively air-cooled by their rotation through the air as well as by the passage of the aeroplane through the atmosphere. The cylinders in the 35 H.P. motor are no mm. bore X 120 mm. stroke. The speed of rotation is usually 1200 revolutions per minute. The total weight of the engine complete is 180 lb, or just over 5 lb per brake horse-power. The subject of aeroplane petrol engines is a most interesting one, and rapid progress is being made.
So far, only 4-cycle engines have been described, and they are almost universal for use in motor-cars and aeroplanes. Some motor cars, however, use 2-cycle engines. Several types follow the "Clerk" cycle (see Gas Engine) and others the "Day" cycle. In America the Day cycle is very popular for motor
Fig. 8.
launches, as the engine is of a very simple, easily managed kind. At present, however, the two-cycle engine has made but little way in motor car or aeroplane work. It is capable of great development and the attention given to it is increasing.
So far, petrol has been alluded to as the main liquid fuel for these motors. Other hydrocarbons have also been used; benzol, for example, obtained from gas tar is used to some extent, and alcohol has been applied to a considerable extent both for stationary and locomotive engines. Alcohol, however, has not been entirely successful. The amount of heat obtained for a given monetary expenditure is only about half that obtained by means of petrol. On the continent of Europe, however, alcohol motors have been considerably used for public vehicles.
The majority of petrol motors are provided with water jackets around their cylinders and combustion spaces. As only a small quantity of water can be carried, it is necessary to cool the water as fast as it becomes hot. For this purpose radiators of various constructions are applied. Generally a pump is used to produce a forced circulation, discharging the hot water from the engine jackets through the radiator and returning the cooled water to the jackets at another place. The radiators consist in some cases of fine tubes covered with projecting fins or gills; the motion of the car forces air over the exterior of those surfaces and is assisted by the operation of a powerful fan driven from the engine. A favourite form of radiator consists of numerous small tubes set into a casing and arranged somewhat Like a steam engine condenser. Water is forced by the pump round these tubes, and air passes from the atmosphere through them. This type of radiator is sometimes known as the "honeycomb"
