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Q. Describe air cooling by flywheel suction.

A. The system of air cooling employed on Franklin motor cars is typical of the method of inducing air current by flywheel suction. This power plant is shown at Fig. 129 and the path of the air currents can be readily ascertained by following the arrows indicated. The motor is carried in a practically air tight compartment, except for an opening at the front end of the hood, and the only way air entering may escape is through the rear end of the motor compartment. The flywheel is a special form having a series of curved blades which have a suction effect as they revolve and

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Fig. 130.-Air-Cooled Motor Having Fourteen Revolving Cylinders

Used for Aeroplane Propulsion.

cy inder.

tend to exhaust the air from the motor compartment. During the entire period of time the engine is in operation the flywheel produces a partial vacuum in the motor compartment by its pronounced draught creating properties and cool fresh air is constantly entering through the front of the hood to replace the warm air drawn out by the blower flywheel. Before the entering air can leave the motor compartment it must pass through sheet metal jackets which surround the cylinders and as it brushes by the vertical radiating flanges it becomes heated and the surplus heat is thus taken from the

A similar system used successfully on the Chase motor truck is outlined at Fig. 129A.

Q. Describe blower system of air cooling.

A. Air cooled cylinders are sometimes cocled by a blast of air directed against them by a pressure blower, as shown at Fig. 128, instead of a suction fan. This form of blower draws in a cool air current and forces it against the cylinders through a suitable air pipe which is connected to an air jacket surrounding the cylinders.

Q. What are the advantages of air cooling?

A. Besides being more efficient as regards fuel consumption an air cooled engine may be operated under conditions of extremely low temperature that would interfere seriously with the operation of water-cooled cars. During cold weather it is necessary to fill the radiators of water-cooled cars with anti-freezing compounds which require constant attention and which in some cases are actually harmful to the various components of the cooling system. An air-cooled motor will work as well in cold weather as it will during the warmer season and there is no necessity of making any changes in the cooling systems to provide for lower temperatures.

Q. What are the defects of air cooling?

A. One of the main defects of air-cooled motors, as heretofore constructed, has been the necessity of careful driving and intelligent lubrication and mixture adjustment. The air-cooled motor is not as suitable a form for general use as the water-cooled type because it becomes overheated under certain conditions of abuse, where the overheating of a water-cooled engine under similar con

ditions would not be so apparent on account of the greater capacity of a water-cooling system to absorb heat. When used under conditions of overload or maximum power generation for extended periods, the air-cooled engine is not as suitable as the water-cooled type.

Q. Where is air cooling particularly desirable?

A. Air-cooled engines are widely applied as power plants where maximum simplicity and lightness for a certain horse power are essential.

Q. Where are air cooled enrines widely used?

A. Air-cooled engines have been almost universally applied to motorcycle propulsion, have been used extensively as light port able power plants for farm use and have also received some appli cation in aeroplane service.

LESSON FOURTEEN

TYPICAL WATER COOLING SYSTEMS

Q. What is the common method of cooling by water?

A. In usual water cooling systems the cylinder is provided with a water jacket which is kept constantly filled with water, this passing out of the jacket when it becomes heated and returning again when it has been cooled by external means.

Q. Name the two systems of water cooling.

A. There are two common methods of cooling by water, the simplest of these being the thermo-syphon or natural system; the other is the pump circulat on method.

Q. How does the thermo-syphon system operate?

A. The conventional arrangement of parts of a thermo-syphon cooling system is outlined at Fig. 131. A radiator or water container supplies water to the lower portion of the water jacket by means of a manifold pipe and after the water becomes heated it passes out of the top of the water jacket, through another manifold to the top of the radiator. The circulation is maintained by a natural law that hot water being lighter than cool water will rise and be replaced by water at lower temperature. In the system outlined the heated water from the engine passes through the radiator and is cooled and falls to the bottom of the radiator where it is again conducted to the bottom of the cylinder. Circulation is maintained automatically as long as the engine is in operation and the radiator is filled with water.

Another method of cooling by the thermo-syphon system, in which the radiator is carried at the back of the power plant instead of at the front end, is shown at Fig. 132. The principal parts consist of a radiator, which serves as a water cooler and storage tank,

a centrifugal fan member to draw air through the radiator, and suitble pipes to connect the water jacket with the upper and lower portions of the radiator respectively.

Q. What precautions are necessary to successfully use thermo-syphon cooling?

A. Where the water is circulated by natural means it is necessary to have a radiator of large capacity and also large water jackets and manifold pipes as circulation due to the heating and cooling of water is more sluggish than in systems where a pump is employed.

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Fig. 131.-Illustraíing Action of Simple Thermo-Syphon Water-Cool

ing System.

Thus large water passages are necessary so the flow of liquid will not be impeded by small water spaces or resistance of small bore water pipes.

Q. What are the advantages of the forced circulation method?

A. When a pump is employed to circulate liquid, as shown at Fig. 133, the cooling system may be made lighter because less water is needed in the radiator and the water pipes and water spaces around the cylinders may be made smaller. The pump is driven by mechanical connection with the engine crankshaft and as the speed

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