with a series of vertical strips which give the effect of the conventional honey-comb cooler. When water is circulated in large passages there is no retarding effect offered by the friction of the tubing walls and as the passages are direct they are not liable to become clogged with rust or other foreign matter in the water. The disadvantages of the large water passages are that a greater volume of water is needed on account of the reduced cooling effect. When water is spread out in thin sheets it is easy to cool the entire mass but when

Fig. 141.-Sectional View of Flat Tube Radiator Showing Large Water Spaces Provided by this Construction.

it passes through tubes of large bore only the outside of the column of water is exposed to the cool walls of the metal tube and the inner core remains warm. Water coolers having large tubes are better adapted for the natural or thermo-syphon cooling systems.

Q. How is air circulated through radiators?

A. The usual method of supplying a stream of air is to use some form of simple fan placed immediately back of the radiator to draw the air through the spaces between the tubes while in those forms

where the radiator is carried at the rear of the hood, as shown at Fig. 138, a fan blade flywheel is often employed to produce the air draft.

Q. How are various members of the cooling system coupled together?

A. As is clearly outlined at Fig. 134 the various members of a cooling system are joined together by means of rubber and metal piping. Metal pipe is used at all points where the members are held rigid and are not liable to vibrate, while rubber hose joins two members which are liable to have motion relative to each other. For instance, in practically all cars the radiator is joined to the water jackets at the motor top and to the circulating pump by means of flexible non-metallic conductors. If metal pipe is used, the vibration is apt to crystallize it or open the joints.

Q. How are tight joints insured with the various forms of pipe?

A. Water conductors of metal are usually provided with flanged fittings which join them to the water jackets and other parts, and a tight joint is insured by interposing a gasket or packing member which is tightly squeezed between the pipe flange and the member to which it is connected and thus forms an effective seal to prevent leakage of water. In some constructions the ends of the metal pipe are pushed into a suitable opening made to receive them and a tight joint is insured by a packing gland and hemp wicking. Tight joints may be made with rubber hose by using the regular form of hose clamps which constrict around the hose and bring it in firm contact with the pipe over which it is slipped.

Q. Name two methods of constructing water manifolds.

A. Water manifolds may be cast in one piece or may be built up of various cast fittings and lengths of tubing joined together by a brazing or soldering process.

Q. Why are built-up metal manifolds preferable to cast manifolds?

A. The usual form of cast manifold unless of very large volume has rough interior walls that are apt to impede the flow of water

and that also encourage the accumulation of foreign matter because projecting particles of metal serve as anchorage points. In a builtup manifold the castings are usually so small that one has no difficulty in cleaning them out thoroughly and all roughness of interior walls may be removed. The tubing has smooth walls and with a properly built-up manifold one provides a conductor for the cooling liquid having minimum internal resistance.

Fig. 142.—Outlining Method of Driving Radiator Cooling Fan. A-By Flat Belt. B-By Enclosed Shaft and Gearing.

Q. Name the various forms of air circulating fans.

A. Air fans may be of three main types. The most common form is a six blade fan having the blades inclined to such an angle that they draw in an air current through the radiator. Another type made in two or three blades is based more on the lines of the propellers used in marine and aeroplane service. The third type is formed ntegral with the flywheel and may consist of spokes having fan blade curvature and angular disposition or may be a series of blades fastened to the flywheel periphery.

Q. How are circulating fans driven?

A. Air circulating fans may be driven by positive or flexible means depending upon the preferences of the designer. Fans have been operated by positive gearing, such as bevel, spur and spiral gears, or silent chains and by flexible gearing, such as round steel wire or leather belts and flat and V leather belt. When positive gearing is employed in connection with the usual form of built-up fan it is customary to interpose some form of slipping drive between the fan hub and the gearing in order to relieve the fan of any sudden jerks which might result in throwing off a fan blade when the motor is started or stopped suddenly or when accelerated too quickly. When flexible driving means such as belts are used some form of automatic belt tension regulator is included in the design in order to keep the belt tight and insure positive drive. The flat belt is widely used on account of its simplicity and cheapness, while a V belt is utilized by some designers because it will furnish more positive drive than the flat belt and its tension does not have to be so carefully regulated. A V belt will drive when loose, whereas the flat belt is apt to slip under the same conditions.

LESSON FIFTEEN

USE OF CLUTCH AND VARIOUS TYPES DESCRIBED

Q. What is the clutch and where is it generally placed?

A. The clutch is used to transmit power from the engine to the gearset and is a form of drive coupling that may be released when it is desired to allow the power generating and energy transmitting members to run independently of each other. A typical power plant, clutch, and gearset assembly is outlined at Fig. 143 with all parts clearly indicated. The power generated by the explosion of the gas against the pistons of the motor imparts a rotary movement to the crankshaft, and from thence to the flywheel which is rigidly connected thereto. The motor flywheel serves as one member of the clutch and is machined with a taper into which the cone or male member of the clutch fits. The cone is held in frictional contact with the flywheel rim by a spring and when the parts are in the positions indicated practically the full power delivered to the engine crankshaft will be transmitted through the clutch cone to the clutch shaft which is joined to the main shaft of the gearset by a positive drive coupling. If the cone is pulled away from the flywheel rim by means of the clutch release pedal provided for the purpose, the engine crankshaft may run independently of the gearset.

Q. Why is a clutch needed with a gas engine and not with a steam or electric motor?

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A. A steam or electric motor may be started under load because the real motive power, which is steam or electricity, as the case may be is under pressure in a suitable container and this working medium may be directed to the power plant and sets it in motion against its load. In order to get a start it is possible to supply an excess of