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Aviation History
1917
1917 - 0136.PDF
FEBRUARY 8, 19171 AN INTERESTING' CONTACT BREAKER FOR MAGNETOS. OF all the many causes to which engine failure can be traced,ignition troubles are by no means the least frequent. Some- times the trouble is found in sooted-up sparking plugs or inleaky connections, but in a good many cases the cause is to be found in the magneto itself. This is, perhaps, more fre-quently the case with the magnetos of seaplane engines, owing to the always present possibility of sea-water gettinginto the magnetq. One source of trouble often met with in magnetos in which the pivot for the bell-crank lever is sup-ported in a fibre bush, is that, when water gets into the contact breaker, t\e bush expands and may do so to such an extentthat the bell-crank lever becomes inoperative, owing to seizure. It was with a view to obviate this trouble, amongothers, that the contact breaker illustrated in the accom- panying sketches was thought out. In its present form thenew contact breaker—which was designed by Mr. G. F. Cooke, of 2, Fairfax Road, Bedford Park, W.—is the resultof many experiments, and in several trial runs with one of these contact breakers some excellent results were obtained,and Mr. Cooke—who, in a long association with the Bosch firm has had a great deal of experience in magneto work—isconfident that his invention in its present form will be found thoroughly reliable for all classes of work. The Cooke contact breaker has, as will be seen from aninspection of the accompanying illustrations, a phosphor At the bottom the moving contact is given a curvedsurface, at the lowest point of which is inserted a small pad of fibre in order to reduce wear and noise. Fitting intorecesses near the lower end of the moving contact are two flat steel springs, resting in grooves in the base and securedat their other end by screws. These springs ensure the positive return of the moving contact. The fixed contact is formed by a piece of phosphor bronzeof the shape shown in the sketch, and insulated from the base by the mica packing. It has three holes—one conical toreceive the large screw that secures the whole contact breaker, one for the smaller fixing screw at the bottom end, anda third hole tapped to receive the platinum-tipped contact point. A transverse slot in the fixed contact enables thecontact point to be locked in position by simply tightening up the centre screw. In order to adjust the distance betweenthe contact points, a small spanner, shown in the illustration, is employed. A small inspection window is provided in thebase, through which the distance between the contact points can be ascertained. For purposes of inspection all that isnecessary in order to remove the contact breaker is to un- screw the large central screw, when the whole base comesaway bodily, and the contact points can be inspecte'd and adjusted. If further examination is desired the wholecontact breaker is dismantled by unscrewing the small screw — PHOSPHOR RRQNZL BASE. ST[/l UUCP Details of the Cooke contact breaker for magnetos. bronze base machined to the shape shown. Into the forwardprojections of this base is driven a steel liner, forming one of the bearing surfaces for the ball-bearings of the movingportion of the.contact breaker. The second bearing surface is formed by the contact breaker itself, which is of steel andshaped as shown. A ball cage of phosphor bronze or brass, bent as shown in the sketch, retains the six balls, three oneach side, which are accommodated in slots in order to allow for the travel of the moving contact. In bending the ballcage the metal is not pressed into close contact, a small space, which can be seen in the sketch, being left betweenthe two surfaces. This space serves as a reservoir for lubricant, which is held therein by capillary attraction. in the fixed contact and the two screws securing the leafsprings. The fixed contact can then be removed and the moving contact slipped out of its bearings. Being guidedby the ball race the moving contact, on being inserted, is always in line with the fixed contact, and the only adjust-ment ever necessary is that of the distance between the contact points. From the mechanical point of view the Gooke contactbreaker appears to be a thoroughly sound piece of work, positive in its action, and with no parts likely to get out oforder even under the most trying conditions. It is, we understand, easily fitted to any Bosch type of magneto,and should recommend itself for a thorough trial. French Honour for Greek Officer. GENERAL SARRAIL has awarded the Croix de Guerre with Palms to Major Verikios, an officer of the Greek Army of National Defence, for distinguished service in the air. A French Farmer's Capture. DETAILS have reached Paris of how two German aviators •were captured by a farmer the other day in Normandy in a field in the Eure Department. It appears that the farmer, whose eldest son had been killed in the war, was in his field with a gun. and the two German officers, one of whom hadthe inevitable Iron Cross, put up their arms and surrendered. They said they were dying of hunger, and on being given a4-Ib. loaf of bread ate it heartily. They explained afterwards that they had flown over Amiens, anti-aircraft guns scoreda hit on their motor, and then they lost their way, and after wandering about for some time their engine stopped, andthey had to come down. They did not appear very sorry t» be taken prisoners. 136
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