From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Page from an automotive engineering journal comparing battery versus magneto ignition systems, and detailing distributor designs.
| Identifier | ExFiles\Box 37\1\ scan 169 | |
| Date | 1st July 1927 | |
| Vol. XXI July, 1927 No. 1 38 THE JOURNAL OF THE SOCIETY OF AUTOMOTIVE ENGINEERS vacuum-drying at 250 deg. fahr. and revarnishing the exterior (3) Upper rotor-shaft bearing replaced with new bearing having integral oil-retaining washer (4) Bakelite coil-housing and aluminum distributor-cup replaced with new parts accurately machined to assure concentric distributor track (5) Suitable oil-drain holes provided to remove the excess oil (6) Fire-proof vent-holes in distributor cup These changes have virtually eliminated troubles from carbon on the track and oil leakage. Four distributors were run on the bench for 350 hr. without attention and no “tracking” was experienced. Service tests in flight have shown a similar freedom from carbon troubles. The only new designs have been a magneto-replacement unit for a nine-cylinder radial engine, shown in Figs. 13 and 14, and an ignition distributor for 12-cylinder 60-deg. V-type engines, shown in Fig. 15. The magneto-replacement unit has two breakers, two coils and a double 18-point air-gap distributor. The spark-advance is adjusted by advancing the cam through a spiral slot in the driving-shaft. The entire unit is enclosed for radio shielding. Although somewhat bulky, on account of using the standard parts available at the time, the unit has given practically no trouble. This was an emergency magneto-replacement unit and will not be continued. The 12-cylinder 60-deg. V-type distributor, shown in Fig. 15, was developed to meet the requirement for a light compact high-speed battery-ignition system for engines in airplanes that carry other electrical equipment requiring a generator and battery. The particular type shown was designed for driving from the camshaft drive-shaft-housings on the Packard 1500 and 2500 engines. Following are the principal design features: (1) Twelve-lobe cam with double breakers (2) Air-gap distributor (3) Separate ignition-coils This type of distributor has given satisfactory service and can be adapted to different engines without difficulty. BATTERY VERSUS MAGNETO IGNITION The old controversy between battery and magneto ignition is no nearer a solution than ever; in fact, it is like Lincoln's silk hats: “They mutually excel each other.” The following brief statements outline the situation as regards their application to aircraft engines, no attempt being made to draw conclusions: (1) No evidence indicates that the spark-plugs know where the sparks come from; therefore, one good spark is equal to another good spark (2) Thousands of engines are operating satisfactorily on magneto and on battery ignition-systems (3) When electrical equipment is required for radio or lights, the battery ignition-system should not be charged with any of the battery or generator weight, as this cannot be reduced by using magnetos. Therefore battery ignition is lighter than magneto ignition as now available (4) When radio shielding is required, the additional shielding of the generator and of the lighting circuits, required with battery ignition, may offset the additional weight of magneto ignition (5) The sparking rates of high-speed multiple-cylinder engines are approaching the limits obtainable from present-type battery ignition-coil operating at from 12 to 15 volts. The speed limitations of magneto ignition are principally mechanical and are not likely to be reached soon (6) Battery ignition does not require a hand-starting magneto (7) The sparking ability of a magneto is not dependent on a battery and therefore is not affected by long periods of storage or idleness (8) A battery ignition-system is cheaper than a magneto system This list can be added to indefinitely, but the above considerations are enough to show that the choice between battery and magneto ignition depends almost entirely on factors aside from that of spark intensity, which is the usual subject of controversy. The following tabulation gives the weights of several battery and magneto ignition-systems on different types of engine. In some cases the weights of both battery and magneto systems are given for the same engine, thus affording direct comparison. For those who insist that battery ignition be charged with a part of the generator and battery weight in proportion to the ratio of the average ignition current to FIG. 14—DELCO DISTRIBUTOR WITH SHIELD REMOVED The Assembly Includes Two Coils, Two Contact-Breakers and a Double 18-Point Air-Gap Distributor. The Spark-Advance Is Adjusted by Advancing the Cam through a Spiral Slot in the Driving-Shaft | ||