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).
Magneto sparking performance, comparing different models and the effect of long cams.
| Identifier | ExFiles\Box 48\2\ Scan351 | |
| Date | 27th January 1926 | |
| Contd. -2- EFC {E. Fowler Clarke - Electrical Engineer} 3/T27.1.26. It is quite a definite fact that these other magnetos will spark very much more readily a given set of ordinary gaps, or on leaky gaps, at higher speeds than the standard Watford. The low speed sparking will not be adversely affected by fitting long cams. As we have already remarked, the low speed sparking characteristics would not be seriously affected either one way or the other, owing to the time available for the current to build up, though one feels there might be some little effect at the very slow speeds, where every little bit may make a difference. That is to say, if there is any difference at all, it would certainly be in a direction of giving rather better low speed performance with the longer cams than with the shorter. On electrical principle, the correct time to make contact is at the instant when the armature is in the position in which it would be statically held by the flux. But owing to the fact that the rate of change of flux on either side of this point is not rapid, a variation within ± 10° or so is not of much consequence. This consideration is further simplified in the Watford magneto by the use of the sleeve, because it is approximately the case that the movement of the sleeve is equivalent to a rotation of the whole magnet system Contd. | ||