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).
Performance of Standard Watford magnetos, comparing flat cams with long cams.
| Identifier | ExFiles\Box 48\2\ Scan350 | |
| Date | 27th January 1926 | |
| To Wd. {Mr Wood / Mr Whitehead} from EFC. {E. Fowler Clarke - Electrical Engineer} c. BY. {R.W. Bailey - Chief Engineer} EP. {G. Eric Platford - Chief Quality Engineer} X8796 EFC {E. Fowler Clarke - Electrical Engineer} 3/T27.1.26. X.8796 - STANDARD WATFORD MAGNETOS. It would be interesting to know why the Watford Magneto Co. fit the magnetos which they supply to us with flat cams on the contact breaker. Flat cams are cheaper to make, but on electrical principle they do not result in such correct performance. With a long period of make of the contact breaker, such as is provided with flat cams, the instant of making contact is too early, finding as it does, the armature core flux being built up to the maximum previous to being withdrawn. This results in an E.M.F. in the windings which sets up a reverse current, which current has to be reversed to the right direction by the positive E.M.F. which follows later while the flux is being withdrawn. This will not make a great deal of difference at low speed because there is time for these changes to take place. Hence the low speed sparking of the Watford magneto (which in any case is good as a result of using the sleeve) is not seriously affected by this argument. It is, however, a matter of experimental observation that we never do get such good results in high speed sparking on the Watford magneto as we get on magnetos with long cams, such, for instance, as the Lucas, B.T.H. and Simms magnetos which we are at present testing. Contd. | ||