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).
Letter from North & Sons Ltd. discussing the technical difficulties of improving magneto efficiency and advance range.
| Identifier | ExFiles\Box 48\2\ Scan429 | |
| Date | 10th February 1926 | |
| COPY OF LETTER FROM:- NORTH & SONS LIMITED. WHIPPENDELL ROAD, WATFORD. Your Ref. Wd {Mr Wood / Mr Whitehead} 7/NJ1226. Our Ref. CHK/HC.8. 10th February 1926. Dict. 9th February. Messrs. Rolls-Royce Ltd., DERBY. Dear Sirs, We thank you for your letter of the 1st inst., with copy of report EFC {E. Fowler Clarke - Electrical Engineer} 3/T27.1.26. We are quite in agreement with the view that the electrical efficiency of a magneto can be improved by fitting longer cams than those which are used in our Model E.O.6 magneto. We think however that we are right in assuming that neither of the magnetos mentioned in this report give a range of advance of 60°. The difficulty with regard to fitting cams which maintain the break through a longer angle is that throughout this angle the distributor brush must be in contact with the segment. With a movement of 60° the distributor brush in the E.O.6 magneto is only on the segment at each end sufficiently far to be safe, while the amount of insulation between the segments cannot be reduced. Therefore to make a machine with a longer period of breaking and at the same time to retain the angle of advance of 60° it would be necessary for the machine to be considerably larger in order that the angle of the segments could be increased while at the same time the smaller angle which remained for the insulation gave the same thickness of insulation as at present. With regard to the suggestion that an improvement would be made by making the break 15 to 20° later we beg to say that in our view this alteration would very seriously affect the low speed performance, and that, a spark always occurring in what is effectively a retarded position, even with the magneto running at high speed with the spark fully advanced, would result in excessive sparking between the platinum points and thus reduce the life of the points quite appreciably. - contd - | ||