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 curves and firing speeds for three types of magnetos.
| Identifier | WestWitteringFiles\F\March1921\ Scan58 | |
| Date | 31th March 1921 | |
| To R.{Sir Henry Royce} & E.{Mr Elliott - Chief Engineer} from EFC. c. to CJ. & PN.{Mr Northey} c. to By.{R.W. Bailey - Chief Engineer} & Bn.{W.O. Bentley / Mr Barrington} c. to Da.{Bernard Day - Chassis Design} & EP.{G. Eric Platford - Chief Quality Engineer} c. to EWT. for R.R.Inc. ORIGINAL. EFC5/T31.3.21. X. 3723 X. 3515 X. 4210 X.430. MAGNETOS- GENERAL. Referring to our EFC5/T21.3.21 we now attach open circuit volt-speed curves and short circuit ampere-speed curves of three magnetos - (1) Dixie Aero 648. (2) B.T.H. type F.M.6. (3) Conner " C.M.1. which may be compared with similar curves already issued for the Bosch and Watford magnetos. Of these three magnetos, the Conner C.M.1. has given a favourable impression and we must make enquiries as to the possibility of purchasing this to considerable advantage as suggested in your R2/G24.3.21. Please find attached, as promised, table of lowest speeds for regular firing on 5.5 mm. gaps in air. The range between advance and retard has been 34° in all cases (with one exception), this range having been chosen in every case to give the best low speed sparking result at retard consistent with satisfactory high speed sparking at advance, and also differs from the variable maker's ranges in respects of which the details are given in the remarks column. In some cases, e.g. Conner and Watford E.O.6b owing to the slow sparking speed being lower in the retarded position than in the advanced, the 34° range was selected from Contd... | ||