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 loss on a Watford E.6 magneto caused by its securing strap short-circuiting the magnetic flux.
| Identifier | WestWitteringFiles\F\May1921\ Scan46 | |
| Date | 10th May 1921 | |
| To R & E.{Mr Elliott - Chief Engineer} from EFC. c. CJ c. EWH. for R.R.Inc. c. Ry. c. Da.{Bernard Day - Chassis Design} c. EP.{G. Eric Platford - Chief Quality Engineer} ORIGINAL EFC4/T10.5.21. X.3630 - MAGNETO WITH SLOPING BASE. Mr. Olley has suggested that the strap used to secure the magneto on the sloping base short circuits an appreciable proportion of the magnetic flux of the magneto, and they believe they have detected considerable evidence of this defect. In order to decide whether the effect was appreciable, we have compared the performances of a standard Watford E.6 magneto, with and without the strap, on - (1) Open circuit voltage & (2) Short circuit amperes (3) Low sparking speeds on 5.5 mm. gaps in air, and in each case we have been able to appreciate the loss of flux due to the strap. (1) We find there to be nearly 5% lost open circuit volts. (2) We find there to be approximately 3% lost short circuit amperes. (3) On the low speed sparking tests with 5.5 mm. gaps in air, we find the greatest effect to occur at retard, the speed for regular firing without the strap being in one instance 302 r.p.m. and 330 r.p.m. with the strap, showing a difference in the speed of 10%. The differences of other positions of advance are proportionately less as the advance increases, until at full advance the difference is very small. The matter of re-arranging this item to overcome this defect has been taken up verbally with Ry. EFC. | ||