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).
Modification and testing of Watford IS.12 magnetos, comparing them to B.T.H. magnetos.
| Identifier | ExFiles\Box 43\4\ Scan254 | |
| Date | 26th February 1930 | |
| X4021. To EP.{G. Eric Platford - Chief Quality Engineer} from EFC. c. Rg.{Mr Rowledge} EFC2/AD26.2.30. X.4021. WATFORD IS.12. MAGNETOS NOS. 98033/4. In these two magnetos at present in your hands on Type test we increased the H.T. safety gap from 7.7 mm. to 8.5 mm. we considered it advisable to do this in view of the fact that there was a tendency on bench test for the H.T. discharges to take the alternative safety gap route instead of the 5.5 mm. test gap. We have pointed out to Messrs. North the fact that the length and correspondingly the spark over voltage of the safety gaps was not in accordance with our General Specification of magneto requirements for aero engines as in the case of the B.T.H. magnetos which satisfy our requirements in this respect. NB. On actual test we have obtained the following figures :- B.T.H. H.T. safety gap 8.6 mm. and sparking over voltage 12,500 Watford. H.T. safety gap 7.7 mm. and sparking over voltage 10,000 After making the change of safety gap on these Watford magnetos we found that the missing in the sparking on bench test was thereby cured. It was understood from Mr. Allen of Messrs. North that Farnborough were in agreement with the 7.7 mm. gap - therefore the alteration, which is not disagreed to by Messrs. North comprises a feature on Type test of these magnetos which has so far not been officially approved. We desire an opportunity of inspecting these machines after completion of the Type test. EFC. | ||