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).
The insulation testing of Watford Aero Magnetos and safety gap settings.
| Identifier | ExFiles\Box 43\4\ Scan282 | |
| Date | 14th May 1930 | |
| X4021 WE.23. 14.5.30. X.4021. X.4513W. WATFORD AERO MAGNETOS. It will be remembered that the Watford IS.12 magnetos Nos.98033/4 on the recent "F" engine type test were run with the safety gap set at 8.5 mm. instead of 7.7 mm. as specified or passed by Farnborough R.A.E. Objection was raised at the time by our own A.I.D. that as the safety gap was not operating during the type test it was not a fair test on the insulation of the H.T. secondary circuit. We have therefore carried out a 100 hour test on a similar magneto No.83132 with the distributor open circuit and the H.T. discharges passing across the safety gap continuously, the gap being set at 8.5 mm. to test the insulation of the armature etc. This test has now been completed OK. thus demonstrating that the armature insulation will stand up to the possible increased voltage conditions. The only weak place elsewhere on the H.T. circuit is the insulation of the H.T. rotor and fan. At the beginning of the test we had to replace these units due to a breakdown occurring along the surface of the rotor spindle insulation through the bakelite fan to the frame. Are we now doing anything further to ensure that all aero magnetos delivered to us shall have safety gaps set to a minimum of 8.5mm? This magneto now requires returning to Messrs. North for examination and overhaul we presume at R.R. expense. EFC/HEW. | ||