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).
Results of performance tests on 12-cylinder, four-spark-per-revolution magnetos for an F engine, noting multiple specification failures.
| Identifier | WestWitteringFiles\V\2January1931-April1931\ Scan059 | |
| Date | 3rd March 1931 | |
| -2- EFC5/AM3.3.31. contd. breaker at different speeds and observing the average current indicated on the moving coil ammeter. A blue print copy of the result is attached which shews up the Scintilla contact breaker very badly in comparison with the B.T.H. It would appear that the designers have not given sufficient attention to this all important matter. Both magnetos have been put through tests in accordance with our general specification of performance of 12 cylinder four spark per revolution magnetos for F.{Mr Friese} engine. It was found that these magnetos did not pass this general specification in several items. The results of these tests quoted under correspondingly numbered paragraphs to those of our general specification, have been reported in my assistant's report No.85 as follows :- * (3) The total range is only 27º N.B. The specification calls for 30º ± 1º (4) (a) On the endurance test occasional misfiring on the test gaps was traced to sparking over inside the magnetos. This we consider, is due to the air inside being strongly ionized, no ventilation for the armature or jump spark distributer being apparent. (4) The magnetos would not spark at all at any speed or in any position of the contact breaker lever on the standard leaky test gap. (6) During the high speed test on magneto No.207577 the contact breaker suddenly began to be erratic in action causing misfiring to occur at speeds in excess of 3500 r.p.m. This was found to be due to the short spring supporting the main contact lever spring having fractured. The tests on this magneto were thus prematurely terminated. The maximum regular sparking speed of the other magneto No.207580 was found to be 4800 r.p.m. N.B. The specification calls for a maximum speed of 4500 r.p.m. in the fully advanced positi | ||