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).
Experimental work testing the effect of an external gap on magneto and coil sparking performance.
| Identifier | ExFiles\Box 37\1\ scan 144 | |
| Date | 8th March 1923 guessed | |
| -2- Contd. It appears that with the leak at its present value, the test is reasonable for the magneto, and also for the coil on 12 volts, but rather severe for the coil on 8 volts. During some preliminary experimental work, it was found that an external gap had a very marked effect on the sparking at the standard gap, when the latter was shunted by the leak. Further tests showed that with condition 2 in each case above, and the addition of an external gap the results were as follows :- Condition 3. Gap, shunted by leak, but with external gap. Regular sparking obtained at :- Magneto 90 r.p.m. B coil (8 V) 960 r.p.m. As will be seen, the effect of the external gap, is to practically neutralise that of the leak in the case of the magneto, and considerably raise the working speed of the coil. It was also found that the external gap, to function under the worst conditions, had to be of a size within certain limits. For the magneto the maximum and minimum of the gap were 3.3 mm. and 2.7 mm. and for the coil they were 6.0 and 5.0 respectively. This, added to the fact that there is no appreciable difference in effect between an external gap close to the sparking gap and one close to the distributor terminals, suggests that a jump spark distributor would serve the same purpose providing the gap between rotor and tip and spark point CAP. | ||