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 and road test report regarding the standardisation of a half-inch longer ignition coil in a stabalite case.
| Identifier | ExFiles\Box 45\4\ Scan180 | |
| Date | 24th July 1923 | |
| (Expl. & Road Test Report to accompany standardisation sheet). x4079 X4596 HALF INCH LONGER IGNITION COIL IN STABALITE CASE. X445 x4079 The present proposal is to standardise a combination of two items (coil and case) each of which is known to be separately satisfactory from numerous bench and road tests. The present standard coil, both for the 40/50 and 20 H.P. chassis consists of an original size coil in a stabalite case. No suggestion of trouble due to the material of the case has ever been experienced but there have been a few failures, all of which have been clearly due to the restricted space available for primary insulation, (in this connection see our EFC2/T29.1.23, R6/M29.1.23 and R5/M31.1.23). With a view to overcoming this, coils have been made half an inch longer. This has allowed a four-layer in place of a six-layer primary to be used, the wire used being enamelled and cotton covered, in place of double silk covered. Experimental coils of this type have been made up in mouldensite and latterly in Redmanol cases. Mouldensite cases for the original (short) coils were definitely unsatisfactory at the high temperatures reached, owing to the peculiar properties of this material, which allowed leakage and dielectric hysteresis loss to take place. The longer coils in mouldensite cases, though considerably better, have not shown themselves to be absolutely immune from this effect, but latterly cases (for longer coils) have been made in Redmanol, and five such coils are at present on test on experimental cars. Though no suggestion of failure has so far been experienced in the case of this material, so that possibly this may be suitable for ultimate standardisation, at the moment there is not sufficient evidence of perfect satisfaction to warrant the standardisation of this combination. On the other hand, no failures have been experienced with the longer coils of the nature of breakdown of the primary winding, it having been experienced on several occasions both with the short and longer coils, that the substitution of stabalite for mouldensite cases has caused the trouble at high temperatures to disappear. Apart from failures due to material of the case, longer coils of the type proposed for standard have done the following mileages without breakdown:- Contd. | ||