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).
Comparison of Rotax and Bosch machine performance, focusing on field winding resistance and output curves.
| Identifier | WestWitteringFiles\F\March1921\ Scan41 | |
| Date | 17th March 1921 | |
| Contd. -2- EFC3/T17.3.21. remember that other machines have been compared for heating on the output mentioned above. It would appear that the field winding of the Rotax is unnecessarily low in resistance, and we think it would be better generally, and render the curve more nearly equal to that of our specified performance, if this field winding were made suitable for a somewhat higher voltage, so that the curve would be more or less shifted to the right, i.e. to higher speeds, and made to coincide more nearly with our specified performance. The cold resistance of the field winding is only 1.81 ohms which is very low compared with other machines, the U.S.A. Bosch for instance being 5.5 ohms. We might be able to approximate this other condition by inserting additional resistance in the field winding, except that this would not be quite fair to the machine, as some of the field watts would then be ineffective in producing ampere turns. Corresponding curves for cold condition are more peaky at the maximum, as already illustrated on our previously issued curves which you have. Some time ago we carried out comparative heating tests of Rotax A.T.12 and U.S.A. Bosch machines, in each case with the control at makers' setting, but with speed continually adjusted to secure maximum output, and the results of these tests are given on first sheet attached. Contd. | ||