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).
Instrument gear ratios and the adoption of a non-proportional speed scale for a Phantom chassis.
| Identifier | ExFiles\Box 59\2\ Scan118 | |
| Date | 24th March 1931 | |
| EEM/AD24.3.31 contd. -3- It will be understood that this lower figure represents a compromise largely arising out of the fact that the present standard speed scale is proportional and that in order not too greatly to lower the speed readings at the high speeds and at the same time to keep the instrument reasonably correct within itself i.e. unfaked, this lower figure for the revolutions per mile of the instrument was necessary. The adoption of a non-proportional scale not only alters the whole aspect of the matter but at the same time gives us a correctly arranged instrument for the purpose and one that can quite reasonably be considered to be scientifically arranged and entirely unfaked. If it is impossible to have an instrument internally geared for 816 revolutions per mile and it were possible to alter the gear ratio of the drive, then it would be necessary to retain the ratio of the instrument figure to the gear ratio in the proportion of 816 / 1,346 = 606 = 616 x 44.27 / 45.00 We are writing to the A.T. Co. to see whether 816 is a possible figure for these instruments. The specification of an instrument to give satisfactory allround results on a Phantom chassis will now be seen to be as follows :- (1) The instrument arranged to register one counter mile for every 816 revolutions of its driving spindle. (2) The instrument must be provided with a contracted speed scale contracted in accordance with the table given on page 10 of our notes and as therein specifically described. | ||