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).
Speedometer calibration issues for the Phantom model and updating the instrument specifications.
| Identifier | ExFiles\Box 59\2\ Scan135 | |
| Date | 1st April 1931 | |
| By.{R.W. Bailey - Chief Engineer} from EFC. c. PN.{Mr Northey} C. c. Wor.{Arthur Wormald - General Works Manager} Hs.{Lord Ernest Hives - Chair} X6051. EFC2/ADL.4.31. X.6051. A.T. SPEEDOMETERS. Further to our EFC4/AD27.3.31 you have now advised me verbally that grave difficulties are involved in the alteration of the chassis gear ratio of the speedometer drive and that for this reason you query whether instruments adapted to 810 revolutions per counter mile and provided with a contracted scale would not be reasonably suitable for our purpose. Our answer to this is that we agree that in view of the difficulty of alteration, instruments adapted for the figure 810 would be reasonably near. The resulting very slight error will be that the mileages will read high by slightly under 1% on the average and the speed readings will (though they need not) read higher also to the same extent. In specifying the instrument, we must think of it as if we are going to drive it accurately at 810 revolutions per mile though actually we are going to drive it at 816. The specification of the instrument for the Phantom now becomes modified to the following :- (1) The instrument must be arranged to register one counter mile for every 810 revolutions of its driving spindle. (2) The instrument must be provided with a contracted speed scale contracted in accordance with the scale given on page 10 of our notes and as therein specifically described. | ||