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).
Recalibration of A.T. speedometers using a parabolic scale to improve accuracy at higher speeds.
| Identifier | ExFiles\Box 59\2\ Scan114 | |
| Date | 8th March 1931 | |
| X6051 To C. from EFC. c. PN.{Mr Northey} By.{R.W. Bailey - Chief Engineer} c. Wor.{Arthur Wormald - General Works Manager} Hs.{Lord Ernest Hives - Chair} EFC1/AD18.3.31. X.6051 A.T. SPEEDOMETERS. We have your C7/C13.3.31 written as a result of our EFC3/AD12.3.31 and have duly noted your various remarks. We are now taking the matter up fully with a view to getting the speedometers on a correct basis which involves the replacment of the proportional scale of miles per hour by a scale arranged with a parabolic contraction of the scale to overcounteract the effect of centrifugal force on the tyres which otherwise causes proportionately lower readings at the higher speeds. In this way we shall be able to make the mileage recorder as accurate as it is possible to make it without causing the speed readings to be too low at the higher speeds. We would remind you, however, that the combined effect of tyre size variation, degree of inflation and speed may, at the extreme limits of each, cause a summed difference of as much as 7½% though actually it would be extremely unlikely that 5% of variation was ever exceeded therefore it is necessary to adopt what is judged to be the most reasonable average so that the average miles recorded on all cars is as nearly as possible correct. You will realise that there are quite a number of various effects to take into account so that the whole matter is somewhat complicated. It has been preliminarily expressed in our EFC2/AD4.9.30, this still being O.K. as regards the text but needing slight revision as regards the figures. A further report to the above will, however, shortly be issued in which will be given the mathematical basis for the desired modified miles per hour scale law. EFC. | ||