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).
Letter to The A.T. Speedometer Co. Ltd. detailing the results of tests conducted on a speedometer instrument.
| Identifier | ExFiles\Box 50\4\ Scan200 | |
| Date | 12th June 1928 | |
| Y4308 B.247. c. Roy. {Sir Henry Royce} c. By. {R.W. Bailey - Chief Engineer} EFC {E. Fowler Clarke - Electrical Engineer} 1/T. 12th June, 1928. Messrs. The A.T. Speedometer Co.Ltd., 20, Avonmore Road, West Kensington, W.14. Dear Sirs, Further to ours of the 3rd. may, ref. EFC {E. Fowler Clarke - Electrical Engineer} 5/T. we have now completed on another speedometer instrument the careful tests of which we spoke. We have conducted these as referred to with a small circulating fan. We have had the thermometer in two different positions and the heater in two different positions, and obtained results which, though subject to slight variations as a result of these changes of position, nevertheless are reasonably consistent and are all contained in the statement given below, which statement refers all the time to a driving speed of 600 r.p.m. exactly. Instrument No. B.247.D.730. 15/52. This instrument reads correctly, e.g. 48.2 ± .1 m.p.h. at 28.6°C. At 18°C. it reads 49.5 ± .3 m.p.h. and at 30°C. it reads 48.1 ± .1 m.p.h. The percentage drop of reading from 18°C. to 30°C. lies between 2.25 and 3.3, the limits of experimental error. It will be seen that though our very careful tests have resulted in our figure of the percentage drop being considerably less on this later instrument than we found more approximately on an earlier one, the percentage fall of reading between 18°C. and 30°C. appears to exceed 1.6%, which we think was the figure you gave as a maximum. Contd. | ||