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).
Revised specifications for the Spectre's servo and speedometer drive.
| Identifier | ExFiles\Box 165\4\ img254 | |
| Date | 9th November 1934 | |
| To - RM.{William Robotham - Chief Engineer} Copy to [REDACTED]/Ha/WST. [Handwritten]: WST HDY.{William Hardy}1/MN. 9/11/34. [Handwritten]: 7606S. Servo & Speedometer Drive - SpectreCodename for Phantom III. N Sch. 4257 herewith gives the revised servo and speedometer drive for SpectreCodename for Phantom III in accordance with our HDY.{William Hardy}1/HP.B/11/34. The servo ratio is 2/21 and the speedometer 24/9 which gives 725 revolutions per mile of the speedometer with an axle of 4.25 : 1 and tyres of the larger size proposed (7 x 18) which have an effective radius of approximately 15.1". The diametral pitch is reduced from 7 to 8 (12 1/2%) but the worm wheel radius is increased by 13% with a corresponding reduction of tooth-load and an increase in the number of teeth in contact. HDY.{William Hardy} N Sch. 4257. | ||