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).
Calculations for the sequence starter motor required for a Phantom Engine with a 13:1 ratio.
| Identifier | WestWitteringFiles\Q\2April1927-June1927\ 142 | |
| Date | 1st June 1927 | |
| EFC/T1.6.27. X.7625. SEQUENCE STARTER MOTOR. (To start Phantom Engine with 13 : 1 ratio). Maximum normal torque required to turn Phantom Engine = 1100 lb-inches. Taking 85% gearing efficiency, effective torque ratio = .85 x 13 = 11.0 say. Motor torque when rolling engine is therefore required to be 100 lb-inches. Maximum available electrical H.P. on characteristic of supply assumed of 1 volt drop from 12 volts per 50 amperes = 6 x 300 = 1800 watts. We must have a good margin of E.H.P. supplied in relation to this maximum. If we try an engine speed of 35 R.P.M. this means a motor speed of 455 R.P.M. and a motor power of 539 watts or .72 H.P. A reasonable efficiency to expect of the motor at this speed and torque is .375 which means a supplied power of 1440 watts or 166 amperes at 8.68 volts, which gives a reasonable margin for overload. The running torque of the motor at 166 amperes is to be 100 lb-inches. The static torque will be about 10% greater, i.e. 110 lb-inches. Contd. | ||