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 and specifications for a sequence starter motor for a Phantom engine.
| Identifier | WestWitteringFiles\Q\2April1927-June1927\ 197 | |
| Date | 22th June 1927 | |
| SEQUENCE STARTER MOTOR. (To start Phantom engine with 16 : 1 ratio). Maximum normal torque required to turn Phantom engine assumed to be 1100 lb-inches. Taking 85% gearing efficiency, then effective torque ratio = .85 x 16 = 13.6. Motor torque when rolling engine is therefore 1100 / 13.6 = 81 lb-inches. (say) 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 40 r.p.m. this means a motor speed of 640 r.p.m. and a motor power of .825 HP. or 615 watts. A reasonable efficiency etc to expect of the motor at this speed and torque is .41 which means a supplied power of 1510 watts or 180 amperes at 8.40 volts which gives a reasonable margin for overload. The running torque of the motor at 180 amperes is to be 81 lb-inches. The static torque will be about 10% greater, i.e. 89 lb-inches. Assume a useful polar flux density of 6500 lines per cm^2 reckoned on the minimum pole face. Armature dia. 3.100 inches. | ||