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 adapting a Goshawk size starter motor for an E.A.C. engine.
| Identifier | ExFiles\Box 35\4\ scan 149 | |
| Date | 30th April 1923 | |
| 1-1 30.4.23. X.9620 - E.A.C. STARTER MOTOR. (Calculations for adaptation of Goshawk size of motor to this work) Torque required to turn E.A.C. engine = 900 lb-inches (say) Speed reduction ratio = 32 Taking 85% gearing efficiency effective torque ratio = .85 x 32 = 27.2 Motor torque when rolling engine is therefore required to be 33.1 lb-inches. Engine speed required to be 55 R.P.M. Motor " " " 1760 R.P.M. Motor power (rolling condition) is therefore .925 H.P. Assuming 60% efficiency electrical H.P. becomes 1.54 Watts = 1150 Amperes = 120 Volts = 9.6 Static torque at this current must be 10% greater (say) than running torque, i.e. must be 36.4 lb.inches. Take a useful polar flux density of 6500 lines per cm2 reckoned on minimum pole face. Armature diameter = 2.850" Armature circumference corresponding to five slot pitches (69% polar embrace) Contd. | ||