Rolls-Royce Archives
         « Prev  Box Series  Next »        

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 adaptation of a Goshawk-sized starter motor for an E.A.C. engine.

Identifier  ExFiles\Box 64\1\  scan0123
Date  30th April 1923
  
1-1-
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.
  
  


Copyright Sustain 2025, All Rights Reserved.    whatever is rightly done, however humble, is noble
An unhandled error has occurred. Reload 🗙