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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.
  
  


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