Rolls-Royce Archives
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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 and notes on crankshaft system inertia, stiffness, and shaft frequency.

Identifier  ExFiles\Box 25\3\  Scan299
Date  1st January 1928 guessed
  
This increases the total inertia of the crankshaft system by 70% of 25.2% or 17.5%.

Old shaft-frequency = 1/2π √(29900/.02031) = 193 osc/sec
New shaft-frequency = 1/2π √(41860/.0237)

= 1/2π √1,770,000

= 1330 / 2π = 212 osc/sec

Or an increase of ≅ 10%

If the stiffness of the shaft were increased 40% without any increase in inertia, the period, which varies as the √ of the stiffness, would be raised 20%.

Therefore we can state that the effect of stiffening the shaft by attacking the big ends is to raise the period by one half the amount that would be gained by incorporating the same increase in over-all stiffness in the journals. Thus attacking the pins, besides saving the main bearings, does push the critical period up appreciably.
  
  


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