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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).
Crankshaft stiffness and torsion tests for Phantom and 20 HP models.

Identifier  ExFiles\Box 25\3\  Scan320
Date  29th April 1928 guessed
  
-2- Contd.

The results of tests with various numbers of bearings are included in the above tables, but we give below the effect on three shafts of removing all but the two end and the centre bearings. The reduction in stiffness is :-

Standard Phantom ------ 6.5%
Sports Phantom ------ 21.0%
Standard 20 HP. ------ 6.0%

The second shaft, the "Sports Phantom", was finally abandoned, as it was torsionally too weak. It was an attempt to reduce inertia.by using smaller crankpins and big-ends. The shaft was 15% weaker than standard, and although the period speed was little changed, we did not proceed with it.

In all our torsion tests we correct the measured stiffness on the whole shaft before comparing with the formula. The formula only includes a certain length of main bearing, and we therefore always subtract from the measured deflections the deflections in the flexible nose, if any, and in the extra length of main bearings, under the same torque. We find that these two items may account for 20% of the total deflection, and we think this accounts for the airly close agreement shown in Fig.4 between calculated and test results. Some of these crankshafts have been sent you before. We should be interested to know if you intend this correction to be used in conjunction with your formula.

When we observed the marked stiffening effect of bearings, we did an experiment to measure the movement in

Contd.
  
  


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