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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).
Comparison of centre bearing loads and performance factors for flat, V-type, and Phantom III engines.

Identifier  ExFiles\Box 115\2\  scan0507
Date  16th November 1939
  
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RM{William Robotham - Chief Engineer}/TAS.{T. Allan Swinden}8/JH.16.11.39.

In connection with the high bearing loads in every case, it should be noted that due to the forked rods on each crank pin there is a constant rotating force of 3630 lbs.

Although the centre bearing diagram is very large the bearing itself is 60% longer than the intermediate bearings, giving a considerably better P.V. factor.

From the drawings of the white bus engine it would appear that their centre bearing is 87% longer than the intermediate. This high centre bearing loading is the inevitable result of having two adjacent throws in the same direction, and will always occur with this type of crankshaft when the rotational speed is high enough to bring big inertia forces into action.

In order to compare the flat engine with a 60°V engine of similar dimensions, the centre bearing diagram was replotted at half scale and upon it was imposed the diagram for the 60°V engine. The latter has its firing characteristics 60° apart instead of 180° and due to high inertia forces lining up at the same time actually has a high maximum load.

Comparative figures for the centre bearing are given in the table below, and with them are figures for the smaller bore Phantom III engine.

| | Proj. area of centre bearing sq.in. | Max. press. lb/in.sq. | P.V. factor at 3500 rpm. | Max. load lbs. |
|---|---|---|---|---|
| Flat 12 cyl. engine. | 4.81 sq.in. | 1250 | 52400 | 6000 |
| 60°V engine of similar dimension. | " | 1320 | 55500 | 6350 |
| Phantom III engine | " | 1220 | 51000 | 5850 |
  
  


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