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).
Analysis of engine running speeds, explosion pressures, and bearing loads, comparing Bentley and Wraith models.
| Identifier | ExFiles\Box 115\2\ scan0372 | |
| Date | 5th December 1938 | |
| - 2 - the critical speed) would be increased to a less degree if the balance weights were made of material of higher density. The distribution of the weights should, in any case, be revised. The running speed is taken as 3500 r.p.m. throughout and the explosion pressure is taken as 600 lbs/sq.in. (gauge) in both engines. This is probably about right for the Bentley, and may be rather high for the Wraith, but this makes little difference at the 120° crank angle at which the combined load on bearing F.{Mr Friese} is greatest, that is to say when cranks 3 and 4 are at T.D.C. and Crank 6 is on its firing stroke. The component forces in the vertical plane of engine (plane of paper), then acting on and in the vicinity of bearing F are shown for the Wraith in the sketch below. Incidentally, it will be observed that at this crank position the balance weights help to neutralise the explosion loading, as well as serving their primary purpose. The p.v. figures for bearing F.{Mr Friese} will be very high at maximum engine revs. since they will increase nearly as cube of speed. Thus at 4500 r.p.m. they will be approximately doubled. | ||