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).
Torsional vibration tests conducted on a B.80 No.2 engine.
| Identifier | ExFiles\Box 124\1\ scan0075 | |
| Date | 22th April 1939 | |
| 10HH (See file 116. for Rm{William Robotham - Chief Engineer}'s covering note Rm{William Robotham - Chief Engineer} S/R.2.H.4.39) Rm{William Robotham - Chief Engineer}/JR.{Mr James Royce}2/JH.22.4.39. TORSIONAL VIBRATION TESTS ON B.80 No.2. With Report Rm{William Robotham - Chief Engineer}/JR.{Mr James Royce}10/JH.13.2.39. was a curve show-ing the variation with speed,of the amplitude of torsional vibration for B.80 No.1 without a damper. Unfortunately this curve came to a premature conclusion at 2800 r.p.m. owing to a failure of the Tummers indicator due to the large amplitudes involved. In order to get a complete,or nearly complete, record of the behaviour of the crankshaft without a damper, it was decided to carry out a test on B.80 No.2. In order to avoid breaking the instrument the critical range was run through at light throttle and readings were taken from either side and as near to this range as was safe. The curve obtained corresponds closely to the part obtained before,but has the advantage of showing more clearly the more important minor critical speeds. The major critical speeds shown by the 4th. and 8th. harmonics are outstanding and occur at 2930 and 1460 r.p.m. respectively giving a figure of 11700 vibrations per minute, as the natural frequency of the crankshaft system. For this engine the firing order is 1,6,2,5,8,3,7, 4, and for a single node mode of vibration the harmonic likely to cause the largest amplitudes are the two series :- the 1½, 5½, 9½, and the 2½, 6½, 10½, orders. These are quite well defined in the curve, the critical speeds being :- 2130, 1800, 1230 and 1110 r.p.m. for the 5½, 6½, 9½, and 10½ harmonics respectively. The next largest amplitudes should be caused by the ½, 4½, 8½, and the 3½, 7½, 11½ harmonic series and while these are not so noticeable as those previously mentioned they can be distinguished. | ||