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 vibration criticals, orders, and resonance speeds in various cylinder configurations.
| Identifier | ExFiles\Box 63\4\ scan0071 | |
| Date | 9th March 1929 guessed | |
| The 2/3'rd method is derived from the continuous shape, uniformly distributed + C. No claims made for new engines, or for two-node vibration. criticals to be investigated. These may be important, e.g. in a normal six cylinder line 4 stroke engine with airscrew attached, the major critical is of the 3rd.order, i.e. three vibrations per revolution. Theory indicates that the 4½ order minor critical may be of serious amplitude; this vibration must occur at two thirds of the 3rd.order critical speed. In the case of a 12 cylinder 60° Vee engine, the 3rd.order critical should be very small, but the 6th.order critical may be important. The 4½ order critical should be about √2 times the magnitude appropriate to one bank of cylinders, and may thus be serious. This order of vibration will occur at four thirds the speed of the 6th.order vibration. If the angle of Vee is 45°, the magnitude of the 4½ order vibration is nearly double the magnitude appropriate to one bank of cylinders, and both the 3rd. and 6th.order vibration occur. If the angle of Vee were 80°, the 4½ order vibration would disappear. A complete account of this matter would be a long story, but the foregoing is mentioned because some tests made on a 12 cylinder engine having a 45° Vee, have shewn very clearly the existence of 6th.order and 4½ order vibration. The 6th.order resonance speed calculated for this engine by the flywheel method before the tests were made was 1050 r.p.m. The torsiograms shew that the 6th.order vibration occurs at about 975 r.p.m., 4½ order vibration is serious in the region of 1250 - 1400 r.p.m. and 3½ order vibration is revealed at the highest test speed, viz. 1700 r.p.m. With the 6th.order critical at 975 r.p.m. the 4½ order should be at four thirds 975 = 1300 r.p.m. and the 3½ order at 6 x 975/3.5 = 1670 r.p.m. These results will be of particular interest to yourself as you will remember that during your visit to the R.A.E. some time ago we calculated the 6th. order resonance speed of the F.XI engine to be 1050 r.p.m. which happens to be the same value as that calculated for the engine referred to; the angle of Vee is different, however. You will appreciate the foregoing better for having read "Torsional Vibration in the Diesel engine" Trygformar by / | ||