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).
Cylinder vibration characteristics for a Vulture I engine, detailing test positions and results from vibrograph readings.
| Identifier | ExFiles\Box 138\2\ scan0157 | |
| Date | 11th July 1938 guessed | |
| - 2 - (i) Stud-bosses on outside of valve cover - Vibrograph in horizontal plane. (ii) Front end of block - Vibrograph horizontal. (iii) Rear end of block - Vibrograph horizontal. (iv) Centre line of valve cover - Vibrograph vertical. (v) Centre point of top water rail - Vibrograph horizontal. It was found that all points on the valve cover introduced spurious high-frequencies in some degree which resulted in the production of blurred or 'fuzzed' diagrams as mentioned under Series I. Similar diagrams with a very pronounced high-frequency component were also obtained at various points on the water-connections. However, the diagrams taken from the stud-bosses on the valve cover where the former might be assumed rigidly connected to the main cylinder structure, were clearly revealed as a periodic wave with a marked third harmonic. Consequently, position (i) with the vibrograph held in the horizontal plane against the central stud-boss was assumed to provide a true indication of the main cylinder block vibration, and this location was adapted for all subsequent testing unless otherwise specified. (This position was particularly suitable for the operator with the vibrograph as it enabled him to clear the exhaust manifolds with comfort). An investigation was then made with the standard position on 'B' block and constant climbing boost of 5½ lb/sq.in. to determine the effect of speed upon the diagrams. With speeds of 3000, 2900, 2800, 2700, 2600 and 2500 r.p.m. it was found that the greatest amplitudes were recorded in the region of 2600-2700 r.p.m., where the diagrams were almost free from any extraneous frequencies. At higher speeds the amplitude was found to fall off, but the presence of a component at approximately 3 x fundamental frequency became more marked. The results of these trials are given in Table I and an interesting connection is observed between the fundamental vibration frequency and the airscrew shaft frequency, this member being driven through a reduction gear of 0.40 -1. TABLE I. CYLINDER VIBRATION CHARACTERISTICS. 5½ lb/sq.in.boost. 'B' BLOCK. VULTURE I NO.1. (REDUCTION GEAR 0.40-1). (MASTER ROD IN 'D' BANK). Crankshaft R.P.M. Airscrew Shaft Frequency. Vibrograph Frequency. Amplitude. 3000 20.0 17.6 0.007" 2900 19.3 16.7 0.009" 2800 18.6 16.7 0.009" 2700 18.0 16.5 0.015" 2600 17.3 16.3 0.013" 2500 16.7 14.5 0.010" * The figures for the semi-amplitude are based upon the static calibration and are therefore to be regarded as relative only. | ||