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).
Report page detailing calculations for torsional oscillations and the nodal point in a crankshaft system.
| Identifier | WestWitteringFiles\P\2July1926-September1926\ Scan140 | |
| Date | 4th September 1926 guessed | |
| contd :- -13- For the case under consideration the node would be close to the flywheel due to its large moment of inertia. Let ( n₁ = oscns/sec. with one end fixed. ( n₂ = " " " other " " ( n = natural period. ( c = torsional rigidity in lbs.ft. ( I = moment of inertia. Then n₁ = 1/2π √c/I₁ n₂ = 1/2π √c/I₂ and n₁² + n₂² = n² hence the natural period of oscillation can be determined. The inertia of the crankshaft is dealt with by assuming an equivalent of one third of its moment of inertia added to the inertia of the mass at the free end in turn, while the other end is fixed. This gives us the result that the natural frequency of oscillation is 172.5 oscillations per second which agrees fiarly closely with the result from the vibration diagram at 3350 r.p.m. which gave a frequency of 167.5 oscillations per sec. A rough calculation shows us that the nodal point would be approximately 1.4" from the flywheel end and it will be remembered that it was at no.6 crank pin that fractures took place during previous experiments. contd :- | ||