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 body resonance, frame flexibility, and a comparison of chassis differences between P.I. & P.2 models.
| Identifier | WestWitteringFiles\V\March1931-September1931\ Scan082 | |
| Date | 25th March 1931 guessed | |
| (3) transmit. Hence being damped or weighted would not effect their action. We note that you have had jacks under the frame, but we believe that to destroy the torsional flexibility of the frame it would be necessary to have six jacks under the frame, two in front, two behind, and two in the neighbourhood of the dash. There may be no resonant medium in the body, and body merely acts as a sound box collecting the note emitted by the scuttle, but tests on bodies with Sonometer indicate that there is. We would like to make tests to discover which are the parts or part of the body which provide this resonance. The flat surfaces are usually the most suspected. It cannot be the air in the body itself being resonant, like the air in an organ pipe or else the opening of all the windows would effect a cure. This it does not, but merely helps because some of the reverberating surfaces have been removed. These surfaces are capable of amplifying the sound emitted by the scuttle speaker by reflexion without themselves being in resonance. It may seem strange that, varied as the types of bodies are, they should should all possess a part or parts which have approximately the same frequency. It might be explained this way. The resonance complained of appears to exist over a range of from 53 to 68.M.P.H. Some bodies may peak nearer one end of that range than the other. Measured in frequencies of, say, three times engine speed it is quite a wide range; a range as wide as the other divergencies cover. e,g.{Mr Griffiths - Chief Accountant / Mr Gnapp} Range of heights, 46ins. to 50ins. Range of widths, 50ins. to 58ins. Length of any single compartment 70ins. to 85ins. The roof, which is admittedly the chief cause of booming, is of shallow thickness, hence it is very difficult to change its natural frequency by stiffening, as the effect of the added weight is almost enough to nullify the effect of the added stiffness. It would be helpful to make a series of tests on various bodies with the Resonator or Sonometer to see what natural frequencies exist in bodies of different types and makes both on PhantomI, and P.2. DIFFERENCES BETWEEN P.I. & P.2. Source of Energy. It is difficult to see why the driving vibration should not exist on both chassis. Transmission of Energy. The steering column fixing on P.I. is 15ins. from the dash and on P.2. it is 20ins. There would be more pumping of the column at its fixing on the dash on P.2. (see Fig.I.) The frame of P.2. has less torsional rigidity in front of the dash than P.I. and more than P.I. aft of the dash. Therefore with P.I. engine mounting it might be thought that the amplitude of the frame wave would be less than when a similar mounting is applied to P.2. This might be a reason for P.I. mounting not being a cure or as good on P.2. | ||