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).
Secret memorandum regarding the design of a complete welded exhaust system for the 'Myth' project.
| Identifier | ExFiles\Box 110\2\ scan0002 | |
| Date | 24th October 1940 | |
| 1030 To Rm.{William Robotham - Chief Engineer} from Ev.{Ivan Evernden - coachwork} c. to Rm{William Robotham - Chief Engineer}/HH. c. to Rm{William Robotham - Chief Engineer}/Wym.{G. Harold Whyman - Experimental Manager} SECRET. 723 Ev.{Ivan Evernden - coachwork}5/JH.24.10.40. re Myth Exhaust System. On Myth we desire to have a complete exhaust system welded up and without joints. Now that we have on this car, a frame with either a cross or 'A' member, together with subsidiary cross-members, we really need to know something about the size and position of the exhaust silencer or expansion box prior to setting out the frame. We are given to understand that Vauxhall's made preliminary investigations theoretically when setting out the exhaust layout of the 10 H.P. Model and their method is described in a paper by D.B.Foster Ph.D. published in the I.A.E. Journal for October 1939. On PL.379 (original attached to Rm{William Robotham - Chief Engineer}/HH's. copy of this memo.) we shew an exhaust pipe, on which we have plotted the nodal points for the 3rd. 5th. and 7th. harmonics. It is the more effective to treat the nodes nearest the open end of the pipe, but practical considerations rather preclude our dealing with the 1st. node of the 7th. harmonic or the 1st. node of the 5th. The exhaust silencer shewn, based on Vauxhall, treats the 2nd. node of the 5th. and the 2nd. node of the 7th. by resonance chambers at each end of a single silencer, whilst the centre section deals with high frequency residual noise. Should the centre chamber be larger than is required, two separate resonators would be used with a box integral with one of them to deal with residual noise. The resonance chambers have been designed with capacity to deal with the individual frequencies and a 4.000 dia. box appears to be suitable. We have copied Vauxhall in not treating the 1st. node of the 3rd. harmonic which occurs at 37 M.P.H. at firing rate, and 18.5 M.P.H. at twice firing rate, but we have space available for a resonator should tests prove this to be a serious acoustical period. The frequency of this harmonic is 80 cycles per sec. which is low and not likely to cause a boom in such a P.T.O. | ||