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).
The investigation and comparative testing of a faulty Watford Aero Magneto from a Falcon engine.
| Identifier | ExFiles\Box 43\4\ Scan068 | |
| Date | 25th February 1927 | |
| X4021 To A.I.D. from EFC. c. Wd.{Mr Wood/Mr Whitehead} R.G.A c. Mr. Payne. EFC2/T25.2.27. WATFORD AERO MAGNETO NO. 83136. LORX-4021 X3832 This magneto has been removed from Falcon engine F.X.10. on account of development of misfiring at all speeds, and positions of the advance and retard lever. On inspection the contact breaker appears to be unduly oily and there is evidence of deposition of carbon dust on the edge of the hole in the contact breaker plate, through which the spindle passes, as if blowing had taken place through the space between this and the spindle. Also the contact points are rather badly burnt down, and the strength of the spring in the resulting position appears to be too weak, indicating possibly that the spring has lost some of its temper, or alternatively, that the rating and set were not of suitable amounts originally. It would still appear that the contact breaker housing is not sufficiently protected from oil from the inside. So far as we can make out, it does appear to be fairly well protected from the outside. In this connection Wd.{Mr Wood/Mr Whitehead} will remember that we are still awaiting from Messrs. Norths an arrangement drawing of this magneto. Within the last day or two we have made some interesting comparative tests of the operation of the B.T.H. and Watford magneto contact breakers (on new magnetos) in a way which consists of connecting up the contact breaker in series with a battery, ammeter, and purely non-inductive resistance, and driving the contact breaker at various speeds. So long as the contact breaker makes effective contact with the correctly maintained make ratio, the current shown by the instrument will maintain constancy with increase of speed. But so soon as any irregularity of contact breaker action begins to occur a drop of average current will be noticed. Working in this way, we have found that with the B.T.H. contact breaker satisfactory mechanical operation is maintained practically right up to the maximum speed at which these magnetos would be run, viz. 3450 r.p.m. magneto speed and 2500 r.p.m. engine speed. Y4628 In the case of the Watford contact breaker in spite of the lighter duralumin lever as compared with the B.T.H. steel lever, we find there to be above magneto speeds of about 1200 r.p.m., a progressive reduction of average current as shown by the instrument, the reduction being in one case from .54 amperes to .435 ampere at the highest speed of 3450 referred to. It is not really a great reduction, and had it not been for the fact that in one case at least we have been able to show a steady constancy of current nearly up to this maximum speed, we should have been led to consider that it was an electrical effect of the circuit not being entirely | ||