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).
Technical memorandum discussing ignition options for the Goshawk engine, comparing battery versus magneto systems.
| Identifier | WestWitteringFiles\J\April1923\ Scan9 | |
| Date | 26th April 1923 | |
| TO RV. FROM R.{Sir Henry Royce} C. to Cd. Rd. HGH. C. to FH. RS.{Sir Henry Royce's Secretary} FPC. C. to RH.{R. Hollingworth} MS. ORIGINAL 3-2 R1/M26.4.23. X.3485 RE. IGNITION - GOSHAWK. X3551 You will remember that I recommended every Goshawk to be turned out with two ignitions available, so that in the event of one failing the car ought not to be stopped for more than 15 minutes. That the principle ignition shall be the battery, because it gives advantages which cannot be obtained from magneto. Thus, it is more accurately governed for advance than is possible with any magneto. It permits of the very slowest running with reliable sparking (one is not so liable to stop the engine) it is easier to start by hand, and with this ignition the engine can usually be re-started without using the starting motor. It is also easier to diagnose a fault, and repair a failing. X4575 X.4574 We have lately introduced another position of the coil which is cooler and with this lower position of the coil and the modifications to the distributor I suggested the possibility of using a plain H.T. magneto without a distributor, and using the battery distributor for either ignition. The advantages of this scheme are it's obvious simplicity (less wiring), the possibility of disconnecting the magneto drive (for silence and absence of wear), and minimum cost and --weight etc. Naturally a magneto to be of any use in case of battery failure must be capable of firing the engine when it is turned slowly by hand, and since it is desirable to have the advance to the magneto controlled by hand it has been found that the sleeve type of magneto is the most satisfactory. A magneto with sleeve advance has ample range of advance so that the magneto need not be set so early as to spark before the distributor of the battery ignition is in the correct position for firing. Therefore it is (A) possible to stop the magneto and arrange for it to be coupled up in only one position of it's revolution, (such as a blank tooth) every revolution of such a magneto being correct (not 1 out of 3 in case where distributor is on the magneto), (B) it is desirable that magneto should be equally as late as battery ignition when retarded, so that battery ignition distributor shall be in a suitably timed position to allow spark to pass in any position of the control. If this is done the auto advance of the distributor will take care of itself. A sleeve magneto is the only one suitable for this, i.e. a magneto with ample range of advance and capable of sparking efficiently in late position of control so that when engine is turned slowly by starting handle there is no risk of starting failure. It will be remembered that the magneto should be as small in dimensions (height etc) as possible, so as to permit of tappet adjustment. This I understand can be achieved by the use (1) | ||