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 necessity and design considerations for radio screened sparking plugs in aero engines.
| Identifier | ExFiles\Box 179\2\ img251 | |
| Date | 15th February 1932 | |
| R.{Sir Henry Royce} From He/Wst. C. to Sg.{Arthur F. Sidgreaves - MD} Wor.{Arthur Wormald - General Works Manager} C. to Sg.{Arthur F. Sidgreaves - MD} R.{Sir Henry Royce} C. to Sy. ORIGINAL He/Wst.11/MA.15.2.32. RADIO SCREENED AERO ENGINE SPARKING PLUGS. XC102 It now becomes necessary for us to use sparking plugs on our aero engines which are fitted with earthed metal caps connected to the metal braiding on the H.T. cables. These caps are necessary for two reasons :- (1) To avoid radio interference on the extremely short wavelengths now coming into use in the service. Previously we have managed to avoid the use of these screen-ed{J. L. Edwards} plugs owing to the fact that the metal cowling over our type of engines in aircraft has to a certain extent prevent-ed{J. L. Edwards} radio disturbance on all normal and long wavelengths. Air cooled radial engines, we understand, have had to use these shielded plugs already. (2) To avoid sparking across from the H.T. terminals on the plugs to the earthed induction pipe at extremely high altitudes. The distances between the live parts of the plug and the engine are so small in the case of the inlet plugs that it becomes necessary to interpose insulation in the exist-ing air gap owing to the fact that barometric depression reduces the voltage necessary to break down a given air gap by as much as 66% at 30,000 ft. The K.L.G. Co., have produced a very attractive design of screened plug which is easy to manipulate and very light. We are therefore obtaining a set of these to try out experimentally on an engine. Arising out of the problem of suitable screened spark-ing plugs for various types of engines the Air Ministry (vide. Major Bulman and Mr. Haireto at the recent conference) expressed the opinion that it is undesirable and very inconvenient to impose the usual "universal standardisation" limits on such plugs, as obviously it is much easier to provide for any given type of screened plug on an air cooled radial than on a Vee water cooled engine. | ||