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).
Letter from North & Sons clarifying the type numbering system for 12-cylinder aircraft magnetos.
| Identifier | ExFiles\Box 43\4\ Scan216 | |
| Date | 3rd February 1930 | |
| E.F.C. SPEEDOMETERS X4021. THE BRITISH MADE Watford & MAGNETOS. NORTH & SONS, LTD. WHIPPENDALL ROAD, WATFORD. TELEPHONES: LONDON 1346 GERRARD WORKS: 692 & 623 WATFORD. CONTRACTORS TO THE ADMIRALTY, WAR OFFICE, AIR MINISTRY, CROWN AGENTS FOR THE COLONIES, INDIA OFFICE. TELEGRAMS: AEROMAGS WESTCENT LONDON AEROMAGS WATFORD. Ref. CHK/DD Your ref. EFCl/AD. 3rd. February, 1930. Messrs. Rolls-Royce Ltd., DERBY. Dear Sirs, We thank you for your letter of the 31st ult., and regret to note that the alteration in our type numbers for aircraft magnetos has caused some confusion. All spigot mounted 12 cylinder magnetos were classed as I.S.12, but in order to bring our numbering into line with the Air Ministry's views, and to provide for modifications in detail, we decided on the designation S.P.-12 followed by a further distinguishing number. The range at present is:- S.P.12-1 Spigot mounted, screened with grouped leads. S.P.12-2 Spigot mounted, screened with radial leads. F type. S.P.12-5 Spigot fitting, radial leads unscreened. R type. You have had magnetos both screened and unscreened numbered I.S.12 but the two magnetos 98033 and 98034 sent to you on January 30th after fitting new contact breaker bases, although they still bear the original type number I.S.12 are in all | ||