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 performance of 14 m.m. Wizard spark plugs in various aircraft engines.
| Identifier | ExFiles\Box 58\2\ Scan270 | |
| Date | 21th December 1935 guessed | |
| -2- A.J.Rowledge, Esq. engines at any rate, prevent the fusion of the deposits, which has actually proved to be the case. To my mind this 14 m.m. Wizard plug is much superior to the 18 m.m. Wizard because it is not only considerably lighter but has the mica on the inner end of the central electrode ~~and~~ arranged as I always wanted to have it arranged in the 18 m.m. Wizard. There are one or two other and minor differences between these two types such as, for example, the cylindro-conical head of the central electrode being turned upside down and the peripheral serrations omitted, but these, as you will readily appreciate, are not significant. Experience with the 14 m.m. Wizard in test engines has satisfied us that the 18 m.m. size should be dropped by all engine builders and to this I would add that, so far as we can judge after considerable experience with 12 m.m plugs, this size is too small and delicate for every-day use. The principal achievements of the 14 m.m. Wizard to date are:- (1) Two plugs ran for 200 hours in "Rapier" and "Dagger" units under severe research conditions and were still in very good condition. - What were conditions? (2) One of the two plugs mentioned in (1) ran 125 hours in a "Perseus" research unit and was found in quite serviceable condition but was broken when being replaced in the cylinder. At that time only these two 14 m.m. Wizards were available. (3) We have run several, in 18 m.m. adaptors, in re-conditioned engines on test at Croydon and up to date they have accomplished 90 hours each without the slightest trouble or attention. (4) We sent 20 to Messrs. Armstrong Siddeley Motors Limited to get them approved in the "Tiger VI" engines which we are to use in our new A.W.27 land-planes. They put 14 of them into a "Tiger VII" fully supercharged engine for type test and ran them 208 hours under test conditions and this period included the 100 hours official test. Colonel Fell told me that he has had much trouble with other makes of plugs in high duty engines with leaded fuel and after | ||