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).
Comparing the specifications of Watford and B.T.H. magnetos.
| Identifier | WestWitteringFiles\N\2October1925-December1925\ Scan268 | |
| Date | 12th June 1925 | |
| R.R. 493A (50 H) (D.D. 31, 12-6-25) J.H.D. EXPERIMENTAL REPORT. Contd. -2- Expl. No. REF: M/A.7/H.12.6.25. (3) The H.T. safety gaps in the two magnetos are:- Watford 8.5 mm. B.T.H. 7.5 mm. In regard to the B.T.H. safety gap being less than specified; they state that this is accounted for by the fact that they slightly round off the points of the electrode and that it is equivalent to a minimum spark-over voltage of 12,000 as required by our specification. (4) Primary point gaps:- Watford .012" B.T.H. .010" As regards the contact breaker timing the B.T.H. magnetos have rather longer cams than the Watford so the period of make is rather less. The contact breaker timing in relation to the sleeves is absolutely similar in the two machines. As a matter of interest the working open circuit effective flux of the two machines for various positions of the sleeve from full advance to full retard has been taken up by observing the open circuit voltages of the primary windings in the two cases, these flux variations being exhibited on the two small photostat curves herewith. (5) The range of the Watford magneto in magneto degrees is 63°, and the B.T.H. 50°. Contd. | ||