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 discussion on Bosch magneto and armature specifications, including performance graphs and material composition.
| Identifier | ExFiles\Box 49\5\ Scan227 | |
| Date | 4th May 1921 | |
| Oyll/G4521 - Contd. -2- May 4th 1921. On taking this matter up with the Bosch Company, they say that they have made an error in giving us the E.D.18 magneto with what is known as the N.B. armature. They originally intended to give us the E.D.19 with the B.B. armature. The magneto you took to England was I believe E.D.18, and probably "N.B." armature, while the one they showed us on test was E.D.19 and B.B. armature. What the original Z.R.6 is that Clark is running his tests on we do not know. You can very quickly verify the armature by taking off the H.T. brush and cover plate, when you will find the armature symbol stencilled in white on the windings at the driving end. The difference is that prior to 1916 the B.B. winding was used on all ZRs6, giving a large primary current and slow-running curve (5 mm. gaps) as below: [Graph showing a line from 36 RPM at Full advance to 105 RPM at 36° Retard] Handwritten note on graph: Gaps with third points After 1916 trouble was met with in obtaining the required percentage of iridium in the platinum to avoid trouble with the high primary current. A number of modified windings were tried which finally boiled down to one winding, the N.B. as used on the E.D-18 magnetos. The slow speed characteristics of this winding under the same conditions as above are: [Graph showing a line from 70 RPM at Full advance to 140 RPM at 36° Retard] The B.B. winding and E.D.19 magneto, which we now specify, also includes contact points of high iridium content and mica condenser. [Upside down text at bottom] M.R.H. (1001) H.S.'31. 10-12 '01 C.E.O. N° 2947 | ||