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 memorandum comparing the suitability of a Goshawk starter motor for an E.A.C. engine, including E.M.F. calculations.
| Identifier | ExFiles\Box 64\1\ scan0113 | |
| Date | 5th May 1923 | |
| X9620 To E.{Mr Elliott - Chief Engineer} from EFC. c. E/Mr. Stent. EFCl/T5.5.23. RE E.A.C. & GOSHAWK STARTER MOTORS. X9620 X4384 Having investigated the suitability of adaptation of the Goshawk starter motor to the E.A.C. engine, with the engine speed (1760 R.P.M.) and reduction ratio (32) given, I do not find that this is any more suitable with the present number of slots (29) than the previously proposed E.A.C. motor with 37 slots. There is always a rough fundamental relation, namely, that Ø Z N = 2 to 2.25 x 10^10 (4 pole machine) according to the degree of loading, the lower figure being used for the more heavily loaded motor, where Ø = Useful flux per pole Z = No. of armature conductors. N = Motor speed in R.P.M. which relation must be satisfied. The general expression for the E.M.F. (in the present case back E.M.F.) of a revolving armature is E = (Ø Z N P) / (60 x 10^8 x b) whereas Ø, Z, and N are as above, P = No. of poles b = No. of parallel paths through armature. Since P is 4 and b is 2, it will readily be seen that the rough rule is equivalent to a back E.M.F. of from 6 2/3 to 7 1/2 volts. Contd. | ||