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. {E. Fowler Clarke - Electrical Engineer} c. E {Mr Elliott - Chief Engineer} /Mr. Stent. EFCl/T5.5.23. RE E.A.C. & GOSHAWK(Aero Engine)(Codename for 20HP Car / Aero Engine after Kestrel(Aero Engine)) STARTER MOTORS. X9620 X4384 Having investigated the suitability of adaptation of the Goshawk(Aero Engine)(Codename for 20HP Car / Aero Engine after Kestrel(Aero Engine)) 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. | ||
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).