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 memo evaluating the features and performance of Scintilla Type MNG.12-D magnetos.
| Identifier | WestWitteringFiles\V\2January1931-April1931\ Scan058 | |
| Date | 13th March 1931 | |
| To R.{Sir Henry Royce} from EFC. c. Sg.{Arthur F. Sidgreaves - MD} c. Wor.{Arthur Wormald - General Works Manager} E.{Mr Elliott - Chief Engineer} c. Ex. Ey. Rg.{Mr Rowledge} ORIGINAL EFC5/AD13.3.31. X.6111. SCINTILLA TYPE MNG.12-D MAGNETOS. Two Scintilla machines of the above type Nos. 207577 and 207580 have been received by us in connection with the outside proposal that we should use Scintilla machines on the aero engines for the Belgium Government. These machines are, as in the case of other Scintilla aero engine magnetos, of the revolving magnet type and are not fitted with automatic advance. We do not at present know the Moment of Inertia of the revolving magnet for comparison with the M.I's of the B.T.H. and Watford rotors and we cannot remove the magnet from a magneto to find out, but we are endeavouring to obtain this information from the makers as it will almost certainly be greater than that of the B.T.H. which, as will be remembered, is greater than that of the Watford. The outstanding point in favour of these magnetos is their relatively light weight, which complete with screening is only 15 lbs i.e. nearly two pounds lighter than the B.T.H. A disadvantage is that their range of advance is only 27° and another disadvantage, so it would appear, is that they are provided with no ventilation for the armature and jump spark distributor. Still another disadvantage is the poor dynamical action of their contact breakers. This was suspected originally from the observation of the poorness of their high speed operation, subsequently our usual test was made to obtain the curve of contact breaker make ratio against rotational speed of the machine. It will be remembered that this is performed by placing electrically in series with the contact breaker a battery, ammeter and invariable non-inductive resistance, adjusting the flow of current, with the armature stopped on contact, to 1.00 ampere then running the contact | ||