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).
Proposal for a new lightweight aero engine revolution counter using a small alternator.
| Identifier | ExFiles\Box 165\4\ img150 | |
| Date | 6th March 1932 | |
| X1350 To Rg.{Mr Rowledge} from Hs{Lord Ernest Hives - Chair}/Wst. c. Wor.{Arthur Wormald - General Works Manager} c. Ev.{Ivan Evernden - coachwork} Hs{Lord Ernest Hives - Chair}/Wst.1/AML6.3.32. AERO ENGINE REVOLUTION COUNTER All the existing types of aero revolution indicators we have seen are, we consider, too bulky and heavy for the work they have to do. A typical unwieldy example is the R.A.E. electrical revolution indicator. We realise that a simple light weight revolution counter with no mechanical transmission, such as a flexible cable, to the instrument would be very acceptable both to ourselves as a unit which we could supply with our engines or to aeroplane manufacturers. We think we can suggest an original idea as follows:- If we had a very small alternator such as a bicycle generator having a stationary winding and a rotating permanent magnet, driven from the end of the engine camshaft or on the wheelcase we could then deliver an alternating voltage varying proportionally to the speed, to a small Ferranti rectifier instrument on the pilot's instrument board. This instrument actually shows D.C. current measurements rectified from A.C. by means of a small Westinghouse metal rectifier inserted in the instrument. The scale is thus fairly even instead of being a square law scale as is the case with A.C. meters. If the small alternator was well laminated and the current taken by the instrument very small, the losses would be negligible and the reading on the instrument would then be strictly proportional to the volts which would vary strictly proportionally to the speed. The advantages of this scheme would appear to be:- (a) Light weight and simple construction. (b) Elimination of commutator and brush contacts which cause trouble on D.C. machines now in common use for electrical rev. counters. (c) Elimination of the long flexible drive for mechanical indicators. (d) Adaptability, as the recording instrument can be placed wherever suitable the connecting wires being lengthened accordingly. | ||