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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 lengthened dynamo unit, discussing technical modifications, cost implications, and attached performance curves.

Identifier  Morton\M13.2\  img008
Date  1st December 1930
  
-5-
EFC2/AD9.12.30 contd.

field resistance may reasonably be in greater demand.

Suggestion of Lengthened dynamo unit.

There is and will continue to be, we feel, considerable criticism of our system on the grounds of the lateness of the cutting in. As it is practically impossible to increase the size of the dynamos diametrically owing to design and armature peripheral speed, we would like to suggest for R's consideration an increase in the length of the machines of 1/2" or 3/4" as there is plenty of room lengthways and some amount of increase does not appear to be mechanically impracticable. Precisely the same 48 coil armature plates and windings would be used and the cutting in speed would be reduced very approximately in inverse proportion to the increase in the active length of the armature, in other respects the output curve would be similar. As our further investigations are bringing out the fact that a concentric increase of the air gap has the same ultimate effect i.e. after resetting the brushes accordingly as the present standard taper pole modification, we could reasonably start off such an experimental lengthened armature machine with a suitably increased air gap, thus minimising cost of production.

As an illustration of various points referred to in the above, please find attached blue print copies of two sets of 48 coil dynamo output curves, one for 40/50 and one for 20/25, all curves are with the dynamo at a temperature of 80°C. as measured in the usual way.

Curve I. on each sheet represents the output performance to the schedule of operating voltages given at the side.

Curve II. represents the output performance in otherwise precisely the same circumstances but at a constant operating voltage of 14.0 N.B. The big difference in output as affected by voltage will be noted.

Curve III. represents the output at schedule voltage in otherwise similar circumstances but as reduced by the insertion of an external field winding resistance of a stated value.

We also attach blue print technical diagram of the R.R. two-rate switching.

EFC.
  
  


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