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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).
Table of lowest speeds in R.P.M. for various magnetos during regular firing on 5.5mm air gaps.

Identifier  WestWitteringFiles\F\March1921\  Scan60
Date  22th March 1921
  
Handwritten: X 2375, X 4181, X 39/6
Typed: X.430. MAGNETOS.

TABLE OF LOWEST SPEEDS IN R.P.M. FOR REGULAR FIRING ON 5.5mm. GAPS IN AIR.

N.B. Test range between advance and retard 34º in all cases (except Watford E.O.6a. = 32º).

TABLE DATA:

Column Headers: Magneto., Type & No., X. No., Lowest speeds. (Adv., Cent., Retd.), Remarks.

Row 1:
Magneto: Watford.
Type & No.: E.6, 45638.
X. No.: 2375
Lowest speeds - Adv: 150, Cent: 250, Retd: 340
Remarks: Advanced position same as maker's. (Gaps had to be reduced to 4.5 mm. in fixing range by high speed sparking). Retarded position 4º later than maker's.

Row 2:
Magneto: Watford
Type & No.: E.6, 45168
X. No.: 2375
Lowest speeds - Adv: 156, Cent: 226, Retd: 320.
Remarks: Advanced position 3º earlier than maker's. (Gaps had to be reduced to 4.5 mm. in fixing range by high speed sparking). Retarded position 1º later than maker's.

Row 3:
Magneto: Watford.
Type & No.: E.O.6a, 46993.
X. No.: 4181a.
Lowest speeds - Adv: 160, Cent: 140, Retd: 136
Remarks: Increased advance or retard on maker's range unobtainable. Hence working range 32º as maker's.

Row 4:
Magneto: Watford.
Type & No.: E.O.6b, 48919.
X. No.: 4181b.
Lowest speeds - Adv: 170, Cent: 155 (Weighted average of two sets of figures), Retd: 150.
Remarks: Retarded position same as maker's, this setting chosen owing to slower speed for regular sparking obtained on retard. Advanced position 29º later than maker's.

Contd.

Footer Text: R R.{Sir Henry Royce} 285A (OD) (I.S.H. 986. 19-3-21) G.{Mr Griffiths - Chief Accountant / Mr Gnapp} 3018
  
  


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