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).
Calculation sheet for the design and resistance of a field winding.
| Identifier | ExFiles\Box 35\4\ scan 039 | |
| Date | 19th July 1921 guessed | |
| -6- Contd. Ampere turns required = 738 Amperes - 137 .. No. of turns - 5½ per coil. Length of mean turn - 8½" approx. .. Total length of field strip = 4 x 5½ x 8½ + 6" (say) = 187 + 6 = 193" Estimated resistance for field winding (see p.3.) = .0077 w .. Resistance per inch at 20°C (say) = .0077 / 193 = .000040 w = 40 μw Microhms per inch cube of copper at 20°C = .678 .. Cross sectional area of field strip = .678 / 40 = .0170 inch² (nearly). It is found that 5½ turns of square section wire of .150 side (C.S. area .020 with .050 radius on corners) can be comfortably got in the space available. This reduces the field resistance to .00655 w and makes R_F = .34 R_A This is considered suitable. EFC. | ||