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).
Blueprint showing 9th harmonic torsiograms for a Wraith spring drive, with and without balance weights.
| Identifier | ExFiles\Box 124\2\ scan0138 | |
| Date | 5th April 1940 | |
| B. 60 No. 2 WRAITH SPRING DRIVE WITHOUT SLIPPER. WITHOUT BALANCE WEIGHTS AMPLITUDE .6° NAT. FREQ. 16200 PER MIN. 800 R.P.M. WITH BALANCE WEIGHTS AMPLITUDE .6° NAT. FREQ. 16300 PER MIN. 1700 R.P.M. 9TH HARMONIC TORSIOGRAMS RM{William Robotham - Chief Engineer}/JRS 5.4.40. | ||