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 comparing fan speeds corresponding to various thrusts for different 20 HP fan designs.
| Identifier | ExFiles\Box 75\3\ scan0048 | |
| Date | 6th February 1925 | |
| 1900/up FAN SPEEDS CORRESPONDING TO VARIOUS THRUSTS OF VARIOUS FANS. -20 HP- THRUST (lbs) Standard 20 HP fan. Hispano fan. Final modfn. to exol. 20 HP fan. 1 | 1.00 | .965 | 1.023 2 | 1.00 | .967 | 1.007 3 | 1.00 | .955 | .967 4 | 1.00 | .945 | .975 5 | 1.00 | .941 | .980 6 | 1.00 | .935 | .972 7 | 1.00 | .930 | .969 8 | 1.00 | .935 | .972 9 | 1.00 | .939 | .965 10 | 1.00 | .948 | .964 11 12 13 14 6.2.25. .966 WLAv. | ||