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).
Fan blade curvature, performance, and selecting an optimal fan speed ratio.
| Identifier | ExFiles\Box 75\3\ scan0065 | |
| Date | 1st March 1925 | |
| R.R. 493A (50B) (D.B. 175 25-9-24) J.H.D. EXPERIMENTAL REPORT. Contd. -4- Expl. No. REF:EFCG/TBO 3.25. Our experiments now show that the speed-thrust curve may be lowered by increasing the trailing curvature of the blades, up to a certain point, without raising the power-thrust curve; further curvature, however, would do this, i.e. lower what we call the efficiency. An instance of this is contained in the points labelled 16, though in this case it would not so much be due to rapid curvature as to larger width of blade, resulting in too great a trailing angle. All things considered, the fan giving the curves labelled 18 is judged to have the best alround performance. Although this is labelled "wider bladed fan", this only refers to its original condition, though in its final condition it is still slightly wider bladed than 10. Reference to the I group of curves will show that 18 takes more power than 9, 10, 14 and 15 to drive it at a given speed, though it takes less power than (1). Having selected 18, the next question is as to what non-slip engine fan speed ratio of drive should be adopted? As a basis of comparison we take fan (1), the results of which, on the ordinary 40/50 chassis at any rate, are known under road conditions. The lower limit of speed ratio would be that for which the 18 fan would produce the same thrust as (1) for a given engine speed. The ratio of the speeds to give the same thrust for the two fans is Contd. | ||