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).
Test report comparing the cooling performance of different fan configurations on various car models.
| Identifier | ExFiles\Box 97\4\ scan0046 | |
| Date | 13th October 1938 | |
| -2- (2) At low speeds full throttle (40 m.p.h. downwards) the B.III car with the wraith fan and a steam valve has a critical air temperature of 38.5°C which is entirely satisfactory. If no steam valve is used, the C.A. obtained is 32.5°C and this might give trouble in very hot weather on the Continent. Certainly no reduction in fan performance at these speeds is permissible. (3) It has not been possible yet to carry out a satisfactory idling test on B.III fitted with the wraith fan, but approximate tests made with the B.II fan fitted on B.III indicate that this fan is quite inadequate - we anticipate that the wraith fan will be satisfactory. (4) The B.II four blade fan with .9/1 drive ratio is very much inferior to the wraith five blade fan with .85/1 drive ratio, and is not satisfactory for use on B.III. (5) It was impossible to detect any power loss in the form of speed difference on the track between the Wraith fan, B.II fan and no fan at all. Apart from lap times which were not appreciably different, another B.II car which happened to have an identical performance with that of S.S.V. as it arrived at the track, was checked against S.S.V. during each test, and no speed difference due to the fans was detected. (6) The Wraith fan on B.III contributes very considerably to the high speed as well as low speed cooling since (a) On B.III the fan covers a much larger percentage of the matrix area than on former R.H. cars. (b) There is negligible slip at high speeds with our latest Ferogrip belts. As seen from results, it raises maximum speed C.A. from 24.5°C to 39°C (no steam valve). Summary. The B.III radiator as designed (fitted with 3 lbs/sq.in. steam valve) is adequate from a cooling point of view providing the 5 blade wraith fan is used, and if necessary a small further reduction in matrix size is permissible. The wraith 5 blade fan should definitely be used on B.III since its cooling properties are required, it is silent and no disadvantage in the form of increased power loss is discernible. | ||