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).
Methodology for power consumption tests on tyres using a Highfield Dynamometer.
| Identifier | ExFiles\Box 157\3\ scan0027 | |
| Date | 2nd February 1939 | |
| Product Design Division, FORT DUNLOP. LJL/F/C. Feb.2nd. 1939. POWER CONSUMPTION TESTS ON TYRES. The measurements are carried out with a 'Highfield Dynamometer', the principle of which is to measure the force tending to rotate the field resistances of a motor when the armature is rotated. A small D.C. motor is used, the armature and casing holding the field coils both being supported independently in bearings. Any load on the motor will cause the field to rotate in the opposite direction to the armature. Rotation is resisted by a counter-poised lever arm concentric with and fixed to the field casing and supporting a weight at its extremity. The amount - T, by which the weight is reduced under the influence of the tendency to rotate is recorded. The formula for deriving the power consumed is - H.P. = 2 T. A.R. / 33000 where T = Force exerted by field on end of lever arm. A = length of lever arm. R = R.P.M. of motor shaft. Tyre Testing. For testing tyres the motor is coupled to a tyre testing drum 60" diameter. Power of motor is 12.5 H.P. and rated maximum shaft speed is 3400 R.P.M., this being reduced by a reduction gear so that corresponding drum speed is 349 R.P.M. By means of resistances, speed of testing can be varied from 30 - 70 m.p.h. Load on tyre is set by reducing flat surface load 15%. It is found that with such a correction the deflection on a 60" drum is approx. equal to that on a flat surface. Tyre pressure is generally set to that given in the schedule for the particular load in use, (flat surface). | ||