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).
Methods for calculating rolling resistance and wind resistance for car performance.
| Identifier | ExFiles\Box 161\1\ scan0194 | |
| Date | 22th September 1938 | |
| -2- Da{Bernard Day - Chassis Design}/Ev.{Ivan Evernden - coachwork}8/N.22.9.38 Cont'd.{John DeLooze - Company Secretary} (3) Rolling Resistance & Wind Resistance. To calculate the actual value of 'K' from car performance, it is necessary to obtain accurately the following:- (a) The projected facial area. (b) The total drag. (c) The rolling resistance. (a) We can discover the facial area by drawing the car. (b) The total drag can be determined as you suggest by measuring the lap speed at a locked throttle horse power and R.P.M. fixed. M.{Mr Moon / Mr Moore} Andreau gives an empirical formula for directly deriving the 'K'. (V1 - V2)/t is measured whilst decelerating, where (V1 - V2) does not exceed 10 m.p.h. ( see separate memo). We would like to try this method in future and agree with Rm{William Robotham - Chief Engineer}/IMW.{Ivan M. Waller - Head of Chateauroux} that the best way to measure (V1 - V2)/t is to coast across a line at a fixed speed and to measure the time taken to reach a second line at a fixed distance from the first one. The test can be conducted at different initial speeds provided a distance between the lines is chosen in each case such that the velocity difference does not exceed 10 m.p.h. (c) The rolling resistance in the past has been taken as a fixed amount per ton of weight and it is now fairly certain that it increases by a factor between the 3rd. and 4th. power of the speed. M.{Mr Moon / Mr Moore} Andreau has an empirical formula for calculating the rolling resistance in terms of car weight, velocity and tyre pressure ( see separate memo) and in his calculation for the Thunderbolt used this formula, in spite of the fact that it shews the rolling resistance of that car to be twice that of the air at 312 m.p.h. and three times at 344 m.p.h. Cont'd.{John DeLooze - Company Secretary} | ||