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).
Explaining different formulas used for calculating car wind resistance coefficients.
| Identifier | ExFiles\Box 161\1\ scan0244 | |
| Date | 1st December 1938 | |
| To By.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to Da{Bernard Day - Chassis Design}/Ev.{Ivan Evernden - coachwork} c. to Rm{William Robotham - Chief Engineer}/IMW.{Ivan M. Waller - Head of Chateauroux} WINDAGE. Attached is a list of cars with their wind resistances coefficients 'K' calculated, for the sake of comparison on different bases. A.{Mr Adams} Rolling resistance is assumed to remain constant at 30 lb/ton, and K is obtained from first principles - H.P.∝ RV R = KAV² B. As A, except that rolling resistance is obtained from the Andreau formula. RT = (1 / p 0.64) { 245.6 + v 3.7 / 397p 1.44 } Where p = tyre pressure lb/in² C. The Andreau rolling resistance figure is used and K is derived from the formula. K = (W / 2255V₁V₂A) { (101.7 (V₁ - V₂) / t) - RT } Since this is a 'deceleration' formula and only horse power at max. lap speed figures were to hand, (V₁ - V₂) / t was calculated direct from the pull exerted by the hub horse power, and (max. lap speed)² was substituted for V₁V₂. | ||