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).
Formulae for air and rolling resistance, comparing metric and English units.
| Identifier | ExFiles\Box 161\1\ scan0218 | |
| Date | 1st October 1938 | |
| To Da.{Bernard Day - Chassis Design}. from Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions} c. By.{R.W. Bailey - Chief Engineer} Rm.{William Robotham - Chief Engineer} Rm{William Robotham - Chief Engineer}/IMW.{Ivan M. Waller - Head of Chateauroux} Ev.{Ivan Evernden - coachwork} Da{Bernard Day - Chassis Design}/DB.{Donald Bastow - Suspensions}16/N.1.10.38. Air & Rolling Resistance. -------------------- Attached to this memo are prints of formulae extracted from an article by J.{Mr Johnson W.M.} Andreau in "La{L. A. Archer} Vie Automobile" dealing with the above. The formulae given in the article are naturally in metric units and these have been converted to the corresponding English units for convenience of application by ourselves. The formula developed by the "Societe Continentale" from their researches, for rolling resistance is interesting, and may account for some of the apparent difference in K between the wind tunnel and full size tests of the Paulin Bentley. The attached graph of rolling resistance against speed for various inflation pressures shows that for the speeds and pressures normally used the value of the rolling resistance is not appreciably greater than the accepted value of 37.5 lb/ton (see "Some Problems in Chassis Design", L.H.Dawtrey, Proc.I.A.E. Vol.XXVII, p.271). One check was available, some figures on trye drag from tests by the U.S.Rubber Co. which for 28 m.p.h. and 31 lb/in2 gave 28.9 lb/ton, the corresponding value from the formula being 27.9 lb/ton. The tests carried out by Rm{William Robotham - Chief Engineer}/IMW{Ivan M. Waller - Head of Chateauroux}, using 3 throttle stop positions on 28.G.VI, for the two higher speeds gave K as 0.00173 using the "Societe Continentale" formula, whereas the 37.5 lb/ton figure gave K as .00183 for these two higher speeds. In each case the value of K obtained from the lower speed is considerably higher than the other two and has therefore been ignored. Using the "Societe Continentale" formula for the case of 28.G.VI. loaded up to 51.5 cwt, close agreement is obtained for K here, the value being .00178; the increase from the other is less than 3% and is easily within the limits of experimental error. The figure of 37.5 lb/ton gives K .00192, a rather larger increase (9%); this suggests that the formula is more nearly correct than the constant value. Continued..... | ||