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).
Calculation of the air resistance coefficient 'K' for the Vanvoonen Streamline Saloon.
| Identifier | ExFiles\Box 90\1\ Scan198 | |
| Date | 29th October 1937 | |
| To obtain K.{Mr Kilner} for the Vanvoonen Streamline Saloon. Road Wheel H.P. at 125 M.P.H. = 131 H.P. Rolling resistance 30 lbs/ton and Weight 1.5 tons. Total tractive resistance 45 lbs. H.P. due to constant T.R. at 125 M.P.H. = (45 x 125) / 375 = 15 H.P. H.P. due to Windage = 131 - 15 = 116 H.P. lbs. resistance = (116 x 375) / 125 = 348 lbs. R = Wind Resistance in pounds. V = Velosity in M.P.H. A = Area in square feet. P = Horse Power. K.{Mr Kilner} = Co-eff. of air resistance in lbs/sq.ft. projected area per (M.P.H.)^2 R = K.AV.^2 K = 348 / (216 x 125^2) = .00103 This should be the value of K obtained by Sr. from the wind tunnel tests to enable him to arrive at a speed of 200 kilos a l'heure. Our wind tunnel tests with all three methods give us the following relationship, comparing the theoretical K.{Mr Kilner} values with a road test value for a known car, e.g. the 3 1/2 litre Bentley standard saloon at 86 M.P.H. and 92.5 H.P. at the road wheels. Method | Wind Tunnel K.{Mr Kilner} | Road Test K.{Mr Kilner} | Ratio of Error | Correction Factor | % --- | --- | --- | --- | --- | --- With no ground | .001345 | .002040 | .660 | 1.515 | 80 Flat plate | .001480 | .002040 | .725 | 1.380 | 88 Reflexion Method | .001680 | .002040 | .824 | 1.212 | 100 The corrected 'K' for the model would be therefore .00103 x 1.212 = .00125 | ||