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).
Estimation of theoretical pressure under the Spectre bonnet at a car speed of 85 m.p.h.
| Identifier | ExFiles\Box 149a\2\ scan0266 | |
| Date | 6th November 1935 | |
| (Appendix - Sheet 5) This page not sent out Estimation of Theoretical Pressure under SpectreCodename for Phantom III Bonnet at car speed of 85 m.p.h. Area of SpectreCodename for Phantom III matrix (frontal area) = 601 sq." Total area of outlets from bonnet (approx.) = 360 sq." Ratio of air velocity through bonnet outlets to velocity through matrix (calculated on basis of free area = frontal area) = 601 / 360 = 1.670 At 85 m.p.h. air velocity through 84 m.m. Mark V matrix = 28 ft/sec. (This figures was estimated from 52 m.m. and 65 m.m. figures shown on sheet 5 since the 84 m.m. figure was obviously incorrect.) Actual air velocity at exit from bonnet = (1.67 x 28) / .9 (assuming coefficient of discharge of .9, say) = 52 ft/sec. If Sp{Mr Spinney} = difference between static pressure under bonnet and atmospheric pressure Sp{Mr Spinney} = p / 2g { v2^2 - v1^2 } where v1 = velocity of exit from matrix and v2 = velocity of exit from bonnet Sp{Mr Spinney} = .070 / 64.4 { 52^2 - 28^2 } = 2.09 lbs/sq.' = .40 "H2O | ||