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).
Page 2 of a document detailing the mathematical derivation of a formula for the percentage correction to Indicated Horse Power (I.HP).
| Identifier | ExFiles\Box 37\3\ scan 108 | |
| Date | 11th February 1916 guessed | |
| -2- Contd. If we substi[tu]te in the above the atmospheric values of P and T we should obtain a figure to which 100 bears the same ratio as the corrected I.H.P. bears to the observed I.H.P., and we could therefore correct our I.H.P. It will, however, be more convenient to find the % correction to be applied to I and to obtain Io, the I.H.P. at N.T.P. (or corrected I.H.P.) and thence to find the correction to be applied to B (the B.H.P) to obtain Bo, the B.H.P. at N.T.P. (or corrected B.H.P.) Suppose Po exceeds P by p mm. To falls short of T by t°C. (i.e. t°C is the atm. temp). Io exceeds I by i I.H.P. Then:- Io/I = Po/P x √(T/To) or 1 + i/I = Po/(Po - p) * √((To + t)/To) i.e. 1 + i/I = {1 - p/Po}^-1 {1 + t/To}^(1/2) = 1 + p/Po + t/2To (approx). whence. 100 i/I = 100p/Po + 50t/To = 100p/760 + 50t/273 = .1316 p + .1831 t = % correction to I.H.P. Contd. R.R.C.LTD DERBY NO 1913 | ||