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 calculation to correct Indicated Horse Power (I.HP) for atmospheric conditions.
| Identifier | ExFiles\Box 37\3\ scan 118 | |
| Date | 20th September 1917 guessed | |
| Contd. -2- therefore for every 100 I.H.P. at N.T.P. k has the value 100 √289 / 29.9 = 1700 / 29.9 = 5.68 so that I = 5.68 P/√T If we substitute 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 to obtain Io, the I.H.P. at standard state (for 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 standard state (or corrected B.H.P.) Suppose Po exceeds P by p inches. To falls short of T by t°C. (i.e. t°C is the atm. temp. - 16° C). Io exceeds I by i H.P. Then:- Io/I = Po/P x √T/To or (I + i)/I = Po/(Po - p) √(To + t)/To i.e. 1 + i/I = { 1 - p/Po }^-1 { 1 + t/To }^1/2 whence. ≃ 1 + p/Po + t/2To (approx.). 100i/I = 100 p/Po + 50 t/To Contd. | ||