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).
Method for correcting aero engine ground brake horsepower (B.HP) for variations in atmospheric temperature and pressure.
| Identifier | ExFiles\Box 37\3\ scan 107 | |
| Date | 11th February 1916 | |
| X. 3178. -1- X. 3178 CORRECTION OF AERO ENGINE GROUND B.H.P. FOR VARIATION OF ATMOSPHERIC TEMPERATURE AND PRESSURE. We assume the I.H.P. of an engine to vary as the square root of the product of the atmospheric pressure and density i.e. I varies as √PD. and since P/T is constant for all changes of atmospheric conditions (where T is the atmospheric temperature absolute) therefore D varies as P/T and I varies as √P²/T or as P/√T We take as our standard of reference of atmos- pheric state the N.T.P. condition, namely, a barometric height of 760mm. of mercury and a temperature of 0°C. (and cor- rect our powers to this state. Let Po be 760mm. P the barometric reading. to = 0°C. To = 273° abs. t = atm. temp. (°C) T = 273 + t (absolute temp.) since I = k * P/√T therefore for every 100 I.H.P. at N.T.P. k has the value 100 * √273 / 760 = 2.174 so that I = 2.174 * P/√T | ||