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).
Formula to correct aero engine ground brake horsepower for atmospheric temperature and pressure variations.
| Identifier | ExFiles\Box 37\3\ scan 113 | |
| Date | 21th September 1917 | |
| X.8148 ORIGINAL EFC3/T21.9.17 To R.{Sir Henry Royce} from EFC. c. to E.{Mr Elliott - Chief Engineer} c. to BJ. c. to BJ. for Oy. c. to By.{R.W. Bailey - Chief Engineer} c. to Da.{Bernard Day - Chassis Design} c. to EP.{G. Eric Platford - Chief Quality Engineer} c. to EH. RE X.31v8 - CORRECTION TO STANDARD OF AERO ENGINE GROUND B.H.P. FOR VARIATION OF ATMOSPHERIC TEMPERATURE AND PRESSURE. Herewith please receive a Chart of the percentage corrections to be applied to observed Aero Engine B.H.P's. to reduce these to standard atmospheric state, viz., 29.9" barometer and 16°C temperature. This chart is based upon the assumption that the B.H.P. varies directly as the air density and has been compiled as the result of a sheet issued by the A.I.D. copy of which herewith. This assumption is not quite correct, because we know that under altitude conditions (when temperature follows a definite law) the B.H.P. follows a law (density)^1.3 approximately. We make out (see other sheets herewith) that the percentage correction to be applied to the B.H.P. of an engine to reduce this to the B.H.P. at standard atmospheric state (cited above) would be fairly well represented by the expression:- 3.7 p + .19 t where p is the number of inches of mercury by which the barometer reading falls short of 29.9" and t is the Contd. | ||