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Aviation History
1927
1927 - 0831.PDF
OCTOBER 27, 1927 THE AIRCRAFT ENGINEER SUPPLEMENT TOFLIGHT 35 30 25 cji/> 13 Or: h- i 15 IdQ Dr- h,!0 <£ 5 0 -5 - - \\\ .. .1. . i - zo • </j bJ ^TtIf| > i i i CON N - _ 1-8 I 1-7 \ i-6 : is 1-4 - -—- : i-3 ^--^^'^^ • ^~ — ~~~ A : '•I : rO " 0 95 ; - z : - + 40 + 30 +20 +10 o 1 uJ -10 D $ Ld CL-20 S h -30 -40 -50 -60 Fig. 1. In the standard atmosphere there are definite relations l>etween pressure, temperature, density, and altitude, ln an atmosphere which differs from the standard, if the temperature and pressure are known, the density can be calculated and the height in standard atmosphere corresponding to this density obtained from a curve or from tables. The calculation is based on the assumption that Boyle's law applies throughout. I — temperature, degrees Centigrade. p = pressure in inches of mercury. p = density, mass per unit volume, lb.-ft.-sec. Then, up to the lower limit of the isothermal atmosphere 9 ~ (t 4- 273)0 Alxjve this altitude (35.332 ft.) 0 = 0-003378-•9 The Reduction Chart given in Fig. 1 enables the reduction of observed data to conditions of standard atmosphere to be made without any calculations or reference to density curves or tables. It will be seen that it has not been prepared for use for greater heights than 35.000 ft. : as even in these days of supercharged engines such altitudes are not commonly attained on flight tests. It must be understood that the chart is intended for use only in the reduction of height readings as taken from a standard altimeter. An altimeter is simply an aneroid barometer calibrated to read altitudes instead of pressure, and in the standard altimeter the height readings are those corresponding to pressures in standard atmosphere: the height reading being, therefore, a measure of the atmospheric 750c
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