FLIGHT DETERMINATION OF A„ AND hs

For the general case, (2.3,5) suggests that the measurement of hn requires the mea­surement of Cma and CLa. Flight measurements of aerodynamic derivatives such as these can be made by dynamic techniques. However, in the simpler case when the complications presented by propulsive, compressibility, or aeroelastic effects are ab­sent, then the relations implicit in Figs. 2.18 and 2.19 lead to a means of finding h„ from the elevator trim curves. In that case all the coefficients of (2.4,13) are con­stants, and

Thus measurements of the slope of Setr. m vs. CLmm at various CG positions produce a curve like that of Fig. 2.21, in which the intercept on the h axis is the required NR When speed effects are present, it is clear from (2.4,27) that a plot of (d8etrjJdV)s against h will determine hs as the point where the curve crosses the h axis.