Aircraft Stability Analysis Including Unsteady Aerodynamic Effects

56match the experimental data. To add more flexibility to Stagg’s formulation, we define,as additional model parameters, the set containing one different parameter for each of theleft and right wing lateral arms y wl , y wr , free to vary with the roll angle (see Table 3-1).The results of the identification done for this first improvement to the Stagg’sformulation only using static experimental values, and are shown on Figure 2-2 andFigure 2-3. This parameter identification was done by a least –squares fit between thecalculated values of the normal force and rolling moment coefficients and theexperimental data taken from reference [47]. More details about the parameteridentification can be seen in Chapter 3. Figure 2-4 shows the variation of the identifiedwing lateral arms with the roll angle. We see in Figure 2-2 and Figure 2-3 that theexperimental values of the angle of stall change with the roll angle. The originalformulation does not have the flexibility to account for that either. Trying to improve stillfurther the match between the model responses and the experimental data, we let the∗parameters α and σ vary with the roll angle such that there is one different identifiedvalue of each parameter per roll angle value (see Table 3-1). Finally, the series expansionofCNin α and α& in Eq. (1-18) is also increased to a higher order in Eq. (2-5), due tothe high nonlinearity exhibited by the experimental data. After adding thesemodifications, the first unsteady aerodynamic model for the slender delta wing to beinvestigated is obtained and summarized through Eqs. 2-2 to 2-7. The notation used issimilar to that of Section 1.1.6.