Measuring aircraft nonlinearity across aerodynamic attitude flight envelope

A new asymmetric level aerodynamic attitude flight envelope is introduced in this paper. Further, the nonlinearity of a six degree of freedom aircraft simulation model is analyzed with nonlinear index theory across this nontraditional flight envelope. The aerodynamic attitude envelope is an angle of attack vs. sideslip angle region describing the extent of where an aircraft can sustain a slipping horizontal flight condition, and is thus an extension of the more common speed-altitude symmetric level flight envelope. This new envelope can be used for design requirements, dynamic analysis, control synthesis, or performance comparison. Aircraft dynamic properties often change in a nonlinear way across operating conditions. Nonlinear index theory provides a new concept for measuring the strength of these changes and is applied to the asymmetric aerodynamic attitude envelope, as well as the traditional symmetric speed-altitude envelope. This analysis provides new methodology and new insights to aircraft dynamics and control.