Computer Aided Investigation of Nonlinear Aircraft Dynamics
by
Mikhail Goman
Department of Mathematical Sciences, De Montfort University, UK
Coauthors: Andrew Khramtsovsky (Central Aerohydrodynamic Institute (TsAGI), Russia)

Many aircraft dynamics problems are highly nonlinear because of the non-linearities in aerodynamics, inertia coupling, nonlinear constraints in control system, etc. These problems can be effectively investigated using numerically implemented qualitative methods, which have been successfully validated in different applications during the last two decades.

Beyond the normal flight conditions, at high incidence and intensive rotation, an aircraft dynamics becomes nonlinear and coupled. As a result the existence of critical flight regimes (such as wing rock or different spin modes) brings about the multiple attractor dynamics, which cannot be thoroughly investigated using only simulation approach. Qualitative and bifurcation analysis methods help to optimally plan piloted simulation and training, to perform post-design assessment of control laws, etc. The qualitative methods become even more important due to the tendency to expand the flight envelope of modern advanced high-performance aircraft to the region of high angles of attack and intensive rotation.

The paper presents a specialized Matlab toolbox for the investigation of nonlinear aircraft dynamics. The toolbox is based on the continuation technique and numerically implemented qualitative methods. The adequate scenario for qualitative investigation and appropriate database structure were developed to support the aircraft dynamics analysis using different sets of equations of motion. The graphical user interface (for both task definition and post-processing of the results) was found to be very useful since large amounts of information are to be collected and analyzed. Numerical results of qualitative investigations are presented to illustrate the problems under consideration.

References: 1. Goman, M.G. & Khramtsovsky, A.V.,(1997). Global stability analysis of nonlinear aircraft dynamics. AIAA Atmospheric Flight Mechanics Conf., New Orleans, LA, Paper 97-3721. 2. Goman, M.G., Zagainov, G.I.&Khramtsovsky, A.V.,(1997). Application of bifurcation methods to nonlinear flight dynamics problems. J.Progr.Aero.Sci .33, 539-586. 3. Goman, M.G. & Khramtsovsky, A.V.(1998) Application of continuation and bifurcation methods to the design of control systems. Phil.Trans.R.Soc.Lond. A 356, 2277-2295.

Date received: January 11, 2000