Aeroservoelastic stability analysis for flexible aircraft
Aeroelasticity is an important discipline that is used to study the significant variation of the flight envelope of an aircraft along with the flight dynamics and control. The aeroservoelasticity has become an unavoidable analysis problem and is becoming essential for flight controls. The flight dynamics and aeroelasticity are bounded together and both these subjects are related with each other. The natural vibrational frequencies occur due to the low stiffness of the flexible wings in flight dynamics load to their instabilities, experienced by the aircraft among its structural vibrations and vehicle flight dynamics.
In the design stage, aeroelasticity and flight dynamics and control are very important and their interactions are difficult to be studied for flexible aircraft, as they might lead to the significant deformation of the structure. The non-linear coupled dynamics being acted upon by the effect of the control system on the flexible aircraft has become a crucial problem. The unified aeroservoelastic (aerodynamics, structures and controls) analysis framework is needed to be studied for the accurate coupled dynamic modeling that concerns the flight dynamic and aeroelastic features.
Waszak and Schmidt performed the early work for flexible aeroelasticity and flight dynamics studies in . There were many other researchers that suggested that flight dynamics and aeroelasticity should be analyzed as an unified framework to conduct a comprehensive analysis when the study of aeroelasticity and flight dynamics was executed. Due to the large elastic structural deflections and strong coupling between the structural dynamics and the aerodynamics, the aeroelasticity and the flight dynamics and control give (lead) the nonlinear characteristics significantly for the very flexible aircraft.
For flexible aircraft, more researchers, later on, focused on the analysis of the nonlinear flight dynamics, control and aeroelasticity coupling. The Research Laboratory in Active Controls, Avionics, and Aeroservoelasticity (LARCASE) is also conducting research based on controls, avionics, and aeroservoelasticity under its Director, Dr. Ruxandra Botez who is an Engineer, an Aircraft Modeling Specialist, and a Researcher herself at ÉTS in Montreal, Canada. She worked with NASA and Bombardier on aeroservoelastic interactions for the F/A-18 and CL-604 aircraft.
The nonlinear coupled dynamic models that are obtained for flexible aircraft can reflect the special dynamic coupling mechanics. Around the nonlinear equilibrium state, the coupled dynamic equations are linearized for the stability analysis of aeroservoelastic interactions.
To meet the requirements of the modernized aircraft designs in the stability modeling of the control system, the stability of the unified aeroservoelastic framework for the flexible aircraft are analyzed in the time domain. To illustrate an example, the complex aircraft model is selected for the aeroservoelastic stability characteristics, and its rigid/elastic characteristics for the coupled stability.
