Aerodynamic Modelling for the Flutter Analysis of the Sonaca 200 Aircraft

Abstract

Certification of an aircraft is a long and demanding process required by airworthiness requirements of international organisms such as the European Aviation Safety Agency. Being intended to flight schools market, the general aviation Sonaca 200 aircraft has to fulfil huge amount of prerequisites defined by the Certification Specification for Very Light Aeroplane. Among the standards, free-flutter conditions have to be respected and demonstrated by the manufacturer, Sonaca Aircraft. This work concerns the aerodynamic and flutter analyses of a simplified wing model of the Sonaca 200 aircraft. The former study in performed thanks to a time-stepping implementation, developed by KATZ J., of the unsteady Vortex Lattice method. The algorithm is adjusted in order to provide a minimum convergence time to reach a well-defined results accuracy. The method based on the incompressible potential flow theory is adapted to the S200 wing and validated through a comparison with the Sonaca Aircraft aerodynamic results for a flight situation encountered at dive speed and limit load factor. The parallel is carried out in terms of total and spanwise aerodynamic coefficients induced by the lifting surface. The validation of the first method leads to the consideration of the flutter analysis. The second implementation of the unsteady Vortex Lattice method is developed by DIMITRIADIS G. in the frequency domain. This development, combined with a condensate finite element model of the wing, allows to compute the unsteady aerodynamic loads through a Generalised Force Matrix. The modal equations of motion are then solved with the help of a Newton-Raphson scheme and a p-k method. The second wing mode caused the instability leading to the flutter phenomenon caused by a lack of damping at high speed. The flight envelop of the wing is free from flutter in control surfaces blocked and empty fuel tanks setup. Altitude has an influence on the flutter speed and frequency. The critical case appears for a service ceiling altitude on a wing with its implemented wing-tips. Static wing deflections are derived from the method. Further improvements of the aeroelastic model can be performed in order to verify the free-flutter behaviour of the whole Sonaca 200 aircraft in all possible flight conditions.