Analytical Methods of Evaluating Aerodynamic Forces of Aircraft Wings

Abstract

ABSTRACT This paper presented methods to determine the aerodynamic forces that act on an aircraft wing during flight. These methods are initially proposed for a simplified two degree-of-freedoms airfoil model and then are extensively applied for a multi-degree-of-freedom airfoil system. Different airspeed conditions are considered in establishing such methods. The accuracy of the presented methods is verified by comparing the estimated aerodynamic forces with the actual values. A good agreement is achieved through the comparisons and it is verified that the present methods can be used to correctly identify the aerodynamic forces acting on the aircraft wing models. INTRODUCTION During flight, aircraft wings always subject to varying aerodynamic loadings and as a consequence, generate varying structural responses. The varying aerodynamic loadings and structural responses are coupled to create a complicated vibration effect known as structural coupling dynamics. This effect can significantly reduce the aircraft’s service life. Even worse, sometimes the sustained vibration at natural frequencies of airfoils may lead to catastrophic structural failure. Recently, a number of researchers have dedicated tremendous effort to developing and choosing light material for the aircraft in order to obtain effective loading capacity. However, as the aircraft speed continues to increase, its structural flexibility is becoming a dominant concern in aircraft design and causing serious flutter in the airfoil and other components. Considering a typical cross-sectional plane of an airfoil, the gravity center G is usually located at 42% ~ 45% of the chord line, and the elasticity center is located at 38% ~ 40% of the chord line (Fig. 1). The gravity center is not coincident with the elastic center, which results in another coupling effect between the translational and rotational degree-of-freedoms of the aircraft wing. This coupling effect and the aforementioned structural coupling dynamics make it too difficult to correctly determine the aerodynamic forces acting on the aircraft wings. The current methods of studying the dynamic response of the aircraft structure consider the structural model and the aerodynamic model separately and therefore fails to precisely simulate the two coupling effects. In this paper, new methods are presented to determine the aerodynamic forces acting on aircraft wings during flight, which considers the model’s structural elasticity and aerodynamics as a combined mathematical system. The methods are initiated based on a simplified two degree-of-freedoms airfoil system and then they will be applied for a finite element aircraft wing model, which is a multi-degree-of-freedom system. The accuracy of the present methods will be verified by comparing the estimated aerodynamic forces with the actual values.