Classification of airfoils

The main geometric parameters describing the shape of a wing are wingspan, wing area (the projected area of the wing in pitch), swept-back angle (mainly leading edge swept-back angle, 1/4 chord swept-back angle, etc.), upward angle of inversion, and the shape of the wing profile (airfoil shape) (Figure 2a). Commonly used basic airfoil shapes are low-speed airfoils, cusp airfoils, supercritical airfoils, and supersonic airfoils with sharper leading edges. In addition, there are some important relative parameters as follows: (1) Spread Chord Ratio: the ratio of the wing wingspan to the average chord length (wing area divided by the wingspan); (2) Tip Root Ratio: the ratio of the wing tip chord length to the wing root chord length; and (3) Relative Thickness of the Airfoil: the ratio of the maximum thickness of the airfoil to the chord length.

These parameters have an important influence on the aerodynamic characteristics of the wing, the wing loaded and structural weight.

The wings of an airplane can be classified into three basic types of wings according to the shape of the top-view plane. The wing has a leading edge swept back angle of about 60°, and the trailing edge is basically no swept back, with a triangular shape in the top view projection. The chord ratio is about 2, and the relative thickness is 0.03~0.05. It is mostly used for supersonic aircraft, especially for tailless aircraft.

Measures to improve the aerodynamic characteristics of the wing of supersonic aircraft commonly used swept back and triangular thin wing there are low-speed large angle of approach characteristics of the shortcomings. In wing design, in addition to the appropriate selection of shape parameters, the following additional measures are often used. It refers to the wing chordwise member, which consists of ordinary wing ribs and reinforced wing ribs. The function of ordinary wing ribs is to maintain the shape of the wing profile and to transfer the aerodynamic loads from the skin to the web in the form of shear flow. The reinforced wing ribs are used to spread the concentrated forces from the ailerons, flaps and landing gear joints to the wing beams, longitudinal walls and skins.

Wings are categorized into beam wings and monolithic wings according to their main bending structural elements. The thicker skins and trusses form the upper and lower wall panels of the wing, which are subjected to bending moment loads in the form of tension and compression along the spreading direction. Both the front and rear wing beams are weak. The leading and trailing edges of the wing are equipped with movable airfoils such as leading edge flaps, trailing edge flaps, and ailerons, so the monoblock wing is only a stressed upper and lower ledge in the center portion between the front and rear beams, forming an airfoil box known as a box girder (Fig. 7).

Supersonic fighter aircraft are commonly used in thin wings with small aspect ratios. Due to the small thickness of the wing, the aerodynamic load is large, in order to ensure a certain degree of torsional stiffness, it is necessary to use a thick skin, the upper and lower trusses into a single piece, forming a multi-beam (or multi-web) structure of the wing. This kind of wing can eliminate the common wing ribs. On delta wings, a similar multi-beam structure is mostly used due to the large chordwise dimensions.