Slightly down-turned wingtip and wing for maintaining lateral static stability of wing

Abstract

The present invention discloses a micro-reverse winglet and a wing that can maintain the lateral static stability of a wing unchanged. The winglet adopts a reverse angle; the installation angle between the winglet and the wing is a negative installation angle; the winglet has a cross-sectional shape with a positive curvature; and a smooth transition section is arranged between the winglet and the wing for connection. The reverse angle of the micro-reverse winglet is 7.5°. By optimizing the airfoil, span and installation angle, a moderate lift is generated on the winglet. The winglet tip and the wing tip simultaneously generate two wingtip vortices rotating in the same direction. The two vortices weaken each other, thereby reducing the total wingtip vortex strength and the induced drag. The drag reduction effect is not lower than that of the traditional winglet. The larger the reverse angle of the winglet, the smaller the lateral static stability of the wing. The reverse angle of 7.5° can keep the lateral static stability of the wing basically unchanged, so that it can be widely used in various types of aircraft.

Description

Technical Field

[0001] The invention belongs to the field of aircraft wing design, in particular to a slightly down-reverse wingtip winglet and a wing which can keep the lateral static stability of the wing unchanged. Background Art

[0002] The fuel consumption rate of transport aircraft during cruising flight is directly proportional to the drag, so aerodynamic drag reduction is of great significance to improving aircraft endurance performance and reducing operating costs. About 60% of the aerodynamic drag of an aircraft during cruising flight is zero-lift drag, and about 40% is induced drag. The former is mainly determined by the aircraft's wetted area and streamline, and it is difficult to further reduce it under a certain technical level. The latter is mainly reflected in the energy loss caused by the wingtip vortex. By optimizing the design of the wingtip shape to weaken the wingtip vortex, the induced drag can be significantly reduced. The wingtip winglet, invented in the late 1970s, is a widely used design measure to reduce induced drag. The design of the wingtip winglet also needs to consider the limitations of the structural bearing capacity, and the bending moment at the wing root is generally used as a constraint. See the schematic diagram of the traditional wingtip winglet. Figure 1 .

[0003] Traditional winglets usually use a large dihedral angle (i.e., the angle between the winglet plane and the wing plane). Although the aerodynamic drag is reduced relative to the original wing, the dihedral effect causes the aircraft's lateral static stability to increase significantly, with an increase of up to 100%, which has a great impact on the aircraft's lateral-to-heading moment stability matching design. For medium and large passenger aircraft, active stabilization technology can be used to overcome this defect, but for small aircraft, active stabilization cannot be used due to cost constraints and other factors. The excessive lateral static stability brought by this winglet will cause the aircraft's handling characteristics to deteriorate, and even fail to meet airworthiness requirements or technical indicators. Summary of the invention

[0004] The purpose of the present invention is to provide a slightly downward-inverted winglet and a wing that can maintain the lateral static stability of the wing unchanged, which can reduce aerodynamic drag on the one hand and avoid the upward inversion of the winglet on the other hand, so that the lateral static stability of the wing remains unchanged, thereby being widely applicable to various types of aircraft.

[0005] The technical solution to achieve the purpose of the present invention is:

[0006] A slightly reversed winglet capable of maintaining the lateral static stability of a wing unchanged, wherein the winglet adopts a reverse angle; the installation angle between the winglet and the wing is a negative installation angle; the winglet has a cross-sectional shape with a positive curvature; and a smooth transition section is arranged between the winglet and the wing for connection.

[0007] Furthermore, the anhedral angle of the winglet 1 is 7.5°.

[0008] Furthermore, the ratio of the maximum thickness of the airfoil of the winglet to the chord length is 12%.

[0009] Furthermore, the installation angle between the winglet and the wing is -8°.

[0010] Furthermore, the total span of the winglet and the transition section is 0.77 times the chord length of the wingtip.

[0011] A wing and winglet combination of a general aircraft comprises a slightly down-converted winglet.

[0012] Compared with the prior art, the present invention has the following significant advantages:

[0013] The dihedral angle of the micro-inverted winglet is 7.5°. By optimizing the airfoil, span and installation angle, moderate lift is generated on the winglet. The winglet tip and the wing tip simultaneously generate two wingtip vortices rotating in the same direction. These two vortices weaken each other, thereby reducing the total wingtip vortex strength and induced drag. The drag reduction effect is not lower than that of traditional winglets. The greater the dihedral angle of the winglet, the lower the lateral static stability of the wing. The use of a 7.5° dihedral angle can keep the lateral static stability of the wing basically unchanged, making it widely applicable to various types of aircraft. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of a conventional winglet in the background technology.

[0015] Figure 2 Schematic diagram of the original wing.

[0016] Figure 3 It is a schematic diagram of the structure of the slightly downward-reversed wingtip winglet of this embodiment.

[0017] Figure 4 It is a comparison curve diagram of the drag characteristics of the slightly down-turned winglet of this embodiment, the traditional winglet and the original wing.

[0018] Figure 5 It is a comparison curve of the rolling moment coefficient of the slightly down-type inverted winglet of the present embodiment, the traditional winglet and the original wing.

[0019] Figure 6 It is the velocity vector diagram in the cross section 0.5m behind the slightly down-turned winglet of this embodiment. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0021] Combination Figure 3In this embodiment, a slightly downward-reversed winglet capable of maintaining the lateral static stability of the wing is provided. The winglet 1 adopts a downward angle of 7.5°, that is, the winglet plane and the wing plane form an angle of -7.5°; the installation angle between the winglet 1 and the wing 2 is a negative installation angle, that is, the winglet head is lowered at a certain angle and then installed and combined with the wing; the winglet 1 has a cross-sectional shape with a positive curvature, that is, the winglet cross-section has a curvature and the curvature direction is upward; the winglet adopts an airfoil with a maximum thickness to chord length ratio of 12%, specifically a NACA4412 airfoil; a smooth transition section 3 is provided between the winglet 1 and the wing 2 for connection.

[0022] Figure 2 The original wing is not equipped with a winglet and is used as a comparative benchmark for evaluating the aerodynamic characteristics of the winglet. In this embodiment, the total span of the winglet 1 and the transition section 3 is 0.77 times the chord length of the original wing tip (ie, 0.77Ct).

[0023] Furthermore, the installation angle between the winglet 1 and the wing 2 is -8°.

[0024] The selected airfoil, anhedral angle, span and installation angle are interrelated and obtained through parameter matrix optimization. The functions of each parameter are as follows: the adopted anhedral angle of 7.5° can adjust the lateral static stability of the wing. The larger the anhedral angle of the winglet, the smaller the lateral static stability of the wing. Too large or too small lateral stability may lead to deterioration of flight characteristics, and even fail to meet airworthiness or design index requirements. The adoption of anhedral angle of 7.5° can keep the lateral static stability of the wing basically unchanged, thereby maintaining the original flight characteristics of the aircraft; the installation angle of -8° and the span of 0.77 times the wingtip chord length are used to adjust the load of the wing and the winglet 1, so that the wing root bending moment of the wing 2 is equivalent to that of the traditional winglet. The deviation of the installation angle and the span from the given values ​​will lead to adverse effects such as deterioration of aerodynamic characteristics or increase of wing root bending moment; the stall characteristics of the airfoil with a relative thickness of 12% are excellent; the transition section enables the winglet 1 to be smoothly connected to the wing 2 without generating additional airflow separation and resistance.

[0025] The anhedral angle of the slightly reversed winglet is 7.5°. By optimizing the airfoil, span and installation angle, moderate lift is generated on the winglet. Two wingtip vortices rotating in the same direction are generated at the wingtip and the wing tip at the same time. These two vortices weaken each other, thereby reducing the total wingtip vortex strength and induced drag. This flow feature can be observed through the velocity vector diagram in the cross section 0.5m behind the wing, see Figure 6 .

[0026] The present invention uses numerical calculation method to evaluate the drag characteristics and lateral moment characteristics of micro-downward inverted winglet, traditional wingtip winglet and original wing. Figure 4 , Figure 5 It can be seen that the aerodynamic drag of the slightly down-type winglet is significantly lower than that of the original wing, and it also has advantages over the traditional winglet. The slope C of the rolling moment coefficient curve with the sideslip angle β lβ That is the lateral static stability, the partial derivative of the rolling moment coefficient with the sideslip angle β C lβ The absolute value represents the magnitude of the lateral static stability. From the curve, we can see that the C of the traditional winglet is lβ The wing has been increased by about 150% compared to the original wing, and the slightly lower reverse winglet C lβ Basically the same as the original wing.

Claims

1. A slightly down-turned wingtip winglet for maintaining the lateral static stability of the wing, characterized in that: The winglet has an anhedral angle; the installation angle between the winglet and the wing is a negative installation angle; the winglet has a cross-sectional shape with a positive curvature; a smooth transition section is provided between the winglet and the wing for connection; The downward angle of the winglet is 7.5°; The ratio of the maximum thickness of the airfoil of the winglet to the chord length is 12%; The installation angle between the winglet and the wing is -8°; The total span of the winglet and the transition section is 0.77 times the chord length of the wingtip.

2. A wing and winglet combination for a general aircraft, characterized in that: It comprises the micro-downward reverse wingtip winglet as claimed in claim 1.

Images