Flat-tail-free high-stealth aerodynamic layout pitching moment pitch-up suppression method

Abstract

The invention discloses a horizontal-tail-free high-stealth aerodynamic layout pitching moment pitch-up suppression method, and belongs to the technical field of aerodynamic design of aviation aircrafts. Edging is conducted on the lateral edge of the front fuselage, rounding is conducted along the lateral edge line of the front fuselage, small-radius smooth transition is achieved, and the edging effect of the lateral edge of the front fuselage is reduced; the plane shape of the wing adopts a Lamda wing, the Lamda wing comprises an inner wing section and an outer wing section, and the inner wing section and the outer wing section form a lambda shape; the trailing edge of the inner wing section of the Lamda wing is swept forward, the inner side area of the trailing edge of the wing is increased, the effect of partially replacing a horizontal tail is achieved, and the aerodynamic focus is changed by designing parameters of the Lamda wing. According to the invention, the edging of the fuselage edge is realized by rounding the lateral edge of the front fuselage, and the flowing characteristic of the upper surface of the wing is changed, so that the pitch angle of pitch moment is delayed by 1 degree when the aircraft is at a low speed and a large angle of attack; the designed Lamda wings can generate larger head lowering torque at a large incidence angle, so that the pitching moment and the pitching incidence angle are delayed by more than 1 degree at the low speed and the large incidence angle of the aircraft; and the stealth performance of the whole aircraft is not influenced.

Description

Technical Field

[0001] The invention belongs to the technical field of aerodynamic design of aviation vehicles, and relates to a method for suppressing the pitching moment of an aerodynamic layout of a high-stealth aircraft without a horizontal tail. Background Art

[0002] For fighter aircraft with conventional layout, the horizontal tail is an important pitch control surface. Its aerodynamic focus is close to the tail of the fuselage, and it also plays the role of suppressing the pitch moment.

[0003] Since the horizontal tail and the vertical tail form a dihedral angle, they are strong scattering sources of radar signals, and the elimination of the horizontal tail design is an important appearance feature of modern stealth aircraft. One of the aerodynamic characteristics caused by the design without a horizontal tail is that the pitch angle of attack is reduced during the pitch moment, and the pitch moment characteristics become worse. The poor pitch moment characteristics of the aircraft make it impossible for the aircraft to return to the small angle of attack state in time at a low speed and a large angle of attack, causing the aircraft to lose control. For the sake of safety and the minimum acceptable flight quality requirements, devices with angle of attack protection functions such as push rods must be used to limit the maximum usable angle of attack; so that the actual maximum angle of attack is much smaller than the stall angle of attack.

[0004] Therefore, it is an urgent hope for aircraft designers to find corresponding technical solutions to overcome or reduce the pitching moment. For aircraft that do not consider stealth performance, the main technical means used to improve the moment pitching characteristics are to install vortex generators, guide vanes, stall strips, leading edge slats, etc. These technical means will form dihedral angles, gaps, protrusions, etc. on the aircraft body, which seriously affect the stealth performance of the aircraft. Therefore, these technical means are rarely used on stealth aircraft. Summary of the invention

[0005] A typical high-stealth, long-flight aerodynamic layout without a horizontal tail is as follows: Figure 1 This layout has a large aspect ratio (A>5) and lift-to-drag ratio (K>14), but the horizontal tail is eliminated, and the projection area of ​​the vertical tail in the plane of the aircraft is very small, resulting in a very poor pitch moment characteristic at a large angle of attack (α≥12°), a sharp increase in pitch moment, and an obvious pitch-up characteristic, which can easily cause the aircraft to lose control.

[0006] In this regard, the purpose of the present invention is to propose a method for suppressing or delaying the pitch moment of such a high-stealth aerodynamic layout without a horizontal tail without affecting the stealth performance.

[0007] The technical solution of the present invention is:

[0008] The pitch-up suppression method of the high-stealth aerodynamic layout without a horizontal tail is as follows:

[0009] The side edges of the front fuselage are striped and rounded along the side edges of the front fuselage to achieve a smooth transition with a small radius and reduce the strip effect of the side edges of the front fuselage; the wing plane shape adopts a Lambda wing, and the Lambda wing includes an inner wing section and an outer wing section, which form a "λ" shape; the trailing edge of the inner wing section of the Lambda wing is swept forward to increase the inner side area of ​​the wing trailing edge and partially replace the role of the horizontal tail. The aerodynamic focus is changed by designing the parameters of the Lambda wing.

[0010] Further, the rounded area is from 10% to 100% of the length of the front fuselage; and the radius of the rounding is 3-10 mm.

[0011] Furthermore, the sweep angle of the trailing edge of the inner wing section of the Lambda wing is 30° to 40°; the increased wing area accounts for 10% to 25% of the wing area of ​​the inner wing section.

[0012] Beneficial effects of the present invention: The present invention uses the rounding method of the side edges of the front fuselage to achieve the edge striping of the fuselage edge, which changes the flow characteristics of the upper surface of the wing, so that the pitch moment of the aircraft at low speed and high angle of attack is delayed by 1°; the lambda wing designed by the present invention generates a larger nose-down moment at a large angle of attack, so that the pitch moment of the aircraft at low speed and high angle of attack is delayed by more than 1°; it has no effect on the stealth performance of the entire aircraft. The pitch moment of the aircraft body of the present invention increases the pitch angle by more than 2°. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a typical aerodynamic layout with high stealth and long flight time without a horizontal tail.

[0014] Figure 2 This is a schematic diagram of the removal of the side edges of the fuselage.

[0015] Figure 3 It is the pitch-up suppression effect of the fuselage side edge removal.

[0016] Figure 4 It is a partial schematic diagram of the Lambda wing, where (a) increases by 10% and (b) increases by 20%.

[0017] Figure 5 It is the pitch-up suppression effect of the Lambda wing pitch moment.

[0018] Figure 6 is the rounded area.

[0019] Figure 7 It is a comparison chart of the results of the optimized design of the present invention and the original aircraft design. DETAILED DESCRIPTION

[0020] The technical solution of the present invention is further described in detail below through embodiments and drawings.

[0021] like Figure 2As shown, the fuselage side edge is rounded along the fuselage side edge. If the rounding radius is too large, the fuselage lateral stealth performance will be affected. If the rounding radius is too small, the edge removal effect is not obvious. Therefore, the rounding radius along the fuselage side edge is between 3mm and 10mm. Figure 6 As shown by the thick line, it accounts for 90% of the length of the front fuselage of the aircraft. Experiments were conducted with the fillets of 10mm, 5mm, and 3mm as examples. The results are shown in Figure 3 As shown in the figure, due to the removal of the side strips, the vortex intensity is weakened, which changes the flow on the upper surface of the wing and generates a larger nose-down moment at a large angle of attack.

[0022] like Figure 4 As shown in the figure, the Lambda wing design divides the wing into two wing sections, the inner and outer wing sections. The trailing edge of the inner wing section is swept forward, with a sweep angle of 30° to 40°, and is combined with the outer wing section to form a "λ" shape. The increased wing area accounts for 10% to 25% of the wing area of ​​the inner wing section. The Lambda wing makes the wing aerodynamic focus, the nose-down moment increases at large angles of attack, and the wing area with a smaller backward shift increases ( Figure 4 (a) in the figure increases by 10%), which can significantly improve the bottom characteristics of the moment curve. The larger wing area increases ( Figure 4 (b) in (20%) increases the moment pitch angle by more than 1°. The result is as follows Figure 5 shown.

[0023] The pitch moment suppression method was applied to a certain type of high stealth unmanned combat flight platform without horizontal tail. The pitch moment angle of attack was increased by 2° during the low-speed takeoff phase. The results are as follows: Figure 7 shown.

Claims

1. A pitch-up moment suppression method for a high-stealth aerodynamic layout without a horizontal tail, characterized in that: The details are as follows: The side edges of the front fuselage are striped and rounded along the side edges of the front fuselage to achieve a smooth transition with a small radius and reduce the strip effect of the side edges of the front fuselage; the wing plane shape adopts a Lambda wing, and the Lambda wing includes an inner wing section and an outer wing section, which form a "λ" shape; the trailing edge of the inner wing section of the Lambda wing is swept forward to increase the inner side area of ​​the wing trailing edge and partially replace the function of the horizontal tail. The aerodynamic focus is changed by designing the parameters of the Lambda wing.

2. The pitch-up moment suppression method of the high-stealth aerodynamic layout without a horizontal tail according to claim 1 is characterized in that: The rounded area is from 10% to 100% of the length of the front fuselage; the radius size of the rounding is 3-10mm.

3. The pitch-up moment suppression method of the high-stealth aerodynamic layout without a horizontal tail according to claim 1 or 2 is characterized in that: The sweep angle of the trailing edge of the inner wing section of the Lambda wing is 30° to 40°; the increased wing area accounts for 10% to 25% of the wing area of ​​the inner wing section.

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