CN110104160B

CN110104160B - Middle-distance coupling folding double-wing aircraft

Info

Publication number: CN110104160B
Application number: CN201910332057.4A
Authority: CN
Inventors: 蒋崇文; 李志豪; 许晨豪; 高振勋; 李椿萱
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2019-04-24
Filing date: 2019-04-24
Publication date: 2021-01-01
Anticipated expiration: 2039-04-24
Also published as: CN110104160A

Abstract

The invention discloses a middle-distance coupling folding double-wing aircraft, and belongs to the technical field of aircraft pneumatic layout design. The aircraft uses a traditional columnar fuselage, the tail of the aircraft is provided with three empennages with the same geometric appearance, in the flight form, the front wing is provided with a sweepback angle to ensure that the trailing edge line of the front wing is vertical to the axis of the fuselage, the rear wing is a lower single wing, and the length of the rear wing chord is 50 percent of the chord length of the front wing; the rear wing has a forward sweep angle, and the vertical distance between the front wing and the rear wing is the vertical height of the fuselage; the front wing and the rear wing can be folded backwards in a rotating way; when the folding state is carried out, the front wing is hidden at the side of the machine body, and the rear wing is hidden below the machine body. The invention can utilize the airflow acceleration effect of the upper surface of the rear wing and the low-pressure area of the upper surface of the rear wing to enhance the capability of the airflow at the rear edge of the front wing to overcome the adverse pressure gradient, thereby increasing the lift-drag ratio of the aircraft and leading the lift-drag ratio to reach the level which is close to or even exceed the aerodynamic efficiency of the single-wing aircraft.

Description

Middle-distance coupling folding double-wing aircraft

Technical Field

The invention belongs to the technical field of aerodynamic layout design of aircrafts, and particularly relates to an aerodynamic layout of an aircraft with middle-distance coupling folding double wings.

Background

The folding wing aircraft is an aircraft capable of folding and containing the wing surface of the aircraft, and has the characteristics of small occupied space and convenience in storage and carrying. Has positive significance in the fields of military investigation and civil mapping.

Since the wings of a folding wing aircraft need to be folded close to the fuselage. The maximum length of the wing is limited due to the limited length of the fuselage. Considering that the wing strength of the folding wing is poor, even if the limit of the length of the fuselage is not considered, the unfolding length is not too long. Therefore, in order to increase the wing area and enable the aircraft to obtain enough lift force, a double-wing layout is formed in the folding wing aircraft, for example, a U.S. Switchable flick unmanned aerial vehicle is provided with a pair of folding wings with the same length and length in the nose and the tail, so that the wing area and the generated lift force of the aircraft are effectively increased. However, other problems arise, because the wake air flow of the front wing/upper wing can generate adverse aerodynamic interference on the rear wing/lower wing, the aerodynamic efficiency of the double-wing aircraft is lower than that of a single-wing aircraft with the same wing area and aspect ratio, and the energy utilization rate and the cruising time of the double-wing aircraft are reduced.

Based on aerodynamics-related definition parameters, the flight environment of a folding wing aircraft mostly belongs to medium reynolds number, such as the environment with the reynolds number of 50 to 300 ten thousand, so that the air flow characteristics on the surface of the aircraft are different from those of a large aircraft (the reynolds number is in the order of 1000 to several tens of millions). The traditional aircraft design experience shows that to improve the lift-drag ratio of a double-wing aircraft with the same chord length, the front-back and vertical distances between two wings should be increased as much as possible so as to reduce the adverse aerodynamic interference of the double wings of the aircraft. Like the flick knife unmanned aerial vehicle, the wings respectively arranged at the head position and the tail position enable the distance between the two wings to reach the maximum level within the design range. However, the layout design method which aims at reducing adverse effects is limited in improving the aerodynamic efficiency of the double-wing aircraft with medium reynolds number, and the lift-drag ratio of the single-wing aircraft with the same airfoil area and aspect-chord ratio cannot be achieved or exceeded. This is because the twin wing arrangement has both an adverse and a beneficial effect on aerodynamic effect, and increasing the fore and aft wing distances in unison results in a reduction in the adverse aerodynamic effect while the beneficial aerodynamic effect is also reduced in the same proportion. It is therefore possible and necessary to propose a new aerodynamic layout that reduces as far as possible the adverse aerodynamic interference of the two wings and exploits the advantageous aerodynamic interference of the two wings at the corresponding medium reynolds numbers of the folding aircraft.

Disclosure of Invention

The invention provides a folding wing aircraft adopting a middle-distance coupling double-wing layout based on the characteristics of medium Reynolds number air flow from a pneumatic angle. According to the layout, the rear wing with small chord length is arranged below the rear edge of the front wing, the airflow at the rear edge of the front wing is guided and accelerated by the airflow acceleration action of the upper wing surface of the rear wing, the pressure intensity of the rear edge of the front wing is reduced by the low-pressure area of the upper wing surface of the rear wing, and the capability of the airflow on the upper surface of the front wing to overcome the inverse pressure gradient is enhanced. The chord length of the rear wing is only 50% of that of the front wing, the proportion of the adverse aerodynamic influence of the front wing on the rear wing in the whole aerodynamic is reduced, and the effect of the adverse aerodynamic influence is increased. The lift-drag ratio of the aircraft as a whole is higher than that of a conventional two-wing aircraft. The coupling mode utilizing the aerodynamic interference of the rear wing forms a novel middle-distance coupling double-wing layout.

The invention provides a middle-distance coupling folding double-wing aircraft, which uses a traditional columnar fuselage, wherein the tail of the aircraft is provided with three empennages with the same geometric appearance, one empennage is vertical to the horizontal plane of the fuselage and faces upwards, and the other two empennages are arranged on two sides of the tail and are vertical to the left and right symmetrical planes of the aircraft. The front wing has a sweep angle such that its trailing edge line is perpendicular to the fuselage axis when the aircraft is in flight configuration. The rear wing is a lower single wing, and the length of the rear wing chord is 50% of that of the front wing chord. The rear wing has a forward sweep angle in flight form, and the forward sweep angle ensures that the chord-wise distance between the front edge of the rear wing and the front edge of the front wing always accounts for about 90 percent (± 10 percent) of the chord length of the front wing. The vertical distance between the front wing and the rear wing is the vertical height of the fuselage. The front wing and the rear wing are respectively connected with the fuselage through a front wing rotating shaft and a rear wing rotating shaft, so that the front wing and the rear wing can rotate and fold backwards. The spread length of the front wing is not more than the distance between the rotating shaft of the front wing and the tail wing, and the spread length of the rear wing is not more than the distance between the rotating shaft of the rear wing and the tail wing, so that the wings can not form structural interference with the tail wing when the aircraft enters a folded state. When the aircraft enters a folded state, the front wings rotate backwards along the two sides of the aircraft body and are hidden at the side of the aircraft body, and the left rear wings and the right rear wings rotate backwards by 90 degrees along a plane of a top view and are hidden below the aircraft body. The aircraft appears cylindrical from a top view.

The invention has the advantages that:

the invention provides a pneumatic layout of a folding double-wing aircraft, which solves the problem of double-wing pneumatic interference of medium Reynolds number. The layout can utilize the airflow acceleration effect of the upper surface of the rear wing and the low-pressure area of the upper surface of the rear wing to enhance the capability of the airflow at the rear edge of the front wing to overcome the adverse pressure gradient, so that the lift-drag ratio of the aircraft is increased, and the aerodynamic efficiency level of the aircraft is close to or even exceeds that of a single-wing aircraft.

Drawings

Fig. 1a, 1b, 1c, 1d, which are respectively a top view, a bottom view, a front view and a left side view of a layout of a mid-range coupled folding two-wing aircraft in an unfolded state;

2a, 2b, 2c, 2d, respectively, a top view, a bottom view, a front view and a side view of a mid-range coupled folded two-wing aircraft layout in a folded state;

FIG. 3 is a schematic view of the relative positions of the front and rear wings on the airfoil section;

FIG. 4 is a schematic diagram of the design constraint of the spatial position of the front wing rotating shaft;

FIG. 5 is a comparison of lift-to-drag ratios for different two-wing cases and equivalent single-wing layouts;

fig. 6 is a comparison of lift coefficients for different two-wing cases and an equivalent single-wing layout.

In the figure:

1. a front wing; 2. a rear wing; 3. a body; 4. a tail wing; 5. a tail nozzle; 6. a front wing rotating shaft; 7. a rear wing rotating shaft.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

The invention provides a middle-distance coupling folding double-wing aircraft, which is mainly composed of a front wing 1, a rear wing 2, an aircraft body 3, a tail wing 4 and a tail nozzle 5 by combining figures 1 a-1 d and figures 2 a-2 d, wherein the tail nozzle 5 is positioned at the tail part of the aircraft body. The left part and the right part of the front wing 1 are respectively connected with the top of the fuselage 3 through two front wing rotating shafts 6, and the left part and the right part of the rear wing 2 are respectively connected with the bottom of the fuselage 3 through two rear wing rotating shafts 7. The front wing 1 can rotate about a front wing rotation shaft 6 arranged obliquely. The rear wing 2 can rotate in the plane in the direction of the tail of the aircraft by taking the rear wing rotating shaft 7 as an axial direction. The spreading length of the front wing 1 is not more than the horizontal distance between the front wing rotating shaft 6 and the front edge of the tail wing 4, so that the front wing 1 cannot collide and interfere with the tail wing 4 in the rotating process, and the root of the front wing 1 is cut so as to ensure that the front wing 1 cannot structurally interfere with the fuselage 3 in the rotating spreading/retracting process of the front wing 1. The front wing 1 is swept backward without upper and lower negative angles, and the design requirement of the swept-back angle is to ensure that the rear edge line of the front wing 1 is perpendicular to the axis of the fuselage. The span length of the rear wing 2 is the same as that of the front wing 1, and the chord length of the rear wing 2 is 50% of that of the front wing 1. The rear wing 2 is forward swept, has no upper and lower dihedral angles, and the forward sweep angle is designed to ensure that the horizontal distance s between the front edge point of the rear wing 2 and the front edge point of the front wing 1 in each wing section is 0.9 +/-0.1 times of the chord length of the front wing 1. If the positional relationship between the front wing 1 and the rear wing 2 is shown as an example in fig. 3, the horizontal distance s in the drawing is required to be 0.9 ± 0.1 times the chord length of the front wing 1, and the vertical distance g is equal to the vertical thickness of the fuselage 3.

The front wing rotating shaft 6 is an inclined rotating shaft AB, a connecting line of A, B points in fig. 1 a-2 d is the position of the front wing rotating shaft 6, the left front wing rotating shaft 6 and the right front wing rotating shaft 6 share a point B, and the two points A are symmetrical about the longitudinal axis of the fuselage. The point A is positioned at the left side and the right side of the fuselage 3 and is close to the top of the fuselage 3, and the front-back distance between the point A and the empennage 4 is more than or equal to the spread length of the front wing 1; point B is located in the middle of the fuselage height, forward and below point a in side view, and inboard and below point a in front view. The relative spatial position relationship between the point B and the point a is shown in fig. 4, that is, the relative position of the point A, B is equivalent to two diagonal points of a cube, and the projections of the connecting line A, B in the top view direction, the front view direction and the side view direction of the aircraft form an angle of 45 degrees with the horizontal direction and the vertical direction, and the front wing rotating shaft 6 arranged under the angle relationship can complete the rotation process of the front wing 1 from the horizontal plane to the left and the right sides of the fuselage.

Example 1:

the front wing 1 and the rear wing 2 have the same airfoil shape, and are selected to be NACA 4412, the chord length of the rear wing 2 is 50% of that of the front wing 1, the flow Reynolds number Re is 3000000, the position relationship in FIG. 3 is defined, two schemes of s being 0.25 times the chord length of the front wing 1 and s being 0.9 times the chord length of the front wing 1 are adopted, the vertical distance is uniformly adopted to be the vertical thickness of the fuselage, in the embodiment, the vertical thickness of the fuselage is 1.0 times the chord length of the front wing 1, and aerodynamic performance data of the two different schemes are calculated. The rear wing is located right below the front wing when s is 0.25 times the front chord length, and the two-wing layout used in the present invention is represented by s is 0.9 times the front chord length. The calculation results are shown in fig. 5 and 6. Fig. 5 and 6 show lift-drag ratio and lift coefficient data of a two-wing layout in which the horizontal distance s is 0.25 times and 0.9 times the chord length of the front wing, and a single-wing layout equivalent to the airfoil area and the aspect ratio of the rear wing 2 of the front wing 1, respectively. It can be seen that the lift-drag ratio at s-0.9 is very close to the lift-drag ratio of the equivalent single-wing layout, and the lift-drag ratio and lift coefficient of the double-wing layout at s-0.9 at an angle of attack equal to 0 ° are even slightly higher than those of the equivalent single-wing layout, which is an effect that cannot be achieved by the conventional double-wing layout. And the lift-drag ratio and the lift coefficient of the double-wing layout with s equal to 0.25 at each attack angle are lower than those of the first two, which proves that the double-wing layout with s equal to 0.9 has a positive effect on the aerodynamic performance of the double wings.

In conclusion, the invention provides a novel middle-distance coupling folding double-wing aircraft by reasonably arranging the double-wing layout, and the aerodynamic efficiency of the novel middle-distance coupling folding double-wing aircraft is superior to that of the traditional double-wing layout by utilizing the low pressure of the upper surface of the rear wing and the airflow acceleration effect. The above is only a study of the examples. And specific analysis is carried out on other design conditions, and then support wing design parameters such as Renuo number, wing airfoil shape, vertical distance g and the like are determined. The layout of the aircraft wing generally meets the design requirement that the front-rear horizontal distance is equal to 0.9 +/-0.1 times the chord length of the front wing.

All of the embodiments described above are exemplary only, and not exclusive. The dimensions, cross-sectional shapes and relative positions of the various components of the invention are determined according to design requirements and are suitable for aerodynamic layout design of aircraft of any size, all variations which are within the scope of or equivalent to the scope of the claims of the present invention being embraced by the present invention.

Claims

1. A middle-distance coupling folding double-wing aircraft comprises a front wing, a rear wing, a fuselage, a tail wing and a tail nozzle, wherein the tail nozzle is positioned at the tail part of the fuselage; the method is characterized in that: when the aircraft is in a flight state, the front wing has a sweepback angle so that the trailing edge line of the front wing is perpendicular to the axis of the fuselage; the rear wing is a lower single wing, and the length of the rear wing chord is 50 percent of that of the front wing chord; the rear wing has a forward sweep angle in the flying state, and the forward sweep angle ensures that the chord-wise distance between the front edge of the rear wing and the front edge of the front wing always accounts for 80-100% of the chord length of the front wing; the vertical distance between the front wing and the rear wing is the vertical height of the fuselage; the front wing and the rear wing are respectively connected with the fuselage through a front wing rotating shaft and a rear wing rotating shaft, so that the front wing and the rear wing can rotate and fold backwards; the spread length of the front wing is not more than the distance between the rotating shaft of the front wing and the tail wing, and the spread length of the rear wing is not more than the distance between the rotating shaft of the rear wing and the tail wing, so that the wings can not form structural interference with the tail wing when the aircraft enters a folded state; when the aircraft enters a folded state, the front wings rotate backwards along the two sides of the aircraft body and are hidden at the side of the aircraft body, and the left rear wings and the right rear wings rotate backwards by 90 degrees along a plane of a top view and are hidden below the aircraft body.

2. The mid-range coupled folding two-wing aircraft according to claim 1, wherein: the machine body adopts a traditional column-shaped machine body; the three tail wings are positioned at the tail of the aircraft body, the three tail wings have the same geometric appearance, one of the three tail wings is vertical to the horizontal plane of the aircraft body and faces upwards, and the other two tail wings are arranged at the two sides of the tail and are vertical to the bilateral symmetry plane of the aircraft.

3. The mid-range coupled folding two-wing aircraft according to claim 1, wherein: the left part and the right part of the front wing are respectively connected with the top of the fuselage through two front wing rotating shafts, and the left part and the right part of the rear wing are respectively connected with the bottom of the fuselage through two rear wing rotating shafts.

4. The mid-range coupled folding two-wing aircraft according to claim 1, wherein: the root of the front wing is cut, so that the front wing cannot generate structural interference with the fuselage in the rotating unfolding or folding process of the front wing.

5. The mid-range coupled folding two-wing aircraft according to claim 1, wherein: the front wing rotating shaft is defined as an AB line segment, the left front wing rotating shaft and the right front wing rotating shaft share a point B, and the two points A are symmetrical about the longitudinal axis of the fuselage; the point A is positioned at the left side and the right side of the fuselage and is close to the top of the fuselage, and the front-back distance between the point A and the empennage is more than or equal to the spread length of the front wing 1; the point B is positioned in the middle of the height of the fuselage, is positioned in front of and below the point A in a side view, and is positioned in the front view and is positioned on the inner side of and below the point A; A. the relative position of the point B is equivalent to two diagonal points of a cube, and the projections of the A, B connecting lines in the overlooking direction, the front-looking direction and the side-looking direction of the aircraft form an angle of 45 degrees with the horizontal direction and the vertical direction.