CN107957575B

CN107957575B - Method for realizing conical scanning by two-branch one-hanging support system

Info

Publication number: CN107957575B
Application number: CN201711477341.8A
Authority: CN
Inventors: 何国瑜; 李志平; 王正鹏; 武建华
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2017-12-29
Filing date: 2017-12-29
Publication date: 2021-11-02
Anticipated expiration: 2037-12-29
Also published as: CN107957575A

Abstract

The invention relates to a method for realizing cone scanning by two-support-by-one-suspension support systems. The two supporting rods are fixed on the rotary table and are vertical to the surface of the rotary table. The two struts are mechanically connected to the aircraft at points b and c. And a lifting rope fixed on the roof is connected with a point a on the back of the airplane, and the lifting rope is superposed with the axis of the rotary table. The airplane is fixed in the air through the three points a, b and c. The invention also discloses a method for realizing cone scanning through multi-axis linkage, which enables a rotating shaft of a large target to be vertical to the target in the measuring process instead of the ground, and the two-branch one-hanging bracket is compared with the traditional foam bracket and the low-scattering bracket: the load bearing capacity is high, the target erection mechanism does not damage the target, and the method has good application prospect in RCS measurement of a 1:1 real airplane.

Description

Method for realizing conical scanning by two-branch one-hanging support system

Technical Field

The invention belongs to the technical field of low observability, and particularly relates to an application method and technology of a target supporting and hanging system in RCS measurement of a stealth aircraft in real operation.

Background

In the field of numerical control machines, multi-axis linkage is relatively mature. However, in the measurement system, especially in the RCS test of a 1:1 mounting aircraft, the multi-axis linkage technology is still a new technology to be explored.

In the RCS measurement, the rational design of the stent system is a complicated task. Different targets, different weights, and different rack system options should be used.

Although the method for completing the conical scanning by two cranes and one crane through five-axis linkage has many advantages, the technology is not adopted in large stealth aircraft tests such as F22 and the like in order to ensure the safety of an aircraft test system. On the other hand, in the RCS test of the target (stealth unmanned aerial vehicle) that the weight is lighter that the size is less, the method of this patent has extensive application prospect.

The Radar Cross Section (RCS for short) of a complex target is a function of frequency F, polarization states (HH, VV, VH, HV), and characteristic attitude angles θ, φ.

The characteristic attitude angle represents an included angle between the plane electromagnetic wave direction and the target, and is shown in fig. 2. For accurately describing the attitude angles theta and phi, a target coordinate system is established on the tested airplane, the airplane is aligned to an x 'axis and is coincided with the axis of the airplane body, the horizontal plane of the airplane is coincided with an x' y 'plane, and a z' axis is vertical to the back of the airplane.

In FIG. 2, θ is the angle between the z' axis and the electromagnetic ray, and is called zenith angle; phi is the included angle between the projection of the electromagnetic wave ray on the plane x ' y ' and the x ' axis, and is called the azimuth angle. The radar is a point in a target coordinate system, and the radar position is determined by three independent parameters r, theta and phi.

x＝r sinθcosφ

y＝r sinθsinφ(1)

z＝r cosθ

When theta belongs to (0, pi/2) and phi belongs to (0,2 pi), the radar can cover all angles of the plane irradiated by the radar, and a full-space and unique radar scattering cross section sigma (theta, phi) can be obtained.

In order to distinguish from a pitch angle, a yaw angle and a roll angle in flight mechanics, when discussing a radar scattering cross section, an included angle theta and phi between a radar ray and an airplane is defined as a characteristic attitude angle.

Typically, the static RCS measurement on the ground is to change the attitude angle measurement σ (θ, φ) between the target and the radar rays at a given frequency, polarization. The method of changing the attitude angle θ, φ relies primarily on the rotating mechanism of the target holder, as shown in FIG. 3: fig. 3(a) shows a metal stent in which the electromagnetic radiation is tilted with respect to the rotation axis, which is defined as a cone scan. FIG. 3(b) is a foam stent, in which the electromagnetic wave rays are perpendicular to the rotation axis, defined as a great circle scan. The azimuth angles of the two types are phi and phi respectively₁. For cone scanning, when the azimuth angle phi changes, the zenith angle theta is constant, and the pitch angle alpha is a (phi); for scanning a great circle, azimuth angle phi₁When the angle is changed, alpha is constant, and the zenith angle theta is equal to theta (phi)₁)。

The normal working mode of two-boom and one-boom is shown in figure 4, and belongs to the large circle scanning type. The measurement result is σ (α, φ)₁). The required σ (θ, φ) can be obtained indirectly via coordinate transformation, see FIG. 5. Wherein, FIG. 5(a) shows a pitch angle α and a turntable azimuth angle φ₁Distribution of measurement points on a plane; FIG. 5(b) is a distribution of measurement points on the zenith angle θ and aircraft azimuth φ planes. Points on the graphs of fig. 5(a) and 5(b) correspond one-to-one.

The explanation of fig. 5(b) is as follows: when alpha is equal to-15 degrees, the azimuth angle phi of the rotary table₁When the angle is equal to 0, the zenith angle theta is equal to 75 degrees; phi is a₁When equal to 90, θ is equal to 90 °; phi is a₁ When 180, θ is 105 °; phi is a₁ When 270, θ is 90 °; phi is a₁ When 360, θ is 75 °.

When alpha is 15 deg., the rotating platform azimuth angle phi₁0, 105 degrees at the zenith angle theta; phi is a₁When equal to 90, theta is equal to 90 DEG, phi₁When 180, θ is 75 °; phi is a₁ When 270, θ is 90 °; phi is a₁ When 360, θ becomes 105 °.

All curves with pitch angle α from-15 ° to 15 ° must fall in the region between the red curves with α ± 15 °. Test data is present in this region, and no data points are outside this region. Thus, areas with data points are referred to as measurable areas and areas without data points are referred to as non-measurable areas.

Due to the non-linear nature of the coordinate transformation, at α, φ₁The uniformly distributed measuring points on the plane have non-uniform distribution of data points on the theta, phi plane. It can be demonstrated that the data has an area of 64% for the measurable region and 36% for the non-measurable region.

Data loss occurs in large circle scanning, and the RCS detection of a mounting airplane has a problem. Both the foam holder and the two-suspension system of the conventional working mode belong to great circle scanning.

Disclosure of Invention

The invention provides a method for realizing conical scanning in a two-branch one-hanging support system through multi-axis linkage, aiming at solving the problem of large circle scanning data loss.

The invention provides a method for realizing cone scanning by a two-support-by-one-hanging support system.A one-dimensional rotary table is arranged below a pitching rotating mechanism in the two-support-by-one-hanging support system, the table surface of the rotary table is parallel to the ground, and the rotating shaft z of the rotary table is vertical to the ground; the supporting rods I and II are fixed on the rotary table and are vertical to the table surface of the rotary table, and the two supporting rods are mechanically connected with the airplane at points b and c; the lifting rope fixed on the roof is connected with a point a on the back of the airplane, the lifting rope is superposed with the axis of the rotary table, and the airplane is fixed in the air through the three points a, b and c; the coordinate system of the rotary table is xyz, the coordinate system of the target is x 'y' z ', the included angle between the x axis and the x' axis is the aircraft pitch angle alpha, and the pitch angle alpha can be changed by adjusting the length of the lifting rope; the included angle between the axis point O of the rotary table and the connecting line of the two support rods is gamma; the included angle between the z' axis and the electromagnetic wave ray is called zenith angle theta; the included angle between the projection of the electromagnetic wave ray on the plane x ' y ' and the x ' axis is called the airplane azimuth angle phi; wherein, when RCS measurement is carried out, the position of the lifting rope guarantee point a is unchanged, and when the rotary table rotates, the azimuth angle phi of the airplane changes, and the height h of the two support rods is adjusted₁And h₂And the vertical distance L from the connecting line of the two support rods to the axial center point O of the turntable and the distance d between the two support rods realize cone scanning through multi-axis linkage.

Further, in the method for realizing cone scanning by the two-branch one-hanging support system, the parameters of multi-axis linkage are as follows:

(1) the height of the support rod I is as follows:

the height of the support rod is linked;

(2) the height of the support rod II is as follows:

the height of the support rod is linked;

(3) the distance between the two support rods:

the supporting rods are linked left and right;

(4) the distance from the connecting line of the two support rods to the center of the turntable is as follows:

the supporting rods are linked front and back;

wherein h is₀Is the average height of the strut, r is the radius of motion of the strut, L₀When the zenith angle theta is equal to 90 degrees, the perpendicular distance from the connecting line of the two supporting rods to the point O, d₀The distance between two struts is indicated by h1 ═ h 2.

The invention has the following advantages:

1. the RCS measurement of 1:1 actual installation has the defects of small bearing capacity of the foam support, inconvenient posture angle adjustment and the like. The metal support has small bearing capacity, a hole must be formed in the airplane, and the RCS test of the solid-mounted airplane cannot be completed. The two-support one-crane support system rotary table is arranged below the support, the bearing capacity is high, and the pitch angle alpha and the azimuth angle phi can be controlled through the support rods and the lifting ropes₁Without the need to make holes in the target to destroy the aircraft, and is therefore suitable for RCS testing of 1: 1-mounted aircraft.

2. The disadvantage of the large circle scanning mode is the existence of data incompleteness: scanning the great circle to measure the result sigma (alpha, phi)₁) To σ (θ, φ), the area with data in the (θ, φ) plane is only around 64%. Whereas in the cone scanning method, the rotation axis is z', and the zenith angle θ is equal to a constant when the target is rotated. Therefore, no measurement data is lost in the new two-crane one-crane working mode. The area of valid test data is 100%. The development and innovation of the working mode have important practical significance in the aspect of engineering.

Drawings

FIG. 1 is a two-boom one-crane support system;

FIG. 2 aircraft coordinates and feature attitude angle definitions;

FIG. 3 shows two types of attitude angle scanning devices, wherein FIG. 3a is cone scanning and FIG. 3b is great circle scanning;

FIG. 4 shows a general working mode of two cranes;

FIG. 5(α, φ)₁) To (θ, φ) coordinate transformation;

FIG. 6 strut height versus aircraft;

FIG. 7 strut and sash-line position;

fig. 8 is a graph of a zenith angle θ of 75 ° and a pitch angle α (Φ);

FIG. 9 is a graph of strut to center of rotation;

FIG. 10L (. phi.) curve;

FIG. 11 is a variation of the spacing between two struts;

FIGS. 12S 1 and S2 curves;

the curves of fig. 13 h1 and h 2;

FIG. 14 plot of strut spacing d and azimuth angle;

FIG. 15. gamma. Angle variation of two strut height curves;

FIG. 16 plots of strut height h1, h 2;

FIG. 17 φ (φ)₁) Graph is shown.

Detailed Description

The invention is further described with reference to the following figures and detailed description.

As shown in fig. 1, in the two-support one-suspension support system, a one-dimensional turntable is arranged below a pitching rotation mechanism, the table surface of the turntable is parallel to the ground, and the rotation axis z of the turntable is vertical to the ground; the supporting rods I and II are fixed on the rotary table and are vertical to the table surface of the rotary table, and the two supporting rods are mechanically connected with the airplane at points b and c; the lifting rope fixed on the roof is connected with a point a on the back of the airplane, the lifting rope is superposed with the axis of the rotary table, and the airplane is fixed in the air through the three points a, b and c; the coordinate system of the rotary table is xyz, the coordinate system of the target is x 'y' z ', the included angle between the x axis and the x' axis is the aircraft pitch angle alpha, and the pitch angle alpha can be changed by adjusting the length of the lifting rope; the included angle between the axis point O of the rotary table and the connecting line of the two support rods is gamma; the included angle between the z' axis and the electromagnetic wave ray is called zenith angle theta; the included angle between the projection of the electromagnetic wave ray on the plane x ' y ' and the x ' axis is called the airplane azimuth angle phi; the invention realizes cone scanning by the following scheme, when RCS measurement is carried out, the position of a lifting rope guarantee point a is unchanged, when the rotary table rotates, the azimuth angle phi of the airplane changes, and the height h of two support rods is adjusted₁And h₂Two supporting rods are connected to the axial center point of the rotary tableAnd the vertical distance L of the O and the distance d between the two support rods realize cone scanning through multi-axis linkage.

When the given parameters are: (1) a zenith angle theta; (2) the positions and sizes of the aircraft lifting points and the pivot points a, b and c; (3) average height h of strut₀. The included angle gamma from the motion radius r of the strut, the original point O to the connecting line of the two struts can be calculated.

The parameters of the multi-axis linkage are as follows:

(1) the height of the support rod I is as follows:

the height of the support rod is linked;

(2) the height of the support rod II is as follows:

the height of the support rod is linked;

(3) the distance between the two support rods:

the supporting rods are linked left and right;

the supporting rods are linked front and back;

Azimuth angle phi of the rotary table₁Given the zenith angle theta, phi is obtained as phi (phi) which is an active variable of the system₁). Aircraft azimuth angle phi and turntable azimuth angle phi₁FIG. 17 and the following table. When the azimuth angle is small, the error between the two is small.

\|α\|	15	10	5
				\|Δφ\|	1	0.45	0.1

The axis of the airplane body is x ', the rotating shaft vertical to the airplane body is z', the zenith angle is theta, and the azimuth angle of the airplane is phi. The distance from the strut to the center O of the turntable is r₀The vertical distance from the connecting line of the two support rods to the point O is L₀The angle between the connecting lines of the two supporting rods is gamma₀The distance between two supporting rods is d₀. The aircraft rotates about the z ' axis in the x ' y ' plane, with the S plane parallel to the ground. The projection of the strut I on the S axis is S1, and the projection of the strut II on the S axis is S2.

In the case where the zenith angle θ is 90 °, the aircraft is parallel to the ground,

for example, L0-7 m, d 0-6 m, r 0-7.61577 m, γ₀＝46.3972°。

When the zenith angle theta is 75 degrees, the aircraft nose faces downwards. When the azimuth angle phi is changed from 0-360 degrees, the pitching angle alpha of the airplane is changed.

φ	0	90	180	270	0
						α	-15	0	15	0	-15

According to equation (4), when θ is 75 °, a relationship curve of the pitch angle α and the azimuth angle Φ of the aircraft is obtained, as shown in fig. 8. The position of the strut and the lifting cord is shown in figure 7. In FIG. 7(a), the distance r from the point b to the center of the turntable₀Independent of the azimuth angle phi. In fig. 7(b), r is related to the azimuth angle,

the curve of r obtained from equation (5) is shown in fig. 9, and the curve shape approximates a cosine function. When theta is approximately equal to 90 degrees, the airplane is parallel to the ground, and r is equal to r₀(ii) a When θ ↓, general case r ↓; however, when the azimuth angle phi is 90/270 DEG, r is r₀。

In the same way, the method for preparing the composite material,

the included angle between the strut I and the strut II to the origin O is gamma. When theta is 0 and phi is 0,

when θ is not equal to 0, and Φ is 0,

when theta is not equal to 0 and phi is not equal to 0,

l in FIG. 7(b)₀Is a function of the azimuth angle phi, see fig. 10. At the azimuth angles Φ 0 ° and 180 °, the minimum value L is 6.7615 m. At 90 ° and 270 °, L₀7 m. L, when phi changes, struts I and II must be linked in the fore-aft direction.

The height and spacing of the two struts is related to the azimuth angle phi, see figure 11. In the case of a conical scan, the axis of rotation is z ' and the plane of motion of the aircraft is in the x ' y ' plane. The heights h1 and h2 of the connection points b and c of the aircraft upper struts vary with azimuth.

The calculation formula of the height of the supporting rod I is as follows:

S₁the projection distance r from the strut I to the rotation center isProjection of the S axis. When phi is equal to gamma₀At/2, | S₁And | max. Phi ═ y (gamma)₀+ π)/2, S₁＝0。S₁And S₂See fig. 12.

The calculation formula of the height of the support rod II is as follows:

the relationship of strut height to aircraft is shown in figure 6. The height profile of the two struts is shown in figure 13.

In a conical scan, strut height h₁And h₂The variation with azimuth phi is approximated as a cosine function. When phi is 0 DEG, h₁＝h₂Phi ↓, h1 decrease, h2 increases, and when phi is 180 °, h₁＝h₂。

The spacing between the two struts is a function of the azimuth angle, and when phi is 0, pi, 2 pi, the two struts are equal in height and spaced apart by d is d₀At 6m max, pi/2, 3 pi/2, the height difference between the two struts is the largest, and the distance d is 5.7672m the smallest, see fig. 14. The change in D means that the struts are interlocked in the left-right direction.

The vertical distance L from the lifting rope to the strut changes, the distance d changes, then the angle gamma changes, and the distance between the maximum values of the two struts changes, see fig. 15.

The profile of heights h1 and h2 of struts I and II will also vary, taking into account the variation of L (φ) and d (φ), as shown in FIG. 16. For comparison, d is equal to d₀And curves with d ═ d (φ) are plotted in FIG. 16. The curve in which the d-d (phi) influence is not considered is black, and the curve in which the d-d (phi) influence is considered is red. We see that the red and black curves coincide around 0 and 180 deg., with some small differences around 90 deg. and 180 deg..

Claims

1. Two-branch one-hanging supporting system for realizing cone scanningIn the two-branch one-hanging support system, a one-dimensional rotary table is arranged below a pitching rotating mechanism, the table surface of the rotary table is parallel to the ground, and a rotary shaft z of the rotary table is vertical to the ground; the supporting rods I and II are fixed on the rotary table and are vertical to the table surface of the rotary table, and the two supporting rods are mechanically connected with the airplane at points b and c; the lifting rope fixed on the roof is connected with a point a on the back of the airplane, the lifting rope is superposed with the axis of the rotary table, and the airplane is fixed in the air through the three points a, b and c; the coordinate system of the rotary table is xyz, the coordinate system of the target is x 'y' z ', the included angle between the x axis and the x' axis is the aircraft pitch angle alpha, and the pitch angle alpha can be changed by adjusting the length of the lifting rope; the included angle between the axis point O of the rotary table and the connecting line of the two support rods is gamma; the included angle between the z' axis and the electromagnetic wave ray is called zenith angle theta; the included angle between the projection of the electromagnetic wave ray on the plane x ' y ' and the x ' axis is called the airplane azimuth angle phi; the method is characterized in that: when RCS measurement is carried out, the position of a lifting rope guarantee point a is unchanged, and when the rotary table rotates, the azimuth angle phi of the airplane changes, and the height h of the two support rods is adjusted₁And h₂The vertical distance L from the connecting line of the two support rods to the axial center point O of the turntable and the distance d between the two support rods realize cone scanning through multi-axis linkage; the method specifically comprises the following steps:

when the given parameters are: (1) a zenith angle theta; (2) the positions and sizes of the aircraft lifting points and the pivot points a, b and c; (3) average height h of strut₀(ii) a The motion radius r of the support rod and the included angle gamma from the original point O to the connecting line of the two support rods can be calculated;

the parameters of the multi-axis linkage are as follows:

(1) the height of the support rod I is as follows:

the height of the support rod is linked;

(2) the height of the support rod II is as follows:

the height of the support rod is linked;

(3) the distance between the two support rods:

the supporting rods are linked left and right;

the supporting rods are linked front and back;