Shulou(Shulou.com)11/24 Report--

Ahem, the broken plane here is not that the plane carrying a large wave of passengers broke down in the sky.

Instead, there is a mysterious and professional organization (bushi) whose task is to find ways to break down a good plane.

This job is the aircraft test flight, "organization" related units is the China Flight Test Research Institute (AVIC Industrial Flight Test Center) referred to as the Flight Test Institute. Aircraft test flight refers to the experimental flight of the aircraft before formal use, to grasp the degree of deformation of each part of the aircraft, the deformation limit and the limit speed, pressure and other condition information within the bearable range. The test flight is divided into three stages: engineering test flight, stereotype test flight, and weapon target test flight. Here, we focus on the almost destructive test flight, that is, what conditions are needed to make him bad? How to determine quantitatively and intuitively to what extent it is "bad"?

The traditional method is to record the cumulative flight time of the wing according to the setting standard of the experienced test pilot. after reaching a certain length of time, the wing needs to be replaced.

The deformation survey is to compare the effective data such as point elevation and coordinates before and after deformation, and then determine the degree of deformation of the observed object by measuring the changes of relevant data in different periods. Conventional measurement techniques include total station observation method, photogrammetry method, three-dimensional laser scanning method, BIM visual modeling method and so on.

What is close-range photogrammetry? This photography is not the other photography, photogrammetry refers to the use of a combination of camera and film to measure the shape, size and spatial position of the object. After repeatedly shooting the observed object, because the photos taken by different cameras have a little overlap, the points of the same position on different photos are called homonym points, making use of the relative position relationship of homonym points and lines of the same name. the two-dimensional image information can be converted into a three-dimensional model.

(like this bear) the collinear condition equation shows that at the moment of photography, the projection center, the object point and the image point are on the same line:

Because the aircraft is three-flat and four-round, there are differences in deformation measurement positions under different flight test missions. We divide the whole aircraft into four parts: the fuselage, the wing, the tail and the power plant. This kind of region division is helpful to obtain data location information and subsequent image stitching through image judgment.

Through some feature points on the fuselage, combined with three-dimensional laser scanning technology to obtain three-dimensional coordinate information, the relative position relationship between some feature points is obtained, thus an independent coordinate system is established on the aircraft, and the three-dimensional coordinate data on the ground is combined with the aircraft coordinate system. After a series of coquettish operations, a first-level control network for observation of control points is established. The so-called feature points are characteristic points (feihua), while the surface of the aircraft has a single hue and lacks texture, (that is to say, no features), so artificial signs need to be posted on the wings and important parts of the fuselage. Long ↓, so as to facilitate the automatic identification and measurement of the image acquisition process.

The spherical target can take into account that posting and removing the landmarks is time-consuming (and tiring), and the throwing point meter is used to effectively reduce the time of affixing artificial marks, but a small number of feature points are still needed to meet the needs of subsequent three-dimensional laser scanning coordinate acquisition and conversion.

PRO-SPOT projector what is 3D laser scanning? Three-dimensional laser scanning is to measure the oblique distance, horizontal angle and vertical angle between the measured object surface and the scanner by emitting laser from the scanner, so as to establish the relative position relationship between them and obtain the three-dimensional data of the measured point. that is, the coordinates obtained are the spatial relative coordinates between the scanner and the measured point.

Scanner collects data space relative position coordinate system XP=Scos β cos α

YP=Scos β sin α

ZP=Scos β

On the other hand, when scanning the aircraft, the handheld 3D scanner cooperates with the global photogrammetry system to eliminate the cumulative error and improve the accuracy. Multi-beam laser is used to obtain the surface of the object, and the point position information is used to determine the spatial position of the scanner in the scanning process through visual marks to complete the overall reconstruction of the three-dimensional point cloud on the surface of the object. As the project involves ┓ ('∀ `) ┏, a small aircraft model is used to simulate the aircraft surface modeling process to visualize the data containing point information. Comparing the three-dimensional models before and after flying, we can intuitively and accurately know which part is more prone to damage under specific conditions, or the extent to which the fuselage is broken or sunken under a certain limit speed or pressure.

Photogrammetric MeshLab modeling intention is like this, we have a complete understanding of the aircraft test flight from measuring the degree of damage to visualization. Due to the length of space, the conversion of different axes and error analysis have not been carried out one by one. Aircraft flight test engineering is an important guarantee to ensure aircraft flight safety and an important link in the national aerospace field. It can be seen that as an important basic discipline, geoscience is shining and glowing in various important fields. This article is from the official account of Wechat: stone popular Science Studio (ID:Dr__Stone). Author: Fang Yuan.

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