Black Hawk Helicopter - Australian Army
BAE Systems Australia was required to upgrade the electronic technology for the Australian Army’s fleet of Black Hawk Helicopters. As part of this project BAE Systems Australia needed to establish 3D CAD information which accurately reflected the current state of build of the airframe and ancillary equipment.
It was decided that the quickest and most efficient method was to scan or digitise an actual aircraft so that real 3D data could be captured as a factual basis for design and installation upgrade.
BAE Systems Australia contracted Scan-Xpress to undertake 3D Photogrammetry and 3D Scanning of the aircraft. Both external and internal data was required
BLACK HAWK – OBJECTIVES & OVERVIEW
The objectives for the 3D Scanning project were to –
1. Measure the external airframe and produce 3D scan data to within a verifiable accuracy of 0.1 mm.
2. Measure certain internal areas of interest to the same accuracy.
3. Produce an integrated set of data with both the external and internal data in the same co-ordinate frame work.
4. Complete the work on site and within the required project time frame.
5. Model the aircraft using the scan data and produce an integrated 3D model for CAD analysis.
CAD model developed from scan data ( WIP)
Fuselage Size – Length 15.4 M Width 2.4 M Height 2.3 M
Because of the size of the aircraft and tight accuracy requirements, normal digitising techniques could not be used. A combination of Photogrammetry and Optical Scanning was needed.
A GOM TRITOP ( Photogrammetry ) and ATOS ( Optical Scanning ) system was used to carry out the 3D measurement. These systems are accurate and portable, thus allowing data capture on site in the working environment.
The TRITOP system
The TRITOP system takes 3 dimensional pictures of objects to provide an accurate larger scale 3D co-ordinate framework by using digital photogrammetry techniques. These techniques are similar to those used in large scale construction and land surveying. In this case coded markers are applied to the object to be measured and each position is precisely recorded by means of a digital camera. The three dimensional co-ordinates are then calculated by the computer to produce a reference framework for measurement or scanning purposes.
The ATOS system
The ATOS (Advanced Topometric Sensor) system is a white light optical scanner which scans three dimensional objects and converts them to high density point clouds This allows accurate measurement and capture of the shape and size of the external surface of almost any 3D object.
The measurement principle is based on optical triangulation and uses the precise nature of light waves to produce very accurate image data. A light projector is used to project striped fringe patterns onto the object's surface which are grabbed by two cameras from different angles. With the help of digital image processing, 3D-coordinates are computed with high accuracy for upto 4 million camera pixels. The images captured are calibrated simultaneously during each measurement so that possible changes of projection do not effect the result. The image data is automatically analysed and evaluated within seconds by ‘state of the art’ digital image processing.
The TRITOP & ATOS systems used to scan a car
The Aircraft structure was previously prepared with all doors and hatches in place. Scan-Xpress then placed coded and un-coded targets onto the airframe.
Reference datums were established and accurately measured.
Fuselage prepared for scanning
In total 41 scan data files were created covering both external and internal areas of the aircraft. These contained 12,000 million data points while maintaining an accuracy of 0.1 mm overall
Stage 1 - TRITOP
A base calibration was set-up and calibrated and then a photogrammetric survey was carried out with the TRITOP system. The results of this first stage are shown in the screen dump below.
The accuracy of this first stage was checked by confirming several physical measurements.
External Skin panels - Scan data established by TRITOP ( photogrammetry)
Total Number of Points 9,000 - Accuracy 0.1 mm over 15 metres
Stage 2 - ATOS
After the TRITOP stage had been completed the ATOS 3D scanning stage was commenced. A typical area – the nose section, is shown below
Nose – prepared for scanning with ATOS
Nose – Scan cloud data from ATOS ( optical white light )
Stage 3 – Modelling
Following the data capture stages the scan data was checked cleaned and processed from a point cloud format into a polygon mesh format (STL).
The polygon model was then registered to the aircraft datum position.
The total project consisted of 24,000 million polygons and was subdivided into a number of distinct areas for ease of handling.
Each area was then modelled using a combination of 3D CAD packages. The overall model was used by BAE Systems Australia to plan and design the electronic upgrades.
RESULTS AND BENEFITS
1. Quick and accurate data capture of a relatively large object
2. Confidence that the data reflects the “as built” state of the aircraft.
3. Data that can readily be imported into the desired CAD software for planning and design purposes.
4. Savings in time and cost compared to more traditional methods