Fritz Boden

Advanced In-Flight Measurement Techniques

Advanced optical measurement techniques are beneficial compared to classical sensor measurements in terms of non-intrusiveness, measurement time and areal measurement. Although those techniques (e.g. the Particle Image Velocimetry (PIV) or the Image Pattern Correlation Technique (IPCT)) are well established in wind-tunnel and laboratory applications, it is a very challenging task to make them easily applicable for flight testing. Therefore, about more or less nine years ago the first EC project “Advanced In-flight Measurement Techniques” (AIM) was launched. Researchers and specialists proofed in general the feasibility of applying their non-intrusive measurement techniques to industrial flight testing. Later the follow up project AIM² has been started in 2010 intended to improve the AIM techniques towards routinely application in flight testing. The main achievements of the two AIM projects will be presented and some examples of the in-flight application of the AIM techniques will be given.

Application of image pattern correlation for non-intrusive deformation measurements of fast rotating objects on aircrafts

The Image Pattern Correlation Technique (IPCT) in combination with high-speed stroboscopic imaging enables nonintrusive measurements of surface deformation of fast vibrating or rotating objects. This paper describes a dedicated instrumentation for the measurement of the deformation of aircraft propellers as well as the results of its application. The further ideas of imaging technologies based on the collected experiences, in particular the high-power pulsed object illumination based on semiconductor light sources are also presented.

Optical In-Flight Wing Deformation Measurements with the Image Pattern Correlation Technique

This chapter addresses image based deformation measurements and the development of specific optical deformation metrology for experimental flight test installations. Apart from the technical background it is a contribution to the national funded research projects FTEG-InnoLA and HINVA (LuFo IV). Based on a standard setup the measurement equipment required to perform the Image Pattern Correlation Technique (IPCT) was adapted to an application on an ultralight aircraft. In order to design the test setup a digital camera mock-up (camera DMU) was used. The analysis of selected flight test data proved the capability of the miniaturized IPCT system. A second flight test setup was developed for the DLR research aircraft Airbus A320 “ATRA” using the experience gained from the ultralight measurements. Here, the design of the IPCT components also made use of the camera DMU. Both the overall wing deformation and that of high lift devices have been measured in high-lift configuration.

Application of high-speed videography for in-flight deformation measurements of aircraft propellers

A combination of high-speed stroboscopic imaging with the Image Pattern Correlation Technique (IPCT) enables for non-intrusive measurement of surface deformation of fast vibrating or rotating objects. In this paper the dedicated instrumentation for the measurement of the deformation of aircraft propellers as well as first results of its application will be described.

In-flight measurements of propeller blade deformation on a VUT100 cobra aeroplane using a co-rotating camera system

Knowledge of propeller or rotor blade behaviour under real operating conditions is crucial for optimizing the performance of a propeller or rotor system. A team of researchers, technicians and engineers from Avia Propeller, DLR, EVEKTOR and HARDsoft developed a rotating stereo camera system dedicated to in-flight blade deformation measurements. The whole system, co-rotating with the propeller at its full speed and hence exposed to high centrifugal forces and strong vibration, had been successfully tested on an EVEKTOR VUT 100 COBRA aeroplane in Kunovice (CZ) within the project AIM2—advanced in-flight measurement techniques funded by the European Commission (contract no. 266107). This paper will describe the work, starting from drawing the first sketch of the system up to performing the successful flight test. Apart from a description of the measurement hardware and the applied IPCT method, the paper will give some impressions of the flight test activities and discuss the results obtained from the measurements.

In-flight measurements of aircraft propeller deformation by means of an autarkic fast rotating imaging system

ABSTRACT The non-intrusive in-flight measurement of the deformation and pitch of the aircraft propeller is a demanding task. The idea of an imaging system integrated and rotating with the aircraft propeller has been presented on the 30 th International Congress on High-Speed Imaging and Photonics (ICHSIP30) in 2012. Since then this system has been constructed and tested in the laboratory as well as on the real aircraft. In this paper we outline the principle of Image Pattern Correlation Technique (IPCT) based on Digital Image Correlation (DIC) and describe the construction of a dedicated autarkic 3D camera system placed on the investigated propeller and rotating at its full speed. Furthermore, the results of the first ground and in-flight tests are shown and discussed. This development has been found by the European Commission within the 7 th frame project AIM 2 (contract no. 266107). Keywords: propeller blade deformation, non-intrusive measurement, 3D imaging, IPCT, DIC, video stroboscope, phase shifter, stochastic dot pattern, in-flight test

IPCT Wing Deformation Measurements on a Large Transport Aircraft

Aircraft wings are subject to deflection. Designers must therefore take into account in-flight wing bending and torsion, so that structural loads are well taken care of and that the wing has optimum aerodynamic performance. Models are used to calculate wing torsion and bending. These models need to be validated in flight and therefore non-intrusive measurement methods are preferred in order to avoid aerodynamic interferences. A photogrammetry method is already applied for these measurements, although this method has some constraints. Only static measurements are provided and accuracy depends on careful and time-consuming calibrations. Within the AIM (Advanced In-flight Measurement techniques) project various novel advanced non-intrusive measurement techniques are introduced for usage in flight. One of these novel techniques is the IPCT (Image Pattern Correlation Technique) applying advanced image correlation techniques as used in Particle Image Velocimetry (PIV) on surfaces. Applying the IPCT can improve the accuracy, reduce installation time, provide local surface deformations and give dynamic results. IPCT uses image correlation to calculate the deformation of a wing with a speckled pattern. In this chapter the measurement technique, the installation on a large transport aircraft i.e. the A380 and the test performed in June 2009 will be described. At the end some results of the test will be presented.

IPCT Ground Vibration Measurements on a Small Aircraft

One of the AIM subtasks required the measurement of structural vibration using IPCT on a small aircraft. This has been done in an industrial environment on a Piaggio P 180, without interfering with production testing and other flight test activity. A ground test, simulating flight conditions and measuring wing vibration was initially done and, due to budget restrictions, only a limited IPCT flight test could be completed using the ground set-up. For the ground tests, a set of accelerometers was also installed to compare the IPCT results with those obtained with traditional means. For these tests, an exciter, driven by a PC, was placed at the wing tip to generate a signal at the desired frequency. With this system, a frequency sweep was performed around the known natural frequencies, exciting the first wing bending mode. Furthermore, accelerometers were installed on the camera support in order to evaluate whether the camera itself was vibrating. During ground testing, the IPCT method showed promising results for in-flight testing, although the resolution was insufficient for the higher frequency, lower amplitude results. These limitations would require supplementing any IPCT system with traditional accelerometer measurements. In what follows, a brief description of the test set-up, the test instrumentation, the data analysis and the results of the ground vibration measurements will be presented.

In-Flight IPCT Wing Deformation Measurements on a Small Aircraft

After the successful application of the Image Pattern Correlation Technique (IPCT) on the P 180 experimental test aircraft for wing vibration measurements on ground, the complete camera installation has been certified for flight testing to perform a feasibility test with in-flight IPCT for wing deformation measurements. Finally, several successful flight tests have been executed at the Piaggio Aero Industries plant in Genova (Italy). As the measurement technique and the measurement installation have been described in a detailed way in Chap. 4, this paper mainly contains a brief description of the applied installation, the performed flight tests and a presentation of the measurement results.

In-Flight Application of Pressure Sensitive Paint

A feasibility test for in-flight pressure measurement using Pressure-Sensitive Paint (PSP) techniques has been performed in the frame work of the research project Advanced In-flight Measurement Techniques (AIM). PSP was applied to a pylon surface of the VFW 614 ATTAS aircraft. In the test, three PSP measurement methods: “intensity method with LED-array”, “intensity method with Electro Luminescence (EL) foil”, and “image based lifetime method” were employed to measure pressure distributions and the results were compared. The results showed the good feasibility of PSP measurements at in-flight testing. All three methods could represent the pressure distribution on the pylon. Especially the intensity method with LED-array and EL foil could provide results in good image quality. An EL foil which was applied to the pylon surface outside of the cabin and firstly employed in flight tests worked very well even at high altitudes. From the obtained results, one can conclude that the PSP technique successfully passed the first feasibility tests. The lessons learned from the experiences in the flight test are presented in the following chapter.