Highly Accurate Aircraft In-Flight Wing Deformation Measurements Based on Image Correlation

NLR developed a system for in-flight wing deformations measurement based on the Image Pattern Correlation Technique (IPCT) as part of the AIM project (Advanced In-flight Measurement Techniques) funded by EC under FP6. The IPCT system was first tested in a laboratory environment and subsequently integrated into NLR’s Swearingen Metro II research aircraft. Aircraft integration tests were performed at the hangar, while also verification measurements of the aircraft-integrated IPCT system versus micrometer were made. The ground-based verification demonstrated the inherently high accuracy of the method. The IPCT system was used successfully in-flight for wing deformation measurements. The aircraft wing deflection was measured under various load conditions ranging from 0 to 2.5 g. Optical displacements of a randomly speckled part of the wing relative to a reference frame were determined using cross correlation techniques. These optical displacements were converted to geometrical wing deformations in a reference frame relative to the wing in reference condition. With respect to these geometrical wing deformation results a wing deflection model could be fitted. From this model various wing deflection parameters were determined and presented as function of the wing load. Parameters included e.g. change in wing heave, dihedral, torsion. Also the dynamic behaviour of the wing, e.g. during landing, can be investigated with high accuracy using IPCT. The flight trial demonstrated the usefulness of the IPCT technique for high accuracy, static and dynamic in-flight wing deflection measurement.