High accuracy in flight wing

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High Accuracy In-flight Wing Deformation Measurements based on Optical Correlation Technique
Presented by H.W. Jentink National Aerospace Laboratory NLR Amsterdam, The Netherlands Contributions from NLR, DLR and Airbus France Aerospace Testing, Hamburg, 19 May 2010
Nationaal Lucht- en Ruimtevaartlaboratorium – National Aerospace Laboratory NLR

Introduction of the project andobjectives Measurement requirements Equipment and measurement setup Post-processing and analysis approach Results Metro tests static wing deflection wing dynamics aileron deflection, rotation, gap Airbus A380 test campaign Conclusion on in-flight DIC performances


AIM – EC 6th Frame Work Programme
AIM: Advanced In-flight Measurement techniques Introduction of innovative optical measurementtechniques in flight testing Digital Image Correlation (DIC) technique for wing deflection measurement as alternative to proven techniques photogrammetry accelerometer strain gauges Requirements and objectives defined by European aircraft manufacturing industry: Airbus (Fr) Piaggio (It) Eurocopter (Fr+Dl) EVEKTOR (Cz)

Principles of Digital Image Correlation (DIC) technique

4 Stereoscopic Approach


Requirements for in-flight wing deflection at Metro aircraft

Wing heave: accuracy at least 0.5 mm feasibility to measure relationship wing heave and normal load Wing torsion: accuracy at least 0.1° Wing vibration modes: frequencies up to 8 Hz Measurement feasibility for aileron: rotation gap with main wing Assessment of degradation from: standard aircraft Plexiglas windowinstead of optical glass poor locations, e.g. fuselage


IPCT on one of NLR’s research aircraft: Fairchild Metro II


Camera positions on Metro aircraft

Measurement area


Rigid camera / IRS frame


Camera timing, triggering and synchronization

PC User Interface System Control GPS Antenna

Ethernet HUB Camera A Jai TM-1327GE Laptop A GigE FAST ethernet Timed datastorage + camera control

Datum GPS TCG Common Time Reference System


Synchronisation & Time Server

Accurately Timed Frame triggering

Camera B Jai TM-1327GE Laptop B GigE FAST ethernet Timed data storage + camera control To analog instrumentation + analog video System


Aircraft Installation of Camera Frame


IRS installation at the Camera frame


3-axisaccelerometer installed at wing tip


Dot generation software tool


Newly developed at NLR: complete 3D approach for Visual Geometrical Coordinate System transformation Visual grid (Xopt,Yopt) in pixel coordinates Geometrical coordinate system (X,Y,Z) aligned with flat (reference) wing
Optical grid on main wing Geometrical grid on main wing


Hangar activitiescalibrations & verifications – curved Plexiglas effects – reference grid – deflection (micrometer) – vibration (vs. accelerometer, IRS)


Hangar test: Verification DIC vs. Micrometer

Fuel re-fill


Hangar: DIC verification vs. micrometer
Micrometer 0-300 liter fuel: 3.55 mm wing deflection at ref point DIC using PivView: DIC using Matlab: extrapolation to ref. point:3.47 mm extrapolation to ref. point: 3.46 mm

Only 0.08 mm: 2% rel. error (due to small deflection amplitude)

With full 3D approach excellent agreement with micrometer measurement obtained!


... and then: the in-flight DIC measurements ....


In-flight DIC images: wing frames at 0g and 2 g


Vertical displacements of wing surface at 0 g and 2 g relative to 1 g(straight level flight)


Desired End Result: Determined coefficients(n) of Wing Deflection Model by least square fitting of results obtained at various loads Wing Deflection Model: z = c0 + cXX + cYY + cXYXY + cX2X2 + εz

where: X coordinate parallel to fuselage centre line (X=0 wing’s main beam) Y coordinate towards wing tip (Y=0 at tip, end of main beam) z local geometrical displacement...
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