Wind Tunnel Testing and Balances with highest AccuracyDR. CLAUS ZIMMERMANN, RUAG AG, SWITZERLAND

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Agenda

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1. Introduction to Wind Tunnel Testing

2. Requirements for Sensors and Data Acquisition

3. RUAG’s Solution with MGCplus in the Wind Tunnel

4. RUAG Balances and their Calibration with DMP

5. Summary

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Speaker’s Intro

Head of Measurement / IT in the Aerodynamics Department since 2002

The team is providing the soft- and hardware needed for data acquisition, data processing, and operation of the controlled systems within the wind tunnel facility

The team is developing and manufacturing strain-gauge balances for internal use as well as for external customers

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RUAG AGA leading supplier, service provider, and

integrator of systems and components for civil and military applications – on ground and in the air

Headquarter in Emmen, Switzerland2’200 employees

Just over 70 years ago, the aerodynamics research department of RUAG's predecessor company, EidgenössischesFlugzeugwerk F+W established its first wind tunnel

Independent and full service provider for wind tunnel testing for customers from all over the world

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Wind Tunnel Testing

Determination of aerodynamic, aeroelastic or aeroacoustic characteristics of an object

Highly homogeneous and vortex-free flow Full scale objects or properly scaled models Main measurands with high reliability and

repeatability comprise: - velocity around an object- loads or pressures upon the object

Results: overall stability, dynamic stability, efficiency, structural response, …

Costs (investment / operation) Reduced demand for wind tunnel testing due to

computional fluid dynamics (CFD). However, CFD results are still not completely reliable and wind tunnels data are needed to verify these predictions.

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2 low speed wind tunnels:LWTE: 7 x 5 x 12 [m] 68 [m/s] maxAWTE: 2.45 x 1.55 x 3.80 [m] 60 [m/s] max

Full-scale or scaled-down models Aircrafts, race cars, building, sports … Quantitative and qualitative measurement techniques Full service provider: design, manufacture, test, analysis

Experimental Wind Tunnel Testing at RUAG

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Six-component balance Powerful hydraulic propeller motors 6-component rotating shaft balances in the hub of each propeller More than 700 pressure taps on the model Local strain-gauge balances to measure forces / moments at control surfaces … and a multiple of sensors for monitoring and controlling the test

Reference: Grant agreements CS-GA-2013-01-LOSITA-620108

Model Losita from European Union's Horizon 2020 Program

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RUAG’s Data Acquisition Upgrade – Challenge

Increasing complexity of wind tunnel testing Wide variety of test objects leads to wide variety of measurands:

forces, moments, strains, accelerations, pressures, temperatures etc. Static and transient data High(est) accuracy, repeatability, and resolution Long-term stability High flexibility, reliability, and productivity

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Requirements for RUAG’s Data AcquisitionNumber of measurement channels: 140 (without transducers which are connected via the CAN bus)

Static measurements with high accuracy, resolution, and repeatability

Dynamic measurements up to approx. 2’000 Hz bandwidth

Synchronized measurement of all measurement channels

Long-term stability

Wide variety of possible sensors

Availability of several accuracy classes / amplifier classes for the various measurands

Possibility of external triggering

Ethernet interface for connecting the wind tunnel software

Cable lengths of up to 50 m between sensor and amplifier

High availability (quasi continuous operation; industrial data acquisition)

Practical handling

On-site calibration required / guaranteed traceability to national standards

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Sensors installed in the model → forces / moments, surface pressure data, … Sensors in the wind tunnel setup → dynamic pressure, wind speed, … Sensors according to specific to customer requirements

Sensor Technology for Wind Tunnel Testing

Measurand Possible sensor types Importance

Force / moment Balance / scale, load cells 1

Inclination Inclinometer, electronic spirit level 1

Pressure Individual pressure transducers in the wind tunnel setup 1

Pressure Individual pressure transducers and multi-channel pressure systems

Temperature Thermocouple, resistance thermometer

Acceleration Piezoelectric, piezo-resistive or capacitive transducers

Angle Potentiometer, Hall sensor, encoder

Length Potentiometer, inductive transducer, laser

Frequency Inductive, optical or magnetic sensors

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Sensor SG bridges (normalized), voltage, current, themocouples etc.

Calibration Systematics

Amplifiers DMP, ML38B, ML01B, ML801B, ML10B, ML460B Accuracy: 5 to 1’000 ppm Bandwith: static to 2’000 Hz

Calibration units HBM for SG bridges Burster / Agilent for voltage, current, frequency, temperature etc. Accuracy: an order smaller than amplifiers

Traceability PTB2 national standard, HBM DKD certificate, RUAG calibration lab

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Architectural design of measurement and calibration racks 3 standard modular enclosure systems on rollers Uniform connection boards for RUAG’s standardized wind tunnel plug connections Reasonable accessibility / interchangeability of amplifier modules Individual driver software (RUAG’s wind tunnel software) via Ethernet interface Air conditioned environment and uninterruptible voltage supply Staff training and documentation (inbuilt components, calibration documents)

Measurement racks, each withMGCplus with ML38 / ML01 / ML801 / ML70 / ML10 / ML460140 channels

Calibration rackHBM BN100A / K-800 / K-3608 / K-148Burster Digistant 4462 / Simulator 4506Agilent 33120A / 34401A

Implementation

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2 standard block-type balance families (scaled with respect to loads / geometry)6 load components, high linearity, low interferences, high accuracy, compact design

Rotating shaft balances (propeller testing)6 components, radial / axial design, up to 12’000 rpm, integrated telemetry data transmission

Component balances (wheel, wing, underfloor, aircraft surfaces, …)customized solutions, 1 to 6 load components

In-house calibration Balances for rent Repair service (also to third party’s balances)

RUAG’s Strain-Gauge Balances

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Suitable for model-internal or model-external installation Tool to select an optimally suited balance for the test in terms of volume and load range Instrumentation with temperature compensation / Young’s module correction Recommendations for optimal installation:

mechanical interface, minimization of temperature effects, wiring, …

RUAG’s Block-type Balances

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Dead weights for calibration and check loading; multicomponent loading HBM DMP data acquisition for highest accuracy and extreme stability Signals often <1 mV/V; with 0.0001 mV/V for repeatability and 0.00001 mV/V for resolution Linear and 2nd order calibration matrices Error analysis Accuracy about 0.03 % for all components (FS design loads)

Balance Calibration

Summary

Thanks to the modularity, flexibility, high precision, and excellent long-term stability of HBM’s MGCplus / DMP DAQsystems, a wide variety of tests is carried out. Together with the RUAG multi-component balances, a measurement chain is available for determining loads such as lift and drag forces. The chain can be optimally configured to provide the aerodynamics engineer with the necessary data for the improvement / validation of his product.

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HBM’s MGCplus amplifier systems were selected and integrated into a compact and mobile overall system for each wind tunnel. This results in a fast and flexible connection of measuring chains with standardized connection cables, and the configuration via an open interface to the wind tunnel software. Further criteria for the solution are efficient calibration with traceability to national standards and long-term delivery reliability by the manufacturer.

HBM’s DMP was selected for the calibration of RUAG’s balances to meet the highest requirements.

Despite high investment and operating costs, aircraft and vehicle manufacturers continue to rely heavily on wind tunnel testing. The complexity and requirements of the tests are increasing. High-quality measurement data –both static and increasingly transient – must be delivered reliably and efficiently. Also, the productivity from installation to delivery of the results is essential.

The calibration of strain-gauge balances, the most challenging sensor in wind tunnel testing, calls for a DAQ with highest precision and long-term stability.

Challenge Solution

Benefit

Thank You

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www.aerodynamcis.chclaus.zimmermann@aerodynamics.ch

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