Twelve PACE 5000 pneumatic pressure controller/indicators from GE's Sensing business have been specified for installation in the calibration facility of the European Transonic Wind tunnel (ETW) in Cologne. The instruments will generate precise pressures which will then be converted into the forces and torques used to calibrate the sensing elements which measure the forces and moments acting on scale aircraft models during wind tunnel tests.
The ETW is thought to be the most advanced aeronautical wind-tunnel facility in the world. Unlike conventional wind tunnels, it uses a very cold (-163°C) nitrogen flow at a pressure of up to 4.5 bar to simulate the airflow about aircraft such as the A380 in model scale. The cryogenic concept allows very high Reynolds numbers to be achieved, the Reynolds number being a decisive factor in air flow. It mainly determines the aircraft drag, and it defines the type of flow, laminar or turbulent, being experienced close to the body. Future aircraft designs aim at maintaining laminar air flow at very high speeds to ensure minimum drag. In addition, using the very cold nitrogen flow allows Reynolds number, Mach number and dynamic pressure to be varied independently, so that their individual effects can be studied.
Measurements of all forces and moments affecting a scale model are at the heart of every wind tunnel test. To achieve this, six force and six torque sensors are integrated in a fixture at the rear end of the model. To deliver accurate data, it is important that these sensors are frequently calibrated and this is done in ETW's own calibration facility at temperatures from cryogenic to ambient. Here, twelve PACE 5000 instruments, six for forces and six for torques, are used to generate precise pressures, which are then converted into forces and moments, utilizing pneumatic force generators. The model sensing elements are subjected to these loads. The precisely known loads are compared to the sensor output readings to derive accurate calibration coefficients.
The PACE 5000 is based on the field-proven and highly reliable Druck 520 platform, which ETW had successfully used previously for some of its calibration tasks. However, the PACE 5000 incorporates the latest generation of piezo-resistive devices and offers significant improvements in overall precision, long-term measurement stability and control performance. Its unique modular design also allows users to enjoy quick and easy parts replacement and fast pressure range change-over, while a touch screen and a high resolution display ensure that the instrument is extremely easy to operate and read.
As Dr Ulrich Jansen of the ETW facility explains, "To date, we have used three DPI 520 instruments to calibrate 12 sensors via a somewhat complex, manually operated manifold system. Thus, only three loads could be applied simultaneously. With our new system, which should be in place by the end of 2010, we shall have a dedicated pair of Pace 5000s (one for push and one for pull) for each force and torque so that all degrees of freedom can be loaded in parallel."
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