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Original Date: 05/08/1995
Revision Date: 01/18/2007
Information : Wind Tunnel Measurement Techniques
The need for improved quality and greater efficiency in wind tunnel test measurement techniques provided the impetus for McDonnell Douglas Aerospace (MDA)-St. Louis to develop three new methods of testing. These improved test methods provide for faster, more accurate measurement of the wind tunnel model's position and pressure points. They also provide for an automated strain gage balance calibration system.
The model position measurement system utilizes a polarized light sensor mounted into the airframe model that allows for very accurate on-board pitch angle measurement. This simple and ruggedized method precludes the necessity of providing offset weights and corrective mechanical measurements to the mounting fixture utilized to suspend the airframe model in the wind tunnel.
The electronic pressure scanning system consists of several very small and lightweight multichannel electronic pressure transducers, which can provide up to 1,024 channels of pressure. These pressure channels are connected to a microcomputer. This portable stand-alone system provides for acquisition of multiple data channels with real-time data display capability.
The wind tunnel automatic balance calibration system allows for faster and safer calibration of the strain gage balance which is used to measure the deflection loading of the airframe models. The strain gage balance is attached to the suspension arm that supports the airframe model during a wind tunnel test. The calibration of the balance is now accomplished with an automated fixture that provides the proper application of calibration loads and electronic locking. The loading of the strain gage balance is performed by a hydraulic cylinder in a computer controlled fixture. This allows the calibration of six component balances over multiple load ranges and allows the calibration of balances with varying diameters. The fixture eliminates the need for the manual application of heavy weights and for manual leveling. Calibration time is reduced and quick calibration comparisons can be made via the test processing software.
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