20-Foot Vertical Spin Tunnel
NASA Langley Research Center
Rotary Balance Rig in Stowed Position.
Direct observation of the test is available during tunnel operations via panoramic control room windows. Also, S-VHS (Y-C) video cameras, time code generators, and tape decks are available for recording views of the model and test section while the tunnel is operating.
Data for free-flying models are obtained from up to four high-grade monochrome CCD video cameras that provide input into the facility dynamic model data acquisition system. These cameras provide 60-Hz imaging of retroreflective targets that are precisely positioned on the surface of the model relative to any appropriate reference system. Rotary balance force and moment measurements are made with internally mounted six-component strain-gage balances. Multiple surface pressure measurements are made with an electronically scanned pressure (ESP) system. Test section air speed is measured with a pitot-static system. In addition, barometric pressure and test section temperature are also measured. A variety of miscellaneous instruments, including hand held anemometers, force gages, electronic levels, and digital volt meters, are also available.
The 20-Ft VST dynamic model data acquisition system is a video based system that stores images of free flying models for posttest determination of attitude, position, and rates. Up to four charge coupled device (CCD) cameras provide input into the system to give maximum test section coverage. The system resides on a unix workstation and uses scientific-grade analog optical disks as storage media. After acquisition and image storage, a "pose estimation" algorithm is used to determine model attitude and location in the test section at up to 1/60-s time intervals from any single camera view. Data files are output in a spreadsheet format that is convenient for plotting. Parameters provided by the system are model roll, pitch, and yaw angles; x, y, and z coordinates of the model reference center in the tunnel reference system; and the spin rate.
The rotary balance data acquisition system is based on a PC desktop platform and is used to acquire and store force, moment, and surface pressure measurement data, as well as for rig motion control. Data output files are stored on disk and can be converted to most standard file formats.
A test rig to determine dynamically scaled model center-of-gravity location and moments of inertia about each axis is available at the facility. Because of the unique requirements of testing dynamically scaled models, direct interaction and consultation with engineers in the facility are required before model construction begins.
Safety and Design Criteria
Both dynamically scaled and rotary-balance models have highly specialized design and fabrication requirements. As such, requirements specified by cognizant Vehicle Dynamics Branch personnel must be met. In addition, the model installation must have the approval of the facility safety head prior to tunnel operation.
