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The figure shows a schematic of the University of Texas Drop Tower Facility (UT-DTF). It is 12.2m tall, with a 2.5m square cross-sectional area. The tower is equipped with a two-ton capacity electric hoist and a helicopter cargo quick-release attached to the end of the hoist's chain. At the bottom of the drop shaft is a deflatable-airbag-type deceleration mechanism. The airbag is contained within a heavy container of dimensions 1.83m high by 1.7m long by 1.12m wide, constructed of welded steel C-section channel. The bottom third (approximately) of the frame is lined with 3.1mm plate steel and the upper portion with expanded metal. The airbag is attached to the steel plate lining the lower part of the steel frame. It is made of a 22oz nylon-coated polyester material similar to that used in boat and trailer covers. The frame is bolted to the floor of the drop shaft and is lined with a single 0.3m thick slab of stiff, high-density (“110lb”) polyurethane foam. The airbag is pressurized using a radial blower. Upon impact of the drop drop-rig/drag-shield, the airbag is deflated through four spring-loaded rectangular blast gates mounted in the steel liner of the base of the container. The blast gates are mechanically restricted in how wide they can open, so as to provide a measure of control of impact deceleration. Deceleration levels at impact are measured to be just 10-15g, well within the survivability limits of the on-board equipment. After allowing for the space taken up by the hoist and deceleration mechanism, the drop-tower has approximately 9.5m of free-fall. This gives approximately 1.1 seconds of low-gravity time per drop.
Click here for a birds eye view of the UT-DTF in action.
Click here for a look at the how the airbag works.
Diagnostics Capability
KHz Frame-rate PLMS/PIV System
The UT-DTF is equipped with a multi-kHz frame-rate planar laser Mie-scattering (PLMS) system. The system uses a large core-diameter fiber-optic cable to deliver pulses from a high-power, diode-pumped Nd:YAG laser into the drop-rig as it falls down the drop-tower during a low-gravity test. A set of optics in the drop-rig are used to shape the beam into a laser sheet which is then directed into the test-section of the flow facility. There, the laser light scatters from alumina particles seeded into the flow and the scattered light is imaged by a high-frame-rate CMOS camera system. This allows us to track and study the large-scale structure of a flow-field even as it moves quickly past the cameras field of view. Up to 2048 full-frame images can be collected at 2000 frames-per-second during a single drop. The system can operate in partial-frame mode at speeds up to 10000 frames-per-second.
Used in another mode (with a narrow-angle 105mm lens), the PLMS system described above becomes a multi-kHz frame-rate cinematographic particle image velocimetry (PIV) system. Using cinematographic PIV allows us to track and analyze such features of the flow as velocity, vorticity and shear. The high frame-rate (6kHz) of the system allows us to gather an immense amount of data even in the short time available in each low-gravity experiment drop.
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