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This is an airspeed profile graph. It shows the airspeed uniformity at the exit. It was made by measuring the airspeed every six inches across a horizontal line crossing through the middle of
the exit. Two lines were made, one on the axis of the machine, the second perpendicular to the machine. These are the two lines on the graph. This shows the jet quality at the exit, which is the air a flier would
experience in a facility with a net at the exit, or if the jet is enclosed in a tube. These measurements were made without a net below the anemometer and so does not show the degradation a net will cause. In
our facility the net is 7 feet above the exit. Due to atmospheric mixing the profile will degrade with height, while the jet will appear to expand. Therefore our flight area is wider than the jet at the exit.
An
airspeed profile is used to determine the jet uniformity and diameter of a wind tunnel. Ideally the profile will be a flat line from one edge of the jet to the other. This would indicate a very uniform jet and is
not only easier to fly in, but also much better for an expert filer. A flat line most closely simulates free fall.
Without an airspeed profile you cannot know the flight area diameter. The flight area of a VWT is
that area in a vertical jet of air in which a person can fly. The standard definition of a VWTs jet diameter is the width of the jet which has an airspeed within 90% of the maximum airspeed. You can see from the
chart that by this definition our jet diameter is approximately 12 feet 7 inches at the exit. The measurements on this graph at 6.5 feet are actually at 6 feet 4 inches, or as close to the edge as our probe could
measure. The actual exit diameter is 12 feet 8-1/8 inches.
These measurements were taken at 375 RPM. These measurements take a while to make, and it is difficult to hold the airspeed probe in the wind when it is
fast. The airspeed differences are the same at any airspeed. So for example, if the maximum airspeed is 60, and it is 55 at another position, at a maximum airspeed of 120 it would be 115 at that position. The
difference is the same, so the chart can be used to determine the profile at any airspeed. To make the measurements for this graph the equipment had to be repositioned three times. Much of the variation between the
left and right side of the jet was probably due to changing conditions during the time it took to make the measurements. Because we rounded to the nearest 100 feet per minute when recording the measurements this may
have caused some of the variation in the graph.
If you compare our airspeed profiles to that of our competition, you will see why we are proud to publish our measurements.
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