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This is an airspeed profile graph. It shows the airspeed uniformity four feet above the exit. It was made by measuring the airspeed every six inches across a horizontal line crossing through the
middle of the jet four feet above the exit, 45 degrees from the two lines made in the exit profile, or parallel to the side of the building (east-west). This shows the jet quality four feet above the exit. These
measurements were made without a net below the anemometer and so do not show the degradation a net will cause.
An airspeed profile is used to determine jet uniformity and diameter. 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 flier. 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 about 12 feet 6 inches, four feet above the exit.
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 the other position. The difference is the same, so the chart can be used to determine the
profile at any airspeed. Due to the difficulty in taking these measurements only half of the jet was measured on 6-10. This data was reflected to complete this graph under the assumption that the jet is symmetrical,
as is shown by the measurements made at the exit.
The airspeed during these tests in any one position was varying by about 50 feet per minute from one reading to the next over 10-20 seconds.
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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