Wind and Turbulence Measurements for the
NAL/NEXST Project
The National
Aerospace Laboratory of Japan (NAL) is developing a supersonic transport
aircraft of the next generation under the acronym NEXST (see http://www.nal.go.jp/eng/research/sst/index.html).. To test the aerodynamic configuration of the SST, a 11m-long unpowered model of the aircraft will be launched
by a rocket to approximately 20km altitude and then glide back to the ground
performing various maneouvre. The tests were to take place within the
It is important to know exactly the state of the
atmosphere through which the model aircraft flies. For this purpose, a VHF wind
profiler was installed near the launch site.
The wind profiler can measure wind speed and direction to altitudes of
about 20km. It also is capable to detect layers of turbulence, the existence
and strength of which is also very important for the flight trials.
To verify the profiler measurements, flights were
carried out with ARA’s Grob G520T Egrett which
is equipped with high resolution wind and turbulence sensors and can reach altitudes
up to 14.7km. In June 2002, three research flights of approximately 5 hours
duration each, plus one 1-hour instrumentation test flight were carried out
over the Woomera area for this purpose.
In addition to the wind measurements, the Egrett was also equipped with two
transponders, supplied by NAL, identical to the ones that will be used in the
SST-model aircraft. Parts of the flights were used to test the tracking
equipment and instrumentation at the
Unfortunately, the flight of the NEXST model
aircraft failed later in the year, as the model separated pre-maturely from the
launch rocket. Another trial is planned for 2003.
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Figure 11: Left: The
ARA Grob G520T Egrett with wind and turbulence probes installed. Right: Sketch
of the NAL NEXST trials.
Apart from the wind profiler, there are
also regular GPS radiosonde launches from the Bureau of Meteorology’s office at
Woomera. The launch point is close to the airport. Sondes are launched twice a
day, at 23:30UTC and at 11:30UTC. The sonde takes approximately 30 minutes to
reach an altitude of 15km. As all three measurement flights commenced at
approximately 09:30LT (ie. 00:00UTC), the initial ascent normally coincided
well with the radiosonde.
Figure 12 shows an example of the aircraft wind and air
temperature profiles plotted together with those from the GPS-sonde. The profiles
agree remarkably well.
The ultimate aim of this project was to compare the
wind data from the VHF-profiler with the wind data from the aircraft.
Profiles of wind direction and speed are available
from the VHF profiler every 10 minutes. Profiles falling into the same time
periods as ascents/descents of the aircraft were analysed and an example is
shown in Figure 13.
As can be seen, the data agrees reasonably well.
However, at altitudes above 10km, there seem to be an increasing number of
faulty estimates from the profiler. A closer inspection of the profile shows
that the VHF profiler does not resolve the vertical structure of the wind as
well as the aircraft, but gives a smoother vertical profile. This was to be
expected, as the vertical resolution of the profiler is about 150m.
Figure 12: Radiosonde data from
launch at 23:30UTC on
Figure 13: Wind profiles as measured from the aircraft (red)