First Field Experiment with the Helicopter-Borne Version of ACTOS:
Winningen'05
Overview
After first test flights with a mock-up system of
ACTOS as an external cargo beneath a helicopter in fall 2004. In April 2005
the first field campaign with the complete ACTOS was performed at the airport
Koblenz/Winningen. The main goal of this experiment was the investigation of
the dynamics and micrphysical parameters of cumulus clouds. The experiment
was supported by the enviscope GmbH and the Rotorflug GmbH. In addition to
our standard instrumentation for cloud measurements a
"Phase-Doppler Interferometer for
Cloud Turbulence" (PICT) was installed to
measure droplet velocities and sizes. These measurements were done in
cooperation with Raymond Shaw from the Physics Department of the Michigan
Technology University, MI, USA. The PICT system was installed side by side to
the M-Fast FSSP to correlate both measurements.
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| Fig 1.: Sketch of ACTOS outrigger (blue:
carbon-fiber tubes, green: sensors) |
Fig 2.: Photo of outrigger with sensors. |
Flight Conditions and First Experiences
The measurements were done with help of a Bell
LongRanger (Bell 206III LR). ACTOS was fixed with a 140 m long tether at the
external cargo hook. A link between ACTOS and the helicopter was established
with a fiber-optic connection to ensure online monitoring during the
measurement flight. ACTOS was completely autonomous and was powered by two
300 W Li-Ion batteries. All data was stored in real time on a compact flash
card onboard ACTOS. To ensure flight safety, a transponder (mode C) was
installed on ACTOS and an anti-collision light was fixed on the top of the
tail. During this experiment, the helicopter was flown under visual flight
regulations (VFR), therefore, ACTOS was dipped into the clouds from above
whereas the helicopter remained outside the clouds.
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| Fig.3: Sketch of the combination of ACTOS with
helicopter. |
To avoid any influence by the helicopter downwash a
forward speed (true air speed, TAS) of 15 m/s was chosen. The selected TAS
ensures stable flight conditions of the helicopter with acceptable vibrations
of the helicopter cell. Due to flight regulations the ceiling was limited to
10.000 ft (3000 m), the maximum climbing rate was 1000 ft/min (5 m/s). After
a first quicklook, ACTOS showed stable flight conditions with angles of
attack and sideslip below 5 degree under most conditions. A smooth pendulum
motion with the frequency of a mathematical pendulum with l = 140 m
(f = 0.04 Hz) and a second mode around 1 Hz in environments with
increased turbulence was observed. Both modes are resolved from the
navigation unit without any problems.
Measurement Example
As a measurement example a short time series of 60 s
was selected from the Winningen'05 campaign. The flight was performed on
2005, April 27th. The data were taken during a level flight in a height of
2350 m about 50 to 100 m below cloud top. In Fig. 4 the time series of LWC
(red line) indicate a short cloud penetration. In the same panel the vertical
wind velocity shows subsidences around cloud edges and updrafts in the middle
of the cloud. Outside the mean vertical velocity is around zero. The
temperature T in the middle panel of Fig. 4 shows sharp jumps at cloud edges
and little variation within the cloud. The lower panel of Fig. 4 presents
particle number concentrations of interstitial aerosol. The blue curve
represents particles in the diameter range between 6 and 12 nm (so-called
"ultrafine particles"). These small particles are an indication for new
particle formation events in that areas.
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| Fig. 4: Time series of different measured
parameters (see text for further details.) |
Last Modification: 2005-12-20
