AIRTOSS – AIRcraft TOwed Sensor Shuttle
The idea of a Tandem Platform
One of the unique features of the Learjet 35A D-CGFD is its capability to carry external loads of up to 450 kg under each wing. GFD, the operator of the aircraft, uses this feature for a variety of special missions for military training, e.g. to carry jammers for training of electronic warfare or to tow targets for ground troops.
The possibility to tow targets with up to 8 km long steel cables and the long lasting experience of GFD in the operation of towed targets (since 1966 without any problems even when flying difficult flight manoeuvres) was the trigger to think about possible utilisations for atmospheric research.
Finally, a scientific project to study the influence of cloud particle size, -shape and -chemical composition on radiative transport was initiated. Headed by Dr. Stephan Borrmann, Professor at the Institute for Physics of the Atmosphere and one of the directors of the Max Planck-Institute for Chemistry, Mainz a group of researchers planned to instrument a towed target with a Forward Scattering Spectrometer Probe (FSSP), up- and downward looking radiation sensors, and a LAser Backscatter Sonde (LABS) in order to study processes within cirrus clouds.
Towing these instruments by a fully equipped Learjet 35A research aircraft with appropriate instrumentation on board and by changing the horizontal and vertical distance between the towed instrumented probe(s) and the research aircraft simultaneous measurements at two (three) different altitudes should be possible. This would enable e.g. the in-situ characterisation of physical and chemical properties of particles and the determination of radiative fluxes at different altitudes. Such simultaneous observations of the radiation balance and particle properties could be used to study the influence of cloud particle size, -shape, and chemical composition on the radiation balance using radiative transport models.
Due to safety regulations such measurements never could be achieved using two or more instrumented aircraft, either the horizontal and/or vertical separation would to be too big (two or more aircraft flying according to IFR rules) or to small (two or more a/c flying wing by wing).
In a first study enviscope developed a concept which uses as carrier a towed target type Do-SK6. This towed target consists of three sections with an inner diameter of approx. 18 cm, has a total length of approx. 266 cm and an empty weight of 19 kg. Manufactured in high quantities by company EADS Friedrichshafen (former Dornier GmbH) and certified to be flown with a max. weight of up to 70 kg the Do-SK6 body offers a cost-effective approach to integrate instrumentation for atmospheric research of up to 30 kg (assuming that basic infrastructure will weigh between 20 and 25 kg).
To make these technique to tow targets available for atmospheric science, the existing types of targets shall be modified and equipped with:
- a modular mounting frame suitable for a variety of instruments,
- a power supply for the scientific instrumentation,
- a flexible data acquisition system open for different users,
- a telemetric system to transfer data and commands between aircraft and AIRTOSS,
- avionic and meteorological basic instrumentation,
- hard points to mount inlet systems and sensors at the fuselage.
In the following picture the mechanical concept of the AIRcraft TOwed Sensor Shuttle (AIRTOSS) is given:
An instrument rack was fixed to the middle section of the towed target in a way that the front and aft section of the housing could be removed easily in order to have good access to the instruments. The front part was designed to accommodate a particle spectrometer, while the middle and aft section enable the mounting of the basic infrastructure like batteries, data acquisition, standard avionic and meteorological instrumentation and the adaptation of instrument modules according to the scientific goals of the missions.
The certification of AIRTOSS was done in close co-operation with EADS Friedrichshafen. Enviscope performed the stress and load analysis and delivered all relevant information to the EADS Design Bureau.
Proof of concept
AIRTOSS was instrumented with the
- Cloud Imaging Probe (CIP)
- stat. pressure and temperature sensors
and sensors to characterize the attitude of the sensor shuttle
- iMAR Inertial Navigation System
- telemetry and data acquisition unit
while the Learjet was instrumented with
- Forward Scattering Spectrometer Probe (FSSP-300)
- Fast In-Situ Stratospheric Hygrometer (FISH)
- VIS and NIR spectrometers for down- and upwelling radiance and irradiance measurements
- Standard Learjet Instrumentation
The team of scientists from Mainz was happy about first data sets measured by the Tandem Platform AIRTOSS-Learjet35A, and GFD and enviscope were happy that the technical concept prooved well and all flights could be performed safely.
Thanks to all groups involved, and especially to Andreas Fleck from EADS for his support.
The data evaluation of the first flights is still in process, first results have been presented at the 15th International Conference on Clouds and Precipitation (ICCP 2008), Cancun, Mexico, 7-11 July 2008.