Cessna Citation II Research Aircraft

The University of North Dakota owns and operates a Cessna Citation II aircraft for the purpose of atmospheric research. This aircraft type has a number of design and performance characteristics that make it an ideal platform for a wide range of atmospheric studies. The Citation II is a twin-engine fanjet with an operating ceiling of 43,000 feet (13.1 km). The turbofan engines provide sufficient power to cruise at speeds of up to 340 knots (175 m s-1) or climb at 3300 feet per minute (16.8 m s- 1). These high performance capabilities are accompanied by relatively low fuel consumption at all altitudes, giving the Citation an on-station time of 3-5 hours, depending on mission type. Long wings allow it to be operated out of relatively short airstrips and to be flown at the slower speeds (140 kts/72 m s-1) necessary for many types of measurements. The Citation is certified for flight into known icing conditions.

The cabin measures approximately five feet in diameter and more than 16 feet in length. The minimum flight crew is pilot, co-pilot and mission scientist or data system operator. Two additional seats are available for scientific observers.

A series of structural modifications have been made to the basic airplane. These include the following: pylons under the wing tips for a variety of probes in the undisturbed air flow away from the fuselage; a gust probe for wind measurement; and air inlet ports for air sampling inside the pressurized cabin. Mounting locations are available for a 6-angle electric field mill configuration. Hemispheric radiometers may also be mounted for upward and downward flux measurements.

Instrumentation: The research instrumentation available on the Citation is listed below in the Summary of Measurement Capabilities. The installation of instruments provided by other investigators can be accommodated, subject to space, weight and electrical requirements. A variety of 19-inch racks are available to accommodate standard instruments.

Meteorology: The basic instrumentation package measures temperature, dew point temperature, pressure, and wind along with aircraft position, attitude and performance parameters. The three-dimensional wind field is derived from measurements of acceleration, pitch, roll and yaw combined with angles of attack and sideslip and indicated airspeed. The aircraft parameters are supplied by an Applanix POS-AV strap-down gyro system with integrated global positioning system (GPS). Strap-down accelerometers provide lateral and longitudinal aircraft accelerations. Turbulence intensity can be derived from differential pressure transducers and accelerometer outputs.

Cloud Physics: Cloud microphysical measurements are made with an array of probes (CDP, 2DS, 2D-C, HVPS) mounted on the wing-tip pylons and a CPI mounted on the fuselage. These probes measure concentrations and sizes of particles from one micrometer to several centimeters in diameter. In addition, there are probes to measure both liquid water content and icing rate.

Air Chemistry and Aerosols: Several gas and aerosol sampling instruments are available. These include a TDL laser hygrometer, PMS passive cavity scattering probe, and a TSI condensation nuclei counter.

Data Acquisition and Display: The data are sampled at various rates from 4 to 200 sec-1. The sampling is controlled and data are recorded by the on-board SEA M-300 data system which also displays the data in real time in graphic and alphanumeric formats. The data system is based on a project-customized windows system to allow flexibility in data acquisition and instrumentation in order to accommodate specific research demands.