About the Research Aircraft

Research aircraft description

(ref: Kochtubajda, 1995)

The primary observational platform used in these studies was the Intera/Alberta Research Council instrumented research aircraft, a Cessna 441 Conquest (photo below), pressurized twin-engine turboprop aircraft. During research missions the aircraft normally flies at 150 kts indicated airspeed.

Cloud physics instruments were located on the escape door (photo below) and beneath the fuselage. The instruments located on the escape door included a Rosemount total temperature sensor, a platinum wire reverse-flow temperature sensor, an E.G.G. dew point sensor, a Johnson-Williams (JW) hot-wire liquid water content (LWC) meter and a cloud water collector.

Particle size spectra were measured with Particle Measuring Systems (PMS) spectrometer probes mounted on a belly pod (photo below) 0.5 m beneath the fuselage skin and 3 m aft of the nose. The instruments included an ASASP (aerosols 0.1-3 um), a 2D-C (25-800 um) with depolarization, 2D-P (200-6400 um), and an FSSP to count and size cloud droplets. The FSSP was usually operated in the 2-30 um range. Comparisons between numerical studies of airflow and particle trajectories and aircraft observations, (Oleskiw et al. 1985 a,b), indicated that the location beneath the fuselage was the most practical for mounting these probes. Predicted changes in droplet mass flux from freestream values were less than 12% in the droplet diameter range 10 um to 2 mm.

Air motions were measured with a Rosemount 858AJ probe mounted on the tip of a nose boom about 2 m ahead of the aircraft. True motions of the aircraft were provided by an inertial navigation system (Litton LTN-76). Vertical and horizontal velocities were determined from nose boom pressure and the INS accelerometer and rate gyro data.

Position-keeping systems onboard the aircraft included an inertial navigation system, a VOR/DME station and an X-band transponder. Data from the instruments were managed by a computer based data system which provided data acquisition, recording, and real-time calculations and display (Johnson et al, 1987). The research aircraft was also equipped with an X-band weather avoidance radar, a video camera and a recorder. A complete list of the instrumentation, measuring techniques, range, accuracy, precision, and sampling rates has been given by Cheng et al. (1986).

An important component of the computer based data system was the homing pointer, a computer program which can track and display the location of a specific cloud region relative to the aircraft. Once the homing pointer was initiated, continuous readings of elapsed time, heading and distance (calculated from an integration of true airspeed and magnetic heading), allowed the pilot to return to the same "pointer" location for successive measurements. Vertical air motions and sheared environments are factors which make the pointer location less accurate with elapsed time. Cheng et al. (1986) estimated that in a steady and non-sheared environment, the uncertainty of the homing routine was about 1.5%. Tracking cloud regions in an air-relative frame of reference has also been used in other studies (Huggins and Rodi, 1985; Stith et al., 1986).

Calibration procedures for the aircraft instrumentation included tower fly-bys, aircraft intercomparisons, ground measurements, and sounding intercomparisons. The JW liquid water probe was calibrated and operated according to the manufacturer's specifications. The JW probe was also independently calibrated in the Ottawa high-speed icing wind tunnel (Strapp and Schemenauer, 1982). The test results indicated that the JW measurements were correct to within 20%. The FSSP was calibrated regularly by measuring the sample area and checking the sizing with the use of glass beads of known size. The FSSP performance can be estimated by comparing the FSSP liquid water to the JW liquid water. Figure 1 shows good agreement between the different liquid water measurements. A correlation coefficient of 0.89 was determined from a least squares regression analysis. Routine bench checks of the 2D probes were conducted to ensure that they operated within the manufacturer's specifications. During 2D data processing, artifacts were removed according to the rejection criteria of Cooper (1978). The criteria are reproduced in Gordon and Marwitz (1984). All remaining images were accepted as real particles. Adjustments to the concentrations were made to include depth-of field and sample volume versus particle size effects, as discussed in Heymsfield and Baumgardner (1985).

References

Cheng, L., E. Peake, D. Rogers, and A. Davis, 1986: Oxidation of nitric oxide controlled by turbulent mixing in plumes from oil sands extraction plants. Atmos. Env., 20, 1697-1703.

Cooper, W.A., 1978: Cloud physics investigations by the University of Wyoming in HIPLEX 1977., Dept. Atmos. Sci., Univ. of Wyoming, 320pp.

Gordon, G.L., and J.D. Marwitz, 1984: An airborne comparison of three PMS probes. J. Atmos. Ocean. Tech., 1, 22-27.

Heymsfield, A.J., and D. Baumgardner, 1985: Summary of a workshop on processing 2-D probe data. Bull. Amer. Meteor. Soc., 66, 437-440.

Huggins, A.W., and A.R. Rodi, 1985: Physical response of convective clouds over the Sierra Nevada to seeding with dry ice. J. Climate Appl. Meteor., 24, 1082-1098.

Johnson, M.R., L.E. Lilie, and B. Kochtubajda, 1987: A data structure for acquisition, analysis, and display of meteorological data. 6th AMS Symp. on Met. Obs. and Instr., New Orleans, AMS, 397-400.

Kochtubajda, B., 1995: The microstructure of selected, small, isolated, cumulus clouds near Red Deer, Alberta. Atmospheric Research, 35, 253-270.

Oleskiw, M.M., K.L. Grandia and R.C. Rudolph, 1985a: Airflow and droplet trajectory model to determine sensor placement on cloud physics research aircraft. J. Wea. Mod., 17, 45-49.

Oleskiw, M.M., K.L. Grandia and R.C. Rudolph, 1985b: Prediction of droplet trajectories to determine sensor placement on cloud physics research aircraft. J. Wea. Mod., 17, 50-58.

Stith, J.L., D.A. Griffith, R.L. Rose, J.A. Flueck, J.R. Miller Jr., and P.L. Smith, 1986: Aircraft observations of transport and diffusion in cumulus clouds. J. Clim. Appl. Meteor., 25, 1959-1970.

Strapp, J.W., and R.S. Schemenauer, 1982: Calibrations of Johnson-Williams liquid water content meters in a high-speed icing tunnel. J. Appl. Meteor., 23, 267-279.