Convair 580 Instrumentation Pylons

To configure the Convair 580 as an atmospheric research aircraft facility, IAR developed the ability to design and mount instrumentation pylons on the Convair. Previously built pylons were not suitable because of problems associated with irregular junction flow at the wing and detached flow over the pylon, which caused cracks in the aileron skins in the trail of the pylons.

PMS probes mounted on pylon.

IAR designers took into account a number of limitations and requirements. Any viable atmospheric research aircraft must provide for instrumentation sites for particle measuring probes, since the measurement of particle size distribution is basic to atmospheric studies. One important design objective called for the pylons to be ideally suited for probes manufactured by Particle Measuring Systems (PMS), while also being useful for other applications. That meant that the design also made it possible to accommodate other canister-mounted instrumentation. Eight sites for standard PMS instrumentation canisters were required.

The design aimed for an aerodynamic shape, with the structural load distributed to the front and rear spar caps. The probes had to be mounted on the pylons such that they would not interfere with large drop stability upstream of the probes. In addition, the pylons were configured for quick installation and removal of instrumentation, and the disturbed airflow over the ailerons was kept to a minimum.

A two-pylon, eight-probe configuration was designed, built and successfully flown on board the Convair. The influence of pylons on aircraft performance has been observed to be small (approximately 5% decrease in speed and range at normal cruise power settings). The significant efforts directed at droplet stability resulted in a design that allows for the accurate measurement of large drops, as evidenced by the results during the Beaufort Arctic Storms Experiment wherein drops of 5 mm diameter were imaged. The pylons will continue to be an important extension to the capabilities of an already versatile, multi-use, airborne research platform.

Underwing pylon installations on the Convair 580.

Cloud Particle Imager (CPI) Pylon

A cloud particle imager (CPI) sensor, designed by SPEC Inc. of Colorado, was recently installed on a pylon under the wing. This pylon is a hollow aerodynamically-shaped aluminum section which suspends the SPEC probe well below the wing and any associated flow disturbances. The aluminum section is attached to the wing itself by means of a composite interface panel to spread the loading over a large area. The pylon worked well mechanically and aerodynamically with the only difficulty experienced being moisture accumulation inside the pylon, which will likely be corrected in a future design.

Related Information

Institutes:

• NRC Institute for Aerospace Research