Unique Capability Tests Rain Erosion at High Speeds

  • Published
  • By Lynn Pfledderer
  • Materials and Manufacturing
WRIGHT-PATTERSON AIR FORCE BASE, Ohio --  A one-of-a-kind supersonic rain erosion (SURE) testing capability, simulating the impact of rain on aerospace systems traveling at transonic and supersonic speeds, has been developed by AFRL researchers. The SURE capability enables both predictive modeling, and large- and full-scale component rain erosion testing.

The SURE capability tests systems, materials and new technologies for missile materials; coatings for aircraft leading edges; optical materials; rotor blades; radomes; antennas; and other commercial technologies at speeds up to Mach 2.5. Because the SURE operates at speeds not offered by the AFRL Rain Erosion Test Facility or the Holloman High Speed Test Track (HHSTT), material and system developers can use the SURE capability to establish a testing baseline in the mid-range, which had been unavailable.

Materials and coatings on systems traveling at transonic and supersonic speeds may be repeatedly exposed to rain droplets, making them susceptible to damage or erosion. Air Force researchers developed the SURE apparatus for investigating the erosion behavior of technologies and materials before they are in service. The SURE apparatus, housed at the AFRL's Materials and Manufacturing Directorate's Coatings Technology Integration Office (CTIO), allows researchers to conduct predictive, multi-scale physical modeling to determine how systems and materials erode or resist erosion in rain while traveling at high speeds. The SURE apparatus produces 1-2 mm diameter water droplets, and achieves 12 gallons of output a minute at 50,000 pounds per square inch. Droplet size is controlled by an interchangeable nozzle; droplet speed is independently controlled by pump pressure.

To date, two pump/motor assemblies, which will produce the rain field, were successfully tested for continuous operation. In addition, because the pumps were not running at their maximum speed, AFRL engineers expect that the SURE apparatus will be capable of generating larger droplets (up to 2.5mm). It is also expected to operate at speeds as high as Mach 2.5.

The SURE capability is operated and maintained by personnel from the University of Dayton Research Institute (UDRI) by way of an on-site contract with the CTIO. A cooperative research and development agreement between AFRL and UDRI accommodates testing for commercial and industrial customers. The CTIO also offers sand erosion testing, which will accommodate customer requests for performance testing with combined effects.

The Weather Encounter Working Group, led by the Army Aviation and Missile Research, Development, and Engineering Center, recently requested a briefing from the CTIO on AFRL's rain erosion testing capabilities. In addition, various agencies and academic institutions have expressed interest in using SURE to conduct high-speed weather encounter research, development, testing and engineering.