Sand and Rain Erosion

Sand and Rain Erosion Testing – EVIAC

Helicopter rotor blade leading edges are subjected to extreme environmental conditions that can be difficult to replicate in a laboratory environment…

What is the EVIAC?

The Extreme Velocity Impact Analysis Chamber (EVIAC) is capable of simulating real world environmental operating conditions of rotor leading edges, optical components, and axial compressors. It allows UPT to reproduce real world erosion from sand, rain, and single or multiple large particles; separating it from traditional; nozzle type erosion testing. Impacts are analyzed through high speed video allowing real time data capture of 60,000 frames per second from each test. Varying run times and media introduction rates allow damage and surface degradation to be documented over the course of time. UPT can then use this data to characterize the effects of the impacts on the tested component and the durability of the candidate substrates.

Rain Erosion

Current leading edge protection systems, such as the blade tapes and spray on urethanes, exhibit good sand erosion and small particle impact protection. However, when exposed to a rain impact environment they quickly delaminate and erode.

Surface degradation occurs as a result of the high velocity water droplet impacts exerting very high impact pressures and stresses on the order of thousands of PSI. These stresses over the course of time can result in the stress cracking of brittle materials and the plastic deformation of materials that are more ductile. The water droplets post-impact outflow from the impact site will then erode the material, starting at the damage point.

Typical rain erosion testing is conducted at tip speeds exceeding 733 fps or approximately 500 mph. Rain rates are usually tested from 0 to 3 inches per hour. The simulated raindrop sizes typically range from 1.5 to 2.5 millimeters in diameter depending on the desired rainfall rate to be simulated.

Sand Erosion

Particles that have a mass above 0.05g will generate sufficient impact energy to damage current leading edges or leading edge protection systems, therefore this value is used as a divider between sand erosion and particle impact. Particles with a mass less than 0.05g are considered in the regime of sand erosion. Impact damage occurs in the form of cuts, tears, gouges or any other anomalies that lead to loss of flight worthiness. Sand can be introduced to the EVIAC by the following:

  • Shot Method – Vertical drop through particle randomizer of weighted sand at a known height across the swept area of tested sample.
  • Aerosol Spray – Sand is sprayed into the EVIAC providing a uniform cloud density.
  • Screw Feed – Sand is dropped through a particle randomizer from a screw fed sand hopper.

Large Particle Impact

One of the most common ways damage occurs to a helicopter rotor blade is through exposure to particle impacts. These particles, frequently referred to as foreign objects, come in many shapes and sizes and can include such items as sand, gravel, rocks, dirt, small trees and brush, trash, birds, safety wire, tools, rags and clothing articles. All of these items can cause Foreign Object Damage (FOD) typically resulting in denting, gouging premature erosion of the leading edge of the main and tail rotors of the helicopter. Of the items listed, sand, gravel, rocks and dirt are the most common contributors to blade wear.

The desert environment, unimproved landing zones and field operations may immediately come to mind as environments where these conditions are encountered, but these conditions can exist in garrison as well. The perimeters of runways and flight lines are the greatest source of stone foreign objects. When disturbed by sweeping, exhaust blasts, aircraft landing gear, ground vehicles, etc., borders tend to loosen so that debris are easily tracked, blown or washed onto runways and aircraft parking areas. Aircraft ground maneuvering is of particular FOD concern. Exhaust blasts or rotor downwash can cause stones and other foreign objects to become airborne and drawn into the rotor system of another aircraft.

The EVIAC is able to reproduce high velocity sand, rain, and large particle impacts on samples to accurately depict how a sample or system would wear on a rotorcraft at an accelerated rate. This tool is used to evaluate wear characteristics of several aircraft components that travel at high velocities.

UPT is capable of providing any of the services noted above to customers with the need for precise analysis. For more information and a quote regarding your inquiry please contact Jeff Neurauter at 704-888-2470 ext. 30.