Ris blown across your face by the wind. When you drive on a highway, it smashes into your car’s windshield with even greater force. At high speeds, raindrops can wear away solid materials, which is a serious concern in the aerospace industry.
For propeller aircraft, rain was primarily a visibility problem, but aircraft in the jet age were vulnerable to raindrops eroding paint coatings and damaging plastic, ceramic and even metal components. The problem was even more acute with rockets; for a spacecraft re-entering the atmosphere at high velocity, each drop is a bullet of liquid.
Engineers needed to investigate the effects from raindrop erosion on the ground before new rockets or aircraft are flown. In the 1950s, the Royal Aircraft Establishment repurposed its swing arm, used to test pilots’ resistance to G-forces, for rain erosion studies.
For higher speeds, researchers used compressed gas guns to fire test articles into water droplets suspended in webs. They have evolved extreme water pistols fire drops at supersonic speeds, simulate flight through rain at mach 5.
The most advanced device was a rocket skid trail at Sandia, New Mexico, which carried nose cones, radar domes and other components through simulated rainstorms.
These tests gave engineers a thorough understanding of how speed, droplet size and exposure time affected rain erosion, and they now build accordingly.
