An outline is presented demonstrating how reasonable estimates of the rain environment, the desired operational capabilities of the aircraft or missile, and laboratory erosion data can be utilized with a rain erosion damage model to provide a fairly reliable estimate of environmental degradation of infrared-transmitting windows and radomes throughout a flight trajectory. If water drop interactions with the flow field around the vehicle are ignored, the suggested approach will provide an upper bound on the extent of the water drop impact damage associated with a particular mission. The design philosophy would then be that if this level of damage can be tolerated the actual impact conditions will not be detrimental. A wide range of flight scenarios can be examined on this basis. If the upper bound computation indicates that a level of damage will result which is well beyond the limit which can be tolerated, then aerodynamic analyses of water drop interactions with the flow field around the vehicle and a more complete statistical analysis of the impact damage will have to be undertaken.
W. F. Adler,
"Development Of Design Data For Rain Impact Damage In Infrared-Transmitting Materials", Proc. SPIE 0297, Emerging Optical Materials, (26 February 1982); doi: 10.1117/12.932496; https://doi.org/10.1117/12.932496