Coatings and radar-absorbent material, or RAM, make only a small contribution to the efforts to hide an airplane from enemy radar, but without them, no airplane can be truly stealthy. The F-22 first gets a base coat of radar-absorbent or deflective materials, over which is applied a topcoat developed by Boeing to counter a broad range of wavelengths, including infrared. The formula was tailored for the Raptor’s wing edges to deter wideband radars; a ceramic RAM cools its hot exhaust nozzles.
When RAM is illuminated by radar, its molecules oscillate, converting the radio waves or microwaves into heat, which dissipates from the skin, rather than reflecting the energy back to its source. The paint’s properties act in roughly the same way as your kitchen’s microwave oven.
A technician guides a paint sprayer to coat an F-117 Nighthawk. Painting the first F-117 took five workers five days; thereafter, a team at Sandia National Laboratories in New Mexico developed a precise, machine-delivery system. The applicator, which rode on a 30-foot rail, had sensors that compared details of the airframe, such as the intersection of angular facets, to a three-dimensional computer model.
Stealth coatings are now applied by robot. Sensors report any condition that could cause flaws in the finish, such as variations in flow rates.