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The F-117 Nighthawk is perhaps one of the most well-known stealth aircraft the US has ever made. Being the world’s first operational stealth fighter, the Nighthawk has a few tricks up its sleeves to retain its low profile.
To help maintain it, the aircraft was fitted with “grilles” over the engine inlets.
These grilles prevented radar from reflecting on the engine compressor inside the inlet. This only worked because the size of the grids was smaller than the wavelengths of most radars.
Meanwhile, those that did make it through the grilles were eventually absorbed by a radar-absorbing material inside the duct.
The grilles did have some drawbacks, though. It was optimized for stealth and not performance, so an intake suction relief door above the inlet would have to be opened when the engine required more air during takeoffs and landings.