Stealth does not mean invisible. It means reducing the energy a radar receives back from an aircraft — often to the point where it cannot be distinguished from noise — using geometry, materials, and careful management of every surface that faces a radar beam.
See the B-2 Spirit stealth bomberRadar cross-section (RCS) is the standard metric for how detectable an aircraft is to radar. It is expressed in square metres, but it does not describe the aircraft's physical size — it describes the area of a perfectly reflective sphere that would return the same radar energy back to the receiver.
To give the numbers meaning: a B-52 Stratofortress has an RCS of roughly 100 m². An unmodified fourth-generation fighter such as the F-16 with external fuel and weapons sits at roughly 5–10 m². The B-2 Spirit has an estimated RCS of approximately 0.1 m² — comparable to a large bird. The F-117 Nighthawk was designed for an RCS below 0.01 m² from its frontal aspect.
Materials can absorb radar energy, but geometry dictates where most of it goes in the first place. Every stealth design follows two hard rules: no surfaces perpendicular to likely radar directions, and align all edges to a small set of parallel angles.
The F-117 solved corner reflectors with a fully faceted design: every surface is a flat panel canted at an angle that deflects radar energy away from the transmitter rather than back to it. The mathematics were worked out in a 1966 paper by Soviet physicist Pyotr Ufimtsev, which Lockheed's Skunk Works team used directly.
The B-2 and F-22 took a different path: smooth blended surfaces with continuous curvature. The B-2's flying-wing planform has no tail surfaces at all — an inherently low-RCS shape since vertical tails are major reflectors. All wing leading and trailing edges align to just two pairs of parallel angles, concentrating any returns into tight known directions.
Where shaping alone cannot reduce returns — edges, inlet lips, canopy frames — radar-absorbent material finishes the job. RAM converts radar energy into heat through resistive or magnetic absorption rather than reflecting it. Early versions used iron-ball paint applied to the F-117. Later aircraft use ferrite tiles, carbon-composite skins, and multi-layer coatings tuned to specific radar frequency bands.
RAM is delicate, moisture-sensitive, and demands intensive maintenance. The B-2's climate-controlled hangars at Whiteman Air Force Base are themselves a cost line. Newer coatings on the F-22 and B-21 Raider are more durable, but hangar facilities remain a non-trivial part of stealth operating costs.
Even a perfectly shaped aircraft becomes radar-visible the moment it hangs weapons on external pylons. Every low-observable combat aircraft from the F-117 onward stores all weapons internally. The F-22 carries six AIM-120 AMRAAMs and two AIM-9X Sidewinders internally. The B-2 carries up to 40,000 lb of bombs or sixteen B83 nuclear gravity weapons in two rotary launchers. The F-35 carries four AIM-120s internally in its primary stealth configuration.
A jet engine's compressor face is a near-perfect radar reflector. Stealth inlets block the line of sight from any forward radar to the compressor. The F-22 uses a serpentine S-duct inlet: the intake channel bends twice so no straight line of sight exists from outside to the engine face. The F-35 uses a diverterless supersonic inlet (DSI) — a bump-shaped compression surface that reduces both RCS and parts count.
Stealth aircraft are optimised against X-band and Ku-band radar. They are far less effective against long-wavelength radars:
Content adapted from publicly available aeronautical engineering and defence references. Vehicle data sourced from the Who That Plane?! gallery.