Detection is a union over bands, so the effective detection range is the largest band, not the average: \(R_\text{det} = \max_b R_b\). In plain terms — you are only as quiet as your loudest band.
A fused defender is cued if any single band crosses its threshold. It needs only one band to succeed, so the band with the longest detection range decides when you are found.
Nothing. The defender is still cued by the loudest band, so investment in a quiet band buys zero range — until that band actually becomes the limiter.
Cutting the loudest band lowers \(R_\text{det}\) only until it meets the next band, which then inherits the limit. Past that point more reduction on the old band does nothing — the curve flattens at the new limiter.
Contrails — engine water vapor freezing into a persistent, sky-wide ice trail — and glint, the brief but very bright specular flashes off the canopy, leading edges, and flat panels.
Tactics and finish counter it: contrail-avoidance routing and altitude, matte finishes, and low-reflectance paint to cut contrast. Radar-absorbing material does not — no coating hides a contrail.
Sound is slow (~340 m/s) and lossy, fading with geometric spread and atmospheric absorption. A high-altitude slant range is long, so little reaches the ground; but low-altitude penetrators, helicopters, and UAS (blade-passage tones) are often heard first.
Three emitters — hot parts (~700–900 K, MWIR), plume (CO₂ near 4.3 µm, MWIR), and aero-heated skin (LWIR) — and two reflectors — reflected solar (day) and reflected sky/earthshine.
MWIR carries the plume and hot parts, which dominate tail-on. LWIR carries the aero-heated skin, which is the all-aspect contributor.
IRST and FLIR (L23) read all five components passively. Passive IR needs no emission of its own to intercept, so there is nothing for a radar-warning receiver to hear and nothing EMCON can deny it.
Radar can be shaped and absorbed and emitters can be silenced, but a hot engine glows on its own and a passive seeker collects that glow. Signature management can only manage which IR component is loudest, not remove the band.
It hides the LWIR aero-heated skin twice a day, when the skin temperature matches the background sky. It does not hide the MWIR plume, which is independent of the time of day.
It is the same loudest-first discipline, moved from within the RCS budget (L26) to across the whole spectrum. Cut the limiter, expect the problem to move to the next band, re-plan, and repeat — L27's materials and discipline being the last-decibel step within a band.
The eyeball floor — a contrail or a glint — and, tail-on, the engine plume. Below those there is nothing to coat, so further material investment buys no range.
Project 3 is a B-21 signature trade against a VHF surveillance radar, an X-band fire-control radar, and an IR MANPADS. The rule decides which investment actually buys survivability: spending on a non-dominant band is wasted, so the trade must attack the limiter and expect it to move.