# L26 Pre-flight **Block 3: IR EW and Signature Management — Lesson 26: The Aircraft RF Signature** *Work this before L26. Pre-flights are never collected — in class, anyone may be cold-called to present any question at the board, and that recitation is the participation grade.* --- ## Assumed pre-class reading - L25 wrap-up (three-factor rule, canonical shapes, the corner trap, median vs mean over aspect) - The Jupyter Book Reading page for L26 — the major RF signature contributors, the four design verdicts (shape, mask, treat, manage), planform alignment, and the loudest-first budget discipline. --- ## Quiz questions (5 items, ~5 minutes) **Q1.** (Multiple choice) On many legacy (non-LO) aircraft, one of the loudest single RF contributors is the engine inlet. Why? - [ ] (a) The spinning compressor blades emit radio waves - [ ] (b) The inlet duct acts as a cavity: energy bounces multiple times inside and returns strongly toward the radar - [ ] (c) The inlet lip is coated in metal paint - [ ] (d) Air flowing into the duct compresses the radar wave --- **Q2.** (Multiple choice) What is **planform alignment**? - [ ] (a) Keeping the aircraft level during penetration to minimize the presented area - [ ] (b) Grouping every edge and seam into a few shared orientations so their spikes stack into a small number of lobes pointed away from the nose - [ ] (c) Aligning the flight path with the terrain to hide in clutter - [ ] (d) Mounting all antennas along the aircraft centerline --- **Q3.** (Multiple choice) A design review finds a $+10$ dBsm corner reflector formed by a tail-fuselage junction on an airframe whose remaining contributors sum to $-20$ dBsm. Which statement best reflects the **budget discipline**? - [ ] (a) Treat all contributors equally; every dB counts the same - [ ] (b) Fix the corner first: contributors add in linear space, so the $+10$ dBsm corner effectively *is* the aircraft's signature until it is fixed - [ ] (c) Add RAM to the wings first, since they have the most surface area - [ ] (d) Ignore it; RCS is set by the largest physical dimension --- **Q4.** (Short answer) In one or two sentences: why do LO fleets require ongoing **signature maintenance** (checks after panel work, careful surface condition), rather than treating stealth as fixed at delivery? --- **Q5.** (Multiple choice) Why must the fire-control **radome and antennas** be "treated" rather than shaped or deleted? - [ ] (a) They are structural and cannot be moved - [ ] (b) An aperture designed to radiate efficiently is also an efficient scatterer, so it gets engineered compromises: frequency-selective radomes, flush conformal apertures, and disciplined emissions - [ ] (c) They are too small to matter to RCS - [ ] (d) Radomes only reflect in the visual band