L26 Pre-flight

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

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