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 radiate RF of their own as they chop the airflow

  • [ ] (b) The duct is a cavity: the wave rattles inside and returns toward the radar

  • [ ] (c) The inlet lip carries a metallic paint that reflects better than the airframe skin

  • [ ] (d) Air rushing into the duct compresses the radar wave as it enters

Q2. (Multiple choice) What is planform alignment?

  • [ ] (a) Holding the aircraft level through the threat ring so the presented area stays minimal

  • [ ] (b) Grouping every edge and seam onto a few shared orientations, aimed off the nose

  • [ ] (c) Aligning the ingress track with terrain features so the return hides in ground clutter

  • [ ] (d) Mounting every antenna along the aircraft’s 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 every contributor equally — each dB removed anywhere buys the same dB off the total

  • [ ] (b) Fix the corner first: until it is gone it effectively is the aircraft’s signature

  • [ ] (c) Add RAM to the wings first, since their surface area dominates the airframe

  • [ ] (d) Ignore it — total RCS is set by the airframe’s 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 load-bearing structure, and the nose is the only place an antenna can see from

  • [ ] (b) An aperture built to radiate efficiently is, by reciprocity, an efficient scatterer

  • [ ] (c) They are far too small a fraction of the airframe’s area to move the total RCS

  • [ ] (d) A radome is transparent to radar and scatters only in the visual band

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