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Rib lacing spacing in the propeller slipstream

Aviation Mechanic Airframe (AMA) practice question 22 of 30 on Non-Metallic Structures. ACS element AM.II.B.K13 · difficulty: recall. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONCompared with the rest of the wing, how must rib lacing be spaced in the area of the propeller slipstream?

  1. AFarther apart, to save cord
  2. BThe same, but with hidden knots
  3. CCloser together
Show the answer and explanation

Correct answer: C. Closer together

  • A — incorrect Wider spacing in the slipstream would leave the fabric less secure in the most turbulent area of the wing.
  • B — incorrect Hidden modified seine knots are an appearance option anywhere on the wing and do not substitute for the closer spacing required in the slipstream.
  • C — correct Greater turbulence in the propeller wash requires closer spacing between the lacing in that area.

BACKGROUND

The fabric on a wing must be secured to the ribs with more than cement because airflow loads are too great for cement alone. Screws, rivets, clips, and lacing are used, and the method must match the one used by the original manufacturer unless a field approval is obtained. Lacing holes are laid out and pre-punched as close to the rib caps as possible to minimize the leverage the fabric could develop while pulling away from the structure. Spacing between lacing holes and knots must adhere to the manufacturer's instructions, or to the spacing guidance taken from AC 43.13-1. Because of greater turbulence in the area of the propeller wash, closer spacing is required there, and that slipstream is considered to be the width of the propeller plus one additional rib.

STUDY TIP

Remember that the slipstream area is defined as propeller width plus one additional rib, and that this area always receives the tighter lacing spacing.

KEY POINTS

  • Rib lacing is spaced more closely inside the propeller slipstream.
  • The slipstream is the propeller width plus one additional rib.
  • Lacing holes are punched as close to the rib caps as possible.

SOURCES

  • ama-airframe/ch03.txt "Rib Lacing"
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SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.