FAA Aviation Mechanic Airframe (AMA)Airframe StructuresHard
A technician performing a composite skin repair per the structural repair manual must taper (scarf) the damaged area at a 30:1 ratio before applying the repair plies. If the skin laminate thickness is 0.060 inch, what is the required scarf length?
- A1.20 inches
- B3.00 inches
- C0.60 inch
- D1.80 inches
Show answer & explanationAnswer & explanation
Correct answer: D. 1.80 inches
Scarf length = scarf ratio × laminate thickness = 30 × 0.060 inch = 1.80 inches. A shallow, long taper like this ensures adequate bonding surface area to transfer loads between the original laminate and the repair plies.
Why the other options are wrong
- A. This equals a 20:1 ratio, still short of the required 30:1 taper.
- B. This would be a 50:1 ratio, more taper than specified, wasting material and increasing repair size unnecessarily.
- C. This would only be a 10:1 ratio, insufficient for the specified 30:1 requirement.
Composite Scarf Joint Repair Ratio
The ratio of scarf (taper) length to laminate thickness used in composite repairs to gradually transfer load between original structure and repair plies; structural repairs commonly specify ratios such as 30:1 per the manufacturer's SRM.
- Scarf length = ratio × laminate thickness.
- Higher ratios provide a shallower taper and larger bonding area.
- Exact ratio (e.g., 20:1, 30:1, 50:1) is specified by the aircraft's structural repair manual.
Memory trick: Scarf length = Ratio × Thickness, like stretching dough thin and long