FAA Aviation Mechanic General (AMG)Physics, Math and Fluid LinesHard
According to general guidance for fabricating fluid lines, the minimum bend radius for aluminum alloy tubing is approximately 3 times the tube outside diameter. What is the minimum allowable bend radius for a 3/8 inch OD aluminum tube?
- A0.375 in
- B1.125 in
- C0.750 in
- D1.500 in
Show answer & explanationAnswer & explanation
Correct answer: B. 1.125 in
Minimum bend radius = 3 × OD = 3 × 0.375 in = 1.125 in. Bending tighter than this radius risks wall thinning, flattening, or cracking.
Why the other options are wrong
- A. This is the OD itself, not multiplied by the bend factor.
- C. This uses a factor of 2 instead of the required factor of 3.
- D. This uses a factor of 4, exceeding the standard multiplier.
Minimum Tube Bend Radius
To prevent tube damage such as flattening, wrinkling, or wall thinning, tubing must be bent no tighter than a minimum radius, typically about 3 times the tube's outside diameter.
- Minimum bend radius ≈ 3 × tube OD (general guidance)
- Bending tighter causes wall thinning and possible cracking
- Applies to aluminum alloy tubing used in fluid line fabrication
Memory trick: 'Three times the tube, keep it smooth' — never bend tighter than 3×OD.