Definition 1 of 2
Definition
In sheet metal work, a bend angle of less than 90 degrees between the flange and the original plane of the material, measured from the inside of the bend. The flange has been bent past perpendicular, closing the angle to something tighter than a right angle.
Plain English
A bend in a piece of sheet metal that is tighter than a square corner. The bent-up part leans inward, making the gap between the two surfaces smaller than 90 degrees.
Context Anchor
Seen in airframe maintenance drawings, sheet-metal layout, and repair instructions when a part must be bent or checked to an angle smaller than 90 degrees.
Derivation
‘Closed’ here is used in its geometric sense — the angle has been brought closer together, narrowing the opening between the two surfaces. The opposite is an ‘open angle,’ where the bend is less than 90 degrees of travel and the surfaces stay farther apart.
Why Pilots Care
Pilots usually do not measure closed angles in flight, but correct bend angles matter because repaired airframe parts must fit properly and handle forces as designed.
Analogy
Think of opening a book. A book opened to a right angle is at 90 degrees. Push the covers further toward each other and the angle between them closes. That tighter, narrower angle is what ‘closed’ means here.
Intuition Check
Closed does not mean sealed or completely shut here. It means the angle is smaller than 90 degrees, with the two sides closer together.
Example Sentence 1
The repair drawing called for a closed angle of 75 degrees, so the technician adjusted the brake to bend the flange past perpendicular.
Example Sentence 2
After annealing, the technician bent the strip into a closed angle without cracking the aluminum.