Definition 1 of 2
Definition
A structural metal extrusion shaped like an angle (an L-shaped cross-section with two legs meeting at roughly 90 degrees) that has a thickened, rounded bead — the 'bulb' — formed along the edge of one leg. The bulb adds stiffness and strength along that edge without significantly increasing the part's weight, making the shape useful as a stringer, stiffener, or framing member in aircraft structures.
Plain English
A piece of metal bent into an L-shape with a small rounded lump running along one edge. The lump makes the edge stronger so the part resists bending without needing to be made thicker overall.
Context Anchor
Seen in aircraft structural drawings, parts lists, and airframe repair work where metal shapes are identified by their form.
Derivation
Bulb' comes from the Latin bulbus, meaning a rounded swelling or onion-like shape, and is used here for the rounded bead along the edge. 'Angle' comes from the Latin angulus, meaning corner — the L-shaped corner formed by the two legs of the section. Together the name simply describes the shape: an angle section with a bulb on it.
Why Pilots Care
A bulb angle may be part of the structure that helps an aircraft skin, frame, or panel keep its shape. Cracks, corrosion, or improper replacement can affect structural strength.
Intuition Check
Do not read angle here as a number of degrees. A bulb angle is a shaped metal part; the bulb is the rounded thickened edge that helps strengthen it.
Example Sentence 1
The technician matched the damaged stringer to a bulb angle of the same dimensions before fabricating the replacement.
Example Sentence 2
Replacing the damaged bulb angle restored the required stiffness to the wing rib.