Definition
Curved in more than one direction at the same time, so the surface bends along two axes rather than one. A compound curved shape cannot be formed by simply rolling a flat sheet; it must be shaped, molded, or laid up to follow curvature in multiple directions simultaneously.
Plain English
A surface that bows in two directions at once, like the outside of a ball or the nose of an aircraft, instead of bending in just one direction like a tube or a cylinder.
Context Anchor
Seen in discussions of aircraft composite construction, where molded materials can form smooth, rounded aircraft shapes more easily than many metal sheets.
Derivation
‘Compound’ comes from Latin componere, meaning ‘to put together.’ A compound curve is literally several curves combined into one surface, curving in more than one direction at once.
Why Pilots Care
Composite materials can form these shapes easily, allowing smoother aerodynamic designs that metal construction cannot achieve without added weight or seams.
Analogy
A soda can is curved in only one direction — you can flatten it by unrolling it. A tennis ball is compound curved — you can’t flatten it without cutting or stretching it.
Intuition Check
Do not read compound here as a chemical mixture. In this context, compound means “made from more than one curve.”
Example Sentence 1
The wingtip fairing has a compound curved surface, which is why it’s molded from composite material instead of bent from sheet aluminum.
Example Sentence 2
Composites let builders create compound curved fuselage sections without the joints required in sheet metal.