Definition
Tight, sharply curved bends formed into the metal skin of an aircraft structure — typically along leading edges or fairings — where the radius of curvature is small and the curve is concentrated over a short distance. These tight bends stiffen the panel and help it hold its aerodynamic shape under load.
Plain English
Sharply curved sections of the metal skin where the curve is tight and concentrated in one small area, rather than gently spread across a wide surface. The tight curve makes the panel stiffer.
Context Anchor
Seen when learning about the structure and inspection of outer wing surfaces and tail sections.
Derivation
‘Radii’ is the plural of ‘radius,’ from the Latin radius meaning ‘ray’ or ‘spoke of a wheel’ — the line from the centre of a circle to its edge. ‘Concentrated’ comes from Latin roots meaning ‘brought together to a centre.’ Together: curves with small, tightly-grouped centres of curvature — meaning sharp bends rather than gentle ones.
Why Pilots Care
Unchecked stress at these points can initiate fatigue cracks that compromise airframe strength and flight safety.
Analogy
Think of bending a sheet of paper. A flat sheet flops easily, but if you put a sharp crease or tight curl along one edge, that edge becomes noticeably stiffer. Concentrated radii do the same thing for aircraft skin.
Grounding Statement
Picture the tight curve where a flat metal surface turns into a bend; that curved spot can carry extra force.
Intuition Check
Concentrated radii does not mean several circles grouped together. Here it means tight curved areas in aircraft structure where force can focus.
Example Sentence 1
The wing’s leading edge uses concentrated radii to give the skin enough rigidity to maintain its airfoil shape under flight loads.
Example Sentence 2
The mechanic noted that the tail cone's concentrated radii showed no deformation after the hard landing.