A part of an aircraft comprising a fixed section and a control surface deflectable relative to the fixed section, the control surface comprising: a leading edge, a trailing edge, and a chord-line defined between the leading edge and the trailing edge, a first aerodynamic surface (36, 40) between the leading and trailing edges, a second surface (37, 41) between the leading and trailing edges, the leading edge being formed by a nose, the nose having a hinge axis extending through the control surface about which the control surface is deflectable relative to the fixed section, the first aerodynamic surface (36, 40) opposing the second surface (37, 41) and converging towards the second surface (37, 41) from the nose to a tail, the first aerodynamic surface having an exposed airflow surface and the nose comprising an arced nose profile section extending from the exposed airflow surface wherein the arced nose profile section is configured to be at least partially exposable to airflow flowing over the control surface, wherein a maximum thickness of the control surface, perpendicular to the chord-line between the first aerodynamic surface and the second surface, is located aft of the hinge axis, and a radius of the arced nose profile section is greater than a perpendicular distance between the chord-line and the point of maximum thickness of the control surface on the first aerodynamic surface, the nose is at least partially received by the fixed section, wherein the fixed section comprises: a boundary edge (22, 54) overlapping the nose, and a boundary region immediately forward of the boundary edge, characterised in that an indent (43, 57) is defined by profiling the boundary region at a juncture of the fixed section and the first aerodynamic surface (36, 40) at the boundary edge (22, 54) when the control surface is in an undeflected position. a leading edge, a trailing edge, and a chord-line defined between the leading edge and the trailing edge, a first aerodynamic surface (36, 40) between the leading and trailing edges, a second surface (37, 41) between the leading and trailing edges, the leading edge being formed by a nose, the nose having a hinge axis extending through the control surface about which the control surface is deflectable relative to the fixed section, the first aerodynamic surface (36, 40) opposing the second surface (37, 41) and converging towards the second surface (37, 41) from the nose to a tail, the first aerodynamic surface having an exposed airflow surface and the nose comprising an arced nose profile section extending from the exposed airflow surface wherein the arced nose profile section is configured to be at least partially exposable to airflow flowing over the control surface, wherein a maximum thickness of the control surface, perpendicular to the chord-line between the first aerodynamic surface and the second surface, is located aft of the hinge axis, and a radius of the arced nose profile section is greater than a perpendicular distance between the chord-line and the point of maximum thickness of the control surface on the first aerodynamic surface, the nose is at least partially received by the fixed section, wherein the fixed section comprises: a boundary edge (22, 54) overlapping the nose, and a boundary region immediately forward of the boundary edge, characterised in that an indent (43, 57) is defined by profiling the boundary region at a juncture of the fixed section and the first aerodynamic surface (36, 40) at the boundary edge (22, 54) when the control surface is in an undeflected position. a boundary edge (22, 54) overlapping the nose, and a boundary region immediately forward of the boundary edge, characterised in that an indent (43, 57) is defined by profiling the boundary region at a juncture of the fixed section and the first aerodynamic surface (36, 40) at the boundary edge (22, 54) when the control surface is in an undeflected position.