Winglets with recessed surfaces, and associated systems and methods

An aircraft system, comprising:

• a wing having an inboard region, and outboard region, an upper surface and a lower surface, the upper surface having a continuously convex shape at the outboard region;
• and
• a winglet connected to the wing at the outboard region, the winglet extending away from the wing along a winglet spanwise axis, the winglet having a first surface facing at least partially inboard and a second surface facing at least partially outboard and away from the first surface, wherein the first surface includes a recessed region that is concave relative to neighboring regions of the first surface, the neighboring regions including a first convex region positioned forward of the recessed region in a chordwise direction, a second convex region positioned aft of the recessed region in the chordwise direction, and a third region positioned away from the wing along the winglet spanwise axis, and wherein a chordwise extent of the recessed region decreases along the winglet spanwise axis in a direction away from the wing.

A method for designing an aircraft system, comprising:

• providing a design for a wing that includes airfoil sections from an inboard region to an outboard region of the wing;
• and
• designing a winglet for use with the wing without changing the general shapes of the wing airfoil sections at the outboard region of the wing, the winglet having a leading edge, a trailing edge, and a first surface facing generally inboard and a second surface generally outboard away from the first surface, wherein designing the winglet includes at least reducing a performance impact of flow at a junction region of the wing and winglet by designing a concave recess in the first surface of the winglet, the concave recess being between first and second convex regions, the first convex region being between the concave recess and the leading edge, and the second convex region being between the concave recess and the trailing edge.