Winglet system

A winglet system for an aircraft wing may include an upper winglet and a lower winglet mounted to a wing tip. The upper winglet root chord and the lower winglet root chord may each have a length of no greater than 100 percent of the wing tip chord. The lower winglet may have a static position when the wing is subject to an on-ground static loading. The lower winglet may be configured such that upward deflection of the wing under an approximate 1-g flight loading causes the lower winglet to move upwardly and outwardly from the static position to an in-flight position resulting in an effective span increase of the wing under the approximate 1-g flight loading relative to the span of the wing under the on-ground static loading.