Performance-enhancing winglet system and method
A winglet system for an aircraft wing may include an upper winglet and a lower winglet mounted to a wing tip. The lower winglet may have a static position when the wing is subject to a 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 from the static position to an in-flight position and resulting in a relative span increase of the wing.
1. A winglet system, comprising:
an upper winglet and a lower winglet mounted to a wing, the lower winglet has a length of between approximately 50 to 80 percent of a length of the upper winglet;
the lower winglet having a static position when the wing is subject to an on-ground static loading, the lower winglet being substantially straight in the static position; and
the lower winglet being 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 a 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.
2. The winglet system of claim 1 wherein:
the lower winglet is oriented at an anhedral angle of no less than approximately 15 degrees during upward deflection of the wing under the approximate 1-g flight loading.
3. The winglet system of claim 1 wherein:
the upper winglet is oriented at a dihedral angle of at least approximately 60 degrees during upward deflection of the wing under the approximate 1-g flight loading.
4. The winglet system of claim 1 wherein:
the lower winglet has a center of pressure;
the wing having a wing torsional axis; and
the center of pressure of the lower winglet being located aft of the wing torsional axis.
5. The winglet system of claim 1 , wherein:
the wing has a wing tip including a wing tip chord;
the upper winglet and the lower winglet each having a root chord; and
the upper winglet root chord and the lower winglet root chord each having a length of at least approximately 50 percent of the wing tip chord.
6. The winglet system of claim 5 , wherein:
the upper winglet root chord and the lower winglet root chord each have a length of from approximately 60 to 100 percent of a length of the wing tip chord.
7. The winglet system of claim 1 , wherein:
at least one of the upper winglet and lower winglet has a leading edge root glove mounted at a juncture of a wing tip with the respective upper winglet and lower winglet.
8. The winglet system of claim 1 , wherein:
the upper winglet and the lower winglet each have a taper ratio of tip chord to root chord in a range of from approximately 0.15 to 0.50.
9. The winglet system of claim 1 , wherein:
the upper winglet and the lower winglet have a leading edge sweep angle of between approximately 20 and 70 degrees.
10. The winglet system of claim 1 , wherein:
the wing has a wing torsional axis;
the upper winglet and the lower winglet having a combined winglet area and a combined center of gravity located at a longitudinal offset from the wing torsional axis; and
the upper winglet and lower winglet being configured such that the longitudinal offset is less than a longitudinal offset of a center of gravity of a single upper winglet having a winglet area that is substantially equivalent to the combined winglet area and having a leading edge sweep angle that is substantially equivalent to the upper winglet leading edge sweep angle.
11. An aircraft, comprising:
a pair of wings each having a wing tip;
an upper winglet and a lower winglet mounted to each one of the wing tips, the lower winglet has a length of between approximately 50 to 80 percent of a length of the upper winglet;
the lower winglet having a static position when the wing is subject to an on-ground static loading, the lower winglet being substantially straight in the static position; and
the lower winglet being sized and oriented such that upward deflection of the wings 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 a span increase of the wing under the approximate 1-g flight loading relative to the span of the wing under an on-ground static loading.
12. A method of enhancing performance of an aircraft, comprising the steps of:
providing an upper winglet and a lower winglet on a wing, the lower winglet having a static position when the wing is subject to an on-ground static loading, the lower winglet being substantially straight in the static position, the lower winglet having a length of between approximately 50 to 80 percent of a length of the upper winglet;
upwardly deflecting the wing under an approximate 1-g flight loading;
moving the lower winglet upwardly and outwardly from the static position to an in-flight position during upward deflection of the wing; and
causing a 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-in response to moving the lower winglet from the static position to the in-flight position.
13. The method of claim 12 , further comprising the step of:
orienting the lower winglet at an anhedral angle of no less than approximately 15 degrees during the upward deflection of the wing.
14. The method of claim 12 , further comprising the step of:
orienting the upper winglet at a dihedral angle of at least approximately 60 degrees during the upward deflection of the wing.
15. The method of claim 12 , further comprising the steps of:
locating the lower winglet such that a center of pressure is aft of a wing torsional axis;
increasing lift of the lower winglet during a gust load; and
exerting a nose-down moment on a wing tip in response to an increase in the lift of the lower winglet.
16. The method of claim 15 , further comprising the step of:
dividing a wing tip aerodynamic load between the upper winglet and the lower winglet, the upper winglet and the lower winglet each having a root chord having a length of at least approximately 50 percent of a wing tip chord.
17. The method of claim 16 , further comprising the step of:
minimizing parasitic drag of the aircraft by using a leading edge root glove on at least one of the upper winglet and the lower winglet.
18. The method of claim 16 , further comprising the steps of:
providing the upper winglet and the lower winglet with a combined winglet area and a combined center of gravity that is longitudinally offset from a wing torsional axis; and
reducing wing flutter by longitudinally offsetting the combined center of gravity by an amount that is less than a longitudinal offset of a center of gravity of a single upper winglet having a winglet area that is substantially equivalent to the combined winglet area and having a leading edge sweep angle that is substantially equivalent to the upper winglet leading edge sweep angle.