Patent ID: 12234008

DETAILED DESCRIPTION OF EMBODIMENT(S)

FIG.1illustrates a prior art aircraft wing1having an inboard wing root2and an outboard wing tip3. A wing tip device comprising an upwardly extending winglet4is fixed to the outboard end3of the wing1. The wing1is shown inFIG.1in a) its ground shape (i.e. with the aircraft on the ground and with a full fuel load in the wing), and b) its flight shape (i.e. with deformation due to aerodynamic load).

FIG.2illustrates Detail A ofFIG.1and the broken line5illustrates a span constraint imposed on the aircraft due to e.g. airport compatibility gate limits or aircraft category flying constraints. The span limit5is applicable for the ground shape shown inFIG.2a).FIG.2b) illustrates the loss6in wing span due to wing deformation in the flight shape. This loss in span6may be up to around 3%.

FIG.3illustrates an aircraft wing101according to a first embodiment having a planar upper winglet104and a planar lower winglet107. The upper winglet104is fixed to the outboard end103of the wing101. The wing101defines a wing plane108. The upper winglet104projects upwardly with respect to the wing plane108. The upper winglet104has a tip109and a root110. The lower winglet has a tip111and a root112. The lower winglet root chord112intersects with the upper winglet104and the lower winglet107projects downwardly from this intersection. The upper and lower winglets104,107each have a leading edge and a trailing edge and the trailing edges are adjacent at the intersection.FIG.3a) illustrates the wing101in its ground shape where the tip109of the upper winglet104and the tip111of the lower winglet107are coincident at the span limit105.FIG.3b) illustrates the wing101in its deformed flight shape and shows how a potential loss in span106due to the upper winglet104is mitigated by an increase in span113gained from the lower winglet107. This gain in span113due to the lower winglet107is approximately 2%.

FIG.4illustrates the aircraft wing101of the first embodiment in greater detail. The lower winglet107is sized and oriented so as to maximise the span increase in the flight shape, whilst minimising interference effects at the intersection between the lower winglet107and the upper winglet104. In addition, a ground clearance height G between the ground and the tip111of the lower winglet107is taken into account. The resultant geometry provides an included angle between the upper and lower wing elements of around 132°, and an included angle between the wing plane108and the lower winglet107of around 128°. The lower winglet107has a winglet planform area of around 20% of the upper winglet104planform area. The relatively small size of the lower winglet107minimises the viscous drag penalty at cruise whilst delivering the required optimum span loading.

FIGS.5and6illustrate graphically the effect of the addition of the lower winglet element107on the lift and vortex drag characteristics of the wing101. InFIGS.5and6the line with circular markers represents a reference wing corresponding to the wing101with a tip near to an imposed span limit without any wing tip device. The line with the cross markers illustrate the wing101with only the upper winglet element104(sized as recommended in NASA T M 81230 entitled “Effect of Winglets on the Induced Drag of Ideal Wing Shapes”; RT Jones and TA Lasinski 1980), and the line with the triangular markers represent the wing101with both the upper and lower winglet elements104,107.FIG.5illustrates the relationship between lift and drag coefficients (CL, CD) and shows an improvement in lift to drag ratio for the wing101with both the upper and lower winglet element104,107as compared to both the reference wing and the wing with only an upper winglet element.FIG.6illustrates a drag saving due to the addition of the lower winglet element107of around 1.9% at the mid-cruise weight lift coefficient (CL=0.5) relative to the wing with upper element104alone. The vortex drag reduction provided by the lower winglet element107is a further reduction of around 25 to 40%.

FIG.7illustrates an aircraft wing201according to a second embodiment having a planar upper winglet204and a non planar lower winglet207. The wing201defines a wing plane208and the upper winglet204projects upwardly with respect to the wing plane208. The upper winglet204is fixed to the outboard end203of the wing201. The lower winglet207has a root chord212which intersects with the upper winglet204. The lower winglet207projects downwardly from the intersection. The upper winglet204has a tip209and a root210. The lower winglet207has a tip211that is coincident in the spanwise direction with the tip209at the span limit205. The upper and lower winglets204,207each have a leading edge and a trailing edge and the trailing edges are adjacent at the intersection. The wing201is illustrated inFIG.7in its ground shape where the span limit205is enforced.

The lower winglet207has increasing curvature of local anhedral from root212to tip211. The lower winglet207may have a toe in on toe-out angle to optimise the low speed performance of the tip device.

The wingtip device for the wing201has been optimised so as to maximise the span increase under flight aerodynamic loads, whilst minimising interference effects between the lower winglet207and the lower surface of the wing201, and between the upper and lower winglets204,207. The resultant optimised geometry has an included angle between the upper and lower winglets204,207of around 120°, and an included angle between the wing plane208and the lower winglet207of around 138°. In the flight shape, the lower winglet207provides a further gain in span as compared to the lower winglet107of the wing101, principally due to the increased root212to tip211height of the lower winglet207and the flexibility of the lower winglet207which straightens under flight loads.

FIG.8illustrates an aircraft wing301according to a third embodiment having a blended upper winglet304and a planar lower winglet307. The wing301has an outboard end303to which is fixed the blended upper winglet304. The upper winglet304has a tip309and a root310. The upper winglet304is fixed to the outboard end303of the wing301by its root end310. The upper winglet304has a substantially planar portion314and an arcuate transition portion315. The transition portion315is adapted to smoothly blend the outboard end303of the wing301into the substantially planar portion314. The arcuate transition portion315has a substantially constant radius of curvature R.

The lower winglet307is fixed to the lower surface of the transition portion315of the upper winglet304. The lower winglet has a tip311and a root312. The root chord of the lower winglet307intersects with the upper winglet304and the lower winglet projects downwardly from the intersection. The upper and lower winglets304,307each have a leading edge and a trailing edge and the trailing edges are adjacent at the intersection. The transition portion315helps reduce interference effects between the substantially planar portion314and the wing301.

The tip309of the upper winglet304is substantially coincident in the vertical x-z plane with the tip311of the lower winglet307at the span limit305. An included angle between the upper and lower winglets304,307at the intersection is around 84°. It is preferable that this angle is at least 80° so as to avoid interference effects between the upper and lower winglets304,307. Since the intersection is on the lower surface of the blended transition portion315, this angle is measured between the transition portion lower surface tangent and the lower winglet307. An included angle between the wing plane308and the lower winglet307is around 125°. The substantially planar portion314of the upper winglet304has a cant angle relative to the vertical x-z plane of around 7° to 15°.

The lower winglet element307has an element planform area of approximately 25% of the upper winglet element304planform area. Whilst the lower winglet307is substantially planar it may have some wing twist from root312to tip311. The lower winglet307may additionally or alternatively have a toe in or toe out angle to optimise low speed performance. Similarly, the upper winglet304may have some twist and may have a toe in or toe out angle. The lower winglet307has a sweep back angle and in particular the leading edge is swept back. The upper winglet304is also swept back and has a swept back leading edge and a swept back trailing edge.

If ground clearance limits allow, then the lower winglet element307could be replaced with a non-planar lower winglet element similar to that described above with reference toFIG.7.

FIG.9illustrates an aircraft wing/wingtip device combination comprising a wing401, a blended upper winglet404and a planar lower winglet407. The wing401has an outboard end403and defines a wing plane408. The upper winglet404includes a substantially planar portion414and a blended transition portion415. The transition portion415smoothly blends the outboard end403of the wing401into the substantially planar portion414of the upper winglet404. The transition portion415is a non-planar curved wing tip extension having continuously increasing curvature of local dihedral, continuously increasing sweep back (at both leading and trailing edges) and continuously decreasing chord in the outboard direction. The non-planar curved wing tip extension portion415provides improved drag performance for the upper winglet404in comparison to the blended upper winglet304shown inFIG.8.

The upper winglet404has a root410and a tip409. The substantially planar portion414of the upper winglet404has a cant angle of around 7° to the vertical x-z plane. A substantially planar lower winglet407is fixed to the lower surface of the non-planar curved wing tip extension portion415of the upper winglet404. The lower winglet407has a tip411and a root412. The root chord of the lower winglet407intersects with the upper winglet404and the lower winglet projects downwardly from the intersection.

An included angle between the upper and lower winglets404,407at the intersection is around 86°. Since the intersection is on the lower surface of the non planar curved wing tip extension portion415of the upper winglet404, this angle is measured from a local surface tangent to the lower surface of the non-planar curved wing tip extension portion415at the intersection. This included angle is preferably greater than 80° to avoid interference effects between the upper and lower winglets404,407. An included angle between the wing plane408and the lower winglet is around 124°. The tip409of the upper winglet404is substantially coincident in the vertical x-z plane to the tip411of the lower winglet407at the span limit405.

FIGS.10and11illustrate perspective and plan views respectively of the wing/wingtip device combination of the fourth embodiment. FromFIG.10in particular it can be seen that the trailing edge416of the upper winglet404, and the trailing edge417of the lower winglet407are substantially adjacent at the intersection. The trailing edges416,417are sufficiently close that the wake from the lower winglet407substantially does not interfere with the flow over the upper winglet404. The upper winglet404has a leading edge418that is swept backwards and the lower winglet407also has a leading edge419that is swept backwards. The trailing edge416of the upper winglet404is swept backwards and the trailing edge417of the lower winglet407is also swept backwards.

InFIG.11, the plan view (i.e. the top down view in the x-y plane) illustrates how the upper winglet404“shadows” at least part of the lower winglet407. This is due to the coincidence of tips409,411of the upper and lower winglets404,407in the vertical x-z plane. As best shown inFIG.10, the root chord412of the lower winglet407occupies only part of the local chord of the upper winglet404at the intersection. Due to the near coincidence of the trailing edges416,417the leading edge419of the lower winglet407is positioned substantially aft of the leading edge418of the upper winglet404.

FIG.12illustrates an aircraft wing/wingtip device combination according to a fifth embodiment, comprising a wing501with a wingtip device comprising an upper non-planar wingtip extension504and a lower planar winglet507. The wing501has an outboard end503and defines a wing plane508. The non-planar wingtip extension504has a root510and a tip509and is fixed to the outboard end503of the wing501by its root510. The non-planar curved wingtip extension504has continuously increasing curvature of local dihedral, continuously increasing sweepback (at both leading and trailing edges518,516), and continuously decreasing chord in the outboard direction, y.

The non-planar curved wingtip extension504is substantially non-planar from root510to tip509. The tip509forms a cant angle of approximately 8° with the vertical x-z plane. The lower winglet507has a tip511and a root512and the root chord intersects with the non-planar curved wingtip extension504, with the lower winglet507projecting downwardly from the intersection. An included angle between the non-planar wingtip extension504and the lower winglet507at the intersection is approximately 82°. This angle is measured between the lower winglet507and a local surface tangent to the lower surface of the non planar curved wingtip extension504at the intersection. An included angle between the wing plane508and the lower winglet507is approximately 126°. The tips509,511of the non-planar curved wingtip extension504and the lower winglet507are substantially coincident in the vertical x-z plane at the span limit506.

FIG.13illustrates the wingtip device in accordance with the fifth embodiment in a perspective view and clearly shows that the trailing edge516of the non-planar curved wingtip extension504is substantially coincident with the trailing edge517of the lower winglet507at the intersection. Both the non-planar curved wingtip extension504and the lower winglet507have a sweepback angle and the leading and trailing edges516,517,518,519each have a respective sweepback angle.

The lower winglet507may be only substantially planar and may feature winglet twist from root to tip and a toe in or toe out angle relative to the free stream flow. Similarly, the non planar curved wingtip extension504may feature wing twist and a toe in or toe out angle relative to the free stream flow. The lower winglet507may be replaced with a substantially non-planar curved lower winglet, similar to that described above with reference toFIG.7if ground height clearance limits allow.

Each of the second to fifth embodiments described above with reference toFIGS.7to13are shown with the respective wing/wingtip device combination in its ground shape. Due to aerodynamic loads on the wing during flight, deformation of the wing will cause rotation of the wingtip device about the wing root such that the tip of the lower wing-like element extends further outboard in the spanwise direction than the tip of the upper wing-like element. The lower wing-like element in each case therefore provides an increase in wing span when compared to wingtip devices having only the upper wing-like element in each case.

The wingtip devices described in the first to fifth embodiments above may be fitted, or retro-fit to the outboard end of an aircraft wing having either no wingtip device or as a replacement for an existing wingtip device. Furthermore, the lower wing-like element may be provided as a retro-fit modification to an existing wingtip device having only an upper wing-like element so as to form a wingtip device according to this invention.

Although the invention has been described above with reference to one or more preferred embodiments, it will be appreciated that various changes or modifications may be made without departing from the scope of the invention as defined in the appended claims.