### FYI: What Are Winglets? | Popular Science

Aviation Partners has been making history in Advanced Winglet Technology since , developing innovations and fuel-saving performance enhancing. Mar 3, Winglets are one of the most successful examples of a NASA aeronautical innovation being utilized around the world on all types of aircraft. This invention relates to winglets adapted to reduce the induced drag created each other and meet at an origin located at the foremost plane of the aircraft (2).

Now, several decades later, winglets are incorporated into the designs of many other business jets such as Gulfstreams and the Global Express: Retrofitting winglets to existing business jets is also a fast-growing market within the aviation industry itself.

Many winglet marketing firms report their products help increase aircraft roll rates and lower approach and takeoff speeds. The first big jetliner to carry the innovation into the air was the MD, originally designed and built by McDonnell-Douglas and now part of the Boeing aerospace family. Other Boeing aircraft flying with winglets are thethe version currently being built, Boeing BBJ business jets which are custom-built s, and the C military transport.

Boeing is also offering winglet options on new advanced models of the series of passenger jets. Most prominent foreign carrier of winglets are the many models of the series of jetliners designed and built by Airbus Industries. The future A3XX Airbus, a huge intercontinental double-deck jetliner now under development, will also utilize winglet technology. The first homebuilts with winglets on the general aviation market were the Vari-Eze and Long-Eze models designed by Burt Rutan, a pioneer in aircraft design innovations.

Now, the majority of homebuilt aircraft coming out of shops, garages, and hangars around the world display winglets of varying shapes and sizes. During toa pair of remotely piloted test aircraft called HiMAT, Highly Maneuverable Aircraft Technology, was flown at Dryden to study high-performance fighter design and construction technologies. Each of the subscale vehicles had blended winglets that generated data for a program that has helped in the development of many military, commercial, and business aircraft.

Testing Winglets The winglet test program conducted at Dryden in followed several years of wind tunnel tests and analytical studies by Dr.

Whitcomb had studied the original winglet concept developed by British aerodynamicist F. Lancaster in the late s. Lancaster's patented concept said a vertical surface at the wingtip would reduce drag. Whitcomb took that concept a step further by making the vertical surface a refined airfoil that reduces drag by interacting with the wingtip airflow circulation and vortex.

These positive conclusions, coupled with Whitcomb's work, prompted the U. Air Force to consider the possible installation of winglets on KC and C transport aircraft. On 18 Februaryblended winglets were announced as an option for the Boeing ; the first shipset was installed on 14 February and entered revenue service with Hapag-Lloyd Flug on 8 May They are also offered as a retrofit option. Boeing ER with raked wingtips Raked wingtips where the tip has a higher wing sweep are featured on some Boeing Commercial Airplanes to improve fuel efficiencytakeoff and climb performance.

Like winglets, they increase the effective wing aspect ratio and diminish wingtip vorticesdecreasing lift-induced drag. The Embraer E-jet E2 wing has a raked wingtip. The Boeing MAX uses a new type of wingtip device. Others had attempted to apply Whitcomb's winglets to gliders before, and they did improve climb performance, but this did not offset the parasitic drag penalty in high-speed cruise.

Masak was convinced it was possible to overcome this hurdle. At the World Gliding Championships in Uvalde, Texasthe trophy for the highest speed went to a winglet-equipped meter class limited wingspan glider, exceeding the highest speed in the unlimited span Open Classan exceptional result. Yet, once the advantages of winglets were proven in competition, adoption was swift with gliders. The point difference between the winner and the runner-up in soaring competition is often less than one percent, so even a small improvement in efficiency is a significant competitive advantage.

Many non-competition pilots fitted winglets for handling benefits such as increased roll rate and roll authority and reduced tendency for wing tip stall.

More details regarding the arc-line blended winglet design are set forth in U. The radius and curvature criteria as given by U. Furthermore, when viewing all of these concepts, both for the prior art and for the present invention, that aircraft wings have a certain handedness, such that when discussing these issues it must be taken into account whether one is dealing with the left wing and left winglet, or the right wing and right winglel. Here, the outer end of the wing meets the inner end of the wingiet at intersection The major axis of an ellipse is shown to extend perpendicular to the wing reference plane and to coincide with the intersection The minor axis of the ellipse extends perpendicular to the major axis and intersects the major axis at center If one were to draw a diagonal line from the center to the outer end or tip of the wingietan acute angle would be defined between the line and the major axis The wingiet height is designated and the wingiet span is designatedThe wing lip cant angle is designated According to the invention, the wingiet curves upwardly and outwardly from intersection to the outer end or tip of the wingiet At intersection stationthe curvature of the wingiet surfaces meets the wing surfaces substantially at a tangent.

The first curve segment closest to the wing, if an arc, has its center on an axis that is substantially perpendicular to the wing reference plane and substantially intersects the location where the outer, or tip, end of the wing is joined to the inner or root end of the winglet.

The first curve segment begins at the wing tip, where it is tangent to the wing reference x,y plane, and extends though an angle beta Boutwardly and upwardly from the wingtip, and has a defined rho value, or radius if it is an arcRl. A reference curve defining the profile of the winglet extending from the wingtips of an aircraft can be generated from a curve through a locus of points having their location at specified percentage of the chord distance for each aerodynamic section profile of the winglet.

If the distance along each aerodynamic section chord line is measured relative to the section trailing edge, then a curve through the locus of points a zero percent of each chord line would define the winglet trailing edge curve profile while a curve through the locus of points at percent of the chord sections would define the winglet leading edge curve profile.

For this invention, the reference curve used to define the shape of the winglet's profile is obtained from the perpendicular projection of a curve through the locus of points described above onto a plane normal to the winglet inner or root chord line. Alternatively, the projection plane could be oriented perpendicular to the aircraft fuselage longitudinal axis or other orientation approximately perpendicular the aircraft's velocity vector.

The preferred curve through the locus points described above being projected is the winglet trailing edge curve. As is well understood, an arc is a section of a circle, which is also a member of the family of curves known as conic sections, i. Based on the angle of this plane relative to the cone axis, there are four commonly named conic sections generated from said intersection. These are the hyperbola, parabola, ellipse and circle.

Thus, the wingiet projected profile curve could be composed of any two or more conic curved segments, wherein the inboard end of the first conic segment is tangent to the wing reference plane, as described above. Acceptable values for rho range from 0.

**Meet the Pyro**

Also within the scope of this invention are compound curve segments which are not limited to curves defined by conic curve segments, but which may be defined by a quadratic, cubic or other higher order equations. The critical design elements are that the curve length of the first curve segment must be of sufficient length to provide for the plan form or developed geometry described herein, specifically that the length of the curve is of sufficient length that the winglet' s leading edge sweep angle in the transition section does not exceed maximum value described herein.

Also the first, or lower curve must have constant or continually increasing radius of curvature, be approximately tangent to the wing reference plane or plane perpendicular to the wind tip airfoil section plane and through the wing tip airfoil chord line at the junction of the winglet to the wing tip, and be contiguous with, and approximately tangent to the second or upper curve defining the wingiet sail section.

The second or upper curve segment generally must also have constant or continually increasing radius of curvature, and have its lower end point connected to, and be approximately tangent to the first or lower curve's upper end.

## FYI: What Are Winglets?

The upper end of the second or upper curve segment is positioned at the desired height above the wing reference plane as may be provided by the winglet plan form or developed shape described herein, and the upper end point of the second or upper curve segment is tangent to a line parallel with a line oriented at the specified cant angle, phi.

It must be noted that when referring to two curves being 'approximately tangent' to each other, this includes a blending region where any discontinuity is smoothed out to maintain a continuously curving profile, even where a mathematically pure tangency is not obtained.

For such configuration, the straight line segment should be parallel with a line oriented at the specified cant angle, phi, and if the line is the outer end of the winglet, the upper end of the line is located at the desired height above the wing reference plane. Under certain circumstances, as where wing bending stress margins are low and the increase in bending loads applied by the winglel must be minimized, it is preferred that the first curve segment is a rho conic curve, quadratic equation curve, cubic equation curve, b- spline curve or other higher order curve, to reduce the winglet' s half-span length.

Other objects, advantages and features of the invention will become apparent from the description of the best mode set forth below, from the drawings, from the claims and from the principles that are embodied in the specific structures that are illustrated and described.

### NASA - NASA Dryden Technology Facts - Winglets

This figure shows the angle of twist about the section trailing edge point relative to the section untwisted chord line line of intersection between the surface of FIG. As shown, each wing has an inner or root endan outer or tip endan upper surfacea lower surface not showna leading edge and a trailing edge Each wingiet has an inner, or root, endan outer or tip endan upper surfacea lower surface not showna leading edge and a trailing edge The inner or root end of each wingiet is connected to the outer or tip end of its wing The upper and lower surfaces of the winglets and the leading and trailing edges of the winglets are contiguous with the upper and lower surfaces of the wing and the leading and trailing edges of the wing Each wingiet follows a generally curved profileas it extends from its inner or root endto its outer or tip end A reference curve defining the profile of the wingiet can be generated from a curve through a locus of points having their location at specified percentage of the chord distance for each aerodynamic section profile of the wingiet.

If the distance along each aerodynamic section chord line is measured relative to the section trailing edgethen a curve through the locus of points formed at a zero percent of each chord line would define the wingiet trailing edge curve profile while a curve through the locus of points formed at percent of the chord sections wouid define the wingiet leading edge curve profile.

For this invention, the reference curve used to define the shape of the wingiet's profile is obtained from the perpendicuiar projection of a curve through the locus of points described above onto a plane normal to the wingiet inner or root chord line Alternatively, the projection plane could be oriented perpendicular to the aircraft fuselage longitudinal axis or other orientation approximately perpendicular to the aircraft's velocity vector.

The preferred curve through the locus points described above being projected is the wingiet trailing edge curve According to this invention, referring to FIG. An arc is also a member of the family of curves known as conic sections. Conic sections get their name from the fact that they can be formed by passing a plane through a double-napped cone.

Based on the angle of this plane relative to the cone axis, there are four commonly named conic section curves generated from said intersection. When using Computer Aided Design CAD software, rho conies are often used for aircraft design wherein the rho value of the conic curve defines its relative conic shape. Generally, the value of the variable rho represents the location of a point at a rho proportional distance along a vector connecting a point mid way between the curve end points to the point of intersection of the specified end point tangent lines.

A conic section curve with end point tangencies, as specified, is then placed though the specified end points and the intermediate rho defined point.

To fully define the rho conic curves, the end point locations and end point tangencies must also be specified. Of course, coordinates for an intermediate point along the conic curve can also be specified as an alternative to specifying a value for rho.

Thus, the winglet projected profile curve could be composed of any two or more rho conic curved segments, wherein the inboard end of the first rho conic segment is tangent to the wing reference plane and begins at the point of intersection of axis and the wing reference plane The exemplified second rho conic curve segment has its starting point a at the upper end b of the first curvewhere it is also tangent to the first curveand extends such that its outboard end point b reaches a distance h above the wing reference plane This distance h is determined at a point where a line parallel to the axis of the first curve is tangent to the second curve.

It should be pointed out that the compound curve segments are not limited to curves defined by arc segments or conic curve segments; other curves, such as may be defined by a quadratic, cubic or other higher order equations are permissible. The critical design elements are that the curve length of the first curve segment must be of sufficient length to provide for the plan form or developed geometry described herein, specifically that the length of the curve is of sufficient length that the winglet's leading edge sweep angle in the transition section does not exceed the maximum value described herein, i.

Also the first, or lower curve must have a constant or a continually increasing radius of curvature, be approximately tangent to the wing reference plane or plane perpendicular to the wing tip airfoil section plane and through the wing tip airfoil chord line at the junction of the winglet with the wing tip, and be contiguous with, and approximately tangent to the second or upper curve defining the winglet sail section.

It should be noted that the second segment could be a straight line and be within the present invention, with the resultant winglet being distinct from the prior art, provided the first curved segment was not an arc, or other constant radius curve. For this configuration, the line would be parallel with a line oriented at the specified cant angle, phi, and the upper end of the line would be located at the desired height above the wing reference plane.

Comparisons of these wingiet profile curves are illustrated in Figures 9A and 9B. It may be desirable to utilize as the first curve segment a rho conic curve, quadratic equation curve, cubic equation curve, b-spline curve or other higher order curve in order to reduce the winglet's half-span length.

This is particularly important in applications where wing bending stress margins are low and the increase in bending loads applied by the winglet must be minimized. An example wherein the first curve segment is a rho conic curve is shown in Figure 9a. If it is desired to maintain the same plan form or developed profile as laid out for the two arc segments design, the rho conic curve length would need to be extended to equal to the arc length of the Rl arc segment.

This would position the y'3 coordinate at the same plan form location determined above for the two arc segment design. The location of the base of the sail section at coordinate y3 in the non-developed would then move from the end point of the original Rl arc segment to the end point of the extended rho conic.

It should also be noted that a single, higher order curve, or other multiple segment contiguous curve, theoretically could be mathematically generated having a contour that closely matches any of the profiles described herein as being formed from two curve segments. Such a curve or multiple composite curve would be considered within the art defined herein if said alternate curve form conforms to the following criteria: