Winglets primarily serve to make airplanes more practical for parking, rather than revolutionizing aerodynamic efficiency. While they offer some drag reduction, their benefits are limited compared to simply increasing the wingspan and aspect ratio of the wing.
Key Points:
Design Complexity: Winglets are challenging to design, requiring intricate engineering to balance drag reduction against added structural weight and bending moments.
Efficiency Trade-Off: Winglets provide only about 50% of the aerodynamic efficiency gains achieved by extending the wingspan directly. This is because they cannot fully replace the lift-distribution benefits of a longer wing.
Operational Constraints: The primary reason for winglets is compatibility with airport infrastructure. Aircraft are classified into design groups based on wingspan, which impacts gate fees and operational costs. Winglets allow for higher effective aspect ratios without increasing physical wingspan, keeping planes in lower cost groups.
This video discusses the âAircraft design groupsâ and then explain that the Private Jet âcrowdâ added winglets not for efficiency but because they thought it made the jets look more modern and cool aka aesthetic over function or trying to save the world.
20:21 âthe aircraft just looks cooler just looks sexier theyâre easier to sellâ
The exact articulation of âaircraft design groups,â the tax the airlines pay for the maximum horizontal wingspan of the aircraft, is here @ 13:06 (below)
More evidence: In nature, birds, insects, and fish demonstrate that increasing aspect ratio is more efficient for reducing induced drag. No species has evolved âwinglets,â further supporting the idea that extending span is fundamentally more effective.
Most recently Boeingâs 777X exemplifies an alternative approach with folding wingtips. This design maximizes span efficiency in-flight while maintaining compatibility with existing gates on the groundâa concept borrowed from military carrier aircraft, that all have to park in tight quarters.
Just last weekend a group of us were dockstarting in Seattle and struck up a conversation with a Boeing engineer out for a walk. He told us the same exact thing.
To be more clear, they are for increasing the effective aspect ratio of the wing without:
having to make a wider wing that doesnât fit at the parking gate
having to have more structure (strength and stiffness) handle the loads from a wider wing
Donât forget #2, it is a real thing. And I expect it will come to foiling as well because for the highest aspect ratio wings with thin profiles, we are stiffness limited. Winglets offer a way out of this stiffness limitation.
Winglets donât increase the area moment as much as a comparable increase in span, that doesnât matter much if you have ailerons, but foiling that effects how much the wing resists changing the roll angle.
Iâve always assumed they reduce span for given lift, so for us better turning instead of parking. And I think they canât kill you as easily since they canât stab as deep.
Thanks for the post. Interesting.
I beg to defer slightly from your perceived conclusion.
Every design has some constraints within which the engineers have to find the best compromises.
Neither are there easy answers, nor is there such thing as a free lunch.
Next to many others, big Airplanes are supposed to stably fly in a straight line most of the time.
Our foils must be able to turn left or right constantly.
While airplane profiles are big and eavy enough to incorporate flaps for takeoff, itâs a bit more complicated for our foils.
If you look at the freefly hinged wings and compare it to the pic below, you will realise nature had indeed found some sort of induced drag reduction solution like advanced winglets, just in a more advanced and technically not so easy to implement way.
I thought that winglets locked in the yah and made wings less skiddy. I had some early Axis stabs with winglets and that is what I felt they did. So what about winglets on stabs?
Iâve had the same experience. I started out on the Lift 32 glide and had trouble keeping the yaw from sliding out. Switched to a 32 carve with winglets and the problem went away immediately.
What I love most about foiling compared to traditional surfing is how much of the performance is centered on the front foil itself, rather than the intricate complexities of surfboard designâlike shape, rocker outline, rails, fins, and fin configurations. Surfing terms such as âdriveâ and âskateâ often felt vague and subjective. In contrast, foiling is rooted in over a century of research, beginning with the Wright brothers on December 17, 1903, over 121 years ago (Anniversary this past Tuesday). Foil designs have been rigorously tested, optimized, and reproduced with consistent, measurable results, eliminating much of the ambiguity inherent in traditional surfing equipment.
On the topic of winglets, when I was in aeronautical engineering school, our team entered an international competition to design a fixed-wing aircraft. The challenge was to carry the maximum possible load within a strict planform area limit of 400 square inches (the shadow area of the aircraft viewed from above). We explored various design options, including flying wings, undercamber profiles, and . . . . winglets.
When we asked our professor about building winglets, his advice was direct: âWinglets need to be designed and tested with extreme precision in a wind tunnel to offer any measurable benefit. The flow interactions at the right-angle base of the winglet are complex, requiring careful smoothing and the elimination of hard edges. Without this level of detail, winglets are unlikely to provide any value. In summary, probably not a good idea.â His words highlighted that while winglets have theoretical benefits, their practical implementation demands a level of precision that exceeds most resources outside of a high-tech wind tunnel.
The competition also offered valuable aerodynamic lessons. We witnessed numerous high-aspect wing failures, including the dramatic sight of wings snapping mid-flight under stress. Another frequent failure mode was wingtip stallâwhen flying at maximum load near stall speed, the difference in tip speed between the inner and outer wings often caused violent spirals, ending in a pile of wreckage on the ground. These experiences underscored the delicate balance between innovation and the limits of practical design, whether in aircraft or hydrofoils.
Here is one of my textbookâs explanation on winglets published in 1989, 35 years ago. Ironically it also concludes with âA last factor is sometimes the desire to look modernâ
The history of airplane design includes many attempts to significantly reduce induced drag. Unfortunately, induced drag (i.e. vortex drag) is a fact of life that will not go away. It is as omnipresent as death and taxes. For a planar wing, the Prandtl equation for an elliptical lift distribution, equation 9.9, defines the minimum induced drag. Less induced drag can be achieved for a given span by nonplanar configurations. A biplane is an example. Another example is a wing with endplates, vertical surfaces at the tip that act to increase effective aspect ratio. These reduce induced drag by permitting significant lift to extend all the way to the tips, instead of dropping to zero at the tips. One can think of endplate and other nonplanar configurations as affecting a deeper region of air and thereby obtaining the lift with less downward velocity imparted to the air. The result is less energy loss. Simple endplates have both parasite drag and weight, so the net drag gain has never justified their use on wings. Vertical tail surfaces placed at the tips of the horizontal tail do increase the effective aspect ratio of the horizontal tail. In this case, most of the weight and parasite drag would be present in a conventional vertical tail anyway. The most notable application of this use of endplates was the Lockheed Constellation (Figure 1.29). Even here the multiple vertical tails may have been chosen to reduce the overall airplane height in order to minimize the required height of the hangars, or possibly just to look unique.
Winglets, developed over the last 10 years, are a special form of endplate: Designed by modern theoretical methods, winglets are generally superior to the simple endplates studied decades ago. The detail design of winglets to optimize induced drag for a given wing weight is very complicated. The aerodynamic interference between winglet and wing, the induced drag of the winglet itself, and the bending moments introduced into the wing by both the higher lift on the outboard wing panel and the direct bending moment of the winglet itself are dependent on winglet shape, size, and angle of incidence. The details are beyond our scope, but some general conclusions can be discussed here.
First, winglets reduce induced drag. Second, the amount of induced drag reduction from well-designed winglets is about the same as extending the original wing span by an amount equal to approximately half of the winglet height. Third, the expected advantage of winglets is that the induced drag decrease is obtained with less wing bending moment and resultant wing weight increase than with a span increase. Objective general studies, (Ref. 9.7), starting with optimized wings, show that this gain is usually very small. The reduction in induced drag due to winglets, compared to a planar wing of greater span but the same wing weight, is about -1% to +2%. The decision on whether to use winglets is likely to be dominated by special circumstances. Among these is a nonoptimum span loading on the original wing, minimum practical skin gauges already used on the outer panel so that the bending moment of the winglet attachment does not require more material, the desire to avoid a span increase for reasons of airport ramp or hanger space, and the possibility of flow separation at the winglet root at high lift coefficient because of flow interference. A last factor is sometimes the desire to look modern.
The textbook addresses âendplatesâ applied to tails. Technically not âwingletsâ on the âwingâ. The DC-6 Constellation was introduced in 1946 so designed ~ 80 years ago. Nothing new. âEven here the multiple vertical tails may have been chosen to reduce the overall airplane height in order to minimize the required height of the hangarsâ aka back to parking airplanes.
Yes tips on the tail will reduce yaw, acting as vertical stabilizers, but there are likely other ways to achieve this more efficiently such as with a single tail or just relying on an elegantly shaped tapered fuselage.
I think the structural considerations for foils is quite different versus airplane wings. Same concepts and math of course, but the scaling factors are non-linear such that generally our high performance foils are entirely stiffness driven design solutions - rather than strength driven design solutions as in airplane wings. Wing loading, aspect ratios, foil thickness percentage are all in completely different ballpark versus airplanes. Additionally, most airplane wings are optimized for fuel carrying, which both makes the optimum point thicker but also distributes much of the payload directly in line with the aerodynamic loading, relieving the root bending moment. We have no such factor.
This is why we see the latest high performance wings utilizing ultra-high-modulus carbon (best possible stiffness, poor strength properties, expensive).
I reject the notion that winglets âare too hard to design.â Plenty of textbooks and old school engineers incorrectly make statements such as this. These days (even completely free open source) Computational Fluid Dynamics software is so incredibly good that optimizations are not only possible but commonplace. Many of these textbooks need a re-write with this in mind.
If it were up to me, Iâd have a round winglet for safetyâs sake. Likely not the most efficient (unless a bunch of time is spent figuring out how to generate thrust from it), but the chances of getting stabbed go way down.
Great topic here. I thought winglets also offered the benefit of dampening the swirling vortices that form on the wingtips by keep the low pressure air from mixing with the high pressure air on the top/bottom of the wing.
