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the reduction of the induced drag is
accomplished by acting like a small sail whose
lift component generates a traction force,
draining energy from the tip vortices.
The wingtip might be considered a
dead zone regarding to the aerodynamic
efficiency, because it generates lots of drag and
no significant lift. The winglet contributes to
accelerate the airflow at the tip in such a way
that it generates lift and improves the wing
loading distribution, which is related to the
induced drag. In addition, the aircraft will fly at
a slightly lower angle of attack for the same lift
coefficient. Thus, it should always be possible
to obtain significant drag reductions by using
wingtip devices even for high-aspect wings. The
Airbus A-340 development illustrates this
assumption well. This airliner was originally
designed with no winglets placed onto its high
aspect-ratio wing. However, the A-340 was
initially intended to use two ultra-high-bypass
engines from International Aero Engines (IAE),
the IAE Superfan, a highly fuel-efficient
concept. This configuration was dropped and
Airbus adopted four smaller less-efficient
engines, instead. At this point, the European
manufacturer installed winglets on the A-340 in
order to keep the original envisaged range.
Airbus is also releasing artist impressions of the
A-380 high-capacity airliner that show
endplates placed at the wingtips in a similar
fashion as for the smaller A-320.
A key advantage of winglets is that
they increase performance while only
fractionally increasing the root bending moment
on the spar compared to a wingspan extension.
It has to be taken into account that a wingspan
extension requires anti-ice or deice devices,
which in turn demand additional bleed air from
the engines increasing thus fuel consumption. A
way to avoid this design issue is to employ
raked wingtips like Boeing did for its 767-400
aircraft. Thanks to winglets the aircraft will
climb to initial altitude faster and save fuel due
to a more efficient climb profile. Otherwise, the
aircraft can takeoff at lower thrust settings,
which reduces the aircraft noise footprint and
extends engine life. Aircraft takeoff weight is
sometimes limited by the requirements in the
second climb segment, which occurs after the
landing gear is retracted. In some situations,
there is enough field length but the airline has to
leave some passengers on ground because the
aircraft cannot fulfill the climb requirements
especially on hot days. In many cases winglets
help to minimize this kind of problem or even
solve it. In the case of some business jets, the
winglets can enable the aircraft to reach
maximum cruising altitude avoiding a fuel
consuming “step-climb”.
Fig. 3– Ipanema EMB-202 agricultural
aircraft (Photo Embraer).
Agricultural aircraft (Fig. 3) operate at
high lift coefficients most of the time. At this
condition winglets could significantly reduce
fuel burn by allowing higher lift-to-drag ratios.
In addition, the counter-rotating vortex pair,
which becoming stronger at such flight
conditions, contributes to lower the productivity
of the spray runs. The drift of pesticides from
the target site during aerial spray applications is
a source of environmental concern due to its
potential human health impacts, downwind
contamination and damage to crops and
livestock, and endangering ecological resources.
Winglet and some wingtip devices prevent the
tip vortices to erratically disperse the chemicals
contributing this way to minimize the related
adverse environmental effects.
The general aviation has seen
increasing adoption of winglets among
traditional planes on the market. Some of the
new aircraft were also designed with winglets
like the Pilatus PC-12. The main reason behind
this new trend is related to the improvement of
the rate-of-climb, since piston-powered aircraft
have usually very low climb rates. Additional
claimed benefits are increased takeoff ramp
weight, and lower stall speeds. A direct effect of
lowering the stall speed is a safer aircraft. A
company that offers a winglet kit for the
Beechcraft Duke published that its product
enabled the lowering of the stall speed by 6
KIAS (flaps at 30o) and the increasing of the
maximum gross weight by 102 kg.
A crucial factor to include in the
overall equation is the cost of retrofitting the
winglet in the first place. If the only operator
consideration is the fuel cost savings over time,
　
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