We have seen that the marginal vortices showed an additional drag called
Il was thought advusabke to reduce or eliminate the induced drag. The aerodynamicist
Richard T. Whitcomb and his team at the research center NASA has invented
" WINGLETS " or " FINS ".
Two cambered surfaces to counter the local flow on the walls are fixed on
the ends of the wing. The lower surface, at internal camber, strong enough
and at low surface, is located towards the leading edge of the salmon. The
upper surface, at external camber, and at stronger surface, is located towards
the rear part of the salmon.
This device is equivalent to a gain of two points of aspect ratio on the
induced drag (Lesson 4 paragraph 4). It may be more economical into mass
of structure (rather than increasing the wing span), especially if the fins
serve of drift. Thus, if the fins are well designed, they modify the flow
of the wing at the ends (where the vortices are formed), so that a part
of the drag produced by the latter is recovered and converted into propulsive
force . Of course, the effect is directly proportional to the importance
of vortices, which means that it is only at high lift that this effect is
beneficial and valuable, that is to say in climb and cruising at high altitude.
At the other flight configurations, their influence is virtually nil, yet
it should not be negative where the need for a wind tunnel study very carefully
and multiple flight tests to determine the best compromise on the shape
and the setting of said "WINGLETS" while taking account of mean
Fuel economy is not negligible since a KC 135 equipped of WINGLETS saves
258,400 liters of fuel a year of use by reducing drag in cruise altitude
of 6%, which is considerable. This economy compensate, easily the costs
incurred by the aircrafts equipment by this system that tends to spread
in the future.
In addition to the beneficial aspect of the fins mentioned above, there
is an operational aspect of the hunter who would be equipped with fins.
Thus they offer vertical surfaces advanced, on the aircraft (other than
the rear fin) that allow control of the transverse lift at the condition
to make them simultaneously mobile. Indeed, in order to escape laterally
to one shot in stern, (rear plane), it will be possible thanks to the
fins tested currently at the USA on F4CCV and, in France with a FALCON
20 , to control laterally the flight . In 1916, the SOPWITH-CAMEL very
unstable, hunted laterally once to move cross bar and sowed his assailant.
In 1940, the Aerospace had developed for this purpose the LEO 48 but could
not continue because of the Second World War.
Currently the idea is very seriously pickup again and will certainly equip
the hunters futur.
LIFT cruise : CZ 0,45 à 0, 55
Drags and lift of the Airbus A340
LIFT takeoff : CZ 1,3 à 1,6
42% friction drag
12% drag of intereaction
2% residual drag
33% induced drag
WIND TUNNEL TESTS MUST BE MADE IN LOW SPEED
MACH 0,2 TO MACH 0,3
THE MODEL USED FOR THE TESTS ( AIRBUS OR ATR)
MUST HAVE AN ASPECT RATIO BETWEEN 7.5 AND 12
THE ONE OF THE AIRBUS BEING 9
NOW THE GAIN ACQUIRED BY THE WINGLETS IS OF :
3 TO 4% OF THE INDUCED DRAG (GROSS GAIN)
AND ABOUT 1.2% OF TOTAL DRAG (NET GAIN)
The Journal of the Technology
Aerodinamisme - The fins boost the Boeing aircrafts
Placed in the wingtip, the fins reduce the drag of the aircrafts.
Boeing go into partnership at the Aviation Pattners company to transform
the wingtips of its planes. The winglets or fins are extensions, arrow in
above that enhance the aerodynamic performance of the aircraft.
Saving of kerosene
The induced drag reduction it results in a performance increase of flight
in cruise , a reducing of fuel, a capacity increased payload, or the access
to air routes previously not allowed. The company thus formed Aviation Partners
Boeing will ensure all operations, from design to installation on all proposed
transport aircraft from Boeing. Already, Aviation Partners has completed
the installation of fins on Gulfstream jets, and the BBJ. The tests showed
an improvement in drag of 5 to 7% on the BBJ model. This fin has a curved
360 ° to loop over the wing. The product itself will not be on the aircrafts
before three years. The pieces are made of composite material and aluminum.
Of variable size, they can reach 2,5 m high and increase the wing span of
|| Loop on the wing, when
the fins will be certified, they will equip Boeing soon.