Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02522553 2005-10-07
Aircraft Wing, Method for Operating_an Aircraft Wind, and Use of a Pivotable
Trailing
Edge on a Main Wing of an Aircraft, for Adiustingthe Shape and the Width of an
Air Gan
Field of the invention
The invention relates to an aircraft wing, a method for operating an aircraft
wing, and the use
of a pivotable trailing edge on a main wing of an aircraft, for adjusting the
shape and the
width of an air gap.
Technological Background
An aircraft is kept airborne by the aerodynamic lift of its wings.
An aircraft wing comprises a main wing, and in many cases also lift-assisting
devices fixed to
said wing. A lift-assisting device is a device on a wing of an aircraft, which
device positively
changes the lift coefficient at least in a range of the flight spectrum.
Lift assisting devices are in particular used during landing and during
takeoff of an aircraft.
The aim is, as a result of the increased lift, to reduce the take-off speed or
landing speed and
thus reduce the distance required for take-off or landing.
Lift-assisting devices can be affixed to the leading edge or the trailing edge
of an aircraft
wing. The so-called Fowler flap is an important example of a lift-assisting
device affixed to
the trailing edge of a wing. A Fowler flap is a control surface which is moved
to the rear
below the trailing edge of the wing and is set at an angle. In this way an air
gap can be formed
between the top and the bottom of the wing, as a result of which the airfoil
curvature is
increased. At the same time the wing surface is also increased.
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Fig. 1 shows a retracted state 100 and an extended state 110 of a Fowler flap
102 affixed to
the trailing edge of a main wing 101. In the retracted state 100 the Fowler
flzp 102 rests
against the main wing 101. In order to move the Fowler flap 102 from the
retracted state 100
to an extended state 110, the Fowler flap 102 is first moved to the rear and
then folded
downward. In this way an air gap 111 is created between the main wing 101 and
the extended
Fowler flap 102. As shown in Fig. 1, the Fowler flap 102 is attached to the
trailing edge 103
of the main wing 101.
A Fowler flap which can be extended to form an air gap jointly with a main
wing is known
from the state of the art, see Rudolph, P "High-Lift Systems on Commercial
Subsonic
Airliners", NASA Contractor Report 4746, section 1.1.2. To achieve good flow
characteristics
with a Fowler flap it is important that the size of the air gap created when
the flap is extended
be well defined, and that a divergent air gap over the entire region of the
Fowler flap be
prevented.
This requirement can be met by various kinematic solutions, wherein according
to the state of
the art the so-called track and rear-link solution (for example implemented in
the Airbus
A340) or the 4-bar linkage solution (for example implemented in the Boeing
777) is used, see
Rudolph, P "High-Lift Systems on Commercial Subsonic Airliners", NASA
Contractor
Report 4746, section I .2.2.
Pivot point kinematics (pivot point or dropped hinge), according to which the
flap is extended
along a circular path, are also used according to the state of the art, for
example in the Boeing
C 17. Such a Fowler flap 200 according to the state of the art is shown in
Fig. 2. The Fowler
flap 200 is brought along a circular direction of extension 201, starting from
a retracted state
100 to an extended state 110.
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Track and rear link kinematics shows good performance in relation to
aerodynamic
characteristics. Pivot point kinematics provide advantages in relation to the
complexity of the
system, which also results in reduced weight.
However, both the track and linkage technology and the pivot point technology
are associated
with disadvantages.
Due to its limitation to a circular extension path, pivot kinematics only
allow the setting of a
desired target state when the flap is in position. The width and the form of
the gap for the
intermediate states during extension result automatically and cannot
themselves be set. As a
rule, the settable target setting is set such that in the fully extended state
110 it produces a
predefinable result. In relation to intermediary extension states the width of
the air gap often
takes on a value that is below the optimum value, as a result of which the
quality of the
functionality of the flap can be reduced, and in particular the flow
characteristics of the flap
can be impeded (risk of confluent boundary layer flow). Due to the circular
movement the
shape of the gap in an intermediate state is partly divergent. Due to local
deceleration of the
flow speed this leads to separation of the boundary layer flow at the flap,
with subsequent
deterioration of lift performance, which in addition can also lead to the
occurrence of
vibration and noise. In a worst-case scenario this effect can lead to a range
of intermediary
flap positions not being useable at all.
Furthermore, in an advanced (high) degree of extension of the flap,
irrespective of the
kinematics used, boundary layer separation at the flap element can occur. This
effect limits
the efficiency of the flap, defines the maximum usable flap angle and causes
vibration of the
flap elements at high angles of extension.
Summary of the Invention
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Thus, there may be a need to provide an aircraft wing in which the lift
performance of the
wing is improved, and undesirable vibration and noise are prevented.
This need may be met by an aircraft wing, by a method for operating an
aircraft wing, and by
the use of a pivotable trailing edge on a main wing of an aircraft, for
adjusting the shape and
the width of an air gap, with the characteristics according to the independent
claims.
The aircraft wing according to the invention comprises a main wing with a,
pivotable trailing
edge and a lift-assisting flap on the rear of the wing, wherein the lift-
assisting flap is coupled
to the main wing and is designed in such a way that in its retracted state it
rests against the
main wing and in an extended state it forms an air gap with the main wing. The
pivotable
trailing edge is pivotable in such a way that by pivoting the pivotable
trailing edge the shape
and the width of the air gap are adjustable.
Furthermore, according to the invention a method for operating an aircraft
wing is created in
which method a lift-assisting flap that is arranged on the rear of the wing
and that is coupled
to the main wing is moved from a retracted state, in which the lift-assisting
flap rests against
the main wing, to an extended state, in which the lift-assisting flap forms an
air gap to the
main wing. Furthermore, a pivotable trailing edge of the main wing is hinged
in such a way
that by pivoting the pivotable trailing edge the shape and width of the air
gap is adjusted.
Moreover, the invention provides for the use of a pivotable trailing edge on
the main wing of
an aircraft, for adjusting the shape and the width of an air gap between the
main wing and an
extended lift-assisting flap on the rear of the wing by pivoting the pivotable
trailing edge.
A fundamental idea of the invention may be found in providing a pivotable
trailing edge of
the main wing, i.e. a pivotable element, may be provided on the rear end
section of a main
wing (i.e. of a wing carrier body affixed to a fuselage), and that the width
and shape of an air
CA 02522553 2005-10-07
gap between a lift-assisting flap (for example a Fowler flap) on the rear of
the wing and the
main wing is set to a desired value by means of rotating the pivotable
trailing edge. If the
width of the air gap is set so as to be constant and free of any divergence,
separation of the
boundary layer flow at the flap may be suppressed, and any resulting
undesirable vibration
and undesirable noise may be considerably reduced or entirely avoided. The
high sensitivity
of the air gap adjustment according to the invention may be due to the fact
that only an end
tip, in other words a small end region, of the main wing, namely the pivotable
trailing edge of
said main wing, may be set in relation to its positioning or angular position.
In this way the
width of the air gap may be controlled very sensitively. Thus according to the
invention only
a finely adjustable end tip is swivelled.
Controlled pivoting of the end tip may make it possible to set the air gap
width by means of
targeted pivoting to and fro of the pivotable trailing edge throughout, in
particular during the
entire process of extending the lift-assisting flap (in particular a Fowler
flap) on the rear of the
wing, from the retracted state to the extended state.
Thus according to the invention the aerodynamics of an aircraft are improved
by moving a
fine end tip on a trailing edge of a wing; in the example shown a movable
shroud trailing
edge. This makes it possible to optimise the aerodynamic design of high-lift
systems, in
particular also for optimising flaps with (circular arc) pivot-kinematics.
Numeric calculations
and wind channel experiments have shown that the aerodynamics of a wing
comprising the
pivotable trailing edge according to the invention are significantly improved
compared to
conventional methods.
The movable trailing edge of the wing according to the invention can extend
across the entire
span of the lift-assisting flap and/or of the aircraft wing, or only across
part of the width. The
pivotable trailing edge can be provided on an upper housing surface of the
aircraft wing or
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can be attached to another movable component on the aircraft wing. For example
a spoiler can
comprise a movable trailing edge.
The trailing edge part of the wing according to the invention can be a
flexible part that can be
swivelled with the use of spring tension or can be operated with the use of an
actuator.
When spring tension is used, for example the extendable device pushes against
the movable
trailing edge part of the wing, subsequently extends it from a retracted state
to an extended
state and leaves it in the extended state in a predefined position. A sprung
plate or memory
material could be an example of such a device.
'The active movement of a movable trailing edge part of the wing according to
the invention
can be brought about in various ways, for example by using of mechanical or
hydraulic
actuation or by other means, for example the use of a bimetal strip that can
be electrically
activated.
When the flap on the kinematic extension path moves towards the rear, starting
from the
retracted position, and the air gap between the shroud and the upper surface
of the flap opens,
the movable trailing edge part of the wing can be extended downward thus
changing the
shape of the air gap in a predefmable way.
The invention can be used either in the design of a new aircraft or it can be
retrofitted to an
already existing aircraft or aircraft model.
According to the invention the angular position of an end tip of the main
wing, i.e. of a
pivotable trailing edge, is set for controlling the gap width or the gap
shape. It is important
that the pivotable trailing edge is provided as a relatively small part of a
larger component
because only in that way will it be possible to achieve particularly fine
control of the gap
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geometry, in particular in a simple extension mechanism. Preferably the length
of the
movable trailing edge is at most 10% of the depth of the wing element to which
said trailing
edge is attached.
The position of the downward pivotable trailing edge sensitively affects fine
adjustment of the
gap width between the flap and the main wing, and thus has an advantageous
influence on the
quality of the flow characteristics at the flap in an intermediate position
between a retracted
state and a fully extended state. According to the invention, the divergence
in the gap is
reduced or even completely compensated for even in a circular extension path,
due to the
spatially adjustable movable trailing edge. Deceleration of the airflow in the
surroundings of
the flap is prevented so that undesirable boundary layer separation is
suppressed and
vibrations and reductions in performance are prevented.
Furthermore, commencement of boundary layer separation at the flap, which
separation is an
issue in particular in large extension angles of a flap, can be delayed. The
useful extension
range of the flap can be expanded towards larger angles, and the flap
performance is
improved. The risk of vibration occurring at a high angle is reduced.
Preferred embodiments of the invention result from the dependent claims.
Below, preferred embodiments of the aircraft wing according to the invention
are described.
They also apply to the method for operating an aircraft wing and to the use of
the invention.
In the case of aircraft wing the pivotable trailing edge can be designed in
such a way that by
pivoting the pivotable trailing edge the width of the air gap is kept constant
or convergent.
With constant width of the air gap, boundary layer separation and other causes
of undesirable
vibration or noise may be prevented.
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The pivotable trailing edge can be designed in such a way that by means of
pivoting the
pivotable trailing edge the width of the air gap during extension of the lift-
assisting flap from
the retracted state to the extended state is at least at times kept constant
or convergent. For
example a control unit can be provided which during extension of the Fowler
flap measures
the corresponding gap and/or the width of the air gap and readjusts a drive
for the pivotable
trailing edge in such a way that the width of the air gap is kept constant or
convergent.
The pivotable trailing edge can extend along the entire span width of the
Fowler flap. As an
alterative, the pivotable trailing edge can extend along only part of the span
width of the
Fowler flap.
The pivotable trailing edge can be attached to a housing of the main wing. In
particular, the
pivotable trailing edge can be attached to an upper section of the housing of
the main wing.
The pivotable trailing edge can be attached to a moveable element which is
attached to a
housing of the main wing. In particular, the pivotable trailing edge can be
attached to a spoiler
which itself is attached to a housing of the main wing. Apart from the normal
spoiler function,
for which the spoiler is extended and thus moved, the spoiler can be operated
in the retracted
state in such a way that at an end section of the spoiler, which end section
is on the rear of the
wing, the pivotable trailing edge is formed which can be hinged across a
predefinable angular
range, so that a predefinable air gap width can be set precisely.
The pivotable trailing edge can be hinged by using a spring element.
As an alternative, the pivotable trailing edge can be swivelled by using a
drive device which
can, for example, be an electrical drive device or a hydraulic drive device.
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Moreover, a vane (slat) can be provided on the aircraft wing, wherein in the
extended state of
the lift-assisting flap said vane is arranged between the main wing and the
lift-assisting flap.
By using such a vane, an aircraft wing with a plurality of air gaps, in
particular with two or
three air gaps, can be formed.
In the extended state of the lift-assisting flap, several air gaps can be
formed between the main
wing and the lift-assisting flap.
The pivotable trailing edge is preferably designed in such a way that it is
attached to the main
wmg.
In the case of the aircraft wing the lift-assisting flap on the rear of the
wing is preferably a
Fowler flap. A Fowler flap is an element which can be moved to the rear below
the trailing
edge and which can be set at an angle. In this way an air gap (or several air
gaps) can be
formed between the topside and the buttomside of the wing, as a result of
which the airfoil
curvature is increased. At the same time the effective wing surface can also
be increased.
According to the invention the width of the air gap is adjusted in that the
pivotable trailing
edge is hinged accordingly.
As an alternative, in the aircraft wing according to the invention the lift-
assisting flap on the
rear of the wing can be a slotted flap. In a slotted flap a control surface is
tilted downward for
extension. This movement simultaneously provides an air gap (or several air
gaps), which
admits (admit) air to the topside of the flap, thus preventing stalling. In a
slotted flap the
airfoil curvature is changed. According to the invention the width of the air
gap is adjusted in
that the pivotable trailing edge is swivelled accordingly.
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l~
The invention can be applied not only to a Fowler flap or a slotted flap but
to any lift-assisting
flap in which in the extended state an air gap is created whose dimensions are
to be
controlled.
Embodiments of the invention are shown in the figures and are described in
more detail
below.
The following are shown:
Fig. 1 a main wing with a Fowler flap according to the state of the art;
Fig. 2 another Fowler flap on a main wing according to the state of the art;
Fig. 3 an aircraft wing according to a first embodiment of the invention;
Fig. 4 an aircraft wing according to a second embodiment of the invention;
Fig. S an aircraft wing according to a third embodiment of the invention;
Fig. 6 an aircraft wing according to a fourth embodiment of the invention; and
Fig. 7A to Fig. 8B numeric flow simulations which show improved flow
characteristics of the
aircraft wing according to the invention.
Detailed Description of Exemplary Embodiments
The drawings in the figures are diagrammatic and not to scale.
Identical or similar components in different figures have the same reference
characters.
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Below, with reference to Fig. 3, an aircraft wing according to a first
embodiment of the
invention is described.
Fig. 3 shows the aircraft wing according to the first embodiment of the
invention in a
retracted state 300 in which a Fowler flap 302 rests against the main wing
301, and in an
extended state 310 in which the Fowler flap 302 forms an air gap 311 with the
main wing
301.
Fig. 3 shows an aircraft wing with the main wing 301, the Fowler flap 302 and
a pivotable
trailing edge 304 of the main wing 301. The Fowler flap 302 is extendably
attached to the
main wing 301 (the corresponding coupling element is not shown in Fig. 3) and
is equipped in
such a way that in a retracted state 300 it rests against the main wing 301,
and in an extended
state 310 it forms an air gap 311 with the main wing 301. The pivotable
trailing edge 304 is
attached to an end section, more precisely to an end section on the rear of
the main wing 301,
and is pivotable in such a way that by pivoting the pivotable trailing edge
304 the width of the
air gap 311 is adjustable.
Fig. 3 shows the pivotable trailing edge 304 in a first pivoted state 304a, in
a second pivoted
state 304b and in a third pivoted state 304c. The second hinged state 304b
shows the end tip
in its rest position. The first hinged state 304a shows an excursion of the
end tip towards the
top when compared to the rest position of the end tip. The third pivoted state
304c shows an
excursion of the end tip towards the bottom compared to the rest position of
the end tip.
Depending on the set pivoted state 304a to 304c, the width of the air gap 311
can be fine-
adjusted, as a result of which undesirable airflow separations, vibration and
noise in the
aircraft interior are prevented. Furthermore, during the entire process of
extension, i.e. during
the transition from the state 300 to the state 310, the width of the air gap
311 can be directed
or controlled.
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The pivotable trailing edge 304 is pivotable in such a way that by pivoting
the pivotable
trailing edge 304 the width of the air gap 311 is held constant, namely during
the transition of
the Fowler flap 302 from the retracted state 300 to the extended state 310.
The pivotable
trailing edge 304 extends in a direction perpendicular to the drawing plane in
Fig. 3 along the
entire span width of the Fowler flap 302. The pivotable trailing edge 304 is
attached to an
upper housing end section of the main wing 301 and is pivotable by a hydraulic
drive unit
(not shown).
Below, with reference to Fig. 4, an aircraft wing 400 according to a second
embodiment of
the invention is described.
The aircraft wing 400 shows a so-called "slotted flap", in other words a
Fowler flap 302,
which at a transition from the retracted state 300 to the extended state 310
only generates a
single air gap. By using of a pivotable arm 401 the Fowler flap 302, by
retraction and
subsequent pivoting, is brought from state 300 to state 310. In order to make
possible a
constant width or convergence of the air gap between the Fowler flap 302 and
the main wing
301 during this transition, a pivotable trailing edge 304 of the main wing 301
according to
Fig. 4 is slightly moved from the top towards the bottom, e.g. using an
electronic motor
control system.
Below, with reference to Fig. 5, an aircraft wing 500 according to a third
embodiment of the
invention is described.
In the case of the aircraft wing S00 a spoiler 501 is provided on the topside
of an end section
on the rear of the main wing 301. If required, the spoiler 501 can be extended
to influence the
aerodynamic properties of the aircraft wing 500. Attached to an end section of
the spoiler 501
is a pivotable trailing edge 304, which in Fig. 5 is shown in two different
operating positions.
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Fig. 5 shows a configuration with a "double slotted flap" so that two air gaps
can be created.
To this effect a vane 502 is formed between the Fowler flap 302 and the main
wing 301.
Below, with reference to Fig. 6, an aircraft wing 600 according to a fourth
embodiment of the
invention is described.
In a way similar to that of the aircraft wing 500, the aircraft wing 600
comprises a "double
slotted flap" and has a configuration in which a main wing 301, a vane 302 and
a Fowler flap
302 form a first air gap 601 and a second air gap 602, respectively. An end
section of the
main wing 301 again comprises a pivotable trailing edge 304, which when the
Fowler flap
302 makes the transition from the retracted state to an extended state is
moved from state 300
to state 310. In other words, state 300 depicts a baseline state of the
pivotable trailing edge
304, while state 310 shows an end state of the pivotable trailing edge 304 in
a position of
maximum excursion.
Below, with reference to Figs 7A to 8B it is illustrated that with the use of
the aircraft wing
600 the aerodynamic characteristics are significantly improved. Figs 7A to 8B
show
computational fluid dynamics (CFD) simulations, i.e. numeric flow simulations,
in which the
eddy viscosity in a region surrounding an aircraft wing is graphically shown.
The CFD
simulations of Figs 7A to 8B have been calculated with an (unstructured)
process using
Navier-Stokes equations.
Figs 7A and 8A show the flow characteristics of an aircraft wing without the
pivotable
trailing edge according to the invention. Figs 7B and 8B show the improved
flow
characteristics when providing a pivotable trailing edge 304.
Figs 7A, 7B show that according to the invention, flow separation at medium
angles of
extension of the Fowler flap 302 (for example 35°) is strongly
suppressed. Furthermore, Figs
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8A and 8B show the improvement according to the invention of the flow
characteristics in a
region surrounding the flap 302 at a large angle of extension (for example
50°).
It should be noted that the term "comprising" does not exclude other elements
or steps and the
"a" or "an" does not exclude a plurality. Also elements described in
association with different
embodiments may be combined. It should also be noted that reference signs in
the claims
shall not be construed as limiting the scope of the claims.
