Note: Descriptions are shown in the official language in which they were submitted.
1
BRACED WING AIRCRAFT
The invention is related to a braced wing aircraft with a fuselage
and a fixed wing arrangement that comprises at least two braced
wings which are arranged laterally and opposite to each other on the
.. fuselage.
Aircrafts with braced wings, in particular with so-called box-wing
or joined-wing configurations, are well known since a long time.
Generally, such box-wing or joined-wing configurations are based on
comparatively complex arrangements of main load carrying members,
such as skins, ribs and spars, which are required to join respective
upper and lower wings together in a sufficiently efficient manner.
However, when using upper and lower wings that are formed on
the basis of conventional wing constructions and, more particularly,
on the basis of conventional staggered braced wing configurations,
usually plural kinks are formed in associated wing spars at least in
the area of respective wing tips. This leads at least in configurations
with propellers or engines resp. propulsion units which are mounted
at the respective wing tips to an increased constructional complexity.
More generally, the challenge of such configurations is to
provide an efficient structure in terms of load continuity of associated
main load carrying members of both wings, i. e. the upper and lower
wings, at a respective wing interconnection region. Furthermore, a
comparatively simple integration of a propeller or engine resp.
propulsion unit into the respective wing interconnection region as well
as of a resulting overall wing assembly is required. In particular, a
safe and efficient wing interaction between the upper and lower wings
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at the respective wing interaction region with maximum stiffness of
the entire braced wing construction should be enabled.
However, in lightweight designs every kink leads to a deviation
in a given load path, which usually needs to be supported by
additional ribs in order to guarantee a required stiffness and strength.
These additional ribs, nevertheless, cause additional weight,
additional cost, additional fatigue sensitivity, a requirement of
associated fasteners and, therefore, increase complexity of an
already complex wing configuration.
Furthermore, in case of an installation of a propeller or engine
resp. propulsion unit into the respective wing interconnection region,
i. e. in the area of the respective wing tips, the spars of the upper and
lower wings need to provide support for the propeller or engine resp.
propulsion unit. In fact, its supports are generally driven by an
underlying wing stiffness. Nevertheless, due to associated interface
areas at the respective wing interconnection region and a cut of the
main load carrying members, the main load path is comparatively
inefficient.
One consequence of the above-described critical design matters
is that, although box-wing or joined-wing configurations are well
known, their practical application is very limited and, thus, there are
only limited examples available for aircrafts with improved wing
configurations. This is even more valid for aircrafts with box-wing or
joined-wing configurations having propellers or engines resp.
propulsion units in the vicinity of the respective wing tips, i. e. in the
respective wing interconnection regions.
An exemplary braced wing aircraft is e. g. described in the
document US 5,046,684 A. More specifically, the latter describes a
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tiltrotor aircraft with a fuselage and a fixed wing arrangement. On
each side of the fuselage a first and a second wing are arranged. The
first wing is fixed substantially at the bottom of the fuselage and the
second wing is fixed substantially at the top of the fuselage, or fixed
to a structure extending above the fuselage. At least one of the first
and second wings has dihedral so that the wings converge to join or
nearly join at their tips. Furthermore, unducted rotor means are
provided for generating aerodynamic lift sufficient for highly efficient
hovering flight and for propelling the tiltrotor aircraft at speeds
approaching roughly four hundred knots in forward cruising flight. The
unducted rotor means are supported on the first and second wings, at
or near the tips of the first and second wings. They can be pivoted for
operation in different orientations in hovering and forward flight
respectively.
In other words, according to the document US 5 046 684 A, the
tiltrotor aircraft features a fixed wing arrangement, wherein the lower,
i. e. first wing is straight and positively swept, and wherein the upper,
i. e. second wing is straight and exhibits a very pronounced negative
sweep. The upper wing is anhedral and connects the tip of the lower
wing of the fixed wing arrangement to the tip of the tiltrotor aircraft's
fin.
The document EP 2 690 011 Al describes a braced wing aircraft
in the form of a compound helicopter with a fixed wing arrangement in
the form of a joined-wing configuration, wherein a lower wing and an
upper wing are provided on each side of the compound helicopter.
Both wings are essentially straight and interconnected to each other
at a wing interconnection region, and a pusher propeller is installed in
the interconnection region behind associated trailing edges of both
wings.
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The document EP 3 141 478 Al describes another braced wing
aircraft in the form of a compound helicopter with a fuselage and at
least one main rotor that is at least adapted for generating lift in
operation. The fuselage comprises a lower side and an upper side
that is opposed to the lower side. The at least one main rotor is
arranged at the upper side. At least one propeller is provided that is
at least adapted for generating forward thrust in operation, the at
least one propeller being mounted to a fixed wing arrangement that is
laterally attached to the fuselage. The fixed wing arrangement
comprises at least one upper wing that is arranged at an upper wing
root joint area provided at the upper side of the fuselage and at least
one lower wing that is arranged at a lower wing root joint area
provided at the lower side of the fuselage. The upper and lower wings
are at least interconnected at an associated interconnection region.
The lower wing comprises an inboard section defining a first quarter
chord line and a first centroidal axis and an outboard section defining
a second quarter chord line and a second centroidal axis. The second
centroidal axis is inclined relative to the first centroidal axis by a
relative dihedral angle that is defined in a first coordinate plane. The
second quarter chord line is inclined relative to the first quarter chord
line by a relative sweep angle that is defined in a second coordinate
plane. The inboard section is connected to the fuselage at the lower
wing root joint area and to the outboard section at a sections
interconnection region. The outboard section is connected to the
inboard section at the sections interconnection region and to the
upper wing at the associated interconnection region. More
specifically, the outboard section comprises wing spars and the
fuselage is provided with wing attachment frames. A hinged joint or
clamped joint connects the wing spars to the wing attachment frames.
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It should be noted that the above described documents are only
described by way of example and that there is a big variety of
documents that are related to the topic of braced wing aircrafts with
box-wing or joined-wing configurations, respectively, but they mainly
describe either an underlying aerodynamic configuration, a given
arrangement of upper and lower wings, and/or a pure design
architecture of such wing configurations. Exemplary documents are
the documents US 5 503 352 A and US 4 365 773 A.
However, in all of these well-known braced wing aircrafts, a
respective arrangement of structural items and members is either
undefined or unclear. In fact, if there is information available, as e. g.
in the documents US 5 046 684 A and/or US 5 503 352 A, then there
is no specific description of a respective arrangement of an
underlying internal structure of spars and an improvement with
respect to a provided load transfer or force flow, respectively.
Otherwise, due to the fact that occurring lifting forces on given wing
surfaces in a box-wing configuration are vertical, respective designs,
such as e. g. described in the document US 4 365 773 A, still only
present a conventional orientation of spars themselves, i. e. vertical,
and do neither describe an underlying interconnection of respective
upper and lower wings at respective wing interconnection regions, nor
their structure resp. mechanical arrangement as a whole. More
particularly, all above-described prior art documents do not describe
internal constructions of respective braced wings, in particular in box-
wing or joined-wing configurations, or they e. g. merely show spars
but do not reveal that there are structure-mechanic issues with
associated wing interconnection regions and attachment areas of the
braced wings to a given fuselage, or with respect to propellers and
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engines resp. propulsion units that are mounted to the associated
wing interconnection regions.
It should be noted that, by way of example, the documents EP 2
789 534 Al and EP 2 772 427 Al describe internal arrangements of
spars in aircraft wings, which may be referred to as "multi-box-wing"
designs. However, these "multi-box-wing" designs are merely
described with respect to aircrafts having singular wings, so that the
described "multi-box-wing" designs are not provided with any wing
interconnection regions that are required for implementing box-wing
or joined-wing configurations in braced wing aircrafts.
The documents US4090681, US2017197709, US2014061367
and EP2886449 have also been considered.
It is, therefore, an object of the present invention to provide a
new braced wing aircraft with braced wings that respectively comprise
at least two staggered and interconnected dependent singular wings
and exhibit an improved structure-mechanic behavior.
This object is solved by a braced wing aircraft with a fuselage
and a fixed wing arrangement, the fixed wing arrangement comprising
at least two braced wings that are arranged laterally and opposite to
each other on the fuselage.
More specifically, according to the present invention a braced
wing aircraft with a fuselage and a fixed wing arrangement is
provided. The fixed wing arrangement comprises at least two braced
wings that are arranged laterally and opposite to each other on the
fuselage. Each one of the at least two braced wings comprises at
least one upper wing and at least one lower wing which are staggered
and interconnected at a predetermined transition region. The at least
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one upper wing is connected to the fuselage at an associated upper
wing root and the at least one lower wing is connected to the fuselage
at an associated lower wing root. The at least one upper wing
comprises at least one upper wing spar that extends from the
associated upper wing root to the predetermined transition region.
The at least one lower wing comprises at least one lower wing spar
that extends from the predetermined transition region to the
associated lower wing root. At least one transition spar is provided at
the predetermined transition region. The at least one transition spar
connects the at least one upper wing spar to the at least one lower
wing spar. The at least one upper wing spar, the at least one lower
wing spar, and the at least one transition spar are arranged in a
single virtually spanned spars plane that is inclined with respect to a
vertical aircraft axis.
Advantageously, a braced wing aircraft with braced wings
having a "straightened" internal architecture can be provided in a way
that any structural kinks and their associated load path deviations can
be avoided entirely. This is achieved by defining a specific structural
wing arrangement which comprises suitable working-planes that are
defined by respective attachment points of the braced wings,
respectively their wing roots, and associated interconnection points of
respective wing spars at the predetermined transition region. These
working-planes advantageously define a minimum kink design which
is, from a structure-mechanic point of view, very stiff and, thus,
provides an improved support for a propulsion device mounted to the
predetermined transition region.
According to one aspect, the braced wings of the inventive
braced wing aircraft are provided with a particular box-wing
respectively joined-wing configuration, wherein a main mechanical
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system is defined by respective attachment points of associated
upper and lower wings to the fuselage. An underlying axis defined by
these attachment points for corresponding front and rear spars in the
upper and lower wings serves as a base for the wing attachment. The
.. attachment points of the upper and lower wings are respectively
provided at associated upper and lower wing roots.
Preferably, in a basic design of a respective front spar
arrangement, a given web of a respective upper wing front spar is
tilted to this axis as well as the lower wing front spar in a way that a
virtually spanned front spars plane can be established by these webs
which extend in spanwise direction of the upper and lower wings.
Preferentially, an at least similar rear spar arrangement is provided
for the upper wing rear spar and the lower wing rear spar so that a
virtually spanned rear spars plane can be defined for the
.. interconnected rear spars. The virtually spanned front spars plane
and the virtually spanned rear spars plane may advantageously be
defined according to underlying sweep angles of the upper and lower
wings and are preferably arranged such that a given distance
between the virtually spanned front spars plane and the virtually
spanned rear spars plane is maximized in order to provide a maximum
possible stiffness to a given braced wing.
It should be noted that the virtually spanned front spars plane
and the virtually spanned rear spars plane must not necessarily be
arranged in parallel. In fact, their orientation and arrangement relative
to each other can be chosen arbitrarily and according to a respective
individual need of a required aerodynamic configuration of the upper
and lower wings. However, a main characteristic is that the front and
rear spars of the upper and lower wings define a plane sectional cut
through the braced wing.
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More specifically, according to one aspect the front spars of the
upper and lower wings and an associated front transition spar
between the front spars of the upper and lower wings extend in one
and the same single plane, i. e. the virtually spanned front spars
plane. Accordingly, no kink is present in the virtually spanned front
spars plane and a correspondingly defined entire front spar and front
transition spar unit operates as a mechanical unit within the virtually
spanned front spars plane. The individual spars, i. e. the front spars
in the upper and lower wings and the associated front transition spar
can either be implemented as an integral component in one piece, or
as individual components that are mechanically fastened to each
other by means of continuous and/or singular joins, such as hinges.
Likewise, according to one aspect the rear spars of the upper
and lower wings and an associated rear transition spar between the
rear spars of the upper and lower wings also extend in one and the
same single plane, i. e. the virtually spanned rear spars plane.
Accordingly, no kink is present in the virtually spanned rear spars
plane and a correspondingly defined entire rear spar and rear
transition spar unit operates as a mechanical unit within the virtually
spanned rear spars plane. The individual spars, i. e. the rear spars in
the upper and lower wings and the associated rear transition spar can
either be implemented as an integral component in one piece, or as
individual components that are mechanically fastened to each other
by means of continuous and/or singular joins, such as hinges.
In more advanced configurations, also an underlying number of
correspondingly provided front and/or rear spar arrangements can be
adapted as required. In other words, preferably there is at least one
such front and/or rear spar arrangement as described above,
however, more than one front and/or rear spar arrangement may
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likewise be used. Even additional secondary spars may be integrated
into each front and/or rear spar arrangement and, preferably,
allocated at the virtually spanned front and/or rear spar planes.
However, such additional secondary spars must not necessarily span
over the whole length of one of the upper or lower wings.
Advantageously, the front and/or rear spar arrangements
provide for an inclined position of associated spars with respect to a
given chord line of each one of the upper and lower wings. In other
words, in contrast to conventional wing arrangements, the spars are
not oriented perpendicular to the chord line.
More specifically, due to the arrangement of the front spars
and/or rear spars with the associated front/rear transition spars in
associated virtually spanned front and rear spars planes, omission of
any kinks can be achieved so that the entire underlying wing structure
as such is comparatively stiff. In fact, each kink reduces an
underlying stiffness of a wing, so that an increased stiffness may be
obtained by avoiding kinks.
It should be noted that an increased stiffness is usually desired
in wing architecture due to aeroelasticity. Thus, as any kink leads to a
loss in stiffness of a lightweight structure or to additional weight, if
the loss of stiffness must be compensated by additional structural
items, the inventive arrangement in virtually spanned front and rear
spars planes offers a very effective means for increasing stiffness. In
fact, it should be noted that stiffness of a wings' structure is mostly a
design driver and mass consumer. In particular, if propulsion devices
are to be installed at respective wing tips, i. e. the predetermined
transition regions, but more generally at any position of a given
braced wing, the need for stiffness is even more important and, thus,
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by increasing the stiffness with the inventive braced wing
architecture, becomes more advantageous.
Furthermore, if there are no kinks in the wing architecture
respectively an underlying spar design, there is no need for additional
ribs as they are required in conventional box-wing or joined-wing
architectures for supporting the kinks. By avoiding such additional
ribs, a respective number of constituent components can be reduced,
thus, reducing cost and weight. Simultaneously, a simplification of the
overall wing assembly can be achieved.
Furthermore, by inclining the spar webs, respectively the
virtually spanned front and rear spars planes, an increase of a
moment of inertia of the overall wing assembly in its weakest principle
axis of inertia can be achieved. This is for box-wing or joined-wing
configurations.
Furthermore, dependent on an underlying concept related to
accounting e. g. for bird strike events, the inclination of the virtually
spanned front and rear spars planes advantageously improves
resistance in bird strike situations, as in such cases the birds
advantageously only penetrate respective leading edges locally.
Thus, a bird must e. g. not be stopped completely by the front spar
which, instead, deviates the bird only according to its inclination
angle. Accordingly, a lower amount of energy emanating from the bird
strike must be dissipated by the spar web and on top the magnitude
of the peak force during the bird strike is lower.
According to one aspect, the spar webs of the front and rear
spars of the upper and lower wings are oriented diagonally, i. e.
essentially in parallel to the main principle axis of the mechanical
system of the braced wings and, thus, offers maximum stiffness since
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the entire web and caps of each one of the front and rear spars is at
nearly the same maximum distance with respect to the principle axis
with lowest moment of inertia, thereby taking maximum profit from the
structural mass of all front and rear spar webs and caps. This allows
avoiding local reinforcements at outermost corners of respective
conventional box-wing configurations, which might be conveniently
applied to maximize stiffness of respective braced wings in box-wing
configurations with spars being perpendicularly oriented with respect
to an underlying wing profile chord line, which is, however,
complicated in manufacturing and costly as well. Thus, with the
inventive braced wings, manufacturing time and costs may be reduced
significantly.
In summary, the inventive braced wing aircraft is advantageous
in that it is suitable to solve issues with respect to stiffness,
architecture complexity, and number of structural supporting elements
required for implementation of the braced wings. More specifically,
the braced wings may be provided with an increased stiffness, a
simplified architecture and a reduced number of structural supporting
elements, such as additional ribs. Thus, a more lightweight braced
wing can be designed, which also saves cost and a respective
manufacturing time.
According to a preferred embodiment, the at least one upper
wing spar, the at least one lower wing spar, and the at least one
transition spar are integrated into a single one-piece component.
According to a further preferred embodiment, the at least one
transition spar is integrated into only one of the at least one upper
wing spar and the at least one lower wing spar into a single one-piece
component.
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According to a further preferred embodiment, the at least one
upper wing spar and the at least one lower wing spar are rigidly
mechanically attached to the at least one transition spar. This rigid
attachment is preferably a hinged joint, with the hinge axis
preferentially oriented perpendicular to the corresponding virtual spar
plane, or a fully clamped joint.
According to a further preferred embodiment, the at least one
upper wing and the at least one lower wing respectively comprise a
chord line, wherein the single virtually spanned spars plane is
.. inclined with respect to the chord line.
According to a further preferred embodiment, the at least one
upper wing comprises an upper wing rear spar and an upper wing
front spar. The at least one lower wing comprises a lower wing rear
spar and a lower wing front spar. The at least one transition spar
comprises a rear transition spar and a front transition spar.
According to a further preferred embodiment, the upper wing
rear spar, the lower wing rear spar and the rear transition spar are
arranged in a single virtually spanned rear spars plane that is inclined
with respect to the vertical aircraft axis. The upper wing front spar,
the lower wing front spar and the front transition spar are arranged in
a single virtually spanned front spars plane that is inclined with
respect to the vertical aircraft axis.
According to a further preferred embodiment, the single virtually
spanned rear spars plane and the single virtually spanned front spars
plane are arranged in parallel to each other.
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According to a further preferred embodiment, the single virtually
spanned rear spars plane and the single virtually spanned front spars
plane are inclined with respect to each other.
According to a further preferred embodiment, the upper wing
rear spar, the lower wing rear spar, the rear transition spar, the upper
wing front spar, the lower wing front spar, and the front transition
spar delimit a main load carrying center box of an associated one of
the at least two braced wings.
According to a further preferred embodiment, the associated
one of the at least two braced wings further comprises a leading
portion and a trailing portion both of which are rigidly attached to the
main load carrying center box.
According to a further preferred embodiment, the upper wing
rear spar, the lower wing rear spar, the rear transition spar, the upper
wing front spar, the lower wing front spar and the front transition spar
are flat beams with closed webs.
According to a further preferred embodiment, the front transition
spar and the rear transition spar are entirely or partly ring-shaped.
According to a further preferred embodiment, a propulsion
device is arranged at the predetermined transition region.
According to a further preferred embodiment, the braced wing
aircraft is embodied as a rotary wing aircraft with at least one main
rotor.
Preferred embodiments of the invention are outlined by way of
example in the following description with reference to the attached
drawings. In these attached drawings, identical or identically
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functioning components and elements are labeled with identical
reference numbers and characters and are, consequently, only
described once in the following description.
- Figure 1 shows a top view of a braced wing aircraft with
braced wings according to the present invention,
- Figure 2 shows a partly transparent, perspective view of one of
the braced wings of Figure 1 with a transition region according to one
aspect,
- Figure 3 shows a partly transparent, exploded perspective
view of the braced wing of Figure 2,
- Figure 4 shows a partly transparent, side view of the braced
wing of Figure 2, seen from the transition region,
- Figure 5 shows a partly transparent, top view of one of the
braced wings of Figure 1 with a common transverse position of
respective wing roots, and
- Figure 6 shows a partly transparent, side cut view of the
braced wing of Figure 4.
Figure 1 shows a braced wing aircraft 1 with a fixed wing
arrangement la and a fuselage 6. The fixed wing arrangement la
preferably comprises two or more braced wings 2 that are
respectively provided with upper wings 3 and lower wings 4.
Illustratively, the fixed wing arrangement la comprises a first braced
wing 2a and a second braced wing 2b that are arranged laterally and
opposite to each other on the fuselage 6. The first braced wing 2a is
exemplarily mounted to a star board side of the braced wing aircraft 1
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and the second braced wing 2b is exemplarily mounted to a board
side of the braced wing aircraft 1.
According to one aspect, the braced wing aircraft 1 is provided
with suitable propulsion devices 5 and an empennage 7. Illustratively,
the propulsion devices 5 are embodied as puller propellers, but they
may likewise be embodied as pusher propellers. Likewise, the
propulsion devices 5 may be fixedly mounted or alternatively be
embodied as tilted rotor assemblies. Preferably, the propulsion
devices 5 are rigidly mounted at respective transition regions 9 of the
braced wings 2a, 2b.
According to one aspect, each one of the braced wings 2a, 2b
comprises at least one of the upper wings 3 and at least one of the
lower wings 4 which are staggered and interconnected at an
associated one of the transition regions 9. More specifically, the
.. braced wing 2a illustratively comprises an upper wing 3a and a lower
wing 4a which are staggered and interconnected at a first
predetermined transition region 9 that is associated with the braced
wing 2a. The braced wing 2b comprises an upper wing 3b and a lower
wing 4b which are staggered and interconnected at a second
predetermined transition region 9 that is associated with the braced
wing 2b.
Preferably, each one of the upper wings 3a, 3b is connected to
the fuselage 6 at an associated upper wing root 10 and each one of
the lower wings 4a, 4b is connected to the fuselage 6 at an
associated lower wing root 11. Each one of the upper wing roots 10
illustratively defines a transverse position 37a of the upper wing root
10 with respect to a longitudinal axis 8 of the braced wing aircraft 1.
The transverse position 37a of the upper wing roots 10 and the
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transverse position 37b of the lower wing roots 11 are distant from
each other resp. spaced apart in the longitudinal direction of the
braced wing aircraft 1, i. e. in direction of the longitudinal axis 8. This
distance resp. spacing apart of the transverse positions 37a, 37b
defines a respective stagger of the upper wings 3 and the lower wings
4 at the wing roots 10, 11, so that the upper wings 3a, 3b and the
lower wings 4a, 4b are said to be staggered.
By way of example, the braced wing aircraft 1 is embodied as an
airplane. However, the braced wing aircraft 1 may likewise be
embodied as a so-called convertiplane or as a rotary wing aircraft
with at least one main rotor on top of the fuselage 6.
Figure 2 shows the braced wing 2a of the braced wings 2 of the
braced wing aircraft 1 of Figure 1 for further illustrating an exemplary
internal constructional arrangement thereof. More specifically, an
internal arrangement and construction of the upper wing 3a, the lower
wing 4a as well as the respective predetermined transition region 9 of
the braced wing 2a is described in more detail hereinafter. However,
it should be noted that the braced wing 2a is only illustrated and
described with reference to Figure 2, as well as with reference to
Figure 3 to Figure 6, by way of example and representative for each
one of the braced wings 2a, 2b of Figure 1 or any other one of the
braced wings 2 of the braced wing aircraft 1 of Figure 1.
According to one aspect, the upper wing 3a comprises at least
one upper wing spar 14, 15 that extends from the upper wing root 10
to the predetermined transition region 9. Similarly, the at least one
lower wing 4a preferably comprises at least one lower wing spar 12,
13 that extends from the predetermined transition region 9 to the
associated lower wing root 11. Furthermore, preferably at least one
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transition spar 29, 28 is provided at the predetermined transition
region 9. The at least one transition spar 29, 28 preferentially
connects the at least one upper wing spar 14, 15 to the at least one
lower wing spar 12, 13. According to one aspect, the at least one
upper wing spar 14, 15, the at least one lower wing spar 12, 13, and
the at least one transition spar 29, 28 are arranged in a virtually
spanned spars plane 16a, 17a that is inclined with respect to a
vertical aircraft axis (32 in Figure 4).
More specifically, according to one aspect the upper wing 3a
comprises an upper wing rear spar 14, and an upper wing front spar
15. The lower wing 4a illustratively comprises a lower wing rear spar
12 and a lower wing front spar 13. Preferably, the transition region 9
is provided with a front transition spar 28 and a rear transition spar
29. The front transition spar 28 preferably connects the upper wing
front spar 15 to the lower wing front spar 13, and the rear transition
spar 29 preferably connects the upper wing rear spar 14 to the lower
wing rear spar 12 in the transition region 9.
According to one aspect, at least one of the upper wing rear and
front spars 14, 15, an associated one of the lower wing rear and front
spars 12, 13, and an associated one of the rear and front transition
spars 29, 28 are integrated into a single one-piece component.
Illustratively, the upper wing rear spar 14, the rear transition spar 29
and the lower wing rear spar 12 are integrated into a first single one-
piece component, i. e. an integral component, and the upper wing
front spar 15, the front transition spar 28 and the lower wing front
spar 13 are likewise integrated into a second single one-piece
component, i. e. an integral component.
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However, it should be noted that such an exemplary one-piece
integration of the upper wing rear and front spars 14, 15, the lower
wing rear and front spars 12, 13 and the rear and front transition
spars 29, 28 is merely described by way of example and not for
limiting the invention thereto. Instead, at least one of the rear and
front transition spars 29, 28 may be integrated into only one of the
respective upper wing rear and front spars 14, 15 or the lower wing
rear and front spars 12, 13 into a single one-piece component and
only be attached rigidly mechanically to the other one of the lower
wing rear and front spars 12, 13 or the upper wing rear and front
spars 14, 15. By way of example, the rear transition spar 29 may be
integrated into a single one-piece component with the lower wing rear
spar 12 and only rigidly mechanically attached to the upper wing rear
spar 14. Alternatively, the rear transition spar 29 could be integrated
into a single one-piece component with the upper wing rear spar 14
and only be rigidly mechanically attached to the lower wing rear spar
12, and so on. The mechanical attachments between the single
elements might be either a simple hinged joint, with the hinge axis
preferably oriented perpendicular to the corresponding virtual spar
plane, or a fully clamped joint.
However, it should be noted that likewise at least one of the
respective front and/or rear transition spars 28, 29 may only be rigidly
mechanically attached to the associated upper wing front or rear spar
15, 14 and to the associated lower wing front or rear spar 13, 12,
without being integrated into a single one-piece component with one
of the spars. In other words, e. g. the rear transition spar 29 may only
rigidly mechanically attached to the upper wing rear spar 14 and to
the lower wing rear spar 12.
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Moreover, it should be noted that the possible interconnections
between the upper wing front and rear spars 15, 14, the respective
front and rear transition spars 28, 29 and the lower wing front and
rear spars 13, 12 were merely described by way of example with
respect to the lower wing rear spar 12, the upper wing rear spar 14
and the rear transition spar 29. However, the described configurations
may likewise be applied to the upper wing front spar 15, the
associated front transition spar 28 and the lower wing front spar 13.
According to one aspect, the lower wing rear spar 12, the upper
wing rear spar 14 and the rear transition spar 29 are arranged in a
single virtually spanned rear spars plane 16a. This single virtually
spanned rear spars plane 16a is illustratively defined by a virtual
connection line 16 between respective rear spar roots 10, 11 of the
lower wing rear spar 12 and the upper wing rear spar 14, i. e.
between the upper wing root 10 and the lower wing root 11, a lower
wing rear spar centroidal axis 18 of the lower wing rear spar 12, and
an upper wing rear spar centroidal axis 20 of the upper wing rear spar
14.
Likewise, the lower wing front spar 13, the upper wing front spar
15 and the front transition spar 28 are arranged in a single virtually
spanned front spars plane 17a. The single virtually spanned front
spars plane 17a is preferably defined by a virtual connection line 17
between respective front spar roots 10, 11 of the lower wing front
spar 13 and the upper wing front spar 15, i. e. between the upper
wing root 10 and the lower wing root 11, a lower wing front spar
centroidal axis 19 that is defined by the lower wing front spar 13, and
an upper wing front spar centroidal axis 21 that is defined by the
upper wing front spar 15.
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Preferably, the single virtually spanned rear spars plane 16a is
inclined with respect to the vertical aircraft axis (32 in Figure 4).
Likewise, the single virtually spanned front spars plane 17a is
preferentially also inclined with respect to the vertical aircraft axis (32
in Figure 4). This is a result of the staggered arrangement of the
upper and lower wings 3a, 4a at their respective wing roots 10, 11.
According to one aspect, the single virtually spanned rear
spars plane 16a and the single virtually spanned front spars plane
17a are arranged in parallel to each other. However, such a parallel
arrangement is not mandatory and the single virtually spanned rear
spars plane 16a and the single virtually spanned front spars plane
17a may alternatively be inclined with respect to each other.
Furthermore, according to one aspect the front and rear
transition spars 28, 29 allow provision of a structural continuity of the
upper wing front and rear spars 15, 14 to the associated lower wing
front and rear spars 13, 12. Furthermore, by arranging the upper wing
front and rear spars 15, 14, the associated lower wing front and rear
spars 13, 12 and the structurally interconnecting front and rear
transition spars 29, 28 respectively in associated single virtually
spanned front and rear spars planes 17a, 16a, any kinks may be
omitted, thus, enabling provision of increased stiffness of the
arrangement.
Figure 3 shows the braced wing 2a of Figure 2 of the braced
wings 2 of the braced wing aircraft 1 of Figure 1 with the upper wing
.. 3a, the lower wing 4a and the transition region 9. According to one
aspect, the upper wing rear and front spars 14, 15, the lower wing
rear and front spars 12, 13 and the associated rear and front
transition spars 29, 28 of the braced wing 2a delimit a main load
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carrying center box 23 of the braced wing 2a. This main load carrying
center box 23 is mounted to a leading portion 23 of the braced wing
2a and a trailing portion 24 of the braced wing 2a.
More specifically, the main load carrying center box 23
preferably comprises an upper wing center box 25 and a lower wing
center box 26, as well as a transition box 27. Preferentially, the upper
wing center box 25, the lower wing center box 26 and the transition
box 27 that interconnects the upper wing center box 25 and the lower
wing center box 26 define an internal volume of the braced wing 2a.
According to one aspect, the lower wing rear spar 12, the rear
transition spar 29 and the upper wing rear spar 14 define in the
longitudinal direction along the longitudinal axis 8 of Figure 1 of the
braced wing aircraft 1 of Figure 1 a rear wall of the main load carrying
center box 23. Likewise, the lower wing front spar 13, the front
transition spar 28 and the upper wing front spar 15 form a front wall
of the main load carrying center box 23. This main load carrying
center box 23 is preferably rigidly attached to the leading portion 22
and the trailing portion 24 of the braced wing 2a.
Figure 3 further illustrates the arrangement of the lower wing
rear spar 12, the rear transition spar 29 and the upper wing rear spar
14 in the single virtually spanned rear spars plane 16a of Figure 2.
Illustratively, the lower wing rear spar 12, the rear transition spar 29
and the upper wing rear spar 14 are implemented as an integrated
single one-piece component, which is exemplarily slightly V-shaped
without any kinks.
This is exemplarily, by not necessarily, achieved by
implementing the rear transition spar 29 in ring-shaped form. An
opened C-Shape (i. e. a ring segment) is as well suitable.
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Furthermore, the lower wing rear spar 12, the upper wing rear spar 14
and the rear transition spar 29 are preferably implemented as flat and
straight longitudinal beams.
However, it should be noted that the above explanations refer to
the lower wing rear spar 12, the upper wing rear spar 14 and the rear
transition spar 29, which are illustratively highlighted in Figure 3,
merely by way of example and representative for all respective spars.
In other words, the above explanation preferably likewise applies to
the lower wing front spar 13, the front transition spar 28 and the
upper wing front spar 15.
Figure 4 shows the braced wing 2a of Figure 2 and Figure 3 of
the braced wings 2 of the braced wing aircraft 1 of Figure 1. In Figure
4, the braced wing 2a is seen from its outermost tip resp. the
transition region 9 in direction of the fuselage 6 of Figure 1, i. e. in
direction of the upper wing root 10 and the lower wing root 11 of the
braced wing 2a. In other words, the braced wing 2a is seen in a side
view, meaning in direction of a symmetry plane of the braced wing
aircraft 1 of Figure 1 which is defined by the longitudinal axis 8 of
Figure 1 and a vertical aircraft axis 32.
Figure 4 further illustrates the lower wing rear spar 12, the rear
transition spar 29 and the upper wing rear spar 14, which are
arranged in the single virtually spanned rear spars plane 16a of
Figure 2, and the lower wing front spar 13, the upper wing front spar
15 and the front transition spar 28, which are arranged in the single
virtually spanned front spars plane 17a of Figure 2. As described
above with reference to Figure 2, the single virtually spanned rear
spars plane 16a and the single virtually spanned front spars plane
17a are inclined with respect to the vertical aircraft axis 32.
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As described above with reference to Figure 2, the single
virtually spanned rear spars plane 16a is defined by the virtual
connection line 16, the lower wing rear spar centroidal axis 18 and
the upper wing rear spar centroidal axis 20. Likewise, the single
virtually spanned front spars plane 17a is defined by the virtual
connection line 17, the lower wing front spar centroidal axis 19 and
the upper wing front spar centroidal axis 21.
According to one aspect, the virtual connection line 16 extends
between respective upper wing and lower wing rear spar roots, i. e.
between the upper wing root 10 and the lower wing root 11. More
specifically, the virtual connection line 16 and the virtual connection
line 17 preferably extend between respective upper spars root
reference points 30 and respective lower spars root reference points
31. The upper spars root reference points 30 are preferably located at
the upper wing root 10 and the lower spars root reference points 31
are preferably located at a lower wing root 11. More specifically, the
upper spars root reference points 30 are defined by respective
intersections of the corresponding upper wing rear and front spars
centroidal axes 20, 21 at the upper wing root 10. Similarly, the lower
spars root reference points 31 are defined by the intersections of the
corresponding lower wing rear and front spar centroidal axes 18, 19
at the lower wing root 11.
According to one aspect, a most relevant impacting parameter
on the inclination of the single virtually spanned rear spars plane 16a
and the single virtually spanned front spars plane 17a is an
associated staggering angle 33 of the braced wing 2a. The staggering
angle 33 of the braced wing 2a is the angle that is defined between
the virtual connection lines 16, 17 and the vertical aircraft axis 32.
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Figure 5 shows the braced wing 2a of Figure 2 to Figure 4 of the
braced wings 2 of the braced wing aircraft 1 of Figure 1, with the
upper wing root 10 and the lower wing root 11. The upper wing root
is located at the transverse position 37a and the lower wing root
5 11 is located at the transverse position 37b, as explained above with
reference to Figure 1. However, in contrast to Figure 1 the transverse
positions 37a, 37b are now according to one aspect defined as a
common transverse position 37, i. e. they are exemplarily aligned in
longitudinal direction along the longitudinal axis 8 of the braced wing
10 aircraft 1 of Figure 1.
However, it should be noted that the arrangement of the upper
wing root 10 and the lower wing root 11 on the common transverse
position 37 is merely described by way of example and not for limiting
the invention thereto. Instead, as shown in Figure 1, differing
.. transverse positions 37a, 37b are likewise contemplated.
Figure 6 shows the braced wing 2a of Figure 4 of the braced
wings 2 of the braced wing aircraft 1 of Figure 1 with the upper wing
3a and the lower wing 4a, as well as the upper wing root 10 and the
lower wing root 11. In accordance with Figure 4, the upper wing 3a is
provided with the upper wing rear spar 14 and the upper wing front
spar 15 and the lower wing 4a is provided with the lower wing rear
spar 12 and the lower wing front spar 13. However, in contrast to
Figure 4, the upper and lower wings 3a, 4a are shown in sectional
view, i. e. the transition region 9 of Figure 4 is cut off in the
representation of Figure 6 by a plane parallel and offset from the
aircraft's symmetry plane. Thus, an exemplary implementation of the
upper wing center box 25 in the upper wing 3a and of the lower wing
center box 26 in the lower wing 4a can be illustrated in further detail.
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Illustratively, the upper wing 3a and the lower wing 4a
respectively comprise a chord line 35. Preferably, the single virtually
spanned front and rear spars planes 17a, 16a of Figure 4 are inclined
with respect to the chord line 35.
According to one aspect, the upper wing 3a and the lower wing
4a are configured such that they work together as a mechanical unit
so that the resulting principal axes of this mechanical unit are
inclined. Accordingly, the reference sign 34 labels a principal axis
with largest moment of inertia and the reference sign 36 labels a
principal axis with lowest moment of inertia, which is perpendicular to
the principal axis 34 with largest moment of inertia.
As can be derived from Figure 6, there is a comparatively big
difference between both principal moments of inertia, wherein the
principal axis 36 with the lowest moment of inertia typically
represents a weak point of the overall wing architecture of the braced
wing 2a as a result of respective relatively small wing chords.
Therefore, it is imperative to arrange as much material as possible as
far away from the principal axis 36 with lowest moment of inertia as
possible. Due to the inclination of the virtual rear spars plane 16a and
the virtual front spars plane 17a, the entire webs of the upper wing
rear and front spars 14, 15 and the lower wing rear and front spars
12, 13 are almost arranged in parallel to the principal axis 36 with
lowest moment of inertia and, hence, optimally placed in terms of
maximizing their contribution to the moment of inertia. It is clearly
visible from Figure 6 that the lower wing rear and front spars 12, 13
and the upper wing rear and front spars 14, 15 are inclined with
respect to the chord line 35, which is mainly a result of the wing
staggering, i. e. of the staggering angle 33 of Figure 4.
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It should again be noted that the above description mainly refers
to the braced wing 2a of the braced wings 2 of the braced wing
aircraft 1 of Figure 1. Furthermore, essentially only the respective
arrangement of rear spars and/or front spars in the braced wing 2a
are described in further detail. This is, however, merely
representative for all braced wings and all spar arrangements
according to the present invention. In other words, all teachings
related to the braced wing 2a may similarly be applied to the braced
wing 2b and all teachings that are merely described for either the rear
spars arrangement or the front spars arrangement may likewise be
applied to the front spars arrangement or rear spars arrangement,
vice versa.
Finally, it should be noted that further modifications are also
within the common knowledge of the person skilled in the art and,
thus, also considered as being part of the present invention.
By way of example, although the lower wing rear and front spars
12, 13, and the upper wing rear and front spars 14, 15, as well as the
rear and front transition spars 29, 28 were described with reference to
Figure 2 to Figure 6 as being flat beams, i. e. flat web beams, they
must not necessarily be designed as beam elements with fully flat and
closed webs. Instead, they may be provided as framework, as truss
construction, as beaded webs, as stiffened webs, as webs with
lightening holes or any kind of structural element that is, however,
preferably provided with a large in-plane bending stiffness and load
capability within the respective virtual plane. Furthermore, the rear
and front transition spars 29, 28, which were illustratively described
as being ring-shaped and enclosing a whole parameter of the
transition region 9 of the braced wing aircraft 1 of Figure 1, must not
necessarily be ring-shaped. Instead, they may respectively only cover
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a portion of the transition region 9, i. e. as a ring segment. According
to the wing spars, the transition regions may use as well any kind of
structural design providing a large in-plane bending stiffness and load
capability within the respective virtual plane. Furthermore, they can
be attached by any suitable means to the upper and lower wing spars,
either by means of a continuous or singular attachment.
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Reference List
1 Braced wing aircraft
la Fixed wing arrangement
2 Braced wings
2a, 2b Braced wing
3 Upper wings
3a, 3b Upper wing
4 Lower wings
4a, 4b Lower wing
5 Propulsion device
6 Fuselage
7 Empennage
8 Aircraft longitudinal axis
9 Transition region
10 Upper wing root
11 Lower wing root
12 Lower wing rear spar
13 Lower wing front spar
14 Upper wing rear spar
15 Upper wing front spar
16 Virtual rear spar roots connection line
16a Virtual rear spars plane
17 Virtual front spar roots connection line
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17a Virtual front spars plane
18 Lower wing rear spar centroidal axis
19 Lower wing front spar centroidal axis
20 Upper wing rear spar centroidal axis
21 Upper wing front spar centroidal axis
22 Braced wing leading portion
23 Main load carrying braced wing center box
24 Braced wing trailing portion
25 Upper wing center box
26 Lower wing center box
27 Braced wing transition box
28 Front transition spar
29 Rear transition spar
30 Upper spars root reference points
31 Lower spars root reference points
32 Aircraft vertical axis
33 Braced wing staggering angle
34 Principal axis with largest moment of inertia
35 Chord line
36 Principal axis with lowest moment of inertia
37 Common transverse position of wing roots
37a Transverse position of upper wing root
37b Transverse position of lower wing root
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