Note: Descriptions are shown in the official language in which they were submitted.
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COAXIAL ROTORNVING AIRCRAFT
FIELD OF THE INVENTION
The invention relates to a type of vertical take-off and landing aircraft
generally
referred as rotor/wing or stop-rotor aircraft.
BACKGROUND
One of the most promising vertical take-off and landing aircrafts (VTOL) is
known
as the stop-rotor or the rotor/wing aircraft. The concept behind this type of
aircraft is
using a set of wings selectively in a rotary-wing mode or in a fixed-wing
mode, in
order to produce vertical lift. In the rotary-wing mode, the rotor/wing
rotates in a
horizontal plane to produce vertical lift similar to a helicopter. In the
fixed-wing mode,
the rotation of the rotor/wing is stopped and positioned traverse to the
fuselage, in
order to produce vertical lift similar to the fixed wings of an airplane.
The rotor/wing aircrafts have many advantages over other concepts of VTOL
aircrafts such as, compound-helicopters, tilt-rotor aircrafts, and even
unpowered
rotary-wings aircrafts commonly known as gyroplanes. The wingspan of the rotor
/wing provides the equivalent of a rotor having a large diameter when
operating in a
powered rotary mode. This enables vertical take-off, vertical landing and
hover with a
low disc loading comparable to helicopters, thus requiring less power than
tilt-rotor
aircrafts and airplanes which have rotors of smaller diameter incorporated
inside
their fixed-wings. The ability to stop the rotation of the rotor/wing and use
alternative
more efficient propulsion systems for horizontal flight enable rotor/wing
aircrafts to
exceed the speed limitation of helicopters and achieve efficient high speed
flight
comparable to airplanes. This concept enables considerable down-sizing, cost
reduction and efficiency in the design of VTOL aircrafts and is desirable for
many
applications ranging from micro aerial vehicles, unmanned drones, and a wide
variety of manned vehicles for military, commercial and general aviation.
However
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rotor/wing aircraft remains a field of research. So far, no practical and
reliable
rotor/wings aircraft is known to exist till date.
The main problem in implementing the rotor/wing concept lies in the difficulty
to
achieve transition between the rotary-wing and the fixed-wing mode. As the
rotor/wing is slowed down to a stop, it becomes seriously affected by the
dissymmetry of lift caused by the advancing portion and retreating portion of
the
rotor/wing. At some point during transition, the retreating potion operates
entirely in
the reverse flow region. The aircraft experiences complete loss of lift on the
retreating side of the rotor/wings. The aircraft is subjected to dangerous
pitching,
io rolling movements and loss of altitude, with serious consequences.
Reduction of the
duration of the transition is often though of as a way to overcome the
problem.
However, it is physically not possible to reduce the transition time beyond
certain
point. Rotor/wings have increased dimension, weight, and rotational inertia,
and they
store significant amount of energy while in the rotary-wing mode. In
accordance with
is the action reaction principle, and conservation laws of energy and
momentum, the
transition between rotary-wing and fixed-wing mode induces destabilizing
reaction
forces on the fuselage of the aircraft. The strength of this reaction force is
inversely
proportional to the duration of the transition, and the duration of the
transition hence
dependents on the ability of the vertical tail stabilisers to compensate for
the sudden
20 and high reaction force acting on the fuselage. The vertical stabiliser
would need to
be excessively out of proportion to compensate the large reaction force and is
not
practical due to extra weigh and drag penalty. In several prior disclosures
the
rotor/wing is allowed to rotate in autorotation for some length of time until
it decays to
an acceptable level, before it can be stopped and locked in position. During
the
25 prologue transition, the aircraft is vulnerable as it continues to
experience unbalance
lateral lift.
The combination of these two forces makes transition between rotary-wing and
fixed-wing mode a critical and lengthy operation which most prior arts have
remained
incapable of dealing effectively. These problems are addressed mostly by
having
30 additional auxiliary fixed wings in order to assist the transition.
Sometime, rotor/wings
with more than 2 blades are proposed in order to reduce the lateral asymmetry
of lift.
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But these auxiliary wings and extra blades erode many of the advantages of the
aircraft in both flight modes, in the form of weigh penalty, increased
aerodynamic
drag and complexity. The operation requires complex coordination of control
surfaces on the auxiliary wings and vertical stabiliser, which are generally
operated
by sophisticated automated system in order to compensate the destabilizing
forces.
For example in US patent 3,327,969 the rotor/wing consisted of three blades
and
included an auxiliary wing in the form of an oversized lifting hub. In US
patent
5,454,530 a canard wing and a lifting tail was proposed to compensate for the
drop
and lateral asymmetry of lift during transition. The invention was implemented
in the
Boeing X-50 dragonfly, but experimentation was discontinued as the invention
failed
to give the expected result. In US patent 6,789,764 B2 and US patent 7,334,755
B2,
the disclosed aircrafts which consisted of tandem rotor/wings also relied
heavily on
auxiliary fixed wings to assist transition between flight modes.
A rotor/wing concept was disclosed in US patent 8,070,090, accordingly to
which,
the wings were made to flip in the direction of the wind to prevent the
condition of
reverse flow during transition. The invention also proposed to reduce the
disturbance
and deviation in flight path during transition by making conversion between
the two
flight modes by quickly stopping/or starting the rotation of the rotor/wing
within 2
seconds and less. The method, by which the reaction force on the fuselage is
countered, is not clearly commented. The invention was directed principally
for
unmanned aircrafts. Application of this concept in larger manned aircrafts may
be
complicated due to possible difficulty to flip larger and heavier set of
wings.
In US patent 7,665,688 B2 an aircraft was disclosed with a different concept
of
rotor/wing which maintained lateral symmetry of lift during transition, thus
enabling
reliable transition between the two flight modes. However this is achieved by
an
increase in complexity, as this arrangement requires a second vertical rotor
system,
consisting of two counter-rotating rotors with titling mechanisms and a set of
additional fixed wings. This arrangement is made compulsory because of the
particular configuration of the rotor/wing system. During the rotary-wing
mode, the
rotor/wing system produces lift which oscillates constantly forward and
backward,
longitudinally about the axis of rotation of the rotor/wing system. In order
to reduce
the resulting vibrations and potential effect on the stability of the flight,
the center of
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gravity of the aircraft is purposely located significantly far away from the
axis of
rotation of the rotor/wing system, somewhere between the two set of vertical
rotor
systems. During fixed-wing mode the second rotor system requires the addition
complexity of a tilt mechanism so that they can contribute to horizontal
flight, and the
vertical lift necessary to maintain balance is transferred to a lifting canard
wing. The
lifting canard wings may be a significant weight penalty during rotary-wing
mode.
The use of the second rotor system, selectively as a mean to produce
horizontal
trust during fixed-wing mode and as a vertical rotor system during rotary-wing
mode
generally results in a reduction of efficiency.
SUMMARY OF THE INVENTION
It is the main object of this invention to provide a method and system to
enable
efficient and safe transition between the two different flight modes in the
type of
aircraft generally referred as rotor/wing aircrafts or stop-rotor aircrafts.
Another objet of the invention is to provide a vertical take-off and landing
aircraft
capable of efficient rotary-wing mode, efficient fixed-wing mode and having
the ability
to transit rapidly between these two flight modes.
Another object of the invention is to provide for a low disc loading VTOL
aircraft
which has a high speed cruise capacity while having a moderate weight and
complexity penalty.
A further objet of the invention is to provide for a vertical take-off and
landing
aircraft having high speed, long range and high cargo capacity with increase
center
of gravity travel capability.
This is achieved as described in the preferred embodiment of the present
invention, by an aircraft comprising a second rotor/wing which is mechanically
connected to the first rotor/wing. The first rotor/wing connects to a
transmission shaft
above the fuselage and the second rotor/wing connects to another transmission
shaft at the bottom of the fuselage. During the rotary-wing mode the two
rotor/wings
rotate coaxially to produce vertical lift. In the fixed-wing mode the two
rotor/wings are
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stopped simultaneously transverse to the longitudinal axis of the fuselage and
produce vertical lift as fixed wings.
During transition between rotary-wing and fixed-wing mode, the synchronous
operation of the second rotor/wing with the first rotor/wing maintains lateral
balance
5 and vertical lift. Transition is stable without the aircraft losing
altitude and
experiencing any dangerous turning moment. As the reactions of the two
rotor/wings
on the aircraft due to sudden stopping or starting are also equal and
opposite, their
effects on the aircraft is cancelled. The rotor/wings can be started or
stopped very
rapidly without affecting the flight stability.
During the rotary-wing mode the second rotor/ wing improves the efficiency by
eliminating the need of an anti-torque device in the form of a lateral tail
rotor. The
coaxial operation of the two rotor/wings also provides a stable vertical
flight and
hover characteristic. During the fixed-wing flight mode, the second rotor/wing
may
contribute to vertical lift together with the first rotor/wing in a biplane
configuration
thus significantly reducing the wingspan of both rotor/wings. The existing
onboard
mechanism which operates the rotor/wings system can also be use to pivot one
of
the rotor/wing in alignment with the longitudinal axis of the fuselage so that
only a
single rotor/wing is used for higher speed. Similarly, both rotor/wings may be
pivoted
in an oblique position on either side of the fuselage for a high aspect ratio
configuration. The rotor/wings may also be folded in a variety of ways.
The claimed invention is a great improvement over the auxiliary fixed wings in
most prior arts. These auxiliary wings would assist only during transition
while
interfering negatively during both flight modes, whereas the second rotor/wing
in the
present invention contributes to both flight modes and enables a practically
smooth
and rapid transition between the rotary-wing and fixed-wing mode. As the two
rotor/wings are mounted on separate transmission systems they are less
complex.
The coaxial rotor/wing aircraft has the advantage of a very low weight and
complexity penalty and would offer a better transport effectiveness than
conventional
helicopters and airplanes. Another advantage of the coaxially connected
rotor/wings
is that the airfoil cross-section of the rotor/wings can be designed to have a
preferred
leading and trailing edge which is most efficient for fixed-wing mode. The
resulting
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imbalance lift of the two rotor/wings during rotary-wing mode compensates each
other, without the need of complex mechanism.
Manned aircrafts in the general aviation category and most particularly the
personal air vehicles commonly referred as PAV can greatly benefit from this
Embodiments of the invention have also wide surveillance and military
20 reconfiguration of the rotor/wings, high efficient subsonic or supersonic
speed
becomes possible.
Embodiments of the invention can have the comparable load capability of a
large
cargo or passenger tandem helicopter, with the range and speed of a jet liner,
by far
exceeding the abilities of current tilt-rotor aircrafts. The higher lift
requirement in such
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required in order to maintain longitudinal static stability under variable
center of
gravity location depending on loading condition.
BRIEF DESCRIPTION OF THE DRAWINGS
The preferred embodiments of the present invention are described in detail
with
reference to the following drawings:
FIG. 1 is a perspective view of the preferred embodiment of an aircraft in
accordance with the disclose invention, shown in fixed-wing flight mode.
FIG. 2 is a perspective view of the aircraft in FIG. 1, shown in rotary-wing
flight
mode.
FIG.3 is a schematic layout of the rear part of the aircraft in FIG. 1, and
shows the
main components of the coaxial rotor/wings in accordance with the invention.
FIG. 4 is the side view of another embodiment of the rotor/wing aircraft
according
to the invention, shown in fixed-wing flight mode.
FIG. 5 is the top view of the embodiment of the aircraft in FIG. 4, shown in
fixed-
wing flight mode.
FIG. 6 is the front view of one variation of the embodiment of the aircraft in
FIG. 4,
with the tips of the lower rotor/wing folded downward, during fixed-wing
flight mode.
FIG. 7 is the front view of a variation of the embodiment of the aircraft in
FIG. 4,
zo with
the both rotor/wing folded in a cross-wing configuration, during fixed-wing
flight
mode.
FIG. 8 is a top view of another embodiment of an aircraft shown in fixed-wing
mode with both wings pivoted in an oblique position.
FIG. 9 is a perspective view of an aircraft for higher load capacity,
consisting of
two set of coaxial rotor/wings and a main fixed-wing, shown during fixed-wing
flight
mode.
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DETAILED DESCRIPTION OF THE INVENTION
The invention is described mainly with reference to the embodiment of an
aircraft
shown FIGS.1-3, and with cross reference to other embodiments as shown in the
accompanying drawings. In the drawings FIGS. 1-8, corresponding components are
designated by the same numerals. In FIG. 9, different numbers are used to
designate similar components.
Concept and structure:
The aircraft 100 is shown in a fixed-wing flight mode in FIG. 1 and in a
rotary-wing
flight mode in FIG. 2. The aircraft 100 comprises an upper rotor/wing 102
which is
rotatably coupled to the fuselage 101 on top of a mast fairing 104, and a
lower
rotor/wing 103 which is rotabably coupled to the fuselage 101 below a mast
fairing
105. These mast fairings 104 and 105 are streamlined in order to reduce
aerodynamic drag and also enclose the transmission shafts, control devices and
other components which secure the rotor/wings 102 and 103 to the fuselage 101.
In
aircraft 100, the mast fairings 104 and 105 also comprise the vertical
stabilisers, and
instead of a conventional rear tail a canard wing 109 is used for pitch
control. The
mast fairing 104 is comparatively longer than the lower mast fairing 105. This
lower
the center of gravity of the aircraft 100 below the combined center of lift of
the two
rotor/wings, and provide a stronger supporting structure for the landing
gears, which
is connected at the underside of the lower rotor/wing 103. However in some
other
embodiments, the mast fairings 104 and 105 may be equal in length and
symmetrical. In other embodiments as shown in FIG 4-8, the upper mast fairing
104
and the lower mast fairing 105 may be designed relatively very short for
increased
structural strength. Separate vertical stabilisers or equivalent devices need
to be
provided. As shown in FIG. 8 the aircraft 202 comprises conventional vertical
stabilisers 113 and rear tail 112.
The fuselage 101 accommodates the passenger or payload compartment at the
front and the mechanical compartment at the rear, in an arrangement which is
most
common in rotary aircrafts. As shown in FIG. 3, the mechanical section
comprises
the main power components such as the engine 11, the transmission system for
the
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rotor/wings 102 and 103, the power source or the fuel tank 10, and other
essential
components necessary to enable safe and reliable flight in both flight modes.
The rotor/wings 102 and 103 are coaxial and mechanically linked together. The
rotor/wings 102 and 103 rotate at the same speed and are in phase, where the
leading edge of the upper rotor/wing 102 is the mirror image of the leading
edge of
the lower rotor/wing 103 along the longitudinal axis of the fuselage 101. As
shown in
FIG. 3, the upper rotor/wing 102 is coupled to the transmission 14 by means of
a
transmission shaft 18 which comprises the swash plate 12 and the control rods.
Similarly, the lower rotor/wing 103 is coupled to the transmission gear 15 by
means
1.0 of a
transmission shaft 19, which comprises the swash plate 13 and the control
rods.
The transmissions 14 and 15 connect to the drive shaft 21 of the engine 11
through
a gearbox 16. The gearbox 16 divides the output of the drive shaft 21 into two
identical counter-rotating drive shafts which connect to the respective
transmissions
14 and 15. The gearbox 16 is coupled to the engine shaft 21 through a clutch
17,
which allows the engine shaft 21 to be engaged or disengaged from the gearbox
16,
depending on the flight mode. The transmissions 14 and 15 remain mechanically
connected by mean of the gearbox 16 during both rotary and fixed-wing mode.
The
swash plates 12 and 13 enable to access and operate the control surfaces on
the
rotor/wings 102 and 103 in both flight modes.
During transition from rotary-wing to fixed-wing flight mode, the rotor/wings
102
and 103 are slowed and stopped simultaneously transverse to the longitudinal
axis
of the fuselage 101, as shown in FIG. 1. During this operation, the clutch 17
disconnects the engine shaft 21 from the transmission system of the
rotor/wings 102
and 103 and a positioning mechanism 20 is activated. The positioning mechanism
20 slows down and stops the shaft 22 so that the rotating wings 102 and 103
are
aligned in a biplane configuration as shown in FIG. 1. The simplest embodiment
of
the positioning mechanism would consist of a drum and frictional pad
arrangement to
produce the strong braking force, and a spring driven or motor driven
mechanism to
stop the shaft 22 is a specific position. The rotor/wings 102 and 103 are then
secured to the fuselage 101 by locking mechanisms 23 and the control surfaces
on
the rotor/wings are adjusted for fixed-wing mode so as to produce aerodynamic
lift
as fixed wings. The synchronized operation of the rotor/wings 102 and 103
ensures
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that the dissymmetry of lift of the first rotor/wing is compensated by the
dissymmetry
of lift of the second rotor/wing, thus lateral balance is maintained
throughout the
transition. At the same time, the reaction force on the fuselage 101 by of the
rotor/wings 102 and 103 mutually cancel themselves as the forces are equal and
5 opposite in direction, provided of course the rotor/wings 102 and 103
have similar
rotational inertia. During transition from fixed-wing mode to rotary-wing
mode, the
lateral balance is also maintained and the reaction force of the rotor/wings
102 and
103 also cancel mutually. In this case the rotor/wings 102 and 103 are
unlocked and
set in rotation when the clutch 17 couples the gearbox 16 to the engine 11.
The
10 control surfaces on the rotor/wings 102 and 103 are adjusted for rotary-
wing mode
so as to produce vertical lift.
The propeller 106 provides horizontal trust during both flight modes. The
propeller
106 and the rotor/wings 102 and 103 are powered by the same engine 11. During
rotary-wing mode, most of the power of the engine 11 is diverted to drive the
rotor/
wings 102 and 103 and a smaller portion is diverted to the propeller 106.
During
fixed-wing mode, all the power is diverted to the propeller 106. The propeller
106
may be ducted or even of the contra-rotating type. The engine 11 may consists
of
several interconnected engines for increased reliability, and could be of a
variety of
types suitable for aircrafts, such as piston engines, jet engines, gas
turbines, wankel
engines, or electrical motors. In other embodiments, multiple engines may be
installed on either side of the fuselage 101, as shown in FIG. 4-7. In some
other
embodiments the engine 11 may be located at some other location and the
aircraft
100 in puller or puller/pusher propeller configuration. In another embodiment
202 as
shown in FIG. 8 the jet engines 120 are installed in the rear of the fuselage
101 with
air-intakes 121 on either side at the front, in an arrangement most familiar
with
supersonic aircrafts.
In aircrafts equipped with jet engines or gas turbines, the rotor/wings 103
and 104
can be powered in either a conventional way as explained earlier, or in a tip
jet
propulsion arrangement. The tip jet arrangement is popular in rotor/wing
aircrafts
because it eliminates the need of an anti-torque device during the rotary-wing
mode.
But these aircrafts experience the same destabilizing forces explained earlier
during
transition between flight modes, and these problems are overcome in a similar
way
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as described earlier by the coaxial rotor/wings arrangement. In these
aircraft, the
upper rotor /wing 102 and the lower rotor/wing 103 remain mechanically,
connected
even if the tip jets are installed in one or both rotor/wings. The drive shaft
21 and
clutch 17 are replaced by ducting and other components particular to tip jet
systems
and the transmissions systems are designed less robust and simpler. The
transmissions 14, 15 and the gearbox 16 are used to synchronise the rotation
and
relative position of the two rotor/wings 102 and 103, and at the same time to
couple
and cancel the turning moments generated by each rotor/ wings, as the result
of lift
asymmetry and reaction forces on the fuselage 101 due to operation of the
rotor/wings, during transition.
The preferred embodiments comprises as explained above, an upper rotor/wing
102 and a lower rotor/wing 103 on separate shafts and separate transmission in
a
coaxial arrangement, because this configuration is the most efficient,
reliable and
easy to implement. However, those skilled in the art will understand that a
plurality of
rotor/wings may be mounted to the fuselage in a counter-rotating configuration
and
operated together in coordination so as to reduce the destabilizing forces
during
transition. For example the rotor/wings may be arranged in a tandem
configuration.
Similarly two smaller rotor/wings may be operated in counter-rotation with a
larger
rotor/wing. These rotor/wings may be located above or below the fuselage. In
fixed-
wing mode the aircraft can take a variety of configuration depending on the
position
of the rotor/wings, such as staggered biplane, tandem or triplet wings. The
plurality
of rotor/wings of different dimension and varied location on the fuselage may
have
different operating parameter in order to reduce lateral unbalance during
transition.
It has to be noted that herein, the term `rotor/wing' may have a variety of
constructional embodiment. The rotor/wings may be constructed similar to
helicopter
rotor comprise of a plurality of wings mounted on a rotor hub, whereby the
rotor hub
by a transmission shaft in order to produce vertical lift during rotary-wing
flight mode,
and where these rotor/wings also produce aerodynamic lift similar to fixed
wings
when the rotor is locked during fixed-wing flight mode. It should also be
noted that
the term 'blades' is often used to refer to rotating wings mounted on a rotor
hub.
Similarly the rotor/wing may be constructed similar to convention fixed wing,
comprising of one continuous transversal panel mounted at its mid section on a
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rotating support or hub. The term coaxial rotor/ wings herein, refers to a set
of two
rotor/wings which are mounted on the same vertical axis and rotate coaxially
and in
phase relative to each other, and where these two rotor/wings are
simultaneously
stopped or set in rotation. The coaxial and synchronous operation of these
rotor/wings may be achieved by a variety of means, comprising mechanical gears
or
other electromechanical, electromagnetic, pneumatic, hydraulic or equivalent
devices which enable the coupling and canceling of the forces transmitted by
the
rotor/wing to the fuselage of the aircraft.
Rotary-wing flight mode:
1.0 During
the rotary-wing mode, the aircraft 100 is able to take off vertically, land
vertically, hover and fly at low speed (speeds that are below the stall speed
of the
fixed- wing mode) with a high degree of manoeuvrability and efficiency,
similar to
helicopters. The aircraft 100 is operated in the same manner like a helicopter
with
coaxial rotors
The two rotor/wings 102 and 103 mutually cancel the turning moment on the
fuselage 101 and hence eliminate the need of an anti-toque device as required
in
helicopters with single rotor or in aircraft with single rotor/wing driven by
a
conventional transmission. The coaxial rotor/wings provide all the advantages
related to helicopters with coaxial rotors, such as: a smaller wingspan; high
stability
during vertical lift; lower noise; lower vibration; and higher efficiency. The
mechanical
complexity is reduced given that the rotor/wings 102 and 103 are installed on
separate transmissions 18 and 19, mounted on separate mast fairings 104 and
105.
As shown in FIG. 3, during rotary-wing mode the clutch 17 connects the shaft
21
to the shaft 22 so the engine 11 drives the upper transmission shaft 18 and
the lower
transmission shaft 19 coaxially. The shafts 18 and 19 drive their respective
rotor/wings 102 and 103 through appropriate coupling mechanisms and hub
assemblies. Vertical lift is obtained by collectively changing the pitch of
the
rotor/wings 102 and 103, or control surfaces or flaps. The lift acts through
the axis of
rotation of the rotor/wings. The center of gravity of the aircraft 100 is
located below
and in alignment with the center of lift generated by the two rotor/wings 102
and 103
for stability. The aircraft 100 may include means to compensate for unequal
payload
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distribution by shifting the center of gravity of the aircraft to the optimum
location,
such as redistribution of fuel in several ballast tanks.
Horizontal flight in rotary-wing flight mode is achieved principally by the
propeller
106 alone, or in some embodiments in combination with cyclic control of the
rotor/
wings102 and 103 for higher agility and manoeuvrability. The yaw control and
steering is achieved by mean of conventional helicopter devices or controlled
dissymmetry of torque in the rotor/wings 102 and 103 as used in coaxial
helicopter.
In the prefer embodiments, this is achieved by lateral thrusters 107 located
on either
side of the nose end encased in the fuselage 101 so that they do not create
aerodynamic drag during forward flight. Vertical thrusters 108 are also fitted
as
shown in aircraft 100 and the other preferred embodiments on the top and
bottom
side of the fuselage 101 so as to provide additional flight control during
hovering and
slow forward flight. These thrusters 107 and 108 are powered by compressed air
from the engine 11 or the exhaust (not shown).
Fixed-wing flight mode:
During fixed-wing mode the rotor-wings 102 and 103 are positioned in a biplane
configuration and firmly secured to the fuselage 101 by a set of locking
devices 23.
The corresponding leading and trailing edges of the rotor-wings 102 and 103
are
configured for fixed-wing flight mode so that at least one of the rotor/wing
produces
vertical aerodynamic lift like fixed wings, and the propeller 106 providing
horizontal
trust. The aircraft 100 is operated in the same manner like an airplane by
mean of
flight control surfaces on the rotor/wings 102 and 103, and the vertical
stabilisers
incorporated in the mast fairings 104 or 105. The preferred embodiments 100
and
200 include a canard wing 109 at the front for improved pitch control in the
fixed-
wing mode, instead of a tail wing. The canard wing 109 is preferably on the
top of the
fuselage 101 so as to ensure good downward visibility for the pilot and
passengers.
During rotary-wing mode the canard wing 109 is may be retractable or foldable
to
ensure improved upward visibility during slow maneuver. In other embodiments
as
shown in FIG. 8, a rear horizontal stabiliser 112 may be used, instead of, or
in
combination with a canard wing.
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For embodiments of the invention within the range of 300km/hr similar to
personal aircraft both rotor/wing may used to produce vertical lift. Biplanes
have
comparable efficiency to single wing aircraft with some extra advantage.
Biplanes
have smaller wing span and generate more lift for the same platform area. The
wingspan may be reduced even further, considering that aircrafts that take-off
and
land vertically, do not need wings with large platform area, resulting in
reduced drag.
Biplanes are still by far more efficient and faster that helicopters.
For even greater speed, the initial biplane configuration can be modified
further
during fixed-wing mode. As shown in FIG. 8, the rotor/wings 102 and 103 of the
1.0 embodiment 202 may be pivoted about their transmission shafts, so that
they form
two symmetrically opposing oblique wings with a high aspect ratio. This is
carried out
by the positioning mechanism 20 turning the shaft 22 by a certain define
amount. In
other embodiments, the aircraft may include feature which independently
position the
rotor/wings so that one rotor/wing is aligned with the longitudinal axis of
the fuselage
and the other rotor/wing is maintained transverse to the longitudinal axis or
in an
oblique orientation to the fuselage to provide lift in a single wing
configuration.
In some other embodiment the lower or upper or both rotor/wings may be
retracted or folded in a variety of ways so as to operate as vertical
stabiliser. For
example as shown in FIG. 6, sections of the lower-wing 103 are folded downward
and used as twin vertical stabilisers. In other embodiments, the lower/wing
103 may
be flipped in an inverted V-tail configuration. In yet other embodiment 201 as
shown
in FIG. 7, the rotor/wing 102 is folded upward in a dihedral configuration and
the
second rotor/wing 103 is folded downward in an anhedral configuration. This
configuration reduces the interference between the two rotor/wings and at the
same
time operates as vertical stabilisers. As shown in FIG. 4-7, in the
embodiments of the
aircraft designed for high speed, the masts fairing 104 and 105 are built
short so as
to provide stronger support for the rotor/wings.
In the fixed-wing mode, the center of lift of the aircraft 100 is ahead of the
axis of
rotation of the rotor/wings, at about the quarter-chord point from the leading
edge of
the rotor/wings 102 and 103. In order to maintain longitudinal static
stability, the
center of gravity of the aircraft 100 is shifted forward, ahead of the center
of lift acting
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on the aircraft. The passenger or payload compartment which is mounted in a
telescopic arrangement with the rear part of the fuselage 101, slides forward
at the
junction 110 by a define amount, driven by actuators and secured by
appropriate
locking devices(not shown). This arrangement changes the aircraft 100 in a
nose
5 heavy configuration, which is particularly advantageous for personal
aircraft. In the
event of engine failure, the aircraft will assume a normal glide for a safe
landing. In
embodiment shown in FIG. 4, the canard wing 109 produces a negative lift so as
to
displace the neutral point backward, without displacing the center of gravity
of the
aircraft 200. In other embodiment 202 as shown in FIG. 8, a tail wing 112
would
io produce the same effect by producing a positive lift. In yet another
embodiment the
center of gravity may be shifted by displacing a define amount of fuel between
ballast tanks at the extreme ends of the aircraft. It is understood that
addition
horizontal and vertical stabilisers may be included as dictated by the
aircraft
configuration and the laws of aerodynamic.
15 Transition between flight modes:
Transition from rotary-wing mode to fixed-wing mode is carried out when the
aircraft exceeds the horizontal stall speed by a certain safety margin.
Transition is
completed when the longitudinal static stability of the aircraft 100 is
adjusted by
displacing the center of gravity forward or by a negative lift by the canard
wing 109 in
aircraft 200.
During transition, the coaxial rotor/wings 102 and 103 continue to produce
vertical lift which is laterally balanced. The vertical lift during transition
is easily
maintained constant by collective control of the control surfaces on the
rotor/wings
102 and 103. The equal and opposite reaction forces of the coaxial rotor/wings
102
and 103 on the fuselage 101 cancel each other, while the rotor/wings are being
slowed and stopped. The rotor/wings can hence be stopped very quickly if
required.
However, since lateral balance of lift and vertical lift are maintained during
the
transition, it becomes no longer necessary to make transition rapidly.
Transition
becomes a safe, smooth and simple operation, which can be carried out quickly
or
gradually. As the aircraft does not suffer loss of altitude, transition may be
carries out
CA 02776121 2012-04-30
16
safely at low altitude. The transition process is very reliable as it does not
require
complex control operation.
Transition from fixed-wing mode to rotary-wing mode is carried out in reverse
sequence at the minimum safe horizontal speed for fixed-wing flight. The
center of
gravity of the aircraft 100 is gradually shifted backward and aligned with the
axis of
rotation of the rotor/wings. The rotor/wings 102 and 103 are reconfigured for
rotary-
wing mode, unlocked and set in rotation as the clutch 17 connects the engine
shaft
21 and the input shaft 22 of the gearbox 16. The coaxial rotor-wings maintain
lateral
lift and cancel all turning moments on the fuselage and enable rapid and
smooth
transition to rotary-wing mode. The canard wings 109 may be folded or
retracted,
and the aircraft is operated like a conventional coaxial helicopter.
The twin coaxial rotor/wings 102 and 103 do not operate in severe high speed
condition since transition to fixed-wings mode is carried out at much lower
horizontal
speed, where problems such as flapping of the wings and vibration is not of
great
concern. Vibration during rotary-wing mode and transition is less severe and
may be
efficiently damped by appropriate damping mechanisms.
Landing gears:
Rotor/wings aircrafts in the present invention retain the ability to take-off
and land
in either fixed-wing or rotary-wing mode. This is a desirable feature since in
fixed-
wing mode the aircraft would have a higher payload. Such an aircraft can take
off in
a fixed-wing mode with a higher load of fuel for long rang operation, and once
the
extra fuel has been used the aircraft can operate in both flight mode.
Similarly, the
aircraft may land in a fixed-wing mode in case of some transmission or engine
failure. Hence the aircraft would in most embodiments include landing gears
suitable
for fixed-wing mode and rotary mode. The landing gears for fixed-wing mode may
consist of a classical tricycle arrangement, with one set of wheel at the
front and two
set of wheels at the rear. The rear wheels can be deployed from cavities in
the lower
wings 103, or from either side of the fuselage 101 (not shown).
Vertical take-off and landing in rotary-wing mode in most embodiments of the
aircraft is achieved by means of a different landing gear which is found at
the
underside of the lower rotor/wing 103. The landing gear as shown in FIG. 3
CA 02776121 2012-04-30
17
comprises of a platform 24 which connects to the inside non-rotating part of
the
aircraft by mean of an extension shaft 25, passing through the transmission
shaft 19
of the lower rotor/wing 103 which is hollow. The platform 24 is centered on
the axis
of rotation of the rotor/wings which is also in alignment with the center of
gravity of
the aircraft 100 during rotary-wing mode. The platform 24 is wide enough to
provide
a stable support to the aircraft and remain stationary when the rotor/wing 103
is
rotating. The extension shaft 25 is supported inside the hollow transmission
shaft 19
on bearings arrangement so as to reduce friction between them. The shaft 25 is
long
enough in order to provide sufficient clearance between the lower rotor/wing
103 and
the ground surface.
In more elaborate landing gears as shown in FIG. 3 the platform 24 may be
locked in one position close to the fuselage 101 so as to reduce aerodynamic
drag
and in another position in order to allow easy access to the cabin. The lower
and
upper transmission shafts 18 and 19 are both made hollow so that the shaft 25
can
travels freely inside. The side of the shaft 25 comprise a rack 26 which
meshes with
a pinion 27. Rotation of the pinion 27 allows the shaft 25 to be raised or
lowered as
required and locked in the required position by a device 28. The pinion 27 can
be
driven from power derived from the main engine 11 or from a separate motor.
When the aircraft is ready to take-off, the shaft 25 is pulled out to its
maximum
extended position so as to provide maximum clearance between the ground and
the
rotor/wing 103 for safety reason, before the rotor/wings are set in rotation.
Once the
aircraft is off the ground the platform 24 is pulled closer to the fuselage
101 in some
intermediate position within a safe minimum clearance from the rotating wings
103,
in order to reduce drag. During the fixed-wing mode, the platform 24 may be
pull
further in close contact with the lower rotor/wing 103 so as to reduce drag
further.
The platform 24 could consist of a simple frame or a body as shown in FIG. 6
and
FIG. 7 that could contain several other devices such as retractable wheels,
useful for
parking or landing in airplane mode. Similarly, the platform 24 may include
various
anchoring device which hold the aircraft firmly to the ground, until the
vertical lift has
reached a desired level to enable a rapid ascend, and at the same time to
overcome
the ground effect phenomena and avoid sideway drifts. One such anchoring
device
CA 02776121 2012-04-30
18
may comprise of a cavity in the underside of the platform 24 at the surface of
contact
with ground, and which is kept at low pressure by a vacuum pump or by the
suction
of the engine until the aircraft is allowed to take-off.
Multiple coaxial rotor/wing aircrafts:
FIG. 9 shows the preferred embodiment of an aircraft 300 designed for large
cargo, consisting of more than one set of coaxial rotor/wings in order to
generate
greater lift. The aircraft 300 comprised of two set of coaxial rotor/wing
mounted at the
front end and the rear end of the fuselage 301, referred respectively as the
canard
3.0 rotor/wing and a tail rotor/wings. The coaxial rotor/wing at the front
end comprises of
the upper rotor/wing 402 and a lower rotor/wing 403 mounted coaxially on their
respective mast fairings 404 and 405. The coaxial rotor/wings at the rear
arrangement comprises of an upper rotor/wing 302 and lower rotor/wing 303
mounted coaxially on their respective mast fairing 304 and 305. The coaxial
rotor/wings are powered by twin jet engines 320 at the rear on either side of
the
fuselage 301. The jet engines 302 also provide horizontal trust in both flight
modes.
It is understood that the two coaxial rotor/wings may be of different wingspan
and
installed on mast of different height so as to minimise interference between
them.
Similarly the two set of coaxial rotor/wings may be mechanically
interconnected, as
they may not necessarily be connected and hence operated at different
rotational
speed during rotary-wing mode. In both case the coaxial rotor/wings are
controlled
independently.
In some embodiment the two set of coaxial rotor/wings, may be sufficient to
sustain vertical lift during rotary-wing mode and during fixed-wing mode in a
tandem
biplane configuration. In other embodiments designed for even heavier load
more
than two set of coaxial rotor/wings may be required. The wingspan of coaxial
rotor/wings is significantly smaller than single rotor/wing, for the same
lift. However
the wingspan of the rotor/wings may have to be limited in order to avoid
overlapping
between the multiple set of coaxial rotor/wings. The rotor/wings in such large
aircraft
may have to operate in a medium or higher disc loading during the rotary-wing
mode
and these rotor/wings alone may not produce enough vertical lift during fixed-
wing
CA 02776121 2012-04-30
19
mode. This problem is solved by means of a set of permanent fixed wing 311 at
about the middle section of the fuselage 301. During fixed-wing mode, the
permanent fixed wing 311 provides most of the vertical lift same like the main
wing in
an airplane, whereas the coaxial rotor/wings are used as canard and tail wings
in a
biplane configuration, as shown in FIG. 9. Vertical stabilisers 312 are
provided on the
tip of the fixed wing 311. Alternatively a rear vertical stabiliser may be
mounted at the
rear, or the rotor/wings 302 and/or 303 folded in order to act as vertical
stabilisers.
Depending on the location of the center of gravity of the aircraft, which may
variable
due to loading condition, the rotor/wings 302 and 303 at the rear, and the
rotor/wings
lo 402 and
403 are configured to produce vertical or negative lift as required, in order
to
maintain longitudinal stability during fixed-wing mode. Similarly, during
rotary-wing
mode, the vertical lift of the coaxial rotor/wings at the front and at the
rear may also
differ depending on the variable loading condition.
The jet engines 320 provide the horizontal trust for the aircraft 300 to move
forward. The aircraft 300 includes horizontal and vertical thrusters or
equivalent
devices for steering and flight control in the rotary-wing mode (not shown).
Transition
between rotary-wing mode and fixed-wing mode takes place when the fixed wing
311 generates enough vertical lift to sustain the aircraft 300 in fixed-wing
mode. The
ability of the coaxial rotor/wings to be stopped or started quickly without
affecting the
stability of the aircraft enable the different set of coaxial rotor/wings to
be slowed
and stop for fixed-wing mode simultaneously for a fast transition. The two
sets of
coaxial rotor/wings may also be operated sequentially and gradually for a very
smooth transition between the two flight modes in coordination with the fixed
wing
311.
The aircraft 300 equipped with appropriate landing gears (not shown) retains
the
ability to take-off and land on a runway like an airplane to carry a greater
payload.
Such an aircraft could take off in fixed-wing mode with a higher payload of
fuel or
troops and then continue its operation in dual flight modes when the load has
been
reduced.
The preferred embodiments of the invention as illustrated in the accompanying
drawings and descriptions are applicable for manned or unmanned aircrafts of
wide
CA 02776121 2012-04-30
range of size whether for military, commercial or personal use. The embodiment
100
as shown in FIG. 1 and FIG. 2 is most appealing for aircrafts in the range of
speed
and characteristics of small personal aircrafts, unmanned drones and micro
aerial
vehicles, due to a compact design. Embodiment 200 as shown in FIG. 4 and FIG.
5
5 is fitted with twin jet engines and is suitable for high speed manned or
unmanned
aircrafts. As vertical stabiliser are most useful in fixed-wing mode, and as a
way of
reducing the drag and mass penalty due to a tail wing and fuselage extension
at the
rear to support the wings, the rotor/wings are folded in a variety of ways as
shown in
FIG. 6 and FIG. 7 after transition to fixed-wing mode to serve as a vertical
stabiliser.
10 Embodiment 202 as shown in FIG. 8 is a very high speed aircraft suitable
for military
application. The aircraft has a conventional fighter aircraft configuration
with rear tail
112 and vertical stabilisers 113 in H-configuration, and achieve very high
speed with
high efficiency by pivoting the wings 102 and 103 in an oblique wings
configuration
as shown. The aircraft 202 is powered by a single or more jet engines 120 with
twin
15 air-intakes 121 at the front. Embodiment 300 in FIG. 9 comprises a
tandem coaxial
rotor/wings convenient for larger aircrafts with increased cargo capacity,
suitable for
military and civil application. All the embodiments of the invention retain
the full
operational advantage of a typical helicopters and an airplane. The safety of
these
types of aircrafts is enhanced because of reduction in complexity and safe
transition.
20 In case of engine failure these aircrafts may land in emergency in a
gliding mode or
in autorotation.
While the invention has been describe in detail with refer to some specific
embodiments, it is understood that various variations may still be made
without
departures from the spirit and scope of the invention, and that the
specification and
drawings are to be considered as merely illustrative and not limiting:
