Note: Descriptions are shown in the official language in which they were submitted.
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Electrical powered tail rotor of a helicopter
Technical Field
The invention is related to an electrical powered tail rotor of a
helicopter.
Background of the Invention
The power consumed by a tail rotor of state of the art
helicopters is supplied from a central energy generator via a main
gear box, a plurality of intermediate gears and a tail rotor shaft. By
removing the main gear box and the rigid mechanical coupling
between energy generator and tail rotor more design flexibility for
the helicopter may be attained. One of the keys to realise an
electrical powered tail rotor of a helicopter is a suitable electrical
motor.
The document US 2004051401 A1 discloses an electric motor
for rotating an object around a central axis. The electric motor
includes a motor casing. A circular segmented rail element is
disposed within the motor casing about the central axis. The
circular segmented rail element includes metallic non-ferrous
segments interleaved with non-metallic segments. Each of the
metallic non-ferrous segments has a predetermined segment
length. At least one coil element is connected to the motor casing.
The circular segmented rail element is disposed adjacent the at
least one coil element. The at least one coil element has a
predetermined coil length that is less than or equal to the
predetermined segment length. The at least one-coil element is
configured to apply electromagnetic energy to the circular
segmented rail element, such that the circular segmented rail
element rotates around the central axis.
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The document WO 0184063 A2 discloses a stator assembly
for a brushless DC ring motor for a cooling fan piloted on the stator
assembly. A ring supports a plurality of fan blades for sweeping an
area inside the shroud. A rotor assembly for the brushless DC ring
motor is attached to the ring of the cooling fan. The rotor assembly
confronts the stator assembly around an outer diameter of the
stator assembly. The cooling system is controlled by an electronic
controller to rotate the cooling fan to provide appropriate cooling
for the vehicle.
A hybrid helicopter drive has been proposed in the document
"The Hybrid Helicopter Drive, ... by Peter Janker et al. at Europ.
Rotorcraft Forum, Sept. 2010" with an integration of an electrical
motor for a Fenestron tail rotor. The electrical motor is realised by
so called disc shaped electrical "Trans-Flux-Motors" with increased
pole numbers. The electrical "Trans-Flux-Motor" for the Fenestron
tail rotor is conceived as a torus around the Fenestron opening, the
blade tips of the tail rotor being fixed to its rotating component. An
electrical "Trans-Flux-Motor" is presented in document DE 10 2007
013 732 A1.
The document DE 102007013732 A1 discloses a direct drive
with a stator and one or multiple support rings that are made of
plastic. The support rings supports the permanent magnets that are
arranged in two or more concentric rings. The annular or sector
shaped stator logs, made of plastic, are arranged in axial direction
adjacent to the concentric rings of the support rings in such a way
that a magnetic flux is allowed in radial direction between adjacent
concentric rings.
The document "The Hybrid Helicopter Drive,... by Peter
Janker et al. at Europ. Rotorcraft Forum, Sept. 2010" further
discloses such electrical "Trans-Flux-Motors" with two disks for the
main rotor.
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The document WO 2005/100154 A1 discloses a rotor for
mounting on a helicopter drive shaft, comprising a hub for location
on the shaft and a plurality of blades mounted to and extending out
from the hub, wherein a pitch angle ([phi]) of at least one of the
blades is controllable with respect to each other blade by an
electrical stepper motor mechanism arranged at the hub. Also
disclosed is a method for determining a pitch angle ([phi]) of the
blades of the rotor, a computer program arranged to, when loaded
onto a computing system, utilise an algorithm for determining blade
pitch angle ([phi]) values for the blades, an alternator for providing
power to motors that control the pitch of the blades and a control
method for implementation by a computer in controlling the pitch of
the blades in real time.
The document US 2009/140095 A1 discloses a rotary-wing
aircraft with an electric motor mounted along an axis of rotation to
drive a rotor system about the axis of rotation
The document US 4953811 A discloses a helicopter engine
turning a tail rotor while it is turning the main rotor. Tail rotors,
while essential components, take power from the engine, introduce
a drag force, add weight, and increase rotor noise. Since the
engine is as close as possible to the main rotor, the complexity,
number of parts, weight and efficiency of the remote tail rotor have
gone unchanged. Those parts and hence their added weights have
been eliminated. A self-driving tail rotor for a helicopter is
provided.
The document WO 2009/129309 A2 discloses a wind
generator in which superconducting ring generators are utilized
without the need for a load bearing drive shaft and other
mechanical components allowing for the use of variable geometry
blades, a decrease in the overall weight, and an increase in the
overall efficiency of the wind generator system.
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The document US 2006/049304 A1 discloses a hover aircraft
with an air impeller engine having an air channel duct and a rotor
with outer ends of its blades fixed to an annular impeller disk that
is driven by magnetic induction elements arrayed in the air channel
duct. The air-impeller engine is arranged vertically in the aircraft
frame to provide vertical thrust for vertical takeoff and landing.
Preferably, the air-impeller engine employs dual, coaxial, contra-
rotating rotors for increased thrust and gyroscopic stability. An air
vane assembly directs a portion of the air thrust output at a desired
angle to provide a horizontal thrust component for flight
maneuvering or translation movement. The aircraft can employ a
single engine in an annular fuselage, two engines on a longitudinal
fuselage chassis, three engines in a triangular arrangement for
forward flight stability, or other multiple engine arrangements in a
symmetric, balanced configuration. Other flight control mechanisms
may be employed, including side winglets, an overhead wing,
and/or air rudders or flaps. An integrated flight control system can
be used to operate the various flight control mechanisms. Electric
power is supplied to the magnetic induction drives by high-capacity
lightweight batteries or fuel cells. The hover aircraft is especially
well suited for applications requiring VTOL deployment, hover
operation for quiet surveillance, maneuvering in close air spaces,
and long duration flights for continuous surveillance of ground
targets and important facilities requiring constant monitoring.
Summary of the Invention
It is an object of the invention to provide for an electrical
powered tail rotor of a helicopter with improved efficiency.
A solution is provided with an electrical powered tail rotor of
a helicopter with the features of claim 1.
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According to the invention an electrical powered tail rotor of a
helicopter (H) comprises a housing around the tail rotor and at
least one permanent magnet energized synchronous motor with an
increased pole number. Said at least one synchronous motor is
5 integrated as a torus in the housing around an opening of the
housing encompassing the tail rotor. Blades of the tail rotor are
fixed to at least one rotating component of said at least one
synchronous motor. Supply means provide electric energy to said
at least one synchronous motor. The invention is characterized in
that blade pitch control means are provided at the torus. As a
major advantage the inventive electrical powered tail rotor of the
helicopter allows replacement of the tail drive shaft by essentially
less weighing cable to the tail rotor. Drive and control of the
inventive electrical powered tail rotor can be integrated and
deletion of a stator at the tail rotor results in considerable less
noise. A further advantage the inventive electrical powered tail
rotor of the helicopter is separation of the propulsion of main rotor
and tail rotor and thus independence between main rotor and tail
rotor in terms of rotational speed allowing higher forward speeds
for the helicopter as the main rotor speed can be adapted over a
wide range to the optimum required. According to a still further
advantage of the inventive electrical powered tail rotor of the
helicopter noise emitted by the rotors can be reduced through
setting of the respective rotor speeds such, that the noise
interaction between main and tail rotor is minimizing the total
emission. A gearbox for the tail rotor is not needed any longer with
the subsequent advantage of a high potential for less weight. There
is as well high potential to ease the process of adjustment for the
tail rotor unit and drastically reduce production cost as the
installation of the drive-shaft, as well as its production, requires
considerable efforts. The inventive electrical powered tail rotor of
the helicopter allows independent control of the tail rotor thrust by
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means of rotational speed, blade pitch and tail rotor torque, thus
making power available independent from the main rotor system for
a wide range of power settings, airspeeds, altitudes and
temperature. As an example the rotor speed can be used to
compensate for altitude effects more efficiently than can be done
by tail rotor blade pitch. According to the invention it would even
be possible to completely stop the tail-rotor during forward flight
and thus reduce the drag and the power demand of the helicopter
as the tail-rotor is not requiring power. The use of an electrical
motor for the drive of the tail rotor of the helicopter allows more
possibilities to shape the core of the ducted tail rotor, and to have
more possibilities to optimize the aerodynamic shape of the
complete tail unit, especially the tail boom. The permanent magnet
energized synchronous motor has excellent control characteristics
and excellent efficiency for the transformation of electrical power
into mechanical power. The electrical motors of the invention have
low weight at high power output with balanced efficiency over a
wide range of speed and power settings and are not less reliable
than traditional mechanical drive trains and engines.
According to a preferred embodiment of the invention an
electrical powered tail rotor of a helicopter comprises two coaxial
synchronous motors with two coaxial rotating components and the
blades of the tail rotor are linked to each of said respective coaxial
rotating components of the two synchronous motors. The two
synchronous motors operate at essentially the same rotational
speed allowing a relative twist between the two coaxial rotating
components for control of the blade pitch of the blades of the tail
rotor by means of a suitable mechanism. The phase shift between
the two coaxial rotating components results in a collective change
of the blade pitch for all blades and thus allows control of the
thrust of the tail rotor. The two synchronous motors of the invention
each have a big diameter and each have little axial length. The two
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synchronous motors for the tail rotor are arranged in a fail safe
concept, i. e. the failure of one will leave at least half of the power
available. The excellent control characteristics of the permanent
magnet energized synchronous motor provide for the precise
control of the blade pitch of the blades of the tail rotor.
According to a further preferred embodiment of the invention
each stator is provided on an inner circumference with a plurality of
poles and each of said two coaxial rotating components with a
corresponding plurality of permanent magnets on an outer
circumference of each of the rotating components. The poles and
permanent magnets are each preferably arranged regularly in
pairs, with the permanent magnets in pairs out of phase to provide
for continuous interference of at least a part of the permanent
magnets.
According to a further preferred embodiment of the invention
the two coaxial rotating components are supported by a magnetic
bearing integrated in the torus around the housing opening
encompassing the tail rotor. The magnetic bearing allows contact
free rotation of the mobile parts of the tail rotor.
According to a further preferred embodiment of the invention
a retainer is provided at the torus around the housing opening
encompassing the tail rotor to withhold said one or two coaxial
rotating components at start or in case of a failure of the magnetic
bearing.
According to a further preferred embodiment of the invention
said two coaxial rotating components are supported by a ball
bearing between a stator and the rotating components of each of
said two synchronous motors.
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According to a further preferred embodiment of the invention
said two coaxial rotating components are linked by a bevel gear to
the blades of the tail rotor.
According to a further preferred embodiment of the invention
said two synchronous motors are asymmetric. One of said two
synchronous motors may be conceived to provide all the driving
power for the blades of the tail rotor whereas the other of said two
synchronous motors solely controls the blade pitch. Blades of this
inventive embodiment are preferable connected without azimuthal
tolerance to the synchronous motors conceived to provide the
driving power. The phase shift of said two synchronous motors
relative to each other solely controls the blade pitch of this further
preferred embodiment of the invention.
According to a further preferred embodiment of the invention
a sliding sleeve is provided at the torus for control of the pitch of
the blades of said one coaxial rotating component of said one
synchronous motor.
Brief Description of the Drawings
Preferred embodiments of the invention are presented by
means of the following description with reference to the attached
drawings, from which
Fig. 1 shows a spatial view of a tail rotor of a helicopter
according to the invention,
Fig. 2 shows a spatial view of stators of electrical motors
around a tail rotor according to the invention,
Fig. 3 shows a spatial view of two coaxial rotating
components of electrical motors of a tail rotor according to the
invention, and
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Fig. 4 shows a cross sectional view of the electrical motor
according to the invention.
Description of Preferred Embodiments
According to Fig. 1 a tail rotor 1 is arranged within a housing
-- 2 of a helicopter's tail boom 3. Blades 4 of the tail rotor 1 are
centrally supported by a hub 5. Hub 5 is essentially ball shaped
towards an inlet side and essentially flat towards an outlet side of
the tail rotor 1.
According to Fig. 2 two coaxial stators 6, 7 are provided on
-- the inner circumference of a torus 8 of a brushless electrical motor
assembly composed of two permanent magnet energized
synchronous motors with a plurality of poles 9 on each of the two
coaxial stators 6, 7.
The poles 9 on each of the two coaxial stators 6, 7 are
-- connected to supply means (not shown) for electrical power. Power
semiconductors (not shown) and microcontrollers (not shown)
provide for two multiphase inverters (not shown) for precise control
of the two brushless synchronous motors.
According to Fig. 3 the electrical motor assembly is
composed of one rotating component 10, 11 for each of said two
synchronous motors. The two rotating components 10, 11 are
coaxial. A plurality of permanent magnets 12 arranged regularly on
an outer circumference of each of the rotating components 10, 11
correspond to the plurality of poles 9 on each of the two coaxial
-- stators 6, 7.
Blade tips of the blades 4 of the tail rotor 1 are held in
between the two rotating components 10, 11.
The blade pitch control means includes the provision of
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phase shift between the two rotating components 10, 11 of the
synchronous motors by rotating the two rotating components 10, 11
coaxially relative to each other. The control of the respective
angular positions of the two rotating components 10, 11 relative to
5 each other
may be effected with special sensors, e. g. on the basis
of Hall effect due to the passing permanent magnets 12 or without
sensors by detecting any voltages induced in momentarily current
free coils.
According to Fig. 4 corresponding features are referred to
10 with the
references of Fig. 1 ¨ 3. The anti-torque system, i. e. the
profiled blades 4 of the tail rotor 1 of a housed concept like the
"Fenestron" is powered electrically by the two coaxial synchronous
motors fitted into the housing 2 of the tail rotor 1.
The tail rotor 1 comprises an inlet fairing 20 for the blades 4
supported in a pivoting mechanism 21 of the hub 5 of said ducted
fan. The blades 4 of the tail rotor 1 are held at their respective
blade tips 22 in a bevel gear 23. The bevel gear 23 is mounted
between the two rotating components 10, 11 of the two coaxial
synchronous motors as a link for the blades 4 to each of the two
rotating components 10, 11. The blades 4 are rotated via the blade
tips 22 with the bevel gear 23. The bevel gear 23 engages with
gears 26, 27 preferably all along inner lateral faces of the rotating
components 10, 11. The gears are provided with small moduli to
allow tolerances for the blade pitch.
The two coaxial synchronous motors comprise the permanent
magnets 12 arranged in pairs regularly on the outer circumference
of each of the rotating components 10, 11 as passive flux rings.
The rotating components 10, 11 are respectively supported by
outer thin annular roller bearings 24 or by magnetic bearings (not
shown) as retainer. The roller bearings 24 support the two rotating
components 10, 11 against a frame type casing 25 of the torus 8.
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Layered sheet metal packages for the respective poles 12 of the
coaxial stators 6, 7 are mounted against the frame type casing 25
on the inner circumference of the torus 8. The layered sheet metal
packages for the respective poles 12 abut laterally against the
inside of the thin annular roller bearings 24 and the inside of flanks
of the frame type casing 25.
A relative rotation of the two rotating components 10, 11 with
regard to each other rotates the bevel gear 23 of the blade pitch
control means. The rotation of the bevel gear 23 is transmitted to
the blade tip 22 of the profiled blade 4 for control of the blade pitch
and thus the thrust of the operating tail rotor 1. The blades 4 of the
tail rotor 1 may be irregularly distributed along the circumference
of the two rotating components 10, 11 for less sound emission of
the tail rotor 1.
The two coaxial synchronous motors may be asymmetric with
regard to drive power, i. e. one of the two coaxial synchronous
motors may take over all of the drive power while the other is the
blade pitch control means exclusively taking care of the control of
the blade pitch of the blades 4. The blades 4 would be linked to the
coaxial synchronous motor taking over all of the drive power in
such a way that there would be no azimuthal move any more.
The provision of phase shift between the two rotating
components 10, 11 of the two coaxial synchronous motors allows a
further control of the thrust provided by the tail rotor 1, namely
supplemental to the control of the thrust by varying solely the
rotational speed of the tail rotor 1.
In case of stationary flight the two coaxial synchronous
motors have exactly the same rotational speed and essentially the
same power rate. The profiles of the blades 4 may be selected with
a so called S-lay-out for a positive zero moment coefficient or this
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moment may be used as retroactive moment by a selection of the
pivot axis of the blades 4 with a few percents before a quarter of
the blade chord. Any of said selections would allow a safe landing
in case of a failure of the control due to a neutral positioning of the
blades 4.
For a tail rotor 1 with only one synchronous motor a sliding
sleeve as the blade pitch control means may be provided at the
torus 8 for control of the pitch from the outer radius of the blades 4
and thus for supplemental control of the thrust of said tail rotor 1
with one coaxial rotating component 10.
