NZ759225B2 - Bistable pitch propeller system with bidirectional propeller rotation - Google Patents
Bistable pitch propeller system with bidirectional propeller rotationInfo
- Publication number
- NZ759225B2 NZ759225B2 NZ759225A NZ75922517A NZ759225B2 NZ 759225 B2 NZ759225 B2 NZ 759225B2 NZ 759225 A NZ759225 A NZ 759225A NZ 75922517 A NZ75922517 A NZ 75922517A NZ 759225 B2 NZ759225 B2 NZ 759225B2
- Authority
- NZ
- New Zealand
- Prior art keywords
- blade
- mechanical stop
- propeller
- pitch
- stop
- Prior art date
Links
- 230000002457 bidirectional Effects 0.000 title description 2
- 150000002500 ions Chemical class 0.000 claims description 7
- 229920001223 polyethylene glycol Polymers 0.000 claims 1
- 239000011295 pitch Substances 0.000 description 96
- 238000010586 diagram Methods 0.000 description 52
- 238000000034 method Methods 0.000 description 19
- 210000001331 Nose Anatomy 0.000 description 14
- 230000000284 resting Effects 0.000 description 8
- 230000005611 electricity Effects 0.000 description 7
- 101700063048 PTER Proteins 0.000 description 4
- 230000000875 corresponding Effects 0.000 description 4
- 239000002184 metal Substances 0.000 description 4
- 239000000463 material Substances 0.000 description 3
- 210000003128 Head Anatomy 0.000 description 1
- 150000001768 cations Chemical class 0.000 description 1
- 238000004590 computer program Methods 0.000 description 1
- JVTAAEKCZFNVCJ-UHFFFAOYSA-N lactic acid Chemical compound CC(O)C(O)=O JVTAAEKCZFNVCJ-UHFFFAOYSA-N 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000009987 spinning Methods 0.000 description 1
- 238000003860 storage Methods 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C11/00—Propellers, e.g. of ducted type; Features common to propellers and rotors for rotorcraft
- B64C11/16—Blades
- B64C11/18—Aerodynamic features
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C11/00—Propellers, e.g. of ducted type; Features common to propellers and rotors for rotorcraft
- B64C11/30—Blade pitch-changing mechanisms
- B64C11/32—Blade pitch-changing mechanisms mechanical
- B64C11/325—Blade pitch-changing mechanisms mechanical comprising feathering, braking or stopping systems
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C11/00—Propellers, e.g. of ducted type; Features common to propellers and rotors for rotorcraft
- B64C11/30—Blade pitch-changing mechanisms
- B64C11/32—Blade pitch-changing mechanisms mechanical
- B64C11/34—Blade pitch-changing mechanisms mechanical automatic
- B64C11/343—Blade pitch-changing mechanisms mechanical automatic actuated by the centrifugal force or the aerodynamic drag acting on the blades
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C11/00—Propellers, e.g. of ducted type; Features common to propellers and rotors for rotorcraft
- B64C11/46—Arrangements of, or constructional features peculiar to, multiple propellers
-
- B64C2201/108—
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C27/00—Rotorcraft; Rotors peculiar thereto
- B64C27/04—Helicopters
- B64C27/08—Helicopters with two or more rotors
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C27/00—Rotorcraft; Rotors peculiar thereto
- B64C27/32—Rotors
- B64C27/46—Blades
- B64C27/467—Aerodynamic features
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C27/00—Rotorcraft; Rotors peculiar thereto
- B64C27/54—Mechanisms for controlling blade adjustment or movement relative to rotor head, e.g. lag-lead movement
- B64C27/80—Mechanisms for controlling blade adjustment or movement relative to rotor head, e.g. lag-lead movement for differential adjustment of blade pitch between two or more lifting rotors
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B64—AIRCRAFT; AVIATION; COSMONAUTICS
- B64C—AEROPLANES; HELICOPTERS
- B64C29/00—Aircraft capable of landing or taking-off vertically, e.g. vertical take-off and landing [VTOL] aircraft
- B64C29/02—Aircraft capable of landing or taking-off vertically, e.g. vertical take-off and landing [VTOL] aircraft having its flight directional axis vertical when grounded
Abstract
Disclosed is a method for controlling the pitch angle of a propeller when the propeller is rotated in opposing directions that is mechanically simpler and lighter than existing systems. A propeller includes a blade free to rotate. A first stop is positioned to mechanically engage one or both of a first portion of the blade and a first structure coupled to the blade when the blade is in a first position at a first end of the rotational range of motion. A second stop is positioned to mechanically engage one or both of a second portion of the blade and a second structure coupled to the blade when the blade is in a second position at a second end of the defined rotational range. The blade rotates to the first position against the first stop when the propeller is rotated in a first direction and to the second position against the second stop when the propeller is rotated in a second direction. rst portion of the blade and a first structure coupled to the blade when the blade is in a first position at a first end of the rotational range of motion. A second stop is positioned to mechanically engage one or both of a second portion of the blade and a second structure coupled to the blade when the blade is in a second position at a second end of the defined rotational range. The blade rotates to the first position against the first stop when the propeller is rotated in a first direction and to the second position against the second stop when the propeller is rotated in a second direction.
Description
BISTABLE PITCH PROPELLER SYSTEM WITH BIDIRECTIONAL
PROPELLER ROTATION
BACKGROUND OF THE INVENTION
Rotors (e.g., those used by helicopters) typically are at a single, relatively shallow
angle of attack to provide good lift. Propellers (e.g., wing-mounted) typically t a relatively
greater angle of attack to more efficiently propel an aircraft through the air. gh systems exist
for varying the pitch of a blade (e.g., so that the same propeller can switch n an angle of
attack which is good for ng and another which is good for forward flight), such systems
typically use complex mechanical mechanisms that add weight and expense. It would be desirable
if new systems could be developed which did not cost as much and/or weight as much.
SUMMARY OF THE INVENTION
[0001A] An aspect of the present invention provides a method, comprising :receiving, from a
user interface, a desired blade pitch for a first position, wherein the desired blade pitch is associated
with a propeller which includes: a blade free to rotate about a longitudinal axis of the blade within
at least a d range of motion; a first ical stop positioned to engage ically one or
both of a first portion of the blade and a first structure coupled mechanically to the blade when the
blade is in the first position at a first end of said defined rotational range of motion; and a second
mechanical stop positioned to engage mechanically one or both of a second portion of the blade and
a second structure d mechanically to the blade when the blade is in a second position at a
second end of said defined rotational range of motion; wherein the blade rotates to the first position
against the first mechanical stop when the propeller is rotated in a first direction and the blade
rotates to the second position against the second mechanical stop when the ler is rotated in a
second direction; determining a new position for the first mechanical stop based at least in part on
the desired blade pitch; and setting a position l for the first mechanical stop to a value which
corresponds to the new position.
[0001B] Another aspect of the present invention provides a method, comprising:
receiving, from a user interface, a desired mode for the first on, wherein the desired mode is
selected from a plurality of modes and the desired mode is associated with a propeller which
includes: a blade free to rotate about a longitudinal axis of the blade within at least a defined range
of motion; a first mechanical stop positioned to engage mechanically one or both of a first portion
of the blade and a first ure coupled mechanically to the blade when the blade is in the first
position at a first end of said defined rotational range of ; and a second mechanical stop
positioned to engage mechanically one or both of a second portion of the blade and a second
structure coupled mechanically to the blade when the blade is in a second position at a second end
of said defined rotational range of ; wherein the blade s to the first position against the
first mechanical stop when the propeller is rotated in a first direction and the blade rotates to the
second position against the second ical stop when the propeller is rotated in a second
direction; determining a new position for the first ical stop based at least in part on the
desired mode; and setting a position control for the first mechanical stop to a value which
corresponds to the new position
BRIEF DESCRIPTION OF THE DRAWINGS
Embodiments of the present invention will now be described, by way of nonlimiting
example only, with reference to the accompanying drawings briefly described as follows.
Figure 1 is a diagram illustrating various views of a bistable pitch ler
embodiment.
Figure 2 is a state diagram illustrating an embodiment of states associated with a
le pitch propeller.
Figure 3 is a diagram illustrating an embodiment of an octocopter which includes
bistable pitch propellers.
Figure 4A is a diagram illustrating an embodiment of peg stoppers which stop a peg
connected to a bearing.
Figure 4B is a m illustrating an embodiment of a blade stopper which is
designed to come into t with and stop a blade.
Figure 5 is a diagram illustrating some embodiments of adjustable stoppers.
Figure 6 is a diagram illustrating an embodiment of a bistable pitch ler, where
the blades are configured to return to a resting position when the propeller is not rotating.
Figure 7 is a diagram illustrating an embodiment of a blade being held in a feathered
blade position using a peg r.
Figure 8 is a flowchart illustrating various embodiments of user interfaces associated
with adjusting the position of a blade.
Figure 9A is a flowchart illustrating an embodiment of a process to receive a d
blade pitch from a user interface and adjust the position of a mechanical stop accordingly.
Figure 9B is a art illustrating an embodiment of a process to receive a desired
blade pitch from a user ace and adjust the position of a mechanical stop accordingly where the
user interface is disabled if the ical stop is in use.
Figure 9C is a flowchart illustrating an embodiment of a process to receive a desired
blade pitch from a user interface and adjust the position of a mechanical stop accordingly where the
desired blade pitch is held until the mechanical stop is free.
Figure 10A is a flowchart illustrating an embodiment of a process to receive a
desired mode from a user interface and adjust the position of a ical stop accordingly.
Figure 10B is a flowchart rating an embodiment of a process to receive a
desired mode from a user interface and adjust the position of a ical stop accordingly where
the user interface is disabled if the mechanical stop is in use.
Figure 10C is a flowchart illustrating an embodiment of a process to receive a
desired mode from a user interface and adjust the position of a mechanical stop accordingly where
the desired mode is held until the mechanical stop is free.
DETAILED DESCRIPTION
Examples may be implemented in numerous ways, ing as a process; an
apparatus; a system; a composition of matter; a computer program product embodied on a computer
readable storage medium; and/or a processor, such as a processor configured to execute instructions
stored on and/or ed by a memory coupled to the processor. In this specification, these
implementations may be referred to as techniques. In general, the order of the steps of disclosed
processes may be altered within the scope of the ion. Unless stated otherwise, a component
such as a processor or a memory bed as being configured to perform a task may be
implemented as a general component that is temporarily configured to perform the task at a given
time or a specific component that is manufactured to perform the task. As used herein, the term
‘processor’ refers to one or more devices, circuits, and/or processing cores configured to process
data, such as computer m instructions.
The invention encompasses numerous alternatives, cations and equivalents.
Numerous specific details are set forth in the following description in order to provide a thorough
understanding of the invention.
A propeller that is mechanically stable in two (or more) different positions
depending on a direction of rotation in which the propeller is rotated is disclosed. In s
embodiments, a propeller blade of the propeller system may be mounted so as to be rotatable about
an at least roughly longitudinal axis of the blade. The blade is constructed and mounted such that
rotation of the propeller in a first direction of rotation results in the blade rotating (if/as necessary)
about the longitudinal axis to a first stable on in which a portion of the blade and/or a
structure coupled mechanically to the blade engages a first ical stop, resulting in the blade
presenting a first angle of attack, while rotation of the propeller in a second (opposite) direction of
on results in the blade ng (if/as necessary) about the longitudinal axis to a second stable
position in which a portion of the blade and/or a structure coupled ically to the blade
engages a second mechanical stop, resulting in the blade presenting a second angle of attack. In
some embodiments, aerodynamic forces act on the propeller blade to rotate the blade about its
longitudinal axis to reach and/or maintain the first or second stable state, as applicable. In some
embodiments, other forces (e.g., in addition to or as an alternative to aerodynamic forces) cause the
blade(s) to rotate, such as torque or centripetal force. gh some examples herein describe
aerodynamic force as the force which causes the blades to rotate, this is not intended to be limiting.
Figure 1 is a diagram illustrating various views of a bistable pitch propeller
embodiment. The bistable pitch propellers described in this figure and below are merely exemplary
and are not intended to be limiting. For example, although two blades are shown in this figure, any
number of blades may be employed. Similarly, the shape of the blade (e.g., any washout, the blade
thickness, the blade width, any tapering, etc.), the on of the axis of rotation, the position of the
aerodynamic center, and the position of the center of mass are merely exemplary and are not
intended to be ng.
In this example, diagram 100 shows a top view of the exemplary bistable pitch
propeller, which in this e has two blades (102). Each blade is connected to a bearing (104),
which permits the blade to rotate about an axis of rotation of the blade (106), mes referred to
as the longitudinal axis. When the propeller rotates in one direction (e.g., clockwise from the top
view shown in diagram 100), the blades pivot on their respective bearings about the axis of rotation
of the blade (106). In some embodiments, the blades are vely lightweight (e.g., to make
rotation of the blades about the axis of rotation easier) and the rotation of the propeller causes an
namic force to be applied to the aerodynamic center (108) of the blade. Since the
namic center is not on the axis of rotation, the blade rotates when the propeller rotates.
Diagram 112 shows a cross section of one of the blades when that blade is in a
hovering mode or configuration. The rotation of the propeller causes the blade to be pushed
because of the aerodynamic force applied to the blade and the blade’s ability to rotate about its
longitudinal axis (106) (e.g., because of the bearing). The aerodynamic force is sufficiently strong
to push and hold the blade t the first stopper (114), holding the blade in that position and at
that pitch (i.e., an angle relative to a plane in which the propeller is being rotated). Diagram 112
thus shows a first blade pitch (or, more generally, blade position) at which the pitch propeller is
stable in (e.g., the blade is rigid in this position and will not move so long as the propeller is being
rotated sufficiently).
In diagram 112, the blade pitch is α1, where α1 is relatively small. A flatter blade is
therefore ted to the ve wind (shown in this diagram going from right to left). This
flatter blade pitch provides more upward thrust and therefore is good for hovering where upward
thrust is desired. For example, α1 may be defined as 0 s, and the blade tip might in that case
have a twist angle of 10-20 degrees. Although an aircraft may be able to hover when the blade(s)
is/are in some other position (e.g., a forward flight position, as is shown in m 116), the
blade(s) may be put into this position when the aircraft is ng in order to improve flight
performance and/or reduce noise.
Diagram 116 shows a cross section of one of the blades when the propeller rotates in
the other direction. The rotation of the ler in this direction causes the blade to flip in the
other direction (e.g., away from the first stopper). As described above, the aerodynamic force
being applied to the blade is ient to pin or otherwise hold the blade against a second stopper
(118). This blade position ) is referred to as a second blade position (pitch).
In this position, the blade pitch is α2 where α2 > α1. The blade pitch presented to the
relative wind (shown in this diagram going from left to right) in this position is therefore steeper.
For example, α2 may be within an angular range of 20 to 30 degrees and might therefore have a
blade twist that is 30 to 50 degrees at the tip. This steeper blade pitch offers better performance for
forward flight, but is not as good for hovering, and may in fact stall in hover. The blade pitch (or,
more generally, blade position) shown in diagram 116 is therefore an example of a second blade
pitch (or, more generally, blade on) which the pitch ler is stable in and the blade may be
put into this position when the aircraft is in a forward flight mode.
A bistable pitch propeller therefore permits two usable blade pitches (or, more
generally, blade positions) using the same propeller and/or blades without requiring electromechanical
or other structures to drive the blades to one or the other of the positions. In this
particular example, the two blade ons are associated with and/or zed for hovering and
forward flight. Naturally, the blade positions of a bistable pitch propeller may be optimized or
adjusted for other flight purposes and/or applications; some examples are described in more detail
below.
In this example, the center of mass (110) of the blade is on the axis of rotation of the
blade (106). In some other embodiments, the center of mass does not lie along the axis of rotation.
For example, this may be desirable because inertia will assist in g the blade into the first
blade position or the second blade on (e.g., when the propeller switches rotational direction).
Some other propellers can be adjusted so that the blades can be in one of a plurality
of blade positions or pitches. r, those propeller systems achieve the different blade
positions using hydraulics or other control isms which are (as an example) built into the
blade itself. In contrast, the propeller described herein does not include such heavy and expensive
hardware, making this propeller design potentially lighter and less expensive (among other things).
Generally speaking, a propeller per the technique described herein es a blade
free to rotate about a udinal axis of the blade within at least a defined range of motion. A first
mechanical stop is positioned to engage mechanically a first portion of the blade (e.g., one of the
flat sides) and/or a first structure coupled mechanically to the blade (e.g., a rotatable bearing which
is connected to the blade) when the blade is in a first position at a first end of said d rotational
range of motion. A second mechanical stop is positioned to engage mechanically one or both of a
second portion of the blade and a second structure coupled mechanically to the blade when the
blade is in a second position at a second end of said defined rotational range of motion. An
aerodynamic center of the blade lies at a prescribed distance from the longitudinal axis of the blade
in a direction such that aerodynamic forces act on the blade to rotate the blade tog the first on
against the first mechanical stop when the propeller is rotated in a first direction and to rotate the
blade to the second position against the second mechanical stop when the propeller is rotated in a
second direction. One e of this is shown in Figure 1 and other examples are described
below.
The following figure more formally describes the various states ated with
ng the propeller in either direction in order to “pin” the blades of the propeller into one of two
(stable) positions.
Figure 2 is a state diagram illustrating an embodiment of states associated with a
bistable pitch propeller. In some embodiments, the ler instructions (e.g., stop, rotate in a first
direction, rotate in a second direction) issued by a flight computer (e.g., implemented using a
processor and memory) cause a bistable pitch propeller to go through the states shown.
In state 200, a bistable pitch propeller is stable in a first position. To get into this
state, a propeller, which includes a rotatable blade, is rotated in a first ion, wherein the
rotation of the propeller in the first direction causes the rotatable blade to be in a first blade
position. For e, as is shown in Figure 1, a blade may be able to rotate because it is
connected to a bearing which is able to rotate. In diagram 112 in Figure 1, the rotation of the
ler causes an aerodynamic force to push the blade (102) against the first stopper (114),
holding blade (102) in the first blade position shown therein. In that example, the blade pitch
shown (i.e., α1) is good for hovering, so (as an example) a propeller may be put into state 200 when
the ft is hovering or is transitioning to hovering.
In state 202, the bistable pitch propeller is stable in a second state. To get into this
state, the propeller is rotated in a second direction different from the first direction, where the
rotation of the propeller in the second direction causes the rotatable blade to be in a second blade
on different from the first blade position. See, for example, diagra m 116 in Figure 1 which
shows the blade (102) in a second blade position. As is shown in Figure 1, the different blade
positions include different blade pitches where α1 ≠ α2. The blade position in this diagram is better
for d flight and so (as an example) a propeller may be put into state 202 when the aircraft is
in forward flight or is transitioning to forward flight.
When the bistable pitch propeller stops, the propeller goes into the stopped
state (204), for example because the aerodynamic force caused by the rotation of the propeller does
not push a blade against a first stopper or a second stopper. In some embodiments, a bistable pitch
propeller is designed so that the blades go in to some resting position (e.g., using springs) when the
propeller is in stopped state 204.
In addition to ing between hovering and forward flight, another example
application is when the ler is used as a wind turbine. If the wind is too strong, too much
electricity may be generated. In one example, if the wind is too strong and/or too much electricity
is being generated, the propeller will switch directions, causing the blades to be in a new position
(e.g., which “catches” the wind to a lesser degree), reducing the amount of electricity generated.
The following figure illustrates an example of an aircraft which uses a bistable pitch
propeller. Naturally, the aircraft shown is merely exemplary and is not intended to be limiting.
Figure 3 is a diagram illustrating an embodiment of an pter which includes
bistable pitch propellers. In this particular example, four of the octocopter’s propellers are bistable
pitch propellers and four of the octocopter’s propellers are not (e.g., those propellers will always
rotate in the same direction). Naturally, some other types of aircraft may be configured differently
(e.g., where all of the propellers are bistable pitch propellers and/or some other number of (bistable
pitch) propellers are included).
m 300 shows a top view of the pter when hovering. From this view,
the directions of rotation for all of the propellers can be observed. In this mode and for this
exemplary aircraft, all of the propellers are rotating in the same direction (in this example,
clockwise).
Diagram 302 shows a side view of the octocopter when hovering. From this view, it
is apparent that the plane of the octocopter (e.g., created by the four crossbars (304) to which the
eight propellers are attached) is horizontal when hovering. In this mode, it is desirable for the
propellers to be optimized for hovering, and the propellers’ directions of rotation (shown in
m 300) cause the bistable pitch propellers to have their blades be in a position which is
optimized for hovering.
To transition from hovering to forward flight, the octocopter “flips up” so that the
plane created by the crossbars (304) is vertical. For example, m 306 shows a side view of the
octocopter in a transitional position where the plane created by the crossbars is at a diagonal.
m 308 shows a side view of the pter in d , where the plane d by the
ars is in a vertical position. In some embodiments, the pter flips up by selectively
spinning the propellers at different rotational speeds to create a lift differential (e.g., the propellers
are fixed to the crossbars and they cannot be angled or repositioned). This lift differential causes
one side of the octocopter to flip up (e.g., the left side from the side views shown in diagrams 302,
306, and 308.
Diagram 310 shows a top view of the octocopter in forward flight. As described
above, half of the propellers are bistable pitch propellers and the other half are not. In ing
diagram 300 and 310, the bistable pitch propellers can be identified e they are the ones
which are rotating in different directions. Note, for example, that propeller 312a in diagram 300
and propeller 312b in diagram 310 are rotating in different directions. Similarly, propeller 316a
and 316b rotate in different directions in diagrams 300 and 310, respectively. In st, propeller
314a in diagram 300 and propeller 314b in diagram 310 are rotating in the same ion. As
shown in this example, in some embodiments, not all of the propellers in an aircraft need to be
bistable pitch propellers.
It is noted that the position or mode of the octocopter and propellers are independent
and the octocopter can be in one mode (e.g., forward flight) while the propeller is in the other mode
(e.g., hovering). For example, in the sequence of diagram 302 to diagram 306 to diagram 308, the
propellers may not be switched from hovering mode to forward flight mode until the octocopter has
flipped up to a forward flight position (see m 308). The blades of the lers would
therefore temporarily be at an angle that better suited to hovering while the octocopter is in forward
flight position (e.g., at least until the blades of the propellers were switched to the more efficient
forward flight mode). Although the performance may not be optimal (e.g., it may be noisy or not
as efficient), it may still be acceptable.
As described above, a variety of stoppers may be employed and the ical
stopper shown in Figure 1 is merely one example. The following figures illustrate some other
examples.
Figure 4A is a m illustrating an embodiment of peg stoppers which stop a peg
connected to a bearing. In the example shown, diagram 400 shows a side view of the exemplary
peg stoppers. In this example, a cross section of the blade (e.g., looking towards the nose piece
from the tip of the blade) is shown with a dashed line (401), where the blade is attached to the
bearing (e.g., extended out of the page). In order to clearly show the peg and peg stoppers, the
blade cross section shown in this figure is transparent. The udinal axis of rotation of the
blade (also not shown) extends out of the page from the center of the g (402). The
aerodynamic center of the blade (also not shown) is at a height below the height of the axis of
rotation of the blade. This s the bottom portion of the blade to be pushed by an aerodynamic
force either towards the first or second peg stopper, depending upon the propeller’s direction of
rotation.
As in the above example(s), bearing 402 is able to rotate. When the bistable pitch
propeller is rotated in the direction shown in diagram 400 (e.g., rclockwise when looking
down on the nose piece from above), an aerodynamic force pushes on the blade (not shown), which
causes the blade and the bearing to rotate towards the first peg stopper (406). A peg (404) is
ed to and radiates outward from the bearing (402) and the bearing rotates until the peg is
stopped by the first peg stopper (406). In this example, the peg stoppers are connected to the nose
piece (412) so that the peg stoppers can stop the peg from moving further, even while the ler
rotates. As is shown in this diagram, the first peg stopper stops the blade at a first blade position
(e.g., a first blade pitch) while the propeller is rotating the direction shown.
Diagram 408 shows the le pitch propeller rotating in the opposite direction. In
this direction, an namic force causes the bearing and peg to rotate towards the second peg
stopper (410). The rotation in this direction is eventually stopped by the second peg stopper (410)
forcing the peg to stop. This holds the blade (a cross section of which is shown with a dashed line)
at a second blade position (e.g., a second blade pitch).
To achieve a d blade position, a peg r is attached to the nose piece to
stop the peg at the appropriate position (e.g., to achieve a steeper blade angle or a more feathered
blade angle). The blade positions or pitches shown here are merely exemplary and are not intended
to be limiting. Some examples are described below where the position of a stopper is adjustable so
that the first blade on and/or second blade position is/are not necessarily fixed (e.g., the peg
stoppers are not welded directly to the nose piece, which would cause them to remain in a fixed
position).
Although the peg and bearing are shown here with a seam (e.g., from welding or
otherwise attaching the peg and g together), the peg and g may comprise a single piece
of metal or other material (e.g., the peg and bearing are cast or cut as a single piece of metal). In
various embodiments, a peg and/or a peg r may comprise a variety of shapes and/or
materials. For example, a peg stopper may be made of metal (e.g., for strength and/or durability)
and have a rubber sleeve or cover (e.g., to cushion the peg which may be pushed forcefully into the
peg stopper, given the expected high propeller speeds). In some embodiments, a peg stopper has
substantially the same height as a peg (e.g., to increase the area where the peg and peg stopper
come into contact which better distributes the pressure and/or to more securely attach the peg
stopper to the nose . In some embodiments, the peg and peg stopper have matching surfaces
where they come into t with each other (e.g., both have a flat surface where they make
t and the flat surfaces match up) to increase the area where they come into contact with each
other.
The ing figure shows a different embodiment where a stopper is designed to
come into direct contact with the blade (e.g., as d to this figure).
Figure 4B is a diagram illustrating an embodiment of a blade stopper which is
designed to come into contact with and stop a blade. In the example shown, diagram 420 shows a
side view when the bistable pitch propeller is rotating in a first direction (e.g., counterclockwise
when looking down on the nose piece from above). When the prop eller is rotating in this direction,
an aerodynamic force pushes against the blade (422), causing the bearing (424) which is attached to
the blade to rotate. The rotation of the blade and bearing is stopped when one (e.g., substantially
flat) side of the blade (426) comes into contact with a first blade stopper (428); this holds the blade
in a first blade position when the propeller is rotating in the direction shown.
Diagram 432 shows a top view; for clarity, the blade is not shown. As is shown in
this view, the first blade stopper (428) and second blade stopper (438) are attached to the nose piece
(430), radiating outward so that it can make contact with the blade (not shown).
Diagram 436 shows a side view when the propeller rotates in the other direction
(e.g., clockwise when looking down on the nose piece from above). In this case, the aerodynamic
force causes the blade to be pushed in the other direction, where the blade is stopped by the second
blade stopper (438). In this case, the second side of the blade (434) is in contact with the second
blade stopper.
For clarity, the exemplary blade cross section shown here has a vely simple
design or shape but this is not intended to be limiting. A blade used in a orld embodiment
may have a design or shape which is optimized to achieve a variety of design and/or performance
objectives.
In various embodiments, the shape and/or materials(s) of a blade stopper may vary.
For e, the shape of the blade stoppers may be aerodynamic since the propeller is expected to
have a relatively high rate of rotation. In some ments, a blade stopper is made of metal with
a rubber sleeve or cover.
As described above, in some embodiments, the position of a stopper is adjustable,
such that the first blade position and/or the second blade position is adjustable. The following
figure illustrates some examples of adjustable stoppers.
Figure 5 is a diagram illustrating some embodiments of adjustable stoppers.
Diagram 500 shows a side view of adjustable peg stoppers. In this example, the position of the first
peg stopper (502) can be positioned anywhere within the first cutout (504) and the second peg
stopper (506) can be positioned anywhere within the second cutout (508). By adjusting the position
of a peg stopper within a cutout, the blade position (e.g., when the propeller is rotated and the peg
is stopped by the appropriate peg r) can be varied. Naturally, the shape of the cutout (in this
e, circular) is merely exemplary and is not intended to be limiting. In some other
embodiments, the cutout is L-shaped, vertical, horizontal, diagonal, etc.
In various embodiments, a variety of adjustment mechanisms may be used in
diagram 500. In one e, the peg stoppers are designed to be ly adjusted, for example,
using an exposed knob or using a screwdriver to turn an exposed screw head. Turning the screw
head or knob in turn causes a corresponding peg stopper to move (for example)
clockwise/counterclockwise, up/down, left/right within a cutout.
In some embodiments, the nose piece (510) includes actuators which permit the
automatic (that is, nual) adjustment of the first and/or second peg stoppers within the first
and second cutouts, respectively. In one e, when the propeller is not rotating or when the
peg (512) is stopped by the first peg r, the second peg stopper can be moved within the
second cutout using the appropriate actuator. Then, when the propeller is rotated in the other
direction, the new position of the second peg stopper will cause the blade to stop in a new, second
blade position. This permits the propeller to go through a ce of three or more blade positions
between takeoff and landing (e.g., (1) rotate propeller clockwise and blade pitch = α1, (2) rotate
propeller rclockwise and blade pitch = α2, (3) adjust first peg stopper, (4) rotate propeller
clockwise and blade pitch = α3, etc.). Some examples of user interfaces associated with setting a
blade position and/or stopper on are bed in more detail below.
Diagram 514 illustrates a side view of an example of L-shaped, telescoping blade
stoppers. In this example, the first blade stopper (516) and second blade stopper (518) are
telescoping, which permits the length of the blade stoppers to be adjusted. This, in turn, stops the
blade at varying blade positions or blade pitches when the propeller is d in the appropriate
direction. Since a blade will come into contact with a telescoping blade r at a variety of
angles (e.g., ing upon the height of the stopper), the telescoping blade stoppers have rounded
ends where the stopper comes into contact with a side of the blade. In some embodiments, some
other tip shape is used. In some ments, the end or tip of a telescoping blade stopper is
rubberized.
As described above, a variety of mechanisms (e.g., manual adjustment using
screw(s) and/or ) or automatic adjustment using ors) may be used to adjust the height
of the telescoping blade stoppers. As described above, in some embodiments the adjustment
mechanism is a manual adjustment mechanism and in other embodiments the adjustment
mechanism is an automatic adjustment mechanism.
The ability to adjust the first and/or second blade position may be especially
desirable in wind turbine applications. In wind turbine applications, the pitch of the blade is
adjusted ing upon wind strength. When the wind is too strong and too much electricity is
being ted, the pitch of the blade is adjusted so that the blades are more red, reducing
the amount of electricity produced. If the wind dies down too much, then the pitch of the blade
may be adjusted so that the blades are at a steeper angle, increasing the amount of electricity
produced.
In some embodiments, the blades of a le pitch propeller are configured to
return to a certain position when the propeller is not rotating. The following figure shows one such
example.
Figure 6 is a diagram illustrating an embodiment of a bistable pitch propeller, where
the blades are configured to return to a resting position when the propeller is not rotating. In this
example, the resting position is a feathered position.
In the example shown, diagram 600 shows the nose piece (602) with two internal
s (604a and 604b). When the propeller is not rotating, there is no aerodynamic force which
pushes down the blade (606) towards either the first mechanical stop or the second mechanical stop
(not shown). The first internal spring and second internal spring therefore collectively push the
blade to the center (i.e., a feathered on). In this e, the internal springs are relatively
weak such that when the propeller is rotating in either direction, the expected aerodynamic force is
greater than the force exerted by the internal springs and the blades can be pushed and held in the
first or second blade position.
Diagram 610 shows an interior view of the nose piece. In this diagram, part of the
bearing (not shown in diagram 610) is connected to a spring-mounted ball bearing (614). It is
noted that the spring-mounted ball bearing (614) is different from bearing 612. When the propeller
is rotated in a first direction and the blade is in the first blade on because of the first peg
stopper, the -mounted ball bearing is in position 616. When the propeller is rotated in the
other direction and the blade is in the second blade position because of the second peg stopper, the
-mounted ball bearing is in position 618. When the ler is not rotating there is no
aerodynamic force g against the blade and so the internal springs shown in diagram 600, as
well as the sloped surface, will cause the spring-mounted ball bearing to come to a rest in position
620 (i.e., the g, red position when the propeller is not ng). The placement of the
“dip” or minima in the sloped surface therefore dictates where the resting position will be. In this
example, the slope(s) (e.g., between positions 616, 620, and 618) is/are relatively shallow and the
springs are relatively weak. This permits the expected aerodynamic force to push the blade (e.g., at
rest) out of the resting position shown and into the first or second blade position when the propeller
is rotating.
Naturally, the mechanisms shown here which cause the blade to go to a resting
position (in this example, a feathered position) when the propeller is not rotating are merely
exemplary and are not intended to be limiting. Any (e.g., mechanical) mechanism which returns
the blade to some desired resting position when the propeller is not rotating may be used.
In some cases, it may be desirable to have the feathered blade position shown here
be one of the blade positions created or defined by a stopper. The ing figure shows an
example of this.
Figure 7 is a diagram illustrating an embodiment of a blade being held in a feathered
blade position using a peg stopper. In the example shown, a peg stopper embodiment is shown, but
naturally the concepts may be extended to other ments. As described above, a bearing ( 700)
which is able to rotate has a peg (702) attached to it. When the propeller is rotated in the direction
shown (e.g., counterclockwise when looking down on the nose piece from , an aerodynamic
force pushes the blade (704) until the peg comes up against the first peg stopper (706) where the
first peg stopper is connected to the nose piece (708). This causes the blade to be held at a
feathered blade position where α3 = 90°. For example, if the bistable pitch propeller is being used
in a wind turbine application, then it may be desirable to have one of the blade positions defined or
created by a stopper be a feathered blade position. The blades may be put into this position when
the wind is too strong (e.g., there is a storm) and too much electricity is being generated.
As is shown in Figure 5, the position of a stopper (and thus a blade position when a
bistable pitch propeller is rotating) is adjustable in some ments. The following figure
illustrates some example user interfaces which may be presented to a pilot or user when there is an
automatic adjustment mechanism (e.g., as opposed to a manual adjustment).
Figure 8 is a flowchart illustrating various embodiments of user interfaces associated
with adjusting the on of a blade. In some embodiments, the user interface is presented to a
pilot or other user by a flight computer (e.g., implemented using a processor and memory) when a
stopper has an automatic adjustment mechanism.
User interface 800 shows an example of a user interface where the pilot or user is
permitted to specify the desired blade pitches (e.g., explicitly). To change or otherwise set the first
blade pitch, the user can input a number (in this e, between 0° and 90°) in input box 802a
and press the set button (804a). The flight computer then moves the adjustable r (see, for
example, Figure 5) to a position which corresponds to the specified blade pitch. Similarly, a
d blade pitch can be specified for the second blade pitch using input box 802b and set button
804b.
User interface 806 shows an example of a user interface where the pilot or user
selects a flight mode from a plurality of ted flight modes. In this example, user ace 806
permits the pilot or user to select a hover mode, a forward flight mode, a wind turbine mode when
the wind is weak, a wind turbine mode when the wind is te, or a wind turbine mode when
the wind is strong (i.e., a feathered mode). To set the first blade position, the desired mode is
selected by clicking on the appropriate radio button and set button 808a is pressed. Similarly, the
second blade position can be set or otherwise adjusted by selecting the desired mode and pressing
set button 808b. Each flight mode may have a ponding stopper position (e.g., corresponding
to a blade pitch which is optimized for that particular mode or application) and the appropriate
stopper is moved to that stopper position.
As described above, in some embodiments an aircraft includes multiple bistable
pitch propellers. See, for e, Figure 3. In such embodiments, the user interface may include
independent controls for each bistable pitch propeller.
In some embodiments, a given stopper can only be adjusted at certain times (e.g.,
when the propeller is not ng or when the blade is being held in position by the other r).
If so, this may be handled by the user interface in a variety of ways in various embodiments. In
some embodiments, the user interface does not permit the pilot or user to specify a desired blade
pitch or desired mode when a given stopper cannot be adjusted. For example, in user ace 800
and user interface 806, the affected input box, radio s, and/or set button may be disabled and
the user may not be able to select those controls and/or input values into those controls. In some
other ments, the pilot or user is able to specify a desired blade pitch or desired flight mode
at any time, but the user interface informs the pilot or user that the change will not be made right
away. When the appropriate stopper is able to be adjusted (e.g., e the blade flips over to the
other stopper or the propeller stops rotating), the user interface may be updated to inform the pilot
or user that the change has been made.
The ing figures more formally be how information received from a user
interface may be used to change the position of an adjustable stopper.
Figure 9A is a flowchart illustrating an embodiment of a process to receive a d
blade pitch from a user interface and adjust the position of a mechanical stop accordingly. At 900,
a desired blade pitch for the first position is received from a user ace. See, for example, user
interface 800 in Figure 8. At 902, a new position for the first mechanical stop is determined based
at least in part on the desired blade pitch. For example, there may be some lookup table which
maps the desired blade pitch to a corresponding position of the stopper. At 904, a on control
for the first mechanical stop is set to a value which corresponds to the new position. For example,
a control for an actuator may be set to some value which causes the stopper to be moved to the new
position determined at step 902.
Figure 9B is a flowchart illustrating an embodiment of a process to receive a desired
blade pitch from a user interface and adjust the position of a mechanical stop accordingly where the
user interface is disabled if the mechanical stop is in use. For brevity, steps that are similar to those
bed above (e.g., fied by identical reference numbers) are not discussed in detail here.
At 912, it is determined if a first mechanical stop is in use. For example, as
described above with respect to Figure 8, the first mechanical stop may only be permitted to be
moved if the propeller is not rotating or the second stopper is the one currently holding the blade or
peg in place.
If it is determined that the first mechanical stop is in use at 912, then one or more
controls associated with receiving a desired blade pitch for the first position are disabled in a user
interface 910. For example, in user interface 800 in Figure 8, a user would not be able to select
and/or input values into input box 802a or set button 804a if the first mechanical stop is holding the
blade in the first blade position or pitch. Similarly, in user interface 806, the radio buttons and set
button 808a may be disabled (e.g., un-selectable) if the first mechanical stop is holding the blade in
the first blade position or pitch. In this example, the process stays in this loop until the first
mechanical stop is no longer in use.
Once (or if) the first mechanical stopper is determined to not be in use at step 912,
the controls are d at 914. This, for example, permits the user to select the previously
disabled controls. At 900, the desired blade pitch for the first position is received from the user
interface. At 902, a new position is determined for the first mechanical stop based at least in part
on the desired blade pitch. At 904, a position control for the first mechanical stop is set to a value
which corresponds to the new position.
Figure 9C is a flowchart illustrating an embodiment of a s to receive a desired
blade pitch from a user interface and adjust the position of a ical stop accordingly where the
desired blade pitch is held until the ical stop is free. As before, steps previously described
are not sed in detail here for brevity.
At 900, a desired blade pitch for the first position is received from a user interface.
At 920, it is ined if a first ical stop is in use.
If the first mechanical stop is determined to be in use at 920, a message indicating
that the desired blade pitch will not be immediately d is displayed at 922. In this example,
the process stays in this loop until the first mechanical stop is no longer in use (e.g., because the
propeller has stopped rotating or the propeller has switched directions of rotation). In this
embodiment, the user ace permits a desired blade pitch to be specified or otherwise input, but
then holds on to that pitch without actually making any changes until the relevant mechanical stop
is no longer being used to hold or otherwise stop the blade or peg (as an example). In various
embodiments, the content of a message displayed at step 922 may vary. In some embodiments, the
message is fairly simple (e.g., “Waiting”). In some embodiments, the message identifies that the
wait is due to the stopper being in use (e.g., “The blade pitch will be changed when the propeller is
turned off or the propeller switches directions.”).
Once (or if) the first mechanical stop is determined to not be in use at 920, a new
position for the first mechanical stop is determined based at least in part on the desired blade pitch
at 902. In some embodiments, a second message is yed to the user, indicating that the desired
blade pitch has been applied (e.g., “Done” or “The blade pitch has been changed”).
At 904, a position control for the first mechanical stop is set to a value which
corresponds to the new position.
Figure 10A is a flowchart illustrating an embodiment of a process to receive a
desired mode from a user interface and adjust the on of a mechanical stop accordingly. At
1000, a desired mode for the first position is received from a user ace, wherein the desired
mode is selected from a plurality of modes. See, for example, user ace 806 in Figure 8 where
le modes are presented and the user selects one. At 1002, a new position is determined for a
first mechanical stop based at least in part on the desired mode. In some embodiments, each
possible mode (e.g., presented to the user) has a corresponding position for the mechanical stop
pre-determined. In some embodiments, a lookup table is used to map a desired mode to a new
ical stop position. At 1004, a position control for the first mechanical stop is set to a value
which corresponds to the new position. As described above, there may be an actuator to move a
peg within a cutout or adjust the height of a telescoping blade stopper, and some control input to
the actuator may be set to the appropriate value.
Figure 10B is a flowchart rating an embodiment of a process to receive a
desired mode from a user interface and adjust the position of a ical stop accordingly where
the user interface is disabled if the mechanical stop is in use. For brevity, steps that have been
previously discussed are not discussed in detail here.
At 1012, it is determined if a first mechanical stop is in use. If so, one or more
controls associated with receiving a desired mode for the first on are disabled in a user
interface at 1010. As described above, this may include making controls un -selectable and/or not
permitting inputs or other values to be entered. In this e, the process stays in this loop until
the first stopper is no longer in use.
Once (or if) the first mechanical stop is determined to not be in use at step 1012, the
controls are enabled at 1014. At 1000, the desired mode for the first position is received from the
user interface, wherein the d mode is selected from a plurality of modes. At 1002, a new
on for the first mechanical stop is determined based at least in part on the desired mode. At
1004, a position control for the first mechanical stop is set to a value which corresponds to the new
position.
Figure 10C is a flowchart illustrating an embodiment of a process to receive a
desired mode from a user interface and adjust the position of a mechanical stop accordingly where
the d mode is held until the mechanical stop is free. As before, steps that have been
previously discussed are not discussed in detail here for brevity.
At 1000, a d mode for the first position is received from a user interface,
wherein the desired mode is selected from a plurality of modes. At 1020, it is determined if a first
mechanical stop is in use. If so, a message indicating that the desired mode will not be immediately
applied is displayed at 1022. As described above, a variety of messages may be displayed.
Once (or if) it is determined at step 1020 that the first mechanical stop is no longer
in use, a new position is determined for the first mechanical stop based at least in part on the
desired mode at 1002. In some embodiments, a new or second e is displayed, for example
indicating that the first mechanical stop has been adjusted to reflect the desired mode.
At 1004, a position control for the first mechanical stop is set to a value which
ponds to the new position.
While various embodiments of the present invention have been described above, it
should be understood that they have been presented by way of example only, and not by way of
limitation. It will be apparent to a person skilled in the relevant art that s changes in form
and detail can be made therein without departing from the spirit and scope of the invention. Thus,
the present ion should not be limited by any of the above described exemplary embodiments.
The reference in this specification to any prior ation (or information derived
from it), or to any matter which is known, is not, and should not be taken as an acknowledgment or
admission or any form of suggestion that that prior ation (or information derived from it) or
known matter forms part of the common general knowledge in the field of endeavour to which this
specification relates.
Throughout this specification and the claims which follow, unless the context
requires otherwise, the word "comprise", and ions such as "comprises" and "comprising", will
be understood to imply the inclusion of a stated integer or step or group of integers or steps but not
the exclusion of any other integer or step or group of integers or steps.
Claims (6)
1. A method, comprising: receiving, from a user interface, a desired blade pitch for a first position, wherein the desired blade pitch is associated with a propeller which includes: a blade free to rotate about a longitudinal axis of the blade within at least a d range of ; a first mechanical stop positioned to engage mechanically one or both of a first portion of the blade and a first structure coupled mechanically to the blade when the blade is in the first position at a first end of said defined rotational range of motion; and a second mechanical stop positioned to engage mechanically one or both of a second portion of the blade and a second structure coupled mechanically to the blade when the blade is in a second position at a second end of said defined rotational range of motion; wherein the blade rotates to the first position t the first mechanical stop when the propeller is rotated in a first direction and the blade rotates to the second position against the second mechanical stop when the propeller is rotated in a second direction; determining a new position for the first mechanical stop based at least in part on the desired blade pitch; and setting a position control for the first mechanical stop to a value which corresponds to the new position.
2. The method of claim 1 further sing, prior to receiving the receiving the d blade pitch for the first position: determining if the first ical stop is in use; and in the event it is determined that the first mechanical stop is in use, disabling, in the user interface, one or more controls associated with receiving the desired blade pitch for the first position; and in the event it is ined that the first mechanical stop is not in use, enabling the controls ated with receiving the desired blade pitch for the first position.
3. The method of claim 1 or 2 further comprising, prior to determining the new position for the first ical stop: determining if the first mechanical stop is in use; and in the event it is determined that the first mechanical stop is in use, displaying a message indicating the desired blade pitch will not be ately applied; and in the event it is determined that the first mechanical stop is not in use, determining the new position for the first mechanical stop based at least in part on the desired blade pitch.
4. A method, comprising: receiving, from a user interface, a desired mode for the first position, wherein the desired mode is selected from a plurality of modes and the desired mode is associated with a propeller which includes: a blade free to rotate about a longitudinal axis of the blade within at least a defined range of motion; a first mechanical stop positioned to engage ically one or both of a first portion of the blade and a first structure coupled mechanically to the blade when the blade is in the first position at a first end of said defined rotational range of motion; and a second mechanical stop positioned to engage mechanically one or both of a second portion of the blade and a second ure coupled mechanically to the blade when the blade is in a second position at a second end of said defined rotational range of motion; wherein the blade rotates to the first position t the first mechanical stop when the propeller is d in a first direction and the blade rotates to the second position against the second mechanical stop when the propeller is rotated in a second ion; determining a new position for the first mechanical stop based at least in part on the desired mode; and setting a position control for the first mechanical stop to a value which ponds to the new position.
5. The method of claim 4 further comprising, prior to receiving the desired mode for the first position: determining if the first mechanical stop is in use; and in the event it is ined that the first mechanical stop is in use, disabling, in the user interface, one or more controls associated with receiving the desired mode for the first position; and in the event it is determined that the first mechanical stop is not in use, enabling the controls associated with receiving the d mode for the first position.
6. The method of claim 4 or 5 further comprising, prior to determining the new position for the first mechanical stop: ining if the first mechanical stop is in use; and in the event it is determined that the first mechanical stop is in use, displaying a message indicating the desired mode will not be immediately applied; and in the event it is determined that the first mechanical stop is not in use, determine the new on for the first mechanical stop based at least in part on the desired mode. Axis of Rotation of Biade (Lengitudinai Axis) namic Center ”£08 Biade 102 Cross Section I Shawn Below Center of Mass; 110 Beafing Top- View r. {.116 Pmpeiier ion _, ‘— Propeiier Directicn of Rotation of Rotation ‘1“ Stopper 1 1 4 ....1 05 Raiative Wanda —> 108 Fiatter Biade Pressented Steeper Biade Presented in When Hovering Forward Fiight (Cross Sectien) (Cross Sectian) PEG. 1 Not Necessariiy to Scale Propetier Rotates Propetter Ratates in 15? Directien in 2“d Direction Pmpeiier 200 Pmpetter 202 Stops Steps Stabie in 15‘ Stabie in 2“d PosMon ter Rotates in Position 15‘ Direction Propeiier Rotates in 2”“ Direction FEG. 2 300 310 V//// /////////////////////// \§\\\\\\\\\\\\\\\\\\\\\\\‘\§\\\\\\\\\\\Vl§ EZ§\\\§§\\\V\
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US15/225,018 | 2016-08-01 | ||
US15/225,018 US10843790B2 (en) | 2016-08-01 | 2016-08-01 | Bistable pitch propeller system with bidirectional propeller rotation |
NZ749455A NZ749455A (en) | 2016-08-01 | 2017-03-13 | Bistable pitch propeller system with bidirectional propeller rotation |
Publications (2)
Publication Number | Publication Date |
---|---|
NZ759225A NZ759225A (en) | 2022-03-25 |
NZ759225B2 true NZ759225B2 (en) | 2022-06-28 |
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