GB2592234A

GB2592234A - An aircraft

Info

Publication number: GB2592234A
Application number: GB2002385.9A
Authority: GB
Inventors: Wilson Fraser
Original assignee: Airbus Operations Ltd
Current assignee: Airbus Operations Ltd
Priority date: 2020-02-20
Filing date: 2020-02-20
Publication date: 2021-08-25
Also published as: GB202002385D0

Abstract

An aircraft 100 has a fuselage 101 with fixed wings 102, 103 located partway along the fuselage and one or more engines 104, 105 for providing forward thrust. The aircraft also includes a propeller 120, comprising a plurality of propeller blades rotatable in a plane of rotation 123, arranged to provide reverse thrust, wherein the propeller is located aft of the fixed wings. One or more of the propeller blades are moveable between a deployed configuration, in which the blade is located within the plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation. The aircraft may include an energy storage device to store energy from the propeller. The aircraft may have a landing gear drive system. The reverse thrust propeller may have several differing shapes and structures.

Description

AN AIRCRAFT

BACKGROUND OF TIIE INVENTION

[0001] The present disclosure relates to aircraft.

[0002] The present invention concerns aircraft. More particularly, but not exclusively, this invention concerns an aircraft having a fuselage, fixed wings, for providing lift and being located partway along the fuselage and one or more engines for providing forward thrust.

[0003] The invention also concerns methods of operating an aircraft.

[0004] Traditionally, there are a number of mechanisms used, and/or used in combination, to retard an aircraft.

[0005] These include use of wheel brakes, such as friction wheel brakes. These are used when the aircraft is on the ground. They can be applied differentially on different sides of the aircraft to provide an overall moment on the aircraft to control the direction of the aircraft. However, these wheel brakes cause wear on brake and wheel components, over time. In addition, in certain conditions, such as on a very rainy day or when there is surface contamination, the friction between the ground and the tyre may be less reliable.

[0006] Another method of retarding an aircraft that uses a gas turbine engine is to use a thrust reverser to direct some of the exhaust gas in a forwards direction, to provide some reverse thrust. Again, these can be used differentially on either side of the aircraft to provide an overall moment on the aircraft to control the direction of the aircraft. However, of course, this requires fuel to be burned in producing the reverse thrust and causes air pollution, which is perhaps of particular concern at an airport.

[0007] Another method of retarding an aircraft with a propeller engine is to reverse the pitch of the propeller blades. Again, these can be used differentially on either side of the aircraft to provide an overall moment on the aircraft to control the direction of the aircraft. However, this is a rather inefficient method of retardation. -2 -

[0008] Another method is to apply braking to one or more wheels through use of a landing gear drive system. The landing gear drive system may provide a reverse force by driving wheel of the landing gear in a reverse direction and/or by providing an electrical (or hydraulic) resistive force to the forwards movement of the wheels.

[0009] Another method is to deploy airbrakes (such as the clamshell airbrake on the Fokker 100). However, these introduce large eddies to the airflow and so produce a large amount of noise, which is undesirable, especially near airports where they would be used. In addition, these are often not particularly effective at speeds below 60-100 knots.

[0010] Deployable parachutes have also been used to retard military (and a few commercial) aircraft after landing. This method is not especially suitable for civil commercial aircraft, however, given the quick turnaround time needed at airports and the time take to recover and re-pack the parachute, as well as the interruption and delay caused to aircraft wishing to land afterwards (as the parachute has to be dropped onto the ground before recovery and repacking).

[0011] The present invention seeks to mitigate the above-mentioned problems.

Alternatively or additionally, the present invention seeks to provide an improved aircraft.

[0012] The improved aircraft may be able to be more efficiently retarded, may involve less component wear, may be more independent of the environmental conditions, may be quieter during landing approach and/or retardation, may burn less fuel and/or may have directional control through its retardation mechanism.

SUMMARY OF THE INVENTION

[0013] The present invention provides, according to a first aspect, an aircraft having a fuselage, fixed wings, for providing lift and being located partway along the fuselage, and one or more engines for providing forward thrust, wherein the aircraft further comprises a propeller, comprising a plurality of propeller blades rotatable in a plane of rotation, arranged to provide reverse thrust, wherein the propeller is located aft of the fixed wings, and wherein one or more of the propeller blades are moveable between a -3 -deployed configuration, in which the blade is located within the plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation.

[0014] In the above and below, in relation to all aspects, the fore and aft directions and the forward and reverse thrust directions are defined in terms of the nomial direction of flight of the aircraft, along the fuselage.

[0015] Such an aircraft is able to have a propeller that does not affect the aerodynamic flow over the fixed wings. The aircraft also provides a stowable propeller. This means that the propeller does not affect the landing angle available to the aircraft. For example, aircraft generally land in an upward landing angle (nose up, tail down). By being stowable, the propeller may not extend significantly lower than the fuselage of the aircraft at, or towards, the aft/tail end of the aircraft and so would not impact the ground during landing. The plurality of blades may he regularly spaced around the plane of rotation. i.e. with the same angle between adjacent blades.

[0016] The aircraft may be a passenger aircraft. The aircraft may be a single or a twin-aisle passenger aircraft. The aircraft may also have a tailplane, for example providing 'vertical" and/or "horizontal" stabilizer surfaces, to provide stability in yaw and/or pitch, respectively. The one or more engines may be located adjacent to or mounted to the fixed wings. The one or more engines may be jet engines, such as a turbofan engine or a turbojet engine. The propeller may be driven independently of the one or more engines.

[0017] Preferably, the propeller is located aft of the one or more engines.

[0018] Preferably, the propeller is located adjacent to, or aft of, a tailplane of the aircraft.

[0019] Preferably, the propeller is located aft of the fuselage.

[0020] Preferably, the plane of rotation of the propeller blades is substantially perpendicular to a fuselage axis.

[0021] The fuselage axis is the axis running along the length of the fuselage. In other words, it is the longitudinal axis of the fuselage. -4 -

[0022] More preferably, the propeller blades are configured to move from the deployed configuration to the stowed configuration, such that they move towards alignment with the fuselage axis.

[0023] Even more preferably, movement from the deployed configuration to the stowed configuration of a propeller blade involves movement of the propeller blade towards the fuselage. Alternatively, movement from the deployed configuration to the stowed configuration of a propeller blade involves movement of the propeller blade away from the fuselage. For example, the propeller blades may be folded towards each other and aftwards. For example, the blades may substantially align with the longitudinal axis of the fuselage.

[0024] Even more preferably, in its stowed configuration, a propeller blade is substantially aligned with an external surface of the fuselage. The above refers to the stowed configuration of the propeller blade. This allows the propeller blades to be effectively stowed, to reduce drag during cruise and to prevent any implications for landing angle of the aircraft.

[0025] The propeller may comprises a locking mechanism for locking (and unlocking) one or more propeller blades in the stowed configuration.

[0026] The blades may be retractable into the fuselage and/or may be stowed at least partially within the fuselage.

[0027] According to a second aspect of the invention there is also provided a method of operating the aircraft as described above, wherein the method comprises the steps of providing the propeller blades in the stowed configuration for cruise, moving the propeller blades to the deployed configuration, and when the propeller blades are in the deployed configuration, rotating the propeller blades and providing a reverse thrust to the aircraft in the air.

[0028] The method steps may occur in the specified order.

[0029] The second method step may be for descent of the aircraft. This enables the approach angle of the aircraft to be steepened and therefore cause approach noise over a smaller area/distance from the airport. By using a propeller, for example with a low tip -5 -speed, (rather than a clamshell airbrake, for example) to steepen the approach angle keeps the approach noise at a low level.

[0030] Preferably, the method comprises the step of moving the propeller blades from the deployed configuration to the stowed configuration for landing.

[0031] This method step may occur after the method steps described above.

[0032] According to a third aspect of the invention there is also provided a method of operating the aircraft as descried above, wherein the method comprises the step of moving the propeller blades from the stowed configuration to the deployed configuration after landing, and when the propeller blades are in the deployed configuration, rotating the propeller blades and providing a reverse thrust to the aircraft on the ground.

[0033] The method steps may occur in the specified order. The method step may occur after the method steps described above.

[0034] According to a fourth aspect of the invention there is also provided a method of operating an aircraft, the method including the following steps providing a forward thrust to the aircraft using one or more engines, providing lift to the aircraft using fixed wings, providing reverse thrust to the aircraft using a propeller, by rotating propeller blades of the propeller in a plane of rotation, the propeller being located aft of the fixed wings, and moving one or more of the propeller blades between a deployed configuration, in which the blade is located within the plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation.

[0035] According to a fifth aspect of the invention there is also provided an aircraft having a fuselage, fixed wings, for providing lift and being located partway along the fuselage, one or more engines for providing forward thrust, wherein the aircraft further comprises a propeller arranged to provide reverse thrust, wherein the propeller is located aft of the fixed wings, and wherein the aircraft further comprises an energy storage device connected to the propeller such that energy harnessed by the propeller can be stored by the energy storage device.

[0036] Such an aircraft is able to have a propeller that does not affect the aerodynamic flow over the fixed wings. The aircraft is also able to capture and store energy. This means that the aircraft is able to, for example, during descent, collect energy -6 -and help to slow the aircraft. This energy may later be used by the propeller to drive it in rotation in reverse pitch to provide a reverse thrust to the aircraft, for example, to slow the aircraft when the aircraft is on the ground, after landing.

[0037] The aircraft may include any, and any combination, of the main or dependent features of any of the other aspects. For example, it may include the "stowable propeller blade" main feature of the first aspect. For example, it may include the "propeller being located aft of the fuselage" dependent feature of the first aspect.

[0038] The aircraft may have an energy storing mode or configuration in which the propeller is arranged to be driven by oncoming airflow, and in which at least some of the kinetic energy of the propeller is captured and stored in the energy storage device. The energy storage device may be arranged to store energy generated by driving of the propeller by the oncoming airflow.

[0039] The one or more engines may be jet engines, such as a turbofan engine or a turbojet engine. The propeller may be driven independently of the one or more engines.

[0040] The energy storage device may be located adjacent to an APU (auxiliary power unit) of the aircraft. The energy storage device may be located adjacent to the propeller. The energy storage device may be located adjacent to, or within, a tailplane of the aircraft.

[0041] The energy storage device may be connected to the propeller via a clutch mechanism.

[0042] The propeller may be provided with a brake mechanism to slow and/or stop rotational movement of the propeller.

[0043] Preferably, the energy storage device is connected to the propeller such that energy can be provided to the propeller from the energy storage device. This enables rotation of propeller blades of the propeller using the energy from the storage device, at a later time. For example, the stored energy may be later used by the propeller to drive it in rotation in reverse pitch to provide a reverse thrust to the aircraft, for example, when the aircraft is on the ground. The energy storage device may be provided with a power transmissions mechanism that can convert torque and speed over a desired operating range. -7 -

[0044] Preferably, the propeller comprises one or more variable pitch blades.

[0045] The blades may be configurable in reverse pitch for providing the reverse thrust. The blades may be configurable in forward pitch to allow the propeller to be spun by an airflow, for example when capturing and storing energy.

[0046] Preferably, the energy storage device comprises a flywheel. Alternatively, or additionally the energy storage device may comprises an electrical, hydraulic, pneumatic and/or chemical energy storage mechanism.

[0047] According to a sixth aspect of the invention there is also provided a method of operating the aircraft as described above, wherein the method comprises the steps of rotating the propeller and harnessing energy from said rotation, and storing the harnessed energy in the energy storage device.

[0048] The rotating of the propeller may occur during descent of the aircraft. The method may include any of the method steps of the main or dependent features of any of the other aspects. For example, it may include the "stowing and/or deploying the propeller blade" main feature of the first aspect.

[0049] According to a seventh aspect of the invention there is also provided a method of operating the aircraft as described above, wherein the method comprises the steps of providing the propeller with energy from the energy storage device, and using the energy to rotate the propeller.

[0050] This method step may occur after the method steps described above.

[0051] The providing of the propeller with energy may occur after landing, when the aircraft is on the ground. Preferably, the propeller is rotated, using the energy from the energy storage device, to provide reverse thrust.

[0052] According to an eighth aspect of the invention there is also provided a method of operating an aircraft, the method including the following steps providing a forward thrust to the aircraft using one or more engines, providing lift to the aircraft using fixed wings, harnessing energy from the propeller and storing the energy in an energy storage device, and providing reverse thrust to the aircraft using a propeller, the propeller being located aft of the fixed wings. -8 -

[0053] The method may include any of the steps of the main or dependent features of any of the other aspects. For example, it may include the "stowing and/or deploying the propeller blade" main feature of the first aspect.

[0054] According to a ninth aspect of the invention there is also provided an aircraft having a fuselage, fixed wings, for providing lift and being located partway along the fuselage, one or more engines for providing forward thrust, wherein the aircraft further comprises a propeller arranged to provide reverse thrust, a landing gear, and a landing gear drive system for driving rotation of one or more wheels of the landing gear.

[0055] Such an aircraft is provided with (at least) two ways of slowing movement of the aircraft on the ground; the propeller and the landing gear drive system. This may mean that the aircraft does not require the one or more engines to be provided with thrust reverser capability. This would enable the engines potentially to be smaller, lighter and easier to maintain. The aircraft may also comprise friction wheel brakes (e.g. made of carbon). However, these may now only need to be used in an emergency situation (for example, rejected take-off or system failure) or for a park brake function. This would mean that the wear experienced by the wheel brakes is reduced, and so they may be able to be smaller, require easier maintenance and/or require less frequent replacement.

[0056] The aircraft may include any, and any cotnbination, of the main or dependent features of any of the other aspects. For example, it may include the "stowable propeller blade" main feature of the first aspect. For example, it may include the "propeller being located aft of the fuselage" dependent feature of the first aspect. For example, it may include the "energy storage device" main feature of the fifth aspect. For example, it may include the "flywheel" dependent feature of the fifth aspect.

[0057] The one or more engines may be jet engines, such as a turbofan engine or a turbojet engine. The propeller may be driven independently of the one or more engines.

[0058] The propeller may be used to retard the aircraft after landing to a given certain speed, and the landing gear drive system may be used to retard the aircraft from that speed to stationary.

[0059] According to a tenth aspect of the invention there is also provided a method of operating the aircraft as described above, the method comprising the steps of landing -9 -the aircraft on the ground, using the propeller to provide reverse thrust to slow movement of the aircraft over the ground, after the aircraft has slowed to a certain speed, using the landing gear drive system to provide a reverse force to further slow the aircraft over the ground.

[0060] The method may include any of the method steps of the main or dependent features of any of the other aspects. For example, it may include the "harnessing energy from the propeller and storing the energy in an energy storage device" main feature of the fifth aspect. For example, it may include the "providing the propeller with energy from the energy storage device" dependent feature of the fifth aspect.

[0061] The landing gear drive system may slow the aircraft to zero speed. The propeller may no longer, or at least no longer actively, provide a reverse thrust to the aircraft during the time that the landing gear drive system is providing, or at least actively providing, a reverse force. The landing gear drive system may provide a reverse force by driving wheel of the landing gear in a reverse direction and/or by providing an electrical (or hydraulic) resistive force to the forwards movement of the wheels.

[0062] According to an eleventh aspect of the invention there is also provided a method of operating an aircraft, the method including the following steps providing a forward thrust to the aircraft using one or more engines, providing lift to the aircraft using fixed wings, providing reverse thrust to the aircraft using a propeller, the propeller being located aft of the fixed wings, and providing a reverse force from a landing gear drive system to slow the aircraft over the ground.

[0063] The method may include any of the steps of the main or dependent features of any of the other aspects. For example, it may include the "stowing and/or deploying the propeller blade" main feature of the first aspect.

[0064] According to a twelfth aspect of the invention there is also provided an aircraft having a fuselage, fixed wings, for providing lift and being located partway along the fuselage, one or more engines for providing forward thrust, wherein the aircraft further comprises a propeller, independently driveable from the one or more engines, wherein the propeller is controllable so as to provide a variable direction of thrust to the aircraft during flight.

-10 - [0065] In other words, the propeller is controllable to provide a vectored propeller thrust. The aircraft may be configured such that the varying the direction of thrust generated by the propeller can produce a moment about the yaw axis of the aircraft. The propeller blades may be orientated in forward pitch in order for them to be spun by an oncoming airflow during flight. The propeller blades may be orientated in reverse pitch in order for them to provide reverse thrust. The propeller blades may be orientated at zero incidence to an oncoming airflow.

[0066] Such an aircraft is able to have a secondary method of steering the aircraft during flight (in addition to the conventional flight control surfaces). This may enable the aircraft to be provided with a smaller and lighter rudder (or elevator or ailerons) than otherwise would have been necessary.

[0067] The aircraft may include any, and any combination, of the main or dependent features of any of the other aspects. For example, it may include the "stowable propeller blade" main feature of the first aspect. For example, it may include the "propeller being located aft of the fuselage" dependent feature of the first aspect.

[0068] Preferably, the cyclic pitch of the propeller is controllable so as to provide the variable direction thrust.

[0069] That is to say, the aircraft comprises a cyclic pitch control configured to control the pitch (i.e. the angle) of the blades of the propeller depending on their rotational position. The rotational axis of the propeller may be fixed relative to the fuselage.

[0070] The propeller may be controllable such that the axis of rotation of the propeller blades is rotatable relative to the fuselage, the rotation being in about the yaw axis.

[0071] According to a thirteenth aspect of the invention there is also provided a method of operating the aircraft as described above, wherein the method comprises the steps of using the propeller to steer the aircraft by providing a variable direction thrust to the aircraft.

[0072] The steering of the aircraft using the propeller may be controlled using the steering control system. For example, the steering from the propeller is integrated into the steering control system, which also integrates the nose wheel steering control and/or the yaw control of the aircraft using the rudder.

[0073] The method may include any of the method steps of the main or dependent features of any of the other aspects. For example, it may include the "harnessing energy from the propeller and storing the energy in an energy storage device" main feature of the fifth aspect. For example, it may include the "providing the propeller with energy from the energy storage device" dependent feature of the fifth aspect.

[0074] According to a fourteenth aspect of the invention there is also provided a method of operating an aircraft, the method including the following steps providing a forward thrust to the aircraft using one or more engines, providing lift to the aircraft using fixed wings, providing a variable direction thrust to the aircraft using a propeller, thus steering the aircraft.

[0075] The method may include any of the steps of the main or dependent features of any of the other aspects. For example, it may include the "stowing and/or deploying the propeller blade-main feature of the first aspect.

[0076] According to a fifteenth aspect of the invention there is also provided an aircraft having a fuselage, fixed wings, for providing lift and being located partway along the fuselage, one or more engines for providing forward thrust, wherein the aircraft further comprises a propeller, for providing reverse thrust, the propeller comprising a first set of propeller blades rotatable in a first plane of rotation, and a second set of propeller blades, rotatable in a second plane of rotation, stacked in relation to the first plane, wherein the propeller is located aft of the fixed wings, the aircraft further comprises an energy storage device connected to the propeller such that energy harnessed by the propeller can be stored by the energy storage device, or one or more of the propeller blades are moveable between a deployed configuration, in which the blade is located within its plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation.

[0077] Such an aircraft gains the benefit of having stacked propeller blades, but also taking advantage of other features, such as the blades being stowable, there being an energy storage device and/or the propeller being aft of the fixed wings.

-12 - [0078] The above refers to the plane of rotation of that propeller blade. 1.e. the first plane if the blade is in the first set of blades.

[0079] The aircraft may include any, and any combination, of the main or dependent features of any of the other aspects. For example, it may include the "stowable propeller blade" main feature of the first aspect. For example, it may include the "propeller being located aft of the fuselage" dependent feature of the first aspect.

[0080] The aircraft could have I, 2 or all 3 of the optional features of the aspect.

[0081] Preferably, the first set of propeller blades is rotatable in a first direction and wherein the second set of propeller blades is rotatable in a second, opposite direction.

[0082] In other words, the sets of blades are contra-rotating.

[0083] Alternatively, the first set of propeller blades is rotatable in a first direction and wherein the second set of propeller blades is rotatable in the same first direction, and wherein each blade of the second set of blades lags behind a corresponding blade on the first set of blades.

[0084] In other words, the sets of blades are co-rotating.

[0085] The lag angle may be less than the angle between the blades in a set. The lag angle may be less than half the angle between the blades. The lag angle may be less than a third of the angle between the blades. For example, if there are three regularly spaced blades in each set of blades with an angle of 120 degrees between the blades, the second set of blades may lag behind the first set of blades by 20 to 40 degrees.

[0086] The blades of the second set my be shorter than the blades of the first set.

[0087] According to a sixteenth aspect of the invention there is also provided a method of operating the aircraft as described above.

[0088] According to a seventeenth aspect of the invention there is also provided an aircraft having a fuselage, fixed wings, for providing lift and being located partway along the fuselage, one or more engines for providing forward thrust, wherein the aircraft further comprises a propeller, for providing reverse thrust, the propeller having a plurality of propeller blades, and wherein at least one of the propeller blades has a tip portion that extends aft from, and out of, the plane of rotation, wherein the propeller is located aft of the fixed wings, the aircraft further comprises an energy storage device connected to the -13 -propeller such that energy harnessed by the propeller can be stored by the energy storage device, or one or more of the propeller blades are moveable between a deployed configuration, in which the blade is located within its plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation.

[0089] Such an aircraft gains the benefit of having radial inflow at the tips of the blades, and therefore reduced tip stalling when providing reverse thrust, but also taking advantage of other features, such as the blades being stowable, there being an energy storage device and/or the propeller being aft of the fixed wings.

[0090] The above refers to the plane of rotation of that propeller blade. I.e. the first plane if the blade is in the first set of blades.

[0091] The aircraft may include any, and any combination, of the main or dependent features of any of the other aspects. For example, it may include the "stowable propeller blade" main feature of the first aspect. For example, it may include the "propeller being located aft of the fuselage" dependent feature of the first aspect.

[0092] The aircraft could have 1, 2 or all 3 of the optional features of the aspect.

[0093] Preferably, the aft tip portion extends aft from the rest of the blade by at least 20% of the length of the rest of the blade.

[0094] More preferably at least 40% or 60% of the length of the rest of the blade.

[0095] Preferably, the aft tip portion extends aft from the rest of the blade by an angle of at least 60 degrees.

[0096] This is measured as the angle between the root to tip line on the rest of blade against the angle between the root to tip line of the aft tip portion. In other words, the angle is the angle deviation from the line of the rest of blade.

[0097] Preferably, all of the propeller blades are provided with such a tip portion that extends aft from, and out of, the plane of rotation.

[0098] According to an eighteenth aspect of the invention there is also provided a method of operating the aircraft as described above.

[0099] According to a ninteenth aspect of the invention there is also provided an aircraft having a fuselage, fixed wings, for providing lift and being located partway along the fuselage, one or more engines for providing forward thrust, wherein the aircraft -14 -further comprises a propeller, comprising a plurality of propeller blades, wherein the propeller is located aft of the fixed wings, and wherein one or more of the propeller blades is provided with one or more spanwise slots such that air can flow from one side of the propeller blade to an opposite side, through the spanwise slots.

[00100] The slots are described as spanwise as they extend longitudinally in a spanwise direction, i.e. along the span (length) of the propeller blade.

[09101] The spanwise slots may act as slotted flaps to prevent the air flow from detaching from the surface of the blades, especially when the propeller is providing reverse thrust.

[00102] The aircraft may include any, and any combination, of the main or dependent features of any of the other aspects. For example, it may include the "stowable propeller blade" main feature of the first aspect. For example, it may include the "propeller being located aft of the fuselage" dependent feature of the first aspect. For example, it may include the "energy storage device" main feature of the fifth aspect. For example, it may include the "flywheel" dependent feature of the fifth aspect.

[00103] The one or more engines may be jet engines, such as a turbofan engine or a turbojet engine. The propeller may be driven independently of the one or more engines.

[00104] Preferably, the one or more spanwise slots extend over at least 50% of the length of the blade.

[00105] Preferably, there is a further one or more spanwise slots extending substantially parallel to the one or more spanwise slots, at a different chordwise position on the blade.

[00106] There could be more than two so another further one or more spanwise slots.

[00107] According to a twentieth aspect of the invention there is also provided a method of using the aircraft as described above, wherein the method comprises the following steps using the propeller to provide a thrust force to the aircraft, and inducing air flow through the one or more spanwise slots.

[00108] According to a twenty-first aspect of the invention there is also provided a propeller comprising a plurality of propeller blades rotatable in a plane of rotation, wherein at least one propeller blade is at least partially in the form of a grid structure -15 -formed of a framework of crossing members defining apertures therebetween that pass through the blade.

[00109] Such a propeller provides a highly effective alternative to conventional propeller blades (aerodynamic fins). They are able to adjust the direction of the air passing over them (and conversely be moved by air flow over them) more effectively.

[00110] In other words, the propeller blades are formed at least partially like a grid fin.

[00111] The propeller of this aspect may be included on an aircraft. That aircraft may include any combination, of the main or dependent features of any of the other aspects. For example, it may include the "stowable propeller blade" main feature of the first aspect. For example, it may include the "stowing movement of the propeller blade towards alignment with the fuselage axis/the fuselage" or "significantly aligned with an external surface of the fuselage in stowed configuration" dependent features of the first aspect.

[00112] Grid fins are also known as lattice or waffle fins. Grid fins are generally comprised of an aerodynamic structural frame within which multiple aerodynamic surfaces (aerofoils/plates) are interlinked into a grid arrangement, such that air can flow through the open cells in between.

[00113] Preferably, the propeller blade is rotatable about its longitudinal axis so as to adjust the pitch angle of the grid framework to an incoming airflow.

[00114] The blade may be able to be rotated so as to be at zero incidence to the incoming airflow.

[00115] Preferably, the propeller blade is moveable between a deployed configuration, in which the blade is located within a plane of rotation of the blades, and a stowed configuration, in which the blade is located out of the plane of rotation.

[00116] Preferably, all of the propeller blades are at least partially in the form of a grid structure formed of a framework of crossing members defining apertures therebetween that pass through the blade.

[00117] According to a twenty-second aspect of the invention there is also provided a method of using the propeller as described above, wherein the method comprises the -16 -following steps rotating the propeller, and providing a propeller force, through air flow through the grid framework.

[00118] According to a twenty-third aspect of the invention there is also provided a propeller comprising a plurality of propeller blades rotatable in a plane of rotation, wherein at least one propeller blade is provided with a duct device, the duct device comprising an air duct, the air duct having an air inlet portion and an air outlet portion, wherein the air outlet portion has a smaller cross section than the air inlet portion.

[00119] As the air flows from the air inlet portion to the air outlet portion, its pressure rises (due to the smaller air outlet portion) which causes its temperature to rise. This enables a more effective conversion of the kinetic energy of the propeller to heat energy and so aids in slowing down movement of an aircraft, if the propeller is used as a braking device (for example by providing a reverse thrust or by being caused to rotate by movement of the aircraft through the air).

[00120] The propeller of this aspect may be included on an aircraft. That aircraft may include any combination, of the main or dependent features of any of the other aspects. For example, it may include the "stowable propeller blade" main feature of the first aspect. For example, it may include the "propeller being located aft of the fuselage" dependent feature of the first aspect.

[00121] The duct may have walls extending from inlet to outlet to contain air, so that air passing through the inlet, passes out of the outlet.

[00122] Air that flows through the duct of propeller blade may not flow over an aerofoil portion of the propeller blade.

[00123] Preferably, the duct device is located towards or at the tip of the propeller blade.

[00124] Preferably, the air duct extends in a direction substantially perpendicular to the propeller blade.

[00125] The air duct may extends perpendicular to a longitudinal axis of the propeller blade.

i001261 The air duct may extend in the direction of rotation.

[00127] Preferably, all of the propeller blades are provided with such a duct device.

-17 - [00128] According to a twenty-fourth aspect of the invention there is also provided a method of using the propeller as described above, wherein the method comprises the following steps rotating the propeller, and inducing air flow through the air duct from the air inlet to the air outlet.

[00129] According to a twenty-fifth aspect of the invention there is also provided a method of operating an aircraft, the aircraft having a propeller, the propeller being provided with a number of propeller blades mounted on a propeller hub and wherein the blades are substantially aligned along a blade axis, the method comprising the step of rotating the hub to a position where the blade axis is substantially horizontal, maintaining the hub in that position, and then landing the aircraft.

[00130] The method of this aspect may be used on any aircraft or with any propeller or in combination with other methods of the preceding aspects. The method may include any combination, of the main or dependent features of any of the other aspects. For example, it may include the "contra-rotating propeller hubs" feature of the fifteenth aspect.

[00131] The propeller hub may be mounting one blade, or two blades that are arranged at approximately 180 degrees to each other.

[00132] The aircraft may include a mechanism for controlling a stop position of a propeller hub.

[00133] Preferably, the method further comprises the step of (when the blade axis is substantially horizontal) rotating one or more propeller blades about its longitudinal axis so that the blade is at a pitch angle of less than 30 degrees to the flight direction of the aircraft.

[00134] More preferably, the method further comprises the step of rotating one or more propeller blades along its longitudinal axis so that the blade pitch angle varies between +30 and -30 degrees to the flight direction of the aircraft.

[00135] Even more preferably, the method further comprises the step of rotating one or more propeller blades based on roll movement of the aircraft. Rotating the propeller blades may provide horizontal stability and can act as extension of a horizontal stabiliser surface of the aircraft. This may mean that the horizontal stabilizer can have smaller area -18 -than it would need otherwise, meaning it may weigh less, and so reduce the weight of the aircraft overall.

[00136] The step of rotating one or more propeller blades may be based on yaw and/or pitch movement of the aircraft.

[00137] The blades may rotate about the longitudinal axis of the blades.

[00138] Preferably, the propeller may comprise more than one huh, with each hub provided with a number of propeller blades mounted on a propeller hub and wherein the blades on the propeller hub are substantially aligned along a blade axis, the method comprising the step of rotating all hubs to a position where the blade axes are substantially horizontal, maintaining the hubs in those positions, and then landing the aircraft.

[00139] The two hubs may rotate in the same direction (co-rotating) or different directions (contra-rotating).

[00140] it will of course be appreciated that features described in relation to one aspect of the present invention may be incorporated into other aspects of the present invention. For example, the method of the invention may incorporate any of the features described with reference to the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

[00141] Embodiments of the present invention will now be described by way of example only with reference to the accompanying schematic drawings of which: [00142] Figure 1 shows a perspective view of an aircraft according to a first embodiment of the invention; [00143] Figure 2 shows a schematic representation of different stages of decent and landing for the aircraft of Figure 1; [00144] Figure 3a shows a side view of the tailplane of the aircraft of Figure I; [00145] Figure 3b shows a side view similar to Figure 3a, also showing some internal components in the tailplane; -19 - [00146] Figure 4a shows a perspective view of a tailplane, with a propeller in a stowed configuration, which could be used instead of the tailplane of Figures 3a and 3b, on the aircraft of Figure 1, according to a second embodiment; [00147] Figure 4b shows a side view of the tailplane of Figure 4a, with a propeller in a deployed configuration, also showing some internal components in the tailplane; [00148] Figure 5 shows a schematic side view of a propeller blade and propeller hub that could be used in the propellers of Figures 3a and 3b or 4a and 4b; [00149] Figure 6a shows a front view of a propeller that could be used as the propellers of Figures 3a and 3b or 4a and 4b; [00150] Figure 6b shows the sectional view along line A-A of Figure 6a; [00151] Figure 7 shows a perspective view of a propeller including a duct device that could be used with the propellers of Figures 3a and 313 or 4a and 4b or with the propeller of Figures 6a and 6b; [00152] Figure 8a shows a perspective view of a propeller including a grid structure that could be used with the propellers of Figures 3a and 3b or 4a and 4b or with the propeller of Figures 6a and 6b or 7; and [00153] Figure 8b shows a different perspective view of the propeller of Figure 8a.

DETAILED DESCRIPTION

[00154] Figure 1 shows a perspective view of an aircraft 100 according to a first embodiment of the invention.

-20 - [00155] The aircraft 100 is a commercial passenger aircraft with a fuselage 101, defining a fuselage longitudinal axis 101a. The fuselage 101 provides aircraft seating arranged on both sides of a single aisle. The aircraft 100 has two main fixed wings; a left (port) wing 102 and a right (starboard) wing 103. Each wing 102, 103 is provided with a jet engine; a first jet engine 104 on the left wing 102 and a second jet engine 105 on the right wing 103. The aircraft 100 is also provided with landing gear including nose landing gear 106, left landing gear (not seen in Figure I) and right landing gear 108.

[00156] The aircraft 100 also comprises a tailplane 110 as a rear portion of the aircraft fuselage 101. This is shown in more detail in Figure 3a. The tailplane 110 has a horizontal stabilizer made up of a left horizontal stabilizer 1 I I and a right horizontal stabilizer 112. Each horizontal stabilizer III, 112 is provided with an elevator (left elevator not seen in Figure 1 and right elevator 113) to control the pitch of the aircraft 100. The tailplane 110 also has a vertical stabilizer 114 provided with a rudder 115 to control the yaw of the aircraft.

[00157] At the very rear of the aircraft 100, aft of the horizontal and vertical stabilizers 111, 112, 114 is a propeller 120, shown schematically in Figure 1.

[00158] The propeller 120 comprises two propeller blades 131, 132 arranged at 180 degrees to each other on a propeller hub 130, as shown in Figure 3a. The propeller blades 131, 132 are 3m long and rotate about the propeller hub 130 to define a plane of rotation 123 of the propeller 120. In other words, the propeller blades rotate within the plane of rotation 123. Of course, the propeller blades can be adjusted, for example to adjust the collective pitch of the blades, for example using a swash plate, servo controlled actuator(s) and/or a moveable coupling (such as a pintel bearing, universal joint, crown spline, Punk coupling and/or Oldham coupling) and so, after this adjustment, may be able to rotate in a different plane of rotation. The propeller 120 in fact is adjustable in collective pitch to have a range of planes of rotation that are possible. The plane 123 shown in Figure 1 is the "default" plane that is perpendicular to the fuselage axis I 10a and provides thrust in a direction substantially parallel to the fuselage axis I I Oa.

[00159] The propeller 120 can he arranged to rotate in a "reverse" configuration (i.e. with the blades to have reverse pitch) so that the thrust it imparts is in an aft direction and -21 -so provides a retardation force to the aircraft 100. In other words, the propeller 120 can act as an air brake.

[00160] The propeller 120 is shown in Figure 1 in its deployed configuration 121. In this configuration, the propeller 120 rotates to provide the reverse thrust described above. The deployed configuration allows for the propeller 120 to rotate in any suitable plane of rotation 123.

[00161] The propeller 120 is stowable, into a stowed configuration 122, as shown in Figure 3a. Here, the blades 131, 132 have been rotated out of the plane of rotation 123 and towards the fuselage 101. Hence, the blades are substantially aligned against an external surface of the tailplane 110.

[00162] Figure 3b additionally shows an APU (Auxiliary Power Unit) 116 of the aircraft, located in the tailplane 110 and an energy storage device 117. The energy storage device includes a flywheel. The flywheel may be a Carbon 1800 flywheel. Both the APU 116 and the energy storage device 117 are electrically connected to the propeller 120, as will be described later.

[00163] Figure 2 shows a schematic representation of different stages of decent and landing for the aircraft 100 of Figure 1.

[00164] The y-axis 200 of the graph of Figure 2 represents the altitude of the aircraft 100. The aircraft 100 is shown at four different altitudes and modes.

[00165] In a first altitude 201, the aircraft is cruising and the propeller 120 is in its stowed position. It is stowed so as to minimise the drag on the aircraft caused by the propeller 120. The propeller 120 will also be stowed for taxi out and take off.

[00166] At a lower second altitude 202, the aircraft has deployed the propeller 120.

The propeller 120 is arranged in a "forwards" configuration (i.e. the blades are in forward pitch) and is rotated by the airflow over it. The propeller is connected to the energy storage device 117 and so the kinetic energy due to rotation of the propeller 120 can be converted (recovered) to electrical energy by the flywheel and stored in the storage device I 17 as electrical energy.

[00167] During this second mode 202, the propeller I 20 may he adjusted to change the collective pitch of the blades and so provide some pitch or yaw directional control to -22 -the aircraft. Hence, because of this the aircraft 100 may be designed with smaller elevators and/or rudder than it otherwise would have had.

[00168] In this mode, the propeller helps to slow the speed of the aircraft, due to the energy recovery. However, it does so without significantly increasing the drag of the aircraft 100 and with a low propeller tip speed, and so does so with minimal increase in noise level. This means there is less disturbance for residents etc. near the airport where the aircraft 100 is going to land. Hence, the approach angle can be steepened without significantly increasing the noise level of the approach. The steeper approach also means that the approach noise is heard over a smaller area/distance. It also means that the approach noise is generated further away from the ground (as the aircraft is higher for longer) and therefore the noise is naturally attenuated more before reaching ground level. Here, the kinetic energy lost due to the reduction in speed of the aircraft is extracted and stored, rather than dissipated as noise (turbulence).

[00169] The duration of this second mode 202 may be decided based on the time taken to reach peak energy storage in the energy storage device 117. 'The propeller 120 may then be braked to stop rotation of the blades and then stowed.

[00170] At a third even lower altitude 203, the aircraft 100 is on approach to a runway. Here, the propeller 120 is stowed and the landing gear has been extended, ready for landing. It is important that the propeller 120 is stowed so that it does not impede landing (at a nose up pitch angle) of the aircraft 100. It also means the noise during approach is minimised, due to lower drag caused by the blades.

[00171] After the aircraft 100 has landed (zero altitude, as shown by 204), and the nose landing gear is on the ground with "weight on wheels", the propeller 120 can be deployed again, this time in a reverse configuration. Here, the blades are driven (in reverse pitch) to provide a reverse thrust to the aircraft 100. This helps to slow the aircraft down.

111191721 This may be done in combination with thrust reversers on the jet engines 104, 105. It may be done, alternatively or in addition, in combination with a landing gear drive system (not shown) connected to one or more wheels of the landing gear, operating to retard rotational movement of the one or more wheels. It may also be done, alternatively -23 -or in addition, in combination with wheel brakes, such as conventional friction wheel brakes.

[00173] For example, the propeller 120 may be used to slow the aircraft 100 down to knots. After that, a different mechanism, such the landing gear drive system, may be used.

[00174] The energy required to drive the propeller 120 is provided by the electrical energy stored in the energy storage device 117. If further energy is required, this may be taken from the APU 116.

[00175] During this fourth mode 204, the propeller 120 may be adjusted to change the collective pitch of the blades and so provide some pitch or yaw directional control to the aircraft. Hence, because of this the aircraft 100 may be designed with smaller elevators and/or rudder than it otherwise would have had. Providing a downwards pitch direction to the aircraft would increase the weight on the landing gear wheels and would increase the efficiency of the wheel braking.

[00176] _Figure 4a shows a perspective view of a tailplane 110, with a propeller 120 in a stowed configuration, which could be used instead of the tailplane of Figures 3a and 3b, on the aircraft of Figure 1, according to a second embodiment.

[00177] Here, the propeller 120 comprises two sets of blades.

[00178] A first set of blades comprises two blades 131, 132 arranged at 180 degrees to each other on a propeller hub 130. The propeller blades 131, 132 rotate about the propeller hub 130 to define a plane of rotation. In other words, this first set of blades is similar to the propeller 120 of Figure 3a. As before, the first set of propeller blades can be adjusted, for example to adjust the collective pitch of the blades, and so, after this adjustment, may be able to rotate in a different plane of rotation.

[00179] A second set of blades comprises two blades 136, 137 arranged at 180 degrees to each other on a second propeller hub 135. The second propeller hub 135 is mounted aft of the first propeller hub 130 and is rotatable independently of the first hub 130. The propeller blades 136, 137 rotate about the propeller hub 135 to define a plane of rotation. In other words, this second set of blades is similar to the first set of blades, but mounted aft of the first set. As before, the second set of propeller blades can be adjusted, -24 -for example to adjust the collective pitch of the blades, and so, after this adjustment, may be able to rotate in a different plane of rotation.

[00180] In Figure 4a, the first and second sets of blades are shown in a stowed configuration 122. Importantly, here, the stowed configuration does not involve the blades being rotated towards the fuselage. Instead, here, both sets of blades are orientated so that the two blades of each set are substantially horizontal. In fact, the hubs 130, 135 include a mechanism (not shown) for ensuring that the blades can be stopped and maintained in this "horizontal" orientation.

[00181] Hence, in this position, they do not impede landing of the aircraft 100. In addition, the blades 131, 132, 136, 137 are arranged at zero incidence (i.e. "zero pitch") so as not to provide any overall thrust to the aircraft 100.

[00182] Figure 4b shows a side view of the tailplane 110 of Figure 4a, with the propeller 120 in a deployed configuration 121. This Figure also shows the APU 116 and energy storage device 117 of the tailplane 110.

[00183] In the deployed configuration 121, the blades 131, 132, 136, 137 are arranged at the required pitch (i.e. not zero pitch) and are rotatable in their planes of rotation. Here, reference numeral 124 represents a blade axis -i.e. an axis extending longitudinally across both blades 136, 137. It is this blade axis 124 that is horizontal in the stowed configuration of Figure 4a.

[00184] Figure 5 shows a schematic side view of a propeller blade 132 and propeller hub 130 that could be used in the propellers of Figures 3a and 36 or 4a and 4b.

[00185] Here, the propeller blade 132 (and all other blades in the set of blades or propeller) is provided with a tip portion 140 that extends aftwards (i.e. in the backwards direction, away from the fuselage 110). Here, arrow 141 represents the forwards direction (direction of travel) of the aircraft 100.

[00186] Arrows 142 represent the airflow over and around the propeller 120 when operating in a "reverse" configuration, showing that the aftwardly extending tip potion 140 helps to increase the airflow back over the blade 132 (because of radial inflow) and prevent diffusion away from the blade 132, and hence prevent tip stall. Region 143 aft of -25 -the blade 132 is a region of less diffusion and increased airflow. Region 144 in front of the blade 132 represents a region of adiabatic temperature rise.

[00187] The blades may be further optimised for the reverse pitch configuration, such as by reversing the blade properties (in comparison to a conventional blade designed for a forward configuration).

[09188] The tip portion 140 extends aft at an angle 145 of 80 degrees from the main portion of the blade 132, and out of the plane of rotation 123.

[00189] Figure 6a shows a front view of a propeller 120 that could be used as the propellers of Figures 3a and 3b or 4a and 4b.

[00190] Here, the propeller has four blades 13!, 132, 133, 134 (each 3m long) as a single set of blades attached to a propeller hub 130. The four blades 131 to 134 are arranged evenly so as to be at 90 degrees apart around the propeller hub 130. Each blade has a rounded end. Each blade is provided with two spanwise slots (collectively 150). The two spanwise slots 151, 152 extend along a major proportion of the length (span) of the blade from near the root of the blade (where it meets the hub 130) to near the tip (rounded end) of the blade.

[00191] The first spanwise slot 151 is located at a chordwise position towards a leading edge of the blade and runs substantially parallel to the leading edge. The second spanwise slot 152 is located at a chordwise position towards a trailing edge of the blade and runs substantially parallel to the trailing edge.

[00192] Figure 6b shows the sectional view along line A-A on blade 134 of Figure 6a.

Here, it can be seen that the spanwise slots 151, 152 extend from a first side (i.e. the front side seen in Figure 6a, that actually faces aft in relation to the aircraft) to a second, opposite side. Hence, both slots enable the leading edge and tailing edge to act as slotted flaps, helping to reduce airflow separation over the propeller blade 134 and help keep the airflow attached.

[00193] The chordwise slots 151, 152 are another way that may be used to optimise the blades for a reverse configuration.

-26 - [00194] Figure 7 shows a perspective view of a propeller 120 including a duct device that could be used with the propellers of Figures 3a and 3b or 4a and 4b or with the propeller of Figures 6a and 6b.

[00195] Here, the duct device 160 comprises an oval inlet 161, an oval outlet 162 and walls 165 extending from the inlet to the outlet to enclose air that enters the inlet, until it reaches the outlet. The inlet has a larger cross-sectional area than the outlet and so the airflow is accelerated as it passes through the duct device 160.

[00196] A duct device 160 is located on each tip of the four blades 131, 132, 133, 134 of the propeller 120. Importantly, the duct device 160 is orientated so that the inlet 161 faces in the direction of rotation 163 of the propeller blades so that air enters the inlet 161 and exits the outlet 162.

[00197] Each duct device 160 has a "default" orientation at 90 degrees to the propeller blade. However, each duct device is rotatable 164 so as to change its orientation and the incidence angle of the inlet to the oncoming airflow.

[00198] Having the airflow accelerate through the duct device 160 causes kinetic energy to be dissipated as heat, as the air temperature and pressure rises. This provides an efficient mechanism to aid slowing down of the aircraft 100 as more energy is dissipated.

[00199] The duct devices 160 are another way that may be used to optimise the blades for a reverse configuration.

[00200] Figure 8a shows a perspective view of a propeller 120 including a grid structure 170 that could be used with the propellers of Figures 3a and 3b or 4a and 4b or with the propeller of Figures 6a and 6b or 7. Figure 8b shows a different perspective view of the propeller 120 of Figure 8a.

[00201] Here, it can be seen that each propeller blade 131, 132, 133, 134 is in the form of the grid structure (or framework) 170. Hence, each propeller blade comprises a number of cells (or apertures) 172 defined by cell walls of the grid. Hence, air flows through the cells 172 of the grid and imparts a force on the grid cell walls to rotate the propeller blades about the hub 130 (in the forward configuration). In the reverse configuration, the propeller hub 130 drives rotation of the blades and so causes air to flow through the cells and impart a force to drive backwards or retard the aircraft.

-27 - [00202] The grid framework is capable of generating large aerodynamic forces, compared to conventional propeller blades.

[00203] It is noted that each blade 131, 132, 133, 134 can rotate about its longitudinal axis about lug 171 on the hub 130. This allows the angle of incidence of the blades to be changed from a forward pitch to a reverse pitch and/or to/from a zero incidence pitch.

[00204] The blades 131, 132, 133, 134 can also rotate about the lugs 172 to stow against the fuselage (similar to as for the blades in Figures 3a and 3b), in a low drag stowed configuration.

[1110205] Whilst the present invention has been described and illustrated with reference to particular embodiments, it will be appreciated by those of ordinary skill in the art that the invention lends itself to many different variations not specifically illustrated herein. By way of example only, certain possible variations will now be described.

[00206] The aircraft 100 may or may not include a landing gear drive system (which may or may not be able to retard the aircraft) and/or engine thrust reversers and/or an emergency ram air turbine.

[00207] A suitable propeller may include any number and combination of the propeller features described here.

[00208] For example, a propeller may have two sets of blades, as described in relation to Figures 4a and 4b, but these sets may each have four (or any other suitable number of blades) in each set, such as shown in Figure 6a.

[00209] As another example, the "folding back" stowing mechanism of Figures 3a and 3b may be used with any other feature of the propeller, such as spanwise slots, aft-extending tips, grid frameworks and/or having any suitable number of blades.

[00210] As another example, one or more (or all) propeller blades in one or more sets may be provided with one or more spanwise slots.

[00211] As another example, the duct device of Figure 7 or the grid framework of Figure 8a and 8b may be used in combination with each other and/or in combination with any suitable number of propeller blades or sets and/or in combination with the use of spanwise slots and/or rear-extending tip portions.

-28 - [00212] The aircraft 100 may be any suitable size. For example, it may be a single-aisle or twin-aisle aircraft.

[00213] The engines 104, 105 may be turbo fan or propeller engines, or any other suitable engine for providing forward thrust to the aircraft 100.

[00214] The landing gear configuration may be any suitable configuration. The wings may be any suitable size and shape. The tailplane surfaces III, 112, 114 and control surfaces 113, I IS may be any suitable size and shape.

[00215] The stowing mechanism of the propeller may be any suitable mechanism. For example, it could be a stowing mechanism described here (folding back towards fuselage and/or being held horizontal) and/or any other suitable mechanism/movement.

[00216] Any suitable energy storage device 117 (that may or may not use a flywheel) may be used. There may be no such device and no energy recovery from the propeller. For example, second mode 202 of Figure 2 may not occur.

[00217] Alternatively, fourth mode 204 may not occur and the propeller may not be used to retard the aircraft on the ground.

[00218] Any number and size and shape of blades may be used in each blade set. For example, there could be two blades, each 3m long. For example, there could be four blades, each 3m long. For example, there could be five blades, each 4.5m long. For example, there could be four blades, each 4.5m long. For example, there could be four blades, each 5m long.

[00219] Any suitable number of blade sets may be used.

[00220] If there are two or more blade sets, the first and second sets may be contra-rotating (the first set of propeller blades being rotatable in a first direction and the second set of propeller blades being rotatable in a second, opposite direction) or co-rotating (the first set of propeller blades being rotatable in a first direction and the second set of propeller blades being rotatable in the same first direction lagging behind, or vice versa). The lagging blades may be slightly shorter than the blades in front.

[00221] The first set of blades may be fore or aft of the second set of blades.

-29 - [00222] The propeller blades 131 to 137 may have variable pitch. The blades may be able to be controlled by controlling cyclic and/or collective pitch of the blades on a set. Any suitable mechanism for rotating the blades may be used.

[00223] The form of the aft-extending tip portion 140 may be any suitable angle 145, shape and length.

[00224] The spanwise slots 151, 152 may be any suitable length, width, shape and size, and may be located anywhere suitable on the blades.

[00225] Any suitable size and shape duct device and inlet/outlets may be used. The duct devices 160 may not be located at the blades tips and instead may be located along the length of the blade(s).

[00226] Any suitable form of gird framework 170 may be used. For example, grid framework may be any suitable size and shape and may not comprise the whole area of the blade. The cells 172 may be any suitable size, shape and through-length.

[00227] Where in the foregoing description, integers or elements are mentioned which have known, obvious or foreseeable equivalents, then such equivalents are herein incorporated as if individually set forth. Reference should be made to the claims for determining the true scope of the present invention, which should be construed so as to encompass any such equivalents. It will also be appreciated by the reader that integers or features of the invention that are described as preferable, advantageous, convenient or the like are optional and do not limit the scope of the independent claims. Moreover, it is to be understood that such optional integers or features, whilst of possible benefit in some embodiments of the invention, may not be desirable, and may therefore be absent, in other embodiments.

[00228] It should be noted that throughout this specification, "or" should be interpreted as "and/or".

Claims

-30 -CLAIMSAn aircraft having: i) a fuselage, ii) fixed wings, for providing lift and being located partway along the fuselage, and iii) one or more engines for providing forward thrust, wherein the aircraft further comprises: iv) a propeller, comprising a plurality of propeller blades rotatable in a plane of rotation, arranged to provide reverse thrust, wherein the propeller is located aft of the fixed wings, and wherein one or more of the propeller blades are moveable between a deployed configuration, in which the blade is located within the plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation.
2. An aircraft as claimed in claim 1, wherein the propeller is located aft of the one or more engines.
3. An aircraft as claimed in claim 1 or claim 2, wherein the propeller is located adjacent to, or aft of, a tailplane of the aircraft.
4. An aircraft as claimed in any of claims 1 to 3, wherein the propeller is located aft of the fuselage.
5. An aircraft as claimed in any of claims 1 to 4, wherein the plane of rotation of the propeller blades is substantially perpendicular to a fuselage axis.
-31 - 6. An aircraft as claimed in claim 5, wherein the propeller blades are configured to move from the deployed configuration to the stowed configuration, such that they move towards alignment with the fuselage axis.
7. An aircraft as claimed in claim 6, wherein movement from the deployed configuration to the stowed configuration of a propeller blade involves movement of the propeller blade towards the fuselage.
8. An aircraft as claimed in claim 7, wherein, in its stowed configuration, a propeller blade is substantially aligned with an external surface of the fuselage.
9. A method of operating the aircraft of any of claims 1 to 8, wherein the method comprises the steps of: - providing the propeller blades in the stowed configuration for cruise, - moving the propeller blades to the deployed configuration, and - when the propeller blades are in the deployed configuration, rotating the propeller blades and providing a reverse thrust to the aircraft in the air.
10. A method of operating the aircraft of any of claims 1 to 8, wherein the method comprises the step of: - moving the propeller blades from the deployed configuration to the stowed configuration for landing.
11. A method of operating the aircraft of any of claims 1 to 8, wherein the method comprises the step of: - moving the propeller blades from the stowed configuration to the deployed configuration after landing, and - when the propeller blades are in the deployed configuration, rotating the propeller blades and providing a reverse thrust to the aircraft on the ground.
-32 - 12. A method of operating an aircraft, the method including the following steps: providing a forward thrust to the aircraft using one or more engines, providing lift to the aircraft using fixed wings, - providing reverse thrust to the aircraft using a propeller, by rotating propeller blades of the propeller in a plane of rotation, the propeller being located aft of the fixed wings, and - moving one or more of the propeller blades between a deployed configuration, in which the blade is located within the plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation.
13. An aircraft having: i) a fuselage, ii) fixed wings, for providing lift and being located partway along the fuselage, iii) one or more engines for providing forward thrust, wherein the aircraft further comprises: iv) a propeller arranged to provide reverse thrust, wherein the propeller is located aft of the fixed wings, and wherein the aircraft further comprises: v) an energy storage device connected to the propeller such that energy harnessed by the propeller can be stored by the energy storage device.
14. An aircraft as claimed in claim 13, wherein the energy storage device is connected to the propeller such that energy can be provided to the propeller from the energy storage device.
-33 - 15. An aircraft as claimed in claim 13 or 14, wherein the propeller comprises one or more variable pitch blades.
16. An aircraft as claimed in claim 13, 14 or 15, wherein the energy storage device comprises a flywheel.
17. A method of operating the aircraft of any of claims 13 to 16, wherein the method comprises the steps of: - rotating the propeller and harnessing energy from said rotation, and - storing the harnessed energy in the energy storage device.
18. A method of operating the aircraft of any of claims 13 to 16, wherein the method comprises the steps of: - providing the propeller with energy from the energy storage device, and - using the energy to rotate the propeller.
19. A method of operating an aircraft, the method including the following steps: - providing a forward thrust to the aircraft using one or more engines, - providing lift to the aircraft using fixed wings, - harnessing energy from the propeller and storing the energy in an energy storage device, and - providing reverse thrust to the aircraft using a propeller, the propeller being located aft of the fixed wings.
20. An aircraft having: i) a fuselage, ii) fixed wings, for providing lift and being located partway along the fuselage, -34 -iii) one or more engines for providing forward thrust, wherein the aircraft further comprises: iv) a propeller arranged to provide reverse thrust, v) a landing gear, and vi) a landing gear drive system for driving rotation of one or more wheels of the landing gear.
21. A method of operating the aircraft of claim 20, wherein the method comprises the steps of: - landing the aircraft on the ground, - using the propeller to provide reverse thrust to slow movement of the aircraft over the ground, after the aircraft has slowed to a certain speed, using the landing gear drive system to provide a reverse force to further slow the aircraft over the ground.
22. A method of operating an aircraft, the method including the following steps: - providing a forward thrust to the aircraft using one or more engines, - providing lift to the aircraft using fixed wings, - providing reverse thrust to the aircraft using a propeller, the propeller being located aft of the fixed wings, and - providing a reverse force from a landing gear drive system to slow the aircraft over the ground.
23. An aircraft having: i) a fuselage, -35 -ii) fixed wings, for providing lift and being located partway along the fuselage, iii) one or more engines for providing forward thrust, wherein the aircraft further comprises: iv) a propeller, independently driveable from the one or more engines, wherein the propeller is controllable so as to provide a variable direction of thrust to the aircraft during flight.
24. An aircraft as claimed in claim 23, wherein the cyclic pitch of the propeller is controllable so as to provide the variable direction thrust.
25. A method of operating the aircraft of claim 23 or claim 24, wherein the method comprises the steps of: - using the propeller to steer the aircraft by providing a variable direction thrust to the aircraft.
26. A method of operating an aircraft, the method including the following steps: - providing a forward thrust to the aircraft using one or more engines, - providing lift to the aircraft using fixed wings, - providing a variable direction thrust to the aircraft using a propeller, thus steering the aircraft.
27. An aircraft having: i) a fuselage, ii) fixed wings, for providing lift and being located partway along the fuselage, iii) one or more engines for providing forward thrust, -36 -wherein the aircraft further comprises: iv) a propeller, for providing reverse thrust, the propeller comprising: - a first set of propeller blades rotatable in a first plane of rotation, and - a second set of propeller blades, rotatable in a second plane of rotation, stacked in relation to the first plane, wherein: - the propeller is located aft of the fixed wings, - the aircraft further comprises an energy storage device connected to the propeller such that energy harnessed by the propeller can be stored by the energy storage device, or - one or more of the propeller blades are moveable between a deployed configuration, in which the blade is located within its plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation.
28. An aircraft as claimed in claim 27, wherein the first set of propeller blades is rotatable in a first direction and wherein the second set of propeller blades is rotatable in a second, opposite direction.
29. An aircraft as claimed in claim 27 or claim 28, wherein the first set of propeller blades is rotatable in a first direction and wherein the second set of propeller blades is rotatable in the same first direction, and wherein each blade of the second set of blades lags behind a corresponding blade on the first set of blades.
30. A method of operating the aircraft of any of claims 27 to 29.
31. An aircraft having: i) a fuselage, -37 -ii) fixed wings, for providing lift and being located partway along the fuselage, iii) one or more engines for providing forward thrust, wherein the aircraft further comprises: iv) a propeller, for providing reverse thrust, the propeller having a plurality of propeller blades, and wherein at least one of the propeller blades has a tip portion that extends aft from, and out of, the plane of rotation wherein: - the propeller is located aft of the fixed wings, - the aircraft further comprises an energy storage device connected to the propeller such that energy harnessed by the propeller can be stored by the energy storage device, or - one or more of the propeller blades are moveable between a deployed configuration, in which the blade is located within its plane of rotation, and a stowed configuration, in which the blade is located out of the plane of rotation.
32. An aircraft as claimed in claim 31, wherein the aft tip portion extends aft from the rest of the blade by at least 20% of the length of the rest of the blade.
33. An aircraft as claimed in claim 31 or claim 32, wherein the aft tip portion extends aft from the rest of the blade by an angle of at least 60 degrees.
34. An aircraft as claimed in claim 31, 32 or 33, wherein all of the propeller blades are provided with such a tip portion that extends aft from, and out of, the plane of rotation.
35. A method of operating the aircraft of any of claims 31 to 33.
36. An aircraft having: -38 -i) a fuselage, ii) fixed wings, for providing lift and being located partway along the fuselage, iii) one or more engines for providing forward thrust, wherein the aircraft further comprises: iv) a propeller, comprising a plurality of propeller blades, wherein the propeller is located aft of the fixed wings, and wherein one or more of the propeller blades is provided with one or more spanwise slots such that air can flow from one side of the propeller blade to an opposite side, through the spanwise slots.
37. An aircraft as claimed in claim 36, wherein the one or more spanwise slots extend over at least 50% of the length of the blade.
38. An aircraft as claimed in claim 36 or claim 37, wherein there is a further one or more spanwise slots extending substantially parallel to the one or more spanwise slots, at a different chordwise position on the blade.
39. A method of using the aircraft of any of claims 36 to 38, wherein the method comprises the following steps: - using the propeller to provide a thrust force to the aircraft, and - inducing air flow through the one or more spanwise slots.
40. A propeller comprising a plurality of propeller blades rotatable in a plane of rotation, wherein at least one propeller blade is at least partially in the form of a grid structure formed of a framework of crossing members defining apertures therebetween that pass through the blade.
-39 - 41. A propeller as claimed in claim 40, wherein the propeller blade is rotatable about its longitudinal axis so as to adjust the pitch angle of the grid framework to an incoming airflow.
42. A propeller as claimed in claim 40 or claim 41, wherein the propeller blade is moveable between a deployed configuration, in which the blade is located within a plane of rotation of the blades, and a stowed configuration, in which the blade is located out of the plane of rotation.
43. A propeller as claimed in any of claims 40 to 42, wherein all of the propeller blades are at least partially in the form of a grid structure formed of a framework of crossing members defining apertures therebetween that pass through the blade.
44. A method of using the propeller of any of claims 40 to 43, wherein the method comprises the following steps: - rotating the propeller, and - providing a propeller force, through air flow through the grid framework.
45. A propeller comprising a plurality of propeller blades rotatable in a plane of rotation, wherein at least one propeller blade is provided with a duct device, the duct device comprising an air duct, the air duct having an air inlet portion and an air outlet portion, wherein the air outlet portion has a smaller cross section than the air inlet portion.
46. A propeller as claimed in claim 45, wherein the duct device is located towards or at the tip of the propeller blade.
47. A propeller as claimed in claim 45 or claim 46, wherein the air duct extends in a direction substantially perpendicular to the propeller blade.
-40 - 48. A propeller as claimed in any of claims 45 to 47, wherein all of the propeller blades are provided with such a duct device.
49. A method of using the propeller of any of claims 45 to 48, wherein the method comprises the following steps: - rotating the propeller, and - inducing air flow through the air duct from the air inlet to the air outlet.
50. A method of operating an aircraft, the aircraft having a propeller, the propeller being provided with a number of propeller blades mounted on a propeller hub and wherein the blades are substantially aligned along a blade axis, the method comprising the step of rotating the hub to a position where the blade axis is substantially horizontal, maintaining the hub in that position, and then landing the aircraft.
51. The method of claim 50, further comprising the step of rotating one or more propeller blades about its longitudinal axis so that the blade is at a pitch angle of less than 30 degrees to the flight direction of the aircraft.
52. The method of claim 51, further comprising the step of rotating one or more propeller blades along its longitudinal axis so that the blade pitch angle varies between +30 and -30 degrees to the flight direction of the aircraft.
53. The method of claim 52, further comprising the step of rotating one or more propeller blades based on roll movement of the aircraft.
54. The method of any of claims 50 to 53, wherein the propeller may comprise more than one hub, with each hub provided with a number of propeller blades mounted on a propeller huh and wherein the blades on the propeller hub are substantially aligned along a blade axis, the method comprising the step of rotating all hubs to a position where the blade axes are substantially horizontal, maintaining the hubs in those positions, and then landing the aircraft.