Systems and methods for propeller blade retention

Apparatus, systems, and methods for a propeller blade retention system. The retention system may include a hub including a socket formed by an inner surface of the hub, a blade extending into the socket and a retention sleeve having a first portion and a second portion. The retention system may include a filler sleeve disposed between the blade and the second portion of the retention sleeve, a first bearing disposed between the second portion of the retention sleeve and the inner surface of the hub, the first bearing having a first race, and a second bearing disposed between the first portion of the retention sleeve and the inner surface of the hub, the second bearing having a second race. The retention system may include a cap comprising a body portion and a flange portion. The retention system may include a shim carrier.

TECHNICAL FIELD

This disclosure relates generally to the field of powered aerial vehicles. More particularly, and without limitation, the present disclosure relates to innovations in retaining aircraft propeller blades.

SUMMARY

The present disclosure addresses systems, components, and techniques primarily for use in a non-conventional aircraft driven by an electric propulsion system. For example, the aircraft of the present disclosure may be configured for frequent (e.g., over 50 flights per work day), short-duration flights (e.g., less than 100 miles per flight) over, into, and out of densely populated regions. The aircraft may be configured to carry 4-6 passengers or commuters who have an expectation of a comfortable experience with low noise and low vibration. Accordingly, it may be desired that components of the aircraft are configured and designed to withstand frequent use without wearing, generate less heat and vibration, and that the aircraft include mechanisms to effectively control and manage heat or vibration generated by the components. Further, it may be intended that several of these aircraft operate near each other over a crowded metropolitan area. Accordingly, it may be desired that their components are configured and designed to generate low levels of noise interior and exterior to the aircraft, and to have a variety of safety and backup mechanisms. For example, it may be desired for safety reasons that the aircraft be propelled by a distributed propulsion system, avoiding the risk of a single point of failure, and that they are capable of conventional takeoff and landing on a runway. Moreover, it may be desired that the aircraft can safely vertically takeoff and land from and into relatively small or restricted spaces compared to traditional airport runways (e.g., vertiports, parking lots, or driveways) while transporting several passengers or commuters with accompanying baggage. These use requirements may place design constraints on aircraft size, weight, operating efficiency (e.g., drag, energy use), which may impact the design and configuration of the aircraft components.

Disclosed embodiments provide new and improved configurations of aircraft components that are not observed in conventional aircraft, and/or identified design criteria for components that differ from those of conventional aircraft. Such alternate configurations and design criteria, in combination addressing drawbacks and challenges with conventional components, yielded the embodiments disclosed herein for various configurations and designs of components for an aircraft driven by an electric propulsion system.

In some embodiments, the distributed electric propulsion system may include twelve electric engines, which may be mounted on booms forward and aft of the main wings of the aircraft. A subset of the electric engines, such as those mounted forward of the main wings, may be tiltable mid-flight between a horizontally oriented position (e.g., to generate forward thrust for cruising) and a vertically oriented position (e.g., to generate vertical lift for takeoff, landing, and hovering). The propellers of the forward electric engines may rotate in a clockwise or counterclockwise direction. Propellers may counter-rotate with respect to adjacent propellers. The aft electric engines may be fixed in a vertically oriented position (e.g., to generate vertical lift). The propellers may also rotate in a clockwise or counterclockwise direction. In some embodiments, the difference in rotation direction may be achieved using the direction of engine rotation. In other embodiments, the engines may all rotate in the same direction, and gearing may be used to achieve different propeller rotation directions

In some embodiments, an aircraft may possess quantities of electric engines in various combinations of forward and aft engine configurations. For example, an aircraft may possess six forward and six aft electric engines, four forward and four aft electric engines, or any other combination of forward and aft engines, including embodiments where the number of forward electric engines and aft electric engines are not equivalent.

In some embodiments, for a vertical takeoff and landing (VTOL) mission, the forward and aft electric engines may provide vertical thrust during takeoff and landing. During flight phases where the aircraft is moving forward, the forward electric engines may provide horizontal thrust, while the propellers of the aft electric engines may be stowed at a fixed position in order to minimize drag. The aft electric engines may be actively stowed with position monitoring. Transition from vertical flight to horizontal flight and vice-versa may be accomplished via the tilt propeller subsystem. The tilt propeller subsystem may redirect thrust between a primarily vertical direction during vertical flight mode to a horizontal or near-horizontal direction during a forward-flight cruising phase. A variable pitch mechanism may change the forward electric engine's propeller-hub assembly blade collective angles for operation during the hover-phase, transition phase, and cruise-phase.

In some embodiments, in a conventional takeoff and landing (CTOL) mission, the forward electric engines may provide horizontal thrust for wing-borne take-off, cruise, and landing, and the wings may provide vertical lift. In some embodiments, the aft electric engines may not be used for generating thrust during a CTOL mission and the aft propellers may be stowed in place. In other embodiments, the aft electrical engines may be used at reduced power to shorten the length of the CTOL takeoff or landing.

Embodiments of the present disclosure include a propeller blade retention system. Some disclosed embodiments include a hub including a socket formed by an inner surface of the hub. Some disclosed embodiments include a blade extending into the socket. Some disclosed embodiments include a retention sleeve having a first portion and a second portion, the first portion abutting the blade. Some disclosed embodiments include a filler sleeve disposed between the blade and the second portion of the retention sleeve. Some disclosed embodiments include a first bearing disposed between the second portion of the retention sleeve and the inner surface of the hub, the first bearing having a first race contacting the inner surface of the hub. Some disclosed embodiments include a second bearing disposed between the first portion of the retention sleeve and the inner surface of the hub, the second bearing having a second race contacting the inner surface of the hub. Some disclosed embodiments include a cap comprising a body portion disposed between the second portion of the retention sleeve and the inner surface of the hub and a flange portion extending outward from the body portion and away from the blade, the flange portion attachable to an end surface of the hub. Some disclosed embodiments include a shim carrier disposed around the second portion of the retention sleeve, the shim carrier enclosing a shim disposed between the shim carrier and the flange portion of the cap.

In some embodiments, the first bearing includes a needle bearing element. In some embodiments, the second bearing includes an angular contact bearing. Some disclosed embodiments include a ball separator cage disposed between the second race and the first portion of the retention sleeve. Some disclosed embodiments include a first virtual center corresponding to the first bearing and a second virtual center corresponding to the second bearing, wherein the second virtual center is axially inward of the blade. In some embodiments, the blade further comprises an internal portion having a cavity disposed around a reversing ring. In some embodiments, the retention sleeve includes a third race and a fourth race. Some disclosed embodiments include a retaining ring disposed radially outward from the retention sleeve with respect to a blade axis, and axially outward from the shim carrier with respect to the blade axis. Some disclosed embodiments include a blade seal disposed around the retention sleeve and the body portion of the cap. Some disclosed embodiments include a sealing ring disposed between the body portion of the cap and an inner surface of the hub. In some embodiments, a distance between the first virtual center and the second virtual center may be sufficiently large to withstand at least one of centrifugal and bending loads sustained during operation of the system.

Some disclosed embodiments include a system for retaining a propeller for an aircraft. In some embodiments, the propeller includes a retention system. Some disclosed embodiments include a hub including a socket formed by an inner surface of the hub. Some disclosed embodiments include a blade extending into the socket. Some disclosed embodiments include a retention sleeve having a first portion and a second portion, the first portion abutting the blade. Some disclosed embodiments include a filler sleeve disposed between the blade and the second portion of the retention sleeve. Some disclosed embodiments include a first bearing disposed between the second portion of the retention sleeve and the inner surface of the hub, the first bearing having a first race contacting the inner surface of the hub. Some disclosed embodiments include a second bearing disposed between the first portion of the retention sleeve and the inner surface of the hub, the second bearing having a second race contacting the inner surface of the hub, wherein the second race is radially flush with the first race in a radial direction from a blade axis. Some disclosed embodiments include a cap including a body portion disposed between the second portion of the retention sleeve and the inner surface of the hub, wherein the body portion is flush with the first race in the radial direction from the blade axis and a flange portion extending outward from the body portion and away from the blade, the flange portion attachable to an end surface of the hub. Some disclosed embodiments include a shim carrier disposed around the second portion of the retention sleeve, the shim carrier enclosing a shim disposed between the shim carrier and the flange portion of the cap.

In some embodiments, the first bearing includes a needle bearing element. In some embodiments, the second bearing includes an angular contact bearing. Some disclosed embodiments include a ball separator cage disposed between the second bearing and the first portion of the retention sleeve. Some disclosed embodiments include a first virtual center corresponding to the first bearing and a second virtual center corresponding to the second bearing, wherein the second virtual center is axially inward of the blade. In some embodiments, a distance between the first virtual center and the second virtual center may be sufficiently large to withstand at least one of centrifugal and bending loads sustained during operation of the system. In some embodiments, the blade includes an internal portion having a cavity disposed around a reversing ring. In some embodiments, the retention sleeve includes a third race and a fourth race. In some embodiments, the retention sleeve includes an annular rib, wherein the first race and the second race are spaced apart by the annular rib, wherein the annular rib is flush with the first race and the second race in the radial direction. Some disclosed embodiments include a retaining ring disposed radially outward from the retention sleeve with respect to a blade axis, and axially outward from the shim carrier with respect to the blade axis. Some disclosed embodiments include a blade seal disposed around the retention sleeve and the body portion of the cap.

DETAILED DESCRIPTION

The disclosed embodiments provide systems, subsystems, and components for new VTOL aircraft having various combinations of an electric propulsion system and cooling systems that maximize performance while minimizing weight.

In some embodiments, an electric propulsion system as described herein may generate thrust by supplying High Voltage (HV) electric power to an electric engine, which in turn converts HV power into mechanical shaft power which is used to rotate a propeller. An aircraft as described herein may include multiple electric engines mounted forward and aft of the wing. The engines may be mounted directly to the wing, or mounted to one or more booms attached to the wing. The amount of thrust each electric engine generates may be governed by a torque command from a Flight Control System (FCS) over a digital communication interface to each electric engine. Embodiments may include forward electric engines that are capable of altering their orientation, or tilt. Some embodiments include forward engines that may be a clockwise (CW) type or counterclockwise (CCW) type. The forward electric propulsion subsystem may consist of a multi-blade adjustable pitch propeller, as well as a variable pitch subsystem.

In some embodiments, an aircraft may include aft electric engines, or lifters, that can be of a clockwise (CW) type or counterclockwise (CCW) type. Some embodiments may include aft electric engines that utilize a multi-blade fixed pitch propeller.

As described herein, the orientation and use of the electric propulsion system components may change throughout the operation of the aircraft. In some embodiments, during vertical takeoff and landing, the forward propulsion systems as well as aft propulsion systems may provide vertical thrust during takeoff and landing. During the flight phases where the aircraft is in forward flight-mode, the forward propulsion systems may provide horizontal thrust, while the aft propulsion system propellers may be stowed at a fixed position to minimize drag. The aft electric propulsion systems may be actively stowed with position monitoring. Some embodiments may include a transition from vertical flight to horizontal flight and vice-versa. In some embodiments, the transitions may be accomplished via the Tilt Propeller System (TPS). The TPS reorients the electric propulsion system between a primarily vertical direction during vertical flight mode to a mostly horizontal direction during forward-flight mode. Some embodiments may include a variable pitch mechanism that may change the forward propulsion system propeller blade collective angles for operation during the hover-phase, cruise-phase and transition phase. Some embodiments may include a Conventional Takeoff and Landing (CTOL) configurations such that the tilters provide horizontal thrust for wing-borne take-off, cruise and landing phases. In some embodiments, the aft electric engines are not used for generating thrust during a CTOL mission and the aft propellers are stowed in place to minimize drag.

It will be recognized that, VTOL aircraft may involve operations unique to VTOL aircraft rather than general aviation aircraft, including changes in orientation of the propellers and/or engine propulsion systems in cruise, lift, or intermediate operational configurations. Such operations may present challenges for propellers for eVTOL aircraft. For example, propellers may experience various loads, such as centrifugal and bending loads, which may be different than loads experienced in other aircraft. For example, eVTOL propellers may be subject to both axial and non-axial inflow (such as edgewise flow) during in-flight propeller articulation during transitions between hover and cruise configurations, as well as during flight. Some eVTOL propellers may also experience overturning moments (e.g., pitching moments caused by a difference in relative speed between a blade advancing into the air and a blade retreating from the air). Further, VTOL propeller blades may use collective pitch control across a full range of tilt and cruise positions. Therefore, in some embodiments these overturning moments must be addressable without the use of a cyclic pitch system. Thus, it will be recognized that there may be a need for retaining propeller blades for eVTOL aircraft to manage such loads.

Disclosed embodiments include propeller blade retention systems. Disclosed retention systems may include bearing configurations configured to handle the loads experienced by eVTOL propeller blades, while also being structurally efficient. For example, disclosed embodiments may include retention systems which can be lightweight and which can employ bearing assemblies configured at a distance (e.g., spread) between virtual centers of bearing elements to further accommodate loads experienced by VTOL and eVTOL propeller blades. In some examples, disclosed embodiments may involve a bearing system configured to provide support for loads via different bearings (e.g., configurations or combinations of bearings may assist with countering centrifugal and/or bending loads). Some disclosed embodiments include arrangements and configurations which can transmit (e.g., translate) various moments into retention hub moments and thereby into shaft moments. Moreover, disclosed embodiments may involve retention systems providing improved ease of assembly and servicing, including by wear regions which protect the hub of the retention system, thereby also providing improved weight savings and durability. Further, disclosed embodiments may include retention systems which may be compact, which can provide weight savings, easier assembly and/or servicing, and improved drag profiles (e.g., increased fuel efficiency) for aircraft described herein.

Exemplary Electric Aircraft Features

FIG.1is an illustration of a perspective view of an exemplary VTOL aircraft, consistent with disclosed embodiments.FIG.2is another illustration of a perspective view of an exemplary VTOL aircraft in an alternative configuration, consistent with embodiments of the present disclosure.FIGS.1and2illustrate a VTOL aircraft100,200in a cruise configuration and a vertical take-off, landing and hover configuration (also referred to herein as a “lift” configuration), respectively, consistent with embodiments of the present disclosure. Elements corresponding toFIGS.1and2may possess like numerals and refer to similar elements of the aircrafts100,200. The aircraft100,200may include a fuselage102,202, wings104,204mounted to the fuselage102,202and one or more rear stabilizers106,206mounted to the rear of the fuselage102,202. A plurality of lift propellers112,212may be mounted to wings104,204and may be configured to provide lift for vertical take-off, landing and hover. A plurality of tilt propellers114,214may be mounted to wings104,204and may be tiltable between the lift configuration in which they provide a portion of the lift required for vertical take-off, landing and hovering, as shown inFIG.2, and the cruise configuration in which they provide forward thrust to aircraft100for horizontal flight, as shown inFIG.1. As used herein, a tilt propeller lift configuration refers to any tilt propeller orientation in which the tilt propeller thrust is providing primarily lift to the aircraft and tilt propeller cruise configuration refers to any tilt propeller orientation in which the tilt propeller thrust is providing primarily forward thrust to the aircraft.

In some embodiments, lift propellers112,212may be configured for providing lift only, with all horizontal propulsion being provided by the tilt propellers. Accordingly, lift propellers112,212may be configured with fixed positions and may only generate thrust during take-off, landing and hover phases of flight. Meanwhile, tilt propellers114,214may be tilted upward into a lift configuration in which thrust from propellers114,214is directed downward to provide additional lift.

For forward flight, tilt propellers114,214may tilt from their lift configurations to their cruise configurations. In other words, the orientation of tilt propellers114,214may be varied from an orientation in which the tilt propeller thrust is directed downward (to provide lift during vertical take-off, landing and hover) to an orientation in which the tilt propeller thrust is directed rearward (to provide forward thrust to aircraft100,200). The tilt propellers assembly for a particular electric engine may tilt about an axis of rotation defined by a mounting point connecting the boom and the electric engine. When the aircraft100,200is in full forward flight, lift may be provided entirely by wings104,204. Meanwhile, in the cruise configuration, lift propellers112,212may be shut off. The blades120,220of lift propellers112,212may be held in low-drag positions for aircraft cruising. In some embodiments, lift propellers112,212may each have two blades120,220extending from a center hub that may be locked for cruising in minimum drag positions in which one blade is directly in front of the other blade as illustrated inFIG.1. In some embodiments, lift propellers112,212have more than two blades. In some embodiments, tilt propellers114,214may include more blades116,216than lift propellers112,212. For example, as illustrated inFIGS.1and2, lift propellers112,212may each include, e.g., two blades, whereas and tilt propellers114,214may each include more blades, such as the five blades shown. In some embodiments, each of the tilt propellers114,214may have 2 to 5 blades, and possibly more depending on the design considerations and requirements of the aircraft.

In some embodiments, the aircraft may include a single wing104,204on each side of fuselage102,202(or a single wing that extends across the entire aircraft). At least a portion of lift propellers112,212may be located rearward of wings104,204and at least a portion of tilt propellers114,214may be located forward of wings104,204. In some embodiments, all of lift propellers112,212may be located rearward of wings104,204and all of tilt propellers114,214may be located forward of wings104,204. According to some embodiments, all lift propellers112,212and tilt propellers114,214may be mounted to the wings—i.e., no lift propellers or tilt propellers may be mounted to the fuselage. In some embodiments, lift propellers112,212may be all located rearwardly of wings104,204and tilt propellers114,214may be all located forward of wings104,204. According to some embodiments, all lift propellers112,212and tilt propellers114,214may be positioned inwardly of the ends of the wing104,204.

In some embodiments, lift propellers112,212and tilt propellers114,214may be mounted to wings104,204by booms122,222. Booms122,222may be mounted beneath wings104,204, on top of the wings, and/or may be integrated into the wing profile. In some embodiments, lift propellers112,212and tilt propellers114,214may be mounted directly to wings104,204. In some embodiments, one lift propeller112,212and one tilt propeller114,214may be mounted to each boom122,222. Lift propeller112,212may be mounted at a rear end of boom122,222and tilt propeller114,214may be mounted at a front end of boom122,222. In some embodiments, lift propeller112,212may be mounted in a fixed position on boom122,222. In some embodiments, tilt propeller114,214may mounted to a front end of boom122,222via a hinge. Tilt propeller114,214may be mounted to boom122,222such that tilt propeller114,214is aligned with the body of boom122,222when in its cruise configuration, forming a continuous extension of the front end of boom122,222that minimizes drag for forward flight.

In some embodiments, aircraft100,200may include, e.g., one wing on each side of fuselage102,202or a single wing that extends across the aircraft. According to some embodiments, the at least one wing104,204is a high wing mounted to an upper side of fuselage102,202. According to some embodiments, the wings include control surfaces, such as flaps and/or ailerons. According to some embodiments, wings104,204may have designed with a profile that reduces drag during forward flight. In some embodiments, the wing tip profile may be curved and/or tapered to minimize drag.

In some embodiments, rear stabilizers106,206include control surfaces, such as one or more rudders, one or more elevators, and/or one or more combined rudder-elevators. The wing(s) may have any suitable design. In some embodiments, the wings have a tapering leading edge.

In some embodiments, lift propellers112,212or tilt propellers114,214may canted relative to at least one other lift propeller112,212or tilt propeller114,214. As used herein, canting refers to a relative orientation of the rotational axis of the lift propeller/tilt propeller about a line that is parallel to the forward-rearward direction, analogous to the roll degree of freedom of the aircraft. Canting of the lift propellers and/or tilt propellers may help minimize damage from propeller burst by orienting a rotational plane of the lift propeller/tilt propeller discs (the blades plus the hub onto which the blades are mounted) so as to not intersect critical portions of the aircraft (such areas of the fuselage in which people may be positioned, critical flight control systems, batteries, adjacent propellers, etc.) or other propeller discs and may provide enhanced yaw control during flight.

FIG.3is an illustration of a top plan view of an exemplary VTOL aircraft, consistent with embodiments of the present disclosure. Aircraft300shown in the figure may be a top plan view of the aircraft100,200shown inFIGS.1and2, respectively. As discussed herein, an aircraft300may include twelve electric propulsion systems distributed across the aircraft300. In some embodiments, a distribution of electric propulsion systems may include six forward electric propulsion systems314and six aft electric propulsion systems312mounted on booms forward and aft of the main wings304of the aircraft300. In some embodiments, a length of the rear end of the boom324from the wing304to the lift propeller312may comprise a similar rear end of the boom324length across the numerous rear ends of the booms. In some embodiments, the length of the rear ends of the booms may vary across the, exemplary, six rear ends of the booms. For example, each rear end of the boom324may comprise a different length from the wing304to the lift propeller312, or a subset of rear ends of booms may be similar in length. In some embodiments, a front end of boom322may comprise various lengths from the wing304to the tilt propeller314across the front ends of booms. For example, as shown inFIG.3, a length of the front end of boom322from the tilt propellers314nearest the fuselage to the wing304may comprise a greater length than the length of the front end of the boom322from the wing304to the tilt propellers314furthest from the fuselage. Some embodiments may include front ends of the booms with similar lengths across the, exemplary, six front ends of booms or any other distribution of lengths of the front ends of booms from the wing304to tilt propellers314. Some embodiments may include an aircraft300possessing eight electric propulsion systems with four forward electric propulsion systems314and four aft electric propulsion systems312, or any other distribution of forward and aft electric propulsion systems, including embodiments where the number of forward electric propulsion systems314is less than or greater than the number of aft electric propulsion systems312. Further,FIG.3depicts an exemplary embodiment of a VTOL aircraft300with forward propellers314in a horizontal orientation for horizontal flight and aft propeller blades320in a stowed position for a forward phase of flight.

As disclosed herein, the forward electric propulsion systems and aft electric propulsion systems may be of a clockwise (CW) type or counterclockwise (CCW) type. Some embodiments may include various forward electric propulsion systems possessing a mixture of both CW and CCW types. In some embodiments, the aft electric propulsion systems may possess a mixture of CW and CCW type systems among the aft electric propulsion systems.

FIG.4is a schematic diagram illustrating exemplary propeller rotation of a VTOL aircraft, consistent with disclosed embodiments. Aircraft400shown in the figure may be a top plan view of the aircraft100,200, and300shown inFIGS.1,2, and3, respectively. An aircraft400may include six forward electric propulsion systems with three of the forward electric propulsion systems being of CW type424and the remaining three forward electric propulsion systems being of CCW type426. In some embodiments, three aft electric propulsion systems may be of CCW type428with the remaining three aft electric propulsion systems being of CW type430. Some embodiments may include an aircraft400possessing four forward electric propulsion systems and four aft electric propulsion systems, each with two CW types and two CCW types. In some embodiments, propellers may counter-rotate with respect to adjacent propellers to cancel torque steer, generated by the rotation of the propellers, experienced by the fuselage or wings of the aircraft. In some embodiments, the difference in rotation direction may be achieved using the direction of engine rotation. In other embodiments, the engines may all rotate in the same direction, and gearing may be used to achieve different propeller rotation directions.

Some embodiments may include an aircraft400possessing forward and aft electric propulsion systems where the amount of CW types424and CCW types426is not equal among the forward electric propulsion systems, among the aft electric propulsion systems, or among the forward and aft electric propulsion systems.

FIG.5is a schematic diagram illustrating exemplary power connections in a VTOL aircraft, consistent with disclosed embodiments. A VTOL aircraft may have various power systems connected to diagonally opposing electric propulsion systems. In some embodiments, the power systems may include high voltage power systems. Some embodiments may include high voltage power systems connected to electric engines via high voltage channels. In some embodiments, an aircraft500may include six power systems, including batteries526,528,530,532,534, and536stored within the wing570of the aircraft500. In some embodiments, the aircraft500may include six forward electric propulsion systems having six electric engines502,504,506,508,510, and512and six aft electric propulsion systems having six electric engines514,516,518,520,522, and524. In some embodiments, a battery may be connected to diagonally opposing electric engines. In such a configuration, first power system526may provide power to electric engines502via power connection channel538and electric engine524via power connection channel540. In some embodiments, first power system526may also be paired with a fourth power system532via a power connection channel542possessing a fuse to prevent excessive current from flowing through the power systems526and532. Further to this embodiment, VTOL aircraft500may include a second power system528paired with a fifth power system534via power connection channel548possessing a fuse and may provide power to electric engines510and516via power connection channels544and546, respectively. In some embodiments, a third power system530may be paired with a sixth power system536via power connection channel554possessing a fuse and may provide power to electric engines506and520via power connection channels550and552, respectively. The fourth power system532may also provide power to electric engines508and518via power connection channels556and558, respectively. The fifth power system534may also provide power to electric engines504and522via power connection channels560and562, respectively. The sixth power system536may also provide power to electric engines512and514via power connection channels564and566, respectively.

FIG.6illustrates block diagram of an exemplary architecture and design of an electric propulsion unit600consistent with disclosed embodiments. In some embodiments, an electric propulsion system602may include an electric engine subsystem604that may supply torque, via a shaft, to a propeller subsystem606to produce the thrust of the electric propulsion system602. Some embodiments may include the electric engine subsystem604receiving low voltage DC (LV DC) power from a Low Voltage System (LVS)608. Some embodiments may include the electric engine subsystem604receiving high voltage (HV) power from a High Voltage Power System (HVPS)610comprising at least one battery or other device capable of storing energy. In some embodiments, a High Voltage Power System may include more than one battery, or other device capable of storing energy, supplying high voltage power to the electric engine subsystem604. It is recognized that such a configuration may be advantageous as to not risk a single point of failure where a single battery failure leads to an electric propulsion system602failure.

Some embodiments may include an electric propulsion system602including an electric engine subsystem604receiving signals from and sending signals to a flight control system612. In some embodiments, a flight control system612may comprise a flight control computer capable of using Controller Area Network (“CAN”) data bus signals to send commands to the electric engine subsystem604and receive status and data from the electric engine subsystem604. It should be understood that while CAN data bus signals are used between the flight control computer and the electric engine(s), some embodiments may include any form of communication with the ability to send and receive data from a flight control computer to an electric engine. In some embodiments, a flight control system612may also include a Tilt Propeller System (“TPS”)614capable of sending and receiving analog, discrete data to and from the electric engine subsystem604of the tilt propellers. A tilt propeller system614may include an apparatus capable of communicating operating parameters to an electric engine subsystem604and articulating an orientation of the propeller subsystem606to redirect the thrust of the tilt propellers during various phases of flight using mechanical means such as a gearbox assembly, linear actuators, and any other configuration of components to alter an orientation of the propeller subsystem606.

As discussed throughout, an exemplary VTOL aircraft may possess various types of electric propulsion systems including tilt propellers and lift propellers, including forward electric engines with the ability to tilt during various phases of flight, and aft electric engines that remain in one orientation and may only be active during certain phases of flight (i.e., take off, landing, and hover).

FIG.7is a schematic diagram illustrating an exemplary tilt electric propulsion system of a VTOL aircraft, consistent with disclosed embodiments. A tiltable electric propulsion system700may include an electric engine assembly702aligned along a shaft724that is connected to an output shaft738that is mechanically coupled to a propeller assembly720comprising a hub, a spinner, and tilt propeller blades. In some embodiments, an electric engine assembly702may include a motor and gearbox assembly704aligned along and mechanically coupled to the shaft724. In some embodiments, a motor and gearbox assembly704may include an electric motor assembly comprising a stator706and a rotor708. As shown inFIG.7, and present in some embodiments, a stator706may include multiple stator windings connected to the inverter716. In such a configuration, a stator706may incorporate one or more redundancies so that, in the event one set of windings were to fail, power would still be transmitted to the stator706via one or more remaining windings, so that the electric engine assembly702retains power and continues to generate thrust at the propeller assembly720.

In some embodiments, a motor and gearbox assembly704may contain a gearbox710aligned along the shaft724to provide a gear reduction between the torque of the shaft724from the electric engine assembly, comprising a stator706and rotor708, and the output shaft738Torque applied to the output shaft738may be transferred to the propeller assembly720. Some embodiments may include a gearbox710containing an oil pump. In such an embodiment, the oil pump may drive a circulation of oil throughout the motor and gearbox assembly704at a speed equivalent to the rotation of the output shaft738to cool and lubricate the gearbox and electric motor components. In some embodiments, the oil pump may drive a circulation of oil at a speed greater than or less than the rotation of the output shaft738. Some embodiments of a motor and gearbox assembly704may include propeller position sensors712present within the housing that may detect a magnetic field produced by the electric engine assembly to determine a propeller position. Further embodiments may include propeller position sensors712that are powered by an inverter716and send collected data to an inverter716.

In some embodiments, an electric engine assembly702may also include an inverter assembly714aligned along the shaft724. An inverter assembly714may include an inverter716and an inverter power supply740An inverter power supply740may accept low voltage DC power from a low voltage system734located outside the electric engine assembly702. An inverter power supply740may accept low voltage DC power originating from a high voltage power system732, located outside the electric engine assembly702, that has been converted to low voltage DC power via a DC-DC converter742. An inverter716may supply high voltage alternating current to the stator706of the electric engine assembly located within the motor and gearbox assembly704via at least one three-phase winding. An inverter assembly714may include an inverter716that may receive flight control data from a flight control computing subsystem736.

In some embodiments, a motor and gearbox704may be located between an inverter assembly714and a propeller assembly720. Some embodiments may also include a divider plate744coupled to the motor and gearbox assembly704and inverter assembly714. A divider plate744may create an enclosed environment for an upper portion of the motor and gearbox assembly704via an end bell assembly, and create an enclosed environment for a lower portion of the inverter assembly714via a thermal plate. In some embodiments, divider plate744may serve as an integral mounting bracket for supporting heat exchanger718. Heat exchanger718may comprise, for example, a folded fin or other type of heat exchanger. In some embodiments, the electric propulsion system700may circulate oil or other coolant throughout the electric engine assembly702, motor and gearbox assembly704, or inverter assembly714to transfer heat generated from the components to the oil or other coolant liquid. The heated oil or other coolant liquid may circulate through heat exchanger718to transfer the heat to an air flow722passing through the fins of the heat exchanger.

In some embodiments, the electric engine assembly702may be mounted or coupled to a boom structure726of the aircraft. A variable pitch mechanism730may be mechanically coupled to the propeller assembly720. In some embodiments, the variable pitch mechanism may abut the electric engine assembly702. In some embodiments, the variable pitch mechanism730may be coupled to the variable pitch mechanism730such it may be remotely mounted within the boom, wing, or fuselage of the aircraft. In some embodiments, the variable pitch mechanism730may include a shaft or component traveling within or adjacent to the shaft724to the propeller assembly720. A variable pitch mechanism730may serve to change the collective angle of the forward electric engine's propeller assembly blades as needed for operation during the hover-phase, transition phase, and cruise-phase. Some embodiments may include the electric engine assembly702being mechanically coupled to a tilt propeller subsystem728that may redirect thrust between a primarily vertical direction during vertical flight mode to a mostly horizontal direction during forward-flight mode. In some embodiments, the tilt propeller subsystem may abut the variable pitch mechanism730. Some embodiments may include a tilt propeller subsystem728comprising various components located in various locations. For example, a component of the tilt propeller subsystem may be coupled to the electric engine assembly702and other components may be coupled to the variable pitch mechanism730. These various components of the tilt propeller subsystem728may work together to redirect the thrust of the tiltable electric propulsion system700.

FIGS.8A-8Care illustrations of an exemplary tilt electric propulsion system of a VTOL aircraft, consistent with disclosed embodiments.FIGS.8A-Cpossess like numerals and refer to similar elements of tiltable electric propulsion systems800A,800B, and800C. As such, similar design considerations and configurations may be considered throughout the embodiments

FIGS.8A and8Billustrate a side profile and perspective view, respectively, of a tiltable electric propulsion system800A,800B in a cruise configuration integrated into a boom812A,812B consistent with this disclosure. A tiltable propeller electric propulsion system800A,800B may comprise an electric engine assembly802A,802B housed within a boom812A,812B of a VTOL aircraft. In some embodiments, a cruise configuration may include the electric engine assembly802A,802B being posited within the boom812A,812B. An electric engine assembly802A,802B may comprise an electric motor assembly, a gearbox assembly, an inverter assembly with power connection channels810A,810B, and a heat exchanger804A,804B, as described herein. The electric engine assembly802A,802B may be mechanically coupled to a propulsion assembly808A,808B comprising a shaft flange assembly806A,806B, a spinner, and propeller blades.

FIG.8Cillustrates a top-down view, along a spinner808C, of a tiltable electric propulsion system800C in a lift configuration integrated into a boom812B consistent with this disclosure. As shown inFIG.8Ca tiltable electric propulsion system800C in a lift configuration may comprise the electric engine assembly802A,802B being posited outside of the boom812C and changing its orientation with respect to the boom812C. In some examples, tiltable electric propulsion system800C may include a propeller blade retention system806C.

As discussed herein, a lift electric propulsion system may be configured to provide thrust in one direction and may not provide thrust during all phases of flight. For example, a lift system may provide thrust during take-off, landing, and hover, but may not provide thrust during cruise.

FIG.9is a schematic diagram illustrating an exemplary lift electric propulsion system of a VTOL aircraft, consistent with disclosed embodiments. A lift electric propulsion system900may be mounted or coupled to a boom structure924of the aircraft. A lift electric propulsion system900may include electric engine assembly902aligned along a shaft940that is connected to an output shaft932that is mechanically coupled to a propeller assembly920comprising a hub and tilt propeller blades. In some embodiments, an electric engine assembly902may include a motor and gearbox assembly housing904aligned along and mechanically coupled to the shaft940. In some embodiments, a motor and gearbox assembly housing904may include an electric motor assembly comprising a stator906and a rotor908. A stator906may include multiple stator windings connected to the inverter916. In such a configuration, a stator906may incorporate one or more redundancies and backup measures to avoid a single point of failure in the case. For example, stator906may include multiple windings such that, if a winding fails, power may continue to be transmitted to the stator906via remaining windings, allowing the electric engine assembly902to retain power and continue to generate thrust at the propeller assembly920.

In some embodiments, a motor and gearbox assembly housing904may contain a gearbox910aligned along the shaft940to provide a gear reduction between the torque of the shaft932from the electric engine assembly, comprising a stator906and rotor908, and the output shaft932. Torque applied to the output shaft932may be transferred to the propeller assembly920. Some embodiments may include a gearbox910containing a fluid pump for circulating cooling and/or lubrication fluid. In the embodiment shown, the fluid pump is an oil pump. In such an embodiment, the oil pump may drive a circulation of oil throughout the motor and gearbox assembly housing904at a speed equivalent to the rotation of the output shaft932to cool and lubricate the gearbox and electric motor components. Some embodiments of a motor and gearbox assembly housing904may include propeller position sensors912present within the housing that may detect a magnetic field produced by the electric engine assembly to determine a propeller position. Further embodiments may include propeller position sensors912that are powered by an inverter916and send collected data to an inverter916that may be transferred to a flight control computing system930among other flight control data.

In some embodiments, an electric engine assembly902may also include an inverter assembly housing914aligned along an axis sharing the axis of the shaft924. An inverter assembly housing914may include an inverter916and an inverter power supply934. An inverter power supply934may accept low voltage DC power from a low voltage system928located outside the electric engine assembly902. An inverter power supply934may accept low voltage DC power originating from a high voltage power system926, located outside the electric engine assembly902, that has been converted to low voltage DC power via a DC-DC converter936. An inverter916may supply high voltage alternating current to the stator906of the electric engine assembly located within the motor and gearbox assembly housing904via at least one three-phase winding. An inverter assembly914may include an inverter916that may send data to and receive data from a flight control computing subsystem930.

In some embodiments, a motor and gearbox housing904may be located between an inverter assembly housing914and a propeller assembly920. Some embodiments may also include a divider plate938coupled to the motor and gearbox assembly housing904and inverter assembly housing914. A divider plate938may create an enclosed environment for an upper portion of the motor and gearbox assembly housing904via an end bell assembly, and may create an enclosed environment for a lower portion of the inverter assembly housing914via a thermal plate. In some embodiments, a divider plate938may serve as an integral mounting bracket for supporting heat exchanger918. Heat exchanger918may comprise, e.g., a folded fin or other type of heat exchanger. In some embodiments, the electric propulsion system900may circulate oil or other coolant fluid throughout the electric engine assembly902, motor and gearbox assembly904, or inverter assembly914to transfer heat generated from the components to the oil or other coolant liquid. The heated oil or other coolant liquid may be circulated through heat exchanger918to transfer the heat to an air flow922passing through the fins of the heat exchanger.

In some embodiments, a tiltable electric propulsion system and a lift electric propulsion system may possess similar components. This may be advantageous with respect to many design considerations present within VTOL aircrafts. For example, from a manufacturability standpoint, different types of electric propulsion systems having similar components may be beneficial in terms of manufacturing efficiency. Further, having similar components may be beneficial in terms of risk management as similar components possess similar points of failure and these points of failure may be well explored and designed around when comparing systems having similar components to systems having different components and configurations.

While a tiltable electric propulsion system may possess additional, and in some embodiments different, components compared to a lift electric propulsion system, it should be understood that in some embodiments a tiltable electric propulsion system and a lift electric propulsion system may possess the same configuration of components. For example, in some embodiments, a tiltable and lift electric propulsion system may contain the same components while the lift electric propulsion system may be coupled to a boom, wing, or fuselage of the aircraft such that it may not be able to provide thrust in as many directions as tiltable electric propulsion system.

FIGS.10A-10Bare illustrations of an exemplary lift electric propulsion systems of a VTOL aircraft, consistent with disclosed embodiments.FIGS.10A and10Bpossess like numerals and refer to similar elements of lift electric propulsion systems1000A and1000B. As such, similar design considerations and configurations may be considered throughout the embodiments

FIG.10Aillustrates a side profile of a lift electric propulsion system1000A in a lift configuration integrated into a boom1010A consistent with this disclosure. A lift electric propulsion system1000A may comprise an electric engine assembly1002A housed within a boom1010A of a VTOL aircraft. In some embodiments, a lift configuration may include the electric engine assembly1002A being posited vertically within the boom1010A. An electric engine assembly1002A may comprise an electric motor assembly, a gearbox assembly, an inverter assembly with power connection channels1008A, and a heat exchanger1004A, as described herein. The electric engine assembly1002A may be mechanically coupled to a propulsion assembly1006A comprising a shaft flange assembly and propeller blades.

FIG.10Billustrates a top-down view of a lift electric propulsion system1000B in a lift configuration integrated into a boom1010B, consistent with this disclosure.

Some embodiments of the disclosed electric engine may generate heat during operation and may comprise a heat management system to ensure components of the electric engine do not fail during operation. In some embodiments, coolant may be used and circulated throughout individual components of the engine, such as an inverter, gearbox, or motor, through some of the components, or through all of the components of the engine to assist with managing the heat present in the engine. Some embodiments may include using air cooling methods to cool the electric engine or using a mixture of coolant and air to manage the heat generated during operation in the electric engine. In some embodiments, the coolant being used may also be the same liquid that is being used as lubricant throughout the inverter, gearbox, or motor. For example, components of the electric engines may be cooled using a liquid or air or using a mixture of air and liquid cooling. As another example, a motor may be cooled using air cooling while the inverter and gearbox are cooled using liquid cooling. It should be understood that a mixture of cooling may be used for any combination of electric engine components or within each component.

In some embodiments, oil may be used as a lubricant throughout an electric engine and may also be used as coolant fluid to assist in managing the heat generated by the engine during operation.

Some embodiments may use oil to lubricate the electric engine and to cool the electric engine. Such embodiments may require additional volumes of oil. In such embodiments, the additional oil may allow for removal of traditional components that may be used to cool such an electric engine. For example, if the electric engine were cooled by another liquid such as glycol, the engine may comprise separate heat exchangers for both the lubricant fluid and the coolant fluid. As such, in embodiments where a single fluid is being used for both lubrication and cooling, such as oil, an increase in oil would be present but there would only be a need for one heat exchanger, so there may be a decrease in mass, due to using less heat exchangers and potentially other components not being required, of the overall system and a more appealing drag profile may be present. Further, using one substance for the lubrication and cooling of the engine may increase efficiency of the system due to the reduction in mass and the benefits of cooling the engine with a substance rather than relying on air cooling which may have issues traveling throughout the engine.

FIG.10Cillustrates a graph1000C of airflow as a function of aircraft speed, consistent with embodiments of the present disclosure. Graph1000C illustrates an example of edgewise flow1022C and axial flow1024C as a function of the airspeed1020C for a tilt propeller. For example, graph1000C may schematically illustrate the airflows during the transition period from a lift configuration to a cruise configuration according to a prescribed tilting schedule of the tilt propeller and blade pitch schedule (e.g., a chosen blade pitch angle as a function of propeller tilt angle). At hover (e.g., zero or low airspeed), there is no axial flow in the present example. As airspeed increases, there is an increase in axial flow1024C and an increase in edgewise flow1022C. As tilt occurs and the aircraft transitions to a cruise configuration, the edgewise flow1022C decreases as the axial flow1024C remains (and increases with increasing airspeed). Thus, it will be recognized that VTOL aircraft may require a bearing system capable of sustaining a wide range of loads from both axial and edgewise airflows.

FIG.10Dillustrates graphs of airflow as a function of aircraft speed, consistent with embodiments of the present disclosure. Graph1030D and graph1034D illustrate the in-plane (e.g., crossflow) velocity component and the out-of-plane (e.g., inflow) velocity component, respectively, on an eVTOL tilter disk according to a prescribed tilting schedule of the tilt propeller and blade pitch schedule. Graph1030D and graph1034D may be non-dimensionalized by propeller rotational speed and propeller radius. It will be appreciated that, as illustrated in graph1030D and graph1034D, the tilt propellers for an exemplary VTOL/eVTOL aircraft can experience various combinations of axial and edgewise flow based on the tilt angle of a tilt propeller. For example, graph1030D may involve a change1032D in vehicle angle of attack (AoA) due to the tilting propellers reaching a cruise setting (e.g., −2 degrees as an example). As such, retention systems for propellers may be configured to sustain varying loads.

Exemplary Propeller Embodiments

Disclosed methods may involve systems, apparatus, and methods for retaining propellers and propeller blades. It will be recognized that propellers, including propeller blades, may experience various forces during operation, including centrifugal forces, as well as torques such as bending torques. For example, centrifugal force may pull a blade away from connections to a propulsion system, including electric propulsion systems as described herein. In some examples, eVTOL propellers may experience large out-of-plane bending loads on the propeller blades from non-axial inflow. Thus, it will be appreciated that propeller blades should be retained to counteract such forces and enable propellers to function during any stage of operation. Retention, as described herein, may refer to preventing an object or component from leaving (e.g., leaving its preferred operating position). Retaining may involve keeping possession of an object, or keeping it in a particular position. For example, retention may refer to preventing an object from becoming displaced from the retaining element by more than a tolerable amount during operation. For example, retention may include preventing an object or component from becoming dislodged, disconnected, or otherwise displaced from a mount, support, guide, or other retaining element. It will be recognized that retention may allow movement in some degrees while restricting movement in other degrees. For example, while a blade may be prevented from completely exiting a point of attachment, the blade my be allowed to rotate freely and/or adjust to appropriate blade angles.

FIG.11illustrates a partial cross-section of a retention system1100for a propeller blade, consistent with embodiments of the present disclosure. Retention system1100may be configured to retain a propeller blade in an aircraft such as, e.g., aircraft100-400ofFIGS.1-4. Retention system1100may include blade1102, which may comprise composite materials. For example, blade1102may include blade laminate1104. Blade laminate1104may include a lightweight, high-strength material such as, e.g., carbon fiber, such as braided carbon fiber, as well as fiberglass, such as flat pattern woven fiberglass. Blade1102may include various properties, including erosion protection and lightning conductive paths. Blade1102may include a continuous fiber path1106having braided carbon fiber in biaxial and unidirectional sleeving. Alternatively or additionally, blade1102may further comprise a flat pattern unidirectional carbon fiber having a continuous fiber path1106. In some examples, fiberglass in blade1102may comprise biaxial sleeving to galvanically isolate carbon from metallic portions of blade1102. It will be appreciated that disclosed embodiments of blades including fiber (e.g., continuous material interlocked around a metallic hoop) may provide stronger load transfer in comparison to blades which rely on adhesives or fasteners for material transfer. In some embodiments, retention system1100may include a reversing ring1108extending through and filling a cavity or bore in a root portion of blade1102. A reversing ring may refer to any retaining element configured to resist centrifugal loads. For example, reversing ring1108may reinforce a root portion (e.g., base) of blade1102so that it may be more securely retained by, e.g., a retention sleeve1110. Fibers of blade1102may be wrapped around reversing ring1108along continuous fiber path1106such that the reversing ring1108counteracts any centrifugal forces pulling on blade1102. In some embodiments, reversing ring1108may be made of metals, such as titanium.

In some embodiments, a propeller blade may contact one or more sleeves. A sleeve may refer to a covering or lining for a component that may partially or completely surround the component along a predetermined direction. In some embodiments, retention system1100may include a retention sleeve1110. Retention sleeve1110may comprise a sleeve configured to assist in retaining a blade such as blade1102. Retention sleeve1110may surround blade1102such that a portion of the retention sleeve1110may abut a portion of blade1102. Retaining sleeve1110may include a first portion1114and second portion1116. In some examples, the entire length of retention sleeve1110in an axial direction of blade1102may abut blade1102. Retention sleeve1110may include metals, such as steel, and may be attached to blade1102such that blade1102may be fixed to retention sleeve1110. In some embodiments, retention sleeve1110may be attached to blade1102by secondary bonding, such as with an adhesive material and/or bond primer. In some embodiments, blade1102may abut first portion1114of retention sleeve1110. It will be appreciated that as blade1102may contact the first portion1114of retention sleeve1110, the blade may also be fastened around reversing ring1108, thereby enabling greater retention against centrifugal loads. In some embodiments, retention system1100may include a filler sleeve1112. For example, filler sleeve1112may contact blade1102, such as by contacting a blade spar (e.g., a structural element of a blade which may carry loads experienced by the blade and which may be formed by fibers as described herein) of blade1102. A filler sleeve may comprise a sleeve configured to transmit bending loads experienced in retention system1100, including transmitting bending loads between portions of blade1102, such as between composite and metallic portions of blade1102. Filler sleeve1112may include any material capable of transmitting loads and/or absorbing forces, including plastics, foam, or rubber, as non-limiting examples. It will be appreciated that filler sleeve1112may include lightweight materials such as plastics, thereby enabling weight savings while also enabling transmission of loads from the blade. In some embodiments, filler sleeve1112may be disposed between blade1102and retention sleeve1110. For example, filler sleeve1112may be positioned between blade1102and retention sleeve1110such that an inner side of filler sleeve1112contacts blade1102and an outer side of filler sleeve1112contacts the second portion1116of retention sleeve1110.

FIG.12illustrates a partial cross section of a retention system1200for a propeller blade, consistent with embodiments of the present disclosure. Retention system1200may include a hub1204, which may comprise any suitable material such as metals (e.g., aluminum). A hub may refer to an assembly, receptacle, or connecting component for one or more propeller blades. In an example, shaft flange assembly806A, as referenced inFIG.8A, may include a hub such as hub1204. A hub may involve a case such that components may be contained within the hub. In some embodiments, a hub may include a socket. A socket may refer to any opening such as a recess, pocket, chamber, or cavity. A socket may involve a hollow portion, or a socket may comprise an inner surface of a hollow portion of the hub configured to receive a propeller blade. For example, a hub may include one or more openings capable of receiving a component such as a propeller blade or a component coupled to a propeller blade. For example, a hub may include multiple openings such that a single hub may be capable of receiving multiple blades. In some embodiments, hub1204may include a socket formed by an inner surface1210of hub1204. A hub may include one or more openings, such as a socket, capable of receiving a component, such as a component which extends through the socket. In some embodiments, the component may comprise a blade1202that may extend into a socket, such as a socket formed by an inner surface of hub1204. Extending into may refer to a component which protrudes or continues past, such as a component which protrudes into an opening. For example, blade1202may extend into a socket of hub1204, such as in a direction of blade axis1201. Blade1202may have a blade axis1201, which may be a virtual line or a reference line along the length of the blade. For example, blade axis1201may be in a longitudinal direction along blade1202. Blade axis may comprise an axis about which blade1202rotates when changing its pitch angle. Therefore, while the arrows inFIG.12may indicate a direction of blade axis1201, the actual blade axis may be offset from the location of the arrows. For example, blade axis1201may correspond to, e.g., blade axis1304ofFIG.13discussed below. As discussed herein, blade1202may be disposed around reversing ring1205such that the reversing ring1205may extend through the blade cavity. In some embodiments, hub1204may include sleeves, bearings, and other components which may assist in retaining blade1202within the hub. For example, retention sleeve1206may be within the hub1204. Retention sleeve1206may include a first portion1207and a second portion1209, as described herein. Retention sleeve1206may be positioned between blade1202and inner surface1210of hub1204such that first portion1207may contact blade1202, and filler sleeve1208may be disposed between blade1202and second portion1209of retention sleeve1206.

In some embodiments, retention system1200may include one or more bearings. Bearings may involve components configured to reduce friction between a plurality of components in relative motion, including assisting in relative motion between moving and/or stationery components. Bearings may have bearing races, such as a bearing having one or more races. Bearing races may refer to tracks or paths which bearings may ride on, enabling lower friction between components which move. For example, a bearing may have an inner race and an outer race, where bearing elements may be disposed on the outer circumference on the inner race and the inner circumference of the outer race. Disclosed embodiments may include bearings with separate races or bearings having a shared race. In some examples, bearing races may comprise metals, such as steel. As a non-limiting example, bearings may include ball bearings, roller bearings, or needle bearings. Some disclosed embodiments may comprise a bearing1212disposed between the second portion1209of retention sleeve1206and the inner surface1210of hub1204. Bearing1212, which may be a first bearing in retention system1200, may be adjacent to the retention sleeve1206. In some embodiments, retention sleeve1206may include one or more races for a bearing. For example, retention sleeve1206may include an inner race for bearing1212and/or an inner race for bearing1216. For example, retention sleeve1206may include a third race, which may refer to an inner race for bearing1216. In some examples, bearing1212may be recessed into retention sleeve1206, such as retention sleeve1206including a slot or notch which forms an inner race for bearing1212. In some embodiments, bearing1212may include a first race1214(e.g., an outer race) which contacts the inner surface1210of hub1204. In some embodiments, bearing1212may include a needle bearing element. For example, bearing1212may include multiple needle bearing elements, which may comprise metals such as steel, contacting first race1214. Some disclosed embodiments include a bearing disposed between the first portion of the retention sleeve and the inner surface of the hub. For example, retention system1200may include second bearing1216which may be disposed between first portion1207of the retention sleeve1206and the hub1204. Second bearing1216may have one or more races, including a second race1218contacting the inner surface1210of hub1204. In some embodiments, first race1214and second race1218may be detachable components that can be removable from the hub, which may enable easier service of the races. In some examples, retention sleeve1206may include a fourth race, such as an inner race for second bearing1216. In some embodiments, second bearing1216may include an angular contact bearing. In some embodiments, second race1218may comprise an inner surface1219that may be radially flush with first race1214in a radial direction from blade axis1201. Two surfaces may be considered flush with each other when the surfaces are aligned with, or parallel to, each other in a reference direction. For example, the inner surface1219of second race1218may be aligned with first race1214at a certain radial distance from blade axis1201. It will be appreciated that a configuration involving second race1218being radially flush with first race1214may enable easier manufacturability. For example, alignment of the races may reduce the size of the hub, thereby reducing weight while still allowing assembly of the blade. In some examples, first race1214and second race1218may comprise separate raceways which can be removable from hub1204for servicing. Races, such as first race1214and/or second race1218, may be press fit to hub1204. Some disclosed embodiments may include a ball separator cage disposed between the second race and the first portion of the retention sleeve. For example, ball separator1220may be disposed between second race1218and first portion1207of retention sleeve1206. In some examples, ball separator1220may assist in preventing balls (e.g., bearing elements) from scraping on each other, and ball separator1220may also provide improvements for assembly by enabling a more efficient process of loading bearing elements into bearing races.

Retention systems according to embodiments of the present disclosure may advantageously be configured to withstand high loads in a compact and lightweight arrangement to satisfy the particular needs of eVTOL or other electric aircraft. For example, in some embodiments, the ratio of the weight of hub1204(e.g., a total weight including bearings1212and1216as well as bushings and mounting hardware, etc.) to the weight of blades1202(i.e., all blades retained in the hub1204) may be minimized, such as within a range of 1.5 to 2.25. In some embodiments, a ratio of the weight of the body of hub1204(e.g., an empty shell excluding bearing elements, etc.) to the weight of the bearings in retention system1212and1216(e.g., the total weight of all bearing for each blade1202) may be in a range of 0.85 to 1.2.

In some embodiments, retention sleeve1206may include an annular rib1225. A rib may refer to a ridge, protrusion, or projection, such as a protrusion of retention sleeve1206. In some embodiments, first race1214and second race1218may be spaced apart by annular rib1225. For example, annular rib1225may separate first race1214from second race1218. In some embodiments, annular rib1225may be flush with first race1214and second race1218in a radial direction, such as in a radial direction with respect to blade axis1201. It will be appreciated that by spacing apart first race1214and second race1218, annular rib1225may prevent wear occurring from contact between first race1214and second race1218and thereby preventing wear to the corresponding bearings, as well as providing a separation or spread between first bearing1212and second bearing1216. Annular rib may further provided structural reinforcement for supporting first bearing1212and second bearing1216.

It will be recognized that a retention system may include various components which can assist in maintenance of the system, including components which can reduce wear in the system. For example, in some embodiments, retention system1200may include a cap1228, as referenced inFIG.12. Cap1228may comprise a selectively removable or attachable cap. A cap may refer to any component for protecting a hub from wear, such as an endcap (e.g., an endcap portion of the hub). For example, cap1228may comprise a portion disposed between blade1202and hub1204, thereby assisting in protecting hub1204from loads due to blade1202. Cap1228may also protect hub1204from damage during operation and/or servicing, including damage from debris. Cap1228may comprise any suitable material, including plastics or metals (such as aluminum which may be coated (e.g., hard anodized) to improve wearability). In some embodiments, cap1228may include a body portion1229and a flange portion1231. Body portion1229may be a section of cap1228which contacts inner surface1210of the hub1204. Body portion1229may be disposed between retention sleeve1206and hub1204. In some embodiments, body portion1229may be disposed between the second portion1209of retention sleeve1206and the inner surface1210of the hub1204. In some examples, body portion1229may be flush with first race1214in a radial direction from blade axis1201. In some embodiments, cap1228may include a flange portion1231. A flange portion may refer to any protruding ridge, such as a lip or rim. Flanges may assist in attachment between components, stabilization, and/or transferring forces between components. Flange portion1231may extend outward from body portion1229. Extending outward may refer to extending in a direction away from a component. For example, the flange portion1231may extend outward from body portion1229, such as in a direction away from blade axis1201. In some embodiments, the flange portion1231may be attachable to an end surface1233of hub1204. Attachable to the end surface may refer to the flange portion being removably fixed and/or permanently fixed to the end surface. For example, the flange portion1231may be coupled to the end surface1233, thereby coupling cap1228to hub1204. In some examples, flange portion1231may be attached to the end surface1233by one or more fasteners, including screws or bolts, such as screw1226which may extend through flange portion1231into hub1204. Screw1226may have a thread locking coating applied to its threads. An exemplary assembly configuration may include screw1226secured under shim1230, shim carrier1232, and retaining ring1234. It will be appreciated that cap1228may assist in reducing wear to hub1204, including wear from the blade1202, such as during changes in blade angle during operation. For example, cap1228may prevent blade1202, retention sleeve1206, or other components from rubbing in wear regions, such as against hub1204or the inner surface of hub1204, thereby offering protection from wear. In some embodiments, cap1228may assist in retaining one or more bearing races, such as race1214, against centrifugal loads. Furthermore, it will be appreciated that the position of cap1228as described herein may allow for easier access to the cap during maintenance or service. For example, cap1228may be a replaceable cap, and may be removably attached, as described herein. Thus, the location of cap1228may enable the cap to be a replaceable wear surface, as the wear region may be separate from the inner surface of the hub, thereby allowing more efficient service. Additionally, cap1228may enable easier installation of bearing races (e.g., first race1214) from the exterior or outside of hub1204rather than having to feed the race from the interior of the hub during assembly, which may involve difficulty in aligning first race1214(e.g., needle race). Further, the position of the cap1228in wear regions may allow cap1228to include different material and coating combinations that enable improved service performance, such as hard anodized coating on the aluminum cap, which can improve the durability of the surface but may not be practical materials for the entire hub, thereby representing an improvement over other systems.

Some disclosed embodiments include a shim carrier disposed around the second portion of the retention sleeve. Referring toFIG.12, retention system1200may include a shim carrier1232. A shim carrier may be any covering or enclosing for a shim, such as shim1230. A shim may be any component configured to fill or occupy a space or gap. Shims may assist in occupying spaces, such as tolerances between mating components, as well as aligning components. For example, shim1230and shim carrier1232may prevent looseness in blade1202, such as when the propeller may not be rotating. In some examples, shims may include materials such as plastics and/or metals, including stainless steel. For example, shim1230may have an annular shape, such as a ring, and may encircle retention sleeve1206. In some embodiments, shim1230may be adjacent to the flange portion1231of cap1228. For example, shim1230may be positioned above flange portion1231. In an example, shim1230may contact a surface of flange portion1231. In some embodiments, shim carrier1232may be disposed around the retention sleeve1206. For example, shim carrier1232may be disposed around the second portion1209of retention sleeve1206, such that the shim carrier1232surrounds or encloses a portion or the entirety of retention sleeve1206. In some embodiments, shim carrier1232may enclose shim1230such that shim1230may be disposed between shim carrier1232and flange portion1231. For example, shim carrier1232may cover a surface of shim1230or shim carrier1232may enclose shim1230by covering one or more surfaces of shim1230. It will be appreciated that shim1230may be a replaceable device for protection against wear, and the configuration of shim1230and shim carrier1232may enable easier access for maintenance and/or replacement over other systems.

As described herein, in some embodiments, a retention system may include a wear region. For example, referring toFIG.12, retention system1200may include components which can assist in preventing wear, such as blade seal1222, sealing ring1224, and retaining ring1234. Some disclosed embodiments involve a retaining ring1234disposed radially outward from retention sleeve1206with respect to blade axis1201. Disposed radially outward may refer to a component being further, in a radial direction (e.g., along a direction pointing along a radius from the center of blade1202, such as going outward from blade1202) with respect to blade axis1201, than another component. For example, retaining ring1234may be disposed around section portion1209of retention sleeve1206. In some embodiments, retention sleeve1206may include a groove or indentation such that retaining ring1234may be recessed into retention sleeve1206. Retaining ring1234may be any fastener, including snap rings, circlips, or clips, which may assist in preventing unwanted component movement, such as limiting undesired movements of blade1202into hub1204(e.g., an axial direction along the blade when the propeller may not be rotating). In some embodiments, retaining ring1234may comprise metal, such as stainless steel. In some embodiments, retaining ring1234may be disposed axially outward from shim carrier1232with respect to the blade axis. Axially outward may refer to a component being further along, in an axial direction, than another component, such as further along a blade axis, in a direction toward a blade tip and away from a blade root or hub. For example, retaining ring1234may be further outward from shim carrier1232in an axial direction with respect to blade axis1201. In some examples, retaining ring1234may contact shim carrier1232, thereby providing retention in an axial direction to components including shim carrier1232and shim1230. For example, retaining ring1234may be configured to retain shim carrier1232while allowing relative motion, in a rotational direction about blade axis1201, between the retaining ring1234and shim carrier1232. Alternatively or additionally, such an arrangement may allow relative rotational motion between shim carrier1232and shim1230. Therefore, blade1202may perform frequent blade pitch changes under various bending loads while absorbing a substantial portion of the associated wear and degradation at inexpensive or easily replaceable components. Further, said components may comprise highly durable materials or hard coatings to further extend the lifetime of such components. For example, retaining ring1234or shim carrier1232may comprise metals, ceramics, anodized layers or other durable materials that could not feasibly be applied to the entire hub1204or retention system1206due to weight, cost, tensile or flexural strength, or other material properties or functional considerations.

Some disclosed embodiments may comprise a blade seal disposed between the retention sleeve and the body portion of the cap. Referring toFIG.12, blade seal1222may be disposed between the retention sleeve1206and the body portion1229of cap1228. Blade seals may be any sealing device or component, such as gaskets or O-rings. In some examples, retention sleeve1206may include a groove or notch such that blade seal1222may be recessed into retention sleeve1206. Blade seal1222may assist in closing or filling gaps. For example, blade seal1222may be an O-ring which contacts and presses against cap1228, such as pressing against the body portion1229. Thus, blade seal1222can assist in sealing the joint between the blade1202and the hub1204(e.g., during movement of the blade), as well as retaining fluids such as lubricants and coolants (e.g., retaining fluids such as oil from escaping) which may be present in retention system1200. For example, oil may be present in retention system1200to assist in lubrication of bearings. In some examples, blade seal1222may also prevent grit, debris, or other contaminants from entering retention system1200.

Some disclosed embodiments include a sealing ring disposed between the body portion of the cap and an inner surface of the hub. A sealing ring may refer to a sealing component, such as an O-ring. Retention system1200may include a sealing ring1224positioned between the body portion1229of cap1228and the inner surface1210of hub1204. In some embodiments, body portion1229may have an incision, and sealing ring1224may be positioned within the incision. Sealing ring1224may provide a static seal between cap1228and hub1204, thereby preventing lubricants such as oil inside hub1204from leaking past cap1228.

It will be recognized that aircraft described herein, including VTOL (e.g., eVTOL) aircraft, may desire to utilize certain constraints for propeller-rotor rotations per minute, including utilizing lower propeller-rotor RPM than general aircrafts to mitigate noise. Further, VTOL propulsion systems, including propellers capable of tilt and/or lift configurations, may be subject to non-axial inflow, such as during articulation between hover and cruise operation modes. Further, in some embodiments, VTOL aircraft may fly for extended periods in intermediate configurations in which a propeller is not fully tilted into either the lift or cruise configurations. For example, tilt propellers may be maintained at intermediate angles between substantially horizontal and substantially vertical, or may be arranged at constantly changing intermediate angles. This may allow a VTOL aircraft to rely primarily on wingborne flight for efficient air travel, yet achieve speeds well below the stall speed of a comparably sized conventional airplane, even transitioning smoothly to a motionless hovering state. A VTOL aircraft may be configured to move seamlessly above and below such a comparable stall speed during flight without any disruption to the passenger experience. Thus, it will be appreciated that VTOL aircraft may experience centrifugal loads on blade retention systems, as well as large bending loads on blades, that may not present an issue for other aircraft.

FIG.13illustrates a cross section of a blade retention system1300, consistent with embodiments of the present disclosure. Blade retention system1300may include blade1302which may have a blade axis1304, as described herein. Retention system1300may include various bearings in various configurations, such as a two-component unit with first bearing1306, which may be, e.g., needle roller and cage assembly bearing, and second bearing1314, which may be, e.g., angular contact ball bearing. First bearing1306may surround blade1302and have a virtual center1322. A virtual center may comprise a point at which the lines of action1310of first bearing1306intersect the axis of rotation of the bearing system. The lines of action may comprise lines of directional load experienced by the bearings, and the axis of rotation of the may substantially coincide with blade axis1304. For example, the lines of action of first bearing1306may run along line of action1310perpendicular to the axis of rotation of first bearing1306. Therefore, first bearing1306may represent the case in which the virtual center1322of first bearing1306substantially coincides with its geometric center. In some examples, first bearing1306along with first race1330may assist in reacting to the lateral loading of blade1302within the hub socket. On the other hand, second bearing1314may have a virtual center1324that is displaced from their geometric center due to the angular lines of action along axes1318(which may be lines of action of loads experienced by second bearing1314). For example, second bearings1314may be angular contact bearings, as described herein, which may provide advantages including improved speed ratings and load carrying for radial and axial loads. As such, it will be appreciated that bearings1314may assist in carrying centrifugal loads, such as centrifugal loads experienced on the blade1302. In an example, the contact surface that bearings1314make with their outer race may form an angle with the blade axis1304, such as, e.g., a 45 degree angle. In some examples, such configurations of bearings1314may result in the line of action of loads intersecting one or more components. For example, lines of action along axes1318(corresponding to the lines of action of bearings1314) may intersect reversing ring1326. For example, in some embodiments, axis1318may intersect reversing ring such that a majority of the mass of reversing ring is located axially inward of the axes1318. Axially inward may refer to the majority of the mass of the reversing ring1326being further inward from axis1318than the remaining mass with respect to an axial direction of blade axis1304. In some embodiments, more than 60%, 70%, or 80% of the mass of reversing ring1326may be located axially inward of axes1318. In this way, the loads exerted on reversing ring1326by bearings1314may press the blade into a retained state within the socket to aid in the retention of blade1302in the hub1332. In this way, disclosed bearing configurations may provide advantages for reacting to and managing loads that may be experienced (e.g., by VTOL and/or eVTOL aircraft). For example, retention system1300may include a spread1328(e.g., a distance) between virtual center1322corresponding to first bearings1306and virtual center1324corresponding to second bearings1314. In an example, referring toFIG.12, annular rib1225may also contribute to the distance between first bearing race1214and second bearing race1218. Such spread1328may enable an improved capacity of carrying bending loads on retention system1300. For example, it may be desired to increase bearing spread (including spread1328) to improve the ability of the retention system to handle loads while minimizing the diameter, axial length, or overall size of the hub and the blade root (e.g., to enable weight savings). In some embodiments, a distance between the first virtual center and the second virtual center may be sufficiently large to withstand centrifugal and/or bending loads sustained during operation of the system. For example, spread1328may be configured to be large enough to handle loads experienced during operation. Additionally, in some embodiments, virtual center1324may be axially inward of blade1302. As discussed above, axially inward may refer to virtual center1324being further inward than blade1302with respect to an axial direction of blade axis1304. Thus, it will be appreciated that bearing configurations of the disclosed retention systems may be capable of handling loads, such as centrifugal loads and bending loads as described herein, while maintaining structural efficiency (e.g., being lightweight). For example, the ratio of the weight of the bearings to the weight of blade1302(e.g., weight of blade not including balance tube ballast weight) may be in a range of 25 to 0.4. In other examples, virtual center1324may be axially flush, or axially outward, from blade1302with respect to blade axis1304.

FIG.14illustrates a propeller1400, consistent with embodiments of the present disclosure. Propellers, as discussed herein, may refer to propeller for tilt and/or lift configurations for VTOL aircraft. Propeller1400may include any number of blades1402, such as five blades, as an illustrative example. In some examples, propeller1400may include hub1404, and each blade1402may be connected to hub1404, or each blade1402may be connected to an individual hub.

FIG.15illustrates a magnified view of a propeller1500, consistent with embodiments of the present disclosure. Propeller1500may include one or more blades, such as blade1502and blade1512, which may each be retained by hub1504. As described herein, first bearing1506may have a bearing race contacting hub1504, and second bearing1508may have a bearing race1510contacting hub1504. It will be recognized that blades in propeller1500may include a retention system as described herein. For example, each blade in propeller1500may include first bearings and second bearings to retain the blade in the hub while propeller1500may be spinning. As described herein, retention systems may include wear regions, such as exemplary wear region1514. In wear region1514, the blade seal may contact the hub socket inner diameter on the cap, as described herein. As such, the contact region may be a region of higher wear. However, disclosed embodiments, such as the replaceable cap1228as illustrated inFIG.12, allow for cheap and efficient maintenance, while preventing the machining of a new hub or repair of the hub, which can be expensive and inefficient in traditional systems.

FIG.16illustrates an exemplary illustration of a propeller cross-section, consistent with embodiments of the present disclosure. Propeller1600may include blade retention systems, as described herein. Propeller1600may include one or more propeller blades, such as blades1602,1604,1606,1608, and1610, which may each be retained by hub1612. In some examples, hub1612may be configured to retain any number of blades, such as having sockets for one or more blades. Propeller1600may include one or more plugs1614which may contact a balance tube1616. For example, balance tube1616, which may be disposed within blade1602, may enclose plug1614. Propeller1600may also include a blade actuating cup1618, which may be disposed within blade1602. Blade actuating cup1618may be configured to blade1602about its axis to maneuver blade1602to a desired pitch, and may contact balance tube1616and an inner surface of blade1602.

It will be appreciated that the disclosed embodiments may comprise propeller blade retention systems with configurations that may provide stiff retention against axial and non-axial loads within a compact, lightweight arrangement as described herein. For example, blade1602may comprise a ratio of hub radial depth1622(e.g., a distance from a rotational centerline of the propeller to the surface of a propeller spinner) to a blade length1624(e.g., a length from the bottom of blade actuating cup1618to a tip of the blade (not shown)) in a range of 0.2 to 0.3. As an example, the compactness of the retention system with respect to size of the hub may be characterized by a ratio of the socket depth1620to hub radius1622. In some embodiments, the ratio of the socket depth1620to the hub radius1622may in a range of, e.g., 0.4 to 0.55. As an additional example, blade1602may have a ratio of socket depth1620to blade length1624in a range of 0.11 to 0.14, which may illustrate the compactness of the retention system with respect to the length of the blade. As described herein, a reduced size of the retention system (e.g., a more compact configuration) may provide weight savings and improved drag profiles. In another example, blade1602may be characterized by other parameters such as a virtual center spread distance (e.g., a distance between virtual centers, such as spread1328between virtual center1322and virtual center1324, as referenced inFIG.13). For example, in some embodiments the ratio of virtual spread distance1328to socket depth1620may be in a range of, e.g., 0.4 to 0.5, which may illustrate the compactness of the arrangement of bearing spread within the retention system, as well as the strength provided by the configurations of bearings consistent with the disclosed embodiments.

The foregoing description has been presented for purposes of illustration. It is not exhaustive and does not limit the invention to the precise forms or embodiments disclosed. Modifications and adaptations of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiments of the inventions disclosed herein.