WO2025244772A2

WO2025244772A2 - Systems and methods for testing vtol aircraft propeller loads

Info

Publication number: WO2025244772A2
Application number: PCT/US2025/025620
Authority: WO
Inventors: Heath SMOOT
Original assignee: Archer Aviation Inc
Current assignee: Archer Aviation Inc
Priority date: 2024-04-19
Filing date: 2025-04-21
Publication date: 2025-11-27
Anticipated expiration: 2026-10-19

Abstract

A propulsion system load test apparatus is disclosed having a frame configured to couple to a propulsion system that comprises an output shaft. The propulsion system comprises a rotatable mass configured to couple to the output shaft. The propulsion system comprises a first loading assembly coupled to the frame. The first loading assembly is configured to apply a load to the output shaft, the load having a direction along a first axis of the output shaft.

Description

SYSTEMS AND METHODS FOR TESTING VTOL AIRCRAFT PROPELLER

LOADS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present disclosure claims the benefit of priority under the Paris Convention to U.S. Patent Application No. 63/636,600, filed April 19, 2024. The aforementioned application is incorporated herein by reference its entirety.

TECHNICAL FIELD

[0002] This disclosure relates generally to the field of powered aerial vehicles. More particularly, and without limitation, the present disclosure relates to innovations in aircraft that use electrical propulsion systems. Certain aspects of the present disclosure generally relate to propeller load testing systems. Other aspects of the present disclosure generally relate to improvements in engine load testing systems that may be used in other types of vehicles but provide particular advantages in aerial vehicles.

SUMMARY

[0003] A propulsion system load test apparatus is disclosed. The propulsion system may have a frame configured to couple to a propulsion system that may comprise an output shaft. The propulsion system may comprise a rotatable mass configured to couple to the output shaft. The propulsion system may comprise a first loading assembly coupled to the frame. The first loading assembly may be configured to apply a first load to the output shaft, the load having a first direction along a first axis of the output shaft.

[0004] A method of testing a propulsion system is disclosed. The method of testing the propulsion may comprise: connecting the frame of the load test apparatus above to the propulsion system; connecting the output shaft to the rotatable mass of the load test apparatus; rotating the output shaft; and applying a load to the output shaft along a first axis of the output shaft.

[0005] A method of testing a propulsion system is disclosed. The method of testing the propulsion system may comprise: connecting a propulsion system to a frame of a load test apparatus, the propulsion system comprising an output shaft; connecting the output shaft to a rotatable mass; rotating the output shaft; applying a load to the output shaft along a first axis; and monitoring a parameter of the propulsion system. BRIEF DESCRIPTIONS OF FIGURES

[0006] Figure 1A illustrates an example VTOL aircraft in a cruise configuration, consistent with embodiments of the present disclosure.

[0007] Figure IB illustrates an example VTOL aircraft in a lift configuration, consistent with embodiments of the present disclosure.

[0008] Figure 2 illustrates an example propeller load test apparatus, consistent with embodiments of the present disclosure.

[0009] Figure 3 illustrates an example propeller load test apparatus with aircraft propulsion system installed, consistent with embodiments of the present disclosure.

[0010] Figure 4A illustrates an example motor mount assembly, consistent with embodiments of the present disclosure.

[0011] Figure 4B illustrates an example motor mount assembly with aircraft propulsion system installed, consistent with embodiments of the present disclosure.

[0012] Figure 5 illustrates an example propeller load test apparatus configured to be driven without an aircraft propulsion motor.

[0013] Figure 6A illustrates an example gearbox assembly, consistent with embodiments of the present disclosure.

[0014] Figure 6B illustrates an interior of an example gearbox assembly, consistent with embodiments of the present disclosure.

[0015] Figure 7 illustrates an example Z-Axis loading assembly, consistent with embodiments of the present disclosure.

[0016] Figure 8 illustrates an example X or Y-Axis loading assembly, consistent with embodiments of the present disclosure.

[0017] Figure 9 illustrates an example two-axis propeller load graph, consistent with embodiments of the present disclosure.

[0018] Figure 10 is a flow diagram of a method of testing a propulsion system, consistent with embodiments of the present disclosure.

[0019] Figure 11 is a flow diagram of a method of testing a propulsion system including multiple loads, consistent with embodiments of the present disclosure.

DETAILED DESCRIPTION

[0020] The present disclosure describes structural components of electric vertical takeoff and landing (eVTOL) aircraft primarily for use in a non-conventional aircraft. For example, the eVTOL aircraft of the present disclosure may be intended for frequent (e.g., over 50 flights per workday), short-duration flights (e.g., less than 100 miles per flight) over, into, and out of densely populated regions. The aircraft may be intended to carry 4-6 passengers or commuters who have an expectation of a low-noise and low-vibration experience. Accordingly, it may be desired that the aircraft’s structural components are configured and designed to withstand frequent use without wearing, that they generate less heat and vibration, and that the aircraft include mechanisms to effectively control and manage heat or vibration generated by the structural components. Further, it is intended that several of these aircraft operate near each other over a crowded metropolitan area. Accordingly, it is desired that their structural 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 desirable for safety reasons that the aircraft are 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 desirable that the aircraft can safely vertically take off and land from and into relatively restricted spaces (e.g., vertiports, parking lots, or driveways) compared to traditional airport runways while transporting around 4-6 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 structural components.

[0021] Disclosed embodiments provide new and improved configurations of aircraft structural components that are not present in conventional aircraft, and/or identified design criteria for structural components that differ from those of conventional aircraft. Such alternate configurations and design criteria, in combination addressing drawbacks and challenges with conventional structural components, yielded the embodiments disclosed herein for various configurations and designs of eVTOL aircraft structural components. [0022] In some embodiments, the eVTOL aircraft of the present disclosure may be designed to be capable of both vertical and conventional takeoff and landing, with a distributed electrical propulsion system enabling a vertical flight mode, a forward flight mode, and transition between the two. Thrust may be generated by supplying high voltage electrical power to the electrical engines of the distributed electrical propulsion system, which may convert the high voltage electrical power into mechanical shaft power to rotate a propeller. Embodiments disclosed herein may involve optimizing the energy density of the electrical propulsion system. Embodiments may include an electrical engine connected to an onboard electrical power source, which may include a device capable of storing energy such as a battery or capacitor, or may include one or more systems for harnessing or generating electricity such as a fuel powered generator or solar panel array. Some disclosed embodiments provide for weight reduction and space reduction of structural components in the aircraft, thereby increasing aircraft efficiency and performance. Given the focus on safety in passenger transportation, disclosed embodiments implement new and improved safety protocols and system redundancy in case of a failure, to minimize any single points of failure in the aircraft propulsion system. Some disclosed embodiments also provide new and improved approaches to satisfying aviation and transportation laws and regulations. For example, the Federal Aviation Administration enforces federal laws and regulations requiring safety structural components such as fire protective barriers adjacent to engines that use more than a threshold amount of oil or other flammable materials.

[0023] In preferred embodiments, the distributed electrical propulsion system may include twelve electrical engines, which may be mounted on booms forward and aft of the main wings of the aircraft. The forward electrical engines may be tiltable mid-flight between a horizontally oriented position (e.g., to generate forward thrust) and a vertically oriented position (e.g., to generate vertical lift). The forward electrical engines may be of a clockwise type or counterclockwise type in terms of direction of propeller rotation. The aft electrical engines may be fixed in a vertically oriented position (e.g., to generate vertical lift). They may also be of a clockwise type or counterclockwise type in terms of direction of propeller rotation. In some embodiments, an aircraft may possess various combinations of forward and aft electrical engines. For example, an aircraft may possess six forward and six aft electrical engines, four forward and four aft electrical engines, or any other combination of forward and aft engines, including embodiments where the number of forward electrical engines and aft electrical engines are not equivalent. In some embodiments, an aircraft may possess four forward and four aft engines, where at least four of these propellers comprise tiltable engines. [0024] In preferred embodiments, for a vertical takeoff and landing (VTOL) mission, the forward electrical engines as well as aft electrical engines may provide vertical thrust during takeoff and landing. During flight phases where the aircraft is in forward flight-mode, the forward electrical engines may provide horizontal thrust, while the propellers of the aft electrical engines may be stowed at a fixed position in order to minimize drag. The aft electrical engines may be passively stowed in the fixed position using, e.g., biasing mechanisms or propeller locking mechanisms. Alternatively or additionally, the aft electrical engines may be actively stowed by operation of the aft electrical engines in combination with propeller angular 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 mostly horizontal direction during forward-flight mode. A variable pitch mechanism may change the forward electrical engine’s propeller-hub assembly blade collective angles for operation during the hover-phase, transition phase, and cruise-phase.

[0025] In some embodiments, in a conventional takeoff and landing (CTOL) mission, the forward electrical engines may provide horizontal thrust for wing-borne take-off, cruise, and landing. In some embodiments, the aft electrical engines may not be used for generating thrust during a CTOL mission and the aft propellers may be stowed in place.

[0026] In some embodiments, an electric engine may be housed or connected to a boom of an aircraft and include a motor, inverter, and gearbox. In some embodiments, the motor, inverter, and gearbox may be interfaced such that they share a central axis. In some embodiments, the torque originating in the motor may be sent away from the propellers of the propulsion system and to a gearbox. In some embodiments, a gearbox may provide a gear reduction and then send the torque, via a main shaft, back through a bearing located inside the motor and to the propeller. In some embodiments, an inverter may be mounted on the rear of a gearbox such that a main shaft does not travel through the inverter when outputting torque to the propeller. In some embodiments, the motor, gearbox, and inverter may be interfaced such that a coolant, such as oil, may be used to service the motor, inverter, and/or gearbox, while sharing a common heat exchanger.

[0027] In some embodiments, a tilt propeller system may include a linear or rotary actuator to change the orientation of a propulsion system during operation. In some embodiments, the pitch of the propeller blades may be changed as a function of the orientation of the propulsion system. In some embodiments, a rotary actuator may include a motor, inverter, and gearbox. In some embodiments, a gearbox may include various types of gears interfacing to provide a gear reduction capable of orienting the propulsion system. In some embodiments, a tilt propeller system may include a redundant configuration such that multiple motors, inverters, and gearboxes are present and interface using a gear. In some embodiments, a configuration utilizing multiple motors, gearboxes, and inverters may allow a failed portion of the redundant configuration to be driven by the motor, inverter, and gearbox of another portion of the configuration. In some embodiments, a gearbox configuration may also allow the tilt propeller system to maintain a propulsion system orientation with the help of, or without, additional power being provided by the system. [0028] In some embodiments, an electrical 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. As mentioned above, an aircraft as described herein may possess multiple electric engines which are boom-mounted forward and aft of the wing. The amount of thrust each electric engine generates may be governed by a torque command from the Flight Control System (FCS) over a digital communication interface to each electric engine.

[0029] As disclosed herein, an electrical engine may include an inverter and motor; or inverter, gearbox, and motor across various configurations, such as representative configurations as described herein. For example, an electrical engine may include an electrical motor, gearbox, and inverter that all share the same central axis. Additionally, the central axis may be configured along an axis of an output shaft going to the propeller of the aircraft. In such an exemplary configuration, the motor, gearbox, and inverter may all share the output shaft as a central axis. Additional embodiments may include a motor, gearbox, and inverter that are mounted together in a sequence, or a configuration where some of the structural components are mounted together, such as the motor and gearbox, and another structural component is located elsewhere, such as the inverter, but wiring systems are used to electrically connect the inverter to the motor. In some embodiments, other propulsion systems, such as a hybrid propulsion system, may be used. A hybrid propulsion system may utilize, e.g., a fuel source to generate electrical energy, or may be configured to use electrical energy or the fuel source to provide propulsion.

[0030] As mentioned above, an electrical engine for an aircraft as described here may include some or all of a motor, inverter, and gearbox. Various configurations may include an inverter and motor such that the output shaft of a motor directly provides the speed and torque for a propeller shaft. Additional embodiments of an electrical engine may include a motor, inverter, and a gearbox, wherein the output of a motor may travel through a gearbox that is connected to the output shaft for the propeller; a motor, inverter, and gearbox wherein the output from the motor travels away from the propeller, through a gearbox, where the output shaft for the propeller travels back through the gearbox and motor to the propeller. As described herein, each configuration or orientation of the electrical engine may include cooling via air-cooling, coolant liquid, or a mixture of both.

[0031] In some embodiments, an inverter may share the same central axis as a motor wherein the inverter may be located in an enclosure that is cantilevered off of the rear of the motor and may be air cooled. It is recognized that such an inverter orientation may not be an optimum configuration in terms of the enclosure required to achieve such a cantilevered orientation. Additionally, a motor in this configuration utilizing air cooling may comprise potting material and air fins to assist with cooling of the motor may lead to an increase in mass of the system.

[0032] Some embodiments may include an electrical engine, wherein inverter modules may be mounted on the outside of a motor enclosure. Additional embodiments may include an electrical engine wherein an inverter may be mounted on top of an electrical motor such that the air-cooling fins of the inverter are underneath the propeller. Further embodiments may include an inverter mounted to the back of a motor with air-cooling fins facing out radially, an inverter mounted to the front of a motor with the air-cooling fins facing out radially, an inverter mounted to a motor where the inverter is cooled by a liquid, such as oil, or any other position of the inverter relative to a motor.

[0033] Embodiments of an electrical motor may comprise a stator enclosure, a wound stator assembly, a rotor, various bearings, and any additional structural components to assist in transferring the speed and torque generated by the motor to a propeller.

[0034] It is understood that an electrical engine may generate heat during operation and may comprise a heat management system to ensure structural components of the electrical engine do not fail during operation due to overheating. In some embodiments, coolant may be used and circulated throughout individual structural components of the engine, such as an inverter, gearbox, or motor, through some of the structural components, or through all of the structural components of the engine to assist with managing the heat present in the engine. Additional embodiments may include using air cooling methods to cool the electrical engine or using a mixture of coolant and air to manage the heat generated during operation in the electrical 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, the inverter, gearbox, and motor may be cooled using a liquid, air, or a mixture of air and liquid cooling could be used, such as cooling the motor using air cooling and using liquid cooling in the inverter and gearbox, or any other combination of air and liquid cooling across the inverter, gearbox, and motor or even subsets of those structural components.

[0035] In some embodiments, different amounts of oil may be used to act as both lubricant and coolant fluid in the electrical engine, such as less than one quart, less than two quarts, or any other amount of oil needed to lubricate and cool the electrical engine, in combination with or without the assistance of air cooling. As has been disclosed herein, an electrical engine may have different primary functionalities such as being used only for lifting and landing, and as such only being used in one orientation, or being used during all stages of flight such as lifting, landing, and in-flight. An engine that is used in all stages of flight may experience various orientations throughout flight and may comprise more lubricant and coolant than the engine only used in one orientation.

[0036] In aircraft development, it may be desirable to perform finite element analysis on computer-aided design (CAD) model structural components. Further, it may be desirable to physically test individual aircraft structural components under the same loads and constraints applied to the CAD model structural components during finite element analysis. Also, it may be desirable to physically test individual structural components individually to prevent adjacent structural components within an assembly from compensating for an individual structural component’s design or manufacturing flaws during physical testing. For example, it may be important in VTOL design to test propeller loads, including moment loads, experienced in operation on the entire electric propulsion system of an aircraft or its individual structural components.

[0037] Known methods for testing propeller loads include securing a propeller system onto a track and driving the entire system around the track to simulate flight. However, such methods are subject to factors that cannot be easily controlled. For example, outdoor trackbased test systems are subject to inconsistent environmental factors, including wind, rain, varying atmospheric pressures, and varying temperatures. Additionally, during aircraft development, it may be desirable to test individual aircraft structural components under worst-case flight conditions, including high winds, crosswinds, and storms. Track-based testing is undesirable for such worst-case testing. For example, it does not allow for isolation of individual structural components, and it requires worst-case conditions to exist and persist long enough to conduct a satisfactory test. Thus, track-based testing may fail to simulate or identify flight conditions that would cause failures of a propeller system. Also, worst-case conditions may be dangerous for the personnel conducting the test, such as observers or a driver of the testing system.

[0038] Comparative indoor testing systems include static load testing and inline dynamic load testing. Static load testing includes applying a single load to a single point on a stationary aircraft propulsion system. However, such methods fail to simulate real world flight conditions. For example, aircraft propulsion systems experience varying loads at varying points during 360 degrees of rotation, which is not simulated by the application of a load to a single point. Inline dynamic load testing systems include securing a non-adjustable load directly to an operating aircraft propulsion system. Such methods also fail to satisfactorily simulate real world flight conditions. For example, despite the operation of the propulsion system during testing, there is no way to adjust the applied load, simulate tilt, or test a range of worst-case flight conditions.

[0039] Embodiments of the present disclosure provide a test apparatus capable of testing propeller loads, including moment loads, experienced in operation on the entire electric propulsion system of an aircraft under a range of flight conditions, including worst-case flight conditions, in a manner that may be more reliable, safer, faster, and more convenient than conventional methods. For example, in some embodiments, the test apparatus may comprise a frame to which a motor and shaft can be mounted. The shaft may be coupled to a simulated propeller of the test apparatus, such as a rotatable mass. In some embodiments, a gearbox assembly may be installed between the output shaft and the simulated propeller to increase the rotation frequency of the simulated propeller, thereby simulating multiple propellers and/or decreasing the time required to reach a failure mode or simulate a specific flight time. In some embodiments, adjustable weights may be removably attached to the rotatable mass to simulate loads experienced in real world and worst-case flight conditions. In some embodiments, adjustable weights may be removably attached at positions about the rotatable mass to reduce unwanted dynamic shear load on the output shaft. For example, adjustable weights may be placed at symmetrical positions about the rotatable mass to reduce unwanted dynamic shear load on the output shaft. The mass and radial placement of the adjustable weights on the rotatable mass may simulate various loads applied to a propulsion system in real world flight conditions involving aircraft tilt.

[0040] Using systems and methods according to the present disclosure, aircraft propeller engines and other structural components may be driven to a failure mode, or otherwise monitored to determine lifetime, durability, stress, strain, etc., in a manner that is more reliable, safer, faster, and more convenient than conventional methods.

[0041] One or more loading assemblies may be coupled to the frame to adjustably load the propulsion system along one or more axes. Thus, during normal operation, the test apparatus may test a propulsion system under worst-case propeller load conditions.

[0042] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the disclosure. Instead, they are merely examples of apparatuses and methods consistent with aspects related to the subject matter recited in the appended claims.

[0043] Figs. 1A and IB illustrate a VTOL aircraft 100 in 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. The aircraft 100 may include a fuselage 102, wings 104 mounted to the fuselage 102, tail 105, and one or more rear stabilizers 106 mounted to the tail 105 or the rear of the fuselage 102. A plurality of lift propellers 112 may be mounted to wings 104 and configured to provide lift for vertical takeoff, landing and hover. A plurality of tilt propellers 114 may be mounted to wings 104 and may be tiltable between the cruise configuration in which they provide forward thrust to aircraft 100 for horizontal flight, as shown in Fig. 1A, and the lift configuration in which they provide a portion of the lift required for vertical take-off, landing and hovering, as shown in Fig. IB. As used herein, a lift configuration may refer to a tilt propeller orientation in which the tilt propeller thrust is providing primarily lift to the aircraft. A cruise configuration may refer to a tilt propeller orientation in which the tilt propeller thrust provides primarily forward thrust to the aircraft. Alternatively, a cruise configuration may refer to a configuration in which a lift propeller is stowed.

[0044] In some embodiments, lift propellers 112 may be configured for providing lift only, with all propulsion being provided by the tilt propellers. Accordingly, lift propellers 112 may be in fixed positions and may only generate thrust during take-off, landing and hover. Meanwhile, tilt propellers 114 may be tilted to lift configurations in which their thrust is directed vertically for providing additional lift.

[0045] For forward flight, tilt propellers 114 may tilt from their lift configurations to their cruise configurations. In other words, the pitch and tilt angle of tilt propellers 114 may be varied from an orientation in which the tilt propeller thrust is directed vertically (to provide lift during vertical take-off, landing and hover) to an orientation in which the tilt propeller thrust is directed horizontally (to provide forward thrust to aircraft 100). The tilt propellers may tilt about axes that may be perpendicular to the forward direction of the aircraft 100. When the aircraft 100 is in full forward flight during the cruise configuration, lift may be provided entirely by wings 104. Meanwhile, lift propellers 112 may be shut off. The blades 120 of lift propellers 112 may be locked in low-drag positions for aircraft cruising. In some embodiments, lift propellers 112 may each have two blades 120 that may be locked for cruising in minimum drag positions in which one blade is directly in front of the other blade as illustrated in Fig. 1A. In some embodiments, lift propellers 112 have more than two blades. In some embodiments, tilt propellers 114 include more blades 118 than lift propellers 112. For example, as illustrated in Figs. 1A and IB, lift propellers 112 may each include, e.g., two blades and tilt propellers 114 may each include, e.g., five blades. In some embodiments, tilt propellers 114 may have, e.g., from 2 to 5 blades.

[0046] In some embodiments, the aircraft may include only one wing 104 on each side of fuselage 102 (or a single wing that extends across the entire aircraft) and at least a portion of lift propellers 112 may be located rearward of wings 104 and at least a portion of tilt propellers 114 may be located forward of wings 104. In some embodiments, all of lift propellers 112 may be located rearward of wings 104 and all of tilt propellers 114 may be located forward of wings 104. According to some embodiments, all lift propellers 112 and tilt propellers 114 may be mounted to the wings — i. e., no lift propellers or tilt propellers may be mounted to the fuselage. According to some embodiments, all lift propellers 112 and tilt propellers 114 may be positioned inwardly of the wing tips 109.

[0047] In some embodiments, lift propellers 112 and tilt propellers 114 may be mounted to wings 104 by booms 122. Booms 122 may be mounted beneath wings 104, on top of the wings, and/or may be integrated into the wing profile. In some embodiments, one lift propeller 112 and one tilt propeller 114 may be mounted to each boom 122. Lift propeller 112 may be mounted at a rear end of boom 122 and tilt propeller 114 may be mounted at a front end of boom 122. In some embodiments, lift propeller 112 may be mounted in a fixed position on boom 122. In some embodiments, tilt propeller 114 may mounted to a front end of boom 122 via a hinge. Tilt propeller 114 may be mounted to boom 122 such that tilt propeller 114 is aligned with the body of boom 122 when in the cruise configuration, forming a continuous extension of the front end of boom 122 that minimizes drag for forward flight. [0048] According to some embodiments, the at least one wing 104 is a high wing mounted to an upper side of fuselage 102. According to some embodiments, the wings include control surfaces, such as flaps, ailerons or flaperons. According to some embodiments, the wings may have curved wing tips 109 for reduced drag during forward flight.

[0049] In some embodiments, rear stabilizers 106 include 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. For example, the wings may have a tapering leading edge or a tapering trailing edge. In some embodiments, the wings may have a substantially straight leading edge in the central section of wings 104. In the context of this disclosure, the term “substantially” may mean within ordinary design, manufacturing, or operational tolerances. [0050] Aircraft 100 may include at least one door 110 for passenger entry and exit. In some embodiments, the door 110 may be located beneath and forward of wings 104 as seen in Figs. 1A and IB.

[0051] Further discussion of VTOL aircraft may be found in U.S. Patent Publication No. 2021/0362849, which is incorporated by reference in its entirety.

[0052] As discussed above, it may be desirable to provide an apparatus for testing propeller loads on the entire electric propulsion system of an aircraft or its individual structural components. However, it is difficult to achieve this according to outdoor, track-based methods that are subject to factors not easily controlled, including wind, rain, varying atmospheric pressures, and varying temperatures. Further, static or dynamic stationary testing systems may fail to simulate real world flight conditions. Embodiments of the present disclosure provide a test apparatus capable of testing worst-case propeller load scenarios on the entire propulsion system of a VTOL or other aircraft, or individual propulsion system structural components. By isolating and securing one or more propulsion system structural components to a frame with one or more mounted loading assemblies, the design may test worst-case propeller loads more safely, reliably, efficiently, and conveniently.

A. Example Propeller Load Test Apparatus Embodiments

[0053] Fig. 2 illustrates an example propeller load test apparatus 200, consistent with embodiments of the present disclosure. The propeller load test apparatus 200 may comprise, e.g.: a motor mount assembly 219 coupled to a frame 204; a gearbox assembly 210 coupled to a rotatable mass 212; a Z-axis load assembly 202 coupled to frame 204, an X-axis load assembly 216; a Y-axis load assembly (not shown); an internal guard 228; one or more tool holders 230; and a secondary drive belt assembly 226.

[0054] In some embodiments, motor mount assembly 219 may comprise a fixed motor mounting bracket 220, a floating motor mounting bracket 222, and a motor mounting plate 224. In general, motor mount assembly 219 may be designed to mimic the mounting structural components of an aircraft or other vehicle into which the propulsion system under test will be installed. This may allow for more accurate simulation of the complex stresses, bending modes, vibrations and inter-component dynamics that may occur during real-world operation. For example, fixed motor mounting bracket 220 may be configured to substantially lock at least a portion of an aircraft propulsion system to frame 204, and floating motor mounting bracket 222 may be configured to attach at least a portion of an aircraft propulsion system to frame 204 while allowing movement in one or more degrees of freedom with respect to frame 204. Thus, fixed motor mounting bracket 220 may cooperate with floating motor mounting bracket 222 to simulate real the world mounting conditions of the aircraft propulsion system, which the propulsion system is allowed to move to, e.g., prevent damage due to over-constraint.

[0055] Propeller load test apparatus 200 may further comprise a rotatable mass 212.

Rotatable mass 212 may be coupled to an output shaft of the propulsion system under test and may be used as a test mass to simulate a propeller or other load on the propulsion system. For example, the output shaft may comprise a propeller flange at its output side configured to mate with a propeller hub of the VTOL or other vehicle in which the propulsion system is to be used. Therefore, rotatable mass 212 or another structural component of test apparatus 200 may comprise a mounting flange configured to mate with the propeller flange in a similar manner. In some embodiments, rotatable mass 212 may comprise a non-uniform mass distribution configured to induce a bending load on the shaft of the propulsion system under test. For example, during testing, the propulsion system may rotate the rotatable mass 212 as if it were a propeller, and the mass distribution may cause rotatable mass 212 to exert a torque on the output shaft that simulates torques experienced during vertical lift. In this way, the mass distribution may simulate the bending loads applied by a propeller to the shaft during flight. In some embodiments, rotatable mass 212 may comprise an even mass distribution, and may be coupled to one or more adjustable masses 214 to achieve a non- uniform mass distribution that simulates aircraft tilt. In some embodiments, rotatable mass 212 may comprise a disc shape. In some embodiments, rotatable mass 212 may comprise a shape other than a disc shape. For example, rotatable mass 212 may take the form of a stunted propeller, a flat hourglass shape, etc. In general, rotatable mass 212 may be shaped and weighted to impart a bending load to the shaft of the propulsion system under test, due to its rotation about the shaft. In some embodiments, a propeller load test apparatus 200 may comprise a plurality of interchangeable rotatable masses 212, each having a predetermined mass distribution, dimension, weight, diameter, shape, or other structural parameter.

[0056] In some embodiments, the one or more adjustable masses 214 may comprise a detachable mass configured to be removably attached to rotatable mass 212 at a desired location. In some embodiments, an adjustable mass 214 may be permanently or removably coupled to rotatable mass 212 such that it is spatially adjustable to adjust the load exerted on the output shaft. For example, an adjustable mass may be movable along a direction having a component vector in radial direction of rotatable mass 212, or movable along a direction having a component vector in an axial direction (parallel to an axis of rotation) of the rotatable mass. Here, a component vector refers to a vector that represents a part of another vector along a chosen direction. For example, on a cartesian coordinate system, a diagonal line has a vector component along the x-axis and a vector component along the y-axis, each vector component corresponding to a projection of the diagonal line onto that vector component’s respective axis. Thus, a load that is applied at a small angle to the axial direction has at least a component vector in the axial direction. Such adjustments may be used to adjust the load applied to the propulsion system under test. In some embodiments, the one or more adjustable masses 214 may comprise a geometry that distributes mass vertically to adjust the load applied to the propulsion system under test.

[0057] In some embodiments (as for example further discussed with respect to Figs. 6A and 6B), rotatable mass 212 may be coupled to the shaft by a gearbox assembly 210. For example, the gearbox assembly 210 may comprise a gear ratio greater than 1, such as 2: 1, to increase the revolutions per minute (RPM) of rotatable mass 212 with respect to the shaft of the propulsion system. This may increase the frequency of bending moments being applied to the propulsion system by rotatable mass 212. For example increasing the rotation frequency of the rotatable mass 212 may simulate multiple propellers and/or decreasing the time required to reach a failure mode or simulate a specific flight.

[0058] In some embodiments (as for example further discussed with respect to Fig. 7), Z-axis load assembly 202 may be coupled to frame 204 and configured to couple to gearbox assembly 210, rotatable mass 212, or to the output shaft of the propulsion system. In some embodiments, an alignment coupling assembly 208 and a Z-axis load mount 206 may be configured to apply a load along an axis substantially similar to the Z-axis to simulate the tensile load applied to the output shaft, or other structural components of the propulsion system, by the lifting force of a propeller.

[0059] In some embodiments (as for example further discussed with respect to Fig. 8), X- axis load assembly 216 may be coupled to frame 204 and configured to apply a load to gearbox 210, rotatable mass 212, or the output shaft of a propulsion system (not shown) along an axis substantially similar to the X-axis. In some embodiments, a torque arm 218 may be coupled to frame 204 and gearbox assembly 210 and may be configured to radially control gearbox assembly 210 along the X-axis and Y-axis. For example, torque arm 218 may comprise one or more alignment couplers, coupled in series and each capable of compensating for up to five degrees of misalignment. Thus, torque arm 218 may dampen the vibration of gearbox assembly 210 and prevent the radial translation and/or deformation of gearbox assembly 210. [0060] In some embodiments (as for example further discussed with respect to Fig. 5), secondary drive belt assembly 226 may be coupled to frame 204 and configured to drive rotatable mass 212, gearbox assembly 210, or an output shaft (not shown). For example, if it is desirable to test a particular aircraft propulsion system without mounting or utilizing the propulsion system’s motor, an output shaft could be tested as described above by coupling the output shaft to one of the rotatable mass 212, gearbox assembly 210, or secondary drive belt assembly 226 and driving the output shaft, directly or indirectly, via secondary drive belt assembly 226.

[0061] Internal guard 228 may be coupled to frame 204 and configured to prevent structural components under test, such as an aircraft propulsion system, from exiting the intended test area. For example, if the structure of the propulsion system under test fails, internal guard 228 may prevent loose structural components from injuring bystanders.

[0062] Tool holders 230 may be coupled to frame 204 and configured to store tools necessary for the operation of propeller load test apparatus 200. For example, tool holders 230 may be configured to hold bolts configured to mount an aircraft propulsion system to the motor mount assembly 219.

[0063] Propeller load test apparatus 200 may comprise a controller 290 configured to control various elements of the testing apparatus such as, e.g., actuators, sensors, and other controls, to perform the operations disclosed herein. For example, the controller may be operatively coupled to the various elements of propeller load test apparatus 200 and configured to send and/or receive, e.g., electrical power and/or signals for controlling propeller load test apparatus 200. In some embodiments, controller 290 may be configured to control X-axis, Y- axis, or Z-axis load assemblies, drive belt assemblies etc., to perform a testing operation. Controller 290 may further be configured to monitor the operations of propeller load test apparatus 200 by sensors such as speed sensors, load cells, strain gauges, etc. In some embodiments, controller 290 may be operatively coupled to the aircraft propulsion system under test in order to drive and monitor the aircraft propulsion system during a testing operation. In some embodiments, controller 290 is operably coupled to one or more input and/or output devices, such as to enable a user or an external system to adjust operations performed by controller 290 and/or output results of controller 290 monitoring operations of propeller load test apparatus 200. Controller 290 may comprise one or more processors and memory storing instructions that, when executed by the one or more processors, perform processes disclosed herein, in part or in their entirety. [0064] Fig. 3 illustrates an example propeller load test apparatus 300 with aircraft propulsion system installed, consistent with embodiments of the present disclosure. Propeller load test apparatus 300 may be e.g., similar to propeller load test apparatus 200 of Fig. 2 except as described below. In Fig. 3 and below, corresponding or similar elements may be labeled with corresponding numbers using the instant Figure number as the leading digit(s). For example, in some embodiments, gearbox assembly 310 of Fig. 3 may be similar to gearbox assembly 210 of Fig. 2. In some cases, elements with corresponding subordinate numbers may represent unrelated features.

[0065] In some embodiments, the aircraft propulsion system installed for testing may include an aircraft motor 332. Aircraft motor 332 may be coupled to frame 304. For example, as further discussed below with respect to Figs. 4A and 4B, aircraft motor 332 may be coupled to frame 304 via motor mount assembly 319. In operation, propeller load test apparatus 300 may be configured such that aircraft motor 332 drives one of an output shaft (not shown), rotatable mass 312, or gearbox assembly 310. In some embodiments, aircraft motor 332 may comprise a lifter motor of a VTOL aircraft. In some embodiments, aircraft motor 332 may comprise an electric motor or an internal combustion engine.

[0066] Figs. 4A and 4B illustrate an example motor mount assembly 400, consistent with embodiments of the present disclosure. Motor mount assembly 400 may be similar to motor mount assembly 219 of Fig. 2. The motor mount assembly 400 may comprise, e.g.: a fixed mounting bracket 420 coupled to a frame 404; a floating mounting bracket 422 coupled to frame 404; a motor mount plate 424 coupled to frame 404; a fixed mounting bolt 434; and a clevis pin 436.

[0067] In some embodiments, motor mount assembly 400 may be designed to mimic the mounting structural components of an aircraft or other vehicle into which the propulsion system under test will be installed. This may allow for more accurate simulation of the complex stresses, bending modes, vibrations and inter-component dynamics that may occur during real-world operation.

[0068] Fixed motor mounting bracket 420 may be coupled to frame 404 and configured to mount at least a portion of an aircraft propulsion system 432 to frame 404 via fixed mounting bolt 434. For example, fixed mounting bolt 434 may be configured to engage a portion of aircraft propulsion system 432, and fixed motor mounting bracket 420 may be configured to receive fixed mounting bolt 434. In some embodiments, fixed motor mounting bracket may be configured to substantially restrain the movement of aircraft motor 432. [0069] Floating mounting bracket 422 may be coupled to frame 404 and configured to mount at least a portion of an aircraft propulsion system 432 to frame 404 via clevis pin 436. For example, clevis pin 436 may be configured to engage a portion of aircraft propulsion system 432, and floating mounting bracket 422 may be configured to receive clevis pin 436. In operation, fixed motor mounting bracket 420 may be configured to substantially lock at least a portion of an aircraft propulsion system to frame 404, and floating motor mounting bracket 422 may be configured to attach at least a portion of an aircraft propulsion system to frame 404 while allowing movement of one or more degrees of freedom with respect to frame 404. Thus, fixed motor mounting bracket 420 may cooperate with floating motor mounting bracket 422 to simulate real world mounting conditions and prevent over constraint as discussed above.

[0070] Motor mount plate 424 may be coupled to frame 404 and configured to mount at least a portion of an aircraft propulsion system 432 to frame 404. For example, motor mount plate 424 may be configured to receive bolts configured to engage at least a portion of aircraft propulsion system 432.

[0071] Fig. 5 illustrates a rear view of an example propeller load test apparatus configured to drive structural components of an aircraft propulsion system without an aircraft motor, such as aircraft motor 332, consistent with embodiments of the present disclosure. Propeller load test apparatus 500 may comprise a secondary drive belt assembly 526 which may further comprise, e.g.: a secondary drive motor 540 coupled to frame 504; a secondary drive pulley 542 coupled to secondary drive motor 540; and a secondary drive belt 543.

[0072] In general, secondary drive belt assembly 526 may be designed to mimic an aircraft propulsion system such as aircraft motor 332. In some embodiments, secondary drive motor 540 may be coupled to frame 504 and configured to drive secondary drive pulley 542. Secondary drive pulley 542 may be configured to drive secondary drive belt 543, which may drive one of a rotatable mass 512, a gearbox assembly, such as gearbox assembly 210, or an output shaft (not shown). For example, if it is desirable to test a particular aircraft propulsion system without mounting or utilizing the propulsion system’s motor, an output shaft could be tested as described above by coupling the output shaft (not shown) to one of a rotatable mass 512, a gearbox assembly (such as gearbox assembly 210 of Fig. 2), or secondary drive belt assembly 526, and driving the output shaft, directly or indirectly, via secondary drive belt assembly 526.

[0073] Figs. 6 A and 6B illustrate an example test assembly 600 of a gearbox assembly 610 coupled to an output shaft connector 646, consistent with embodiments of the present disclosure. Gearbox assembly 610 may comprise, e.g.: a first gear 648 configured to couple to output shaft connector 646; one or more second gears 650; one or more gear shafts 652 coupled to second gears 650; one or more third gears 654 coupled to gear shafts 652; a fourth gear 655; a drive hub 656 coupled to fourth gear 655; a thrust bearing 658; and a Z-axis load mount 606. Output shaft connector 646 may further comprise mounting flange 644 configured to connect to a propeller flange on an output shaft of the propulsion system under test. For example, a mounting surface of mounting flange 644 may be similar to the mounting surface of a propeller hub to which the propulsion system under test would be mounted during use.

[0074] In some embodiments, mounting flange 644 may be coupled to a propulsion system similar to motor 332 of Fig. 3 or secondary motor similar to secondary drive belt assembly 226 of Fig. 2. Further, first gear 648 may be coupled to output shaft connector 646. In such cases, a portion of a propulsion system, such as aircraft motor 332 may drive output shaft connector 646 and first gear 648.

[0075] First gear 648 may be configured to drive one or more second gears 650, thus driving one or more gear shafts 652 and one or more third gears 654. One or more third gears 654 may be configured to drive fourth gear 655 and drive hub 656 at a rotation frequency determined by the rotation frequency of the output shaft connector 646 and the gear ratios of the first gear 648, second gear 650, third gear 654, and fourth gear 655.

[0076] In some embodiments, drive hub 656 may be coupled a rotatable mass 612. In such cases, rotatable mass 612 may rotate at an increased frequency relative to the rotation frequency of the output shaft connector 646 according to the gear ratios of the first gear 648, second gear 650, third gear 654, and fourth gear 655.

[0077] Z-axis load mount 606 may be configured to couple gearbox assembly 610 to a Z-axis load assembly similar to Z-axis load assembly 202 of Fig. 2. Gearbox assembly 610 may further comprise a gearbox housing 657 comprising an X-axis load contact plate 660 and a Y- axis load contact plate 662. X-axis load contact plate 660 and Y-axis load contact plate 662 may be configured to receive a load from a loading assembly similar to X-axis loading assembly 216 of Fig. 2.

[0078] In some embodiments, for example, first gear 648 may be an 80-tooth gear, second gears 650 may be 40-tooth gears, third gears 654 may be 60-tooth gears, and the fourth gear 655 may be a 60-tooth gear. According to these gear ratios, a propeller load test apparatus such as propeller load test apparatus 300 can simulate the loads generated by two revolutions of a VTOL propeller in a single cycle of propeller load test apparatus 300, thus decreasing the amount of time necessary to conduct a given test as a person of ordinary skill in the art may appreciate.

[0079] Fig. 7 illustrates an example Z-axis loading assembly 700, consistent with embodiments of the present disclosure. Z-axis loading assembly 700 may be similar to Z-axis loading assembly 202 of Fig. 2. The Z-axis loading assembly may comprise, e.g.: a track system 768 coupled to a frame similar to frame 304; a Z-axis platform 769; a Z-axis load cell 770 coupled to Z-axis platform 769; an alignment coupling assembly 708 coupled to Z-axis load cell 770; a spring bed 771 coupled to Z-axis platform 769; one or more shafts 777 coupled to platform 769; one or more springs 772; a hard stop 775 coupled to shafts 777; a jack 766 coupled to spring bed 771; an overtravel stop 776 coupled to a frame similar to frame 304; and a lift pin bracket 778 coupled to a frame, such as frame 304 of Fig. 3.

[0080] In some embodiments, track system 768 may be coupled to a frame similar to frame 304 of Fig. 3 and configured to allow Z-axis platform 769 to move along an axis substantially parallel to the Z-axis and restrict Z-axis platform 769 from moving along the X-axis and the Y-axis.

[0081] Z-axis platform 769 may be configured to move along track system 768 and may comprise one or more shafts 777 oriented substantially parallel to the Z-axis. Shafts 777 may be coupled to a hard stop 775.

[0082] Z-axis load cell 770 may be coupled to Z-axis platform 769 configured to couple to a Z-axis load mount similar to Z-axis load mount 306 via alignment coupling assembly 708. Alignment coupling assembly 708 may comprises a first alignment coupler coupled to a second alignment coupler. The first alignment coupler and second alignment coupler may both be capable of compensating for up to five degrees of misalignment, which allows a gearbox assembly similar to gearbox assembly 310 respective freedom of movement. Z-axis load cell 770 may be further configured to measure the load applied to a gearbox assembly similar to gearbox assembly 310 by Z-axis loading assembly 700.

[0083] Spring bed 771 may be configured to move along shafts 777 and may further comprise a plurality of spring receptacles 774.

[0084] Jack 766 may be coupled to spring bed 771 and configured to raise and lower spring bed 771, thus raising and lower Z-axis loading assembly 700. In some embodiments, jack 766 may comprise a screwjack comprising a hand crank 764 configured to allow operators to actuate jack 766 by hand and thus apply Z-axis load to one or more structural components of an aircraft propulsion system under test. In some embodiments, jack 766 may comprise a hydraulic jack. In some embodiments, a cylinder, such as a hydraulic cylinder or a pneumatic cylinder, may be used instead of or to replace jack 766. In some embodiments, jack 766 may be controlled by a computer or programable logic controller.

[0085] One or more springs 772 may be inserted into the plurality of spring receptacles 774 to further adjust the Z-axis load applied to the aircraft propulsion system as described below. In some embodiments, springs 772 may comprise nitrogen gas springs. Some embodiments may use nitrogen gas springs because the spring force of nitrogen gas springs increases more slowly over distance than compression springs.

[0086] In operation, one or more springs 772 may be inserted into one or more spring receptacles 774 of spring bed 771. Jack 766 may raise spring bed 771 along an axis substantially parallel to the Z-axis until the one or more springs 772 begin to contact hard stop 775. As the one or more springs 772 begin to contact hard stop 775, Z-axis platform 769 may begin to move along an axis substantially parallel to the Z-axis. As Z-axis platform 769 moves along an axis substantially parallel to the Z-axis, a tensile load may be applied to a gearbox assembly similar to a gearbox assembly 310 as measured by load cell 770. Jack 766 may further raise or lower spring bed 771 in response to measurements by load cell 770 to adjust the tensile load applied to a gearbox assembly similar to gearbox assembly 310. Further, placing additional springs in spring receptacles may reduce the tensile load applied by Z-axis loading assembly 700, and removing springs from spring receptacles may increase the tensile load applied by Z-axis loading assembly 700 as a person of ordinary skill in the art may appreciate.

[0087] Overtravel stop 776 may be coupled to a frame similar to frame 304 and configured to prevent Z-axis platform 769 from traveling below a desired position. For example, Z-axis platform 769 may contact overtravel stop 776 and stop moving prior to traveling low enough along track system 768 to damage a gearbox similar to gearbox 310.

[0088] Lift pin bracket 778 may be configured to accept a bolt configured to retain Z-axis loading assembly 700 during the installation of a propulsion system, such as aircraft motor 332 of Fig. 3, onto a propeller load test apparatus, such as propeller load test apparatus 300 of Fig. 3

[0089] Fig. 8 illustrates example X or Y-axis loading assemblies 800, consistent with embodiments of the present disclosure. X or Y-axis loading assembly 800 may be similar to X-axis loading assembly 216 of Fig. 2. The X or Y-axis loading assemblies 800 may comprise, e.g.: a base 882 coupled to a frame similar to frame 304 of Fig. 3; a platform 884 adjustably coupled to base 882; a jack 880 coupled to base 882 and platform 884; a shaft 890 coupled to platform 884; a shaft handle 892 coupled to shaft 890; a shaft spring 888 oriented along shaft 890; a load cell 894 coupled to shaft 890; and a roller ball contactor 896 coupled to load cell 894.

[0090] In some embodiments, base 882 may be coupled to a frame similar to frame 304 of Fig- 3 Platform 884 may be adjustably coupled to base 882 and configured to move along axes substantially parallel to one of the X-axis and Y-axis. Further, base 882 may be configured to prevent platform 884 from moving along axes substantially parallel to the Z- axis. In some embodiments, platform 884 may be adjustably coupled to base 882 and configured to move along axes different from axes substantially parallel to one of the X-axis and Y-axis.

[0091] Jack 880 may be coupled to base 882 and platform 884 and configured to move platform 884 along axes substantially parallel to the one of the X-axis and Y-axis. In some embodiments, jack 880 may be, e.g., a screwjack or a hydraulic jack. In some embodiments, jack 880 may comprise a cylinder, such as a hydraulic cylinder or a pneumatic cylinder.

[0092] Shaft 890 may be coupled to platform 884 and configured to move with platform 884. Load cell 894 may be coupled to shaft 890 and roller ball contactor 896. Roller ball contactor 896 may be configured to apply a load to one of a rotatable mass, such as rotatable mass 212, a gearbox assembly, such as gearbox assembly 210, and an output shaft, such as output shaft connector 646. In some embodiments, roller ball contactor 896 may apply a load via contact plates similar to X-axis load contact plate 660 and a Y-axis load contact plate 662. Load cell 894 may be further comprise a sensor configured to measure the load applied by X or Y- axis loading assemblies 800.

[0093] Shaft spring 888 may be oriented between load cell 894 and platform 884 and configured to further adjust the load applied by X or Y- axis loading assemblies 800. Shaft handle 892 may be coupled to shaft 890 and configured to adjust the tension of shaft spring 888. For example, when a user turns shaft handle 892 clockwise, the spring force of shaft spring 890 may increase, thereby increasing the load applied by X or Y- axis loading assemblies 800. Alternatively, when a user turns shaft handle 892 counter-clockwise, the spring force of shaft spring 890 may decrease, thereby decreasing the load applied by X or Y- axis loading assemblies 800.

[0094] Fig. 9 illustrates an example two-axis propeller load graph generated by propeller load test apparatus 300, consistent with embodiments of the present disclosure. The graph depicts the propeller load as a function of rotation angle. The sinusoidal curves MX and MY indicate propeller moment loads applied to an output shaft under test from a rotatable mass in two orthogonal directions x and y, respectively. Intersection points 902 may indicate angular locations on an aircraft propulsion system that experience maximum tension. Intersection points 904 may indicate angular locations on an aircraft propulsion system that experience maximum compression. Intersection points 902 and 904 may adjust in response to, for example: an increase in X, Y, or Z-axis load; decrease in X, Y, or Z-axis load; a change in position of X or Y-axis load assemblies, such as X or Y-axis loading assemblies 800 of Fig. 8; a change in mass and position of one or more adjustable masses, such as adjustable masses 314 of Fig. 3; or a change in rotation speed of an adjustable mass, such as such as rotatable mass 312 of Fig. 3. During development, it may be desirable to place ribs or other reinforcement structures at points of maximum stress or maximum compression on a VTOL motor housing. For example, in some embodiments, it may be sufficient to reinforce aircraft propulsion system at intersection points 902 corresponding to angular locations of maximum tension. Thus, a propeller load testing apparatus according to embodiments of the present disclosure may be utilized to identify locations on an aircraft propulsion system in which reinforcement structures may yield the greatest benefit, in order to optimize a propulsion system design with high strength and low mass.

[0095] Fig. 10 shows diagrammatically a method 1000 for testing a propeller load, consistent with embodiments of the present disclosure. Method 1000 includes step 1002 of connecting a propulsion system, such as aircraft motor 332, to a frame of a load test apparatus, such as to a frame 304 of a load test apparatus 300 in Fig. 3. The propulsion system may comprise an output shaft. Method 1000 includes step 1004 of connecting the output shaft to a rotatable mass, such as rotatable mass 312 of Fig. 3. In some embodiments, step 1004 may be accomplished via output shaft connector 646 of Fig. 6B. Method 1000 includes step 1006 of rotating the output shaft. Method 1000 includes step 1008 of applying a load to the output shaft along an axis. For example, a load may be applied along an axis that extends radially outward from the output shaft, such as by an X- or Y-axis loading assembly 800 of Fig. 8. Alternatively or additionally, an axial load may be applied, such as by z-axis loading assembly 700 of Fig. 7. Method 1000 includes step 1010 of monitoring a parameter of the propulsion system (i.e., during load testing). For example, a moment load exerted on the aircraft propulsion system under test may be monitored as a function of rotation angle, rotational speed, or other parameters. Consistent with some embodiments, the monitoring may include a comparison of a parameter of the aircraft propulsion system to a pass or fail condition. Said comparison may be used to perform an action during testing. For example, during testing, if a fail condition is met, the action may include immediately stopping testing such as by halting rotation of the output shaft or application of a load to the output shaft. [0096] Fig. 11. shows diagrammatically a method 1100 for testing a propeller load including multiple loads, consistent with embodiments of the present disclosure. Method 1100 includes step 1102 of connecting a propulsion system, such as aircraft motor 332, to a frame of a load test apparatus, such as to, e.g., a frame 304 of a load test apparatus 300 in Fig. 3. The propulsion system may comprise an output shaft. Method 1100 includes step 1104 of connecting the output shaft to a rotatable mass, such as rotatable mass 312 of Fig. 3. In some embodiments, step 1104 may be accomplished via output shaft connector 646 of Fig. 6B. Method 1100 includes step 1106 of connecting one or more adjustable masses, such as adjustable masses 314 of Fig. 3, to the rotatable mass. Method 1100 includes step 1108 of rotating the output shaft. Method 1100 includes step 1110 of applying a first load to the output shaft along a first axis. Method 1100 includes step 1112 of applying a second load to the output shaft along a second axis different from the first axis. For example, the first axis may be one of an X, Y, or Z-axis as discussed above with respect to Fig. 10, and the second axis may comprise another of the X, Y, or Z-axis. Method 1100 includes step 1114 of monitoring a parameter of the propulsion system during load testing as discussed with respect to Fig. 10 above. Consistent with some embodiments, the monitoring may include a comparison of a parameter of the aircraft propulsion system to a pass or fail condition. Said comparison may be used to perform an action during testing. For example, during testing, if a fail condition is met, the action may include immediately stopping testing such as by halting rotation of the output shaft or application of a load to the output shaft.

[0097] It should be appreciated that the above steps need not necessarily be performed in the order discussed above in some embodiments of the present disclosure. For example, some steps may be added or omitted, may be performed before a subsequently disclosed step or after a previously disclosed step, or some steps may be performed simultaneously.

[0098] A computer-readable medium, for example a non-transitory computer-readable medium, may be provided that stores instructions for one or more processors of a controller (such as, e.g., controller 290 of Fig. 2) for performing methods according to embodiments of the present disclosure. For example, the instructions stored in the non-transitory computer- readable medium may be executed by the circuitry of the controller for performing any of the above disclosed processes in part or in entirety. Common forms of non-transitory media include, for example, a floppy disk, a flexible disk, hard disk, solid-state drive, magnetic tape, or any other magnetic data storage medium, a Compact Disc Read-Only Memory (CD- ROM), any other optical data storage medium, any physical medium with patterns of holes, a Random Access Memory (RAM), a Programmable Read-Only Memory (PROM), and Erasable Programmable Read-Only Memory (EPROM), a FLASH-EPROM or any other flash memory, Non-Volatile Random Access Memory (NVRAM), a cache, a register, any other memory chip or cartridge, and networked versions of the same. The one or more processors can include any combination of any number of a central processing unit (CPU), a graphics processing unit (GPU), a neural processing unit (NPU), a microcontroller unit (MCU), an optical processor, a programmable logic controller, a microcontroller, a microprocessor, a digital signal processor, an intellectual property (IP) core, a Programmable Logic Array (PLA), a Programmable Array Logic (PAL), a Generic Array Logic (GAL), a Complex Programmable Logic Device (CPLD), a Field-Programmable Gate Array (FPGA), a System On Chip (SoC), an Application-Specific Integrated Circuit (ASIC), or the like. In some embodiments, the one or more processors can also be a set of processors grouped as a single logical component.

[0099] Embodiments of the present disclosure may further be described by the following clauses:

1. A load test apparatus for a propulsion system, the apparatus comprising: a frame configured to couple to a propulsion system, the propulsion system comprising an output shaft; a rotatable mass configured to couple to the output shaft; and a first loading assembly coupled to the frame, the first loading assembly configured to apply a first load to the output shaft, the first load having a first direction along a first axis of the output shaft.

2. The apparatus of clause 1, wherein the propulsion system comprises an aircraft engine.

3. The apparatus of clause 1 or 2, wherein the propulsion system comprises one of a vertical takeoff and landing (VTOL) propulsion system, a conventional takeoff and landing (CTOL) propulsion system, or a hybrid propulsion system.

4. The apparatus of any of clauses 1 to 3, wherein the first load comprises a tensile load.

5 The apparatus of any of clauses 1 to 4, wherein the first loading assembly comprises a load cell.

6. The apparatus of any of clauses 1 to 5, wherein the first loading assembly comprises a screwjack.

7. The apparatus of any of clauses 1 to 6, wherein the first loading assembly comprises a hydraulic cylinder or a pneumatic cylinder. 8. The apparatus of any of clauses 1 to 7, wherein the first axis is parallel to a rotational axis of the output shaft.

9. The apparatus of any of clauses 1 to 7, wherein the first axis is perpendicular to a rotational axis of the output shaft.

10. The apparatus of any of clauses 1 to 9, wherein the rotatable mass further comprises one or more adjustable masses.

11. The apparatus of clause 10, wherein the one or more adjustable masses comprises one of a detachable mass, a radially moveable mass configured to be moved in a radial direction of the rotatable mass, or a vertically movable mass configured to be moved in an axial direction of the rotatable mass.

12. The apparatus of any of clauses 1 to 11, further comprising a gearbox configured to couple to the output shaft and the rotatable mass.

13. The apparatus of clause 12, wherein the gearbox is configured to increase a rotation frequency of the rotatable mass with respect to a rotation frequency of the output shaft.

14. The apparatus of any of clauses 1 to 13, further comprising: a second loading assembly coupled to the frame, the second loading assembly configured to apply a second load to the output shaft along a second axis different from the first axis.

15. The apparatus of clause 14, wherein the first axis is parallel to a rotational axis of the output shaft.

16. The apparatus of clause 14, wherein the second axis is perpendicular to a rotational axis of the output shaft.

17. The apparatus of any of clauses 14 to 16, wherein the first load comprises a tensile load and the second load comprises a shear load.

18. The apparatus of any of clauses 14 to 17, wherein the first loading assembly and the second loading assembly each comprise one of a screwjack, a hydraulic cylinder, or a pneumatic a cylinder.

19. The apparatus of any of clauses 14 to 18, wherein each of the first loading assembly and the second loading assembly comprises a load cell.

20. A method of testing a propulsion system, comprising: connecting a propulsion system to a frame of a load test apparatus, the propulsion system having an output shaft; connecting the output shaft to a rotatable mass; rotating the output shaft; applying a load to the output shaft along a first axis; and monitoring a parameter of the propulsion system.

21. The method of clause 20, further comprising connecting one or more adjustable masses to the rotatable mass.

22. The method of clause 20 or 21, further comprising: applying a second load to the output shaft along a second axis different from the first axis.

23. The method of any of clauses 20 to 22, wherein monitoring the parameter comprises: comparing the parameter to a pass or fail condition; and assigning, if the parameter matches the pass condition, a pass to the propulsion system for the testing, or assigning, if the parameter matches the fail condition, a fail to the propulsion system for the testing.

24. The method of clause 23, wherein if the parameter matches the fail condition, stopping at least one of rotating the output shaft or applying the load to the output shaft.

25. A method of testing a propulsion system, the method comprising: connecting the propulsion system to a frame of the load test apparatus of any of clauses 1 to 19, the propulsion system having an output shaft; connecting the output shaft to the rotatable mass of the load test apparatus; rotating the output shaft; applying a load to the output shaft along a first axis of the output shaft.

26. The method of clause 25, further comprising connecting one or more adjustable masses to the rotatable mass.

27. The method of clause 25 or 26, further comprising: applying a second load to the output shaft along a second axis different from the first axis.

28. The method of any of clauses 25 to 27, wherein monitoring the parameter comprises: comparing the parameter to a pass or fail condition; and assigning, if the parameter matches the pass condition, a pass to the propulsion system for the testing, or assigning, if the parameter matches the fail condition, a fail to the propulsion system for the testing.

29. The method of clause 28, wherein if the parameter matches a fail condition, stopping at least one of rotating the output shaft or applying the load to the output shaft.

30. A computer readable medium that stores a set of instructions that is executable by at least one processor to cause the load test apparatus of any of clauses 1-19 to perform operations comprising: rotating an output shaft of the propulsion system; applying a load to the output shaft along a first axis; and monitoring a parameter of the propulsion system.

31. A computer readable medium that stores a set of instructions that is executable by the at least one processor to cause a load test apparatus for a propulsion system to perform operations comprising: rotating an output shaft of a propulsion system, the propulsion system being connected to a frame of the load test apparatus, the output shaft being connected to a rotatable mass; applying a load to the output shaft along a first axis; and monitoring a parameter of the propulsion system.

32. The computer readable medium of clause 30 or 31, the operations further comprising: applying a second load to the output shaft along a second axis different from the first axis.

33. The computer readable medium of any of clauses 30 to 32, wherein monitoring the parameter comprises: comparing the parameter to a pass or fail condition; and assigning, if the parameter matches the pass condition, a pass to the propulsion system for the testing, or assigning, if the parameter matches the fail condition, a fail to the propulsion system for the testing.

34. The computer readable medium of clause 33, wherein if the parameter matches the fail condition, the operations comprising stopping at least one of rotating the output shaft or applying the load to the output shaft.

35. The computer readable medium of and of clauses 30 to 34, wherein the computer readable medium isa non-transitory computer readable medium.

[0100] 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.

Claims

2. The apparatus of claim 1, wherein the propulsion system comprises an aircraft engine.

3. The apparatus of claim 1 or 2, wherein the propulsion system comprises one of a vertical takeoff and landing (VTOL) propulsion system, a conventional takeoff and landing (CTOL) propulsion system, or a hybrid propulsion system.

4. The apparatus of any of claims 1 to 3, wherein the first load comprises a tensile load.

5. The apparatus of any of claims 1 to 4, wherein the first loading assembly comprises a load cell.

6. The apparatus of any of claims 1 to 5, wherein the first loading assembly comprises a screwjack.

7. The apparatus of any of claims 1 to 6, wherein the first loading assembly comprises a hydraulic cylinder or a pneumatic cylinder.

8. The apparatus of any of claims 1 to 7, wherein the first axis is parallel to a rotational axis of the output shaft.

9. The apparatus of any of claims 1 to 7, wherein the first axis is perpendicular to a rotational axis of the output shaft.

10. The apparatus of any of claims 1 to 9, wherein the rotatable mass further comprises one or more adjustable masses.

11. The apparatus of claim 10, wherein the one or more adjustable masses comprises one of a detachable mass, a radially moveable mass configured to be moved in a radial direction of the rotatable mass, or a vertically movable mass configured to be moved in an axial direction of the rotatable mass.

12. The apparatus of any of claims 1 to 11, further comprising a gearbox configured to couple to the output shaft and the rotatable mass.

13. The apparatus of claim 12, wherein the gearbox is configured to increase a rotation frequency of the rotatable mass with respect to a rotation frequency of the output shaft.

14. The apparatus of any of claims 1 to 13, further comprising: a second loading assembly coupled to the frame, the second loading assembly configured to apply a second load to the output shaft along a second axis different from the first axis.

15. The apparatus of claim 14, wherein the first axis is parallel to a rotational axis of the output shaft.

16. The apparatus of claim 14, wherein the second axis is perpendicular to a rotational axis of the output shaft.

17. The apparatus of any of claims 14 to 16, wherein the first load comprises a tensile load and the second load comprises a shear load.

18. The apparatus of any of claims 14 to 17, wherein the first loading assembly and the second loading assembly each comprise one of a screwjack, a hydraulic cylinder, or a pneumatic a cylinder.

19. The apparatus of any of claims 14 to 18, wherein each of the first loading assembly and the second loading assembly comprises a load cell.

21. The method of claim 20, further comprising connecting one or more adjustable masses to the rotatable mass.

22. The method of claim 20 or 21, further comprising: applying a second load to the output shaft along a second axis different from the first axis.

23. The method of any of claims 20 to 22, wherein monitoring the parameter comprises: comparing the parameter to a pass or fail condition; and assigning, if the parameter matches the pass condition, a pass to the propulsion system for the testing, or assigning, if the parameter matches the fail condition, a fail to the propulsion system for the testing.

24. The method of claim 23, wherein if the parameter matches the fail condition, stopping at least one of rotating the output shaft or applying the load to the output shaft.

25. A method of testing a propulsion system, the method comprising: connecting the propulsion system to a frame of the load test apparatus of any of claims 1 to 19, the propulsion system having an output shaft; connecting the output shaft to the rotatable mass of the load test apparatus; rotating the output shaft; applying a load to the output shaft along a first axis of the output shaft.

26. The method of claim 25, further comprising connecting one or more adjustable masses to the rotatable mass.

27. The method of claim 25 or 26, further comprising: applying a second load to the output shaft along a second axis different from the first axis.

28. The method of any of claims 25 to 27, wherein monitoring the parameter comprises: comparing the parameter to a pass or fail condition; and assigning, if the parameter matches the pass condition, a pass to the propulsion system for the testing, or assigning, if the parameter matches the fail condition, a fail to the propulsion system for the testing.

29. The method of claim 28, wherein if the parameter matches a fail condition, stopping at least one of rotating the output shaft or applying the load to the output shaft.

30. A computer readable medium that stores a set of instructions that is executable by the at least one processor to cause a load test apparatus for a propulsion system to perform operations comprising: rotating an output shaft of a propulsion system, the propulsion system being connected to a frame of the load test apparatus, the output shaft being connected to a rotatable mass; applying a load to the output shaft along a first axis; and monitoring a parameter of the propulsion system.

31. The computer readable medium of claim 30, the operations further comprising: applying a second load to the output shaft along a second axis different from the first axis.

32. The computer readable medium of claim 30 or 32, wherein monitoring the parameter comprises: comparing the parameter to a pass or fail condition; and assigning, if the parameter matches the pass condition, a pass to the propulsion system for the testing, or assigning, if the parameter matches the fail condition, a fail to the propulsion system for the testing.

33. The computer readable medium of claim 32, wherein if the parameter matches the fail condition, the operations comparing stopping at least one of rotating the output shaft or applying the load to the output shaft.

34. The computer readable medium of any of claims 30 to 33, wherein load test apparatus is the load test apparatus of any of claims 1 to 19.