Priority

[0001] This application claims priority to U.S. provisional application having serial number 63/390,999 (filed July 21 ^st , 2022). These and all other extrinsic material discussed herein are incorporated by reference in their entirety. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

Field of the Invention

[0002] The field of the invention is aircraft monitoring.

Background

[0003] Monitoring mast moment is important in rotorcraft with rigid rotors because large mast moments can cause sudden changes in aircraft attitude. Rotor mast moment information can both warn of a dangerous condition as well as characterize the attitude of the aircraft.

[0004] Conventional mast moment sensors can be complex and unreliable. Many conventional mast moment sensing systems use complex optical systems that occupy large amounts of space. The systems are often packaged inside complex powertrain assemblies — rendering the mast moment sensing system difficult to maintain or replace.

Summary

[0005] Mast moment is monitored in one aspect herein using a fiber optic strain sensor configured to measure strain around the proprotor shaft bearings.

Brief Description of the Drawings

[0006] Figure 1 illustrates an aircraft comprising an embodiment of a mast moment sensing system.

[0007] Figure 2 illustrates a cutaway view of a propulsion system comprising an embodiment of a mast moment sensing system. [0008] Figure 3 illustrates a detail view of aspects of the propulsion system of Figure 2.

[0009] Figure 4A illustrates a diagram of a bearing sleeve in an unstrained state.

[0010] Figure 4B illustrates a diagram of a bearing sleeve in a strained state.

[0011] Figure 5 illustrates a different embodiment of a mast moment sensing system implemented in a rotor system comprising a gearbox.

[0012] Figure 6 illustrates methods for determining the mast moment of a propulsion system.

[0013] Figure 7A illustrates a different embodiment of a bearing sleeve and aspects of a fiber optic strain sensor.

[0014] Figure 7B illustrates a section of the bearing sleeve and fiber optic strain sensor aspects of Figure 7B.

[0015] Figure 8 illustrates an isometric view of the same bearings sleeve and fiber optic strain sensor aspects of Figure 7A.

[0016] Figure 9 illustrates an isometric view of aspects of the same propulsion system as the embodiment of Figure 2.

Detailed Description

[0017] The problem is solved in one aspect herein using a fiber optic strain sensor configured to measure strain around the proprotor shaft bearings.

[0018] Fiber optic strain sensors — as implemented in some embodiments herein — can be robust and simple. The embodiment of figure 2 comprises a mast moment sensing system without any moving pieces.

[0019] Illustrated in figure 1 is tiltrotor aircraft 300 comprising a mast moment sensing system 108. The aircraft 300 of figure 1 comprises an electric vertical takeoff and landing (eVTOL) tiltrotor aircraft. However, other embodiments of the mast moment sensing system can be configured for use in any other type of aircraft.

[0020] Figure 2 illustrates proprotor propulsion system 100 comprising an embodiment of a mast moment sensing system. The proprotor propulsion system 100 comprises a proprotor shaft 101 connecting proprotor hub 110 to hub shaft bearings 103a and 103b. Nacelle structure 104 is shown. Interposed between the nacelle structure 104 and the main hub shaft bearings 103a and 103b are bearing sleeves 105a and 105b. The bearing sleeves 105a and 105b comprise grooves 106a, 106b, 106c, and 106d configured to accommodate fiber optic strain sensor cables 107a, 107b, 107c, and 107d. Fiber optic strain sensing cable 107a and 107b are configured to measure the strain of bearing sleeve 105a. Fiber optic strain sensing cables 107c and 107d are configured to measure the strain on bearing sleeve 105b. The fiber optic strain sensing cables 107a and 107b are wrapped around bearing sleeve 105a. Fiber optic strain sensing cables 107c and 107d are wrapped around bearing sleeve 105b.

[0021] Embodiments of the presently described mast moment sensing system can have particular advantages when incorporated with embodiments of the propulsion system described in PCT/US22/13272, filed January 21, 2022, and US Provisional Application 63/140,515, filed on January 22, 2021, which are incorporated by reference herein in entirety.

[0022] Figure 3 illustrates a detail view of aspects of the proprotor propulsion system of Figure 2. Fiber optic strain sensing cables 107a and 107b are shown. Also shown are hub shaft bearings 103a and bearing sleeve 105a.

[0023] In the embodiment of Figure 2, hub shaft bearing sleeve 105a comprises metal. The nacelle structure 102 comprises composite. However, in other embodiments, any appropriate material can be used.

[0024] Mast moment sensing system 108 — illustrated in Figure 5 — comprises fiber optic cables 107a, 107b, 107c, and 107d. Mast moment sensing system 108 can measure the strain of fiber optic strain sensing cables 107a, 107b, 107c, and 107d. When the fiber optic strain sensing cables 107a, 107b, 107c, and 107d are subjected to forces, measured strain will change as the bearing sleeve 105a and 105b deform. It should be recognized that one skilled in the art can interpret fiber optic strain sensing signals into strain readings.

[0025] Figure 4A illustrates a diagram of bearing sleeve 105a in a non-strained state. Figure

4B illustrates bearing sleeve 105a in a strained state. During a certain mast moment force, a force will deform bearing 103a and bearing sleeve 105a. By measuring the strain, the mast moment can be determined.

[0026] The mass moment sensing system 108 of Figure 5 comprises fiber optic strain sensing sensors 107a, 107b, 107c, and 107d that are configured to measure strain in the vicinity of each of the two main rotor shaft bearings 502a and 502b. The mast moment sensor system measures strain transferred through the two rotor shaft bearings — that are the main source of mast moment transfer between the nacelle structure 104 and the rotor shaft 101.

[0027] As opposed to some conventional methods for measuring mast moment, that measured deflection between a first part of the sensor system in the rotating frame and a second part of the sensor system that was in the rotating frame, the sensor system of Figure 2 is in the non-rotating reference frame. Thus, robustness and simplicity can be achieved.

[0028] Shown in figure 5, are fiber optic strain sensor cables 107a, 107b, 107c, and 107d. Figure 6 shows a method by which mast moment module 602 determines a mast moment for proprotor 109. Fiber optic strain sensor module 601 receives a set of signals from the first set of fiber optic cables 107a. Then the fiber optic strain sensor module 601 receives a set of light grating reflections from fiber optic strain sensing cable 107a. The fiber optic strain sensor module 601 computes the strain at the gratings on 107a. Fiber optic strain sensor module 601 sends the grating strain information to mast moment module 602. This process is repeated for fiber optic strain sensing cables 107b, 107c, and 107d. Mast moment module 602 uses the determined grating strain information to determine the magnitude and direction of the mast moment. In the embodiment of Figure 5, the bearings 502a and 502b are located in gearbox 501.

[0029] In some embodiments of a mast moment sensing system, the mast moment module may comprise a lookup table of empirically correlated mast moment to bearing sleeve deformation information that can be used to compute the mast moment. Higher resolution fiber optic strain sensor enables a higher resolution bearing deformation map to be generated. [0030] Figure 7A illustrates a different embodiment of a bearing sleeve 801. In the embodiment of Figure 7A, the outside of the bearing sleeve 801 is configured for a nacelle structure that is straight (non-tapered) at the bearing sleeve-to-nacelle structure interface.

[0031] Figure 8 illustrates bearing sleeve 801. Illustrated is armored fiber optic cable section 803. The armoring protects against environmental damage. The fiber optic cables comprise grating groups 802 spaced about the length of the fiber optic cable. The embodiment of Figure 8 comprises fiber optic temperature sensors 803a and 803b for calibrating the fiber optic strain readings for the current temperature and weather conditions.

[0032] Figure 7B illustrates a cross section of Figure 7A. Figure 8 illustrates an isometric view of bearing sleeve 801. Thus, the bearing sleeve very nicely serves as space for the fiber optic strain sensing cable — resulting in very compact mast moment sensor packaging.

[0033] Figure 9 illustrates an isometric view of aspects of the same proprotor propulsion system as shown in figure 1. For clarity, the main proprotor hubs and proprotor blades are not shown.

[0034] As illustrated in Figure 2, the first and second fiber optic strain sensing cable 107a and 107b are fixed relative to the bearing sleeves 105a and 105b. That is, the fiber optic strain sensors 107a and 107b are in the non-rotating portion of the propulsion system assembly. This facilitates integration because wires can be connected to devices in a fuselage without use of a slip ring or similar device.

[0035] Fiber optic strain sensors may comprise any suitable fiber optic strain sensor including: Fiber Bragg Grating (FBG) sensors; optical time domain reflectometry sensors; or any other suitable sensors.

[0036] The mast moment sensor system results in good mast moment readings. Fiber Bragg Grating (FBG) sensors are both sensitive and robust — enabling consistent and precise measurements. [0037] Mast moment module 602 can use the signals from the fiber optic strain sensor to compute a mast moment load acting on hub shaft 101. The strain information can then be used to determine mast moment.

[0038] It should be understood that the fiber optic strain sensor may use grating frequency or local fiber optic material strain to measure strain.

[0039] It should be noted that any language directed to a fiber optic strain sensor module, mast moment module, or similar should be read to include any suitable combination of computing devices, including servers, interfaces, systems, databases, agents, peers, engines, controllers, or other types of computing devices operating individually or collectively. The computing devices may comprise a processor configured to execute software instructions stored on a tangible, non-transitory computer readable storage medium (e.g., hard drive, solid state drive, RAM, flash, ROM, etc.). The software instructions preferably configure the computing device to provide the roles, responsibilities, or other functionality as discussed above with respect to the disclosed apparatus. In some embodiments, various servers, systems, databases, or interfaces may exchange data using standardized protocols or algorithms, possibly based on HTTP, HTTPS, AES, public-private key exchanges, web service APIs, known financial transaction protocols, or other electronic information exchanging methods. Data exchanges preferably are conducted over a packet-switched network, the Internet, LAN, WAN, VPN, or other type of packet switched network.

[0040] The term proprotor is used herein for convenience. As used herein, the term proprotor should be understood to include rotor, proprotor, propeller, propulsor, fan, ducted fan, or any other similar device.

[0041] It should be recognized by one skilled in the art that the rotor shaft bearings can be of any appropriate type including angular contact bearings, tapered roller bearings, bushings, or any other suitable type of bearings. Furthermore, there can be any number of bearings.

[0042] While some embodiments herein are configured for an electric vertical takeoff and landing (eVTOL) aircraft, embodiments of the mast moment sensing system can be equally applicable to other types of aircraft including helicopters, turbine powered tiltrotors, non-tiltrotor VTOL, turbine powered helicopters, or any other type of aircraft.