Priority

[0001] This application claims priority to U.S. provisional application having serial number 63/407,278 (filed September 16 ^th , 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 propulsion units.

Background

[0003] Conventional proprotor blades extend approximately radially out from the proprotor hub. Many conventional rotors — for example helicopter rotor systems — comprise a hub structure, proprotor feather axis bearing hardware, blade retention mechanisms, and a blade pitch control system. The systems can often account for a significant portion of the size and weight of the proprotor system.

Summary

[0004] Conventional proprotor systems have a large region in the middle of the proprotor disk area that is occupied by the hub mounted systems — including blade pitch control systems and blade retention systems. The hub-mounted systems use rotor disk area that can result in increased drag during forward flight. In one aspect herein, a proprotor assembly comprises proprotor blades that are significantly offset from the hub center.

Brief Description of the Drawings

[0005] Figure 1 illustrates an embodiment of a propulsion system comprising an embodiment of an offset proprotor blade hub.

[0006] Figure 2 illustrates aspects of the same embodiment of a propulsion system as shown in Figure 1. [0007] Figure 3 illustrates an alternate view of the same embodiment of an offset proprotor blade system as the embodiment of Figure 1.

[0008] Figure 4 illustrates a VTOL aircraft comprising an embodiment of an offset proprotor blade hub.

[0009] Figure 5 illustrates a section view of aspects of the same embodiment of an offset proprotor blade system as the embodiment of Figure 1.

Detailed Description

[0010] Conventional proprotor systems have a large non-thrust producing region at the center of the proprotor system. The non-thrust generating area in center of the rotor disk can increase the drag of the aircraft in forward flight. The problem is addressed in one aspect herein by a proprotor assembly in which the proprotor blade feather axis is orthogonally offset from the rotor disk center.

[0011] In some embodiments herein, the blade roots extend past the hub center — addressing additional desired design characteristics. In some embodiments, such as the embodiment shown in Figure 2, the proprotor blade root 112 extends past a hub centerline axis 114 that is perpendicular to the proprotor blade feather axis 105.

[0012] Additional unexpected synergies result when concepts described herein are applied to proprotor systems comprising a compact blade retention 108 and pitch change system 111 — illustrated in Figure 2.

[0013] Conventional variable pitch rotor blades extend approximately radially out from the center of the proprotor hub — the blade feather axis approximately intersects the center of the proprotor hub.

[0014] In many conventional variable pitch proprotor systems, the layout comprises: a proprotor hub at a first, innermost, radial station; a blade pitch system at the next radial station; a blade retention system at a next radial station; and then a blade airfoil region.

[0015] Figure 1 illustrates an embodiment of an offset blade proprotor system 101 comprising first rotor blade 102a.

[0016] Shown in Figure 2 is the same embodiment of an offset blade proprotor system 101 as shown in Figure 1. Proprotor blade 102a is orthogonally offset from a proprotor hub radial 104. Unexpected synergies can be realized. The location of the proprotor blade root 112 along the side of the hub 106 can result in a smaller non-airfoil diameter 107. That is, since the proprotor blade 102a is off to the side of the main hub structure, the radial blade station taken up by the proprotor hub 106 can partially overlap with the radial blade station taken up by the proprotor blade retention system 108. Thus, the drag of the proprotor in forward flight can be decreased. In some embodiments the ratio of non-thrust generating proprotor disk 107 diameter to the feather axis bearing span distance 116 can be less than 3: 1 or in some embodiments less than 4: 1. In the embodiment of Figure 5 the feather axis bearing span distance 116 is the distance between the outermost points on the outermost feather axis bearings 115a and 115b, along the proprotor blade feather axis 105.

[0017] In addition to being more compact, an offset proprotor blade hub system 101 in the embodiment of Figure 2 can be lighter than conventional proprotor hubs. An additional positive attribute of the embodiment is that it can have less rotational inertia relative to conventional proprotor systems due to the compact and light weight system design.

[0018] Overlap between the blade root 112 and the blade retention system can provide further synergies. For proprotor systems that are neither articulated, nor hinged, the rotor blade root 112 can be along the side of the rotor hub 106. Many conventional rotor systems are hinged or articulated rotor systems. However, a proprotor system with rigid rotors can have additional synergies when the rotor blade is offset. In such an arrangement, the proprotor blade retention system 108 can be at least partially disposed alongside the rotor hub 106.

[0019] Illustrated in Figure 2, blade retention system 108 is disposed alongside of the rotor hub 106. The embodiment of Figure 2 comprises a rigid rotor system that is neither hinged nor articulated.

[0020] The embodiment of an offset proprotor blade hub of Figure 2 enables the airfoil to extend very close in diameter to hub bearings 110a and 110b — illustrated in Figure 3. The non-airfoil diameter 107 is relatively small relative to the diameter of hub bearing 110a and 110b — illustrated in Figure 3. Because the proprotor blades 102a, 102b, and 102c are offset from the proprotor hub center 110, the pitch change system 111 and blade retention system 108 can be offset to the side of the hub 106. Unlike conventional proprotor hubs, the pitch change system does not necessitate a hub arm to extend out radially to accommodate feather axis pitch change hardware.

[0021] In the embodiment of Figure 2, the proprotor blade feather axis 105 is offset to the side the proprotor hub 106. The blade is also angled in plane, much more than conventional proprotor blades. The proprotor blade feather axis 105 is at an angle relative to the hub center to proprotor blade center of pressure axis 117. The proprotor blade feather axis — center of pressure angle 113 is illustrated in Figure 2. Proprotor blade center of pressure 118 is also illustrated. In some embodiments the proprotor blade feather axis-to-center of pressure angle can be larger than conventional proprotor systems. The proprotor blade feather axis-to-center of pressure angle can be larger than 10 degrees, larger than 15 degrees, larger than 20 degrees, or any other suitable angle range.

[0022] Illustrated in Figure 2, the blade root 112 overlaps with the blade retention system 108. Thus, a first synergy between the blade root structure and pitch change system 111 can be accomplished. A second synergy can be achieved by the side of the hub 106 structure addressing the need for side support for the pitch change system 103. The embodiment of Figure 1 thus achieves a simplistic hub structure.

[0023] As shown in Figure 2, a desire for a very high ratio of airfoil area to total proprotor disk area can be addressed by embodiments herein — much higher than many conventional rotor systems with similar performance properties.

[0024] The offset proprotor blade hub for an aircraft as illustrated by embodiments herein address significant problems. Offset proprotor blades address the problem of minimizing the radial distance occupied only by the proprotor blade root. In the embodiment of Figure 2, the radial distance occupied by the proprotor rotor blade root at least partially overlaps with the radial distance occupied by the hub structure.

[0025] The offset proprotor blade embodiment of Figure 2 additionally addresses a desire to reduce propulsion system weight. The compact, and structurally efficient design can reduce the weight of the proprotor system. Another additional benefit can be an increase in the thrust producing to non-thrust producing ratio of the proprotor disk area.

[0026] In the embodiment of Figure 1, the proprotor hub comprises composite material, and the proprotor blade retention system 108 comprises metal. However, it should be understood that any suitable materials may be used.

[0027] Figure 4 illustrates aircraft 300. In the embodiment of Figure 4, aircraft 300 comprises an electric vertical takeoff and landing (eVTOL) tiltrotor aircraft. Aircraft 300 comprises fuselage 302, nacelle 303, and an embodiment of an offset proprotor blade system 301. However, the principles described herein can be advantageously implemented in any type of aircraft including helicopters, turbine driven tiltrotors, or any other type of aircraft. Additionally, the principles described herein can be applied to other vehicles besides aircraft, for example fan boats.

[0028] It should be understood that the drawings herein are for illustrative purposes and are not to scale.

[0029] The terms proprotor is used herein for convenience. However, it should be understood that concepts herein can apply equally to rotors, propellers, proprotors, propulsors, or any other like device.