US-12617526-B2 - Fast response rotor system

Abstract

A rotor system comprising a hinge coupled between a rotor blade and a hub, where the hinge comprises a pivot that is angled relative to a rotor axis of rotation to enable pitch of the rotor blade to change when the rotor blade experiences lag. The angle of the pivot controls an amount of pitch that results in response to an amount of lag.

Inventors

• Jean-Paul Francis Reddinger

Assignees

• U.S. Army DEVCOM, Army Research Laboratory

Dates

Publication Date

20260505

Application Date

20211001

Claims (1)

1. 1 . A rotor system for a vertical take-off and landing (VTOL) aircraft, comprising: a hub configured to be rotated by an electric motor housed within the hub, the hub comprising a rotatable shaft defining a vertical axis of rotation; at least one rotor blade, each rotor blade having a root end and a chord extending from a leading edge to a trailing edge, the chord defining a chord length; a pitch-lag hinge assembly mechanically coupled between the root end of the rotor blade and the shaft of the hub, the hinge assembly comprising: a center portion rigidly connected to the shaft of the hub to rotate therewith; an arm having a proximal end fixed to the center portion and a distal end extending radially outward from the vertical axis of rotation, the arm defining an outboard distance from the hub to the blade; a first set of flanges rigidly affixed to the distal end of said arm; a blade coupler mechanically affixed to the root end of said rotor blade at a chordwise hinge location between 0.25 and 0.4 of the chord length, measured from the leading edge of the rotor blade; a second set of flanges rigidly affixed to the blade coupler, said second set of flanges interdigitated with said first set of flanges; and a hinge pin extending through said interdigitated first and second sets of flanges to define a pivot axis of the hinge, wherein the pivot axis is inclined relative to the vertical axis of rotation by a hinge angle in the range of 0 to 75 degrees; wherein said hinge pin permits rotation of the rotor blade about the pivot axis such that lagwise deflection of the rotor blade during operation induces a passive change in blade pitch, the amount of pitch change being proportional to the hinge angle and the lag angle of the rotor blade; wherein said arrangement of the hinge assembly provides coupling between pitch and lag motions, such that increased lag due to aerodynamic drag or dynamic loading results in an automatic increase in blade pitch, thereby enhancing thrust generation and reducing the time required to reach maximum thrust in response to changes in motor input; and wherein said length of the arm affects the stiffness of the lag response, with a longer arm increasing resistance to lag-induced motion about the hinge axis.

Description

GOVERNMENT INTEREST The invention described herein may be manufactured, used and licensed by or for the U.S. Government. BACKGROUND Field Embodiments of the present invention generally relate to rotor systems and, more specifically, to a rotor system for an electric motor having fast response. Description of the Related Art Vertical take-off and landing (VTOL) aircraft, such as drones, that utilize electric motors have entered widespread use. Such aircraft are used, for example, as air taxis and delivery services. To operate economically, the aircraft are required to be light weight and very agile. As such, the electric motors that power the aircraft are small and light weight, yet need to produce a substantial amount of power. Typically, each motor directly drives a fixed pitch rotor comprising multiple blades mounted to a motor hub. In a fixed pitch rotor system, the thrust generated by the rotor is controlled by the revolutions per minute (RPM) rotor-motor combination. For large scale RPM controlled rotors, the inertia of the blades prevents the motor from speeding up or slowing down rapidly. This causes multi-rotor aircraft using electric propulsion to fly “sluggishly” (i.e., with poor handling qualities). In addition, an electric motor produces back electromagnetic force (EMF) as the motor rotates. This back EMF produces a drag on the motor such that the greater the back EMF, the larger the motor power requirement, i.e., the back EMF reduces motor torque at high rotational speeds. Also, the faster the motor rotates, the greater the back EMF that is generated. Therefore, there is a need in the art for a rotor system that reduces back EMF such that, for a given electric motor, more thrust is generated at a specified RPM. SUMMARY Embodiments of the present invention include a rotor system comprising a pitch-lag coupled hinge located between a motor hub and blades of a rotor in accordance with the following description and drawings. BRIEF DESCRIPTION OF THE DRAWINGS So that the manner in which the above recited embodiment of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. FIG. 1 depicts a perspective view of a rotor system in accordance with at least one embodiment of the present invention; FIG. 1A depicts a detailed view of the rotor system along line 1A in FIG. 1; FIG. 2 depicts a model of a portion of the rotor system of FIG. 1 in accordance with at least one embodiment of the present invention; FIG. 3 depicts a graph of thrust and torque for various chordwise locations for a pitch-lag hinge in accordance with an embodiment of the present invention; and Table 1 depicts test results for various rotor systems when a step voltage is applied to the rotor systems. DETAILED DESCRIPTION Embodiments of the present invention include a rotor system comprising a pitch-lag hinge coupled between a root end of a propellor blade and a hub. Use of the pitch lag hinge enables a given motor to produce higher thrust in less time when compared to the same rotor system without the pitch-lag hinge. The hinge is passive and automatically alters the pitch of a blade in response to rotor lag. Embodiments of the pitch-lag hinge coupled rotor system find use in vertical take-off and landing (VTOL) aircraft and, especially in electric VTOL (eVTOL) aircraft. In an eVTOL application, the hub is rotated by an electric motor and the hinge provides a change in pitch to offset back EMF effects. FIG. 1 depicts a perspective view of a rotor system 100 in accordance with an embodiment of the present invention, where the rotor system comprises a pitch-lag hinge 102 coupled between each propellor blade 104A and 104B and an electric motor hub 106. FIG. 1A depicts a detailed view of the pitch-lag hinge 102 in accordance with at least one embodiment of the invention. The hinge 102 comprises a center portion 118 that is coupled to a shaft 120 of the motor hub 106. An electric motor (not shown) is housed inside the hub 106 and, typically, directly drives the shaft 120 to impart rotational torque to the center portion 118. The center portion 118 is connected to a proximal end of an arm 116A and 116B— one arm for each blade 104A and 104B. The length of each arm 116A and 116B establishes an outboard distance of each blade 104A and 104B from the center portion 118. A distal end of each arm ends in a set of flanges 112A and 112B. The flanges 112A and 112B are respectively interspersed with flanges 110A and 110B that couple to a blade coupler 108A and 108B (e.g., a clamp). Flanges 110A and 112A are rotatably coupled via pin 114A. Similarly, flanges