Patent Application
20200140077
Not applicable.
Not applicable.
Conventional rotorcraft feature rotor systems that spin in a single direction. Rotor systems that rotate a single direction utilize rotor blades, or airfoils, specifically configured for a chordwise airstream passing over the rotor blades in a single direction. Conventional rotor blades typically feature a maximum thickness offset closer to a leading edge than the trailing edge, such as between a leading edge of the blade and about one-third of a chord length of the blade nearest the leading edge. The offset maximum thickness and/or camber of conventional airfoils is optimized to generate lift as the airfoil is rotated in a single “normal” direction. Conventional rotors typically operate at a relatively constant RPM and are pitch controlled, wherein their blades are rotated about a spanwise pitch axis to vary the amount of lift generated by the blades.
In this disclosure, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as the devices are depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of this disclosure, the devices, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as “above,” “below,” “upper,” “lower,” or other like terms to describe a spatial relationship between various components or to describe the spatial orientation of aspects of such components should be understood to describe a relative relationship between the components or a spatial orientation of aspects of such components, respectively, as the device described herein may be oriented in any desired direction.
This disclosure describes a rotorcraft having rotors that can change a direction of their rotation and are utilized on rotor systems that vary RPM of the rotor. Changing the direction of a rotor's rotation requires rotor blades that are configured for relatively efficient operation in both directions. The bidirectional rotor blades feature a leading edge along with a trailing edge that are mirrors of each other along a median of the rotor blade. A profile of the leading edge of the rotor blade is identical to a profile of the trailing edge of the rotor blade.
A bidirectional rotor system will have to provide thrust when operated in both the forward direction, with a leading edge leading, and the negative direction, with the trailing edge leading, and an airfoil with a relatively sharp leading edge and a rounded trailing edge will provide lesser flow separation in both rotational directions. Bidirectional rotor systems also present a challenge in requiring the rotor to stop and change directions, but RPM-controlled rotors are typically designed to have reduced chord length and inertia.
Tail rotor system 109 utilizes a bidirectional aircraft rotor blade 103 having a fixed pitch and configured for producing a yaw moment of a selected magnitude and a selective direction. Because the bidirectional aircraft rotor blade 103 is fixed in pitch, the RPM and the direction of rotation are varied by manipulation of the pedals 115 to vary the magnitude and direction of the yaw moment. Rotorcraft 101 features a torque source, such as an engine or electric motor, driving the main rotor system 105 along with the tail rotor system 109. Tail rotor system 109 can be rotationally coupled to a transmission comprising a clutch that enables the tail rotor system 109 to both vary the RPM and the rotational direction of the tail rotor system 109. Alternatively, the tail rotor system 109 is driven by a dedicated bidirectional electric motor. In either case, the bidirectional aircraft rotor blade 103 is affixed to a hub 121.
The bidirectional aircraft rotor blade 103 is comprised of a leading edge that is identical to a trailing edge, both having identical rounded edge profiles. Furthermore, the bidirectional aircraft rotor blade 103 is comprised of an upper surface having a greater upper camber as compared to a lower camber of the lower surface. The combination of the camber and fixed pitch make the bidirectional rotor blade 103 efficient in a forward direction 123, but results in the bidirectional aircraft rotor blade 103 being less efficient in a reverse direction 125.
A thickness of the rotor blade 201 is at its maximum at the median axis 219. Furthermore, the leading edge 203 and the trailing edge 205 are identical in profile shape, and the rotor blade 201 is mirrored about the median axis. Placing the maximum thickness position at 50% of the chord length makes the rotor blade symmetric about the median axis 219, which provides reverse direction performance. In a preferred embodiment, the lower camber is at or below 2% to help reverse direction performance.
A maximum thickness axis 321 is located where a thickness of the rotor blade 301 is at a maximum, and the axis 321 is located a distance away from the median axis 319, resulting in the rotor blade 301 being non-symmetric about the median axis 319. The leading edge 303 and the trailing edge 305 are identical in profile shape.
The flight control computer 413 and the tail rotor controller 415 are wired 417 to the first tail rotor system 407 and wired to the second tail rotor system 409. Both the first tail rotor system 407 the second tail rotor system 409 are in the tail rotor assembly 419. The tail rotor assembly 419 of rotorcraft 401 is attached to the fuselage 405 of the rotorcraft 401 by tail boom 421. The first tail rotor system 407 is comprised of a first tail rotor blade 423 and a second tail rotor blade 425. The second tail rotor system 409 is comprised of a third tail rotor blade 427 and a fourth tail rotor blade 429. The flight control computer 413 can selectively adjust the RPM of each tail rotor system and the direction of rotation of each tail rotor system to produce a yaw moment of a selected magnitude and direction for varying the yaw attitude of the rotorcraft 401.
The first tail rotor system 407 is driven by a first electric motor. A pitch of the first tail rotor blade 423 and the second tail rotor blade 425 is fixed. The RPM and/or a direction of rotation of the first electric motor is varied to vary a yaw moment of the first tail rotor system 407.
The second tail rotor system 409 is driven by a second electric motor. A pitch of the third tail rotor blade 427 and the fourth tail rotor blade 429 is fixed. The RPM and/or a direction of rotation of the first electric motor is varied to vary a yaw moment of the first tail rotor system 409.
Combining the yaw moment of the first tail rotor system 407 with the yaw moment of the second tail rotor system 409 allows the pilot to quickly and efficiently yaw the aircraft. In the preferred embodiment the first tail rotor system 407 has a smaller diameter than the second tail rotor system 409. In alternative embodiments, each tail rotor system is equal in diameter or first tail rotor system 407 has a larger diameter than the second tail rotor system 409.
It should be noted that the bidirectional aircraft rotor provides thrust while moving in both forward and reverse directions. The bidirectional aircraft rotor provides rotorcraft with quicker and more efficient control of yaw during flight, thereby enabling the rotorcraft to be more responsive to the pilot and the flight control system.
At least one embodiment is disclosed, and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of this disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of this disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, Rl, and an upper limit, Ru, is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=Rl+k*(Ru−Rl), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 95 percent, 98 percent, 99 percent, or 100 percent. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention. Also, the phrases “at least one of A, B, and C” and “A and/or B and/or C” should each be interpreted to include only A, only B, only C, or any combination of A, B, and C.
