Patent Description:
Certain rotorcraft, such as helicopters, may be provided with a tail rotor system for providing anti-torque and/or directional control for the rotorcraft. Such tail rotor systems may often include an open tail rotor, which may be considered a safety hazard to aircraft ground personnel and passengers in the vicinity of the tail rotor. A number of alternatives to an open rotor system have been proposed to provide anti-torque features for rotorcraft; however, such alternatives are typically significantly heavier and perform less effectively than a conventional open rotor anti-torque system.

<CIT> relates to a system and method of minimizing the attitude hump phenomenon of a rotary wing aircraft.

<CIT> relates to a fully compounding rotorcraft including a fuselage having first and second wings extending therefrom and configured to provide lift compounding responsive to forward airspeed.

<CIT> relates to a directional and stabilizing device including a faired antitorque rotor, driven in rotation in a transverse aperture formed in a fairing slated with respect to the vertical by an angle between <NUM> DEG and <NUM> DEG.

<CIT> relates to a method for optimizing the operation of at least one first propeller and at least one second propeller of a hybrid helicopter.

JPH10100998 relates to a tail skid and a grip that are integrally formed and mounted on a tail boom to be movable to the longitudinal direction of a body.

<CIT> relates to an operating method for convertible aircrafts, in particular convertible UAVs, more specifically the method of transition from helicopter mode to gyroplane mode and vice versa.

To provide a more complete understanding of the present disclosure and features and advantages thereof, reference is made to the following description, taken in conjunction with the accompanying figures, in which like reference numerals represent like elements:.

The following disclosure describes various illustrative embodiments and examples for implementing the features and functionality of the present disclosure. While particular components, arrangements, and/or features are described below in connection with various example embodiments, these are merely examples used to simplify the present disclosure and are not intended to be limiting. It will of course be appreciated that in the development of any actual embodiment, numerous implementation-specific decisions must be made to achieve the developer's specific goals, including compliance with system, business, and/or legal constraints, which may vary from one implementation to another.

In the specification, reference may be made to the spatial relationships between various components and to the spatial orientation of various aspects of components as depicted in the attached drawings. However, as will be recognized by those skilled in the art after a complete reading of the present disclosure, the devices, components, members, apparatuses, etc. described herein may be positioned in any desired orientation. Thus, the use of terms such as "above", "below", "upper", "lower", "top", "bottom", or other similar 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 components described herein may be oriented in any desired direction. When used to describe a range of dimensions or other characteristics (e.g., time, pressure, temperature, length, width, etc.) of an element, operations, and/or conditions, the phrase "between X and Y" represents a range that includes X and Y.

Additionally, as referred to herein in this specification, the terms "forward," "aft," "inboard," and "outboard" may be used to describe relative relationship(s) between components and/or spatial orientation of aspect(s) of a component or components. The term "forward" may refer to a spatial direction that is closer to a front of an aircraft relative to another component or component aspect(s). The term "aft" may refer to a spatial direction that is closer to a rear of an aircraft relative to another component or component aspect(s). The term "inboard" may refer to a location of a component that is within the fuselage of an aircraft and/or a spatial direction that is closer to or along a centerline of the aircraft (wherein the centerline runs between the front and the rear of the aircraft) or other point of reference relative to another component or component aspect. The term "outboard" may refer to a location of a component that is outside the fuselage of an aircraft and/or a spatial direction that farther from the centerline of the aircraft or other point of reference relative to another component or component aspect.

Further, the present disclosure may repeat reference numerals and/or letters in the various examples. Example embodiments that may be used to implement the features and functionality of this disclosure will now be described with more particular reference to the accompanying figures.

<FIG> illustrate various views of an example embodiment of a rotorcraft <NUM>. Rotorcraft <NUM> includes a fuselage <NUM>, a rotor system <NUM>, and an empennage <NUM>. The fuselage <NUM> is the main body of the rotorcraft, which may include a cabin for the crew, passengers, and/or cargo, and may also house certain mechanical and electrical components, such as the engine(s), transmission, and flight controls. The rotor system <NUM> is used to generate lift for the rotorcraft using a plurality of rotating rotor blades <NUM>. For example, torque generated by the engine(s) causes the rotor blades <NUM> to rotate, which in turn generates lift. Moreover, the pitch of each rotor blade <NUM> can be adjusted in order to selectively control direction, thrust, and lift for the rotorcraft <NUM>. The empennage <NUM> is the tail assembly of the rotorcraft. In the illustrated embodiment, the empennage <NUM> includes a tail rotor system <NUM>, which may be used to provide anti-torque and/or directional control.

In the illustrated embodiment, the empennage <NUM> also includes a horizontal stabilizer <NUM> and a vertical stabilizer <NUM>. In general, a stabilizer is an aerodynamic surface or airfoil that produces an aerodynamic lifting force (either positive or negative). For example, a stabilizer may be a fixed or adjustable structure with an airfoil shape, and may also include one or more movable control surfaces. The primary purpose of a stabilizer is to improve stability about a particular axis (e.g., pitch or yaw stability), although a stabilizer can also provide other secondary aerodynamic benefits.

A horizontal stabilizer (e.g., horizontal stabilizer <NUM>) is primarily used to provide stability in pitch, or longitudinal stability. For example, both the rotor and fuselage of a rotorcraft typically have an inherent negative stability derivative in pitch, and accordingly, a horizontal stabilizer may be used to neutralize pitch instability and improve the overall handling qualities of the rotorcraft. A horizontal stabilizer may also be used to generate lift for a rotorcraft, for example, to aid in climb or ascent. In some cases, a horizontal stabilizer may also include one or more movable control surfaces, such as an adjustable slat to aid in generating lift. The design of a horizontal stabilizer (e.g., airfoil shape, size, position on a rotorcraft, control surfaces) implicates numerous performance considerations and is often an extremely challenging aspect of aircraft design.

A vertical stabilizer (e.g., vertical stabilizer <NUM>) is primarily used to provide stability in yaw, or directional stability. Although considerable yaw stability and control is often provided by a tail rotor, a vertical stabilizer may be used to supplement the performance of the tail rotor and/or reduce the performance requirements of the tail rotor. Accordingly, designing a vertical stabilizer and a tail rotor often implicates numerous interrelated performance considerations, particularly due to the interaction between their respective airflows. For example, a smaller vertical stabilizer may reduce the adverse effects on tail rotor efficiency, but may adversely impact yaw stability and other design requirements (e.g., sideward flight performance, internal capacity for housing components within the vertical stabilizer). Accordingly, various performance considerations must be carefully balanced when designing a vertical stabilizer.

It will be recognized that various embodiments of horizontal and vertical stabilizers with designs that balance a variety of performance considerations to provide optimal performance may be provided. For example, certain embodiments of a horizontal stabilizer may be designed to provide strong aerodynamic performance (e.g., pitch stability and/or generating sufficient lift during climb or ascent) without using slats. Such a horizontal stabilizer may use a tailored airfoil design that is cambered and may form a concave slope on the top surface and/or a convex slope on the bottom surface. In some embodiments, the horizontal stabilizer may be mounted on the aft end of a rotorcraft. By obviating the need for slats, such a horizontal stabilizer design reduces complexity without a performance penalty, thus resulting in a more cost-efficient and reliable solution. Moreover, eliminating the slats similarly eliminates the need to provide anti-icing for the slats, thus providing a further reduction in complexity.

Moreover, certain embodiments of a vertical stabilizer may be designed to provide strong aerodynamic performance. Such a vertical stabilizer may use a tailored airfoil design that satisfies various design criteria, including strong aerodynamic performance (e.g., yaw stability, anti-torque control, minimal flow separation and drag). In some embodiments, for example, the vertical stabilizer may have a cambered airfoil shape that provides the requisite yaw stability and anti-torque control while also minimizing flow separation and drag. The cambered airfoil shape, for example, may enable the vertical stabilizer to provide a portion of the anti-torque required in forward flight (e.g., reducing the anti-torque requirements and power consumption of the tail rotor), and/or may also provide sufficient anti-torque to allow continued flight in the event of a tail rotor failure. The cambered airfoil shape may also enable the vertical stabilizer to provide sufficient aerodynamic side-force to offset the tail rotor thrust in forward flight, thus minimizing tail rotor flapping and cyclic loads and maximizing the fatigue life of components. Moreover, in some embodiments, the vertical stabilizer may have a blunt trailing edge (rather than a pointed trailing edge) in order to reduce the thickness tapering on the aft end without modifying the desired chord length, thus minimizing flow separation and drag while also reducing manufacturing complexity.

It should be appreciated that rotorcraft <NUM> of <FIG> is merely illustrative of a variety of aircraft that can be used with embodiments described throughout this disclosure. Other aircraft implementations can include, for example, fixed wing airplanes, hybrid aircraft, tiltrotor aircraft, unmanned aircraft, gyrocopters, a variety of helicopter configurations, and drones, among other examples.

As described above, helicopters require horizontal and vertical stabilization during forward flight. In accordance with features of embodiments described herein, portions of horizontals and vertical stabilization structures (such as horizontal stabilizers <NUM> and vertical stabilizers <NUM>) may be combined into a structure referred to herein as an inverted V-tail (which, as used herein, includes a pair of inverted V-tail stabilizers comprising airfoils) that may perform certain aspects of both horizontal and vertical stabilization. In accordance with features of embodiments described herein, a conventional tail rotor for a rotorcraft may be provided with a tail rotor shroud integrated with one or more inverted V-tails.

<FIG> and <FIG> respectively illustrate a perspective view from the port side and a top plan view of a portion of an aircraft empennage <NUM> including features of embodiments described herein. As shown in <FIG> and <FIG>, connected to the empennage <NUM> is a tail rotor <NUM>, a forward inverted V-tail stabilizer <NUM> disposed forward of the tail rotor and an aft inverted V-tail stabilizer <NUM> disposed aft of the tail rotor. In the illustrated embodiment, a vertical stabilizer <NUM> may also be connected to a top aft end of the empennage <NUM>. A shroud bar <NUM> extends between the forward inverted V-tail stabilizer <NUM> and the aft inverted V-tail stabilizer <NUM> such that the forward end of the shroud bar is connected to the outboard end of the forward inverted V-tail stabilizer <NUM> and the aft end of the shroud bar is connected to the outboard end of the aft inverted V-tail stabilizer <NUM>. The combination of the inverted V-tail stabilizers <NUM>, <NUM>, and the shroud bar <NUM> comprise a tail rotor shroud <NUM>. Although not labeled with reference numerals, a similar tail rotor shroud structure is similarly connected to the opposite side of the empennage <NUM> (i.e., the side of the empennage opposite the side to which the tail rotor <NUM> is connected).

In accordance with features of embodiments described herein, the inverted V-tail stabilizers <NUM>, <NUM>, extend downward from the empennage <NUM> at an angle such that the shroud bar <NUM> is at an appropriate height to protect aircraft ground personnel, passengers, and/or other individuals, as described in greater detail below. In the illustrated embodiment, the shroud bar <NUM> extends below the tail rotor <NUM> to provide ground strike protection. As best illustrated in <FIG>, in the example embodiment, the inverted V-tails including the inverted V-tail stabilizers <NUM>, <NUM>, may be generally symmetrical (i.e., similar or identical on both port and starboard sides of the empennage <NUM>) to provide balanced ground strike protection. In alternative embodiments, as will be described below, the inverted V-tails may be asymmetrical.

The angle and size (e.g., length and width) of the inverted V-tail stabilizers <NUM>, <NUM>, can be tailored for different aircraft to optimize both the horizontal and vertical component of stabilization and height of the shroud bar <NUM> to optimize protection from the tail rotor <NUM>. It will be recognized that the vertical stabilizer <NUM> may be unnecessary depending on the vertical and horizontal stabilization provided by the inverted V-tail stabilizers <NUM>, <NUM>, but may be included for implementations in which more vertical stabilization is necessary. It will be recognized that the specific physical and aerodynamic characteristics of the inverted V-tails comprising the inverted V-tail stabilizers <NUM>, <NUM>, may be dictated by physical, aerodynamic, and other characteristics of the aircraft for which they are designed to be used.

<FIG> and <FIG> respectively illustrate a perspective view from the port side and a top plan view of an alternative embodiment of an aircraft empennage <NUM> which is similar to the empennage <NUM> (<FIG> and <FIG>) in that it has connected thereto a tail rotor <NUM>, a forward inverted V-tail stabilizer <NUM> disposed forward of the tail rotor, an optional vertical stabilizer <NUM>, and a shroud bar <NUM>; however, in the embodiment illustrated in <FIG> and <FIG>, the shroud bar <NUM> includes a horizontal portion <NUM> and a vertical portion <NUM>. A first end of the shroud bar <NUM> comprising the horizontal portion <NUM> is connected to an outboard end of the forward inverted V-tail stabilizer <NUM> and a second end of the shroud bar comprising the vertical portion <NUM> of the shroud bar is connected directly to the corresponding side of the body of the empennage <NUM> proximate an aft end thereof (e.g., below the vertical stabilizer <NUM>). In contrast to the embodiment illustrated in <FIG> and <FIG>, the embodiment illustrated in <FIG> and <FIG> lacks an aft inverted V-tail stabilizer. The combination of the inverted V-tail stabilizer <NUM> and the shroud bar <NUM> comprise a tail rotor shroud <NUM>. Although not labeled with reference numerals, a similar tail rotor shroud structure is similarly connected to the opposite side of the empennage <NUM> (i.e., the side of the empennage opposite the side to which the tail rotor <NUM> is connected).

In accordance with features of embodiments described herein, the inverted V-tail stabilizer <NUM> extends downward from the empennage <NUM> at an angle such that the horizontal portion <NUM> of the shroud bar <NUM> is at an appropriate height to protect aircraft ground personnel, passengers, and/or other individuals. In the illustrated embodiment, the shroud bar <NUM> extends below the tail rotor <NUM> to provide ground strike protection. As best illustrated in <FIG>, the inverted V-tail comprising the tail rotor shroud structure is generally symmetrical (i.e., similar or identical on both port and starboard sides of the empennage <NUM>) to provide balanced ground strike protection. In alternative embodiments, as will be described below, the inverted V-tail may be asymmetrical.

The angle and size of the inverted V-tail stabilizer <NUM> can be tailored for different aircraft to optimize both the horizontal and vertical component of stabilization and height of the shroud bar <NUM> to optimize protection from the tail rotor <NUM>. It will be recognized that the vertical stabilizer <NUM> may be unnecessary depending on the vertical and horizontal stabilization provided by the inverted V-tail stabilizer <NUM> but may be included for implementations in which more vertical stabilization is necessary.

Alternative embodiments may include movable forward inverted V-tail stabilizers, movable aft inverted V-tail stabilizers, and/or movable control surfaces (e.g., ruddervators) integrated into one or both inverted V-tail stabilizers to add stability and control over fixed stabilizers.

Using the inverted V-tail stabilizer(s) as a primary component of the tail rotor shroud is more weight efficient than including an independent rotor shroud in addition to convention horizontal and vertical stabilizers, since the stabilization function performed by the inverted V-tail stabilizer(s) is necessary for stabilization and control of the aircraft. As illustrated in <FIG> and <FIG>, the shroud bar is designed such that the shroud bar <NUM> (or horizontal portion thereof) maintains an individual <NUM> a safe distance D1 from the tail rotor <NUM>, thus preventing the individual from accidentally extending an arm into the tail rotor. In an example embodiment, D1 is greater than the length of a human arm. Additionally and/or alternatively, D1 may be in the range of <NUM>-<NUM> inches.

Additionally, as noted above, embodiments of the tail rotor shroud shown in <FIG> extend lower than the tail rotor disk, which makes it a very good ground strike protection device. Moreover, the design enables the more efficient operation of the tail rotor, as it causes less blockage in the tail rotor air column cylinder than other types of shrouds. Additionally, the amount of vertical and horizontal stabilization provided by the inverted V-tail stabilizer(s) of the tail rotor shroud may be optimized in concert with the shroud bar height and distance from the tail rotor for optimal safety. Other embodiments allow for active control of the inverted V-tail stabilizer(s) to provide more stability and control and still providing excellent protection from the tail rotor.

Referring to <FIG> and <FIG>, the lengths (e.g., length L1) and angles (e.g., angle Θ1) from horizontal of the inverted V-tail stabilizers of the tail rotor shroud <NUM> may be designed such that a height H1 of the shroud bar <NUM> from the ground impedes aircraft ground personnel, passengers, and/or other individuals of various heights from extending an arm into the tail rotor <NUM>. As shown in <FIG>, the rotor shroud <NUM> may be designed to accommodate a person <NUM> having a height less than that of an average adult (e.g., equivalent to the <NUM>th percentile of adult height) and a person <NUM> having a height greater than that of an average adult (e.g., equivalent to the <NUM>th percentile of adult height). In an example embodiment, H1 may be within the range of <NUM>-<NUM> inches. In another example embodiment, Θ1 may be within the range of <NUM>-<NUM> degrees. L1 may be within the range of <NUM>-<NUM> inches.

<FIG> respectively illustrate a side plan view, a top plan view, and a rear plan view of an aircraft <NUM> including features of embodiments described herein. As shown in <FIG>, the aircraft <NUM> includes a tail rotor <NUM>, a forward inverted V-tail stabilizer <NUM> disposed forward of the tail rotor and an aft connector structure <NUM> disposed aft of the tail rotor. In the illustrated embodiment, a vertical stabilizer <NUM> may also be connected to a top aft end of the empennage of the aircraft <NUM>. A shroud structure <NUM> extends between the forward inverted V-tail stabilizer <NUM> and the aft connector structure <NUM> such that the forward end of the shroud structure is connected to the outboard end of the forward inverted V-tail stabilizer <NUM> and the aft end of the shroud structure is connected to the outboard end of the aft connector structure <NUM>. The combination of the inverted V-tail stabilizer <NUM>, the aft connector structure <NUM>, and the shroud structure <NUM> comprise a tail rotor shroud <NUM>. Although not labeled with reference numerals, a similar tail rotor shroud structure is similarly connected to the opposite side of the empennage of the aircraft <NUM> (i.e., the side of the empennage opposite the side to which the tail rotor <NUM> is connected).

In accordance with features of embodiments described herein, the inverted V-tail stabilizer <NUM> and connector structure <NUM> extend downward from the empennage of the aircraft <NUM> at an angle such that the shroud structure <NUM> is at an appropriate height to protect aircraft ground personnel, passengers, and/or other individuals, as described in greater detail above. In the illustrated embodiment, the inverted V-tail including the inverted V-tail stabilizer <NUM>, may be generally symmetrical (i.e., similar or identical on both port and starboard sides of the empennage of the aircraft <NUM>). In alternative embodiments, the inverted V-tail may be asymmetrical.

<FIG> and <FIG> illustrate an alternative tail rotor shroud <NUM> that may be substituted for the tail rotor shroud <NUM> (<FIG>) of the aircraft <NUM> (<FIG>). As shown in <FIG> and <FIG>, a shroud structure <NUM> of the tail rotor shroud <NUM> is a different shape than the shroud structure <NUM> (<FIG>) of the tail rotor shroud <NUM> (<FIG>) and may address different tail rotor safety concerns and/or provide different aerodynamic performance based on the shape. As shown in <FIG>, tail rotor shroud <NUM> includes a forward guard <NUM> and an aft guard <NUM> positioned relative to the tail rotor such that a person whose height is less than the height-from-ground of the guards <NUM>, <NUM>, (e.g., approximately <NUM> inches) would not be hit by the bottom of the tail rotor should the person walk under one of the guards.

<FIG> and <FIG> respectively illustrate additional alternative tail rotor shrouds <NUM>, <NUM> that may be substituted for the tail rotor shrouds described above and may provide additional and/or alternative tail rotor safety and/or aerodynamic features compared to other tail rotor shrouds illustrated and described herein.

<FIG> respectively illustrate a side plan view, a top plan view, and a rear plan view of an aircraft <NUM> including features of embodiments described herein. In particular, aircraft <NUM> includes an alternative design for a tail rotor shroud <NUM> for preventing unintentional contact with a tail rotor <NUM> in a manner similar to that described hereinabove.

As shown in <FIG>, <FIG>, <FIG>, and <FIG>, tail rotor shrouds <NUM>, <NUM>, <NUM>, <NUM>, may also includes forward and/or aft guards as described above with reference to <FIG>.

<FIG> and <FIG> respectively illustrate a top plan view and a rear plan view of an aircraft <NUM> including features of embodiments described herein. In particular, aircraft <NUM> includes an alternative design for a tail rotor shroud <NUM> for preventing unintentional contact with a tail rotor <NUM> in a manner similar to that described hereinabove. As best shown in <FIG>, tail rotor shroud <NUM> is implemented with asymmetrical inverted V-tails in which one inverted V-tail stabilizer of each pair of stabilizers comprising a V-tail is shorter and disposed at a different angle than the other stabilizer of the pair.

<FIG> respectively illustrate a top perspective view, a side plan view, and a top plan view of an aircraft <NUM> including features of embodiments described herein. In particular, aircraft <NUM> includes an alternative design for a tail rotor shroud <NUM> for preventing unintentional contact with a tail rotor <NUM> in a manner similar to that described hereinabove. In particular, the tail rotor shroud <NUM> may be described as a cage in which two horizontal structures, rather than a single shroud bar, are provided to prevent unintentional contact with the tail rotor <NUM>.

It should be appreciated that the aircraft illustrated herein are merely illustrative of a variety of aircraft may benefit from implementation of tail rotor shrouds as described herein. Indeed, the various embodiments of tail rotor shrouds herein may be used on any type of aircraft including an open tail rotor. Other aircraft implementations can include hybrid aircraft, tiltrotor aircraft, quad tiltrotor aircraft, unmanned aircraft, gyrocopters, airplanes, helicopters, commuter aircraft, electric aircraft, hybrid-electric aircraft, and the like. As such, those skilled in the art will recognize that the embodiments described herein for an electric drive system line replaceable unit can be integrated into a variety of aircraft configurations.

The components of rotor assemblies described herein may comprise any materials suitable for use with an aircraft rotor. For example, rotor blades and other components may comprise carbon fiber, fiberglass, or aluminum; and rotor masts and other components may comprise steel or titanium.

As used herein, unless expressly stated to the contrary, use of the phrase "at least one of," "one or more of" and "and/or" are open ended expressions that are both conjunctive and disjunctive in operation for any combination of named elements, conditions, or activities. For example, each of the expressions "at least one of X, Y and Z", "at least one of X, Y or Z", "one or more of X, Y and Z", "one or more of X, Y or Z" and "A, B and/or C" can mean any of the following: <NUM>) X, but not Y and not Z; <NUM>) Y, but not X and not Z; <NUM>) Z, but not X and not Y; <NUM>) X and Y, but not Z; <NUM>) X and Z, but not Y; <NUM>) Y and Z, but not X; or <NUM>) X, Y, and Z. Additionally, unless expressly stated to the contrary, the terms "first," "second," "third," etc., are intended to distinguish the particular nouns (e.g., blade, rotor, element, device, condition, module, activity, operation, etc.) they modify. Unless expressly stated to the contrary, the use of these terms is not intended to indicate any type of order, rank, importance, temporal sequence, or hierarchy of the modified noun. For example, "first X" and "second X" are intended to designate two X elements that are not necessarily limited by any order, rank, importance, temporal sequence, or hierarchy of the two elements. As referred to herein, "at least one of," "one or more of," and the like can be represented using the "(s)" nomenclature (e.g., one or more element(s)).

Claim 1:
Apparatus for inhibiting accidental contact by a human with a tail rotor connected to an empennage of a rotorcraft, the apparatus comprising:
an empennage (<NUM>) of a rotorcraft comprising a tail rotor (<NUM>);
an inverted V-tail (<NUM>) connected to the empennage (<NUM>) of the aircraft forward of the tail rotor (<NUM>), the inverted V-tail (<NUM>) comprising a first V-tail stabilizer on a side of the empennage (<NUM>) to which the tail rotor (<NUM>) is connected and a second V-tail stabilizer on a side of the empennage (<NUM>) opposite the side of the empennage (<NUM>) to which the tail rotor (<NUM>) is connected, and
a shroud bar (<NUM>) having a first end connected to an outboard end of the first V-tail stabilizer and a second end opposite the first end connected to the empennage (<NUM>) aft of the tail rotor (<NUM>);
wherein a horizontal distance from the shroud bar (<NUM>) to the tail rotor (<NUM>) is greater than a length of an arm of the human.