Fixed-wing aircraft with rear rotor and T-tail

Abstract

This application relates to a fixed-wing aircraft having rear rotors and a T-tail. An aircraft includes a canard having a trailing edge, a forward-swept and fixed wing having a horizontal plane and a trailing edge, and a plurality of tilt rotors. At least one of the plurality of tilt rotors is attached to the trailing edge of the canard, and at least one of the plurality of tilt rotors is attached to the trailing edge of the forward-swept and fixed wing. The aircraft further includes a T-tail having a horizontal plane, wherein the horizontal plane of the T-tail is at an elevation higher than the horizontal plane of the forward-swept and fixed wing.

Description

Technical Field

[0001] This application relates to the field of aircraft. This application is a divisional application, the parent application number of which is 201980098124.9, the filing date of which is September 4, 2019, and the invention title is "Fixed-wing aircraft with rear rotor and T-tail". Background Technology

[0002] New types of aircraft are being developed that can take off and land with a smaller footprint. These aircraft may be used, for example, in areas without airports or runways. Some of these aircraft designs feature tiltrotors attached to the trailing edge of a forward-swept, fixed (main) wing. New features and / or configurations that could further improve aircraft performance are also expected. For example, improved stability and / or control are desired if some or all of the aircraft's horizontal lifting surfaces stall. Attached Figure Description

[0003] Various embodiments of the invention are disclosed in the following detailed description and accompanying drawings.

[0004] Figure 1 This is a top view illustration of an embodiment of a forward-swept fixed-wing multirotor aircraft with tilt rotors.

[0005] Figure 2A This is a bottom view illustration of an embodiment of the boundary layer thickness with the engine off.

[0006] Figure 2B This is a bottom view illustration of an embodiment of the boundary layer thickness with the engine on.

[0007] Figure 3A This is a diagram illustrating an example of a tiltrotor configuration with corresponding lift vectors, thrust vectors, and drag.

[0008] Figure 3B This is a diagram illustrating an example of a fixed-wing configuration with a tiltrotor mounted on the leading edge and the corresponding lift vector, thrust vector, and drag.

[0009] Figure 3C This is a diagram illustrating an embodiment of a fixed-wing configuration with a trailing-edge mounted tiltrotor and corresponding lift vector, thrust vector, and drag.

[0010] Figure 4 This is a diagram illustrating an embodiment of the airflow generated when the tiltrotor mounted on the trailing edge of the main wing is closed.

[0011] Figure 5A This is a diagram illustrating embodiments of forward-swept and tapered wings and straight wings for comparison.

[0012] Figure 5BThis is a diagram illustrating an embodiment of a wing configuration with a forward-swept, tapered main wing and no canards.

[0013] Figure 5C This is a diagram illustrating an embodiment of a wing configuration with canards and straight main wings.

[0014] Figure 5D This is a diagram illustrating an embodiment of the tail fin.

[0015] Figure 5E This is a diagram illustrating an embodiment of a pylon attached to the top surface of the main wing.

[0016] Figure 6A This is a diagram illustrating an embodiment of the change in takeoff roll angle from the hovering position to the cruise position.

[0017] Figure 6B This is a diagram illustrating an embodiment of the change in landing tilt angle from the cruise position to the hovering position.

[0018] Figure 7 This is a diagram illustrating an embodiment of the velocity tilt diagram.

[0019] Figure 8A This is a top view of an embodiment of an aircraft with a three-element tail.

[0020] Figure 8B This is a front view of an embodiment of an aircraft with a three-element tail.

[0021] Figure 8C This is a side view of an embodiment of an aircraft with a three-element tail.

[0022] Figure 9A This is an angled view of an embodiment of an aircraft with a V-tail.

[0023] Figure 9B This is a front view of an embodiment of an aircraft with a V-tail.

[0024] Figure 10 This is an illustration of an embodiment of a multirotor aircraft with a truncated fuselage capable of flying in magic carpet mode.

[0025] Figure 11A This is a top view of an embodiment of a multirotor aircraft with a truncated fuselage and tail.

[0026] Figure 11B This is a side view of an embodiment of a multirotor aircraft with a truncated fuselage and tail.

[0027] Figure 12AThis is a perspective view of an embodiment of a tiltrotor aircraft with features for improved flight control and / or stability.

[0028] Figure 12B This is a side view of an embodiment of a tiltrotor aircraft with features for improved control and / or stability.

[0029] Figure 12C This is a top view of an embodiment of a tiltrotor aircraft with features for improved control and / or stability.

[0030] Figure 12D This is a front view of an embodiment of a tiltrotor aircraft with features for improved control and / or stability.

[0031] Figure 12E This is a top view of an embodiment of a tiltrotor aircraft, which has a narrower canard attached further back compared to the canard at the front.

[0032] Figure 12F This is a top view of an embodiment of a main wing whose trailing edge curves are parallel to the propeller disk when the tilt rotor is in the hovering position.

[0033] Figure 13 This is a diagram illustrating an embodiment of wake interference during forward flight of a tiltrotor aircraft with a horizontal tail.

[0034] Figure 14 This is a diagram illustrating an embodiment of a tiltrotor aircraft with a T-tail.

[0035] Figure 15A This is a diagram illustrating an embodiment of the streamlines and vorticity of a tiltrotor aircraft with a T-tail during deep stall.

[0036] Figure 15B This is a diagram illustrating an embodiment of a tiltrotor aircraft with a T-tail in deep stall.

[0037] Figure 16 This is a flowchart illustrating an embodiment of the stall sequence. Detailed Implementation

[0038] This invention can be embodied in various ways, including as a process; an apparatus; a system; a component of matter; a computer program product implemented on a computer-readable storage medium; and / or a processor, such as a processor configured to execute instructions stored in and / or provided by memory coupled to the processor. In this specification, these embodiments or any other form of the invention may be referred to as technology. Generally, the order of steps of the disclosed process can be varied within the scope of this invention. Unless otherwise stated, components described as configured to perform a task, such as processors or memory, can be implemented as general-purpose components temporarily configured to perform the task at a given time or manufactured as dedicated components to perform the task. As used herein, the term "processor" refers to one or more means, circuits, and / or processing cores configured to process data such as computer program instructions.

[0039] Together with the appendix explaining the principles of the invention Figure 1 Beginning here, a detailed description of one or more embodiments of the present invention is provided. The invention is described in conjunction with these embodiments, but is not limited to any particular embodiment. The scope of the invention is limited only by the claims, and the invention encompasses many alternatives, modifications, and equivalents. Numerous specific details are set forth in the following description in order to provide a thorough understanding of the invention. These details are provided for illustrative purposes, and the invention may be practiced without some or all of these specific details. For clarity, technical materials known in the art related to the invention have not been described in detail, so as not to unnecessarily obscure the invention.

[0040] This document describes various embodiments of an improved tiltrotor aircraft. In some embodiments, the aircraft includes a canard with a trailing edge, a forward-swept wing and a fixed wing with a horizontal plane and a trailing edge, and a plurality of tiltrotors, wherein at least one of the plurality of tiltrotors is attached to the trailing edge of the canard, and at least one of the plurality of tiltrotors is attached to the trailing edge of the forward-swept wing and the fixed wing. The aircraft also includes a T-tail with a horizontal plane, wherein the horizontal plane of the T-tail is at a height higher than the horizontal plane of the forward-swept wing and the fixed wing. As will be described in more detail below, this configuration helps to maintain control to a better extent and / or helps to increase stability in a normal or regular high-speed flight envelope when some or all of the horizontal lifting surfaces stall. First, it may be helpful to describe some earlier versions of tiltrotor aircraft. The following figures illustrate some such early versions.

[0041] Figure 1This is a top view illustration of an embodiment of a forward-swept fixed-wing multirotor aircraft with a tiltrotor. In the example shown, the main wing (100) is a fixed wing, which is attached to the fuselage (102) in a fixed manner or position. In other words, the main wing is not a rotatable tiltrotor. The main wing (100) is also forward-swept (e.g., relative to the pitch axis). For example, for an aircraft embodiment with canards (as shown here), the forward sweep angle could be θ between approximately 14° and 16°. sweep Alternatively, for aircraft embodiments without canards, the forward sweep angle can be as high as 35°.

[0042] In this example, the main wing (100) has six rotors (104) attached to the trailing edge of the main wing. For clarity, these rotors are sometimes referred to as main wing rotors (e.g., to distinguish them from rotors attached to the canard). Naturally, the number of rotors shown here is merely exemplary and not intended to be limiting.

[0043] In addition to the six main wing rotors, there are two rotors (106) attached to the canard (108). These rotors are sometimes referred to as canard rotors. The canard is thinner than the main wing, and therefore, unlike the main wing rotors, the canard rotors are attached to the far end of the canard, rather than the trailing edge.

[0044] All rotors in this example are tiltrotors, meaning they are capable of tilting or otherwise rotating between two positions. In this example, the rotors on the left (i.e., port) side of the aircraft are in a cruise (e.g., forward-facing, rearward-facing, etc.) position. See, for example, the position of canard rotor 106. In this position, the rotors rotate about (e.g., substantially) a longitudinal axis of rotation, such that they provide (substantially) rearward thrust. When the rotors are in this position, the lift keeping the multirotor in the air comes from the airflow above the main wing (100) and the canard (108). In various embodiments, the rotation range of the tiltrotors can be as low as 5 degrees or as high as 95 degrees and is design- and / or implementation-specific.

[0045] The rotors on the right (i.e., starboard) side of the aircraft are in a hovering (e.g., vertical takeoff and landing, downward facing, etc.) position. See, for example, the position of the main rotor 104. In this second position, the rotors rotate about (e.g., substantially) a vertical axis of rotation, such that they provide (substantially) downward thrust. In this configuration, the lift keeping the multirotor in the air comes from the downward airflow from the rotors.

[0046] Generally, tiltrotors, when oriented to output thrust substantially downwards, allow an aircraft to perform vertical takeoff and landing (VTOL). This mode or configuration (e.g., the way the aircraft flies as a whole and / or specifically, the position relative to the tiltrotor) is sometimes referred to as hovering. The ability to perform VTOL allows an aircraft to take off and land in areas without airports and / or runways. Once airborne, the tiltrotor (if desired) changes position to output thrust (substantially) backwards rather than downwards. For forward flight, this allows the aircraft to fly in a more efficient manner; this mode or configuration is sometimes referred to as cruise.

[0047] Canards are useful because they can stall first (e.g., before the main wing), generating a large pitching moment and not losing much lift during stall, whereas a main wing stall would lose a significant amount of lift depending on the pitching moment (e.g., causing the entire aircraft to fall or crash). Therefore, a stall with canards may be less harmful than one without them. Canard stall behavior is particularly beneficial when combined with forward-swept wings, because a main wing stall, if at the wing root, can generate an unfavorable pitching moment, and if at the wingtip, it can generate a large and dangerous rolling moment. Furthermore, canards can generate lift at low airspeeds and increase CL (Clear Coil). max (i.e., maximum lift coefficient), and provides struts for supporting or otherwise attaching the canard engine.

[0048] In some embodiments, the pylon (110) for attaching the rotor to the canard and / or main wing includes hinges and / or rotation mechanisms that allow the tilt rotor to rotate between the two positions shown. Any suitable hinge mechanism can be used. For example, for ultralight aircraft, there are very strict weight requirements, and therefore a lightweight solution may be desired. Alternatively, a fixed tilt solution may also be used to meet very strict weight requirements (as described in more detail below).

[0049] In some embodiments, the aircraft is designed such that the main wing (100) and canard (108) provide sufficient lift to perform a gliding landing when needed during an emergency. For example, some ultralight standards or specifications require the ability to land safely in the event of a failure of one or more rotors, and the ability to perform a gliding landing would meet that requirement. One advantage of using a fixed wing as the main wing (e.g., as opposed to a tiltrotor) is that there is no risk of the wing getting stuck in the wrong position (e.g., a hovering position) where a gliding landing is not possible because the wing position is unsuitable for gliding landings.

[0050] Another benefit of a fixed wing with a trailing-edge mounted tiltrotor is the reduction (or absence) of stall behavior during the transition from hover to cruise, or vice versa. With a tiltrotor, the angle of attack changes during the transition, increasing the risk of stall. A fixed wing with a trailing-edge mounted tiltrotor does not change the wing's angle of attack (e.g., even if the rotor is closed / open or the tiltrotor is displaced). Furthermore, this configuration increases both dynamic pressure and circulation on the main wing, significantly improving behavior during transitions (e.g., from hover to cruise, or vice versa). In other words, a fixed wing with a trailing-edge mounted tiltrotor can perform the transition faster and / or more efficiently than a tiltrotor (as an example).

[0051] Another benefit associated with tiltrotors (e.g., the opposite of tiltrotors) is the smaller mass fraction used for tilt actuators. That is, multiple actuators used for multiple tiltrotors (still) comprise a smaller mass fraction than a single heavy-duty actuator used for a tiltrotor. There are also fewer points of failure for tiltrotors because there are multiple actuators, rather than a single (and heavy-duty) actuator for a tiltrotor. Another benefit is that fixed-wing designs allow for smoother and / or faster transitions (e.g., between cruise mode or position and hover mode or position) compared to tiltrotor designs.

[0052] In some embodiments (not shown), the rotor is a variable-pitch propeller with different blade pitches when the rotor is in a hovering position compared to a cruise position. For example, different (ranges) of blade pitches when in a cruise position (e.g., see rotor 106) compared to a hovering position (e.g., see rotor 104) can enable more efficient operation or flight. When the rotor is in a cruise position (e.g., see rotor 106), setting the blade pitch to a "cruise pitch" (e.g., approximately 26°) enables a small frontal area, which is beneficial for cruise (e.g., lower drag). When the rotor is in a hovering position (e.g., see rotor 104), setting the blade pitch to a "hover pitch" (e.g., approximately 6°) enables a high disk area that is beneficial for hovering. In other words, a blade pitch may be well-suited for cruise mode but not for hovering mode, and vice versa. Using a variable-pitch propeller enables better (e.g., overall) efficiency, resulting in lower power consumption and / or increased flight range.

[0053] The following figures illustrate the relationship with Figure 1 The exemplary aircraft shown illustrates various benefits.

[0054] Figure 2AThis is a bottom view illustration of an embodiment of boundary layer thickness with the engine off. In this example, laminar runs 200a, 202a, and 204a illustrate laminar runs in various regions of the main wing. In this example, it is assumed that the aircraft is cruising (e.g., flying in a substantially forward direction). Figure 1 As shown, in this embodiment, the main wing rotor (206) is attached to the trailing edge of the main wing (208). The next figure shows the boundary layer thickness when the rotor is in operation.

[0055] Figure 2B This is a bottom view illustration of an embodiment of boundary layer thickness with the engine running. In this example, the engine is running and the rotor has an outlet airflow velocity of 30 m / s. With the engine running, a low-pressure region is formed towards the rear of the wing, which increases laminar flow on the main wing. For example, see the diagram corresponding to the... Figure 2A The laminar operation lines 200a, 202a, and 204a are laminar operation lines 200b, 202b, and 204b. Comparison between the two groups shows that laminar operation is increased at the first two positions (i.e., 200a / 200b and 202a / 202b). The last position (i.e., 204a / 204b) has only a slightly longer laminar operation length due to interference from the canard rotor (210).

[0056] The drag from the main wing rotor (more specifically, the drag from the pylons used to attach the main wing rotor to the main wing) is hidden in the wake of the airflow leaving the main wing. See, for example, Figure 2A The diagram more clearly illustrates the pylon (220) connected or otherwise attached to most of the laminar flow operation (222). In the embodiment shown here, the pylon may also retain some boundary layer thickness from the main wing, meaning the pylon has lower drag per unit surface area. This improves drag compared to some other alternative designs or configurations. This is illustrated in more detail in the accompanying figures below.

[0057] Figure 3A This is a diagram illustrating an example of a tiltrotor configuration with corresponding lift vectors, thrust vectors, and drag. In this example, a fixed rotor (300) is attached to a tiltrotor (302) at a fixed position or angle. This is an alternative arrangement to the aircraft embodiment described above. The tiltrotor (302) is rotated to direct the airflow generated by the fixed rotor (300) rearward or downward. As shown here, for this configuration, drag (304) exists at the trailing edge of the tiltrotor, which is undesirable.

[0058] The lift (306) and thrust (308) of this configuration are also shown here, with the tiltrotor shown as being in the middle of a transition (e.g., between the cruise position and the hover position). As shown here, the lift (306) and thrust (308) are substantially orthogonal to each other, which is inefficient. In other words, the tiltrotor is inefficient during its transition.

[0059] Figure 3B This is a diagram illustrating an example of a fixed-wing configuration with a tiltrotor mounted on its leading edge and the corresponding lift vector, thrust vector, and drag. In this example, the tiltrotor (320) is attached to the leading edge of the fixed wing (322). This is another alternative arrangement of the aircraft embodiment described above. The corresponding drag (324) and thrust (326) of this arrangement are also shown. This configuration does not produce useful lift, and therefore the lift vector is not shown here.

[0060] Figure 3C This is a diagram illustrating an embodiment of a fixed-wing configuration with a trailing-edge mounted tiltrotor and corresponding lift vector, thrust vector, and drag. In this example, the tiltrotor (340) is attached to the trailing edge of the fixed wing (342). In this configuration, the drag caused by the trailing-edge mounted tiltrotor (e.g., primarily due to its pylons, not shown) is concealed in the wake of the airflow leaving the main wing. Thus, there is no drag (at least not due to drag from the tiltrotor (340)).

[0061] The trailing-edge mounted tiltrotor (340), positioned relative to the fixed wing (342), also draws in air (344) above the fixed wing, after which the air passes through the rotor and is turned or bent downwards. This flow deflection above the wing generates a relatively large induced lift (346), as shown here. The thrust vector (348) induced by the rotor is also shown here. Note that the induced lift (346) and thrust (348) are essentially in the same direction (i.e., both are essentially upwards), which is a more efficient arrangement, including during the transition. In other words, compared to other rotor and wing arrangements, a fixed wing using a trailing-edge mounted tiltrotor produces less drag and increased efficiency during the transition (e.g., due to the lift and thrust vectors now pointing in essentially the same direction). For example, note separately... Figure 3A and Figure 3B Resistance levels 304 and 324, and Figure 3A The orthogonal positions of the lift 306 and the thrust 308.

[0062] The accompanying figures below illustrate embodiments of flow redirection in more detail.

[0063] Figure 4This is a diagram illustrating an embodiment of the airflow generated when the tiltrotor mounted on the trailing edge of the main wing is closed. In this example, a tiltrotor multirotor aircraft (400) is shown, but for comparative purposes, the main wing rotor is closed. With the rotor closed, the inflow airflow (402) and the outflow airflow (404) move in substantially the same direction. That is, the airflow does not change direction (e.g., downwards) as it passes the rotor.

[0064] Except for the rotor opening, multirotor 420 is shown as the same multirotor as multirotor 400. In this example, the inflow airflow (422) and outflow airflow (424) have significantly different directions, and there is a noticeable airflow deflection or curvature as the airflow passes through the rotor of the exemplary multirotor shown. As mentioned above, this generates significant lift, which is desirable because less power is consumed and / or the range of the multirotor is increased.

[0065] In this example, the main rotor (426) is in a hovering position. As shown here, these rotors are slightly pitched or otherwise angled (e.g., the top of the main rotor is slightly forward-pointing and the bottom is slightly backward-pointing). In this figure, the tilt is shown as θ. pitch (428) and in some embodiments, this is a rotational range or movement of approximately 90° (e.g., from horizontal upwards to 3° (e.g., for minimum drag) when in a cruise position and from horizontal downwards to 93° when hovering, resulting in a rotational range of approximately 96°). While such angled or pitched rotors are not absolutely necessary for flow steering to occur, in some embodiments, the main rotor is angled or otherwise pitched to increase or otherwise optimize the amount of flow steering. In some embodiments, the canard rotor is similarly pitched. Note that the multirotor 420 is shown in a nose-up position, and therefore its vertical axis (e.g., relative to the multirotor) is not perpendicular to the ground and / or a reference frame.

[0066] In some embodiments, when the rotor is in the hovering position, the rotor (e.g., the main wing rotor and / or canard rotor) rolls away from the fuselage or otherwise angles slightly outward. In some embodiments, for greater yaw right, this roll (e.g., outward) is approximately 10°.

[0067] In some embodiments, the main wing is tapered (e.g., the wing narrows outward toward the tip) in addition to being forward-swept. The following figures depict various embodiments of the wing and / or tail.

[0068] Figure 5AThis is a diagram illustrating embodiments of forward-swept and tapered wings and straight wings for comparison. In the example shown, wing 500 is a straight wing without tapering (e.g., the wing has the same width from the center to the tip). An exemplary rotor (502) is shown at the trailing edge of the straight wing (500).

[0069] The thrust center (504), indicated by the dashed line, is determined by the placement or arrangement of the rotors and passes through the center of the main rotor (502). For simplicity, the canard rotor is omitted in this example. The lift center is based on the shape of the wing. For a rectangular wing such as wing 500, the lift center (506), indicated by the solid line, extends downward along the wing center. The calculation of the aerodynamic center is more complex (e.g., the aerodynamic center depends on the wing profile, etc.), and the aerodynamic center 508, indicated by the dashed line, is exemplary and / or typical for this type of wing.

[0070] As shown here, the arrangement of the straight wing (500) and its corresponding main rotor (502) creates a thrust center (504) that is relatively far from both the lift center (506) and the aerodynamic center. This separation is undesirable. More specifically, when the main rotor (502) is in a hovering position, if the thrust center (504) is far from the lift center (506), the transition (e.g., in the context of overall aircraft movement, such as from essentially upward flight to essentially forward flight, or vice versa) will generate very large moments and may overturn the aircraft or impair acceleration or stability and / or require large and / or suboptimal propulsion systems. During cruise, if the thrust center (504) is far from the lift center (506), it is less significant (e.g., because the thrust moment is smaller and more easily balanced by the aerodynamic moment), but it is still undesirable.

[0071] In contrast, the arrangement of the forward-swept and tapered wing (520) and its corresponding rotor (522) along the trailing edge produces thrust centers (524), lift centers (526), ​​and aerodynamic centers (528) that are closer to each other. For example, the forward sweep of the wing causes the rotor to move forward to varying degrees. This causes the thrust center to move forward (e.g., toward the leading edge and other centers). The tapering of the wing prevents the aerodynamic and lift centers from creeping forward excessively (and more importantly, away from the thrust center) due to the forward sweep. For example, with a forward-swept wing without tapering (not shown), the thrust center would move forward by approximately the same amount as the aerodynamic and lift centers, and would result in a greater separation between the three centers than in the case of the wing 520 shown here.

[0072] Other benefits of forward-swept and tapered wings include better pilot visibility and a better fuselage-to-wing engagement (e.g., allowing the main wing spars to pass behind the pilot's seat rather than through the pilot). Furthermore, tapering reduces wing moment and brings the engine's thrust center closer to the wing-to-fuselage attachment, as referenced with respect to flight direction, resulting in less moment carried from the wing to the fuselage, a shorter tail boom (e.g., reducing aircraft weight), and improved pitch stability.

[0073] Figure 5B This is an illustration of an embodiment of a wing configuration with a swept-forward, tapered main wing and no canards. In this example, the main wing (530) is swept forward and tapered (e.g., from the center to the tip of the wing). When the outermost rotor (534) is in the hovering position, the tip (532) is rounded, with the trailing edge following the shape or profile of the outermost rotor (534), as shown here. From a safety perspective, this can be attractive because having the main wing surround the front of the rotor (e.g., where the gap between the rotor blades and the trailing edge of the main wing is relatively small) allows the main wing to act as a shield for at least the front side of the outermost rotor (534). In this example, there are 10 main wing rotors (e.g., including rotor 534) attached to the trailing edge of the main wing (530).

[0074] In this wing configuration, there is no canard. To compensate for the absence of a canard and / or canard rotor, the main wing has a greater forward sweep compared to the configuration with a canard and / or canard rotor. For example, the leading edge or spars shown here have a θ... sweep It can be about 20° or 30°, instead of about 10°-15° when there is a canard and / or a canard rotor.

[0075] This type of wing configuration is attractive in applications where sensor placement or other volumetric or structural requirements preclude attaching a canard to the fuselage forebody area. It also offers the added benefit of providing additional protection for the cockpit even in the event of blade detachment (e.g., blade breakage and / or becoming a projectile), as the main wing blocks most of the blade trajectory cone intersecting with the cockpit. It can also be beneficial in terms of simplifying and reducing the number of components on the system and can be used on aircraft with varying numbers of rotors where a canard would be impractical for encapsulation reasons.

[0076] Figure 5CThis is an illustration of an embodiment of a wing configuration with canards and a straight main wing. In this example, there is a canard (540) with four canard rotors (542) attached to the trailing edge of the canard. There is also a straight main wing (544) with six main wing rotors (546) attached to the trailing edge of the main wing. The center of lift, center of thrust, and aerodynamic center (not shown) may be relatively close to each other, with the center of lift and center of thrust preceding the aerodynamic center; all of these are desirable properties or characteristics.

[0077] This type of wing configuration is attractive in applications where swept wings are structurally or controllably disadvantageous, or where a compact footprint is required while increasing available lift, and where induced drag is not critical. The additional canard area helps generate additional lift during forward flight and transitions, while the additional rotor helps increase lift during hovering. Adding an additional rotor to the canard, rather than the main wing, allows the center of thrust to shift forward, thus matching the forward movement of the aerodynamic center due to the increased canard area, provided the canard has a small area. Increasing the canard area allows the aircraft span to remain constant or even smaller compared to increasing the lift surface area by enlarging a large main wing.

[0078] Figure 5D This is an illustration of an embodiment of a tail fin. In some embodiments, the aircraft includes a tail fin (i.e., a tail fin is not required), and this illustration shows an example of a tail fin. In this example, the tail fin (550) has two control surfaces (552), such as flaps. A control rotor (554) is attached to the center of the trailing edge of the tail fin. As shown here, the control rotor can be oriented such that it pushes air downwards. In various embodiments, the control rotor (554) is a fixed rotor or a tilt rotor. In some embodiments, if the control rotor is a tilt rotor, there will be no leading-edge rotor (556). The tail fin also includes two tail rotors (556) attached to the leading edge of the tail fin. In some embodiments, the leading-edge rotors (556) are fixed rotors.

[0079] Figure 5E This is an illustration of an embodiment of a pylon attached to the top surface of the main wing. Various methods exist for attaching a main wing rotor to the main wing, and this is only one example. In this example, the main wing rotor (560a / 560b) is attached to a pylon (562). This pylon is in turn attached to the top surface of the main wing (564), where a gap (566) exists between the pylon and the main wing. As a result, a duct-like effect exists at the gap 566 between the pylon (562) and the main wing (564). Furthermore, offsetting the pylon from the upper surface of the wing results in additional lift and lower drag on the wing surface, at the cost of increased drag on the pylon skin.

[0080] As shown here, the rear of the pylon (562) is where the rotors (560a / 560b) extend beyond the rear of the main wing (564). This allows the rotors to have sufficient clearance to rotate without hitting the main wing when in a cruise position (see rotor 560a), a hovering position (see rotor 560b), or any position between these two extremes.

[0081] As described above, in some embodiments, the canard rotor (if present) and the main wing rotor are tilt rotors, and these rotors are capable of switching between two positions (if desired) for more efficient flight. (A corollary from this is that slow flight (e.g., below the stall speed of a conventional fixed wing) can be maintained by changing the tilt angle rather than simply tilting between two extreme or terminal positions.) The accompanying figures below depict an exemplary tilt transition of the rotor between a cruise position and a hovering position.

[0082] Figure 6A This is a diagram illustrating an embodiment of the change in takeoff tilt from a hovering position to a cruise position. In some embodiments, the exemplary multirotor aircraft performs this transition shortly after takeoff (e.g., substantially vertical). It should be noted that this tilt transition is optional, and the aircraft can fly with the rotors fully in the hovering position (albeit below optimal performance). For example, this can be done if the tilt maneuver is risky, and it would be better to perform the maneuver at a higher altitude.

[0083] The multirotor aircraft 600 illustrates an exemplary aircraft after performing a vertical takeoff. In this state shown here, the main rotor and canard rotor are in a hovering position (e.g., rotating about a substantially vertical axis of rotation, causing the rotor to generate substantially downward thrust).

[0084] The multirotor then transitions from a completely upward direction of movement to a direction of movement with at least some forward motion, where the rotor remains in a hovering position until the multirotor reaches a desired altitude (602) from which the transition began. In other words, the aircraft transitions first and then changes the rotor tilt. In one example, the altitude at which the multirotor begins the rotor tilt change from the hovering position to the cruise position is high enough to allow for recovery time in the event of a problem during the transition. The transition between the hovering and cruise positions is a riskier time, where the likelihood of problems (e.g., rotor failure, rotor jamming, etc.) is higher. While the multirotor may have appropriate systems and / or technologies for recovery (e.g., compensating for rotor failure by allowing the remaining rotor to output more thrust, deploying parachutes, etc.), these systems and / or technologies require time (i.e., sufficient altitude) to function.

[0085] From position 602, the multirotor flies substantially forward and moves its tilt rotors from a hovering position (e.g., a position where thrust is output substantially downward) to a cruise position. Once in cruise position 604, the rotors rotate about a substantially longitudinal axis, causing them to output rearward thrust.

[0086] Figure 6B This is a diagram illustrating an embodiment of the change in landing tilt angle from a cruise position to a hovering position. For example, an exemplary multirotor aircraft may perform this transition before vertical landing. As with previous transitions, this transition is optional. For example, if desired, the exemplary multirotor aircraft may maintain the tilt rotor in the cruise position and perform a glider-like landing instead of a vertical landing.

[0087] Multirotor 610 is shown with the rotor in a cruise position. As it flies in a generally forward direction, the tilt rotor moves from the cruise position shown in 610 to the hover position shown in 612. When the tilt rotor is in the hover position (612), the multirotor descends with some forward movement (at least in this example) to maintain (lower) power usage and reserve better options in the event of engine or other component failure (e.g., the multirotor could power up the rotor and exit the landing process or path) until it finally lands on the ground.

[0088] Figure 7 This is a diagram illustrating an embodiment of a speed tilt diagram. In the diagram, the x-axis represents the forward speed of the aircraft, and the y-axis represents the tilt (e.g., the position or angle of the tiltwing or tilt rotor), ranging from (e.g., minimum) cruise position (700) to (e.g., maximum) hover position (702).

[0089] The first operating envelope (704), shown by a solid line boundary and filled with a grid pattern, is associated with tiltrotor aircraft. See, for example, [link to relevant documentation]. Figure 4 The multi-rotor aircraft 400 and Figure 3A The tiltrotor 302 and fixed rotor 300 are shown in the diagram. The second operating envelope (706), shown with a dashed boundary and gray fill, is associated with an aircraft having a forward-swept and fixed wing (e.g., comparable). This forward-swept and fixed wing has a tiltrotor mounted on its trailing edge. See, for example, the embodiment described above.

[0090] In the diagram shown here, the tiltrotor operating envelope (706) is a superset of the tiltrotor operating envelope (704), indicating that the former aircraft configuration is safer and / or more airworthy than the latter, and is also capable of flying faster and slower at comparable tilt positions. For a fixed wing, the wing is already (and / or always) pointing in the direction of travel. When the tiltrotor is at or near (e.g., maximum) hover (702), the aircraft can fly almost all the way to stall speed (e.g., V2) without tilting the engines to cruise position. For example, note that the tiltrotor operating envelope (706) can remain at (e.g., maximum) hover (702) until V2. This significantly increases the operational states of the tiltrotor operating envelope (706) compared to the tiltrotor operating envelope (704). For example, note all the gray areas above the tiltrotor operating envelope (704).

[0091] Another effect that can contribute to the extended operating envelope of tiltrotor configurations at or near hover includes flow steering (e.g., see...). Figure 4 The flow deflection above the main wing generates some additional lift. In some embodiments, when in normal hover (e.g., at minimum tilt position 700), this flow deflection and the lift it generates are amplified or optimized by tilting the main wing rotor from directly downward to a slightly rearward angle.

[0092] Conversely, when the tiltrotor is tilted upward in (e.g., at maximum) hover position (702), it presents a large frontal area. As a result, the tiltrotor cannot fly forward at any suitable speed until it is in or near full (e.g., minimum) cruise position (700) or almost so.

[0093] The accompanying figures below illustrate a more detailed embodiment of a forward-swept fixed-wing aircraft with tiltrotor rotors, which includes some optional features not described above.

[0094] Figure 8A This is a top view of an aircraft embodiment with a three-element tail. In the example shown, the exemplary multirotor aircraft includes a tail (800) with three elements: two horizontal stabilizers (802) and a single vertical stabilizer (804). In this example, the tip (806) of the main wing is curved. This may, for example, help to better capture forced airflow from the tip of the propeller, and increase the wing's aspect ratio. For a given power input, this results in lower induced drag and higher available lift. An additional removal is to protect the tip propeller blades from lateral impacts when hovering near buildings. The main wing also includes a shoulder (808), which widens the portion of the main wing that connects to the fuselage and provides structural assistance.

[0095] Figure 8BThis is a front view of an embodiment of an aircraft with a three-element tail. Figure 8B continue Figure 8A Example. As shown here, the canard rotors (820) are positioned such that they are below the plane of the main wing (822). This positioning of the canard rotors improves the thrust line during cruise and reduces the interaction between the canard rotors (820) and the main wing (822).

[0096] Figure 8C This is a side view of an embodiment of an aircraft with a three-element tail. As shown in this view, the canard rotors (840) are positioned such that they are below the plane of the main wing (842).

[0097] Figure 9A This is an angled view of an embodiment of an aircraft with a V-tail. In this example, the multirotor aircraft has a V-tail (900). One benefit of the V-tail (900) is that it helps to avoid interaction between the surfaces of the main rotor (902) and the tail (900). The accompanying figure below shows a front view that illustrates this more clearly.

[0098] Figure 9B This is a front view of an embodiment of an aircraft with a V-tail. Figure 9B continue Figure 9A Example. As shown in this view, the V-tail (910) extends outward from the fuselage to the wingtip, beyond the main rotor. As a result, even when the main rotor is in cruise position (912), the V-tail (910) is not directly behind and / or directly in the wake of the main rotor (912). This minimizes the interaction between the surfaces of the main rotor (912) and the V-tail (910).

[0099] The view also shows (at least in this embodiment) the main wing rotor (914) in hover, tilted slightly rearward and slightly outward at an angle or otherwise. As mentioned above, this is likely desirable because it allows at least some aircraft embodiments to fly in "magic carpet mode," where the rotor remains in a hovering tilted position but can transition to primary wing-borne flight. An example of this is shown in the figure below.

[0100] Figure 10This is an illustration of an embodiment of a multirotor aircraft with a truncated fuselage capable of flying in magic carpet mode. As used herein, the term "magic carpet mode" refers to a mode in which the rotors remain in hover orientation, but the aircraft has accelerated to an airspeed at which the wings generate significant lift. In magic carpet mode, the aircraft speed can be controlled by pitching forward, and altitude can be controlled either by increasing efficiency and thus the rate of climb by increasing speed, or by directly increasing thrust to the rotors. In the example shown, the multirotor aircraft has a canard (1000) with two canard rotors (1002). The main wing (1004), a fixed wing with forward sweep, has six main wing rotors (1006) attached to the trailing edge of the main wing. The fuselage (1008) is relatively short and is referred to herein as a truncated fuselage. For example, note that the end of the fuselage (1010) extends only slightly beyond the end of the last rotor (1012). In this particular embodiment, the rotor is fixed and does not tilt or otherwise change position.

[0101] There are various embodiments of multirotor aircraft that can meet stringent weight requirements (e.g., ultralight standards). In this approach, the fuselage is significantly shorter and there is no tail, both of which reduce weight. Using a fixed rotor (e.g., the opposite of a tiltrotor) can also reduce weight. The shortened fuselage and the absence of a tail also result in a smaller footprint, which facilitates transport (e.g., in a trailer) and the amount of space required for takeoff and / or landing.

[0102] In some embodiments, the rotor is in a fixed position tilted backward, more at the hovering end of the tilt range than at the cruising end (e.g., a rotation axis tilted downward from the horizontal at an angle between 20° and 40° (inclusive)). See, for example, the rotation axis (1020) associated with the fixed rotor (1022), where the tilt angle is between 20° and 40°, which is suitable and / or acceptable for magic carpet mode. This rotor position (though fixed) allows the exemplary multirotor to fly vertically (e.g., not due to aerodynamic lift on the wings, but from airflow generated by the rotor) and forward (e.g., away from the wings). This ability or mode to maintain the rotor in a hovering tilt while flying in a wing-borne manner (e.g., primarily and / or mostly) is sometimes referred to as magic carpet mode. Note that this ability to fly in magic carpet mode is not necessarily limited to fixed rotor embodiments. For example, some or all of the tilt rotor embodiments described above can fly in magic carpet mode (e.g., where the tilt position is the limit or maximum hover position, or a tilt position between two limits).

[0103] Figure 11A This is a top view of an embodiment of a multirotor aircraft with a truncated fuselage and tail. The embodiment shown here is similar to... Figure 10 The embodiments of the previous multirotor aircraft shown are similar, and for the sake of brevity, common features will not be discussed here. Unlike the previous examples, this embodiment has a tail fin (1100). The fuselage (1102) is a truncated fuselage, so the tail fin (1100) and the fuselage (1102) are connected by a tail boom (1104).

[0104] Figure 11B This is a side view of an embodiment of a multirotor aircraft with a truncated fuselage and tail. Figure 11B continue Figure 11A Example. This view shows more clearly other features of the multirotor aircraft, including the horizontal control surface (1106) and vertical control surface (1108) on the tail fin, and the sled-like landing gear (1110).

[0105] Briefly return to Figures 8A-8C Further improvements to the performance of the aircraft shown in these figures would be desirable. The figures below depict alternative aircraft embodiments with better control and / or stability during stall (e.g., partial or deep stall). For convenience and ease of explanation, multiple features and / or improvements are shown in a single exemplary aircraft described below. Naturally, in some embodiments, not all features and / or improvements described below will appear together in the same aircraft.

[0106] Figure 12A This is a perspective view of an embodiment of a tiltrotor aircraft with features for improved flight control and / or stability. To better illustrate the features of this exemplary aircraft, the tiltrotor blades are not shown in this figure and subsequent diagrams. As described above, the blades (not shown) are attached to the distal and / or rear end of the pylons (1206a and 1212a). In this exemplary aircraft, the tail (1200a) is a T-tail (or alternatively, a two-element tail), rather than... Figures 8A-8C The more conventional arrangement shown is (e.g., the tail has three elements: two horizontal and one vertical). Thus, when the aircraft is horizontal (e.g., during forward flight), the horizontal surface of the T-tail is higher than the main wing (1210a) to which the six tiltrotors are attached using pylons (1212a), and also higher than the canards (1204a) to which the two tiltrotors are attached using pylons (1206a).

[0107] The exemplary aircraft shown here also includes a dovetail (1202a), which is a small fin on the bottom of the fuselage facing the rear of the aircraft. In some embodiments, in addition to the aerodynamic benefits during flight (described in more detail below), the dovetail in this exemplary aircraft has the (additional) benefit of acting as a tail skid on which the fuselage rests when the aircraft is on the ground. For example, for landing, the exemplary aircraft will perform more vertical landings than gliding landings. This eliminates the need for wheels due to the more vertically oriented landings, and enabling the dovetail to perform a dual function reduces the weight of the aircraft (which may fall into the ultralight category).

[0108] Alternatively, in some other embodiments, the aircraft has (e.g., in addition to or as a substitute for a dovetail for landing) landing gear (e.g., including retractable or non-retractable wheels) or a rear skid. A rear skid or tail skid is required in some applications because it is suitable for both taxiing and vertical landings, and allows the aircraft to move around (e.g., on one or more skids) if desired. Conversely, a (tail) skid may not be desired in some applications because it may require repair or replacement if the aircraft performs a hard landing.

[0109] The aircraft also includes other canard embodiments (e.g., Figures 8A-8C The embodiment shown is a narrower (e.g., 10-15%) and more rearward (e.g., 2-5%) canard (1204a) attachment compared to the one illustrated. These features and / or design changes contribute to the control and / or stability of the aircraft in a variety of flight scenarios, as will be described in more detail below.

[0110] Figure 12B This is a side view of an embodiment of a tiltrotor aircraft with features for improved control and / or stability. Figure 12B It shows Figure 12A The aircraft, but from a different angle. According to this view, the T-tail (1200b) and swallowtail (1202b) are still visible. Conversely, in this view, the canard (1204b) and main wing (1210b) are obscured by their pylons (e.g., 1206b and 1212b respectively).

[0111] Figure 12C This is a top view of an embodiment of a tiltrotor aircraft with features for improved control and / or stability. According to this view, the T-tail (1200c), canard (1204c), pylon attached to the canard (1206c), main wing (1210c), and pylon attached to the main wing (1212c) are all visible. The dovetail (not shown) is obscured by the T-tail (1200c) and is not visible.

[0112] Figure 12D This is a front view of an embodiment of a tiltrotor aircraft with features for improved control and / or stability. According to this view, the T-tail (1200d), canard (1204d), pylon attached to the canard (1206d), main wing (1210d), and pylon attached to the main wing (1212d) are all visible. The dovetail (not shown) is obscured by the fuselage (1208) and is not visible.

[0113] Figure 12E This is a top view of an embodiment of a tiltrotor aircraft, which has a narrower canard attached further aft compared to the forward canard. In this example, the fuselage 1240 and pylon 1242 are connected by two pylon embodiments: a wider (e.g., front to rear) canard (1244) that attaches the fuselage (1240) and pylon (1242) further forward; and a narrower canard (1246) that attaches the fuselage (1240) and pylon (1242) further aft. (Note: the wider, forward canard (1244) is drawn with dashed lines, while the narrower, rearward canard (1246) is drawn with solid lines.) In one example, the new canard has leading and trailing edges that are within the following ranges relative to the leading edge of the pylon (e.g., 0% corresponds to the leading edge of the pylon, and 100% corresponds to the trailing edge of the pylon): Past Life 40% to 60% trailing edge 55% to 80% Table 1: Figure 12E Exemplary position ranges of the leading and trailing edges of the canard 1246.

[0114] One benefit of the narrower canard (1246), an updated and improved version of the wider canard (1244), is that it improves pitch stability by pushing the lift surface area further back and reducing the area in front of the center of gravity. Another benefit of the narrower canard (1246) is that, due to its new, more aft position below the propeller disk (1248), the canard obstructs less of the area (1250) that generates most of the lift when the tiltrotor is in hover (approximately the outer third of the propeller disk). This improves hovering efficiency when the tiltrotor is positioned or oriented in this way. Yet another benefit is that with the canard positioned further back, it is closer to the rotor's center of thrust, which reduces canard twist and increases the frequency of that mode. In other words, the newer / narrower canard has a more favorable position relative to the center of thrust and center of mass (which is beneficial for structural modes).

[0115] In some embodiments, the trailing edge of the main wing is shaped or otherwise molded to follow the curve of the propeller to (further) improve efficiency during hovering mode. An example of this is shown in the figure below.

[0116] Figure 12FThis is a top view of an embodiment of a main wing with a curved section at the trailing edge that is parallel to the curve of the propeller disk when the tiltrotor is in the hovering position. In this example, circles 1260a–1260c show the circular area occupied by the propeller disk when the tiltrotor is in the hovering (i.e., face down) position. The trailing edge (1262) of the main wing has three curved and / or circular sections (1264a–1264c) that follow the curve of the propeller disk (1260a–1260c) and / or are parallel to its extension. Due to these curved sections, during hovering mode, the main wing no longer obstructs the downward lift or thrust generated by the propeller disk, which helps the aircraft fly more efficiently in this mode.

[0117] As mentioned above, for those with Figures 8A-8C Analysis and flight tests of the horizontal tail aircraft shown in the figure revealed that... Figure 12A-12D The diagram illustrates the undesirable flight performance of the aircraft under certain conditions. The following figure depicts this in more detail.

[0118] Figure 13 This is a diagram illustrating an embodiment of wake interference during forward flight of a tiltrotor aircraft with a horizontal tail. In the example shown, the aircraft (1300) is a tiltrotor aircraft with a horizontal tail (e.g., see...). Figures 8A-8C In the state shown here, the aircraft is flying at a (relatively) low angle of attack, sometimes referred to as forward flight mode. For example, the aircraft's normal angle of attack might be in the range of -4 to 16 degrees, and the angle of attack shown here is approximately 0 degrees. As shown here, the wake from the canard (1302) and the wake from the main wing (1304) interact (negatively) with the horizontal stabilizer (1306) because the two horizontal airfoils are at relatively close altitudes to the canard and main wing. This wake interference causes pitch instability (at least during forward flight). This is undesirable because if part or all of the automatic control system fails, the pilot will need to intervene to maintain pitch stability. Since the aircraft is designed for use by inexperienced pilots, it is undesirable to impose this burden on the pilot during emergency or malfunction situations.

[0119] Tiltrotor aircraft with T-tail (e.g.) Figure 12A-12D The aircraft shown below will not experience this wake interference and instability because the horizontal airfoil of the T-tail is much higher than that of the canard and main wing. The following diagram illustrates various wakes of this aircraft.

[0120] Figure 14 This is a diagram illustrating an embodiment of a tiltrotor aircraft with a T-tail. (Compared to the previous...) Figure 1Similarly, the aircraft (1400) flies at a (relatively) low angle of attack (i.e., in forward flight mode). However, the aircraft has a T-tail (1402) instead of (for example, a conventional) horizontal tail, as... Figures 8A-8C As shown in the diagram. Thus, the wake from the canard (1404) and the wake from the main wing (1406) do not interfere with the horizontal surface of the T-tail (1402), as this surface is much higher than the canard and the main wing. It should also be noted that the T-tail is not subjected to any wake from the fuselage (not shown in the diagram). As a result, the T-tail provides good restoring force (and therefore, good pitch stability), and requires less pilot intervention in the event of a partial or complete failure of the control system.

[0121] Another (incidental) benefit of using a T-tail is that the horizontal section acts as a fence or cap for the vertical section, thereby improving its aerodynamic efficiency and maximum force. This allows the vertical section of the T-tail to be smaller than would otherwise be necessary for aerodynamic stability and permitting purposes.

[0122] In some embodiments, the T-tail is mounted at a height ranging from 0.7 to 1.2 meters above the vertical base. This range may be attractive or otherwise desirable because limiting the height of the horizontal surface of the T-tail results in better structural properties, as the vertical portion of the T-tail (which must transfer loads) ends up being shorter and more "chord-oriented" (i.e., wider in the fore-and-aft direction, which increases torsional stiffness for the same or given thickness) in the case of a lower-mounted tail.

[0123] The accompanying figures below illustrate a tiltrotor aircraft with a T-tail in deep stall and describe the above-mentioned (e.g., Figure 12A-12D How certain features can help during a deep stall (in the context of the problem).

[0124] Figure 15A This is a diagram illustrating an embodiment of the streamlines and vorticity of a tiltrotor aircraft with a T-tail during a deep stall. In the example shown here, the aircraft (1500) has pitched up to such a high angle of attack that the main wing has stalled (in this view, the main wing is shielded by a pylon (1502a) attached to it). This significantly increases the size of the wake (1504) generated by the main wing and the turbulence within the wake. This causes the wake (1504) from the main wing to interact with the horizontal stabilizer (1506a), which itself stalls due to the large angle of attack. This scenario is called a “deep stall,” and in this condition, all pitch control is lost.

[0125] In this situation, the swallowtail wing (1508a) on the underside of the fuselage helps stabilize the aircraft. As shown here, although the horizontal stabilizer of the T-tail (1506a) is negatively affected by the wake (1504) from the main wing, the swallowtail wing (1508a) is located at a lower altitude and is therefore unaffected by the (negative) wake (1504) from the main wing. In this scenario, the swallowtail wing (1508a) will push the nose of the aircraft downwards enough to allow the main horizontal stabilizer of the T-tail (1506a) to disengage from the stalled wake (1504) of the main wing, thereby restoring pitch control.

[0126] For clarity, the following figure shows the same example, but without the vorticity shown here.

[0127] Figure 15B This is a diagram illustrating an embodiment of the streamlines of a tiltrotor aircraft with a T-tail during a deep stall. In this example, the streamline (1520) that passes over the main wing (obscured by pylon 1502b) and subsequently interferes with the horizontal stabilizer of the T-tail (1506b) leading to a deep stall is better seen. As described above, the swallowtail (1508b) pushes the nose of the aircraft downward, allowing the horizontal stabilizer of the T-tail (1506b) to overcome the interference from the main wing, thereby restoring pitch control.

[0128] In some embodiments, tiltrotor aircraft (various examples of which are described above) are designed to have a desired stall sequence. The figure below illustrates an example of this.

[0129] Figure 16 This is a flowchart illustrating an embodiment of a stall sequence. In this example, various sequences or orders of surface stalls (e.g., horizontal aerodynamic lift) are depicted, where this sequence is preferred over certain other stall sequences for the following reasons. As the aircraft's nose rises more and more, the aircraft can advance with the described stall sequence. In some embodiments, the main wing is designed to achieve the stall sequence described herein (e.g., by appropriately selecting the wing twist or other shape or size of the main wing). Note that although... Figure 12C The examples provided are intended to illustrate exemplary surfaces that stall in the described order, but the stall order described herein is also applicable and / or desirable for other embodiments, such as... Figures 8A-8C The embodiment shown.

[0130] At 1600, the canard stalled. For example, at... Figure 12CIn the diagram, the nose of the aircraft can be fully raised, causing the canard 1204c to stall. By first stalling the canard, this provides a downward pitching (i.e., nose-down) moment, which is a restoring moment that counteracts the nose-up (which initially causes the canard to stall). For this reason (i.e., restoring moment and / or movement), it is desirable to first stall the canard.

[0131] In 1602, the mid-section of the main wing stalled. For example, in Figure 12C In the middle, the main wing (1210c) may have wing twist, causing the inner (inner) section 1222, the middle section (1224), and the outer (outer) section 1226 to stall at different times and / or angles of attack. As an example of step 1602, Figure 12C Stalling occurs in the middle section 1224 (e.g., after canard 1204c).

[0132] In 1604, the inner section of the main wing and the surface of the horizontal tail stalled close to each other. For example, in Figure 12C In the middle section, the inner section 1222 and the T-tail 1200c stall approximately simultaneously (but after the canard 1204c stalls first and the middle section 1224 stalls second). It should be noted that the inner section of the main wing and the horizontal tail surface do not necessarily stall exactly simultaneously (i.e., at the same time), but rather close to each other. The exact order could be either one stalling first.

[0133] In 1606, the outer section of the main wing stalled. For example, in Figure 12C In the middle, the outer section 1226 stalls (e.g., after the canard 1204c (first), the middle section 1224 (second), and the inner section 1222 and the T-tail 1200c (third).

[0134] In one example, assume the aircraft is performing an upward pitch maneuver of 5 degrees per second. At least in this example, the minimum acceptable time difference between canard stall (at 1600) and outer segment stall (at 1606) will be approximately 0.5–1 second. This difference will allow the aircraft to remain controllable and / or give the pilot sufficient time to respond to various stalls.

[0135] Figure 12C The exemplary aircraft shown has three main lifting surfaces: a canard at the front (1204c), a main wing in the middle (1210c), and a T-tail at the rear (1200c). In this example, the stall sequence of these surfaces (e.g., when the aircraft pitches up (nose)) is designed to follow the desired sequence shown here. One benefit of following this sequence is that it facilitates feedback to the pilot (e.g., the pilot should lower the nose of the aircraft) and / or results in a balance of forces that cause passive nose-lowering (e.g., in the absence of pilot intervention).

[0136] As mentioned above, since this aircraft is a tiltrotor aircraft, in order to achieve a good distribution of the tilting engine and propeller in hovering mode (i.e., to make the center of thrust close to the center of mass of the aircraft in the horizontal plane), Figure 12C In section 1220), the main wing is swept forward. As a result of the forward sweep of the main wing, the inner section of the main wing ( Figure 12C 1222 in the middle section ( Figure 12C 1224 in) and the outer segment ( Figure 12C The stall sequence (1226) becomes important. This is because, unlike typical general aviation aircraft with straight wings (and therefore, the stall sequence of the wing segments mainly affects roll control considerations), in forward-swept wings, the stall sequence affects not only roll control but also pitch control.

[0137] Typical general aviation aircraft (unlike the various tiltrotor aircraft described in this article) have only two of the three lifting surfaces mentioned above: namely, the main wing and the tail with some horizontal surfaces at the rear. For leverage considerations, such general aviation aircraft typically include control surfaces called ailerons (e.g., on the outer sections of the main wing) to allow roll control. When designing the main wing, the outer section containing the ailerons is typically twisted downwards at its leading edge compared to the rest of the wing. This means that when the entire wing pitches upwards, the relative angle with respect to the wind at the wingtip is lower than that of the rest of the wing. As the wing approaches its stall angle of attack, the inner sections of the wing begin to stall, but the outer sections at lower local angles of attack do not. This allows the ailerons to still allow roll control through stall.

[0138] In contrast, for the various tiltrotor aircraft described in this article, if the outer (outer) section of the main wing (e.g., Figure 12C (1226) Continued stall would be desirable so that the aircraft can maintain roll control for as long as possible. However, the innermost wing sections (e.g., Figure 12C (1222) also cannot allow premature stall because their center of lift (e.g., Figure 12C 1230 in the middle) is located at the center of gravity of the aircraft (e.g., Figure 12C Behind 1220 in the middle. If these inner segments (e.g., Figure 12C If the aircraft stalls (as indicated by 1222), it will experience a nose-up pitching moment, further accelerating the stall sequence. Therefore, the main wing twist is designed to have a position located at the aircraft's center of gravity (e.g., ...). Figure 12C The center of lift in the transverse direction of 1220 (e.g., Figure 12C The middle section (1232) stalls first. This provides feedback to the pilot in the form of flutter. As lift decreases, the nose also tends to passively drop. The inner sections (e.g., Figure 12C (1222 in the middle) then stalled, and the outer segment (e.g., Figure 12C (1226) eventually stalls, thus allowing the aircraft to maintain roll control until the last possible moment (e.g., because the center of lift of the outer section (e.g., Figure 12C 1234) in the middle are located at the center of gravity of the aircraft (e.g., Figure 12C (1220) in front, so a stall here would result in a loss of roll control). This stall sequence allows the aircraft to maintain roll and pitch control for as long as possible, thus allowing the aircraft to break free from any spin or spiral patterns that might be associated with a stall, until the very last possible moment.

[0139] The following table describes the implementation Figure 16 Examples of the angle ranges for different sections of the main wing, as described in the stall sequence: inner section (e.g., Figure 12C 1222 in the middle) -5° to 0° Middle section (e.g., Figure 12C 1224 in the middle) 0° to 5° outer segment (e.g., Figure 12C 1226 in the middle) -5° to 0° Table 2: Implementation Figure 16 Examples of the range of torsion angles for the stall sequence described in the text.

[0140] For completeness, the exemplary stall sequence described herein includes all horizontal lifting surfaces of the aircraft. However, it should be noted that in some applications where the impact on the aircraft is minimal or negligible, the intermediate stall sequence can be altered. For the reasons stated above, it is desirable for the canards to stall first (see step 1600) and the outer section of the main wing to stall last (see step 1606), but the intermediate stall sequence (e.g., steps 1602 and 1604) has some flexibility. For example, depending on the available authority for the tail section, the relative stall sequence of the intermediate and inner wing sections may or may not be critical. For this reason, steps 1602 and 1604 are shown with dashed borders instead of... Figure 16 The solid border in the middle.

[0141] In some embodiments, compared to other types of aircraft, the various exemplary aircraft described herein (e.g., including...) Figures 8A-8C and Figure 12A-12D The horizontal stabilizer exhibits a different lift distribution during cruise (i.e., forward flight). More specifically, compared to other aircraft with canards, the lift on both the canards and tail is significantly lower during cruise than the lift on the main wing. See, for example, the table below (for completeness, this table includes all flight phases except cruise and fast cruise). Note that the horizontal stabilizers mentioned in the rightmost column include various tail configurations (e.g., including...). Figures 8A-8C and Figure 12A-12D (Those tail fins shown): Table 3: Exemplary relative lift on the three main lift surfaces during each flight phase.

[0142] Typically, canard aircraft carry more lift on the canard during cruise (e.g., 25%–30%), but this is not the case for the aircraft described herein. See, for example, the slower and faster cruise runs, where the lift associated with the canard is 8% and 5%, respectively. Generally, the canard in the embodiments described herein has associated lift between 0% and 15% during cruise (i.e., forward flight). Instead, the majority of the lift during cruise is done by the main wing (e.g., 80% to 100%), which increases the aircraft's efficiency. It is also noteworthy that during both slower and faster cruise, all surfaces are associated with lift, and no surface is associated with downward forces (e.g., all lift percentages are positive). This indicates that the aircraft can fly efficiently because the surface with lift does not need to compensate for or otherwise compensate for another surface with downward forces.

[0143] Although the foregoing embodiments have been described in some detail for clarity of understanding, the invention is not limited to the details provided. Many alternative ways of carrying out the invention exist. The disclosed embodiments are illustrative and not restrictive.

Claims

1. An aircraft comprising: A canard with a leading edge and a trailing edge; It features a swept trailing edge and a fixed wing; Multiple tilt rotor submodules, including: The first tiltrotor submodule, in which: The leading edge of the canard contacts the first tiltrotor submodule at a location ranging from 40% to 60% of the length of the first tiltrotor submodule, including end values, where 0% corresponds to the front tip of the first tiltrotor submodule and 100% corresponds to the rear tip of the first tiltrotor submodule; and The trailing edge of the canard contacts the first tiltrotor submodule at a location ranging from 55% to 80% of the length of the first tiltrotor submodule, including the end value; and Multiple other tiltrotor submodules are coupled to the trailing edge of the swept-forward and fixed wing; and A dovetail wing is attached to the underside of the fuselage, wherein the dovetail wing pushes the nose of the aircraft downward during a deep stall, wherein the fuselage rests on the dovetail wing when the aircraft is on the ground, and wherein the forward-swept and fixed wings include corresponding curved sections for each of the plurality of other tiltrotor submodules, wherein the curved sections are parallel to the curve of the propeller disk associated with the plurality of other tiltrotor submodules when the plurality of other tiltrotor submodules are in a hovering position.

2. The aircraft according to claim 1, wherein, The horizontal plane of the forward-swept and fixed wings is at a height higher than the horizontal plane of the canard.

3. The aircraft according to claim 1, wherein, The plurality of tiltrotor submodules include two first tiltrotor submodules connected to the canard and six other tiltrotor submodules connected to the forward-swept and fixed wings.

4. The aircraft according to claim 1, wherein, During cruise mode, the forward-swept and fixed wings have relative lift in a second range of 80% to 100%, including end values.

5. The aircraft according to claim 1, wherein, The forward-swept and fixed wing inner sections have a twist angle in a second range of -5° to 0°, including end values.

6. The aircraft according to claim 1, wherein, The intermediate section of the forward-swept and fixed wing has a twist angle in a second range of 0° to 5°, including end values.

7. The aircraft according to claim 1, wherein, The outer sections of the forward-swept and fixed wings have a twist angle in a second range of -5° to 0°, including end values.

8. The aircraft according to claim 1, wherein, The forward-swept and outer sections of the fixed wing stall behind the canard.

9. The aircraft according to claim 1, wherein, The outer section of the swept-wing and fixed wing stalls after the rest of the swept-wing and fixed wing.

10. A method for constructing an aircraft, comprising: Provides canards with leading and trailing edges; Offers both forward-swept and fixed wings with trailing edges; as well as Multiple tilt rotor submodules are provided, including: The first tiltrotor submodule, in which: The leading edge of the canard contacts the first tiltrotor submodule at a location ranging from 40% to 60% of the length of the first tiltrotor submodule, including end values, where 0% corresponds to the front tip of the first tiltrotor submodule and 100% corresponds to the rear tip of the first tiltrotor submodule; and The trailing edge of the canard contacts the first tiltrotor submodule at a location ranging from 55% to 80% of the length of the first tiltrotor submodule, including the end value; and A dovetail wing is provided attached to the underside of the fuselage, wherein the dovetail wing pushes the nose of the aircraft downward during a deep stall, wherein the fuselage rests on the dovetail wing when the aircraft is on the ground, and wherein a plurality of other tiltrotor submodules are coupled to the trailing edge of the swept-forward and fixed-wing, wherein the swept-forward and fixed-wing includes a corresponding curved section for each of the plurality of other tiltrotor submodules, wherein the curved section is parallel to the curve of the propeller disk associated with the plurality of other tiltrotor submodules when the plurality of other tiltrotor submodules are in a hovering position.

11. The method for constructing an aircraft according to claim 10, wherein, The horizontal plane of the forward-swept and fixed wings is at a height higher than the horizontal plane of the canard.

12. The method for constructing an aircraft according to claim 10, wherein, The plurality of tiltrotor submodules include two first tiltrotor submodules connected to the canard and six other tiltrotor submodules connected to the forward-swept and fixed wings.

13. The method for constructing an aircraft according to claim 10, wherein, During cruise mode, the forward-swept and fixed wings have relative lift in a second range of 80% to 100%, including end values.

14. The method for constructing an aircraft according to claim 10, wherein, The forward-swept and fixed wing inner sections have a twist angle in a second range of -5° to 0°, including end values.

15. The method for constructing an aircraft according to claim 10, wherein, The intermediate section of the forward-swept and fixed wing has a twist angle in a second range of 0° to 5°, including end values.

16. The method for constructing an aircraft according to claim 10, wherein, The outer sections of the forward-swept and fixed wings have a twist angle in a second range of -5° to 0°, including end values.

17. The method for constructing an aircraft according to claim 10, wherein, The forward-swept and outer sections of the fixed wing stall behind the canard.

18. The method for constructing an aircraft according to claim 10, wherein, The outer section of the swept-wing and fixed wing stalls after the rest of the swept-wing and fixed wing.

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