Semi-annular empennage

Abstract

The invention provides a semi-annular empennage which is arranged at the tail part of an aircraft, and the semi-annular empennage starts from the lower part of a wing, extends upwards along an arc-shaped path to exceed the tail end of the tail part of the aircraft, and forms a semi-annular pneumatic structure in a vertical plane; the front edge of the semicircular empennage is in a sweepback structure, and the arc-shaped extending highest point of the semicircular empennage is located behind the tail end of the aircraft tail. The semi-annular empennage is of a semi-annular open structure and has the obvious weight reduction advantage. The semi-annular empennage extends upwards from the lower portion of the wing, high-speed airflow on the upper surface of the fuselage avoids a connecting area of the semi-annular empennage, and interference of the airflow on the aerodynamic configuration of the empennage is avoided. Due to the lower open structure and the sweepback structure exceeding the tail end of the aircraft tail, the situation that the aircraft tail structure shields control airflow is effectively avoided, and the problem that control surface control fails in a large attack angle state is solved; and meanwhile, the lower open structure also facilitates maintenance of the fuselage and the engine below the empennage.

Description

Technical Field

[0001] This invention relates to aircraft tail design, and in particular to a semi-circular tail structure suitable for fixed-wing aircraft, which aims to solve problems such as aerodynamic interference, control lag and maintenance difficulties of traditional tails. Background Technology

[0002] US Patent 5242132 A discloses a multihull-type V-STOL aircraft. This aircraft proposes an integrally articulated curved tail, which lacks traditional control surfaces and relies on hinges connected to the fuselage to drive complex three-axis motions. Essentially, it is a variant of an all-moving tail attempting to reduce weight and drag through a monocoque structure. However, this curved tail design suffers from irreconcilable structural flaws: the large curved surface requires ultra-high-power actuators for three-axis compound deflection, leading to a significant increase in the weight of the drive system, thus offsetting the weight reduction benefits of structural simplification. More seriously, the irregular curved surface causes nonlinear drift of the aerodynamic center during compound motions, making the aircraft's attitude control response unpredictable and requiring extensive wind tunnel testing for verification; however, the patent does not provide dynamic aerodynamic data or actuation schemes. Furthermore, the hinge system with coupled three-axis motion lacks fault redundancy; a single point of failure can trigger omnidirectional loss of control, seriously violating airworthiness and safety principles. These inherent flaws, coupled with the limitations of composite material processes and the lack of dynamic load analysis during the patent publication period, inevitably led the design into a vicious cycle between weight reduction goals and engineering feasibility.

[0003] The existing technology also proposes a traditional tail fin alternative, which includes a separate vertical stabilizer, a horizontal stabilizer, and a rudder. Although the structure and function are no different from the traditional layout, it introduces multiple structural redundancy defects due to the need to adapt to the special configuration of the catamaran hull: its vertical tail must be anchored to the two separate hulls separately through reinforced brackets, and the horizontal tail fin requires additional crossbeams to bridge the two vertical tails, resulting in a doubling of connection nodes, a surge in assembly complexity, and a risk of stress concentration at connection points under asymmetrical land and water loads; this bulky frame, reinforced to accommodate multiple hulls, not only completely negates the advantages of the traditional tail fin's lightness and simplicity, but also increases manufacturing and maintenance costs, forming a contradictory design where the function is not upgraded and the structure is degraded.

[0004] US 6592073 B1 discloses a twin-fuselage amphibious aircraft. Its tail structure design integrates the control surfaces into the ducted propeller casing, resulting in a short and stubby tail structure due to the propeller diameter limitation, leading to a significant increase in drag. The ducted control surface size limit results in insufficient control torque, and the aerodynamic response is sluggish at high angles of attack or engine failure. The propeller wake disturbs the control surfaces at close range, causing nonlinear control responses (such as yaw-induced unintended pitch). Furthermore, the mutual interference between the propeller and control surface airflow can induce structural resonance due to propeller vortex airflow impacting the control surfaces, and the control surface deflection can disturb the propeller inflow, reducing thrust. In addition, propeller maintenance requires disassembling the control surface components, and the high temperature and high vibration environment inside the duct accelerates actuator wear, significantly increasing maintenance complexity.

[0005] WO 2008 / 081098 A1 discloses a ring-shaped tail fin patented by Airbus France. This ring-shaped tail fin uses a closed ring channel formed by the horizontal and vertical fin surfaces to enclose the propeller, aiming to reduce drag and noise. However, because the ring-shaped tail fin forms a closed ring channel with the tail of the fuselage, the control surfaces are blocked by the fuselage at high angles of attack, making it impossible to effectively control the airflow. Furthermore, the large-span cantilever structure of the ring-shaped tail fin in this prior art easily leads to stress concentration at the fuselage connection, requiring reinforcement and weight increase to offset the drag reduction benefits. The propeller wake directly impacts the inner wall of the ring, causing high-temperature ablation of the control surface material and inducing turbulence, resulting in a sharp drop in control effectiveness at high angles of attack and making yaw control prone to coupling with roll loss of control. Even more fatal is the maintenance disaster: twin-engine configurations require disassembling the ring-shaped tail fin, while single-engine configurations require maintenance to be carried out overhead, avoiding the fuselage, which is time-consuming and disrupts aerodynamic integrity. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a semi-annular tail fin to reduce or avoid the problems mentioned above.

[0007] To solve the above-mentioned technical problems, the present invention proposes a semi-circular tail fin, which is disposed at the tail of an aircraft. The semi-circular tail fin starts from below the wing and extends upward along an arc path to beyond the end of the aircraft's tail, forming a semi-circular aerodynamic structure in a vertical plane. The leading edge of the semi-circular tail fin has a swept-back configuration, and its highest point of arc extension is located behind the end of the aircraft's tail.

[0008] Preferably, the horizontal distance between the highest point of the leading edge of the semi-annular tail fin and the end of the aircraft tail is equal to 0.5-0.8 times the chord length of the tail fin airfoil section, and the sweep angle of the leading edge of the semi-annular tail fin relative to the horizontal plane passing through the longitudinal axis of the fuselage is 25-50 degrees.

[0009] Preferably, the starting end of the semi-annular tail fin is rigidly fixed to the underside of the wing via a connecting rod that extends along the longitudinal axis of the aircraft.

[0010] Preferably, the connecting rod is a double-rod structure symmetrically arranged below the wings on both sides, and the double rods are spaced a certain distance from the fuselage sidewall.

[0011] Preferably, a thruster is installed at the tail end of the aircraft, and the plane of the thruster's propeller disk does not spatially interfere with the highest point of the semi-circular tail fin.

[0012] Preferably, a thruster is installed on the nose of the aircraft.

[0013] Preferably, except for the connecting area, the airfoil cross-section of the semi-annular tail fin remains consistent along the arc-shaped extension path.

[0014] Preferably, the trailing edge of the semi-annular tail fin is provided with at least three independent deflection control surfaces, each of which is electrically controlled by an actuator.

[0015] Preferably, the control surface includes a central control surface and two lateral control surfaces, which are distributed circumferentially along the trailing edge of the semi-circular tail fin.

[0016] Preferably, the central control surface is symmetrically arranged along the longitudinal axis of the aircraft, and the lateral control surfaces are symmetrically arranged on both sides of the central control surface in an inclined manner.

[0017] The semi-annular open structure of the semi-annular tail fin of this invention has significant weight reduction advantages. The semi-annular tail fin extends upward from below the wing, and the high-speed airflow on the upper surface of the fuselage avoids the connection area of ​​the semi-annular tail fin, preventing airflow from interfering with the aerodynamic shape of the tail fin. Furthermore, the open lower structure and the swept-back configuration that extends beyond the tail tip of the aircraft effectively prevent the tail structure from obstructing the control airflow, avoiding the problem of control surface failure at high angles of attack. At the same time, the open lower structure also facilitates maintenance of the fuselage and engine below the tail fin. Attached Figure Description

[0018] The accompanying drawings are intended only to illustrate and explain this application and do not limit the scope of the invention.

[0019] Figure 1 The diagram shown is of an aircraft with a semi-circular tail fin according to a specific embodiment of the present invention.

[0020] Figure 2 The image shown is a rear view of an aircraft with a semi-circular tail fin according to another specific embodiment of the present invention.

[0021] Figure 3 The image shown is a side view of an aircraft with a semi-circular tail fin according to yet another specific embodiment of the present invention.

[0022] Figure 4 The image shown is a top view of an aircraft with a semi-circular tail fin according to another specific embodiment of the present invention.

[0023] Figure 5 The diagram shown is a bottom view of an aircraft with a semi-circular tail fin according to another specific embodiment of the present invention. Detailed Implementation

[0024] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments are now described with reference to the accompanying drawings. Identical components are denoted by the same reference numerals.

[0025] In view of the problems existing in the prior art, the present invention proposes a tail structure for aircraft, and particularly relates to a semi-annular tail 1, to solve the problems of aerodynamic interference, control lag and maintenance difficulties of traditional tails.

[0026] like Figure 1-5 As shown, it illustrates a fixed-wing aircraft that can be used in accordance with the present invention, wherein the semi-circular tail fin 1 of the present invention is disposed at the tail of the aircraft.

[0027] Unlike conventional and existing tail designs mentioned in the background section, the semi-annular tail 1 of the present invention starts from below the wing and extends upward along an arc path to beyond the tail end of the aircraft, forming a semi-annular aerodynamic structure in the vertical plane; wherein, the leading edge 12 of the semi-annular tail 1 is swept back, and its highest point of arc extension is located behind the tail end of the aircraft.

[0028] The tail structure of this invention adopts a semi-circular open structure, which has a significant weight reduction advantage compared to existing technologies. The semi-circular tail extends upward from below the wing, and the high-speed airflow on the upper surface of the fuselage avoids the connection area of ​​the semi-circular tail, preventing airflow from interfering with the aerodynamic shape of the tail. Furthermore, the open lower structure of the semi-circular tail and the swept-back configuration that extends beyond the tail tip of the aircraft effectively prevent the tail structure from obstructing the control airflow at high angles of attack, thus avoiding the problem of control surface failure at high angles of attack. At the same time, since the tail structure does not obstruct the tail of the fuselage, it also facilitates maintenance of the fuselage and engine below the tail.

[0029] In one specific embodiment, the starting end of the semi-annular tail fin is rigidly fixed to the underside of the wing by a connecting rod 13, which extends along the longitudinal axis of the aircraft.

[0030] In another specific embodiment, the connecting rod 13 is a double rod structure symmetrically arranged under the wings on both sides, and the double rods are spaced a distance from the fuselage sidewall to avoid fuselage turbulence interference.

[0031] In one specific embodiment, for example, a semi-circular tail fin (airfoil: NACA 0012) can be manufactured using carbon fiber composite material. The semi-circular tail fin originates below the wing, 15-50 cm from the fuselage. The tail fin extends upward along an arc-shaped path, and the highest point of the leading edge of the semi-circular tail fin extends horizontally beyond the tail tip of the aircraft by a distance equal to 0.5-0.8 times the chord length of the tail fin's airfoil section. The sweep angle of the leading edge of the semi-circular tail fin relative to the horizontal plane passing through the longitudinal axis of the fuselage is 25-50 degrees.

[0032] Two titanium alloy connecting rods (10-15cm in diameter) rigidly fix the starting end of the tail fin to the lower surface of the wing, with the rods spaced 0.5-0.8m from the fuselage sidewall (to avoid the turbulence zone of the fuselage).

[0033] Furthermore, in the illustrated embodiment, a thruster is installed at the tail end of the aircraft, with the thruster's propeller disk plane spaced apart from the semi-circular tail fin to avoid spatial interference. In another embodiment not illustrated, the thruster can also be installed at the nose of the aircraft, ensuring that the thruster's slipstream path does not intersect with the semi-circular tail fin, further preventing the thruster from interfering with the airflow of the semi-circular tail fin.

[0034] Because the tail fin and the propeller are effectively isolated in space, the position of the propeller can be flexibly configured. In one specific embodiment, for example, for a tail-mounted propeller configuration aircraft, a turboprop engine can be installed at the tail of the aircraft; or for a front-mounted propeller configuration aircraft, an engine of the same specifications can be installed at the nose of the aircraft; or a dual-engine configuration at both the nose and tail can also be used.

[0035] Furthermore, in one specific embodiment, except for the connecting area, the airfoil cross-section of the semi-annular tail fin remains consistent along the arc-shaped extension path to ensure the continuity of the aerodynamic shape and optimize the flow field, while reducing manufacturing difficulty.

[0036] Furthermore, in one specific embodiment, the trailing edge of the semi-circular tail fin is provided with at least three independent deflection control surfaces, each of which is controlled by fly-by-wire via actuators. Specifically, as shown in the figure, the control surfaces include a central control surface 14 and two lateral control surfaces 15, which are distributed circumferentially along the trailing edge of the semi-circular tail fin. More specifically, the central control surface 14 is symmetrically arranged along the longitudinal axis of the aircraft and is used for pitch control; the lateral control surfaces 15 are symmetrically arranged on both sides of the central control surface 14 in an inclined manner, and when they deflect synchronously, they mainly control yaw; when they deflect differentially, they mainly control roll.

[0037] For example, three carbon fiber control surfaces can be equidistantly distributed along the trailing edge of the tail fin, with the central control surface 14 having a deflection range of ±30° and the lateral control surfaces 15 having a deflection range of ±25°. Unlike traditional yaw / roll and pitch controls which are independent, the two lateral control surfaces of this invention are significantly tilted due to their arc-shaped distribution along the trailing edge of the tail fin. Therefore, when one of the lateral control surfaces 15 is independently manipulated, the pitch and yaw actions of the aircraft can be simultaneously obtained. Thus, although the lateral control surfaces 15 are mainly used to control yaw and roll, the central control surface 14 also needs to be manipulated synchronously to suppress unnecessary pitch actions. For example, when the lateral control surfaces 15 are simultaneously deflected downwards or upwards, while controlling yaw, the tilted lateral control surfaces 15 will also produce pitch control actions on the airflow. To avoid unnecessary changes in pitch attitude during yaw, the central control surface 14 can be manipulated synchronously in the opposite direction to counteract unnecessary pitch.

[0038] Compared with the traditional T-tail, the semi-circular tail fin of this invention can significantly accelerate the airflow velocity along the curved surface and delay airflow separation. In wind tunnel tests at 200 km / h, the cruise drag of the tail fin of this invention (the horizontal distance from the highest point of the leading edge beyond the tail tip of the aircraft is 0.5 times the chord length of the tail airfoil section, and the leading edge sweep angle is 25 degrees) can be reduced by 15%. In addition, the semi-circular tail fin of this invention can still maintain stable control at high angles of attack (α=25°), while the traditional T-tail fin enters a rudder failure state when α>20°. The average stall angle of attack can be increased by about 8 degrees compared with the traditional tail fin structure (based on CFD turbulent kinetic energy analysis). Experimental verification shows that the control surface efficiency of the yaw-roll decoupled control of this invention can be improved by up to 2 times compared with US 5242132 A, especially at high angles of attack (α=25°), the pitch moment coefficient can be increased from 0.08 to 0.16, and the crosswind landing accuracy is improved by more than 30% (1000 Monte Carlo simulations).

[0039] Furthermore, because the semi-circular tail fin of this invention avoids the tail structure of the fuselage, it prevents slipstream impact vibration and improves the fatigue life of the tail fin structure. For example, through 2000 hours of bench vibration testing, the fatigue life of the tail fin structure of this invention is on average 2.5 times higher than that of the traditional T-tail fin. Simultaneously, comparative experiments show that the tail fin of this invention (with the highest point of the leading edge extending 0.8 times the chord length of the tail airfoil section beyond the aircraft's tail tip, and a leading edge sweep angle of 50 degrees) reduces noise by 7 dB (FAR 36 standard measurement point) compared to US6592073 B1 due to the avoidance of ducted flow interference. Regarding tail fin maintainability, the open structure of the tail fin of this invention reduces engine replacement maintenance time from 4 hours to 1.5 hours compared to the traditional T-tail fin.

[0040] Overall, the semi-annular tail fin of this invention can accelerate airflow speed in terms of aerodynamic efficiency. For example, the highest point of the leading edge of the semi-annular tail fin extends 0.7 times the chord length of the tail airfoil section beyond the tail tip of the aircraft. When the leading edge sweep angle is 35 degrees, the boundary layer separation point is delayed to 85% of the chord length (verified by infrared thermal imaging). The lift-to-drag ratio is improved to 9.2 compared to the traditional T-tail fin (7.1 improvement compared to the traditional tail fin). The open structure of the annular tail fin of this invention shows in ballistic impact tests that local damage only leads to the failure of a single control surface (in contrast, the annular tail fin of WO 2008 / 081098 A1 showed overall instability). Redundant control surfaces can maintain controllable flight, and the structure can reduce weight by up to 15% compared to the B737-800 avionics simulator structure, while improving fuel efficiency by more than 12%.

[0041] Those skilled in the art should understand that although the present invention has been described with reference to multiple embodiments, not every embodiment contains only one independent technical solution. This description is provided merely for clarity; those skilled in the art should understand the specification as a whole and consider the technical solutions involved in each embodiment as being able to be combined with each other to form different embodiments to understand the scope of protection of the present invention.

[0042] The above description is merely an illustrative embodiment of the present invention and is not intended to limit the scope of the invention. Any equivalent changes, modifications, and combinations made by those skilled in the art without departing from the concept and principles of the present invention should fall within the scope of protection of the present invention.

Claims

1. A semi-circular tail fin, disposed at the tail of an aircraft, characterized in that, The semi-circular tail fin starts from below the wing and extends upward along an arc path to beyond the tail end of the aircraft, forming a semi-circular aerodynamic structure in the vertical plane; wherein, the leading edge of the semi-circular tail fin has a swept-back configuration, and its highest point of arc extension is located behind the tail end of the aircraft.

2. The semi-annular tail fin as described in claim 1, characterized in that, The leading edge of the semi-circular tail fin has a sweep angle of 25-50 degrees relative to the horizontal plane passing through the longitudinal axis of the fuselage.

3. The semi-annular tail fin as described in claim 1, characterized in that, The starting end of the semi-circular tail fin is rigidly fixed to the underside of the wing via a connecting rod that extends along the longitudinal axis of the aircraft.

4. The semi-annular tail fin as described in claim 3, characterized in that, The connecting rods are symmetrical double-rod structures located below the wings on both sides, with a distance set between the double rods and the fuselage sidewall.

5. The semi-annular tail fin as described in claim 1, characterized in that, A thruster is installed at the tail end of the aircraft, and the plane of the thruster's propeller disk does not have spatial interference with the highest point of the semi-circular tail fin.

6. The semi-annular tail fin as described in claim 1, characterized in that, The aircraft is equipped with a thruster at the nose.

7. The semi-annular tail fin as described in claim 1, characterized in that, Except for the connecting area, the airfoil section of the semi-annular tail fin remains consistent along the arc-shaped extension path.

8. The semi-annular tail fin as described in claim 1, characterized in that, The trailing edge of the semi-circular tail fin is provided with at least three independent deflection control surfaces, each of which is electrically controlled by an actuator.

9. The semi-annular tail fin as described in claim 8, characterized in that, The control surfaces include a central control surface and two lateral control surfaces, which are distributed circumferentially along the trailing edge of the semi-circular tail fin.

10. The semi-annular tail fin as described in claim 9, characterized in that, The central control surface is symmetrically arranged along the longitudinal axis of the aircraft, and the lateral control surfaces are symmetrically arranged on both sides of the central control surface in an inclined manner.

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