Patent Description:
As a conventional compound helicopter, a rotary wing aircraft of PTL <NUM> is known. The rotary wing aircraft includes a body, a main rotor, a pair of propellers for propulsion, and a stabilizer. The main rotor is arranged on the body. The pair of propellers for propulsion are arranged at both sides of the body. The stabilizer is arranged at a rear end of the body. Each of the propellers for propulsion includes blades, and a flap is disposed at the stabilizer.

According to the rotary wing aircraft of PTL <NUM>, the pair of propellers for propulsion and the flap are adjusted for flight stabilization. However, PTL <NUM> does not describe the improvement of a flight efficiency by the propellers for propulsion.

The present disclosure was made to solve the above problem, and an object of the present disclosure is to provide a compound helicopter whose flight efficiency is improved. <CIT> discloses a rotorcraft having a fuselage surmounted by a main rotor. The rotorcraft has a first propeller and a second propeller driven in rotation respectively about a first secondary axis of rotation and a second secondary axis of rotation. A mobility system turns the second propeller relative to the fuselage, the mobility system turning the second secondary axis of rotation relative to the fuselage from a first position where the second propeller exerts thrust in a first direction to a second position where the second propeller exerts thrust in a second direction opposite to the first direction.

A compound helicopter according to the appended claims.

A compound helicopter <NUM> according to Embodiment <NUM> is an aircraft including components that generate propulsive force in addition to components that generate lift force. As shown in <FIG>, the compound helicopter <NUM> includes a body <NUM>, a main wing <NUM>, a main rotor <NUM>, a pair of propellers <NUM> and <NUM> that are different in specifications from each other, a landing gear <NUM>, an empennage <NUM>, and a controller <NUM>.

The main rotor <NUM> and the landing gear <NUM> are arranged so as to sandwich the body <NUM> in an upper-lower direction. A side of the landing gear <NUM> which side is closer to the main rotor <NUM> is referred to as an upper side, and its opposite side is referred to as a lower side. Moreover, the first propeller <NUM> and the second propeller <NUM> are arranged so as to sandwich the body <NUM> in a left-right direction. The first propeller <NUM> is arranged at a right side of the main wing <NUM> in a proceeding direction, and the second propeller <NUM> is arranged at a left side of the main wing <NUM> in the proceeding direction. As described below, when the proceeding direction is regarded as positive, the first propeller <NUM> generates only positive thrust, and the second propeller <NUM> generates positive thrust and negative thrust. Therefore, the first propeller <NUM> and the second propeller <NUM> are different in specifications from each other. In the following description, the "positive thrust" is also referred to as "forward thrust," and the "negative thrust" is also referred to as "backward thrust.

The body <NUM> extends from a nose <NUM> toward a tail <NUM> in an aircraft axis direction. When a plane is defined as a virtual symmetry plane VP, that is orthogonal to the left-right direction at a middle point of the body <NUM> in the left-right direction, the body <NUM> has a shape symmetrical with respect to the virtual symmetry plane VP. The shape of the body <NUM> may be, for example, a prolate spheroid that is long in a front-rear direction or may not be symmetrical with respect to the virtual symmetry plane VP.

A main driving structure <NUM> that rotates the main rotor <NUM> is arranged at an upper portion of the body <NUM>. The main driving structure <NUM> includes, for example, a prime mover, such as an engine.

The main rotor <NUM> includes a main rotor rotating shaft <NUM> and four main rotor blades <NUM> and generates lift force. The main rotor rotating shaft <NUM> is arranged at a middle of the body <NUM> in the left-right direction and at or in front of a middle of the body <NUM> in the front-rear direction. The main rotor rotating shaft <NUM> includes a lower end attached to an output portion of the main driving structure <NUM> and extends in a vertical direction. The main rotor rotating shaft <NUM> may be a tilt rotor that is inclined relative to the upper-lower direction.

Each main rotor blade <NUM> is, for example, a rectangular elongated member and includes one end portion connected to the main rotor rotating shaft <NUM>. The main rotor blades <NUM> are arranged at regular intervals in a circumferential direction about the main rotor rotating shaft <NUM> and extend radially from the main rotor rotating shaft <NUM>.

An output of the main driving structure <NUM> is transmitted to the main rotor blades <NUM>, through the main rotor rotating shaft <NUM>, to rotate the main rotor blades <NUM> about the main rotor rotating shaft <NUM>. Pitch angles of the main rotor blades <NUM> may be controlled such that the lift force generated by the main rotor <NUM> becomes maximum.

The main wing <NUM> includes a first main wing portion <NUM> and a second main wing portion <NUM>, and generates lift force during forward flight. The first main wing portion <NUM> extends from the right side in a proceeding-direction of the body <NUM>, and the second main wing portion <NUM> extends from the left side in a proceeding-direction of the body <NUM>. The first main wing portion <NUM> and the second main wing portion <NUM> are formed symmetrical with respect to the virtual symmetry plane VP, and extend in respective directions intersecting with (for example, orthogonal to) the virtual symmetry plane VP.

Each of the main wing portions <NUM> and <NUM> includes a wing root <NUM> and a wing tip <NUM>, and the wing root <NUM> is connected to the body <NUM>. For example, in a top view, each of the main wing portions <NUM> and <NUM> has such a trapezoidal shape that a dimension of the wing root <NUM> in the front-rear direction is larger than a dimension of the wing tip <NUM> in the front-rear direction.

The first propeller <NUM> that generates propulsive force and a first driving structure <NUM> that rotates the first propeller <NUM> are disposed at the wing tip <NUM> of the first main wing portion <NUM>. The second propeller <NUM> that generates propulsive force and a second driving structure <NUM> that rotates the second propeller <NUM> are disposed at the wing tip <NUM> of the second main wing portion <NUM>. The first driving structure <NUM> and the second driving structure <NUM> are driven by, for example, a drive shaft connected to the main driving structure <NUM>. The first propeller <NUM> includes a first rotating shaft <NUM> and four first propeller blades <NUM>. The second propeller <NUM> includes a second rotating shaft <NUM> and four second propeller blades <NUM>.

The first rotating shaft <NUM> and the second rotating shaft <NUM> extend in a direction parallel to the aircraft axis direction. A rear end portion of the first rotating shaft <NUM> is attached to an output portion of the first driving structure <NUM>, and a rear end portion of the second rotating shaft <NUM> is attached to an output portion of the second driving structure <NUM>. With this, the rotating shaft <NUM> rotates by the driving structure <NUM> at, for example, a fixed speed, and the rotating shaft <NUM> rotates by the driving structure <NUM> at, for example, a fixed speed.

The first propeller blades <NUM> are attached to a front end portion of the first rotating shaft <NUM> and arranged at regular intervals in the circumferential direction about the first rotating shaft <NUM>. The second propeller blades <NUM> are attached to a front end portion of the second rotating shaft <NUM> and arranged at regular intervals in the circumferential direction about the second rotating shaft <NUM>. Each of the front end portion of the rotating shaft <NUM>, to which the propeller blades <NUM> are attached, and the front end portion of the rotating shaft <NUM>, to which the propeller blades <NUM> are attached, has a pyramid shape, such as a cone shape, which projects forward.

The propeller blades <NUM> rotate about the rotating shaft <NUM>, and the propeller blades <NUM> rotate about the rotating shaft <NUM>. At this time, the first propeller blade <NUM> rotates counterclockwise at a fixed speed v, and the second propeller blade <NUM> rotates clockwise at the fixed speed v. As above, the first propeller blade <NUM> and the second propeller blade <NUM> rotate in respective directions opposite to each other at the same rotational speed.

A first pitch variable structure <NUM>, that varies the pitch angles of the first propeller blades <NUM>, is disposed at a portion to which the first propeller blades <NUM> are attached. Similarly, a second pitch variable structure <NUM>, that varies the pitch angles of the second propeller blades <NUM>, is disposed at a portion to which the second propeller blades <NUM> are attached. The direction and magnitude of propulsive force generated by each propeller blade <NUM> and the direction and magnitude of propulsive force generated by each propeller blade <NUM> are controlled by changing the pitch angles.

Specifically, the first pitch variable structure <NUM> sets the first propeller blade <NUM> to the positive pitch angle to make the first propeller blade <NUM> generate forward thrust (positive thrust). On the other hand, the second pitch variable structure <NUM> sets the second propeller blade <NUM> to the positive or negative pitch angle in accordance with a flight state, to make the second propeller blade <NUM> generate forward thrust (positive thrust) or backward thrust (negative thrust).

For example, the first and second propeller blades <NUM> and <NUM> are smaller than the main rotor blades <NUM>, are rectangular, and extend radially from the respective rotating shafts <NUM> and <NUM>. Each propeller blade <NUM> includes a base end portion 53a and a tip portion 53b at both end portions thereof in a longitudinal direction. Each propeller blade <NUM> includes a base end portion 63a and a tip portion 63b at both end portions thereof in the longitudinal direction. The base end portions 53a of the propeller blades <NUM> are connected to the rotating shaft <NUM>, and the base end portions 63a of the propeller blades <NUM> are connected to the rotating shaft <NUM>.

As shown in <FIG>, <FIG>, each first propeller blade <NUM> includes a leading edge 53c and a trailing edge 53d, and each second propeller blade <NUM> includes a leading edge 63c and a trailing edge 63d. The leading edge 53c is connected to one end of the base end portion 53a and one end of the tip portion 53b, and the leading edge 63c is connected to one end of the base end portion 63a and one end of the tip portion 63b. The trailing edge 53d is connected to the other end of the base end portion 53a and the other end of the tip portion 53b, and the trailing edge 63d is connected to the other end of the base end portion 63a and the other end of the tip portion 63b.

For example, a blade section of the first propeller blade <NUM> has a round shape at the leading edge 53c and a sharp shape at the trailing edge 53d, and a thickness of the first propeller blade <NUM> is larger at the leading edge 53c than at the trailing edge 53d. For example, a blade section of the second propeller blade <NUM> has a round shape at the leading edge 63c and a sharp shape at the trailing edge 63d, and a thickness of the second propeller blade <NUM> is larger at the leading edge 63c than at the trailing edge 63d.

An angle of attack of the first propeller blade <NUM> decreases from the base end portion 53a to the tip portion 53b, i.e., is designed as washout. An angle of attack of the second propeller blade <NUM> decreases from the base end portion 63a to the tip portion 63b, i.e., is designed as washout.

A washout angle, that is a difference between an angle of incidence of the base end portion 53a of the first propeller blade <NUM> and an angle of incidence of the tip portion 53b of the first propeller blade <NUM>, is an acute angle between a chord line 53a1 of the base end portion 53a and a chord line 53b1 of the tip portion 53b and is, for example, <NUM> degrees or more and <NUM> degrees or less. Moreover, a washout angle that is a difference between an angle of incidence of the base end portion 63a of the second propeller blade <NUM> and an angle of incidence of the tip portion 63b of the second propeller blade <NUM> is an acute angle between a chord line 63a1 of the base end portion 63a and a chord line 63b1 of the tip portion 63b and is, for example, <NUM> degrees or more and <NUM> degrees or less. The chord line 53a1 is a line connecting the leading edge 53c and the trailing edge 53d at the base end portion 53a. The chord line 53b1 is a line connecting the leading edge 53c and the trailing edge 53d at the tip portion 53b. The chord line 63a1 is a line connecting the leading edge 63c and the trailing edge 63d at the base end portion 63a. The chord line 63b1 is a line connecting the leading edge 63c and the trailing edge 63d at the tip portion 63b.

Specifications of the first propeller <NUM> are different form specifications of the second propeller <NUM>. Specifically, the specifications are set such that the negative thrust generated by the second propeller <NUM> is larger than the negative thrust generated the first propeller <NUM> under conditions that: the main rotor <NUM> rotates counterclockwise; the pitch angles of the first propeller blades <NUM> and the pitch angles of the second propeller blades <NUM> are set to the negative pitch angles; and the first propeller blades <NUM> and the second propeller blades <NUM> rotate at the same rotational speed. Moreover, the specifications are set such that a difference between an absolute value of thrust generated when the main rotor <NUM> rotates counterclockwise, the pitch angles of the first propeller blades <NUM> and the pitch angles of the second propeller blades <NUM> are set to the positive pitch angles, and the first propeller blades <NUM> and the second propeller blades <NUM> rotate at the same rotational speed and an absolute value of thrust generated when the pitch angles of the first propeller blades <NUM> and the pitch angles of the second propeller blades <NUM> are set to the negative pitch angles, and the first propeller blades <NUM> and the second propeller blades <NUM> rotate at the same rotational speed is smaller in the second propeller <NUM> than in the first propeller <NUM>. For example, in the present embodiment, a washout angle θ2 of the second propeller blade <NUM> is smaller than a washout angle θ1 of the first propeller blade <NUM>.

The empennage <NUM> includes a vertical stabilizer <NUM> and a horizontal stabilizer <NUM> and has a T shape disposed at the tail <NUM> of the body <NUM>. When the main rotor <NUM> rotates counterclockwise, the vertical stabilizer <NUM> generates lift force acting toward the right side in a proceeding-direction.

The landing gear <NUM> is disposed at a lower portion of the body <NUM>. For example, a landing foot, such as a skid, is used as the landing gear <NUM>. The landing gear <NUM> is an apparatus that receives impact and supports the body <NUM> and the like, when the compound helicopter <NUM> lands on the ground.

The controller <NUM> is a calculation processing unit, such as a processor, which is arranged in the body <NUM> and controls respective components of the compound helicopter <NUM> for flight. The controller <NUM> controls the respective components, such as the main driving structure <NUM> and the pitch variable structures <NUM> and <NUM>, based on outputs from a maneuvering device, various sensors, and the like.

The functionality of the elements disclosed herein may be implemented using circuitry or processing circuitry which includes general purpose processors, special purpose processors, integrated circuits, ASICs ("Application Specific Integrated Circuits"), conventional circuitry and/or combinations thereof which are configured or programmed to perform the disclosed functionality. Processors are considered processing circuitry or circuitry as they include transistors and other circuitry therein. In the disclosure, the circuitry, units, or means are hardware that carry out or are programmed to perform the recited functionality. The hardware may be any hardware disclosed herein or otherwise known which is programmed or configured to carry out the recited functionality. When the hardware is a processor which may be considered a type of circuitry, the circuitry, means, or units are a combination of hardware and software, the software being used to configure the hardware and/or processor.

<FIG> is a diagram schematically showing forces generated during the flight of the compound helicopter <NUM> and shows propulsive force and some forces which contribute to yaw rotation of an airframe.

In a top view, the main rotor <NUM> rotates counterclockwise during the flight of the compound helicopter <NUM>. Therefore, in a top view, each main rotor blade <NUM> rotates about the main rotor rotating shaft <NUM> from the tail <NUM> side (rear side) of the body <NUM> through the first main wing portion <NUM> side (right side) to the nose <NUM> side (front side) of the body <NUM>.

During the flight of the compound helicopter <NUM>, each of the first propeller <NUM> and the second propeller <NUM> rotates at a fixed speed in a fixed direction. The first propeller <NUM> and the second propeller <NUM> rotate in respective directions opposite to each other. For example, in a front view, the first propeller <NUM> rotates counterclockwise, and the second propeller <NUM> rotates clockwise.

During the hovering of the compound helicopter <NUM>, a forward speed is <NUM> kt (<NUM>/ s), and the compound helicopter <NUM> stands still in the air. At this time, the rotational torque of the main rotor <NUM> becomes high so that the lift force corresponding to the weight of the airframe itself is generated by the rotation of the main rotor <NUM>. By this rotational torque, the body <NUM> receives a moment M0 acting in a direction (clockwise) opposite to the rotational direction of the main rotor <NUM>. The moment M0 increases as the rotational torque increases.

To cancel the rotational torque of the main rotor <NUM>, forward thrust (positive thrust) F0 is generated by the first propeller <NUM>, and backward thrust (negative thrust) S0 is generated by the second propeller <NUM>. Specifically, the first pitch variable structure <NUM> adjusts each first propeller blade <NUM> to the positive pitch angle, and the second pitch variable structure <NUM> adjusts each second propeller blade <NUM> to the negative pitch angle. Then, the moment M0 is canceled by the positive thrust F0 and the negative thrust S0. Thus, the compound helicopter <NUM> maintains its posture without rotating in a yaw direction. Moreover, the negative thrust S0 is equal to or substantially equal to the positive thrust F0, and therefore, the compound helicopter <NUM> does not move in the front-rear direction.

To make the compound helicopter <NUM> perform forward flight at low speed (for example, <NUM> kt, ca. <NUM>/s) from the hovering state, the positive thrust of the first propeller <NUM> is increased from F0 to F1.

By this forward flight, the lift force is generated by the main wing <NUM>, and the contribution of the lift force generated by the main rotor <NUM> decreases. Thus, the rotational torque of the main rotor <NUM> decreases. Therefore, a moment M1 of the body <NUM>, which is a reaction of the rotational torque, becomes smaller than the moment M0. With this, the negative thrust of the second propeller <NUM>, that is generated to cancel the rotational torque of the main rotor <NUM>, decreases from S0 to S1. Moreover, a lift force R1 acting toward the right side is generated at the vertical stabilizer <NUM> by the forward flight.

The moment M1 is canceled by the lift force R1 generated by the vertical stabilizer <NUM>, the positive thrust F1, and the negative thrust S1. Thus, the compound helicopter <NUM> maintains its posture without rotating in the yaw direction. Moreover, the positive thrust F1 is larger than the negative thrust S1, and therefore, forward thrust T1 is given to the compound helicopter <NUM>. Thus, the compound helicopter <NUM> moves forward.

As above, the first propeller <NUM> generates the positive thrust, and the second propeller <NUM> generates the negative thrust, during the low-speed flight that is an initial stage of the forward flight from the hovering state.

To increase the forward speed of the compound helicopter <NUM> to <NUM> kt (ca. <NUM>/s), the positive
thrust of the first propeller <NUM> is increased from F1 to F2. At this time, the second pitch variable structure <NUM> changes the pitch angle of the second propeller blade <NUM> from the negative pitch angle to the positive pitch angle to make the second propeller <NUM> generate positive thrust S2. With this, the thrust F2 of the first propeller <NUM> and the thrust S2 of the second propeller <NUM> are used as the forward thrust, and the compound helicopter <NUM> moves forward while increasing its speed by the positive thrust T2.

By this speed increase, the lift force generated by the main wing <NUM> further increases. With this, the moment of the body <NUM> decreases to M2. Moreover, the lift force of the vertical stabilizer <NUM> increases from R1 to R2. The moment M2 is canceled by the lift force R2, the positive thrust F2, and the positive thrust S2. Thus, the compound helicopter <NUM> maintains its posture without rotating in the yaw direction.

Then, the forward speed of the compound helicopter <NUM> further increases and becomes, for example, <NUM> kt (ca. To increase the propulsive force in the forward direction, the positive thrust of the first propeller <NUM> increases from F2 to F3, and the positive thrust of the second propeller <NUM> increases from S2 to S3. The positive thrust of the compound helicopter <NUM> increases to T3 that is the sum of the positive thrust F3 and the positive thrust S3. Thus, the compound helicopter <NUM> moves forward at high speed. The positive thrust S3 is equal to or substantially equal to the positive thrust F3.

The moment of the body <NUM> decreases to M3 in accordance with a further increase in the lift force generated by the main wing <NUM>, the further increase being caused by the speed increase. Moreover, the lift force of the vertical stabilizer <NUM> increases to R3. The moment M3 is canceled by the lift force R3. Thus, the compound helicopter <NUM> maintains its posture without rotating in the yaw direction.

As above, both the first propeller <NUM> and the second propeller <NUM> generate the positive thrust, during the forward flight after the low-speed flight.

To change the thrust of the first propeller <NUM>, the thrust of the second propeller <NUM>, and the direction of the thrust in accordance with the flight state, such as the hovering, the low-speed forward flight, or the high-speed forward flight, appropriate washout angles of the first and second propeller blades <NUM> and <NUM> are set.

<FIG> is a graph showing efficiencies of the propellers during the hovering of the compound helicopter <NUM>. <FIG> is a graph showing the efficiencies of the propellers during the high-speed flight (<NUM> kt, ca. <NUM>/s) of the compound helicopter <NUM>. In each graph, a horizontal axis represents the washout angles of the propeller blades <NUM> and <NUM>, and a vertical axis represents required horsepower of rotating each propeller to generate thrust required in each flight state.

In each graph, a line passing through square dots represents a relation between the required horsepower of the first propeller <NUM> and the washout angle θ1 of the first propeller blade <NUM>. A line passing through triangle dots represents a relation between a sum of the required horsepower of the first propeller <NUM> and the required horsepower of the second propeller <NUM>, and the washout angle θ2 of the second propeller blade <NUM>. A thick line represents a propeller horsepower upper limit (i.e., a value obtained by subtracting required horsepower of rotating the main rotor <NUM>, from a horsepower upper limit of the main driving structure <NUM>).

The scales of the vertical axes of <FIG> are not necessarily equal to each other. Moreover, when the compound helicopter <NUM> moves forward, the main driving structure <NUM> is air-cooled. Therefore, the propeller horsepower upper limit during the high-speed flight of <FIG> is larger than the propeller horsepower upper limit during the hovering of <FIG>.

The first propeller <NUM> generates the positive thrust regardless of the flight state. Therefore, as shown in <FIG>, the required horsepower does not significantly change regardless of the washout angle, but the required horsepower of the first propeller <NUM> decreases as the washout angle θ1 of the first propeller blade <NUM> increases. In this case, when the washout angle θ1 is <NUM> degrees, the required horsepower of the first propeller <NUM> becomes minimum. Therefore, a thrust efficiency of the first propeller <NUM> improves as the washout angle θ1 increases (for example, as the washout angle θ1 approaches <NUM> degrees).

On the other hand, the direction of the thrust of the second propeller <NUM> changes in accordance with the speed of the compound helicopter <NUM>. The second propeller <NUM> generates the negative thrust during the hovering and the low-speed flight that is the initial stage of the forward flight, and generates the positive thrust during the high-speed flight. Therefore, as shown in <FIG>, the required horsepower of the second propeller <NUM> significantly changes by the washout angle θ2. The tendency of the change in the required horsepower of the second propeller <NUM> differs between during the hovering of <FIG> and during the high-speed flight of <FIG>. Therefore, the washout angle θ2 of the second propeller <NUM> is set to a value which is smaller than the propeller horsepower upper limit and by which both the required horsepower during the hovering and the required horsepower during the high-speed flight become small.

For example, as shown in <FIG>, as with the first propeller <NUM>, during the high-speed flight, the required horsepower of the second propeller <NUM> decreases as the washout angle θ2 of the second propeller blade <NUM> increases. Therefore, as the washout angle θ2 increases (for example, the washout angle θ2 approaches <NUM> degrees), the thrust efficiency of the second propeller <NUM> improves.

On the other hand, as shown in <FIG>, during the hovering, as the washout angle θ2 of the second propeller blade <NUM> decreases, the required horsepower of the second propeller <NUM> decreases. Therefore, as the washout angle θ2 decreases, the thrust efficiency of the second propeller <NUM> improves.

As above, as shown in <FIG>, the upper limit of the washout angle θ2 is, for example, <NUM> degrees that is a value at which the sum of the required horsepower of the first propeller <NUM> and the required horsepower of the second propeller <NUM> and the propeller horsepower upper limit coincide with each other. As shown in <FIG>, the lower limit of the washout angle θ2 is, for example, <NUM> degrees that is a value at which the sum of the required horsepower of the first propeller <NUM> and the required horsepower of the second propeller <NUM> and the propeller horsepower upper limit coincide with each other. Within this range, the washout angle θ2 is set to, for example, <NUM> degrees in consideration of a margin.

As above, the required thrust of the first propeller <NUM>, the required thrust of the second propeller <NUM>, and the direction of the thrust change in accordance with the flight state, such as the hovering, the low-speed flight, or the high-speed flight. Therefore, the specifications of the left propeller and the specifications of the right propeller do not have to be the same as each other, and the propellers most suitable for the compound helicopter can be realized.

Specifically, the second propeller <NUM> generates the negative thrust during the hovering and the low-speed flight that is the initial stage of the forward flight, and generates the positive thrust after the low-speed flight. On the other hand, the first propeller <NUM> generates the positive thrust regardless of the flight state.

The propeller specifications are set by, for example, adjusting the washout angles of the propeller blades. The washout angle θ2 of the second propeller blade <NUM> is smaller than the washout angle θ1 of the first propeller blade <NUM>. With this, if the first propeller blades <NUM> and the second propeller blades <NUM> rotate at the same rotational speed and the same negative pitch angle, the negative thrust of the second propeller blade <NUM> is larger than the negative thrust of the first propeller blade <NUM>.

Moreover, if the first propeller blades <NUM> and the second propeller blades <NUM> rotate at the same rotational speed and the same positive pitch angle, i.e., an angle +β, the first propeller blades <NUM> generate positive thrust +Fp, and the second propeller blades <NUM> generate positive thrust +Sp. Furthermore, if the first propeller blades <NUM> and the second propeller blades <NUM> rotate at the same rotational speed and the same negative pitch angle, i.e., an angle -β, the first propeller blades <NUM> generate negative thrust -Fm, and the second propeller blades <NUM> generate negative thrust -Sm.

At this time, when the washout angle is <NUM> degree and an absolute value of the positive pitch angle and an absolute value of the negative pitch angle are equal to each other, an absolute value of the positive thrust generated at the positive pitch angle and an absolute value of the negative thrust generated at the negative pitch angle become equal to each other. Moreover, when the absolute value of the positive pitch angle and the absolute value of the negative pitch angle are equal to each other, the absolute value of the positive thrust is larger than the absolute value of the negative thrust as the washout angle increases. In this case, a difference (Sp - Sm) between the absolute values of the thrusts of the second propeller blade <NUM> is smaller than a difference (Fp - Fm) between the absolute values of the thrusts of the first propeller blade <NUM>.

Therefore, the first propeller blade <NUM> is formed in a shape suitable for the generation of the positive thrust. On the other hand, the second propeller blade <NUM> is formed in a shape which suppresses a decrease in efficiency for the positive thrust and the negative thrust. Therefore, a flight efficiency of the compound helicopter <NUM> improves.

Moreover, by the thrust of the first propeller <NUM> and the thrust of the second propeller <NUM>, the compound helicopter <NUM> is increased in speed, and the movement of the compound helicopter <NUM> in the yaw direction can be controlled.

In the compound helicopter <NUM> according to Embodiment <NUM>, the most suitable propellers are realized by making the washout angles of the first propeller <NUM> and the second propeller <NUM> different from each other among the specifications of the propellers. On the other hand, in the compound helicopter <NUM> according to Embodiment <NUM>, as shown in <FIG>, the blade sectional shapes of a first propeller blade <NUM> and a second propeller blade <NUM> are made different from each other.

A camber of the second propeller blade <NUM> is smaller than a camber of the first propeller blade <NUM>. The camber of the first propeller blade <NUM> is a difference between a camber line 153f and a chord line <NUM>. The camber line 153f is a center line of a thickness of the sectional shape of the first propeller blade <NUM>, and the chord line <NUM> is a straight line connecting leading and trailing edges of the first propeller blade <NUM>. The camber of the second propeller blade <NUM> is a difference between a camber line 163f and a chord line <NUM>. The camber line 163f is a center line of a thickness of the sectional shape of the second propeller blade <NUM>, and the chord line <NUM> is a straight line connecting leading and trailing edges of the second propeller blade <NUM>. For example, as shown in <FIG>, the first propeller blade <NUM> is a camber blade whose camber is larger than zero. As shown in <FIG>, the second propeller blade <NUM> is a symmetric blade whose camber is zero. The propeller blades <NUM> and <NUM> are not designed as washout.

An external form line 153e is a line representing the shape of a section orthogonal to a longitudinal direction of the propeller blade <NUM>, and an external form line 163e is a line representing the shape of a section orthogonal to a longitudinal direction of the propeller blade <NUM>. The center line 153f is a line passing through a center between parts of the external form line 153e which parts are located at upper and lower sides of the chord line <NUM> that is the straight line connecting a leading edge 153c and a trailing edge 153d, and the center line 163f is a line passing through a center between parts of the external form line 163e which parts are located at upper and lower sides of the chord line <NUM> that is the straight line connecting a leading edge 163c and a trailing edge 163d.

In the first propeller blade <NUM>, the center line 153f is located above the chord line <NUM>, and a camber <NUM> is larger than zero. In this case, the first propeller blade <NUM> easily generates the positive thrust because the first propeller blade <NUM> is curved toward one side from the chord line <NUM>.

In the second propeller blade <NUM>, the center line 163f coincides with the chord line <NUM>, and the camber is zero. As above, the second propeller blade <NUM> easily generates both the positive thrust and the negative thrust because the second propeller blade <NUM> has a symmetrical shape with respect to the chord line <NUM>.

Therefore, if the first propeller <NUM> and the second propeller <NUM> rotate at the same rotational speed and the same negative pitch angle, the negative thrust generated by the second propeller <NUM> becomes larger than the negative thrust generated by the first propeller <NUM>. Thus, the flight efficiency of the compound helicopter <NUM> can be improved.

As with Embodiment <NUM>, in Embodiment <NUM>, the propeller blade <NUM> may have the washout angle θ1, and the propeller blade <NUM> may have the washout angle θ2. To be specific, the second propeller blade <NUM> as the symmetric blade and the first propeller blade <NUM> as the camber blade are designed as washout, and the washout angle θ2 of the second propeller blade <NUM> is smaller than the washout angle θ1 of the first propeller blade <NUM>.

In all of the above embodiments, except for the differences regarding the washout and the sectional shape, the shape of the first propeller blade <NUM> and the shape of the second propeller blade <NUM> may be the same as each other or may be different from each other. For example, the specifications of the propellers may be set such that a planar shape surrounded by a base end portion 153a, a tip portion 153b, the leading edge 153c, and the trailing edge 153d in the first propeller blade <NUM> and a planar shape surrounded by a base end portion 163a, a tip portion 163b, the leading edge 163c, and the trailing edge 163d in the second propeller blade <NUM> are made different from each other.

Moreover, in each of the embodiments, the rotational frequency of the first propeller <NUM> and the rotational frequency of the second propeller <NUM> are the same as each other. However, the rotational frequency of the first propeller <NUM> and the rotational frequency of the second propeller <NUM> may be different from each other such that the thrust and the direction of the thrust which correspond to the flight state are realized.

In all of the above embodiments, the first propeller <NUM> and the first driving structure <NUM> are attached to the first main wing portion <NUM>, and the second propeller <NUM> and the second driving structure <NUM> are attached to the second main wing portion <NUM>. However, the position of the first propeller <NUM> and the position of the second propeller <NUM> are not limited to these as long as the first propeller <NUM> is disposed at one side of the body <NUM>, and the second propeller <NUM> is disposed at the other side of the body <NUM>. For example, the first propeller <NUM> and the first driving structure <NUM> may be attached to one side of the body <NUM>, and the second propeller <NUM> and the second driving structure <NUM> may be attached to the other side of the body <NUM>.

The angle of attack of the first propeller blade <NUM> decreases from the base end portion 53a toward the tip portion 53b, i.e., is designed as washout, but is not limited to this. Moreover, the angle of attack of the second propeller blade <NUM> decreases from the base end portion 63a toward the tip portion 63b, i.e., is designed as washout, but is not limited to this. The angle of attack of each propeller blade may increase from the base end portion toward the tip portion, i.e., is designed as negative washout (wash-in).

The above embodiments may be combined with each other as long as they do not exclude each other. From the foregoing explanation, many modifications and other embodiments of the present disclosure are obvious to one skilled in the art. Therefore, the foregoing explanation should be interpreted only as an example and is provided for the purpose of teaching the best mode for carrying out the present disclosure to one skilled in the art.

Claim 1:
A compound helicopter (<NUM>) comprising:
a body (<NUM>);
a first main wing portion (<NUM>) extending from the body toward a right side in a proceeding direction of the body;
a second main wing portion (<NUM>) extending from the body toward a left side in the proceeding direction of the body;
a main rotor (<NUM>) disposed at an upper side of the body;
a first propeller (<NUM>) that is disposed at the first main wing portion and generates positive thrust when the proceeding direction is regarded as positive; and
a second propeller (<NUM>) that is disposed at the second main wing portion and generates positive thrust and negative thrust, wherein
the first propeller includes a first propeller blade (<NUM>) that is a propeller blade whose rotation axis extends in a direction parallel to an axis of the compound helicopter; and
the second propeller includes a second propeller blade (<NUM>) that is a propeller blade whose rotation axis extends in a direction parallel to the axis of the compound helicopter;
wherein
specifications of the first propeller (<NUM>) are different from specifications of the second propeller (<NUM>), and
characterized in that the specifications of the first propeller and the second propeller include at least one of: a washout angle (θ) corresponding to a change in an angle of attack from a base end (53a, 63a) of each propeller blade to a tip (53b, 63b) thereof; a blade sectional shape of each propeller blade (<NUM>, <NUM>); or a planar shape of each propeller blade.