FIELD OF THE INVENTION

The invention relates to the field of flapping wing aerial vehicles, and more specifically to attitude control mechanisms for flapping wing aerial vehicles.

BACKGROUND OF THE INVENTION

A flapping wing aerial vehicle, FWAV, with a first and a second wing, and with flapping mechanisms directly coupled to the leading edge spars of those wings is known from WO 2018/217079 A1 for which a first, second and third attitude control mechanism provide separate pitch, yaw and roll control, respectively. In this known solution, the pitch control mechanism relies on a mechanically synchronized dihedral control of the wings exerted on the leading edge spars, whereas yaw control is achieved by means of a separate mechanism deflecting a wing root bar coupled to root spars which are in turn coupled to the respective wings. The roll control moment is generated by effecting different flapping motions of the respective first and second wings through control of the flapping mechanisms that are coupled with the leading edge spars.

Disadvantageously, the solution known from WO 2018/217079 A1 discloses separate mechanisms to be able to exert attitude control around three different axes, which leads to a complex, and possibly heavy, inflexible mechanical design that may hinder the implementation options for smaller sized flapping wing aerial vehicles, such as micro or nano flapping wing aerial vehicles. It is a further disadvantage that the control options for the wings within the dihedral plane are limited to particular wing positions, while excluding other positions.

US 2014/0319267 A1 discloses a micro aerial vehicle capable of controlled transitory or sustained gliding flight. The vehicle includes a fuselage. A pair of articulated wings are forward of a center of gravity of the vehicle, the wings being articulated and having trailing edge flaps, and having actuators for controlling the dihedral angles of the wings and the flaps for effective yaw control across the flight envelope. The dihedral angles can be varied symmetrically on both wings to control the aircraft speed independently of the angle of attack and flight-path angle, while an asymmetric dihedral setting can be used to control yaw and the actuators control the dihedral settings of each wing independently. The aircraft lacks a vertical tail or other vertical stabilizer.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved flapping wing aerial vehicle. More specifically, it is an object of the invention to provide a wider spectrum of attitude control options for a flapping wing aerial vehicle, whilst simplifying the mechanical design of the flapping wing aerial vehicle.

To better address one or more of these concerns, in a first aspect of the invention a flapping wing aerial vehicle is provided, for which an imaginary right-hand sided axis system comprising an X-axis, a Y-axis, and a Z-axis is defined. The flapping wing aerial vehicle comprising: a first wing and a second wing, the second wing being opposite to the first wing, each wing comprising a wing membrane, a root section, a leading edge section, and a trailing edge section; a support structure, to which the wings are coupled; a first flapping mechanism for flapping the first wing, comprising a first leading edge spar and a first flapping actuator , wherein the first leading edge spar is attached to the wing membrane at or near the leading edge section of the first wing, the first flapping actuator being configured to pivot the first leading edge spar with respect to a first flapping pivot axis substantially parallel to the Z-axis for inducing a first flapping motion of the first wing; a second flapping mechanism for flapping the second wing, comprising a second leading edge spar and a second flapping actuator, wherein the second leading edge spar is attached to the wing membrane at or near the leading edge section of the second wing, the second flapping actuator being configured to pivot the second leading edge spar with respect to a second flapping pivot axis substantially parallel to the Z-axis for inducing a second flapping motion of the second wing; an attitude control mechanism for inducing at least one of a yaw moment and a pitch moment, the attitude control mechanism comprising: o a first attitude control arm and a first attitude control actuator, wherein the first attitude control arm is coupled between the support structure and the first flapping mechanism, and wherein the first attitude control actuator is configured to pivot the first attitude control arm with respect to a first attitude control pivot axis substantially parallel to the Z-axis to allow the dihedral angle of the first wing to be varied; and o a second attitude control arm and a second attitude control actuator, wherein the second attitude control arm is coupled between the support structure and the second flapping mechanism, and wherein the second attitude control actuator is configured to pivot the second attitude control arm with respect to a second attitude control pivot axis substantially parallel to the Z-axis to allow the dihedral angle of the second wing to be varied; and an attitude controller for controlling the first attitude control actuator and the second attitude control actuator independently from each other.

As a result, the present invention allows to pivot the first wing and the second wing, coupled to the respective flapping mechanisms, independently from each other. So, advantageously, the dihedral angle of the first wing and the second wing may now, independently from each other, be changed arbitrarily at any time and at any rate within the designs constraints of the FWAV. Thereby the FWAV according to the invention provides a wide spectrum of dihedral angle control positions of the first wing and the second wing.

The first and second leading edge spars may for example be pivotable in the same direction, in independent directions and/or the leading edge spars may be pivoted simultaneously or at different times and/or at pivot rates that are similar or different for the first and second leading edge spars, respectively. The first leading edge spar and second leading edge spar may for example be pivotable in opposite directions simultaneously or independently to induce at least a yawing moment. Additionally, the first leading edge spar and second leading edge spar may be pivotable in the same direction, simultaneously or independently to induce at least a pitching moment. Combinations of these pivot directions, times and rates are also conceivable for the generation of any combination of pitching and/or yawing moments of variable magnitudes.

Furthermore, an FWAV according to the invention may provide the advantage of employing a simple attitude control mechanism having few components, and yet generating a variety of control moments of pitch and yaw around the body axes of the FWAV as it comprises an attitude control mechanism to induce pitch moments of variable magnitudes and directions, and yaw moments of variable magnitudes and directions to the FWAV by tilting/re-aligning and/or displacing the thrust vectors generated by the flapping motion through control of the dihedral angle of the first and second wings, or possibly wing pairs. The reduction in attitude control mechanisms and corresponding mechanical parts leads to a relatively compact and light FWAV.

By providing precise attitude control including pitch, yaw and roll control, an FWAV is provided that can be stably controlled in substantially all flight conditions without the need for a tail structure, i.e. the FWAV according to the invention may be tail-less. This aids in the FWAV being compact, small, light-weight and agile.

The FWAV may for example be a flapping wing micro aerial vehicle, a flapping wing nano aerial vehicle, or any other flapping wing aerial vehicle. For the smaller sized FWAVs a compact and light mechanical design like that of the FWAV according to the invention would be advantageous.

The FWAV according to the invention, in general, is able to perform both vertical and horizontal flight. This horizontal flight may be done with a velocity of up to or more than 4 m/s.

It should be understood by those skilled in the art that it is also possible to make turns, to ascend and descend, and to make other flight manoeuvres besides only flying horizontally and vertically with the disclosed FWAV. Pure horizontal flight and pure vertical flight are not the limiting flight options.

As is the convention in the art, in steady, hovering flight, the positive X-axis of the FWAV points forward. The positive Z-axis points down in this steady, hovering flight condition, and the positive Y-axis then points to the left, completing a right-hand sided axis system.

The axis system is fixed with respect to the FWAV and is tilted when the flapping wing MAV transfers between horizontal and vertical flight, and vice versa. Therefore, some definitions are needed regarding the performed manoeuvres. Within the context of this disclosure, a pitch manoeuvre or moment is defined as a rotation or moment around the Y-axis of the FWAV, a roll manoeuvre or moment is defined as a rotation or moment around the X-axis of the FWAV, and a yaw manoeuvre or moment is defined as a rotation or moment around the Z-axis of the FWAV. This definition is maintained in all possible flight modes.

The FWAV according to the invention comprises at least a first wing and a second wing, the second wing being opposite to the first wing, each wing comprising a wing membrane, a root section, a leading edge section, and a trailing edge section. As such, embodiments are for example conceivable wherein the FWAV comprises a left wing and a right wing. Further embodiments are for example conceivable wherein the FWAV comprises a left wing pair, and a right wing pair, each pair comprising a front wing section and a rear wing section, adjoined near the root section of the respective wing.

It is noted that, where this document refers to a force or a moment, generated by the FWAV, for example a thrust force or a pitch moment, in general a wing cycle averaged force or a wing cycle averaged moment is meant, i.e. the average force or moment that is generated during one cycle of a flapping motion of the wing. An embodiment is conceived comprising more than one, e.g. two, flapping actuators that may be operated at different flapping frequencies. For such an embodiment, the cycle averaged moment or cycle averaged force is defined as the average force or moment generated over the average duration of a wing cycle, measured over multiple wing cycles, e.g. measured over three or more wing cycles.

The FWAV according to the invention further comprises a support structure, to which the wings are directly or indirectly connected. For example, the at least two wings may be adjoined at the support structure, or the at least two wings may be arranged separate from each other, with a spacing between them, each wing having a root spar, which root spar is directly or indirectly connected to the support structure. The support structure may further provide an attachment for one or more actuators, a battery, an attitude controller, a flapping mechanism, and other components. Said components are preferably spread along a length of the support structure to optimize the location of the centre of gravity of the FWAV.

The FWAV according to the invention comprises a first flapping mechanism for flapping the first wing, the first flapping mechanism comprising a first leading edge spar and a first flapping actuator, wherein the first leading edge spar is attached to the wing membrane at or near the leading edge section of the first wing, the first flapping actuator being configured to pivot the first leading edge spar with respect to a first flapping pivot axis substantially parallel to the Z- axis for inducing a first flapping motion of the first wing. The FWAV according to the invention further comprises a second flapping mechanism for flapping the second wing, the second flapping mechanism comprising a second leading edge spar and a second flapping actuator, wherein the second leading edge spar is attached to the wing membrane at or near the leading edge section of the second wing, the second flapping actuator being configured to pivot the second leading edge spar with respect to a second flapping pivot axis substantially parallel to the Z-axis for inducing a second flapping motion of the second wing. Embodiments of the respective flapping mechanisms may comprise at least one electric motor, such as DC or AC electric motor, to drive a gear wheel and linkage transmission coupled to the respective leading edge spars. A direct drive of the respective leading edge spars by associated electric servomotors is also conceivable. The flapping mechanisms may be configured to produce fixed flapping ranges at variable frequencies, to produce variable flapping ranges at fixed frequencies, and/or to produce variable flapping ranges at variable frequencies.

The FWAV according to the invention comprises an attitude control mechanism for inducing at least one of a yaw moment and a pitch moment. The attitude control mechanism comprising a first attitude control arm and a first attitude control actuator, wherein the first attitude control arm is coupled between the support structure and the first flapping mechanism, and wherein the first attitude control actuator is configured to pivot the first attitude control arm with respect to a first attitude control pivot axis substantially parallel to the Z-axis to allow the dihedral angle of the first wing to be varied. The attitude control mechanism further comprises a second attitude control arm and a second attitude control actuator, wherein the second attitude control arm is coupled between the support structure and the second flapping mechanism, and wherein the second attitude control actuator is configured to pivot the second attitude control arm with respect to a second attitude control pivot axis substantially parallel to the Z-axis to allow the dihedral angle of the second wing to be varied. The first attitude actuator may pivot the first attitude control arm independently from the second attitude actuator pivoting the second attitude control arm.

Although the FWAV comprising the present attitude control mechanism that can generate a variety of combinations of pitch and yaw moments may require control inputs that are slightly more complex to generate, the overall complexity of the mechanical design of the FWAV may be reduced, as well as the weight and/or the part count of the FWAV. The FWAV according to the invention comprises an attitude controller for controlling the first attitude control actuator and the second attitude control actuator independently from each other.

In an embodiment, the flapping wing aerial vehicle further comprises a wing root structure mounted to the support structure, wherein the wing root structure is coupled to a first wing root spar attached to the first wing at or near the root section thereof, and coupled to a second wing root spar attached to the second wing at or near the root section thereof.

In an embodiment, the wing root structure may be mounted fixedly to the support structure, i.e. the wing root structure is coupled to the first wing root spar at a predetermined location within the YZ-plane spaced from the Z-axis, and the wing root structure is coupled to the second wing root spar at a predetermined location in the YZ-plane spaced from the Z-axis. The wing root structure may e.g. comprise a bar having opposite ends being coupled to the first and second wing root spars. The coupling may be flexible to allow a pivoting of the first and second wing root spars when varying the dihedral angle of the first and second wings, respectively. In such an embodiment, the combination of the wing root structure and the support structure may provide a high stiffness of the FWAV. This simple mechanical structure may lead to a centre of gravity lying relatively high, which results in a relatively low moment of inertia and thus in relatively high agility.

In a further embodiment of the FWAV, the wing root structure is coupled to the first wing root spar at a location along the chord of the first wing between at or near the trailing edge section of the first wing and the middle of the first wing chord, and wherein the wing root structure is coupled to the second wing root spar at a location along the chord of the second wing between at or near the trailing edge section of the second wing and the middle of the second wing chord. The location of the coupling between the wing root structure and the first and second wing root spars advantageously may be selected to produce a desired wing membrane position, tension or behaviour.

In a further embodiment, the wing root structure is coupled to the first wing root spar spaced from the Z-axis, and the wing root structure is coupled to the second wing root spar spaced from the Z-axis, wherein the attitude control mechanism further comprises at least one wing root actuator coupled to the first and second wing root spars, and wherein the wing root actuator is configured to deflect the wing root spars with respect to the YZ-plane. Advantageously, the actuation of the wing root structure further increases attitude control options for yaw and pitch, providing more nuanced and possibly stronger yaw and pitch moments.

In a practical embodiment, the first flapping axis lies further outward from the Z-axis than the first attitude control pivot axis, and wherein the second flapping axis lies further outward from the Z- axis than the second attitude control pivot axis. This non-zero positive distance between the flapping axes and the corresponding attitude control pivot axis leads to an effective tilt of the thrust vectors generated by the flapping wings when pivoting the leading edge spars with respect to the YZ-plane.

In an embodiment, the attitude controller is configured to generate a first control signal for the first attitude control actuator to pivot the first leading edge spar with respect to the YZ-plane and to generate a second control signal for the second attitude control actuator to pivot the second leading edge spars with respect to the YZ-plane. The generation of the first control signal may be independent from the generation of the second control signal, and also a direction, range and/or rate of pivoting of the first leading edge spar by the first attitude control actuator may be different from a direction, range and/or rate of pivoting of the second leading edge spar by the second attitude control actuator. The various combinations provide a host of attitude control options for agile maneuvering.

In an embodiment, the attitude controller is configured to generate a pitch control signal for the first attitude control actuator and the second attitude control actuator to pivot the first leading edge spar and the second leading edge spar in substantially the same direction with respect to the YZ-plane to induce a pitch moment. The pitch moment is a result of the displacement of the thrust vectors in the same X-direction and the tilting of the thrust vectors relative to the YZ-plane in the same direction due to pivoting the first and second leading edge spars in substantially the same direction with respect to the YZ-plane, thereby varying the dihedral angle of the first and second wings. The attitude controller of the FWAV may control the first and second attitude control actuators to obtain a substantially symmetrical or asymmetrical position of the first and second leading edge spars. In the latter case, not only a pitch moment, but also a yaw moment is induced on the FWAV.

In an embodiment, the attitude controller is configured to generate a yaw control signal for the first attitude control actuator and the second attitude control actuator to pivot the first leading edge spar and the second leading edge spar in substantially opposite directions with respect to the YZ-plane to induce a yaw moment. The yaw moment is a result of the displacement of the thrust vectors in the positive and negative X-direction and the tilting of the thrust vectors out of the YZ-plane in opposite directions due to pivoting the first and second leading edge spars in substantially the opposite directions with respect to the YZ-plane, thereby varying the dihedral angle of the first and second wings. The attitude controller of the FWAV may control the first and second attitude control actuators to obtain a substantially point-symmetrical position of the first and second leading edge spars.

In an embodiment of the flapping wing aerial vehicle, the attitude controller is configured to generate a pitch and yaw control signal for the first attitude control actuator and the second attitude control actuator to pivot the first leading edge spar and the second leading edge spar to different respective pivot angles with respect to the YZ-plane and/or at a different pivot rate to induce a pitch moment and a yaw moment. In such a case, not only a yaw moment, but also a pitch moment is induced on the FWAV.

In an embodiment of the flapping wing aerial vehicle, the attitude controller further is configured to generate a roll control signal for the first and second flapping mechanisms causing the flapping motion of the first wing to be different from the flapping motion of the second wing to induce a roll moment. By effecting differences in flapping motion, the thrust force generated by the first wing may be different from the thrust force generated by the second wing, and roll control can be implemented in a compact way, akin to nature.

In a further embodiment, at least one of the first flapping actuator and the second flapping actuator are configured to vary the flapping frequency of the first and second flapping motion, respectively. Advantageously, varying the flapping frequency through use of the flapping actuators themselves leads to compact and light FWAV. Adjusting the flapping frequency of a first wing such that it is different from a second wing leads to a difference in thrust generated by the first wing in comparison to the second wing, thereby causing a roll moment about the X-axis. It should be noted that due to time-scale separation that the FWAV will only dynamically respond to the low-frequency roll moment and will remain insensitive to the high frequency effects of the flapping frequency differences between the first and second flapping motions.

In a further embodiment, at least one of the first flapping actuator and the second flapping actuator are configured to vary the flapping range of the first and second flapping motion, respectively. Advantageously, varying the flapping range through use of the flapping actuators themselves leads to compact and light FWAV. Adjusting the flapping range of a first wing such that it is different from a second wing leads to a difference in thrust generated by the first wing in comparison to the second wing, thereby causing a roll moment about the X- axis. It should be noted that due to time-scale separation that the FWAV will only dynamically respond to the low-frequency roll moment and will remain insensitive to the high frequency range variation effects of the flapping range differences between the first and second flapping motions.

In an embodiment, the attitude controller is configured to generate a first roll control signal for the first flapping actuator and a second roll control signal to the second flapping actuator to allow the flapping motion of the first wing to be different from the flapping motion of the second wing. For example, the flapping frequency and/or the flapping range of the first and second wings may be different from one another.

In an embodiment of the flapping wing aerial vehicle, the first wing and the second wing each comprise a rear portion and a front portion, adjoined at the root section of the wing, wherein the rear portion and the front portion are configured to move away from and towards each other when a flapping motion of the wing is induced. The use of a wing pair as compared to a single wing compensates some of the inertia forces that are induced by the flapping motion of the wings. This may result in a simpler attitude control of the FWAV. In a practical embodiment, the support structure extends substantially parallel to the Z-axis. Such a support structure provides options for a payload and/or actuators and/or other components to be mounted along the length of the support structure such that the location of the centre of gravity of the FWAV is optimized. It is noted that the support structure does not necessarily have to (just) extend along Z-axis. Any adequately rigid structure that can also carry actuators, a battery, an autopilot, a camera, etc. would suffice, regardless of its shape.

In a practical embodiment, the first and second flapping actuators each comprise a motor coupled with a transmission connected to the respective leading edge spar.

In a further practical embodiment, the first and second attitude control actuators each comprise a servomotor.

These and other aspects of the invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description and considered in connection with the accompanying drawings in which like reference symbols designate like parts.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 schematically depicts an isometric view of an embodiment of a flapping wing aerial vehicle according to the invention.

Figure 1 A shows a detail of the view of Figure 1 on an enlarged scale.

Figure 2A schematically illustrates, in isometric view, a first attitude effect and a second attitude effect of operating an attitude control mechanism of the flapping wing aerial vehicle of Figure 1.

Figure 2B schematically illustrates, in isometric view, a third attitude effect of operating the attitude control mechanism of the flapping wing aerial vehicle of Figure 1.

Figure 2C schematically illustrates, in isometric view, a fourth attitude effect of operating the attitude control mechanism of the flapping wing aerial vehicle of Figure 1.

Figure 2D schematically illustrates, in isometric view, a fifth attitude effect of operating the attitude control mechanism of the flapping wing aerial vehicle of Figure 1.

Figure 3A schematically further illustrates, in top view, the third attitude effect illustrated by Figure 2B.

Figure 3B schematically further illustrates, in bottom view, the fourth attitude effect illustrated by Figure 2C. Figure 4 schematically depicts an isometric view of another embodiment of a flapping wing aerial vehicle according to the invention.

Figure 5A schematically illustrates, in isometric view, a first and second attitude effect of operating an attitude control mechanism of the flapping wing aerial vehicle of Figure 4.

Figure 5B schematically illustrates, in isometric view, a fourth attitude effect of operating the attitude control mechanism of the flapping wing aerial vehicle of Figure 4.

DETAILED DESCRIPTION OF EMBODIMENTS

Figures 1 and 1A schematically depict an isometric view of a first embodiment of a flapping wing aerial vehicle 100, and a detail thereof on an enlarged scale. In this embodiment, the flapping wing aerial vehicle, FWAV, 100 is a flapping wing micro aerial vehicle, FWMAV, wherein a wing span is less than about 0.25 m, or a flapping wing nano aerial vehicle, FWNAV, wherein a wing span is less than about 0.025 m. However, the present invention can be put into practice in various kinds of FWAVs having wing spans of more than 0,25 m.

For the FWAV 100, an X-axis X, a Y-axis Y and a Z-axis Z in a right hand coordinate system are defined. As indicated in Figure 1, the FWAV 100 is oriented substantially vertically, the positive X-axis X being directed substantially forwards. When hanging substantially still in the air, the corresponding flight mode is a hovering flight mode of the FWAV. In this hovering position of the FWAV 100, the positive Y-axis Y generally points to the left, and the positive Z-axis Z generally points downwards, and intersects the center of gravity CG of the FWAV 100, wherein the center of gravity is indicated schematically by a dashed circle.

It is desired that the FWAV 100 can manoeuvre with respect to this hovering position. For example, it is desired that the FWAV 100 can perform a roll manoeuvre wherein the FWAV 100 rotates around the X-axis X, a pitch manoeuvre wherein the FWAV 100 rotates around the Y-axis Y, and a yaw manoeuvre wherein the FWAV 100 rotates around the Z-axis Z, and combinations of any of roll, pitch and yaw manoeuvres.

As can be seen in Figure 1, the FWAV 100 comprises a first wing 102 and a second wing 104, the second wing 104 being opposite to the first wing 102. In the embodiment shown in Figure 1, the first wing 102 and the second wing 104 each are wing pairs, wherein the first wing 102 comprises a first wing rear portion 102A and a first wing front portion 102B, adjoined at a first root section 112 of the first wing 102, and wherein the second wing 104 also comprises a second wing rear portion 104A and a second wing front portion 104B, adjoined at a second root section 114 of the second wing 104. In other embodiments, the first and second wings each may comprise only one portion, so that it is not strictly necessary that the first and second wings 102, 104 comprise a first and second wing rear portion 102A, 104A and a first and second wing front portion, 102B, 104B, respectively.

The first wing 102 comprises a first wing membrane 122, a first leading edge section 132, and a first trailing edge section 192. The second wing 104 comprises a second wing membrane 124, a second leading edge section 134, and a second trailing edge section 194. The first and second wing rear portions 102A, 104A and the first and second wing front portions 102B,

104B each comprise a leading edge spar 142A, 144A, 142B, 144B, respectively, arranged at or near the respective first and second leading edge sections 132, 134 of the first and second wings 102, 104, and attached to the first and second wing membranes 122, 124 thereof.

The leading edge spars 142A, 142B of the first wing 102 form part of a first flapping mechanism 152 for flapping the first wing 102. The first flapping mechanism 152 further comprises a first flapping actuator 162, and may comprise one or more gears and linkages and/or other transmission elements arranged between the first flapping actuator 162 and the spars 142A, 142B. The leading edge spars 144A, 144B of the second wing 104 form part of a second flapping mechanism 154 for flapping the second wing 104. The second flapping mechanism 154 further comprises a second flapping actuator 164, and may comprise one or more gears and linkages and/or other transmission elements arranged between the second flapping actuator 164 and the leading edge spars 144A, 144B. The first and second flapping actuators 162, 164 each are configured to pivot the respective associated leading edge spars 142A, 142B, and 144A, 144B with respect to respective first and second flapping pivot axes F1 , F2 which are substantially parallel to the Z-axis Z for inducing a first and second flapping motion of said first wing 102 and said second wing 104, respectively. The first and second flapping motions may also be indicated as clap and peel motions, caused by the back and front wing portions 102A, 102B and 104A, 104B of the respective first and second wings 102, 104 interacting with each other.

In the first flapping motion, the leading edge spars 142A, 142B are movable towards and away from each other between an extended position, as shown in Figure 1, and a collapsed position, indicated by dashed lines 142A’, 142B’, by activating the first flapping actuator 162 inducing the first flapping motion of the first wing rear portion 102A and first wing front portion 102B attached to the respective leading edge spars 142A, 142B. The first wing rear portion 102A and the first wing front portion 102B are configured to move towards and away from each other, each one of the leading edge spars 142A, 142B moving across a flapping range between the extended and the collapsed positions, as seen in the XY-plane. Hereby, a thrust force TF1 is produced, as indicated in Figure 1 by an arrow. It is noted that a similar (average) thrust force would also be generated when the first wing 102 would only comprise one portion instead of two.

Similarly, in the second flapping motion, the leading edge spars 144A, 144B are movable towards and away from each other between an extended position, as shown in Figure 1, and a collapsed position, indicated by dashed lines 144A’, 144B’, by activating the second flapping actuator 164 inducing the second flapping motion of the second wing rear portion 104A and second wing front portion 104B attached to the respective leading edge spars 144A, 144B. The second wing rear portion 104A and the second wing front portion 104B are configured to move towards and away from each other, each one of the leading edge spars 144A, 144B moving across a flapping angle, as seen in the XY-plane. Hereby, a thrust force TF2 is produced, as indicated in Figure 1 by an arrow. It is noted that a similar (average) thrust force would also be generated when the second wing 104 would only comprise one portion instead of two.

As visible in Figure 1, the FWAV 100 comprises first and second flapping mechanisms 152, 154. An attitude controller 110 is configured to control the first and second flapping motion induced by each one of the first and second flapping actuators 162, 164 separately, i.e. independent from each other. The attitude controller 110 is configured to send a first flapping motion signal to the first flapping mechanism 152, and to send a second flapping motion signal to the second flapping mechanism 154. The first and second flapping motion signals may be such that the first and second flapping mechanisms 152, 154 induce a synchronized first and second flapping motion, i.e. the flapping frequency and the flapping range for the first and second flapping motion are the same. The attitude controller 110 may further be configured to generate first and second flapping motion signals such that the first flapping mechanism 152 induces a first flapping motion which is different from the a second flapping motion induced by the second flapping mechanism 154. In the latter case, the first flapping motion may have an range which is different from the range of the second flapping motion, and/or the first flapping motion may have a frequency which is different from the frequency of the second flapping motion. Generally speaking, the lower the flapping range, the lower the thrust force TF1, TF2 generated by the respective first or second wing 102, 104, and the higher the flapping range, the higher the thrust force TF1 , TF2 generated by the respective first or second wing 102, 104. Also generally speaking, the lower the flapping frequency, the lower the thrust force generated by the respective first or second wing 102, 104, and the higher the flapping frequency, the higher the thrust force generated by the respective first or second wing 102, 104. Thus, by varying the flapping range and/or the flapping frequency between the first and second wings 102, 104, the first wing 102 may produce a thrust force TF1 which is different from the thrust force TF2 produced by the second wing 104.

Figure 1 A shows a detail of the view of Figure 1 , for an explanation of the embodiment of the first and second flapping mechanisms 152, 154. Many other embodiments inducing a first flapping motion and a second flapping motion are envisageable. In the embodiment of Figures 1 and 1A, the first flapping actuator 162 and the second flapping actuator 164 each comprise an electric motor 105, which is configured to drive gearwheel 106 fixed to gear wheel 107, which gearwheel 107 in turn drives a set of inter-engaging gear wheels 108. Each one of the gearwheels 108 is configured to excentrically drive move one end of a link of which another end is rotatably coupled to one end of an arm fixed to a corresponding leading edge spar 142A, 142B, 144A, 144B. The pair of leading edge spars 142A, 142B and the pair of leading edge spars 144A, 144B each are rotatably mounted on a shaft 109. Accordingly, rotation of the gear wheels 108 caused by the corresponding electric motors 105 leads to a flapping motion of the first wing portions 102A, 102B through pivoting movements of the corresponding leading edge spars 142A, 142B around the respective common shaft 109, and leads to a flapping motion of the second wing portions 104A, 104B through pivoting movements of the corresponding leading edge spars 144A, 144B around the respective common shaft 109.

Again referring to Figures 1 and 1A, the FWAV 100 comprises a support structure 120 to which the first wing 102 and the second wing 104 are coupled in a manner to be described in more detail below. The support structure 120 may be embodied in different forms, and may comprise a plurality of interconnected bodies, wherein each one of the bodies may have an elongate shape, a block shape, a spherical shape, and ellipsoid shape, and various other shapes, and wherein the interconnection may be fixed or flexible. In the embodiment shown in Figure 1, the support structure 120 comprises a body support structure 121, and a wing support structure 141 mounted to the body support structure 121.

The FWAV 100 further comprises an attitude control mechanism 171 comprising a first attitude control arm 172 and a first attitude control actuator 182, wherein the first attitude control arm 172 is coupled between the support structure 120 (wing support 141) and the first flapping mechanism 152. The first attitude control actuator 182 is configured to pivot the first attitude control arm 172 with respect to a first attitude control pivot axis P1 extending substantially parallel to the Z-axis Z to allow the dihedral angle of the first wing 102 to be varied. The attitude control mechanism 171 further comprises a second attitude control arm 174 and a second attitude control actuator 184, wherein the second attitude control arm 174 is coupled between the support structure 120 and the second flapping mechanism 154. The second attitude control actuator 184 is configured to pivot the second attitude control arm 174 with respect to a second attitude control pivot axis P2 extending substantially parallel to the Z- axis Z to allow the dihedral angle of the second wing 104 to be varied. The attitude controller 110 is configured for controlling the first attitude control actuator 182 and the second attitude control actuator 184 independently from each other.

Figure 1 A is again referred to, for an explanation of the embodiment of the first and second attitude control arms 172, 174, and the first and second attitude control actuators 182, 184. The first and second attitude control actuators 182, 184 each comprise an electric motor 115 which is configured to pivot an arm 116 which is coupled to a respective first and second attitude control arm 172, 174. The attitude control arms 172, 174 each are coupled to the support structure 120 (in particular, to opposite locations of the wing support structure 141) and are rotatable around the respective first and second attitude control pivot axis P1, P2. Accordingly, pivoting of the arms 116 caused by the corresponding electric motors 115 leads to pivoting movements of the corresponding attitude control arms 172, 174 around the respective first and second attitude control pivot axis P1, P2.

The support structure 120 carries the attitude controller 110 and a battery 150. The battery 150, which may be a rechargeable battery, provides a power supply for the first and second flapping actuators 162, 164, the first and second attitude control actuators 182, 184, and the attitude controller 110.

The FWAV 100 further comprises a wing root structure 130 mounted to the support structure 120, wherein the wing root structure 130 is coupled to a first wing root spar 146 attached to the first wing 102 at or near the first root section 112 thereof, and coupled to a second wing root spar 148 attached to the second wing 104 at or near the second root section 114 thereof. In the embodiment shown in Figure 1, the wing root structure 130 comprises a bar 131 which forms two oppositely extending arms. The wing root structure 130 is coupled to the first wing root spar 146 at a first predetermined location within the YZ-plane and spaced from the Z-axis Z. The wing root structure 130 is further coupled to the second wing root spar 148 at a second predetermined location within the YZ-plane and spaced from the Z-axis Z. In the embodiment shown in Figure 1, these wing root couplings are at the opposite ends of the bar 131 forming the wing root structure 130. The wing root couplings may have some provision for the first and second wing root spars 146, 148 to pivot with respect to the wing root structure 130 or bar 131. For example, the bar 131 may be provided at its opposite ends with openings accommodating the respective first and second wing root spars 146, 148. The wing root couplings may be located at any location along the lengths of the respective wing root spars 146, 148 spaced from the respective first and second leading edge sections 132, 134 of the respective first and second wings 102, 104.

The first flapping axis F1, the second flapping axis F2, the first attitude control pivot axis P1 and the second attitude control pivot axis P2 all are spaced from the Z-axis Z. The first flapping axis F1 lies further outward from the Z-axis Z than the first attitude control pivot axis P1. Likewise, the second flapping axis F2 lies further outward from the Z-axis Z than the second attitude control pivot axis P2.

In Figures 2A, 2B, 2C and 2D, the structural components of the FWAV 100 are depicted schematically: the body support structure 121, the wing support structure 141, the first attitude control arm 172 and first attitude control actuator 182, the second attitude control arm 174 and second attitude control actuator 184, the first and second attitude control pivot axes P1, P2, the first and second flapping mechanisms 152, 154, the leading edge spars 142A, 142B, 144A, 144B, the first and second flapping pivot axes F1, F2, the first wing rear portion 102A, the first wing front portion 102B, the second wing rear portion 104A, the second wing front portion 104B, the first and second wing root spars 146, 148, and the bar 131. Furthermore, in Figures 2A, 2B, 2C and 2D, the X-axis X, Y-axis Y and Z-axis Z are indicated.

Figure 2A schematically illustrates, in isometric view, a first attitude effect and a second attitude effect of operating the attitude control mechanism 171 of the flapping wing aerial vehicle 100 of Figure 1. In a ‘normal’ condition, when there is no external influence, such as an influence of wind, the wings 102, 104 may produce a thrust force TF1, TF2 when the first and second flapping mechanisms 152, 154 are active to produce the first flapping motion and the second flapping motion, respectively. The thrust forces TF1, TF2 may be substantially equal for the first wing 102 and the second wing 104, such that the FWAV 100 can be stably controlled. The combined thrust forces TF1+TF2 being upwardly directed may be equal in magnitude to the force exerted by gravity CG on the mass of the FWAV 100, and when no other forces are generated by the first flapping motion and the second flapping motion, the FWAV 100 may be hanging still in the air, i.e. such that the FWAV 100 is hovering.

To reach this first attitude effect, a hovering effect, the first and second flapping mechanisms 152, 154 are controlled by the attitude controller 110 to each produce the (same) required thrust force TF1, TF2, respectively, and the first and second attitude control actuators 182,

184 are controlled by the attitude controller 110 to control the angular position of the arms 172, 174 to be in line with each other, parallel to the Y-axis Y. When the attitude control mechanism 171 changes the flapping motion of the first wing 102 and/or the second wing 104, e.g. by changing a flapping frequency, such that the flapping frequency of the first wing 102 differs from the flapping frequency of the second wing 104, a roll moment R may be induced by which the FWAV 100 rotates around the X-axis X, as indicated by an arrow R in Figure 2A. This is a second attitude effect obtainable by the attitude control mechanism.

To reach this second attitude effect, a roll effect, the first and second flapping mechanisms 152, 154 are controlled by the attitude controller 110 to each produce thrust forces TF1, TF2, respectively, which differ from each other, and the first and second attitude control actuators 182, 184 are controlled by the attitude controller 110 to control the angular position of the arms 172, 174 to be in line with each other, parallel to the Y-axis Y.

The direction of the roll moment R follows from the difference between the thrust forces TF1, TF2 produced by the first wing 102 and the second wing 104, respectively. In other embodiments, wherein the flapping range of the first and second wings 102, 104 can be varied, a roll moment R may be induced by changing the flapping range, such that the flapping range of the first wing 102 differs from the flapping range of the second wing 104. In still other embodiments, both a flapping frequency and a flapping range of the first and second wings 102, 104 may be varied in combination to induce a roll moment R.

Figure 2B schematically illustrates, in isometric view, a third attitude effect of operating the attitude control mechanism 171 of the flapping wing aerial vehicle 100 of Figure 1. The first and second attitude control actuators 182, 184 are controlled by the attitude controller 110 to control the angular position of the arms 172, 174 to assume an angle a1, a2, respectively, each being different from zero, relative to the Y-axis Y. Thereby, the leading edge spars 142A, 142B, 144A, 144B may pivot in the same direction with respect to the YZ-plane. The first and second wing root spars 146, 148 may pivot in the same direction with respect to the YZ-plane and to a lesser extent in opposite directions with respect to the XZ-plane towards each other, with respect to their wing root couplings with the wing root structure 130 (bar 131). The absolute values of the angles a1, a2 may be equal to produce a pure pitch effect.

The wings 102, 104 may produce a thrust force TF1 , TF2 when the first and second flapping mechanisms 152, 154 are active to produce the first flapping motion and the second flapping motion, respectively. The thrust forces TF1, TF2 may be substantially equal for the first wing 102 and the second wing 104. The thrust forces TF1 , TF2 now each are tilted with respect to the YZ-plane, and have a component in the direction of the X-axis X, and thereby induce a pitch moment P around Y-axis Y, as indicated by an arrow P in Figure 2B, and the third attitude effect, a pitch effect, is reached. The absolute values of the angles a1, a2 may be equal to produce a pure pitch effect.

The displacement in the X-direction makes the Z-component of the thrust forces generate the dominant part of the pitch moment. The X-component also contributes, but depending on the CG location, the pitch moment this component generates can be in the same or in the opposite sense to the Z-component-induced moment.

Figure 3A schematically further illustrates, in top view, the third attitude effect illustrated by Figure 2B. A first flapping motion M1 of the first wing 102 and a second flapping motion M2 of the second wing 104 are indicated by double arrows.

Figure 2C schematically illustrates, in isometric view, a fourth attitude effect of operating the attitude control mechanism 171 of the flapping wing aerial vehicle 100 of Figure 1. The first and second attitude control actuators 182, 184 are controlled by the attitude controller 110 to control the angular position of the arms 172, 174 to assume an angle a3, a4, respectively, each being different from zero, relative to the Y-axis Y. Thereby, the leading edge spars 142A, 142B associated with the first wing 102 may pivot in one direction with respect to the YZ-plane, and the leading edge spars 144A, 144B associated with the second wing 104 may pivot in the opposite direction with respect to the YZ-plane. The first and second wing root spars 146, 148 may pivot in opposite directions with respect to the YZ-plane and to a lesser extent in opposite directions with respect to the XZ-plane towards each other, with respect to their wing root couplings with the wing root structure 130 (bar 131).

The wings 102, 104 may produce a thrust force TF1 , TF2 when the first and second flapping mechanisms 152, 154 are active to produce the first flapping motion and the second flapping motion, respectively. The thrust forces TF1, TF2 may be substantially equal for the first wing 102 and the second wing 104. The thrust forces TF1, TF2 now are tilted in opposite directions with respect to the YZ-plane, and have oppositely directed components along the X-axis X, and thereby induce a yaw moment J, as indicated by an arrow J in Figure 2C, and the fourth attitude effect, a yaw effect, is reached. The absolute values of the angles a3, a4 may be equal to produce a pure yaw effect.

Figure 3B schematically further illustrates, in bottom view, the fourth attitude effect illustrated by Figure 2C. Figure 2D schematically illustrates, in isometric view, a fifth attitude effect of operating the attitude control mechanism 171 of the flapping wing aerial vehicle 100 of Figure 1. The first and second attitude control actuators 182, 184 are controlled by the attitude controller 110 to control the angular position of the arms 172, 174 to assume an angle a5, a6, respectively, each being different from zero, relative to the Y-axis Y. Thereby, the leading edge spars 142A, 142B, 144A, 144B may pivot in the same direction with respect to the YZ-plane. However, in Figure 2D, the angles a5, a6 differ from each other. The first and second wing root spars 146, 148 may pivot in the same direction with respect to the YZ-plane and to a lesser extent in opposite directions with respect to the XZ-plane towards each other, with respect to their wing root couplings with the wing root structure 130 (bar 131).

The wings 102, 104 may produce a thrust force TF1 , TF2 when the first and second flapping mechanisms 152, 154 are active to produce the first flapping motion and the second flapping motion, respectively. The thrust forces TF1, TF2 may be substantially equal for the first wing 102 and the second wing 104. The thrust forces TF1, TF2 now each have a (different) component in the direction of the X-axis X, and thereby induce a pitch moment P around Y- axis Y, as indicated by an arrow P in Figure 2D. At the same time, the different angles a5, a6, producing a differential component of the thrust forces TF1, TF2 in the direction of the X-axis X, induce a yaw moment J. Accordingly, the fifth attitude effect, a combined pitch and yaw effect, is reached.

Figure 4 schematically depicts an isometric view of a second embodiment of a flapping wing aerial vehicle, FWAV, 400. A large part of the structure of the FWAV 400 is equal or similar to the structure of the first embodiment of the FWAV 100. However, the FWAV 400 comprises a wing root structure 430 being different from the wing root structure 130 of the FWAV 100.

The wing root structure 430 is coupled to the first wing root spar 146 and to the second wing root spar 148. In the embodiment shown in Figure 4, the wing root structure 430 comprises a bar 431 which forms two oppositely extending arms. The wing root structure 430 is coupled to the first wing root spar 146 at a first predetermined location within the YZ-plane and spaced from the Z-axis Z. The wing root structure 430 is further coupled to the second wing root spar 148 at a second predetermined location within the YZ-plane and spaced from the Z-axis Z. In the embodiment shown in Figure 4, these wing root couplings are at the opposite ends of the bar 431 being part of the wing root structure 430. The couplings may have a provision for the first and second wing root spars 146, 148 to pivot with respect to the wing root structure 430 or bar 431. For example, the bar 431 may be provided at its opposite ends with openings accommodating the respective first and second wing root spars 146, 148. The wing root couplings may be located at any location along the lengths of the respective wing root spars 146, 148 spaced from the respective first and second leading edge sections 132, 134 of the respective first and second wings 102, 104.

In the embodiment of Figure 4, the bar 431 of the wing root structure 430 is rotatable around the Z-axis Z across a predetermined range by a wing root actuator 432. Thus, the wing root actuator is configured to deflect the wing root spars 146, 148 with respect to the YZ-plane. In fact, the wing root couplings between the bar 431 and the respective first and second wing root spars 146, 148 may be moved out of the YZ-plane in opposite X-directions by control of the attitude controller. The battery 150 provides a power supply for the wing root actuator 432.

Figure 5A schematically illustrates, in isometric view, a first attitude effect and a second attitude effect of operating the attitude control mechanism 171 of the flapping wing aerial vehicle 400 of Figure 4. In a ‘normal’ condition, when there is no external influence, such as an influence of wind, the wings 102, 104 may produce a thrust force TF1, TF2 when the first and second flapping mechanisms 152, 154 are active to produce the first flapping motion and the second flapping motion, respectively. The thrust forces TF1, TF2 may be substantially equal for the first wing 102 and the second wing 104, such that the FWAV 400 can be stably controlled. The combined thrust forces TF1+TF2 being upwardly directed may be equal in magnitude to the force exerted by gravity CG on the mass of the FWAV 400, and when no other forces are generated by the first flapping motion and the second flapping motion, the FWAV 400 may be hanging still in the air, i.e. such that the FWAV 400 is hovering.

To reach this first attitude effect, a hovering effect, the first and second flapping mechanisms 152, 154 are controlled by the attitude controller 110 to each produce the (same) required thrust force TF1, TF2, respectively, and the first and second attitude control actuators 182, 184 are controlled by the attitude controller 110 to control the angular position of the arms 172, 174 to be in line with each other, parallel to the Y-axis Y. The wing root actuator 432 is controlled by the attitude controller 110 to control the angular position of the bar 431 to assume a zero angle relative to the Y-axis Y, i.e. to be in line with Y-axis Y.

When the attitude control mechanism 171 changes the flapping motion of the first wing 102 and/or the second wing 104, e.g. by changing a flapping frequency, such that the flapping frequency of the first wing 102 differs from the flapping frequency of the second wing 104, a roll moment R may be induced by which the FWAV 400 rotates around the X-axis X, as indicated by an arrow R in Figure 5A. This is a second attitude effect obtainable by the attitude control mechanism.

To reach this second attitude effect, a roll effect, the first and second flapping mechanisms 152, 154 are controlled by the attitude controller 110 to each produce thrust forces TF1, TF2, respectively, which differ from each other, and the first and second attitude control actuators 182, 184 are controlled by the attitude controller 110 to control the angular position of the arms 172, 174 to be in line with each other, parallel to the Y-axis Y.

The direction of the roll moment R follows from the difference between the thrust forces TF1, TF2 produced by the first wing 102 and the second wing 104, respectively. In other embodiments, wherein the flapping range of the first and second wings 102, 104 can be varied, a roll moment R may be induced by changing the flapping range, such that the flapping range of the first wing 102 differs from the flapping range of the second wing 104. In still other embodiments, both a flapping frequency and a flapping range of the first and second wings 102, 104 may be varied in combination to induce a roll moment R.

Figure 5B schematically illustrates, in isometric view, a fourth attitude effect of operating the wing root structure 430 of the flapping wing aerial vehicle 400 of Figure 4. The wing root actuator 432 is controlled by the attitude controller 110 to control the angular position of the bar 431 to assume an angle a7 being different from zero, relative to the Y-axis Y. Thereby, the first and second wing root spars 146, 148 may pivot in opposite directions with respect to the YZ-plane and to a lesser extent in opposite directions with respect to the XZ-plane towards each other, with respect to their wing root couplings with the wing root structure 430 (bar 431).

The wings 102, 104 may produce a thrust force TF1 , TF2 when the first and second flapping mechanisms 152, 154 are active to produce the first flapping motion and the second flapping motion, respectively. The thrust forces TF1, TF2 may be substantially equal for the first wing 102 and the second wing 104. The thrust forces TF1, TF2 now have oppositely directed components along the X-axis X, and thereby induce a yaw moment J around the Z-axis Z, as indicated by an arrow J in Figure 5B, and the fourth attitude effect, a yaw effect, is reached. Since the inclinations of the first and second root spars 146, 148 with respect to the YZ-plane and the XZ-plane are the same in magnitude and oppositely directed, a pure yaw moment is generated. The wing root structure 430 may be particularly effective to increase the agility of the FWAV 400. For example, for yaw effects, if the attitude controller 110 controls the first and second attitude control actuators 182, 184 to pivot the arms 172, 174 in opposite directions with respect to the YZ-plane, as illustrated in Figure 2C, and at the same time the attitude controller 110 controls the wing root actuator 432 to rotate the bar 431 to pivot the bar 431 with respect to the YZ-plane, as illustrated in Figure 5B, the inclination of the wing root spars 146, 148 is increased (with respect to any one of the inclinations illustrated in Figures 2C and 5B), and the yaw effect is increased accordingly.

The attitude controller 110 is electrically connected to the first and second flapping actuators 162, 164, first and second attitude control actuators 182, 184, and the wing root actuator 432, if present, for communication of control signals and possibly also electrical power. The battery 150 powers the attitude controller 110 and the actuators 162, 164, 182, 184, 432.

The compact design of the FWAV according to the present invention allows for short electrical connections. Actuators and electrical connections may be integrated into structural components of the FWAV.

As explained in details above, a flapping wing aerial vehicle comprises: a first wing and a second wing opposite to the first wing, a support structure to which the wings are coupled, first and second flapping mechanisms for flapping the first and second wings, and an attitude control mechanism for inducing at least one of a yaw moment and a pitch moment. The attitude control mechanism comprises: a first attitude control arm coupled between the support structure and the first flapping mechanism, and a first attitude control actuator configured to pivot the first attitude control arm; and a second attitude control arm coupled between the support structure and the second flapping mechanism, and a second attitude control actuator configured to pivot the second attitude control arm. An attitude controller controls the first attitude control actuator and the second attitude control actuator independently from each other.

As required, detailed embodiments of the present invention are disclosed herein. However, it is to be understood that the disclosed embodiments are merely exemplary of the invention, which can be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in any appropriately detailed structure. The terms "a'V'an", as used herein, are defined as one or more than one. The term plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and/or having, as used herein, are defined as comprising (i.e. , open language, not excluding other elements or steps). Any reference signs in the claims should not be construed as limiting the scope of the claims or the invention.

The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

The term coupled, as used herein, is defined as connected, although not necessarily directly.