Patent Description:
The invention relates generally to aircraft designs, and, more particularly, to aircraft designs that combine the features of a fixed wing aircraft and vertical takeoff and landing (VTOL) aircraft.

Various aircraft designs attempt to combine the vertical takeoff and landing (VTOL) and hover capabilities of a helicopter with the increased speed and range capabilities of fixed wing aircraft. These hybrid designs reduce the footprint necessary for launch and recovery. However, they tend to be more complex than either helicopters or conventional take-off and landing aircraft, as they generally incorporate multiple propulsion systems, each used for a different flight mode. These designs can include "tail sitter" configurations, so named because the aircraft takes off and lands from a tail-down orientation. Other designs can include "nose sitter" configurations, so named because the aircraft takes off and lands from a nose-down orientation.

One example of a nose-sitter design includes a VTOL hybrid, which includes a conventional propeller for fixed wing flight and a folding rotor near the tail of the aircraft. These designs may have high hover efficiency; however, they also require complex mechanical systems and weigh more than other designs due to the requirement of two separate propulsion systems, one for each flight mode.

Other VTOL designs can include "tail sitter" configurations, so named because the aircraft takes off and lands from a tail-down orientation. Conversion from vertical to horizontal flight for these hybrid designs typically requires a configuration change and dedicated engines for each configuration. Prior solutions that combine VTOL and cruise performance compromise performance in both flight modes.

Document <CIT> discloses an aircraft with two wings and joined thruster propellers serving as rotary wings in helicopter mode and as fixed wings in airplane mode. The thrusters along the wingspans or at the wing tips drive both rotary wing rotation and airplane flight. Large-angle controlled feathering about the pitch change axes of the left and right wings and thrusters allows them to rotate, relative to each other, between facing and thrusting forward in the same direction for airplane flight or facing and thrusting oppositely for helicopter flight.

Document <CIT> discloses an aircraft for use in fixed wing flight mode and rotor flight mode. The aircraft can include a fuselage, wings, and a plurality of engines. The fuselage can comprise a wing attachment region further comprising a rotating support. A rotating section can comprise a rotating support and the wings, with a plurality of engines attached to the rotating section. In a rotor flight mode, the rotating section can rotate around a longitudinal axis of the fuselage providing lift for the aircraft similar to the rotor of a helicopter. In a fixed wing flight mode, the rotating section does not rotate around a longitudinal axis of the fuselage, providing lift for the aircraft similar to a conventional airplane. The same engines that provide torque to power the rotor in rotor flight mode also power the aircraft in fixed wing flight mode.

A VTOL airplane or UAV that uses the same propulsion for both flight modes would have many structural benefits, including reduced complexity and weight of the launch equipment and ease of operation in more remote locations, as well as numerous mission benefits that are enjoyed today by helicopters. These include hover-and-stare in urban-canyons and sit-and-stare for extended silent surveillance. Further, sit-and-wait operation allows the airplane or UAV to be pre-deployed to a forward area awaiting mission orders for remote launch of the aircraft. Upon receiving the mission order, the vehicle can launch without leaving any expensive launch equipment at the launch site.

Some existing VTOL designs suffer from poor endurance and speed. Forward flight efficiency may be improved by partial conversion to an aircraft like the V-<NUM> but endurance issues remain. Many VTOL aircraft also require a high power-to-weight ratio. These aircraft may be used for high-speed flight if the aircraft is fitted with a special transmission and propulsion system. However, achieving high endurance requires efficiency at very low power. Thus, the challenge exists to create a virtual gearbox that equalizes power and RPM for VTOL and fixed wing flight achieving highly efficient cruise with the benefits of a vertical takeoff and landing configuration.

VTOL aircraft are runway independent so they can be deployed to undeveloped areas. Helicopters are the classical VTOL solution, but because of rotor limitations, they lack long range and high cruise speed. Range and speed are strengths for fixed-wing airplanes, conventional takeoff and landing (CTOL).

Hybrids have been explored to combine VTOL and efficient cruise. Existing solutions have much more complexity relative to helicopters and CTOL airplanes. Conversion from vertical to horizontal flight requires a configuration change, dedicated engines for each mission element, or very complex engines that do both tasks. Further, the solutions compromise VTOL and cruise performance significantly.

In addition, existing VTOL designs often sacrifice payload considerations to provide desirable flight performance, such as endurance. For example, other existing VTOL designs describe tail sitter configurations where the fuselage is oriented vertically when hovering or on the ground. The vertical fuselage makes it difficult to load and unload payloads, and also subjects the payloads to a <NUM>-degree pitch change twice in a mission. A design is needed wherein this pitch change can be eliminated, while still maintaining a simple engine design to avoid for complicated configuration changes and more simplistic cruise performance.

It should, therefore, be appreciated that there exists a need for a VTOL aircraft with improved performance and payment capacity.

Briefly, and in general terms, an aircraft capable of fixed wing and rotor flight modes according to claim <NUM> is disclosed that is capable of vertical takeoff and landing (VTOL). The aircraft comprises a fuselage body having a longitudinal axis (Af) and a plurality of wings affixed above the fuselage. The wings are mounted for both a fixed wing flight mode and for a rotor flight mode. The fixed wing flight mode is defined as flight in which said wings are maintained rotationally stationary relative to the axis of rotation (Ar). The rotor flight mode is defined as flight in which said wings rotate about the axis of rotation (Ar).

More particularly, the plurality of engines secured to said wings, including a first engine secured to said first wing and a second engine secured to said second wing. The wing attachment assembly comprises a central support to which the plurality of dual-purpose wings attach. The central support includes a hopper tank for providing fuel to the plurality of engines. The fuselage body includes a fuel tank operatively coupled to the hopper tank to provide fuel thereto.

In exemplary embodiments in accordance with the invention, the aircraft can be provided in manned or unmanned configurations (UAV).

The wing attachment assembly is attached to the fuselage body in an intermediate region thereof above the fuselage body.

In another detailed aspect of an exemplary embodiment, the plurality of wings consist of a pair of wings having a wingspan greater than the length of the fuselage body.

In another detailed aspect of an exemplary embodiment, the plurality of engines are each secured to said wings at an equalizing position along the semi-span of each wing.

A method of an aircraft transitioning between fixed wing mode and rotor flight mode according to claim <NUM> is also provided.

For purposes of summarizing the invention and the advantages achieved over the prior art, certain advantages of the invention have been described herein. Of course, it is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment of the invention. Thus, for example, those skilled in the art will recognize that the invention may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein.

All of these embodiments are intended to be within the scope of the invention herein disclosed as long as they not depart from or are further developments of the scope of the appended claims. These and other embodiments of the present invention will become readily apparent to those skilled in the art from the following detailed description of the preferred embodiments having reference to the attached figures, the invention not being limited to any particular preferred embodiment disclosed but only by the appended claims.

These and other features, aspects, and advantages of the present invention will now be described in connection with a preferred embodiment of the present invention, in reference to the accompanying drawings. The illustrated embodiments, however, are merely examples and are not intended to limit the invention, the invention being defined by the appended claims.

With reference now to the drawings, and particularly <FIG>, there is shown an aircraft <NUM> that includes multi-purpose wings <NUM>, <NUM> operable in a rotor flight mode (<FIG>) and a fixed wing flight mode (<FIG>). The wings are rotatably coupled to a central support <NUM> of a wing attachment assembly <NUM> above a fuselage <NUM>. The central support defines an axis of rotation (Ar) that is transverse to a longitudinal axis (Af) of the fuselage.

When the aircraft is in rotor flight mode, the wings rotate as a rotor above the fuselage. The rotation of the wings acts similarly to the rotor of a traditional helicopter, providing vertical thrust to vertically propel the aircraft and maintain a hovering altitude. However, the rotation of the wings is propelled by engines <NUM>, <NUM> mounted on the wings, rather than an engine mounted within the fuselage as in traditional helicopter designs. When in fixed wing flight mode, the wings are oriented such that the engines face the same direction to provide the thrust required to power the aircraft in fixed wing flight.

As such, this arrangement provides the features of a rotor-flight aircraft and a fixed-wing aircraft, while reducing performance losses due to the weight requirements of complex mechanical machinery needed for configuration changes. Moreover, multiple propulsion systems are not required for flight in more than one flight mode.

This exemplary embodiment also allows for a wide variety of payloads to be carried, as the payload compartment size is not related to the rotor geometry, and is largely decoupled with the horizontal fuselage. Embodiments of the invention can include features such as but not limited to improved payload capacity, vertical take-off and landing (VTOL) capability, efficient hover, high speed, and long-range endurance in a single flight. Additionally, embodiments of the invention include aircraft in manned or unmanned configurations (UAV).

With continued reference to <FIG>, the aircraft <NUM> is shown in fixed wing flight mode, similar to that of a conventional airplane, such as a Piper Seneca or Beech King-Air. The aircraft <NUM> comprises a fuselage main body <NUM> having nose <NUM>, payload compartment <NUM>, wing attachment assembly <NUM>, and tail section <NUM>. The wings attach to a top portion of the fuselage.

The payload compartment <NUM> is located within the fuselage <NUM> between the nose <NUM> and tail section <NUM>. The interior of the fuselage <NUM> comprises a volume, which contains crew seating, the payload compartment, as well as fuel tanks (shown in <FIG>) or other mission specific equipment.

The wing attachment assembly <NUM> comprises the central support <NUM> to which the wings <NUM>, <NUM> preferably attach, with one wing on each side thereof, spaced equiangularly about the central support. The wings <NUM>, <NUM> and central support <NUM> rotate around the axis of rotation (Ar) when the aircraft <NUM> is in rotor flight mode (<FIG>). The central support <NUM> is preferably locked in place to prevent rotation about axis of rotation (Ar) when the aircraft is in fixed wing flight mode (<FIG>).

The wings <NUM>, <NUM> may also comprise one or more control surfaces <NUM>, <NUM> to control the attitude of the aircraft while in both fixed wing and in rotor flight modes. These control surfaces may be controlled by servos located within the fuselage <NUM> of the aircraft <NUM>. Alternatively, servos can be disposed in the wings.

In a preferred embodiment, the wings may comprise a symmetric airfoil. The wings <NUM>, <NUM> each have a leading edge <NUM>, <NUM>, and a trailing edge <NUM>, <NUM>. The wings can have a greater chord length, or leading edge to trailing edge, closer to the fuselage. Alternatively, the wings may have substantially the same chord length along the span of the wing from wing tip to wing tip.

Engine <NUM>, <NUM> are secured to each wing <NUM>, <NUM>. In other embodiments, one or more engines may be secured to each wing <NUM>, <NUM>. In a preferred embodiment, the engines <NUM>, <NUM> of the aircraft <NUM> are aligned substantially parallel with a longitudinal axis of the fuselage with the propellers <NUM>, <NUM> configured to pull the aircraft <NUM> through the air when the aircraft <NUM> is in fixed wing flight, as depicted in <FIG>. In other embodiments, the engines <NUM>, <NUM> and propellers <NUM>, <NUM> may be configured in a push-type configuration in which the propellers <NUM>, <NUM> are oriented toward the tailing edge <NUM>, <NUM> of the wings <NUM>, <NUM> to push the aircraft <NUM> rather than to pull the aircraft <NUM> when the aircraft <NUM> is flying in a fixed wing flight mode. A "pusher" style configuration where the engines and propellers are oriented to push the aircraft <NUM> through the air.

With continued reference to <FIG>, the engines <NUM>, <NUM> are secured to the wings <NUM>, <NUM> (not the fuselage <NUM>). As such, the location of the engines <NUM>, <NUM> on the wings <NUM>, <NUM> eliminates the need for extension shafts from the fuselage to the propellers. Extension shafts typically connect an engine mounted within or directly on the fuselage via a gearbox or other linkage to the propellers on the wing. Locating the engines within or directly on the fuselage typically also requires a central gearbox located within the fuselage. By eliminating the extension shafts and the central gearbox in a preferred embodiment, the weight of the aircraft <NUM> may be decreased, allowing for greater payload capacity, longer range, and endurance, among other benefits conceivable by those skilled in the art.

In other embodiments, engines <NUM>, <NUM> may be secured at any point on the rotating section comprising the wings <NUM>, <NUM> and central support <NUM>. In the illustrated embodiment, two engines are depicted. Additional embodiments may have more numbers of engines depending on mission requirements; other aircraft design considerations, or other considerations known to those skilled in the art.

<FIG> further illustrates that, in a preferred embodiment, the engines <NUM>, <NUM> are attached to the wings <NUM>, <NUM> at a position an equal distance to either side of the central support <NUM>. Locating the engines <NUM>, <NUM> in this balanced orientation may provide benefits of balance and stability to the aircraft. Additionally, the engines <NUM>, <NUM> are preferably secured to the wings <NUM>, <NUM> at an equalizing position along the semi-span of each wing, defined as the distance along the wing <NUM> or <NUM> from the wing attachment assembly <NUM> to the wing tip <NUM> or <NUM>.

When the engines <NUM>, <NUM> are located at the equalizing position in a preferred embodiment, the thrust of the engines <NUM>, <NUM> and the flight speed of aircraft <NUM> when the aircraft <NUM> is flying in a fixed wing flight mode desirably equal the torque and rpm, or rotations per minute, required by the aircraft <NUM> when the wings rotate around a longitudinal axis of the rotor <NUM> when the aircraft <NUM> is operating in a rotor flight mode. In a preferred embodiment, the torque demands of the wings <NUM>, <NUM> when acting as a rotor are matched to the in-flight demands of the aircraft <NUM> when flying in fixed wing mode, using the same engines <NUM>, <NUM> and propellers <NUM>, <NUM>. Locating the engines <NUM>, <NUM> at the point where these demands are matched may also allow the wing tip <NUM>, <NUM> speed to approach sonic (when the wings <NUM>, <NUM> are acting as a rotor in rotor flight mode) while keeping the blades of the propellers <NUM>, <NUM> well under sonic. Locating the engines <NUM>, <NUM> at the point where these forces and requirements equalize preferably eliminates the need for complex gearboxes and other heavy equipment that may decrease the long-range endurance capabilities of the aircraft. Additional discussion of the determination of this point where these forces and requirements equalize is included below.

With reference now to <FIG>, the aircraft <NUM> is depicted in rotor flight mode. The engines <NUM>, <NUM> face in opposing directions, to cause wings to rotate about the axis of rotation (Ar). The wings <NUM>, <NUM> are mounted to the central support <NUM> in a manner that enables each wing to rotate independently about its span-wise axis (length) (Aw). As such, the wings and the engines can provide variable pitch, in both flight modes. The rotation of the wings <NUM>, <NUM> may preferably be achieved by servos or actuators located within the central support <NUM>. Also, the rotation of at least one wing is used to transition between rotor flight and fixed wing flight. In the exemplary embodiment, one wing can rotate at least <NUM> degrees about its span-wise axis (Aw). During start-up and shutdown, the wings can be rotated so the propeller blades <NUM>, <NUM> are not below the surface swept by the wings. This affords extra safety from the spinning propellers.

<FIG> depicts a front view of the aircraft <NUM> in fixed-wing flight mode, in which the leading edges <NUM>, <NUM> of the wings <NUM>, <NUM> face forward. Additionally, engines <NUM>, <NUM> may also rotate relative to the wings <NUM>, <NUM> around a span or lengthwise axis (Aw) of the wings. The rotation of engines <NUM>, <NUM> around a span-wise axis of the wings <NUM>, <NUM> may be in addition to the rotation of wings <NUM>, <NUM> described above. The rotation of engines <NUM>, <NUM> may be between <NUM> and <NUM> degrees, desirably between <NUM> and <NUM> degrees, or more desirably between <NUM> and <NUM> degrees.

Preferably, the wings <NUM>, <NUM> each have at least one spar. A spar runs lengthwise along the internal or external span of the wing from connection with the central section <NUM> to the wing tip to provide structural rigidity. At least one spar of each wing <NUM>, <NUM> attaches to the central support <NUM> of wing attachment assembly. <FIG> depicts one spar <NUM> of wing <NUM> connected to central support <NUM>. The wings may rotate about the spar or a span-wise or wingtip-to-wingtip axis (Aw) of the wing to position the wings <NUM>, <NUM> for hover or vertical flight. Desirably, spar <NUM> extends at least to the point of attachment of engine <NUM> on wing <NUM> to provide structural rigidity to the wing. Wing <NUM> may be attached to wing attachment assembly via a second spar <NUM>. Wing <NUM> is preferably able to rotate as described above about the spar <NUM> to orient engine <NUM> to a new direction required to power rotation of wing <NUM> around a longitudinal axis (Ar). Desirably, wing <NUM> also rotates about a second spar to achieve the orientation of engine and propeller <NUM> as depicted in <FIG>.

The engines <NUM>, <NUM> are attached to the wings <NUM>, <NUM> such that the rotating inflow speed of air to the engines <NUM>, <NUM> when the wings <NUM>, <NUM> are acting as a rotor is substantially similar to the cruise inflow speed of air to the engines <NUM>, <NUM> when the aircraft <NUM> is flying in fixed wing mode. This preferably allows the propellers <NUM>, <NUM> and the engines <NUM>, <NUM> of the aircraft <NUM> to be optimized for efficient cruise. The aircraft <NUM> also relies on the same engines <NUM>, <NUM> as those used for vertical takeoff and landing and hovering flight when the aircraft <NUM> is in fixed wing flight. In a preferred embodiment, there is no torque-to-ground force as is found with traditional helicopter designs, so no tail rotor is needed.

As shown in <FIG>, takeoff and rotor flight is achieved when the wings <NUM>, <NUM> are preferably oriented substantially parallel to the ground with the engines <NUM>, <NUM> facing in opposite directions. <FIG> depicts one embodiment of the invention in which one engine <NUM>, <NUM> is attached to each wing <NUM>, <NUM>; however, a different number of engines may be attached to each wing. The application of power via the rotation of the propellers <NUM>, <NUM> attached to each engine <NUM>, <NUM> causes the wings <NUM>, <NUM> to rotate around a longitudinal axis <NUM> of the rotor <NUM> similar to a helicopter rotor in the direction indicated in <FIG>. The pitch, or angle of attack, of each wing <NUM>, <NUM> may be altered at the same time (known in the art as collective pitch) or may be changed depending on the position of each wing <NUM>, <NUM> as it rotates (known in the art as cyclic pitch). These pitch changes may be provided by control surfaces on the wings <NUM>, <NUM> such as flaps, tabs with free-to-pitch wing bearings, or dedicated servos. As depicted in <FIG>, the engines <NUM>, <NUM> are attached to the wings <NUM>, <NUM> at a position where the torque demands of the rotor created by the rotation of the wings <NUM>, <NUM> about a longitudinal axis of the rotor <NUM> are matched to the in-flight demands of the aircraft <NUM> when the wings <NUM>, <NUM> do not rotate relative to the fuselage in fixed wing flight mode. In a preferred embodiment, the aircraft <NUM> uses the same engines <NUM>, <NUM> and propellers <NUM>, <NUM> for flight in fixed wing mode and rotor flight mode. This configuration may also allow the rotor tips <NUM>, <NUM> to approach sonic speed while keeping the propellers <NUM>, <NUM> well under sonic.

The same engines <NUM>, <NUM> and propellers <NUM>, <NUM> that provide the thrust necessary to turn the wings <NUM>, <NUM> like a rotor when the aircraft <NUM> is in rotor flight mode also provide between <NUM>% and <NUM>% of the thrust necessary to fly the aircraft <NUM> in fixed wing flight mode. In other embodiments, engines <NUM>, <NUM> desirably provide between <NUM>% and <NUM>% of the thrust necessary to fly the aircraft <NUM> in fixed wing flight mode, and more desirably provide between <NUM>% and <NUM>% of the thrust necessary to fly the aircraft <NUM> in fixed wing flight mode. In some embodiments, at least <NUM>% of the thrust necessary to fly aircraft <NUM> in fixed wing flight mode is provided by the same engines <NUM>, <NUM> that power the aircraft in rotor flight mode, while in other embodiments desirably at least <NUM>% of the necessary thrust is provided by the same engines <NUM>, <NUM>, while in still other embodiments more desirably at least <NUM>% of the necessary thrust is provided by the same engines <NUM>, <NUM>.

Each wing <NUM>, <NUM> may comprise a spar <NUM>, <NUM> that runs lengthwise through the wing from the point of attachment with the fuselage <NUM> to at least the point of attachment of engine <NUM>, <NUM> with wing <NUM>, <NUM>. Each spar <NUM>, <NUM> provides structural rigidity for each wing <NUM>, <NUM>, as may be appreciated by those skilled in the art.

In a preferred embodiment, the sparof each wing is attached to central support <NUM>. The spars are preferably attached to the central support <NUM> such that each wing <NUM>, <NUM> is allowed to rotate about the axis (Aw) defined by the spar such that the leading edge <NUM> of one wing and the leading edge <NUM> of the other wing face in substantially opposite directions, as shown in one embodiment in <FIG>. The rotation of the wings <NUM>, <NUM> about their spars will also result in the engines <NUM>, <NUM> attached to each wing to face in substantially opposite directions. Power generated by the engines <NUM>, <NUM> will turn the propellers <NUM>, <NUM>, which will produce thrust causing the rotation of the wings <NUM>, <NUM> about an axis of rotation (Ar).

A preferred transition to fixed wing flight is shown in <FIG>. At initiation position A, the aircraft <NUM> is shown with the engines and propellers oriented in opposite directions. The aircraft may be on the ground G1 awaiting take off or may be hovering or flying in rotor flight mode above the ground G2. Between positions A and B, the aircraft preferably climbs to a desired height above ground level. At both positions A and B, the wings <NUM>, <NUM> are rotating about the rotor of the aircraft to provide thrust for rotor flight. At throttle down position B, the aircraft is preferably throttled down from a climb to hover while in rotor flight mode. Between throttle down position B and fixed-wing position C, the aircraft preferably begins to rotate a wing <NUM> by <NUM> degrees to align with the second wing <NUM> which transitions the aircraft to a fixed wing orientation in which the engines <NUM>, <NUM> face in substantially the same direction. This direction being the desired direction of travel for flight as a fixed wing or conventional airplane.

The transition can be accomplished while simultaneously reducing engine throttle. The reduction in throttle desirably reduces rotor speed (the rotation of the wings acting as a rotor) substantially to zero. At fixed wing flight mode position C, the aircraft has fully transitioned from a rotor flight mode to a fixed wing flight mode, meaning that the wings are no longer rotating. The central support may be locked to prevent rotation but this is not required. Additionally, the engines preferably face substantially in the direction of travel. At fixed wing flight mode, engine throttle is preferably advanced, which accelerates the aircraft allowing for traditional fixed wing flight. Once sufficient airspeed is developed, the aircraft is flying "on-the-wing" similar to that of a conventional airplane and may be controlled with conventional tail surfaces.

<FIG> depicts a method of transitioning from fixed wing flight to rotor flight. At fixed wing flight mode position C, the aircraft is oriented for flight in fixed wing mode, as described with respect the same flight mode and position in <FIG>. Throttle is reduced, and a one wing <NUM> is rotated <NUM> degrees to face an opposite direction from wing <NUM>. Thereafter, throttle is increased to initiate rotor-wing flight mode. At position D, the aircraft's <NUM> configuration is changed from that required for fixed wing flight to that required for rotor flight, during which time the wings <NUM>, <NUM> rotate in opposite directions <NUM> such that the engines <NUM>, <NUM> and propellers <NUM>, <NUM> face in opposite directions. At rotor wing flight mode position D, the wings begin to spin around the axis of rotation (Ar) due to the torque generated by the engines <NUM>, <NUM> attached to the wings <NUM>, <NUM>, which now face in opposite directions. The rotor speed at rotor-wing flight mode position D is preferably increased beyond the speed required for hover flight. Finally, between rotor wing flight mode position D and fully transitioned position E, the engines may be throttled down for stable descent and landing. However, actual landing of the aircraft <NUM> at this point may not be required if mission considerations and requirements require the aircraft to maintain hover flight at a specific altitude or to complete other aerial maneuvers while in vertical flight mode.

With reference now to <FIG>, the wings <NUM>, <NUM> include control surfaces <NUM>, <NUM>. The control surfaces can be used to generate aerodynamic forces to compensate for torque forces generated in rotor flight mode. In <FIG>, an aircraft <NUM> includes a tail rotor <NUM> to compensate for torque forces generated in rotor flight mode.

With reference now to <FIG>, the aircraft <NUM> includes a fuel tank <NUM> mounted in the fuselage <NUM> coupled to hopper tanks <NUM>, <NUM> in the wings. The hopper tanks feed the engines <NUM>, <NUM>. In use, fuel <NUM> can be transferred from the fuel tank <NUM> to the hopper tanks when the rotor is stopped. The hopper tanks can feed the engines <NUM>, <NUM> while in rotor mode, as shown in <FIG>.

With reference now to <FIG>, the aircraft can include a displacement bearing assembly in the central support <NUM>. The bearing assembly is configured to isolate rotor spike moments and vibration from the fuselage <NUM>.

As mentioned above with regard to <FIG>, the torque demands of the wings <NUM>, <NUM> when acting as a rotor are desirably matched to the in-flight demands of the aircraft <NUM> when flying in fixed wing mode, using the same engines <NUM>, <NUM> and propellers <NUM>, <NUM>. The engines <NUM>, <NUM> are desirably positioned at a point on the wings <NUM>, <NUM> where these requirements are substantially equalized. As discussed above, these requirements may have a difference between them of between <NUM>% and <NUM>%, desirably between <NUM>% and <NUM>%, or more desirably between <NUM>% and <NUM>%. In some embodiments, the difference between these requirements is desirably no more than <NUM>% or more desirably no more than <NUM>%. The following discussion describes a preferred method to calculate the position on wings <NUM>, <NUM> where the engines <NUM>, <NUM> are attached to substantially equalize these requirements. The exact values used in the calculation are for example purposes and are not intended to limit the calculation or the invention in any way.

With reference now to <FIG>, the transition of the aircraft <NUM> from fixed-wing-flight mode to rotor-flight mode is depicted. <FIG> shows the aircraft <NUM> in fixed-wing flight. Both engines <NUM>, <NUM> are facing the same direction (forward), and the propellers <NUM>, <NUM> provide the propulsive power to move the aircraft <NUM> forward. <FIG> shows the wings <NUM>, <NUM> as they begin their transition from fixed-wing-flight mode, to rotor-flight mode. The wings' <NUM>, <NUM> incidence is increased symmetrically, as shown, causing the aircraft <NUM> to pull-up and decelerate. <FIG> shows the wings <NUM>, <NUM> once they have been rotated to a transition orientation. In the transition orientation, chord axis of each wing is aligned with the axis of rotation (Ar). In the exemplary embodiment, wings are oriented <NUM> degrees relative to the longitudinal axis in the transition orientation, and the aircraft <NUM> is at a minimum airspeed.

<FIG> shows the wings <NUM>, <NUM> as they are rotated from the transition orientation. One wing <NUM> is rotated forward, and the other wing <NUM> is rotated backward, such that engine <NUM> is oriented in a forward facing direction and engine <NUM> is oriented in a rearward facing direction, initiating the spin of the central rotary <NUM>. <FIG> shows the aircraft <NUM> in rotor-flight mode. The wings <NUM>, <NUM> have been rotated such that the engines <NUM>, <NUM> and propellers <NUM>, <NUM> face opposite directions. The wings <NUM>, <NUM> have been rotated to their hover incidence, resulting in a steady spin of the wings and the central rotary <NUM> about the Ar axis.

The table below provides a list of abbreviations used in the example calculations that follow:.

It has been well established in the art that VTOL power required follows this relation: <MAT>.

Where VTOL_SHPreqd is the Shaft horsepower required for vertical take-off and landing.

Assuming that the aircraft requires <NUM>% excess lift capability in the rotor the equation for VTOL_SHPreqd becomes: <MAT>.

For an airplane, the SHPreqd is set by the climb or takeoff requirement of the airplane. Since takeoff is not required when the aircraft is in fixed wing flight mode, climb is the key consideration. Initial climb rate at takeoff altitude is a good surrogate for the ceiling capability of an airplane. The greater the ROC, or rate of climb, of an aircraft is at low altitude, the higher the ceiling, or the maximum altitude the aircraft may achieve. For many VTOL vehicles, a typical ceiling is <NUM>,<NUM> ft. This ceiling is approximately equivalent to a sea level ROC of <NUM>,<NUM> fpm (or feet per minute) for a long range or high endurance airplane. Using the classical climb equation we can solve for the SHP required when the aircraft is climbing in fixed wing flight mode.

If the wings are used as the rotor, the rotor diameter equals the wingspan.

Further, if the flight engines are used to power the rotor, the propeller efficiency must be included in the calculation to determine the engine SHP required for VTOL.

For flight in fixed wing mode the equation becomes: <MAT>.

Therefore; <MAT> As an illustrative example only, for a very efficient <NUM> lb airplane, assume the following:.

Solving for the RotorDiameter or wingspan when the engine power for VTOL equals the engine power for climb will result in a preferably balanced design in which the wings are utilized as the rotor for rotor flight.

In this example only, RotorDiameter = wingspan = <NUM> ft.

The previous calculations matched engine power provided by a propeller for vertical and hovering flight and fixed wing flight climb. However, to eliminate the need for mechanical gearing between the flight modes, the engine is desirably secured laterally on the wing to provide the desired rotor torque at the rotor RPM.

Assuming the aircraft when it is in fixed wing configuration has an aspect ratio (AR) of <NUM> the RPM and torque required may be determined.

Near an advance ratio of zero (hover) an AR = <NUM> wing has these properties.

RotorThrust Coefficient, CT = <NUM> <MAT> <MAT>.

Solving for the rotor rotations per minute results in <NUM> rpm for the wings when they act as a rotor. Recall: <MAT>.

Therefore: <MAT>
and Torque = <NUM>,<NUM> ft-lbs.

Assuming the thrust of the engines in VTOL or vertical/hovering flight is defined as: <MAT>.

Where V@prop is the relative wind at the engine station on the rotating wing, given by: <MAT>.

For engines secured at <NUM>% semispan the available thrust is: <MAT>.

Solving the equation results in Total Thrust Available = <NUM>,<NUM> lbs.

Since the rotor diameter, or total wingspan, is <NUM> ft, as calculated above for this example only, an engine located at <NUM>% semi-span has a lever arm (Y) of <NUM> ft.

Therefore, in this example, the Total Thrust Required is <NUM>,<NUM> lbs, which equals the Total Thrust Available as calculated above.

The equivalence of the Total Thrust Available and the Total Thrust Required illustrates that for this example, a balanced design was achieved without needing a gearbox.

It should be appreciated from the foregoing that the present invention provides an aircraft capable of fixed wing and rotor flight modes is disclosed that is capable of vertical takeoff and landing (VTOL). The aircraft comprises a fuselage body having a longitudinal axis (Af) and a plurality of wings affixed above the fuselage. The wings are mounted for both a fixed wing flight mode and for a rotor flight mode. The fixed wing flight mode is defined as flight in which said wings are maintained rotationally stationary relative to the axis of rotation (Ar). The rotor flight mode is defined as flight in which said wings rotate about the axis of rotation (Ar).

Claim 1:
An aircraft (<NUM>) capable of fixed wing and rotor flight modes, comprising:
a fuselage body (<NUM>) defining a longitudinal axis (Af), the fuselage body having a nose (<NUM>) and a tail (<NUM>),
a wing attachment assembly (<NUM>) coupled to the fuselage body for rotation about an axis of rotation (Ar) transverse to the longitudinal axis (Af);
a plurality of dual-purpose wings (<NUM>, <NUM>), including a first wing (<NUM>) and a second wing (<NUM>), rotatably mounted to said wing attachment assembly above the fuselage body for a fixed wing flight mode and for a rotor flight mode, in which the fixed wing flight mode is defined as flight in which said wings are maintained rotationally stationary relative to the axis of rotation (Ar) and the rotor flight mode is defined as flight in which said wings rotate about the axis of rotation (Ar); and
a plurality of engines secured to said wings, including a first engine (<NUM>) secured to an intermediate region of said first wing (<NUM>) and a second engine (<NUM>) secured to an intermediate region of said second wing (<NUM>);
wherein the wing attachment assembly (<NUM>) comprises a central support (<NUM>) to which the plurality of dual-purpose wings (<NUM>, <NUM>) attach;
wherein the central support (<NUM>) includes a hopper tank for providing fuel to the plurality of engines (<NUM>, <NUM>); wherein the fuselage body (<NUM>) includes a fuel tank (<NUM>) operatively coupled to the hopper tank to provide fuel thereto; and
wherein the aircraft is configured such that the fuel is transferred from the fuel tank to the hopper tank when the wing rotation about the axis of rotation (Ar) is stopped.