Patent Description:
Wingborn flight is a challenge and its achievement has been inhibited by the lack of power-to-weight ratios associated with internal combustion engines available in the first decades of the <NUM>th century. Vertical flight poses an even greater challenge and the need for extreme overall system efficiencies in order to sustain a thrust-born flight, takeoff and landing.

The classical solution which is currently accepted by those in this art is the traditional helicopter which typically includes one large main rotor for lift generation and a smaller rotor to counteract main rotor torque to achieve stabilization. Other stable configurations include two main rotors rotating in opposite directions, although the use of such multiple main rotors is less common and limited to specific missions and scenarios (e.g., the Chinook helicopter in the inventory of the US Army).

Currently, helicopters (and other VTOL aircraft) are usually powered by one or more internal combustion engines (either reciprocating or turbo-shaft), that produce powered transmitted to the rotors through gearboxes. With the advent of new and improved electrical powertrains, it is increasingly becoming possible to use a so-called "distributed propulsion" concept, which imposes advantages for multi-copters in particular scenarios.

Trimmed flight is required for any aircraft. An aircraft is said to be trimmed when it achieves equilibrium (i.e., sum of forces and moments are equal to zero) without pilot input. Currently, fly-by-wire (FBW) systems can provide auto-trim functionality. In order to meet operational and certification requirements, an aircraft must be capable of being trimmed and controlled even in an aerodynamic destabilizing effect associated with an engine/motor failure event.

For the specific case of multi-copters, the operational and certification requirements imply that after the loss of one engine/motor/rotor, the sum of moments and forces will continue to add up to zero, so the static equilibrium is obtained. Unfortunately, sum of moments and forces is only part of the problem since controllability and stability are also relevant in such a scenario. Maintaining both controllability and stability throughout the entire flight, even during and after an engine/motor/rotor failure, is also a challenge.

Each rotor of a multi-copter not only provides providing lift but also provides control. As such, it is possible to have more control actuators (rotors) than states to be controlled (degrees of freedom). A technical solution to the problem therefore relies on the design and placement of the rotors in such a way that the overall rotor configuration is able to meet the control and stability requirements of an inoperative engine/motor/rotor event. The combination of the number of rotors and the positional placement of the rotors provides for multiple possible solutions. For example, hexa-copters may be provided with different rotor displacement to in turn provide different degrees of controllability, stability, and performance characteristics during both normal operation or even during a rotor failure.

Other multi-copter characteristics are sensible to rotor displacement. For instance, during forward flight, a tandem configuration (displaced rotors that are aligned alongside a fuselage centerline) is susceptible to interference between rotors, reducing vehicle performance. Rotor interference increases noise level and battery consumption.

Electrical vehicles for urban air mobility are subject to several restrictions such as:.

Actual infrastructure imposes superior dimensional boundaries (footprint). On the other hand, noise literature indicates that disk-loading reduction is effective to reduce noise intensity. This reduction is possible by reducing vehicle weight or increasing rotor diameter. Weight is function of mission profile, payload, cabin dimension, vehicle sweat area, vehicle efficiency, crashworthiness requirements, flight loads, systems availability, and others. Limitations on rotor diameter are related to dynamic response and vehicle footprint.

Safety and electrical requirements enable distributive propulsion architecture. Some multiple rotor configuration tolerates rotor loss and system failures. However, there is an additional penalty due to rotor interference, reducing overall vehicle efficiency.

A lift plus cruise e-VTOL configuration comprises two different flight phases, namely wing-born flight and thrust-born flight, each one with their own specific technical requirements. To avoid using tilting rotors or tilting wing mechanisms, and considering hover rotors forward flight characteristics (retreating blade stall), one must consider minimizing transition speed from wing- to thrust-born phases. Therefore, it is necessary to increase wing area.

The amount of variables considered in an e-VTOL project increases its complexity. Evidence of such complexity is the variety of vehicle architectures available in the general media, i.e., there is no consensus regarding the best vehicle topology. In addition, different vehicle topology optimizes different project criteria. For example, energetic optimization leads to a different vehicle topology when compared to user experience, operational cost, maneuverability, or even vehicle price optimization. Each business model requires a different vehicle topology.

It would therefore be desirable if an aircraft could be provided having VTOL capability, especially eVTOL capability, which provide for a vehicle topology considered to be a good trade-off between the vehicle objectives for the next prototype and which solves the technical problems noted hereinabove. It is towards providing such a solution that the embodiments disclosed herein are directed. An aircraft with a plurality of rotors arranged under an aft wing and a forward wing is known from <CIT>, wherein the aft wing and the forward wing are arranged at equal heights. <CIT> discloses an aircraft with a forward canard wing inclined downwards and an aft wing inclined upwards. The roots of the forward canard wing and of the aft wing can be in different horizontal planes. Each wing includes two or more engines mounted on a rotatable axis. <CIT> discloses a VTOL aircraft with a plurality of rotors arranged in the same horizontal plane and in longitudinal rows. <CIT> discloses a multicopter with pairs of rotors arranged only under a front wing, with no rotor being supported by an aft wing of the aircraft. <CIT> describes an aircraft with a plurality of rotors arranged in the same horizontal plane and in longitudinal rows. <CIT> describes an aircraft in which rotors are arranged on a front wing and on an aft wing, with the rotors on the aft wing being longitudinally aligned, in plan view, with the rotors on the front wing. The substantially horizontal plane of the aft pair of port and starboard wings is displaced upwardly relative to the substantially horizontal plane of the forward pair of port and starboard wings.

The present invention relates to a VTOL aircraft, especially e-VTOL aircraft, according to claim <NUM>.

The VTOL aircraft of the invention is provided with a fuselage (which may include a pair of ground-engaging skids) defining a longitudinal axis of the aircraft, forward and aft pairs of port and starboard aerodynamic wings extending laterally outwardly from the fuselage and forward and aft pairs of port and starboard rotor pods each being in substantial alignment with the longitudinal axis of the fuselage. According to the invention, each of the forward and aft pairs of port and starboard rotor pods comprises a forward and aft pair of rotor assemblies.

The forward pairs of port and starboard rotor pods are positioned forwardly of a center of gravity (CG) of the aircraft, while the aft pairs of the port and starboard rotor pods may be positioned aft of the aircraft CG.

According to the invention, one-half of the rotor assemblies in the VTOL aircraft described herein is caused to rotate in one direction while a remaining one-half of the rotor assemblies rotate in a counter direction relative thereto.

According to the invention, each of the forward and aft pairs of port and starboard aerodynamic wings is positioned in a respective substantially horizontal plane, and wherein the substantially horizontal plane of the aft pair of port and starboard wings is displaced upwardly relative to the substantially horizontal plane of the forward pair of port and starboard wings. The aft pairs of port and starboard aerodynamic wings are, according to the invention, in a gull wing configuration whereby in inboard portion of the wing extends upwardly and outwardly from the fuselage while an outboard portion of the wing then extends substantially horizontally outwardly from the terminal end of the inboard portion.

According to the invention, port and starboard propulsive rotors are provided with each generating thrust along the longitudinal axis of the fuselage. The port and starboard propulsive rotors comprise a pusher propeller assembly.

These and other aspects and advantages of the embodiments of the present invention disclosed herein will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof.

The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary nonlimiting illustrative embodiment in conjunction with the drawings of which:.

Accompanying <FIG> schematically depicts a VTOL aircraft <NUM> in the form of a multi-rotor vehicle having a fuselage <NUM> which includes a forward cabin region 12a for pilot and passengers which is provided with transparent windows 12b and a door 12c for ingress/egress from the interior cabin region 12a. A vertical stabilizer <NUM> located at the aft end of the fuselage <NUM> may be provided so as to provide directional control about the Z (yaw) axis of the aircraft <NUM>. Control about the X (roll) and Y (pitch) axes may be provided by suitable control surfaces (not shown) associated with the forward and aft pairs of port and starboard wings, 16a, 16b and 18a, 18b, respectively. Laterally separated ground skids 13a, 13b extend from the bottom of the fuselage <NUM> so as to support the aircraft when positioned on the ground surface.

According to the embodiment depicted in <FIG>, the aircraft <NUM> will include respective pairs of port and starboard side rotor pods 20a, 20b and 22a, 22b at the terminal end of each of the port and starboard wings 16a, 16b and 18a, 18b, respectively (i.e., in a generally T-shaped configuration). Each pair of port and starboard side rotor pods 20a, 20b and 22a, 22b are aligned with the longitudinal axis AL of the aircraft <NUM> with the aft rotor pods 22a, 22b being positioned laterally outwardly of the forward rotor pods 20a, 20b relative to the XZ plane of the aircraft fuselage <NUM>. Each of the side rotor pods 20a, 20b and 22a, 22b will operably contain pairs of forward and aft side rotor assemblies 24a1, 24a2, 24b1, 24b2, 26a1, 26a2, 26b1 and 26b2 aligned with the longitudinal axis AL of the aircraft <NUM>.

To enhance stability of the aircraft <NUM> it is preferred that one-half of the side rotor assemblies 24a1, 24a2, 24b1, 24b2, 26a1, 26a2, 26b1 and 26b2 will rotate in one direction about the Z-axis while the other half will rotate in an opposite direction. Since the side rotor assemblies 24a1, 24a2, 24b1, 24b2, 26a1, 26a2, 26b1 and 26b2 generate moments around the X-axis, the counter-rotation of one-half of such side rotor assemblies 24a1, 24a2, 24b1, 24b2, 26a1, 26a2, 26b1 and 26b2 thereby allow the sum of moments about the Y- and X-axes to be zero. Further it is preferred that the forward pairs of rotor assemblies 24a1, 24a2 and 24b1, 24b2 are situated forwardly of the CG of the aircraft <NUM>. Control of the pairs of rotor assemblies 24a1, 24a2, 24b1, 24b2, 26a1, 26a2, 26b1 and 26b2 can be effected by the embodiments disclosed in copending <CIT>.

As shown in <FIG>, aerodynamic pairs of port and starboard wings 16a, 16b and 18a, 18b project laterally from the fuselage <NUM> and serve to structurally join the pairs of port and starboard rotor pods 20a, 20b and 22a, 22b to the fuselage <NUM>, respectively. The pairs of port and starboard wings 16a, 16b and 18a, 18b, respectively, serve to provide aerodynamic lift during propulsive flight of the aircraft <NUM> in the direction of the X-axis. In order to achieve propulsive flight of the aircraft <NUM> in the direction of the X-axis (both forwardly and rearwardly), a pair of port and starboard pusher propeller assemblies 30a, 30b, respectively, are positioned laterally of the longitudinal axis AL of the fuselage <NUM> at an aft-facing position on the wings 18a, 18b, respectively. The port and starboard pusher propeller assemblies 30a, 30b are preferably positioned rearwardly of the CG of the aircraft <NUM>.

The aft wings 18a, 18b are preferably configured in a "gull wing" fashion so that the wings 18a, 18b are positioned in a generally horizontal plane parallel to the X-Y plane that is displaced above the generally horizontal plane parallel to the X-Y plane in which the forward wings 16a, 16b are aligned. Moreover, the span of the aft wings 18a, 18b is greater that the span of the forward wings 16a, 16b so as to positioned the rotor pods 22a, 22b, respectively, laterally outwardly of the rotor pods 20a, 20b.

The rotor assemblies 24a1, 24a2, 24b1, 24b2, 26a1, 26a2, 26b1 and 26b2 and/or the pusher propeller assemblies 30a, 30b may optionally be ducted.

Claim 1:
A vertical take-off and landing - VTOL - aircraft comprising:
a fuselage (<NUM>) defining a longitudinal axis (AL) of the aircraft (<NUM>);
forward and aft pairs of port and starboard aerodynamic wings (16a, 16b, 18a, 18b) extending laterally outwardly from the fuselage (<NUM>), wherein the aft pairs of port and starboard aerodynamic wings (16a, 16b, 18a, 18b) are in a gull wing configuration, wherein a span of the aft wings (18a, 18b) is greater than a span of the forward wings (16a, 16b);
forward and aft pairs of port and starboard rotor pods (20a, 20b, 22a, 22b) respectively arranged at the terminal end of the port and starboard wings (16a, 16b, 18a, 18b), each being in substantial alignment with the longitudinal axis (AL) of the aircraft (<NUM>); and
port and starboard propulsive rotors (30a, 30b) each providing thrust along the longitudinal axis of the fuselage (<NUM>), wherein each of the port and starboard propulsive rotors (30a, 30b) comprise a pusher propeller assembly;
wherein each of the forward and aft pairs of port and starboard aerodynamic wings (16a, 16b, 18a, 18b) are positioned in a respective substantially horizontal plane, and wherein the substantially horizontal plane of the aft pair of port and starboard wings (18a, 18b) is displaced upwardly relative to the substantially horizontal plane of the forward pair of port and starboard wings (16a, 16b);
wherein each of the forward and aft pairs of port and starboard rotor pods (20a, 20b, 22a, 22b) comprises a forward and aft pair of rotor assemblies (24a<NUM>, 24a<NUM>; 24b<NUM>, 24b<NUM>; 26a<NUM>, 26a<NUM>; 26b<NUM>, 26b<NUM>) aligned with the longitudinal axis (AL) of the aircraft (<NUM>);
wherein the aft rotor pods (22a, 22b) are positioned laterally outwardly of the forward rotor pods (20a, 20b) relative to a vertical plane (XZ) of the aircraft fuselage (<NUM>) perpendicular to a pitch axis (Y) thereof;
wherein one-half of the rotor assemblies (24a<NUM>, 24a<NUM>; 24b<NUM>, 24b<NUM>; 26a<NUM>, 26a<NUM>; 26b<NUM>, 26b<NUM>) rotate in one direction about a yaw axis (Z) and a remaining one-half of the rotor assemblies (24a<NUM>, 24a<NUM>; 24b<NUM>, 24b<NUM>; 26a<NUM>, 26a<NUM>; 26b<NUM>, 26b<NUM>) rotate about the yaw axis (Z) in a counter direction relative thereto.