Patent Description:
One of the main challenges of designing a Vertical Take-off and Landing (VTOL) aircraft is sizing the propulsion system to be efficient in both VTOL and hover phases as well as cruise conditions. Since the propulsion system fraction of the total weight needs to be kept low to maximize payload and fuel reserves, the challenge is how to employ a system that produces roughly <NUM>-<NUM> times more thrust at take-off (in lift-by -thrust-only mode) or in hover, compared to in wing-borne and cruise conditions. In the first case the thrust is balancing the weight of the aircraft and much larger engines and power or thrust are required, whereas in cruise conditions the size of the engine needs to be much smaller to balance drag as the wings of the aircraft balance the weight.

Traditionally VTOL was achieved with either separate systems (lift/cruise compromising weight but separating propulsion) or pure rotorcraft such as helicopters (compromising wing-borne capabilities). The most successful aircraft employing VTOL capabilities use the same system for both vertical and wing-borne phases. Examples are jump-jets such as Harrier Hawker, which vectors its turbofan jets (but ends up oversizing the engine for the missions in wing-bome phase) and the V22 Osprey, which utilizes turboprops with tilting capabilities. The tilt-rotor approach is not without risks including vibrations, vortex ring state (VRS) and large footprints, as well as complex architectures.

For smaller systems (i.e., <NUM>-<NUM> passenger aircraft) especially in the growing Urban Air Mobility market, large lift+cruise airplanes are the dominant design. Especially for electric VTOL, this results in very large footprint and moving parts between <NUM>-<NUM> large rotors for efficiency reasons. The wingspan for carrying <NUM>-<NUM> passengers may be as large as the wingspan of a small regional plane. The weight of the aircraft due to today's low energy density batteries also impose large-size wings and complex operation with the multi-rotors, increasing risk.

<CIT>, <CIT> and <CIT> all describe examples of propulsion systems for VTOL aircraft.

Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings:.

This patent application is intended to describe one or more embodiments of the present invention. It is to be understood that the use of absolute terms, such as "must," "will," and the like, as well as specific quantities, is to be construed as being applicable to one or more of such embodiments, but not necessarily to all such embodiments. As such, embodiments of the invention may omit, or include a modification of, one or more features or functionalities described in the context of such absolute terms.

A fluidic propulsion system (FPS) according to an embodiment introduces an alternate approach where thrusters without rotating parts can be tilted for transitioning from hovering to cruise. During VTOL and hover, thrust augmentation can be obtained using a pressurized fluid as source. One or more embodiments may include a system that is used in all phases of flight (vertical and wing-borne) while still obtaining an augmentation for thrust in a forward moving direction.

An embodiment includes a lift+cruise solution involving a source of compression such as a fan or compressor of fluids including air, as well as a dual capability to switch from an augmented thrust in vertical flight (VTOL+hover) and a separate turbofan configuration in cruise. Such a configuration and operation would eliminate the restriction in speed and allow a VTOL vehicle to move forward at very high velocity, higher altitude capabilities and operate very efficient by lowering significantly the fuel burn (specific fuel consumption.

More descriptively, a fan or compressor or similar machine receives mechanical work and compresses ambient air to a pressure ratio of between <NUM>-<NUM>. The component may have one or several stages and may be driven preferably by a gas turbine stage such as the free turbine of a turboshaft engine, without the need of a reduction gear. This element is optionally advantageous as the weight and moving parts reduction will allow a lighter and simpler construction to be employed.

Referring to <FIG>, a shaft <NUM> receives the mechanical power from the free turbine of a turboshaft or electric motor, and transmits the power to a fan <NUM> to compress the air to the aforementioned pressure ratios. The air is pumped into a plenum <NUM> immediately downstream of the fan <NUM>, and from there the air may be directed into side ports <NUM> and <NUM> or axially downstream through a nozzle having variable vanes <NUM>. Vanes <NUM> can be fully closed or fully opened via mechanisms known in the art. For example, one such mechanism could be the variable guide vanes employed in a typical compressor. Another mechanism could be a mechanical screw rotating the hub of the vanes <NUM> and forcing the vanes to close. When closed as seen in <FIG> and <FIG>, the entire flow from the fan <NUM> is forced into the side ports <NUM> and <NUM> of the plenum <NUM> and into FPS system elements <NUM>, <NUM> connected fluidically to the plenum <NUM> via valves <NUM>.

In one embodiment the fan <NUM> receives a power of, for example, <NUM> kW from a free turbine of a gas turbine of the turboshaft type that spins at, for example, <NUM>,<NUM> RPM. This value is typical of a machine such as a typical turboprop architecture, before the reduction gear, at full speed. Such power and speed can yield a compressed air stream of, e.g., <NUM> atmospheres (a pressure ratio of <NUM> or <NUM> kPa approximately) and a flow of circa <NUM>/s assuming an efficiency of <NUM>% on the part of the fan.

The fan <NUM> itself may be manufactured of ultralight materials such as titanium or even composite materials, the former using wide chord, compound swept fan blades for higher efficiency and manufactured in one piece as a blisk. A design with low noise features is included.

At <NUM>/sec, <NUM>-<NUM> kPa total pressure, and assuming an air temperature of <NUM> Kelvin, stream <NUM> is split and transmitted to FPS elements <NUM>, <NUM> embedded within an airframe of an aircraft. The FPS elements <NUM>, <NUM>, which are described in greater detail as ejectors in, for example, <CIT> and <CIT>,
can augment the thrust which would otherwise result from accelerating and expanding the flow simply to the atmospheric pressure to at least <NUM>:<NUM> and up to <NUM>:<NUM> ratios. In this example, the thrust achieved via ejector augmentation is given in Equation <NUM> below:
<MAT>
as opposed to a thrust of <NUM> kN if a simple nozzle is employed. In this case <NUM> J/kg-K is the air constant, <NUM> is the air exponential factor, <NUM> is the discharge temperature from the fan <NUM> compression, <NUM> is the augmentation ratio and <NUM>/s is the total mass flow rate.

With further optimization of the FPS elements <NUM>, <NUM>, the total thrust may reach an augmentation ratio of <NUM>, meaning <NUM> kN, for the same amount of mechanical input power of <NUM> kW supplied to the fan <NUM>.

<FIG> illustrates a cross-section of the upper half of an ejector <NUM>, the structure and functionality of which is similar or identical to that of elements <NUM>, <NUM>. A plenum <NUM> is supplied with hotter-than-ambient air (i.e., a pressurized motive gas stream) from, for example, a combustion-based engine that may be employed by the vehicle. This pressurized motive gas stream, denoted by arrow <NUM>, is introduced via at least one conduit, such as primary nozzles <NUM>, to the interior of the ejector <NUM>. More specifically, the primary nozzles <NUM> are configured to accelerate the motive fluid stream <NUM> to a variable predetermined desired velocity directly over a convex Coanda surface <NUM> as a wall jet. Additionally, primary nozzles <NUM> provide adjustable volumes of fluid stream <NUM>. This wall jet, in turn, serves to entrain through an intake structure <NUM> secondary fluid, such as ambient air denoted by arrow <NUM>, that may be at rest or approaching the ejector <NUM> at non-zero speed from the direction indicated by arrow <NUM>. In various embodiments, the nozzles <NUM> may be arranged in an array and in a curved orientation, a spiraled orientation, and/or a zigzagged orientation.

The mix of the stream <NUM> and the air <NUM> may be moving purely axially at a throat section <NUM> of the ejector <NUM>. Through diffusion in a diffusing structure, such as diffuser <NUM>, the mixing and smoothing out process continues so the profiles of temperature (<NUM>) and velocity (<NUM>) in the axial direction of ejector <NUM> no longer have the high and low values present at the throat section <NUM>, but become more uniform at the terminal end <NUM> of diffuser <NUM>. As the mixture of the stream <NUM> and the air <NUM> approaches the exit plane of terminal end <NUM>, the temperature and velocity profiles are almost uniform. In particular, the temperature of the mixture is low enough to be directed towards an airfoil such as a wing or control surface.

When vanes <NUM> are closed and the fan <NUM> supplies this power, enough thrust may be obtained from such a system to enable lifting of an aircraft that weighs, for example, between <NUM> and <NUM> kgs. This type of aircraft may direct the thrust upwards via swiveling FPS elements <NUM>, <NUM> supplied from the fan <NUM> via ports <NUM> and <NUM>, which can also rotate with respect to their principal axes via swiveling joints <NUM>. The swiveling or vectoring of FPS elements <NUM>, <NUM> can change the attitude of the aircraft first in vertical takeoff, further in hovering via small angle changes and finally in transition to wing borne operation via swiveling of the FPS elements to direct the thrust at <NUM> degrees (as shown in <FIG>) up to <NUM> degrees perpendicular to the original VTOL position shown in <FIG>.

The angles in the swiveling joints <NUM>, which also allow the passage of the flow to the elements <NUM>, <NUM>, can be gradually changed to allow a perfect balancing of the aircraft from hover to gaining speed and increase the lift of the wings of the aircraft at forward velocities of, e.g., <NUM>% more than stall velocities of the aircraft. For example, an aircraft according to an embodiment of a VTOL aircraft may reach a speed of <NUM> mph within a few tens of seconds after hovering at a fixed point, while still balancing some of the weight via FPS <NUM>, <NUM> pointing at <NUM> degrees upwards in the direction of flight, and still accelerating in the forward direction while the wings begin supporting, e.g., <NUM>% of the weight of the aircraft flying forward. At this point in time and while the aircraft is rapidly still accelerating to <NUM> mph, FPS elements <NUM>, <NUM> are moving into perfectly horizontal position (<NUM> degrees or more perpendicular to their original VTOL position) and a balance between the drag force and thrust is achieved using purely the FPS system (i.e., all air <NUM> is routed via ports <NUM> and <NUM> to supply the FPS elements with motive fluid). Close to a forward air speed of, for example, <NUM> mph, the vanes <NUM> begin to open and allow the air stream <NUM> to pass through the vanes thus pushing the aircraft forward in a faster manner. During said transition to fully wing-borne operation, the augmentation ratio of the FPS is lowered due to the increasing ram drag imposed by the incoming air into the FPS elements <NUM>, <NUM>. The final thrust obtained in wing borne operation can be increased by switching to fully open vanes <NUM> as shown in <FIG> and <FIG> and closing valves <NUM> thereby blocking the air supply to the ports <NUM> and <NUM> and forcing the entirety of air <NUM> to exit the plenum <NUM> via vanes <NUM> resulting in an accelerated stream <NUM> and propelling the aircraft in the forward direction and wing-borne mode at speeds that can be modulated by the RPM of fan <NUM>.

In this manner, an embodiment solves the problem of mismatches between separate takeoff and cruise powerplants by using the same powerplant to supply the mechanical work via shaft <NUM> to the fan <NUM>. In addition, reduction of fuel flow to the main gas turbine providing mechanical power results in slowing down the fan <NUM> similar to a turbofan operation. By shutting off the air to the FPS elements <NUM>, <NUM> at the end of the transition and during fully wing-borne high-speed flight, the fan speed reduction via mechanical work reduction will result in fuel savings and will allow a much wider flight envelope in altitude, speed, and maneuverability, since the aircraft will require significantly lower thrust for forward moving. For instance, <NUM>% of the thrust needed for VTOL using the FPS elements <NUM>, <NUM> can now be supplied by using the nozzle vanes <NUM> for high speed cruising whilst operating the fan <NUM> at lower than maximum speed. This means adjusting to a thrust calculated with an augmentation ratio of <NUM> per Equation <NUM>:
<MAT>
when the aircraft is in full wing-borne mode. A typical general aviation aircraft achieving such thrust would have no problem accelerating to speeds exceeding <NUM> mph and high altitudes. Conversely, a transition can be achieved for transferring from cruise, as illustrated in <FIG>, to hovering via closure of vanes <NUM> and forcing the air through ports <NUM> and <NUM> to open the FPS operation and reverse the swiveling movement of FPS elements <NUM>, <NUM> from nearly horizontal and embedded into the fuselage of the aircraft to nearly vertical position for hovering or landing. With the rotation of FPS elements <NUM>, <NUM>, they can also be used as air brakes slowing down the aircraft to a point where gradually the wings provide less lift and the elements <NUM>, <NUM> provide most of the balance to the weight of the aircraft. At the point where the aircraft has slowed down sufficiently and is nearly stationary in the hovering mode, the modulation of the fan <NUM> (now operating with vane system <NUM> fully closed and ports <NUM> and <NUM> fully opened) allows for the thrust to decrease to a point where the aircraft lands.

No moving parts for FPS elements <NUM>, <NUM> other than swiveling of the elements to help with smooth transition from vertical to cruise (wing borne) operation.

Low temperature of the air discharge from the fan <NUM> with modes <NUM> pressure ratio means low temperature and lightweight materials can be used for the FPS elements <NUM>, <NUM>, such as thermally resistant plastic composites.

High speed can be achieved in cruise by switching to fan type of operation.

The gas turbine can be replaced with an electric motor for use with batteries of high energy density.

A high-efficiency system and same size turboshaft turbine can be used hence minimizing cost and weight.

An embodiment of an aircraft <NUM> can be further refined by integrating the FPS system into aerodynamic control surfaces, such as airfoils, for decreased drag during high-speed flight. Such an embodiment is illustrated in <FIG> and <FIG>. In <FIG>, propulsive elements <NUM>, <NUM>, similar in functionality to that of elements <NUM>, <NUM>, are rotated to a horizontal configuration to match the profile of the main aircraft wing <NUM>. In this configuration, thrust is solely generated through the turbofan nozzle <NUM>, and valves <NUM> are closed preventing airflow through FPS elements <NUM> and <NUM>. As illustrated in <FIG>, the FPS propulsive elements <NUM>, <NUM>, as well as accompanying surfaces <NUM>-<NUM>, are rotated relative to wing <NUM> so that thrust is generated upwards for hover and VTOL. In this configuration, the variable nozzle vanes <NUM> are closed and all airflow is directed through the FPS elements <NUM> and <NUM>.

<FIG> illustrates the geometry of this alternate embodiment. Compressed air is directed from the main plenum <NUM> into wall jets (not shown) in devices <NUM>, <NUM>. These wall jets entrain ambient air at a high bypass ratio through the slot-shaped periphery across trailing surfaces <NUM>, <NUM>. Surfaces <NUM> and <NUM> are partially circumscribed by sidewalls 34a, 34b, 35a, 35b. These sidewalls taper toward the airfoils trailing edges <NUM> and <NUM>.

In <FIG>, the surfaces <NUM>, <NUM> play a role in generating more lift (lift augmentation) at angles shallower than <NUM> degrees to the horizontal (direction of flight). In this case and at the speeds of interest, the suction side of the surfaces <NUM>, <NUM> that see the emerging flow from the elements <NUM> and <NUM> will experience a larger local velocity compared to the aircraft <NUM> velocity. In this case, and just prior to switching to the turbofan nozzle jet modus operandum, the additional lift generated by the difference in pressures on the suction and pressure sides of the surfaces <NUM>, <NUM> will create more lift, as it is known in the industry and by the conditions dictated by Bernoulli. The moment of switch from using elements <NUM> and <NUM> for propulsion during VTOL, acceleration and climb of the vehicle, to guiding the compressed air through the nozzle vanes <NUM>, is anticipated to coincide with best conditions for which the aircraft is moving at fastest, safe speeds, in good coordination with the valves <NUM> making the switch and attitude of the aircraft <NUM>. The switch to using the compressed air as a motive/primary air to the thrusters (elements <NUM> and <NUM>) with entrainment to a direct jet via expansion through nozzle vanes <NUM> at high speeds will coincide with the point where elements <NUM> and <NUM> incur a too-large RAM drag via entrained air to possibly produce enough net force to further accelerate the aircraft <NUM>. For example, a vehicle employing this system may accelerate to speeds in the range of <NUM>-<NUM> mph and reach steady-state flight; for the vehicle to accelerate to <NUM> mph the switch is required. The vehicle may hence suffer an increase in velocity as well as in fuel consumption, due to the elements <NUM> and <NUM> no longer being employed and producing no longer a net force sufficient for acceleration. At this point, the air mass entrainment by these elements and hence thrust augmentation may fall below the acceptable levels, and a switch to use the compressed air flowrate via expansion in nozzle vanes <NUM> allows for further acceleration. At this point the thrusters <NUM>, <NUM> would be able to be aligned with a streamlined profile reducing the drag and the RAM drag existing while in operation. The reverse is valid for slowing down and flying economically in lower speed regimes, at lower speeds but higher efficiency. Such a system results in the fastest possible commercial or military application with VTOL capability.

The switch from thrusters (fluidic) entrainment mode to fan mode results in an optimized thermal and propulsive efficiency between the two regimes. In a regime lower than <NUM> mph approximately, a high thermal efficiency and better propulsive efficiency is obtained using the fluidic (thrust augmentation) via entrainment of ambient air, even if RAM drag increases with entrainment. The entrainment ratio may be for instance ><NUM> and the velocity emerging for the mixture of compressed and entrained air may reach <NUM>/s (<NUM> mph). As entrainment diminishes and RAM increases with speed, a switch to use the entire primary air as direct jet is made beyond <NUM> mph. This way the thermal efficiency increases at a different rate and a high overall total efficiency, as the product between the propulsive and thermal efficiencies is obtained.

Although the foregoing text sets forth a detailed description of numerous different embodiments, it should be understood that the scope of protection is defined by the words of the claims to follow. The detailed description is to be construed as exemplary only and does not describe every possible embodiment because describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, the scope of protection being defined by the appended claims.

Claim 1:
A propulsion system for an aircraft, comprising:
a plenum (<NUM>) having an intake port and an output port;
a powered fan (<NUM>) coupled to a motor configured to power the powered fan (<NUM>), the powered fan (<NUM>) configured to compress ambient air entering the intake port;
one or more ejectors (<NUM>,<NUM>) fluidically coupled to the plenum (<NUM>) via one or more valves (<NUM>); and
a nozzle disposed within the output port, the nozzle comprising a set of nozzle vanes (<NUM>), wherein:
the propulsion system operates in a first configuration in which the nozzle vanes (<NUM>) are closed and the compressed ambient air exits the plenum (<NUM>) only through the one or more valves (<NUM>) into the one or more ejectors (<NUM>,<NUM>),
characterized in that
the propulsion system operates in a second configuration in which the one or more valves (<NUM>) are closed, the nozzle vanes (<NUM>) are open and the compressed ambient air exits the plenum (<NUM>) only through the output port.