Patent Description:
Aircrafts that can hover, take off and land vertically are commonly referred to as Vertical Take-Off and Landing (VTOL) aircrafts. This classification includes fixed-wing aircrafts as well as helicopters and aircraft with tilt-able powered rotors. Some VTOL aircrafts can operate in other modes as well, such as Short Take-Off and Landing (STOL). VTOL is a subset of V/STOL (Vertical and/or Short Take-off and Landing).

For illustrative purposes, an example of a current aircraft that has VTOL capability is the F-<NUM> Lightning. Conventional methods of vectoring the vertical lift airflow includes the use of nozzles that can be swiveled in a single direction along with the use of two sets of flat flapper vanes arranged <NUM> degrees to each other and located at the external nozzle. The propulsion system of the F-<NUM> Lightning, similarly, provides vertical lifting force using a combination of vectored thrust from the turbine engine and a vertically oriented lift fan. The lift fan is located behind the cockpit in a bay with upper and lower clamshell doors. The engine exhausts through a three-bearing swivel nozzle that can deflect the thrust from horizontal to just forward of vertical. Roll control ducts extend out in each wing and are supplied with their thrust with air from the engine fan. Pitch control is affected via lift fan/engine thrust split. Yaw control is through yaw motion of the engine swivel nozzle. Roll control is provided by differentially opening and closing the apertures at the ends of the two roll control ducts. The lift fan has a telescoping "D"-shaped nozzle to provide thrust deflection in the forward and aft directions. The D-nozzle has fixed vanes at the exit aperture.

The design of an aircraft or drone more generally consists of its propulsive elements and the airframe into which those elements are integrated. Conventionally, the propulsive device in aircrafts can be a turbojet, turbofan, turboprop or turboshaft, piston engine, or an electric motor equipped with a propeller. The propulsive system (propulsor) in small unmanned aerial vehicles (UAVs) is conventionally a piston engine or an electric motor which provides power via a shaft to one or several propellers. The propulsor for a larger aircraft, whether manned or unmanned, is traditionally a jet engine or a turboprop. The propulsor is generally attached to the fuselage or the body or the wings of the aircraft via pylons or struts capable of transmitting the force to the aircraft and sustaining the loads. The emerging mixed jet (jet efflux) of air and gases is what propels the aircraft in the opposite direction to the flow of the jet efflux.

Conventionally, the air stream efflux of a large propeller is not used for lift purposes in level flight and a significant amount of kinetic energy is hence not utilized to the benefit of the aircraft, unless it is swiveled as in some of the applications existing today (namely the Bell Boeing V-<NUM> Osprey). Rather, the lift on most existing aircrafts is created by the wings and tail. Moreover, even in those particular VTOL applications (e.g., take-off through the transition to level flight) found in the Osprey, the lift caused by the propeller itself is minimal during level flight, and most of the lift force is nonetheless from the wings.

The current state of art for creating lift on an aircraft is to generate a high-speed airflow over the wing and wing elements, which are generally airfoils. Airfoils are characterized by a chord line extended mainly in the axial direction, from a leading edge to a trailing edge of the airfoil. Based on the angle of attack formed between the incident airflow and the chord line, and according to the principles of airfoil lift generation, lower pressure air is flowing over the suction (upper) side and conversely, by Bernoulli law, moving at higher speeds than the lower side (pressure side). The lower the airspeed of the aircraft, the lower the lift force, and higher surface area of the wing or higher angles of incidence are required, including for take-off.

Large UAVs make no exception to this rule. Lift is generated by designing a wing airfoil with the appropriate angle of attack, chord, wingspan, and camber line. Flaps, slots and many other devices are other conventional tools used to maximize the lift via an increase of lift coefficient and surface area of the wing, but it will be generating the lift corresponding to at the air-speed of the aircraft. (Increasing the area (S) and lift coefficient (CL) allow a similar amount of lift to be generated at a lower aircraft airspeed (V0) according to the formula L = ½ ρV<NUM>SCL. , but at the cost of higher drag and weight. ) These current techniques also perform poorly with a significant drop in efficiency under conditions with high cross winds.

While smaller UAVs arguably use the thrust generated by propellers to lift the vehicle, the current technology strictly relies on control of the electric motor speeds, and the smaller UAV may or may not have the capability to swivel the motors to generate thrust and lift, or transition to a level flight by tilting the propellers. Furthermore, the smaller UAVs using these propulsion elements suffer from inefficiencies related to batteries, power density, and large propellers, which may be efficient in hovering but inefficient in level flight and create difficulties and danger when operating due to the fast-moving tip of the blades. Most current quadcopters and other electrically powered aerial vehicles are only capable of very short periods of flight and cannot efficiently lift or carry large payloads, as the weight of the electric motor system and battery is already well exceeding <NUM>% of the weight of the vehicle. A similar vehicle using jet fuel or any other hydrocarbon fuel typically used in transportation will carry more usable fuel by at least one order of magnitude. This can be explained by the much higher energy density of the hydrocarbon fuel compared to battery systems (by at least one order of magnitude), as well as the lower weight to total vehicle weight ratio of a hydrocarbon fuel based system.

<CIT> discloses a nozzle comprising an internal surface, a curved surface merging into the internal surface, a narrowed throat in the internal surface located towards the leading edge of the nozzle, a jacket surrounding the internal surface, an annular internal slot located in the internal surface between the curved surface and the narrowed throat and communicating with the jacket. The fluid under pressure is supplied through the slot the arrangement of the slot being such that the fluid is ejected at an acute angle of under <NUM>° to the direction of the exit flow tangentially to the curved surface.

<CIT> discloses that the Jetstream flowing through a tubular thrust ejector may be prevented from detaching from the inner surface thereof by admitting a portion of the boundary layer of the Jetstream into holes which terminate within an area encircling the aft portion of said inner surface and which communicate with the forward portion of the ejector throat.

<CIT> discloses that, to achieve rapid mixing between a jet flow and its surrounding medium a vane is mounted in the jet downstream of the jet nozzle exit. The vane is oscillated in either pitch or plunge by an appropriate excitation mechanism at a constant frequency. The amplitude of oscillation is typically only a few degrees. The oscillation frequency may be varied to control the entrainment rate.

Accordingly, there is a need for enhanced efficiency, improved capabilities, and other technological advancements in aircrafts, particularly to UAVs and certain manned aerial vehicles.

This 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. In addition, the headings in this application are for reference purposes only and shall not in any way affect the meaning or interpretation of the present invention.

One embodiment of the present invention includes a propulsor that utilizes fluidics for the entrainment and acceleration of ambient air and delivers a high-speed jet efflux of a mixture of the high-pressure gas (supplied to the propulsor from a gas generator) and entrained ambient air. In essence, this objective is achieved by discharging the gas adjacent to a convex surface. The convex surface is a so-called Coanda surface benefitting from the Coanda effect described in <CIT>. In principle, the Coanda effect is the tendency of a jet-emitted gas or liquid to travel close to a wall contour even if the direction of curvature of the wall is away from the axis of the jet. The convex Coanda surfaces discussed herein with respect to one or more embodiments do not have to consist of any particular material.

<FIG> illustrates a cross-section of the upper half of an ejector <NUM> that may be attached to a vehicle (not shown), such as, for non-limiting examples, a UAV or a manned aerial vehicle, such as an airplane. A duct, such as 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.

In an embodiment, and as best illustrated in <FIG>, V-shaped, vortex generating secondary nozzles <NUM> are staggered when compared to a normal rectangular primary nozzle <NUM> and injecting at least <NUM>% of the total fluid stream <NUM> before the balance of the fluid stream massflow is injected at a moment later by nozzles <NUM>. This injection by nozzles <NUM> prior to that of nozzles <NUM> results in a higher entrainment rate enough to significantly increase the performance of the ejector <NUM>. Secondary nozzles <NUM> introduce a more-favorable entrainment of the secondary flow via shear layers and are staggered both axially and circumferentially in relation to the primary nozzles <NUM>.

Primary nozzles <NUM> include an airfoil, such as a delta-wing structure <NUM>, that is provided with a supporting leg <NUM> connected to the middle point of the primary nozzle <NUM> structure at its innermost side, with a delta-wing structure apex pointing against the fluid stream <NUM> flow to maximize entrainment. This in turn generates two vortices opposed in direction towards the center of the delta wing <NUM> and strongly entraining from both sides of primary nozzle <NUM> the already entrained mixture of primary and secondary fluid flows resulting from nozzles <NUM>. Supporting leg <NUM> may, in an embodiment, serve as an actuating element capable of causing structure <NUM> to vibrate.

Additionally, an embodiment improves the surface for flow separation delay via elements such as dimples <NUM> placed on the Coanda surface <NUM>. The dimples <NUM> prevent separation of the flow and enhance the performance of the ejector <NUM> significantly. Additionally, surfaces of the diffuser <NUM> (see <FIG>) may also include dimples <NUM> and/or other elements that delay or prevent separation of the boundary layer.

Other arrangements not embodying the invention may employ structures different from delta wing <NUM> to enhance entrainment and the attachment of the flow produced through nozzles <NUM>.

For example, one approach may employ thermophoresis in which a cold fluid is made available to cool off surface <NUM> where the separation propensity at high speeds is greater. By cooling off several regions of the surface <NUM>, the hot motive fluid is diverted towards the cold portion of surface <NUM> through the force of thermophoresis. In one embodiment bleed air from the compressor discharge of a jet engine acting as a gas generator is routed towards an internal channel system (not shown) of ejector <NUM> that allows the cooling of hot spots where separation occurs. A typical difference in temperature goes from <NUM> F uncooled to 500F (hot stream temperature of a nozzle <NUM> is <NUM> and wall temperature is brought down to 700F).

Another approach may employ electrophoresis in which elements (not shown) embedded into surface <NUM> generate a local field that enhances fluid attachment and delays or eliminates separation. The current source for such elements can be provided by a battery or a generator coupled with the main gas generator of the vehicle.

Another approach may employ plasma in a manner similar to electrophoresis as in the use of electric fields, albeit in this case acting at high altitudes where plasma generation is less energy-intensive. Specially placed elements (not shown) may enhance attachment and eliminate separation.

Yet another approach may mechanically reduce or enlarge the height of the nozzles <NUM>. By reducing the wall height, it is possible to increase local velocity. Such may be achieved by curving the inlet portion of the individual channels where the hot flow is guided from the plenum to the nozzles <NUM> and manipulating the flow in that manner.

In an embodiment, intake structure <NUM> may be circular in configuration. However, in varying embodiments, and as best shown in <FIG>, intake structure <NUM> can be non-circular and, indeed, asymmetrical (i.e., not identical on both sides of at least one, or alternatively any-given, plane bisecting the intake structure). For example, as shown in <FIG>, the intake structure <NUM> can include first and second opposing edges <NUM>, <NUM>, wherein the second opposing edge includes a curved portion projecting toward the first opposing edge. As shown in <FIG>, the intake structure <NUM> can include first and second lateral opposing edges <NUM>, <NUM>, wherein the first lateral opposing edge has a greater radius of curvature than the second lateral opposing edge.

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, using either current technology or technology developed after the filing date of this disclosure.

Claim 1:
An ejector system (<NUM>) for propelling a vehicle, the system comprising:
a diffusing structure (<NUM>);
a duct (<NUM>) coupled to the diffusing structure (<NUM>), the duct (<NUM>) comprising a wall having openings (<NUM>) formed therethrough, the openings (<NUM>) configured to introduce to the diffusing structure (<NUM>) a primary fluid produced by the vehicle; and
characterised in that each opening (<NUM>) has an airfoil (<NUM>) positioned within the flow of the primary fluid through the opening (<NUM>).