ELECTRICAL VERTICAL TAKE-OFF AND LANDING AIRCRAFT

Technical field

The present invention relates to the field of airborne and flying vehicles. More specifically it relates to an electrically powered aircraft having vertical take-off and landing as well as stationary flight capabilities.

Background

Currently available vertically capable aircraft, also known as vertical take-off and landing (VTOL) aircraft are generally denied permission for routine powered ternninal operations (e.g. take-off, low altitude climb, landing, etc.) in populated, built-up areas for one or more of four reasons: safety, noise, exhaust emissions, or outwash velocity. Further, current rotary-wing VTOLs, except for very advanced tilt rotor aircraft, cannot compete with similar payload-class, fixed-wing, propeller-driven aircraft in speed and range when unrestricted expansive take-off and landing facilities and climb corridors are conveniently available at both ends of a mission. So the simultaneous attainment of radically improved terminal safety, tolerable noise and fumes, modest outwash velocity and competitive fixed-wing speeds, efficiencies, and ranges would enable rotary-wing aircraft to dominate the current light aircraft market, subject to price differentials, and open up the vast denied market for terminal operations in built-up areas. Two other factors, though not essential to correct the above rotary-wing shortfalls, add to the market expansion potential for the subject electrically-powered propeller craft: (1 ) independence from logistically burdensome fuels (e.g., JP, hh, etc.) at light-duty bases, particularly in built-up areas, and (2) fully autonomous flight control/management to relieve the stiff requirement for specialized pilot proficiency, thus eliminating another disincentive for vertical aircraft ownership/operation.

Although numerous low-performance electric fixed-wing aircraft have been built, the only widely publicized claims to an electric tilt rotor aircraft are made by FALX AIR™ Hybrid Tilt Propeller. To the degree that popular descriptions are accurate: (1 ) the configuration is a low aspect ratio tilt-wing, not a tilt-propeller; (2) the batteries in the FALX AIR are supplemental to the internal combustion engine to assist Hover-Out-of- Ground-Effect (HOGE) and climb and do not provide separate full HOGE power; hence, the FALX AIR lacks fully redundant power in the dead man zone for silent, safe take-off and landing in built-up areas; (3) the dual electric motors/nacelle are insufficient at this moderately high disk loading to supply HOGE with one-propulsion-motor- inoperative (OPMI), thus severely compromising safety in built-up areas; and (4) the FALX AIR makes no pretence of basing-independence allowing all-electric operation for basing in the absence of conventional logistic fuels.

Another concept has been patented from Kuhn Ira, where he claims to invent an electric tiltrotor aircraft. This aircraft however is controlled like regular tiltrotor aircrafts. So steering will be done by the at least 2 rotors in place for roll, pitch and yaw steering - similar to helicopters. These concepts are highly complicated and expensive to develop and produce as you need helicopter systems.

Similarly, the Aurora Flight Science's™ Excalibur concept VTOL electric hybrid is not a tilt-propeller configuration, but rather a direct thrust turbofan, 70% of vertical lift, with supplemental electric ducted fan lift during HOGE.

Four recent advances in disparate technologies can synergize to enable efficient electric tilt-rotor VTOL aircraft. Tilt-rotor aerodynamic, structural, and propulsive efficiencies have improved. Extremely flight-efficient tilt-rotor aircraft, far beyond the V- 22's anaemic lift-to-drag ratio, low propulsion efficiency, and high structural weight fraction result in more than 2 times the V-22's specific payload/times/range. Electric motor power densities have increased. High-performance, light-weight electric motors and generators can have more than three times the power-density of motors being introduced in electrically propelled automobiles. Battery energy densities have also increased and can provide specific energy densities of 100, 200, 300, or even up to 400 W-h/kg (watt-hour per kilogram). Furthermore, autonomous flight control and management systems have dramatically improved. For example, autonomous flight control and route/ATC management with pilot override, which allow for totally autonomous flight from take-off to landing have been demonstrated in the A-160 Hummingbird. All of the above individual subsystem elements for a new electrically-powered tiltrotor VTOL (E-VTOL) have already been separately demonstrated: (1 ) Hardware has been demonstrated with prototypes of very high performance electric motors/generators, small/light/low-sfc turbines, moderately high performance lithium batteries, variable speed rigid propellers, light weight all-carbon structures, and autonomous flight/management of rotary wing VTOLs. (2) Extensive vetting by independent parties of related aerodynamically efficient tilt- propeller airframe designs (though not with electric propulsion architectures) has testified as to the practicality of the assumed aerodynamics and weights. (3) Finally, the very high-performance lithium batteries necessary for the purebred battery electric architectural variant are at the bench chemistry stage within the National labs and less visibly with private firms, thus developable with expected vigour. What has yet to be appreciated is that the above advances can now be combined to realize many new capabilities that address issues with the known art. The contemplated E-VTOL aircraft have tolerable noise, zero emissions, or acceptable outwash velocity necessary for powered terminal operations in populated, built-up geography. An E-VTOL aircraft has vertical flight safety improvements to bring rotary- wing aircraft into parity with fixed-wing competitors (e.g., factor of 10 reductions in accidents per flight-hour) and makes vertical flight politically compatible with terminal operations in built-up areas, such as elimination of the "dead man's zone". Electrically- powered, vertically-capable aircraft can have market-competitive speed and range relative to current personal, executive, light cargo, public safety, and military fixed-wing, propeller-driven aircraft below 20Ό00 lb gross weight. Such aircraft also have the benefit of basing-independence from conventional on-site liquid fossil fuel support for short range operations where only electrical power would likely be required for recharging batteries. The aircraft also have naturally low infra-red and acoustic signature in terminal operations where combat threats are most prevalent. Contemplated designs also eliminate a requirement for a two-speed gearbox or mechanical cross shafting that would ordinarily be necessary for optimized vertical lift, horizontal cruise propeller RPM, and safe vertical terminal operations when separate propeller nacelles are driven by conventional turbine engine mechanical drive trains. Designs can also include non-tilting back-up and/or secondary engines in the electric hybrid which avoid lubrication problems and engine design specialization in typical "engine-in-nacelle" tilt-propeller aircraft. Additionally electric hybrid VTOL (E-VTOL) have a wide flexibility in choice of back-up and/or secondary energy source types or sizes within the same airframe to suit the desired cruise speed and altitude with no change in propeller electric drive motors which are sized for vertical flight and hence over-powered for all but highest speed cruise.

The above advanced capabilities can be achieved using multiple electric motors to drive each propeller through one or more fixed reduction gearboxes and a choice of at least two power supply architectures, all of which enable full redundancy in both propeller drive motors and electric power supply for safe, hover-out-of-ground- effect (HOGE) in built-up areas. All two are purely electric during quiet, emission-free operations in built up areas. A heavy hybrid can be entirely electric, hence basing- independent, for short range operations (e.g., less than 50 nautical miles). A purebred battery architecture can be innately all-electric for full flight range (e.g., greater than 200 nm). A light hybrid offers full range (e.g., on the order of 1000 nm) flight, but can require traditional logistic fuel availability under normal basing conditions even though it retains quiet, safe, all-electric terminal operations capability. All designs benefit from fully autonomous flight control with pilot override to reduce or eliminate pilot skill requirements and further improve safety of this inherently complex vertical lift aircraft.

Therefore, there remains a considerable need for methods, systems, and configurations for providing VTOL tilt- propeller aircraft.

Summary of the invention

In view of the foregoing disadvantages or limitations of existing VTOL aircraft the present invention proposes an improved VTOL aircraft in the form of a winged electrically-powered vertical take-off and landing aircraft, comprising: a cockpit having a longitudinal axis, and at least two wings extending each along an axis from the cockpit symmetrically with respect to said longitudinal axis of the cockpit, and at least one electrical propeller unit arranged on each of the wings, each of said propeller unit comprising an electrical motor and a propeller directly or indirectly linked to an arbor of the electrical motor so as to rotate about an axis of rotation, and each of said propeller and/or at least part of the wings being tiltable in a vertical plane containing the propeller's axis of rotation with respect the axis of the wing on which it is arranged, and each of said propeller unit being electrically connected to primary electrical energy source disposed in said cockpit, wherein the aircraft further comprises an air-blowing steering system arranged at a tail of the aircraft so as to blow air in a downward direction for stabilized hover, pitch steering and yaw steering of the aircraft. The VTOL aircraft according to the invention provides a much simpler and cost- effective solution than the VTOLs aircraft known from the prior art as it relies essentially on electrically powered tiltable propellers associated with an inventive air-blowing steering system at the tail of the aircraft to provide any necessary steering and/or control of the aircraft during stationary hovering phases, vertical take-off and landing phases as well as pitch steering of the aircraft to engage forward flying thereof. The aircraft of the invention thereby does not require use of complex, heavy and energy- consuming tilt-rotors assembly as known from other VTOLs or helicopters.

The aircraft of the invention therefore offers a simpler, more reliable and cost- effective design, making it a viable commercial solution, as opposed to existing aircraft of the kind, reserved for an up-market client range.

In a first embodiment of the invention, the air-blowing steering system comprises a fan.

In addition to the fan, the air-blowing steering system advantageously comprises an air projection turret arranged downstream with respect to the air stream projected by the fan so as to direct said air stream projected by the fan in a chosen direction.

Advantageously, the air projection turret may be electrically adjustable in orientation with respect to the cockpit to steer the aircraft.

Preferably, the fan is of turbofan or turbojet type, i.e. it comprises an air turbine disposed in line with the fan ducted in an air conveying funnel arranged in the aircraft. In a second embodiment of the invention, the air-blowing steering system comprises a pressurized air tank.

As in the first embodiment the air-blowing steering system may comprises an air projection turret arranged with respect to a pressurized air outlet of the tank so as to direct an pressurized air stream projected, said air projection turret being electrically adjustable in orientation to steer the aircraft.

According to further preferred embodiments of the invention:

- the primary electrical energy source comprises a first rechargeable battery having at least 1 kW/kg power density and at least 150 W-h/kg usable energy density; - the primary electrical energy source is repositionable within the cockpit of the aircraft for adjusting the centre of gravity thereof;

- it further comprises at least one back-up and/or secondary electrical energy source configured to generate sufficient electricity to power the electric motors of the propeller units and/or at least partially recharge the primary electrical energy source; - the at least one back-up and/or secondary energy source is selected from the group consisting of a second rechargeable battery having a usable energy density of at least 200 W-h/kg, a second rechargeable battery and a fuel driven electric generator that sequentially supply power, where the second rechargeable battery has a usable energy density of at least 200 W-h/kg, and a fuel driven engine with a generator, - the at least one back-up and/or secondary energy source comprises a second rechargeable battery having a usable energy density of at least 200 W-h/kg, such that the aircraft is configured to fly at least 200 nautical miles at the cruise speed of up to 165 knots and at an altitude of at least 4Ό00 feet using only the second rechargeable battery; - the at least one back-up and/or secondary energy source comprises a second rechargeable battery and a fuel driven electric generator that sequentially supply power, where the second rechargeable battery has a usable energy density of at least 200 W- h/kg, such that the aircraft is configured to fly at least 50 nautical miles at the cruise speed of up to 165 knots and at a altitude of at least 6Ό00 feet using only the second rechargeable battery, and at least 650 nautical miles at the cruise speed of 210 knots and at an altitude of up to 18Ό00 feet using the fuel driven electric generator; - the at least one back-up and/or secondary energy source comprises a fuel driven engine with a generator, such that the aircraft is configured to fly up to 1 '200 nautical miles at the cruise speed of up to 300 knots and at an altitude of up to 37Ό00 feet using only the fuel driven engine with the generator; - the primary electrical energy source is configured to be recharged from the at least one back-up and/or secondary energy source;

- the at least one back-up and/or secondary energy source is further configured to retain a preferred orientation relative to gravity as the first and second nacelles tilt.

The electrical VTOL aircraft of the invention is advantageously designed such that the electrical motors of the propeller units can support fail-over operation where a first motor can service a second motor's propeller while the second motor is inoperative. In such embodiments the aircraft can achieve HOGE with one propulsion motor inoperative (OPMI). The motors can be deployed within tiltable nacelles accommodating the propeller units, each nacelle having a corresponding propeller or multiple corresponding propellers. It is also contemplated that the nacelles could house one, two, or more additional redundant motors.

Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments, along with the accompanying drawing figures in which like numerals represent like components.

Description of drawings

FIG. 1 -7 present various views of an electrical VTOL aircraft according to a preferred embodiment of the invention as a 2-seater aircraft; FIG. 8 presents a longitudinal cross section of the electrical VTOL aircraft of figures 1 -7 taken along a vertical plane containing a longitudinal axis of the cockpit of the aircraft Detailed description of preferred embodiments

The present invention pertains to an electrically driven VTOL tilt-propeller aircraft 1 , which may be described and referred to in the following description under the acronym E-VTOL. The E-VTOL aircraft 1 of the invention, an example of which is represented in the appended figures, exploits advanced electric propulsion technology together with highly efficient, autonomously piloted Vertical Take-Off and Landing (VTOL) systems with pilot override. The E-VTOL aircraft 1 of the invention has been developed by the inventors with the aim of bringing the VTOL capable aircraft to a completely new status and commercial relevance and viability thanks to a tilt-propeller design relying on electrical power as energy for driving tiltable propeller units. The E-VTOL aircraft 1 of the invention accordingly offers a safe, legal, and practical flying vehicle to operate within populated, built-up localities, and to achieve speeds and ranges competitive with current fixed wing, propeller-driven aircraft of the same payload class, while less efficient rotary wing aircraft (e.g., helicopters and compounds) innately show lower lift-to-drag ratios preventing them from competing with fixed-wing, propeller-driven aircraft in speed and range.

The inventive subject matter encompasses at least three fundamentally different electric propulsion architectures (e.g., purebred battery; light hybrid; and heavy, basing- independent hybrid, etc.) which, when mechanized on advanced, high-efficiency tilt- propeller vertical take-off and landing (VTOL) aircraft, substantially expand the performance envelope, safety, or basing options over that currently available with conventional helicopters, tiltrotor and fixed wing aircraft, be it electrically or combustion powered.

The significant differentiation of the tilt-propeller aircraft 1 of the present invention compared to regular tilt-rotor aircraft known from the prior art is the massively different way of steering.

Regular tilt-rotors have two or more rotors which take over all roll/pitch/yaw steering. The tilt-propeller aircraft 1 of the invention has a steering concept like a drone and is therefore a stable platform. Instead of rotors we only operate propellers 2 with pitch steering or not. This will allows a roll steering through different propeller speeds or different propeller blade angles. The roll and yaw steering of the aircraft 1 will be done by a fenestra, fan device 3 or with pressurized air that has been produced during travel at the tail 4 or everywhere on the aircraft to provide stable hover, a smooth translation to forward speed. In regular travel speed, the aircraft 1 will be steered like a regular plane with aerodynamic rudders in any kind of configuration.

Battery energy will provide energy to have a stable take off, hover and translation to travel speed for minimum of 3 minutes. As soon as the aircraft 1 reaches travel speed, the electric engines will be switched to generators that will be propelled by a fuel driven engine of any kind and produce the needed energy to a) supply the electricity to recharge the batteries for approach and landing operation and as well the energy for the propulsion electric engines on the nacelles or it can be used as well as a purebred electric VTOL.

Myriad high energy density batteries are currently available having a wide variety of applications. Such battery technologies can be adapted for use within the disclosed subject matter. Example batteries 6 can include the BA 5590 L1-O2 battery produced by Saft Inc. having a specific energy density of 250 W-h/kg. Another example battery can include the BA 7847 Lithium-Manganese Dioxide battery having an energy density of 400 W-h/kg offered by Ultralife Batteries, Inc. It is also contemplated that Lithium-air exchangeable recyclable primary batteries based on Lithium perchloride could supply energy densities in excess of 1000 W-h/kg, where such batteries have a theoretical energy density greater than 3000 W-h/kg as discussed in "Lithium Primary Continues to Evolve" by Donald Georgi from the 42 ^nd Power Sources Conference, June 2006. For example, it is also contemplated that automotive plug-in hybrid can be adapted for use with in the inventive subject matter. The batteries 6 representing the electrical energy store of the VTOL aircraft 1 can also be configured to be field-replaceable for ease of maintenance. Thus, a VTOL aircraft could carry one or more spare batteries 6', 6" that can be swapped with a failed or failing battery 6 in the field during a mission without requiring a maintenance facility. The previously discussed propulsion systems can be applied to numerous types of aircraft markets. In a preferred embodiment, the propulsion systems can be directly applicable to rotary wing and fixed wing aircraft markets. For example, general aviation (e.g., personal, light business, executive business, public safety, light military, light charter, and light cargo class with 1-14 total seats or at least 3'500 lbs payload) aircraft would benefit from such designs by reducing noise, emissions, or other undesirable characteristics. Additionally, unmanned aviation with a gross weight of less than 20Ό00 lbs could leverage the disclosed techniques.

One should appreciate that many other configurations for a driveline are possible, all of which are contemplated. Furthermore, one should note that the drivelines can lack cross shafts coupling the motors to the propeller, or lack a shifting gearbox as is typical in traditional combustion-based designs of efficient tilt propellers as opposed to inefficient tilt propeller aircraft (e.g., the V-22).

Combining the approaches outlined above for propulsion systems and drivelines confers many abilities or capabilities to the inventive E-VTOL aircraft 1. By providing the ability to safely achieve HOGE while under electrical power, contemplated E-VTOL aircraft 1 can be used or otherwise operate in built-up or populated arenas. The aircraft 1 has low levels of noise and low level emissions. An all-electric, quiet vertical propulsion system simply produces no unacceptable location emissions during vertical flight regime or initial climb.

An E-VTOL aircraft 1 based on the disclosed systems can provide for a market- viable purebred all-battery configuration, where the aircraft can have a range in excess of 200 nm with a vertical ascent within three minutes. Such an aircraft can also have descent and powered vertical landing reserves of at least one minute.

A heavy hybrid having a battery-only range in excess of 50 nm could operate locally to and from a logistically unsupported base. These bases are expected to provide electrical recharge energy to recharge the heavy hybrid's batteries. Contemplated configurations also lack a requirement for a 2-speed gearbox normally required to efficiently match the large variation in required propeller RPM between hover and cruise operation modes due to poor turn- down fuel consumption of typical turbine-powered propeller with mechanical drive trains using fixed ratio gearboxes. Rather, the contemplated designs exploit the large turndown required in propeller RPM for cruise efficiency without a multi-speed gearbox. The contemplated designs have safety exceeding that of conventional mechanical driveline rotary-wing aircraft. For example, the contemplated designs not only have a normal innate ability to provide safe auto-rotation upon loss of all drive power, the electrically propelled propellercraft hybrids can descend for controlled battery-powered hover or vertical landing after loss of a back-up and/or secondary energy/power source (e.g., larger batteries, fuel-cells, semi-cells, engine/generator, etc.). In a similar vein, hybrids can hover or land vertically using the back-up and/or secondary energy/power source should the batteries become debilitated. The electrically propelled purebred battery-powered tilt-propellers 2 or hybrid propellercraft in battery mode can perform powered hover or vertical landing after partial battery debilitation because the batteries can be split into sections for electrical isolation of a failed battery section. The same reasoning applies to elimination of the dead man's zone during take-off or landing, particularly in built-up areas.

Light propulsion motor weight (e.g., less than 0.35 Ibs/shp 4-minute output) allows for installation of at least two full-lift power propulsion motors per nacelle 21. In some embodiments, a nacelle could house at least three half-lift power propulsion motors in each propeller nacelle without requiring mechanical cross-shafting to share load while under OPMI during terminal operations. Such an approach is considered advantageous in conditions where the dead man's curve or auto-rotation creates unacceptable risk in built-up areas.

Contemplated E-VTOL aircraft 1 has altitude-independent maximum continuous power from electric propulsion limited by continuous power available from the batteries 6 or from back-up and/or secondary energy/power sources 6', 6". E-VTOL aircraft lack a requirement for coupling propeller/propulsion motor RPM from a back-up and/or secondary RPM if such a back-up and/or secondary relies on rotating generators, thus simplifying design or implementation criteria. Additionally, the designs also eliminate a requirement for multiple axis thermal engine operation in hybrids, hence removing special design restrictions for multi-axis lubrication on typical nacelle mounted tilt rotor engines. For operations in built-up areas with civilian personnel, the electric tilt-propeller aircraft 1 will, as with other rotary wing aircraft, keep disk loading below 15 Ibs/sq. ft for outwash velocity reasons and propeller tip speed below Mach 0.7 at sea level in a standard atmosphere for acoustic reasons. Such a configuration allows for achieving HOGE while generating less than 60 dB of sound as measured by an observer on the ground 1 '500 feet from the aircraft.

FIG. 1 -7 show the layout of a 2-place, cabin class, and 1 '650 lb gross weight t i It— propeller. The aircraft 1 is capable to hover OGE at 8Ό00 ft at ISA +20°C and carry a payload of 400 lb. Tilt-propeller aircraft is capable to hover for max. 8 min. (at today's battery technology) and accelerate up to 165 kt travel speed for up to 3 hours endurance before again landing configuration can be met for 8 min. The big difference to regular tiltrotor, and electric tiltrotors is the fact that a tilt-propeller aircraft has only regular pitch-propellers (instead of rotors) and the steering is made by moving air at the specific requested place to become a stable hover configuration.

FIG. 8 presents the schematic working concept of the 2-seater. Clearly visible is the way we produce the tail 4 airflow to steer the aircraft. Using as well one or more electric engines that propel a fan 3 or fenestra that can be directed into different directions (up/down/right/left/forward/backward). Additionally the electric engine 5 that is driving the fan 3 is used as a generator during travel speed.

The disclosed inventive EVTOL aircraft 1 makes strides over known art by combining various subsystems in manners that achieve unexpected results. Ordinarily, designers would avoid using a plurality of electric drive motors within a VTOL aircraft due to the complexities of de-clutching such motors from a combining gearbox after motor failure. However, the applicants have appreciated that the benefits far outweigh the inefficiencies. The complete new way of steering makes the concept completely new. We do not rely on complex helicopter kind of rotors but on regular propellers and fans. The inventive subject matter is considered to include at least three architectures of electrically driven vertical take-off and landing (VTOL) tilt-propeller aircraft which are (1 ) politically compatible in safety, noise, exhaust emissions, and outwash velocity with terminal operations (powered hovering, VTOL) in densely populated built-up areas, (2) market competitive in range and speed, with existing equivalent class, fixed-wing and rotary-wing aircraft, (3) basing-independent to a degree by reliance on electric energy recharge instead of entirely on on-board electrical generators using logistic fuels, and which are variously composed of previously demonstrated, independently vetted, technically equivalent, aerodynamically efficient, lightweight airframes, efficient multi- RPM propellers, lightweight reduction gears - if any, high power density electric drive motors and generators, high energy and power density batteries, efficient lightweight engines and fuel cells, and autonomous flight management systems and multiple additional safety sensors that as well allow pilots independent flight like a drone today.

One should appreciate that presented concepts also allow for E-VTOL aircraft having the following characteristics as discussed above: An electric motor-driven, high aspect ratio (>12) tilt-propeller aircraft, with glide ratio≥14, cruise propeller propulsive efficiency≥0.85, empty weight fraction <0.50 (absent electrical energy/power package source) A plurality of electric drive motors for each propeller with each motor of sufficient power that one propulsion motor inoperative (OPMI) will not prevent hover- out-of-ground effect (HOGE) and will allow continued HOGE without the requirement for propulsion cross-shafting, For light- hybrid electric power train architecture, sufficient rechargeable electric energy storage (e.g., battery) at >150 W-h/kg (usable) to enable 8 minutes of take-off and climb and 8 minute of landing, all at HOGE power draw, and power capacity to execute 30 second vertical landing with half electrical energy storage inoperative, all without recourse to non-stored electrical back-up and/or secondary energy/power For heavy-hybrid electric power train architecture, sufficient rechargeable stored electric energy (e.g., battery) at >200 W-h/kg (usable) to enable≥ 50 nm range without recourse to non-stored electrical back-up and/or secondary energy/power For purebred electric power train architecture, sufficient rechargeable stored electric energy (e.g., battery) at >400 W-h/kg (usable) to enable,≥ 200 nm range with no non-stored electrical back-up and/or secondary energy incorporated in the power architecture Propeller tip velocity <0.7M, and Disk loading < 15 Ibs/sq. ft.