Patent Application
20230174229
The field of the invention is a tiltrotor aircraft.
The background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
All current operational or flight-tested tiltrotor aircraft (Bell XV-15 (
Large tiltrotor aircraft such as the 250,000 pounds Karem Aircraft TR75 (
Engine size and configuration choices for a tiltrotor aircraft are also influenced by the engine operation. Engines are certificated with specific time allowances at different power output, called ratings. Common ratings are:
Maximum power required by a helicopter or tiltrotor aircraft occurs in hover flight, typically near the ground where there is the lowest margin for recovery from any air disturbance or aircraft component failure affecting the aircraft altitude-holding or rate of climb. To maximize safety, an aircraft would be designed with entirely redundant engines where engine failure has no impact on flight safety. While most military tiltrotor aircraft, by allowing aircraft takeoff weights close to those requiring full MRP, accept the increased risk of insufficient OEI power to continue flight, multi-engine commercial manned aircraft must avoid it. Additionally, to minimize engine maintenance cost per flight hour, an aircraft would be designed to use no more than MCP for all flight conditions. The 30-second limited OEI rated power is typically no higher than 35% greater than MRP, resulting in the original flight trajectory being unsustainable following a single engine failure in a twin-engine tiltrotor aircraft at takeoff weight with close to MRP power. Special takeoff and landing profiles are prescribed for large commercial helicopters (no existing large commercial tiltrotor aircraft) to accommodate this shortcoming.
Moreover, very low (and continuously improving) turbine engine inflight failure rates in scheduled commercial flight result in one OEI event in 300,000-600,000 flight hours. This further motivates the conventional tiltrotor practice of installing two engines per aircraft.
After considering the size and number of engines in an aircraft, they must be positioned on the aircraft. Conventional multi-engine tiltrotor aircraft have engines positioned at the wingtips near the rotors. This layout has several benefits: lower empty weight. lower cabin noise, higher wing bending relief load and easier maintenance access. Engines may be fixed to the tilting rotor system or alternatively fixed to the static wing structure. Examples of these layout selections are the V-22 Osprey and the Bell V-280 Valor. Rotors are typically coupled with a torque transmitting cross-wing shaft and gearbox system. This system is designed to transmit approximately half of the OEI power of the operating engine to the other rotor in the case of single engine failure.
Past single-engine tiltrotor aircraft naturally placed the engine at or near the aircraft centerline in the fuselage. The experimental Bell™ XV-3, which predated widely available turboshaft engines, was constructed with a single fuselage-mounted 450 hp radial piston engine. Its configuration sacrificed fuselage utility, which is not necessary on an experimental flight demo vehicle, to minimize the engine count. A more recent example of a tiltrotor with a fuselage mounted engine can be found in the proposed unmanned Bell™ V-247 Vigilant, envisioned as operating from amphibious assault ships. U.S. Pat. No. 10,279,901 (Ivans) describes the drivetrain configuration of the V-247. Without engines in the nacelles, the folded footprint is minimized, this being a critical feature of a ship-based naval aircraft.
The U.S. Pat. No. 10,279,901 patents as well as all other extrinsic materials discussed herein are incorporated by reference to the same extent as if each such materials were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.
Turbofan powered fixed-wing transport aircraft are powered by two, three or four engines. The fact that turbofan engines provide their thrust by integrated engine and thruster in a compact assembly allow the engines to be mounted around the fuselage tail cone such as twin-engines in the Bombardier CRJ-500, three-engines in the Boeing 727, and four-engines in the Vickers VC-10. Such engine placement is not desired for tiltrotors which need the engines to power the outboard located rotors.
The engine position justifications mentioned herein apply only to aircraft in which the engines power rotors on the wings. Turbojet and turbofan aircraft exist with a combination of fuselage and wing-mounted engines, such as the Lockheed™ L-1011 and Douglas™ DC-10. Conventional helicopters also include multiple engines mounted to the fuselage, such as the Sikorsky™ CH-53E and Boeing™ CH-47. These applications and the associated design considerations are dissimilar to the tiltrotor application of the inventive subject matter.
The inventive subject matter provides apparatus, systems, and methods in which an aircraft with tilting rotors is configured with a combination of wing-mounted engines and a fuselage-mounted engine.
The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus, if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
As used herein, and unless the context dictates otherwise, the term “coupled to” is intended to include both direct coupling (in which two elements that are coupled to each other contact each other) and indirect coupling (in which at least one additional element is located between the two elements). Therefore, the terms “coupled to” and “coupled with” are used synonymously.
The inventive subject matter incorporates a fuselage-mounted engine in a tiltrotor with wing-mounted engines. Engines can be any powerplant such as reciprocating engine, turbine engine, or electric motor. It provides additional safety through redundancy and additional capability through higher total power beyond what can be achieved by a conventional tiltrotor with exclusively wing-mounted engines. These benefits come without the full operating cost impact of simply including additional engines.
Envisioned operation of the inventive configuration includes helicopter-mode flight with the fuselage-mounted engine at low power to minimize engine noise in the cabin. In the case of a wing-mounted engine failure, the fuselage-mounted engine power increases to compensate. This allows continued safe flight at the critical takeoff, initial climb, and landing conditions. Additional power output from the fuselage-mounted engine also expands the power-limited hover and low-speed flight envelope.
Alternatively, another operating mode consists of the fuselage-mounted engine sharing power equally with the other engines. This produces more noise in the cabin when all engines are in use, which may be undesirable for passenger transportation but would be acceptable for cargo transportation. All engines could operate at or below MCP rating during takeoff and landing, maximizing the TB 0 of all engines and minimizing the time for power to increase to the required level during an engine failure event.
During cruise flight in airplane-mode, the fuselage-mounted engine power can be reduced, or the engine can be shut down to minimize cabin noise and vibration, especially when transporting passengers. Limiting the operation of the fuselage-mounted engine to takeoff and landing segments will reduce the maintenance required compared to the other engines. This limits the additional cost per flight hour impact of the fuselage-mounted engine. The preferred embodiment includes a variable position exhaust flap which minimizes the drag of the fuselage-mounted engine in cruise when the engine is at low power or shut down.
In alternative embodiments, the aircraft 400 may not include outboard wings 460. In alternative embodiments, the aircraft 400 may not include tails 470, or the tails 470 may be of other configurations such as T-shape or H-shape.
As in
Fuselage mounted engine 512 may be of higher or lower maximum output than the other engines. The propulsion drive system 510 power and torque capacities are sufficient to accept the highest output of any engine.
As in
In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, reaction conditions, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the invention may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements.
As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention. Unless a contrary meaning is explicitly stated, all ranges are inclusive of their endpoints, and open-ended ranges are to be interpreted as bounded on the open end by commercially feasible embodiments.
Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
It should be apparent to those skilled in the art that many more modifications besides those already described are possible without departing from the inventive concepts herein. The inventive subject matter, therefore, is not to be restricted except in the spirit of the appended claims. Moreover, in interpreting both the specification and the claims, all terms should be interpreted in the broadest possible manner consistent with the context. In particular, the terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Where the specification claims refers to at least one of something selected from the group consisting of A, B, C . . . and N, the text should be interpreted as requiring only one element from the group, not A plus N, or B plus N, etc.
