Patent Application
20130327879
The present disclosure relates to rotary-winged aircraft. More specifically, the present disclosure relates to helicopters with high-speed operational capabilities.
Helicopters have historically suffered from low operational cruise speeds, of up to about 160 knots. To increase the speed of operation of a conventional helicopter above that threshold, there is a tendency to increase a main rotor forward tip angle relative to the freestream airflow, which results in a high degree of main rotor flapping, reduced propulsive efficiency, reduced rotor stall margin, and reduced lift-to-drag ratio. Further, a negative fuselage angle of the helicopter relative to the freestream airflow is increased, the overall result being that the fuselage is downloaded, which requires yet more rotor power to overcome. The conventional tail of the helicopter including a conventional tail rotor adds drag due to the tail rotor hub position and tail rotor H-force drag, also requiring increased main rotor power to overcome.
Historically helicopters have included a wing extending from the fuselage to provide additional lift at the fuselage to compensate for the download and to increase stall margin of the main rotor. Including a wing, however, also often compromises helicopter design in other ways. First, the addition of the wing increases empty weight of the helicopter and increases vertical drag during hover operation. This results in lower payload capabilities and increased cost due to the additional components. The wing also increases parasitic drag during cruise operations, thus increasing cruise power required to attain the high speed operation and also increasing fuel burn. Finally, the physical size and location of the wing on the fuselage makes positioning of components such as cargo doors and rescue hoists difficult. The wing inhibits personnel movement aboard the helicopter, blocks visibility, and makes shipboard operations, where components such as main rotors are folded to save space, difficult.
A rotary wing aircraft includes an airframe and an extending tail extending from the airframe. A main rotor assembly is operably connected to the airframe and includes a plurality of rotor blades operably connected to a rotor shaft, and one or more active adaptive devices located at one or more rotor blades of the plurality of rotor blades. The one or more active adaptive devices are operably connected to an aircraft flight control system such that, when activated, the one or more active adaptive devices change one or more operational characteristics of the rotor assembly. A tail rotor is operably connected to the extending tail. The tail rotor is rotatable about a tail rotor axis, the tail rotor axis movable from laterally-extending to rearward-extending.
A method of operating a rotary wing aircraft includes rotating a plurality of rotor blades of a main rotor assembly about a rotor shaft. One or more active adaptive devices located at one or more rotor blades of the plurality of rotor blades are activated. Activation of the one or more active adaptive devices results in changes in one or more operational characteristics of the rotor assembly. A plurality of tail rotor blades of a tail rotor are rotated about a tail rotor axis, the tail rotor located at an extending tail of the rotary wing aircraft. The tail rotor is moved such that the tail rotor axis changes from laterally-extending to rearward-extending.
These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings.
The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which:
The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings.
The invention described herein is to enable efficient high speed helicopter forward flight. The configurations described herein reduce helicopter performance penalties incurred by conventional, wingless helicopters and reduces penalties associated with a winged helicopter configuration, which has been historically used to eliminate the aforementioned conventional helicopter performance penalties. This is achieved by the integrated design of an adaptive rotor system enabling efficient high speed forward flight with a tail rotor that is reconfigurable to an auxiliary propulsor. The combination enables a new synergistic thrust and/or power sharing relationship between a main rotor, fuselage, horizontal tail, vertical tail, and auxiliary propulsor.
The rotor blades 20 include one or more active adaptive devices which allow the rotor blades 20 and main rotor assembly 12 to adapt to different flight regimes and the unique requirements of each mission. The adaptive devices, when selectively activated based on mission requirements, may, for example, increase maximum rotor blade 20 lift, suppress characteristics such as vibration and/or noise, increase flight speed, improve hover performance at high gross weights, increase maneuverability, or the like. A primary goal is to use the combination of multiple devices to enhance overall rotor attributes and performance. An individual on-blade device typically enhances one or two rotor attributes such as low noise, low vibration, efficiency, maneuverability, payload, or speed. The purpose is to use multiple devices to provide a rotor increased capabilities among all these attributes. The devices can be turned on or off as the mission segment requires. The devices are also designed to work synergistically to maximize rotor capabilities.
Referring to
Referring to
It is highly desirable to reduce the noise of rotor assembly 12 in flight. A powerful means to reduce noise is to reduce rotational speed of rotor assembly 12. However, rotational speed reductions come at the expense of rotor assembly lift and aircraft speed and maneuverability. The reductions are due to rotor assembly stall occurring at reduced flight speeds and/or reduced gross weights. In order to maintain aircraft speed and maneuverability and not sacrifice aircraft gross weight, the flaps 28 and air outlets 36 are utilized at lower rotor assembly rotational speeds. Thus rotor assembly lift, and aircraft speed and maneuverability can be maintained at adequate levels. As such, synergy between flaps 28, outlets 36, and the rotational speed of the rotor assembly 12 reduces rotor assembly noise levels. In some embodiments rotational speed reductions between about 10% and 15% can be attained. In situations where an increased rotor assembly rotational speed is required or desired, such as when increased gross weight capability is desired, another active measure may be utilized to reduce rotor assembly 12 noise. For example, the rotor blade 20 may include a tip jet outlet 48 (shown in
Airflow 46 pumped through the duct 40 creates a high pressure mass source at the blade tip 50. The mass source, when modulated by releasing airflow 46 through the tip jet valve and outlet 48, at a once per rotor 12 revolution frequency cancels rotor blade 20 thickness noise. The airflow 46 released through the tip jet outlet 48 creates a positive pressure pulse shape which counteracts a negative pressure pulse shape of the rotor blade 20. Rotor blade 20 noise is a result of this negative pressure pulse and by counteracting it with the positive pressure pulse the rotor blade 20 noise is reduced. In some embodiments, the airflow 46 through the tip jet outlet 48 is activated when the rotor blade 20 is advancing. Further, the airflow 46 through the tip jet outlet 48 may be modulated as a substantially constant flow to diffuse a vortex at the blade tip 50, thereby reducing blade vortex interaction noise.
The mission-adaptive rotor blade 20 as described above allows for operational cruise speed of the aircraft 10 of about 220 knots.
Referring again to
The combination of the adaptive main rotor 12 and the tail rotor 18 enables full aircraft 10 weight to be supported by the main rotor 12 with adaptive devices, thus eliminating the need for a wing. The laterally-extending to rearward-extending tail rotor 18 relieves the main rotor 12 from propulsive force, thus shifting the main rotor 12 from a nose down attitude to a near level attitude. The near level main rotor 12 attitude eliminates large main rotor 12 flapping thus reducing vibrational loads and increasing rotor head component life. The near level rotor attitude also increases rotor stall margin and rotor lift to drag ratio. It also raises fuselage 14 attitude from an uncomfortable negative download condition to a comfortable nose up lifting condition. The same attitude change drives the horizontal tail 16 from a negative download condition to a positive upload condition. The tail rotor 18 movement from lateral expending to rearward extending position reduces tail rotor 18 drag and further increases aircraft 10 efficiency. All of these advantages are dependent on the combination of active device main rotor 12, reconfigurable tail rotor 18, and the new combination of thrust and lift sharing derived from the new method of aircraft trim.
While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.
