Patent Application
20130161444
1. Technical Field
The present invention relates generally to the field of aviation and more specifically relates to equipment and methods for increasing overall operational efficiency of certain helicopters.
2. Background Art
The most common propulsion system for helicopters, which historically has been generally employed in both commercial and military helicopters, comprises a series of mechanical interconnections of a rotor to an engine through various types of mechanical transmissions. Several disadvantages are inherent in such conventional systems, whether an internal combustion engine is used as the primary power source or whether a turbine engine is employed. A primary disadvantage of conventional helicopter power systems is that significantly high torque loads are placed on the airframe structure that is used to support the vertical shaft connecting the rotor blades with the engine.
For controllable and sustainable flight, this rotational torque must be counteracted to prevent an undesirable counter rotation of the airframe with respect to the rotor. Typically, this is accomplished by mounting a small tail rotor in a vertical plane with the hub positioned at right angles to the fore-aft axis of the helicopter body. The force applied to the body of the helicopter by the tail rotor is controlled by coordinating the pitch of the tail rotor with the drive power applied to the main rotor blades in order to obtain stable flight operation for the helicopter. Although this configuration is operable, an enormous amount of stress is placed on the body members of the helicopter fuselage as well as the transmission components used to interconnect the engine with both the main rotor and the tail rotor.
It is readily apparent that a large number of rotating and moving parts are required in a conventional helicopter in order to drive and control the two rotors. This is a significant disadvantage because many bearings, operating under significant stress (rotational, centrifugal and the like), must be employed. These bearings and the other moving mechanical parts are costly and require frequent and expensive maintenance. In fact, the maintenance and repair hours generally exceed the actual flight hours of most conventional helicopters. As a result, maintenance is a significant cost factor to be considered for the operation of a conventional helicopter.
Various attempts have been made to overcome the disadvantages of conventional mechanical drive train mechanisms. One approach is to place a jet engine or turbine at the end of each of the rotor blades. This removes the structural requirements placed upon the vertical rotor shaft in conjunction with the interconnection of the rotor to an engine located within the body of the helicopter. The hub of such a rotor-tip, jet-turbine driven helicopter then can comprise a simple rotating disc or the like with its center at the vertical rotor support shaft.
Significant fuel delivery problems, however, exist for supplying fuel from the body or fuselage of the helicopter up through the rotor support shaft and through the hub to the rotating blades. This may also present an extreme safety hazard because of the high volatility of the fuel; and leaks between the hub, the non-rotating rotor shaft, and rotating rotor blade are difficult to prevent. Furthermore, the centrifugal force acting upon the fuel due to the rotating rotor blades changes depending upon the speed of the blade. This can result in either a too rich or too lean fuel mixture supplied to the engine. In addition, the jet engines must breath their own exhaust. Consequently, power failures occur with such helicopters unless complex control mechanisms are provided for controlling the fuel supply to the engines.
To take advantage of the simplified structural requirements of the rotor blade acting as a simple rotating disc, but without the problems of conveying volatile fuel to jet engines mounted on the tips of the rotor blades, various designs utilizing the flow of pressurized air delivered through a hollow rotor shaft to hollow rotor blades have been developed. In systems using this general design, a flow of air passes through the rotor blades to nozzles or air reaction engines located at the tips of each of the blades. Consequently, air discharging through the nozzles results in reactive forces in the opposite direction to rotate the blades about the hub. A variety of attempts to develop practical helicopters using this concept of an air-driven rotor have been made in the past.
For example, in a “cold cycle” pressure jet helicopter system, a power plant drives a compressor that, in turn, delivers compressed air to the hollow axis (or mast) of the main rotor. The air passes through the hollow mast to a hollow hub, which then distributes the air to hollow rotor blades. The air passes through the hollow blades and is discharged rearward through the blade tip nozzles thereby driving the rotor by jet reaction.
This system is called “cold cycle” because the compressed air is not burned anywhere along the circuit. However, it is important to note that the air is heated by compression to around 400° F. Compression ratios are in the 2.8 to 4.0 range (absolute). Being pneumatically driven from the blade tip, the tip jet helicopter has no torque reaction and hence no tail rotor is required. However, since directional control is still desirable, some small auxiliary device is used to provide directional control to the pilot of the helicopter. Typically, the directional control comprises a directional vane mounted in the path of the engine exhaust. The pressure jet rotor blades tend to be heavy which further contributes to increased stability and safer autorotation characteristics for this helicopter.
The pneumatic drive system of the tip jet helicopter also eliminates the need for a heavy mechanical transmission that further reduces the need for maintenance and can increase reliability. The combination of these features results in a helicopter that is generally easier to fly, safer to land in power out emergencies, requires less maintenance, and is generally more reliable.
While air-driven, jet tip helicopter designs are feasible in concept, they are typically less than half as efficient as a shaft driven helicopter. This is unacceptable for most uses because of the high cost of the fuel consumed by a helicopter in flight and the necessity for storing large amounts of fuel in the helicopter fuselage, which inherently results in added weight and additional reductions in operational efficiency.
These efficiency losses occur for several reasons. For example, the relatively long path that the compressed air must travel from the compressor located within the fuselage up through the support shaft and out through the entire lengths of the blades to the tips limits the practical volume flow rate of air. Further, heat may be lost from air along the path, reducing thrust. Additional inefficiencies develop as the airflow becomes turbulent during the delivery cycle to the tips of the rotors. Accordingly, without improvements in the current drive system for tip jet helicopters, the overall process and user experience will continue to be sub-optimal.
The various implementations of the present invention provide a high efficiency “wye” rotor hub that is introduced into the airflow of the compressed air as the compressed air is delivered to the blades of the helicopters. The conventional hub assembly is replaced by a hub that has a plurality of hollow tubes that more efficiently guide the compressed air into the hollow blades, thereby improving the efficiency of the engine. In the most preferred embodiments of the present invention, the hollow rotor tube hub insert looks much like a “ram's horn” where the flow area of the compressed air entering the hollow mast from the air compressor is diverted equally into a plurality of generally circular tubes or air channels, with each tube having a substantially equal cross-sectional diameter and area and where the number of circular tubes is equal to the number of rotor blades. For a two bladed rotor assembly, the rotor insert would be bifurcated, for a three bladed rotor assembly, the rotor insert would be trifurcated, etc.
The preferred embodiments of the present invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and:
The various implementations of the present invention provide a high efficiency “wye” rotor hub that is introduced into the airflow of the compressed air as the compressed air is delivered to the blades of the helicopters. The conventional hub assembly is replaced by a hub that has a plurality of hollow tubes that more efficiently guide the compressed air into the hollow blades, thereby improving the efficiency of the engine. In the most preferred embodiments of the present invention, the hollow rotor tube hub insert looks much like a “ram's horn” where the flow area of the compressed air entering the hollow mast from the air compressor is diverted equally into a plurality of generally circular air channels or tubes, with each tube having a substantially equal cross-sectional diameter and area and where the number of circular tubes is equal to the number of rotor blades. For a two bladed rotor assembly, the rotor insert would be bifurcated, for a three bladed rotor assembly, the rotor insert would be trifurcated, etc.
By channeling the compressed air more efficiently to the hollow rotor blades of the helicopter, airflow stagnation, which can be common in conventional tip jet hub designs, may be significantly reduced or eliminated which, in turn, reduces the power required to keep the blades rotating at the desired speed and results in a more efficient use of fuel.
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It should also be noted that the high efficiency hub of the present invention may be offered as a retrofit hub for existing helicopters or deployed as a new rotor assembly for original equipment manufacturers of helicopters and helicopter engines. Further, in at least one of the most preferred embodiments of the present invention, a high efficiency hub as set forth herein is packaged in a kit, with instructions on how to obtain the other components necessary (e.g., fuselage, hollow rotor blades, air compressor, engine, instrumentation, etc.) to allow an individual to construct their own helicopter, in accordance with the Federal Aviation Administration's Amateur Built Experimental Aircraft guidelines and regulations.
From the foregoing description, it should be appreciated that high efficiency hub for pressure jet helicopters disclosed herein presents significant benefits that would be apparent to one skilled in the art. Furthermore, while multiple embodiments have been presented in the foregoing description, it should be appreciated that a vast number of variations in the embodiments exist. Lastly, it should be appreciated that these embodiments are preferred exemplary embodiments only and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description provides those skilled in the art with a convenient road map for implementing a preferred exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in the exemplary preferred embodiment without departing from the spirit and scope of the invention as set forth in the appended claims.
