Abstract:
Embodiments refer generally to systems and methods for providing autorotative enhancement for helicopters using an autorotative assist unit coupled to the transmission of the helicopter. Methods of utilizing an autorotative assist unit as well as retrofitting an autorotative assist unit to an existing helicopter are also disclosed. By employing an autorotative assist unit, improved autorotation may be achieved without the need to increase the weight of the rotor.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Not applicable. 
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0002]    Not applicable. 
       REFERENCE TO A MICROFICHE APPENDIX 
       [0003]    Not applicable. 
       BACKGROUND 
       [0004]    In the event of engine failure, a helicopter may employ autorotation to execute a safe landing, wherein the main rotor system of the helicopter is turned by the action of air moving up through the rotor. This generates lift and drag to slow the descent of the helicopter. Autorotation may allow the helicopter to descend and land safely without the use of the main engine. Autorotation may be particularly useful for single engine helicopters. 
       SUMMARY 
       [0005]    In some embodiments of the disclosure, an autorotative assist system for a rotor helicopter is disclosed as comprising a transmission coupled to the rotor, an engine coupled to the transmission (via a drive shaft with a freewheeling unit allowing for free rotation of the rotor upon loss of engine power), and an autorotative assist unit couple to the transmission (typically independent of the engine primary drive system (e.g. drive shaft and/or free-wheeling unit) and/or without any intervening component or gearing such as the freewheeling unit), wherein the autorotative assist unit is operable to store energy during normal engine operation, and the autorotative assist unit is operable to drive the rotor through the transmission to provide supplemental autorotative assistance upon loss of engine power (e.g. when the engine rpm level falls below the rpm level of the rotor). 
         [0006]    In other embodiments of the disclosure, a method of providing autorotative assistance for a rotor helicopter having an autorotative assist unit is provided that comprises, upon loss of engine power, placing the helicopter into autorotation, and providing autorotative assistance to the rotor from the autorotative assist unit (thereby driving the rotor as a supplement to autorotation). 
         [0007]    In yet other embodiments of the disclosure, a method is disclosed for retrofitting a helicopter for improved autorotation capabilities, wherein the helicopter includes a rotor, a transmission having a generator off the transmission housing, and an engine, the method comprising replacing the generator on the transmission with a motor-generator, providing a high capacity/high discharge rate battery system, and electrically connecting the motor-generator to the battery system so that, during normal engine operation, the motor-generator charges the battery system, but upon loss of engine power, the motor-generator is operable to draw energy from the battery system to drive the rotor for autorotative assistance. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    For a more complete understanding of the present disclosure and the advantages thereof, reference is now made to the following brief description, taken in connection with the accompanying drawings and detailed description: 
           [0009]      FIG. 1  illustrates a helicopter comprising an autorotative assist unit according to an embodiment of the disclosure; 
           [0010]      FIG. 2A  is a schematic illustration of an autorotative assist unit according to an embodiment of the disclosure; 
           [0011]      FIG. 2B  is a flowchart illustrating a method of providing autorotative assistance for a rotor helicopter; 
           [0012]      FIG. 3A  is a side view of a system including the transmission, engine and rotor of a helicopter without an autorotative assist unit, shown within the helicopter; 
           [0013]      FIG. 3B  is a side view of a system including the transmission, engine and rotor of a helicopter without an autorotative assist unit; 
           [0014]      FIG. 3C  is a top view of a system including the transmission, engine and rotor of a helicopter without an autorotative assist unit; 
           [0015]      FIG. 3D  is an perspective view of a system including the transmission, engine and rotor of a helicopter without an autorotative assist unit; 
           [0016]      FIG. 4A  is a side view of another system including the transmission, engine and rotor of a helicopter comprising an autorotative assist unit, shown within the helicopter; 
           [0017]      FIG. 4B  is a side view of a system including the transmission, engine and rotor of a helicopter comprising an autorotative assist unit; 
           [0018]      FIG. 4C  is a top view of a system including the transmission, engine and rotor of a helicopter comprising an autorotative assist unit; 
           [0019]      FIG. 4D  is an perspective view of a system including the transmission, engine and rotor of a helicopter comprising an autorotative assist unit; 
           [0020]      FIG. 4E  is a flowchart illustrating a method of retrofitting a helicopter for improved autorotation capabilities; 
           [0021]      FIG. 5A  is a side view of yet another system including the transmission, engine and rotor of a helicopter comprising an autorotative assist unit, shown within the helicopter; 
           [0022]      FIG. 5B  is a side view of a system including the transmission, engine and rotor of a helicopter comprising an autorotative assist unit; 
           [0023]      FIG. 5C  is a top view of a system including the transmission, engine and rotor of a helicopter comprising an autorotative assist unit; 
           [0024]      FIG. 5D  is an perspective view of a system including the transmission, engine and rotor of a helicopter comprising an autorotative assist unit; and 
           [0025]      FIG. 5E  is a flowchart illustrating another method of retrofitting a helicopter for improved autorotation capabilities. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]    It should be understood at the outset that although an illustrative implementation of one or more embodiments are provided below, the disclosed systems and/or methods may be implemented using any number of techniques, whether currently known or in existence. The disclosure should in no way be limited to the illustrative implementations, drawings, and techniques illustrated below, including the exemplary designs and implementations illustrated and described herein, but may be modified within the scope of the appended claims along with their full scope of equivalents. 
         [0027]    In some cases, it may be desirable to provide enhancement or assistance to the autorotation of a helicopter in the event of engine failure. An autorotative assist unit may be operable to enhance the safety of the descent and landing of a helicopter using autorotation. The autorotative assist unit may provide supplemental power to the rotor system of a helicopter during autorotation, such as a landing flare of energy operable to slow descent of a helicopter right before landing, for example. A landing flare may be used to execute a safe landing during autorotation. Design criteria for helicopters may require the ability to complete autorotation from a certain density altitude, such as around 7,000 feet, for example. To meet the criteria, an autorotative assist unit may be used to enhance the autorotative capabilities of the helicopter. 
         [0028]    Referring to  FIG. 1 , a system  100  according to an embodiment of the disclosure is shown. The system  100  comprises a helicopter  120 , wherein the helicopter  120  comprises a fuselage  121 , a transmission  102 , an engine  104  mechanically coupled to the transmission  102 , a rotor system  108  mechanically coupled to the transmission  102 , and an autorotative assist unit  110  mechanically coupled to the transmission  102 . The rotor system  108  may comprise a mast  107  coupled to the transmission  102  and rotor blades  109  coupled to the mast  107 . The transmission  102  may be coupled to the engine  104  via a drive shaft  105  and/or a freewheeling unit  106 , wherein the freewheeling unit  106  allows for free rotation of the rotor  108  upon loss of power from the engine  104  (such may be needed to allow autorotation). The engine  104  may comprise a turbine or piston engine, for example, and the helicopter  120  may be a single engine helicopter or a multi-engine helicopter. In one embodiment, the helicopter  120  may comprise a single engine helicopter with a rotor  108 . The autorotative assist unit  110  is not typically used during normal engine operation (e.g. climb, cruise, hover, descent, etc.). Instead, the autorotative assist unit  110  may be operable to store energy (for example, excess engine energy not required to drive the rotor  108 ) during normal engine operation. In the event of failure of the engine  104 , the freewheeling unit  106  may disengage the transmission  102  from the engine  104 , and the autorotative assist unit  110  may be operable to provide power to the transmission  102  and therefore the rotor  108  (as a supplement to normal autorotation). The autorotative assist unit can be applicable to all rotor hub types, but it may be particularly helpful in helicopters with articulated or low inertia rotors. 
         [0029]    During autorotation, a pilot of the helicopter  120  may control the energy output from the autorotative assist unit  110  to the rotor  108 , for example, deciding when to use the supplemental power from the autorotative assist unit  110  and/or how much of the available autorotative assist unit  110  power to use. The flight crew may be provided with an indication of the amount of energy stored in the autorotative assist unit  110 . In other embodiments, the output of energy may be controlled automatically by the autorotative assist unit  110 . In some embodiments, a “landing flare” of energy from the autorotative assist unit  110  may be used to slow the descent of the helicopter  120  right before landing. In other embodiments, energy from the autorotative assist unit  110  may be used to slow the helicopter  120  throughout the descent and/or at the landing. Additionally, the energy input from the autorotative assist unit  110  may be used to stop descent, hover, level cruise, or possibly lift the helicopter  120  if necessary (for example, to traverse an obstacle). Several different methods may be used to input the energy from the autorotative assist unit  110  to the rotor  108  based on the conditions of the descent and landing and the abilities and decisions of the pilot of the helicopter  120 . 
         [0030]    In some embodiments, the autorotative assist unit  110  may respond to sensor input from sensors within the helicopter  120  to automatically provide autorotative assistance. Sensors may provide information comprising engine revolutions per minute (rpm), rotor rpm, descent rate, and/or altitude, as well as energy stored in the autorotative assist unit  110 . In one embodiment, the autorotative assist unit  110  may be triggered to provide autorotative assistance when the rpm level of the engine  104  falls below the rpm level of the rotor  108 . Autorotative assistance may also be controlled by a model or function executed by a controller coupled to the autorotative assist unit  110 . 
         [0031]    In some embodiments, the autorotative assist unit  110  may comprise an electric motor-generator, a battery system electrically coupled to the motor-generator operable to store and discharge energy, and a controller operable to control autorotative assist by communicating commands from a pilot and/or receiving sensor data. In another embodiment, the autorotative assist unit  110  may comprise a hydraulic pump-motor, a hydraulic accumulator in fluid communication with the hydraulic pump-motor operable to store and discharge energy, and a controller operable to control release of the energy stored in the hydraulic accumulator. In yet another embodiment, the autorotative assist unit  110  may comprise a mechanical power storage system, such as a flywheel or spring arrangement, for example. 
         [0032]    Referring now to  FIG. 2A , a schematic illustration of an autorotative assist system  200  is shown, according to an embodiment of the disclosure. The autorotative assist system  200  may comprise a transmission  202 , an engine  204  mechanically coupled to the transmission  202  via a freewheeling unit  206 , a rotor  208  mechanically coupled to the transmission  202 , and an autorotative assist unit  210  mechanically coupled to the transmission  202  (typically without any intermediate gearing). In some embodiments, the autorotative assist unit  210  may comprise a motor-generator  212  mechanically coupled to the transmission  202 , a battery system  214  electrically coupled to the motor-generator  212 , and a controller  216  for operating the motor-generator  212 . In an embodiment, the battery system  214  may comprise a high capacity/high discharge rate battery system, such as a Lithium (Li) ion battery for example. The battery system  214  may be operable to store energy during normal operation of the engine  204  and discharge this energy for autorotative assistance. By having a high discharge rate, the battery system  214  may allow for a boost of power for autorotative assistance. A high capacity/high discharge rate battery system  214  may be operable to recover energy in a short period of time, which may enable repeated autorotative assistance, such as may be used during a training exercise, for example. 
         [0033]    The controller  216  may be operable to communicate commands to the motor-generator  212  for directing the stored power in the battery system  214  of the autorotative assist unit  210  to power the motor-generator  212  to drive the rotor  208 . In one embodiment, the controller  216  may receive commands from a pilot of the helicopter, for example. In other embodiments, the controller  216  may receive sensor input and, based on the sensor input, may automatically trigger the motor-generator  212  to provide autorotative assistance. Additionally, a combination of automatic and manual control of the autorotative assist unit  210  may be provided by the controller  216 . In some embodiments, the energy input to the rotor  208  may be spread out during the descent and/or the energy may be used during the landing flare. This control of the energy output may be scheduled by the controller  216 , it may be triggered by a pilot, or a combination of the two may be used. For example, the autorotative assist unit  210  may automatically put the helicopter in an autorotative state when the engine  204  fails, and the energy remaining after doing so may be used at the discretion of the pilot. In some embodiments, the autorotative assist unit  210  may be operable to provide about 80 hp for about 6-7 seconds. In other embodiments, the autorotative assist unit  210  may be operable to provide about 45 hp for about 3-4 seconds. In yet other embodiments, the autorotative assist unit  210  may be operable to provide about 45-80 hp for about 3-7 seconds. In some embodiments, the autorotative assist unit  210  may weigh about 62-64 pounds. Typically, the weight of such an autorotative assist unit may be less than the additional weight that would have to be added to the rotor to achieve rotational inertia for comparable autorotation landing performance. 
         [0034]    Some embodiments of the disclosure include methods  240 , shown in  FIG. 2B  of providing autorotative assistance for a rotor helicopter, wherein the helicopter comprises an autorotative assist unit  210 . The method  240  may comprise, at block  244 , placing the helicopter into autorotation upon loss of engine power. This may be done manually by the pilot or automatically by controls in the helicopter. Then, when necessary, the method  240  may comprise, at block  246 , providing autorotative assistance to the rotor  208  from the autorotative assist unit  210 , thereby driving the rotor  208  as a supplement to autorotation. In some embodiments, the method  240  may also comprise, at block  242 , storing energy in the autorotative assist unit  210 , such as in the battery system  214 , during normal engine operation (wherein the storing energy may precede the steps at blocks  244  and  246 ). Autorotative assistance may be triggered manually by pilot control and/or automatically based on sensor input, wherein the helicopter may comprise sensors operable to provide information to the autorotative assist unit  210 , such as engine rpm, rotor rpm, speed, descent rate, and altitude, as well as energy stored in the battery system  214 . In some embodiments, the autorotative assistance comprises providing about 45-80 hp for about 3-7 seconds to the rotor  208 . Autorotative assistance may be provided at landing flare and/or during the descent of the helicopter (prior to landing flare) to slow the descent of the helicopter. In some embodiments, the method  240  may further comprise, at block  248 , after use of the autorotative assist unit  210 , recharging the stored energy in the autorotative assist unit  210  (such as in the battery system  214 ) after discharge. The step of recharging may be used in training for autorotation, for example. 
         [0035]    Referring now to  FIGS. 3A-3D , different views of a rotor drive system  300  that does not comprise an autorotative assist unit are shown. The transmission  302  may be coupled to the rotor  308  (or mast of the rotor system) and to the engine  304  via a drive shaft  305  and a free-wheeling unit  306 . The free-wheeling unit  306  may be operable to disengage the engine  304  from the transmission  302  upon engine failure to allow for autorotation. The transmission  302  may also be coupled to a hydraulic pump system  322  and an electric generator  324 . The hydraulic pump system  322  and electric generator  324  may couple to the transmission  302  independently of the drive shaft  305  or the free-wheeling unit  306 . 
         [0036]    Referring now to  FIGS. 4A-4D , a detailed view of a system  400  comprising an electrically-based autorotative assist unit  410  is shown. Similarly to the system  300  shown in  FIGS. 3A-3D , the transmission  402  is coupled to the engine  404 , via a drive shaft  405  and a free-wheeling unit  406 , and to the rotor  408  (or mast of the rotor system). The transmission  402  may also be coupled to a hydraulic pump system  422  and an autorotative assist unit  410 . The autorotative assist unit  410  may comprise a motor-generator  412 , a battery system  414  and a controller  416 . In some embodiments, the motor-generator  412  of the autorotative assist unit  410  may take the place of an electric generator  324  (as shown in  FIGS. 3A-3D ). 
         [0037]    Some embodiments of the disclosure may include methods, as shown in  FIG. 4E  of retrofitting a helicopter for improved autorotation capabilities, wherein the helicopter  420  comprises a rotor  408 , a transmission  402  having a generator  324  (as shown in  FIGS. 3A-3D ) off the transmission housing  402 , and an engine  404 . The method  440  may comprise, at block  442 , replacing the generator  324  on the transmission  402  with a motor-generator  412 . Then, at block  444 , the method may comprise providing a high capacity/high discharge rate battery system  414 , wherein, in some embodiments, the new battery system  414  may replace a portion of the battery system already existing in the helicopter  420 . The method may then comprise, at block  446 , electrically connecting the motor-generator  412  to the battery system  414  so that during normal engine operation, the motor-generator  412  charges the battery system  414 , but upon loss of engine power, the motor-generator  412  is operable to draw energy from the battery system  414  to drive the rotor  408  for autorotative assistance. Additionally, the transmission  402  may couple to a free-wheeling unit  406 , and the motor-generator  412  and the engine  404  may be coupled to the transmission  402  on opposite sides of the freewheeling unit  406 . In other words, the motor-generator  412  may be coupled to the transmission  402  independently of a drive shaft  405  (and/or free-wheeling unit  406 ) from the engine  404 . Typically, the motor-generator  412  may be coupled to the transmission without any intervening components, such as gearing. The method may additionally comprise, at block  448 , providing a controller  416 , as well as optionally one or more sensors in communication with the controller  416 , for triggering the motor-generator  412  to draw energy from the battery system  414  to provide power to the rotor  408  during autorotation. In some embodiments, the motor-generator  412  and battery system  414  may be operable to provide about 45-80 hp to the rotor  408  for about 3-7 seconds during autorotation. Additionally, the motor-generator  412  and battery system  414  may weigh no more than about 65 pounds, for example about 60-65 pounds, in some embodiments. 
         [0038]    Referring now to  FIGS. 5A-5D , a detailed view of a system  500  comprising a hydraulically-based autorotative assist unit  510  is shown. Similarly to the system  300  shown in  FIGS. 3A-3D , the transmission  502  is coupled to the engine  504 , via a drive shaft  505  and a free-wheeling unit  506 , and to the rotor  508  (or mast of the rotor system). The transmission  502  may also be coupled to an electric generator  524  and an autorotative assist unit  510 . The autorotative assist unit  510  may comprise a hydraulic pump-motor  512 , a hydraulic accumulator  514  and a controller  516 . In some embodiments, hydraulic pump-motor  512  of the autorotative assist unit  510  may take the place of a hydraulic pump system  322  (as shown in  FIGS. 3A-3D ). Although not specifically shown, it should be understood that the AAU in some embodiments may comprises both electrical and hydraulic features. 
         [0039]    Some embodiments of the disclosure may include methods, shown in  FIG. 5E , of retrofitting a helicopter for improved autorotation capabilities, wherein the helicopter comprises a rotor  508 , a transmission  502  having a hydraulic pump  322  (as shown in  FIGS. 3A-3D ) off the transmission housing  502 , and an engine  504 . The method  540  may comprise, at block  542 , replacing the hydraulic pump  322  on the transmission  502  with a hydraulic pump-motor  512 . Then, at block  544 , the method may comprise providing a hydraulic accumulator  514  in fluid communication with the hydraulic pump-motor  512 , wherein during normal engine operation, the hydraulic pump-motor  512  pressurizes (e.g. stores hydraulic energy in) the hydraulic accumulator  514 , but upon loss of engine power, the hydraulic pump-motor  512  draws pressure (energy) from the hydraulic accumulator  514  to drive the rotor for autorotative assistance. In some embodiments, the hydraulic accumulator  514  may comprise a pressure vessel. Additionally, the transmission  502  may couple to a free-wheeling unit  506  and the hydraulic pump-motor  512  and the engine  504  may be coupled to the transmission  502  on opposite sides of the freewheeling unit  506 . In other words, the hydraulic pump-motor  512  may be coupled to the transmission  502  independently of a drive shaft  505  from the engine  504 . Typically, the pump-motor may be coupled to the transmission without any intervening components, such as gearing. The method may additionally comprise, at block  546 , providing a controller  516 , as well as optionally one or more sensors in communication with the controller  516 , for triggering the hydraulic pump-motor  512  to draw energy from the hydraulic accumulator  514  to provide power to the rotor  508  during autorotation. In some embodiments, the hydraulic pump-motor  512  and hydraulic accumulator  514  may be operable to provide about 45-80 hp to the rotor  508  for about 3-7 seconds during autorotation. Additionally, the hydraulic pump-motor  512  and hydraulic accumulator  514  may weigh less than about 65 pounds, for example about 60-65 pounds, in some embodiments. 
         [0040]    As has been described above and shown in the figures, certain embodiments of the disclosure include a shim that is used to bond a component to a bearing. The shim may have an elastic modulus value that is lower than an elastic modulus value of the component being bonded to the bearing. In such a case, as torsional strain is applied to the component, the shim absorbs a portion of the torsional strain. This reduces an amount of torsional strain experienced by an adhesive layer. Accordingly, since the amount of torsional strain in the adhesive layer is reduced, the adhesive layer may be less likely to fail during operation and may require less maintenance. Additionally, the use of a shim may be advantageous in that it can replace custom molded bearings and components, which may have long lead times and be difficult to assemble and replace. 
         [0041]    At least one embodiment is disclosed and variations, combinations, and/or modifications of the embodiment(s) and/or features of the embodiment(s) made by a person having ordinary skill in the art are within the scope of the disclosure. Alternative embodiments that result from combining, integrating, and/or omitting features of the embodiment(s) are also within the scope of the disclosure. Where numerical ranges or limitations are expressly stated, such express ranges or limitations should be understood to include iterative ranges or limitations of like magnitude falling within the expressly stated ranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than 0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numerical range with a lower limit, R 1 , and an upper limit, R u , is disclosed, any number falling within the range is specifically disclosed. In particular, the following numbers within the range are specifically disclosed: R=R 1 +k*(R u −R 1 ), wherein k is a variable ranging from 1 percent to 100 percent with a 1 percent increment, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5 percent, . . . , 50 percent, 51 percent, 52 percent, . . . , 95 percent, 96 percent, 97 percent, 98 percent, 99 percent, or 100 percent. Unless otherwise stated, the term “about” shall mean plus or minus 10 percent of the subsequent value. Moreover, any numerical range defined by two R numbers as defined in the above is also specifically disclosed. Use of the term “optionally” with respect to any element of a claim means that the element is required, or alternatively, the element is not required, both alternatives being within the scope of the claim. Use of broader terms such as comprises, includes, and having should be understood to provide support for narrower terms such as consisting of, consisting essentially of, and comprised substantially of. Accordingly, the scope of protection is not limited by the description set out above but is defined by the claims that follow, that scope including all equivalents of the subject matter of the claims. Each and every claim is incorporated as further disclosure into the specification and the claims are embodiment(s) of the present invention.