Abstract:
One embodiment of the present application is directed to a unique method for powering one or more critical loads in an aircraft. Another embodiment is a unique apparatus for powering one or more critical loads upon failure of one or more engines. Other embodiments include unique methods, systems, devices, and apparatus&#39; for powering power loads in an aircraft. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to aircraft power systems, and more particularly, but not exclusively, to aircraft emergency power systems and methods. 
       BACKGROUND 
       [0002]    In many aircraft, the aircraft&#39;s main engines provide propulsion for the aircraft, and also provide power to the aircraft&#39;s electrical power system generally by driving a generator. In the event of an engine failure or multiple engine failures, it is desirable to provide power to the aircraft&#39;s electrical power system in order to compensate for the loss of power that was generated by the main engines. 
         [0003]    There remains a need for more efficient and more precise approaches to power loads when an aircraft is not in a normal operating condition. Accordingly, further contributions are needed in this area of technology. 
       SUMMARY 
       [0004]    One embodiment of the present application is directed to a unique method for powering one or more critical loads in an aircraft. Another embodiment is a unique apparatus for powering one or more critical loads upon failure of one or more engines. Other embodiments include unique methods, systems, devices, and apparatus&#39; for powering power loads in an aircraft. Further embodiments, forms, features, aspects, benefits, and advantages of the present application shall become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0006]      FIG. 1  illustrates some aspects of a non-limiting example of an aircraft in accordance with an embodiment of the present invention. 
           [0007]      FIG. 2  is a schematic diagram illustrating some aspects of a non-limiting example of an emergency power system in accordance with an embodiment of the present invention. 
           [0008]      FIG. 3  is a schematic diagram illustrating some aspects of a non-limiting example of a controller in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
         [0010]    In modern aircraft, and particularly in More Electric Aircraft (MEA) systems, the total electrical power required for non-propulsion use, including critical loads, is generally increasing due to the replacement of some or all hydraulic and/or pneumatic systems with electrical systems, as well as due to the use of new devices, flight controls, and landing gear systems that rely on electrical power. As a result, more electrical power is required from an emergency power system to power critical loads when one or more of the propulsion engines and/or other engines used to generate electrical power in an aircraft fail. Power from a typical emergency power generator alone, e.g., under some aircraft operating conditions, may not be sufficient to power the critical aircraft loads. However, increasing the size of the emergency power generator to provide sufficient power under all operating conditions may result in an emergency power generator that is larger than necessary, e.g., for steady-state conditions. 
         [0011]    In one embodiment of the present application, the power from an emergency power generator is supplemented with power from a fuel cell, and in some embodiments, another electrical power source, such as a battery. In one form, in the event of failure of one or more of the engines, the fuel cell and/or other electrical power source powers the critical loads until the emergency power generator output is sufficient for powering the critical loads. In other embodiments, the emergency power generator may power the critical loads until the fuel cell output is sufficient for powering the critical loads. In one form, once the emergency power generator starts generating electric power, power from the emergency power generator may be combined with power from the fuel cell and/or other electrical power source to power the critical loads. In some embodiments, the emergency power generator may power most, if not all, of the critical loads, while the fuel cell powers other loads. In some embodiments, the emergency power generator may be reduced in size because of the addition of the fuel cell system, e.g., relative to other systems that do not employ fuel cell systems for electrical power generation. In some embodiments, power output from the emergency power system may be combined with the power output from one or more of the engines that have not failed but do not otherwise have the capacity to satisfy critical and/or other loads. 
         [0012]    Referring to  FIG. 1 , some aspects of a non-limiting example of an aircraft  100  in accordance with an embodiment of the present invention are schematically illustrated. Aircraft  100  includes, among other things, one or more of an engine  110 , and includes a power system  120 . In one form, engine  110  is configured as a propulsion power plant for providing propulsive thrust to aircraft  100 . In one form, engine  110  is a gas turbine engine. In a particular form, engine  110  is a turbofan engine. In other embodiments, engine  110  may take other forms, and may be, for example, a turboshaft engine, a turboprop engine, a turbojet engine, a combined cycle engine or any other type of engine, gas turbine or otherwise. As shown in  FIG. 1 , engine  110  is coupled to a generator  115 . Generator  115  is electrically coupled to power system  120 . Generator  115  is configured to supply electrical power to power system  120 , e.g., electrical loads. In addition, in various embodiments, engine  110  may be configured to supply hydraulic power and/or pneumatic power, e.g., bleed air, to power system  120 . 
         [0013]    In one form, power system  120  includes various loads  125  associated with aircraft  100 , including critical loads. Generator  115  is coupled to and configured to supply electrical power to loads  125 , including critical loads. Loads  125  may include, for example and without limitation, flight computer systems, navigational and communication systems, radar systems and other hazard detection/avoidance systems, flight control surface positioning systems, landing gear systems, air conditioning systems for the cabin, hydraulic systems, and any other device or component that requires electrical, hydraulic and/or pneumatic power to operate, depending upon the particular application. Power system  120  includes an engine powered auxiliary power unit (APU)  130  and an emergency power system  140 . In various embodiments, APU  130  may include one or more generators (not shown) and/or hydraulic pumps (not shown) that are driven by one or more APU engines (not shown). In some embodiments, the hydraulic pumps may be electric motor driven hydraulic pumps. In various embodiments, APU  130  is configured to provide electrical power, hydraulic power and/or pneumatic power to loads  125  on aircraft  100  when aircraft  100  is undergoing ground operations, whereas generally, engine  110  provides the power for loads  125  during normal flight operations. In some embodiments, APU  130  may supply power for loads  125  in addition to or in place of engine  110  during normal flight operations. 
         [0014]    Emergency power system  140  is configured to provide power to certain loads when aircraft  100  is not operating in a normal condition, such as when aircraft  100  is operating in an in-flight emergency condition. For example, in situations where one or more engines  110  fail during aircraft  100  flight operations, auxiliary power unit  130  may be incapable of providing all of the required power for loads  125 , or may be incapable of providing any power, e.g., depending upon the altitude of aircraft  100 . As another example, a failure of APU  130  may otherwise leave aircraft  100  without sufficient power in situations where one or more engines  110  have failed. 
         [0015]    Emergency power system  140  is configured to supply power to certain loads  125  in the event of a failure scenario in which engine(s)  110  and/or APU  130  are incapable of providing sufficient power to loads  125 , which is referred to as an emergency operating condition. During emergency operating conditions, emergency power system  140  supplements or replaces power that would otherwise be provided by engine  110  and/or auxiliary power unit  130 . In particular, emergency power system  140  is configured to provide power to aircraft critical loads  128 . Critical loads  128  in aircraft  100  are a subset of loads  125 , for example and without limitation, loads that are deemed critical to flight safety, and loads that are critical to passenger health. Critical loads  128  may include, for example and without limitation, flight control systems, flight control surface positioning systems, communication, navigation and hazard detection/avoidance systems, other avionic systems, landing gear systems, environmental control systems, and other systems, such as hydraulic systems, including electric motor-driven hydraulic pumps and hydraulic systems powered thereby. 
         [0016]    As set forth herein emergency power system  140  includes an emergency power generator and a fuel cell for powering critical loads  128  when aircraft  100  is operating in an emergency operating condition (e.g., inoperative engines  110  and flight at an altitude where APU  130  is not capable of providing adequate or any power). The emergency power generator and the fuel cell provide power to critical loads  128  during emergency operating conditions. During the amount of time required for the emergency power generator to spool up and generate the required power, the fuel cell provides power to the critical loads. In some embodiments, one or more batteries or other electrical power sources may be employed, e.g., to provide power until the fuel cell is able to supply sufficient power. Emergency power system  140  thus provides redundancy for powering critical loads  128 , thereby improving the safety of aircraft  100 . 
         [0017]    Referring to  FIG. 2 , some aspects of a non-limiting example of an emergency power system  140  in accordance with an embodiment of the present invention are schematically depicted. Emergency power system  140  includes an emergency power generator  150  and a ram air turbine (RAT)  155 . RAT  155  is configured to generate mechanical power from the airstream adjacent to aircraft  100  that results from the forward motion of aircraft  100  through the air during flight operations. In one form, RAT  155  is normally disposed internal to aircraft  100 , and is deployed externally to aircraft  100  into the airstream adjacent to aircraft  100  in response to the occurrence of emergency operating conditions. In other embodiments, RAT  155  may be disposed within aircraft  100  and be supplied with flowing air from the airstream via an inlet and ducting system (not shown). 
         [0018]    RAT  155  is configured to supply shaft power to drive emergency power generator  150 . In one form, emergency power generator  150  is an air driven generator (ADG)  150  coupled directly to and deployed with RAT  155 . In other embodiments, emergency power generator  150  may be physically positioned away from RAT  155 , and supplied with shaft power from RAT  155 , e.g., via a shaft and/or belt drive system. Emergency power generator  150  is configured to generate electrical power, e.g., AC power, when driven by RAT  155 , e.g., during emergency operating conditions. Under normal operating conditions, RAT  155  is not deployed or otherwise supplied with flowing air from the airstream adjacent to aircraft  100 , and emergency power generator  150  does not produce power. 
         [0019]    In one form, the AC power produced by emergency power generator  150  is three-phase AC power. In other embodiments, other types of AC power may be employed, including single-phase and multi-phase. In one form, emergency power generator  150  is a synchronous generator, e.g., having a substantially constant speed, controlled by a clutch mechanism (not shown). In other embodiments, emergency power generator  150  may be an asynchronous generator. In still other embodiments, other generator or alternator types may be employed, at fixed or variable speeds. 
         [0020]    In one form, emergency power system  140  also includes a hydraulic pump  160  coupled to and driven by RAT  155 . Hydraulic pump  160  is configured to convert shaft power from RAT  155  to hydraulic power for use by critical hydraulic loads  165  of aircraft  100 , which are a subset of critical loads  128 . In other embodiments, emergency power system  140  may not include a hydraulic pump coupled to and driven by RAT  155 . Some embodiments of aircraft  100  may not include critical hydraulic loads  165 , whereas other embodiments may include critical hydraulic loads  165  that are powered by one or more electric-motor driven hydraulic pumps  168  that are powered by emergency power generator  150 . 
         [0021]    In one form, emergency power generator  150  is coupled to a rectifier  170 . Rectifier  170  is electrically coupled to a DC bus  180 . Rectifier  170  is configured to rectify the output of emergency power generator  150  and supply the rectified DC voltage to DC bus  180 . In one form, rectifier  170  is an active rectifier. In some embodiments, active rectifier  170  may be configured to improve the power factor of emergency power generator  150 . In other embodiments, rectifier  170  may be a passive rectifier. In one form, the DC voltage supplied by rectifier  170  is 270V DC. In other embodiments, other voltage levels may be employed. 
         [0022]    In one form, emergency power system  140  also includes a DC-DC converter  190  and one or more of a fuel cell  200 . DC-DC converter  190  is coupled to DC bus  180 . Fuel cell  200  is coupled to DC-DC converter  190 . DC-DC converter  190  is configured to receive electrical power from fuel cell  200 , which generates a DC voltage, and to convert the DC voltage from fuel cell  200  into an appropriate DC voltage for DC bus  180  and supply the converted DC voltage to DC bus  180 . Rectifier  170  and DC-DC converter  190  convert the AC voltage from emergency power generator  150  and the fuel cell  200 , respectively, to the same DC voltage and output that DC voltage onto DC bus  180 . In some embodiments, a DC-DC converter may not be employed, e.g., where the output of fuel cell  200  is appropriate for direct use DC bus  180 . 
         [0023]    Under normal operating conditions, fuel cell  200  is used as a stand-by power source for critical loads  128 . In one embodiment, under emergency operating conditions, until emergency power generator  150  has achieved sufficient output to satisfy the power requirements for critical loads  128 , e.g., during deployment and startup of RAT  155  and emergency power generator  150 , fuel cell  200  provides the power to some or all critical loads  128 , e.g., including electrically-driven hydraulic pumps. In one form, fuel cell  200  is a solid oxide fuel cell. In other embodiments, other fuel cell types may be employed, for example and without limitation, in other embodiments, fuel cell  200  may be a proton exchange membrane fuel cell, a molten carbonate fuel cell, or any other fuel cell suitable for operation in aircraft  100 . In some embodiments, fuel cell  200  may be operated to continue to supply power to critical loads  128  in parallel to emergency power generator  150 . 
         [0024]    In one form, fuel cell  200  is maintained in a standby mode during normal aircraft  100  operations, which allows fuel cell  200  to quickly shift into power production mode in the event of an occurrence of emergency operating conditions. In some embodiments, fuel cell  200  may not be operated in a standby mode during normal aircraft  100  operations. In such embodiments, emergency power system  140  may include a battery and/or one or more other electrical energy storage systems  205  coupled to DC bus  180 , which may be employed to provide power to critical loads  128  until fuel cell  200  has been started and has reached sufficient output levels to power critical loads  128  without the assistance of battery and/or other electrical energy storage system  205 . In other embodiments, a battery and/or one or more other electrical energy storage systems may not be employed. Other electrical energy storage systems may include, for example and without limitation, flywheel/motor/generator systems that convert between flywheel inertial energy and electrical energy. 
         [0025]    In one form, emergency power system  140  includes a control power supply  210  coupled to DC bus  180  and coupled to one or more control or other control systems  220 . In one form, systems  220  are critical loads, and are a subset of critical loads  128 . In other embodiments, some or all of systems  220  may not be critical loads. Control power supply  210  is configured to receive a DC voltage from DC bus  180 , to convert the DC voltage from DC bus  180  into a DC voltage suitable for systems  220 , for example and without limitation, 28V DC, and to supply that voltage to one or more control systems  220 . Systems  220  may include, for example and without limitation, flight control systems and/or other aircraft  100  components and systems. 
         [0026]    In one form, emergency power system  140  includes a DC-DC converter  230  coupled to DC bus  180  and to one or more DC loads  240 . In one form, DC loads  240  are critical loads, and are a subset of critical loads  128 . In other embodiments, DC loads  240  may not include critical loads. DC-DC converter  230  is configured to receive power from emergency power generator  150 , fuel cell  200  and/or battery and/or other electrical energy storage system  205  through DC bus  180 . DC-DC converter  230  is configured to convert the DC voltage from DC bus  180  into one or more DC voltages suitable for the one or more DC loads  240 . DC-DC converter  230  is configured to supply the converted DC voltages to the one or more DC loads  240 , which may include, for example and without limitation, one or more full authority digital engine control (FADEC) systems and/or one or more various MEA systems and/or other aircraft  100  systems. 
         [0027]    In one form, emergency power system  140  also includes a DC-AC inverter  250  coupled to DC bus  180  and to one or more AC loads  260 . In one form, AC loads  260  are critical loads, and are a subset of critical loads  128 . In other embodiments, one or more AC loads  260  may not include critical loads. DC-AC inverter  250  is configured to receive the DC power from DC bus  180  and to convert the DC voltage into one or more AC voltages such as 115V AC. DC-AC inverter  250  is configured to supply the AC voltages to the one or more AC loads  260 , which may include, for example and without limitation, electrically driven hydraulic systems, environmental control systems (ECS) and/or other aircraft  100  systems. 
         [0028]    In some embodiments, emergency power system  140  includes an energy management controller  270  and a fuel cell controller  280 . Energy management controller  270  is coupled to emergency power generator  150 , rectifier  170 , DC bus  180 , DC-DC converter  190 , DC-DC converter  230 , DC-AC inverter  250 , and fuel cell controller  280 . Fuel cell controller  280  is coupled to fuel cell  200 . Energy management controller  270  is configured with operating logic for controlling emergency power generator  150 , rectifier  170 , DC-DC converter  190 , DC-DC converter  230 , DC-AC inverter  250 , and fuel cell controller  280 . Fuel cell controller  280  is configured with operating logic to control the operations of fuel cell  200 . Energy management controller  270  may also be in communication with other controllers or sensors on aircraft  100 , e.g., sensors that may transmit a signal to energy management controller  270  indicating that aircraft  100  is not operating in a normal condition and request deployment of RAT  155  and startup of emergency power generator  150 . 
         [0029]    In one form, during the operation of aircraft  100 , if energy management controller  270  receives an indication (e.g., a signal) that aircraft  100  is not operating in a normal condition (e.g., an engine  110  failure), energy management controller  270  activates RAT  155  and emergency power generator  150  by sending a signal. In some embodiments, energy management controller  270  may control how power from emergency power generator  150  and/or fuel cell  200  is distributed, e.g., including prioritizing which critical loads  128  receive power in the event emergency power system  140  is unable to supply power to all critical loads  128 . In some embodiments, energy management controller  270  may send a signal to active rectifier  170  to control the DC voltage output by rectifier  170  to DC bus  180 . 
         [0030]    In one form, emergency management controller  270  is configured to transmit a signal to fuel cell controller  280  indicating a failure of one or more of the main engines. In embodiments wherein fuel cell  200  is kept in standby mode during normal aircraft operation, fuel cell controller  280  is configured to transmit a command signal to fuel cell  200  to switch from standby mode to power production mode in response to the failure(s), in order to power critical loads  128 . In other embodiments, fuel cell controller  280  may transmit a signal to fuel cell  200  to start up fuel cell  200  to power critical loads  128  upon detection of the failure of the engine(s). In still other embodiments, other control means to activate fuel cell  200  may be employed. In some embodiments, fuel cell controller  280  is configured to control the voltage level and power outputs of fuel cell  200 . In some embodiments, emergency management controller  270  is configured to transmit a signal to engage the battery and/or other electrical energy storage system  205  to power the critical loads until fuel cell  200  and/or emergency power generator  150  have been started and have achieved sufficient output to power critical loads  128 . 
         [0031]    In one form, energy management controller  270  is configured to determine the amount of power to be drawn from each fuel cell  200  and emergency power generator  150  by transmitting signals to fuel cell controller  280  and emergency power generator  150 , respectively, e.g., to optimize the total flow of power drawn from fuel cell  200  and emergency power generator  150  when both are in operation. This may increase or maximize the duration of provision of emergency power to critical loads  28  under adverse conditions, e.g., at low altitudes under emergency conditions. In other embodiments, the power balance as between emergency power generator  150  and fuel cell  200  may be otherwise determined. In some embodiments, energy management controller  270  is configured to determine the amount of power to be drawn from each of fuel cell  200 , emergency power generator  150  and battery and/or other electrical energy storage system  205 , e.g., to optimize the total flow of power to critical loads  28 . 
         [0032]    In one form, management controller  270  is configured to transmit a signal to DC-DC converter  230  and DC-AC inverter  250  to control the operation of DC-DC converter  230  and DC-AC inverter  250 . For example, in the event emergency power generator  150  and fuel cell  200  are not providing sufficient electrical power for all electrical critical loads  128 , management controller may alter or eliminate the power flow to DC loads  240  and/or AC loads  260 , in order to provide power to other critical loads  128 . In other embodiments, DC-DC converter  230  and DC-AC inverter  250  may be otherwise controlled. 
         [0033]    It is contemplated that in some embodiments, energy management controller  270  and fuel cell controller  280  may be combined into one controller. Furthermore, it is contemplated that in some embodiments, energy management controller  270  may be in communication with other controllers and/or sensors on aircraft  100  to receive other information regarding the status other aircraft  100  components and/or systems, and/or to transmit control signals to other aircraft  100  components and/or systems, including some or all of loads  125  and/or critical loads  128 . Received information may include indications, for example and without limitation, that one or more of engines  110  has failed, that auxiliary power unit  130  cannot provide all of the aircraft&#39;s required power, and/or auxiliary power unit  130  has failed. Control signals may include, for example and without limitation, signals instructing one or more loads  125  and/or critical loads  125  to shut down or change operating modes in response to the occurrence of emergency operating conditions and the present capability of emergency power system  140  to supply power to such loads. 
         [0034]    During emergency operating conditions on aircraft  100 , e.g., during and subsequent to an engine  110  failure, emergency power generator  150  and fuel cell  200  provide the power to critical loads  128 . The power output of RAT  155  and hence emergency power generator  150  varies with the altitude and speed of aircraft  100 , with the available power from emergency power generator  150  being lower at lower altitudes. In some embodiments, in situations where conditions are such that emergency power generator  150  output is insufficient to meet power demand, e.g., when aircraft  100  is at lower altitudes and/or speeds, fuel cell  200  provides supplemental power, in order to maximize the capability to provide power to critical loads  128 . In various embodiments, fuel cell  200  may be used to supply power to critical loads  128  in emergency operating conditions during only certain flight conditions or throughout all flight conditions. 
         [0035]    Referring to  FIG. 3 , a schematic diagram illustrates some aspects of a non-limiting example of a controller  300  in accordance with an embodiment of the present invention. In various embodiments, controller  300  may be employed as one or both of energy management controller  270  and fuel cell controller  280  shown in  FIG. 2 . Controller  300  includes a processing device  302 , an input/output device  304 , a memory  306 , and operating logic  308 . 
         [0036]    In various embodiments, processing device  302  may be of a programmable type, a dedicated, hardwired state machine, a combination of these or any other type of processor suitable for use as an energy management controller and/or fuel cell controller. In addition, some embodiments of processing device  302  may include multiple processors, Arithmetic-Logic Units (ALUs), Central Processing Units (CPUs), or the like. In other embodiments, other types of processing devices may be employed in addition to or in place of those mentioned herein. For forms of processing device  302  with multiple processing units, distributed, pipelined, and/or parallel processing may be utilized as appropriate. In various embodiments, processing device  302  may be dedicated to performance of just the operations described herein or may be utilized in performing one or more additional operations. In the depicted form, processing device  302  is of a programmable variety that executes algorithms and processes data in accordance with operating logic  308  as defined by programming instructions (e.g., such as software or firmware) stored in memory  306 . Alternatively or additionally, operating logic  308  for processing device  302  is at least partially defined by hardwired logic or other hardware. In various embodiments, processing device  302  may be formed of one or more components of any type suitable to process the signals received from input/output device  304  or elsewhere, and provide desired output signals. Such components may include digital circuitry, analog circuitry, or a combination of both. 
         [0037]    Input/output (I/O) device  304  is configured to perform input/output operations for processing device  302  for communications to and from components of emergency power system  140 . In some embodiments, I/O device  304  is also configured to perform input/output operations for processing device  302  for communications to and from other components and/or systems of aircraft  100 , e.g., in some embodiments including critical loads  128  or other loads  125 . I/O device  304  may be any type of I/O device or combination of I/O devices that allows controller  300  to communicate with other devices and components, such as emergency power generator  150 , rectifier  170 , DC-DC converter  190 , DC-DC converter  230 , DC-AC inverter  250 , and/or other controllers or devices, and provides for transmitting and receiving data from various devices, such as sensors. In various embodiments, input/output device  304  may be comprised of hardware, software, and/or firmware. It is contemplated that in some embodiments, input/output device  304  includes a plurality of ports for transmitting and receiving data. 
         [0038]    Memory  306  may be of one or more memory types, such as a solid-state variety, electromagnetic variety, optical variety, or a combination of these forms. In various embodiments, memory  306  may be volatile, nonvolatile, or a combination of both. In some embodiments, some or all of memory  306  may be of a portable and/or mass storage variety, such as a disk, tape, memory stick, cartridge, or the like. In various embodiments, memory  306  stores data that is manipulated by operating logic  308  of processing device  302 , such as data representative of signals received from and/or sent to input/output device  304  in addition to or in lieu of storing programming instructions defining operating logic  308 , just to name one example of many. In one form, memory  306  is considered a part of processing device  302 . In other embodiments, memory  306  may be coupled to processing device  302 . 
         [0039]    Some embodiments of the present invention may provide, for example, for supplying reliable power after an engine failure over the entire operating regime of aircraft  100 , even during at lower altitudes, e.g., due to the inclusion of fuel cell  200 . As another example, more electrical loads can be powered under emergency conditions, e.g., due to the inclusion of fuel cell  200 , as compared to some other emergency power systems that do not employ one or more fuel cells. 
         [0040]    As yet another example, the size of emergency power generator  150  may be made smaller than otherwise, because fuel cell  200  provides power that may otherwise be required to be supplied by an emergency power generator alone. In relatively large aircraft, the power requirement for critical loads is approximately 60-80 KVA. In a relatively medium-sized aircraft, the power requirement is approximately 40-50 KVA. Once the peak power requirements for critical loads for an aircraft have been determined, the capacity of the fuel cell can be determined, and then an emergency power generator may be chosen, which is generally smaller due to the addition of the fuel cell. In some embodiments, emergency power generator  150  is configured to supply the full power requirement for critical loads  128 . In other embodiments, emergency power generator  150  is not capable of supplying the full power requirement for critical loads, but rather, is used in conjunction with fuel cell  200  to meet the power requirements for critical loads  128 . In some embodiments, fuel cell  200  is configured to supply the full power requirement for critical loads  128 , in which case emergency power generator  150  may be used to supply power to non-critical loads. 
         [0041]    In one embodiment, a method of supplying power to the critical loads in an aircraft when one or more of the engines of the aircraft fail includes using a fuel cell in parallel with an emergency power generator to supply power to some or all critical loads. 
         [0042]    In another embodiment, a battery is used in parallel with the emergency power generator and fuel cell to provide the required power. The battery is connected to the DC bus to provide power to any loads connected to the DC bus. 
         [0043]    In yet another embodiment, the emergency power generator powers the most critical loads, whereas one or more fuel cells provide the power to less critical and other needed loads during the entire flight with the failed main engines. 
         [0044]    In still another embodiment, under normal operating conditions, the fuel cell powers the critical loads. In another embodiment, in normal operating conditions, the fuel cell is operating in a stand-by mode with a minimum amount of power output to power some critical loads. 
         [0045]    Embodiments of the present invention include a method, comprising: monitoring an operating condition of an engine of an aircraft; starting an emergency power generator when the operating condition indicates a failure of the engine; and powering critical loads in the aircraft using power from a fuel cell and the emergency power generator. 
         [0046]    In a refinement, the method further comprises powering the critical loads with the fuel cell until a power output of the emergency power generator is sufficient to power the critical loads. 
         [0047]    In another refinement, the method further comprises powering the critical loads using power from only the emergency power generator once the power output of the emergency power generator is sufficient to power the critical loads. 
         [0048]    In yet another refinement, the method further comprises powering other aircraft electrical loads using power from the fuel cell while the emergency power generator powers the critical loads. 
         [0049]    In still another refinement, the method further comprises powering the critical loads with the fuel cell and with the emergency power generator until a power output of the emergency power generator is sufficient to power the critical loads alone. 
         [0050]    In yet still another refinement, the method further comprises powering at least one critical load using the fuel cell while the aircraft is operating in a normal condition. 
         [0051]    In a further refinement, the method further comprises powering only the critical loads with the fuel cell until the emergency power generator is capable of powering the critical loads, then powering other loads with the fuel cell. 
         [0052]    In a yet further refinement, the aircraft includes more than one engine and the operating condition indicates a failure of all of the engines. 
         [0053]    In a still further refinement, the aircraft includes more than one engine and the operating condition indicates a failure of one of the engines. 
         [0054]    In a yet still further refinement, the method further comprises powering the critical loads with the emergency power generator, the fuel cell, and a battery. 
         [0055]    In yet another refinement, wherein the starting of the emergency power generator includes deploying at least one of a ram air turbine and an air driven generator. 
         [0056]    Embodiments of the present invention include an apparatus for powering a critical load upon failure of one or more engines, comprising: an emergency power generator configured to output an AC voltage; a DC bus; a rectifier coupled to the emergency power generator and the DC bus, wherein the rectifier is configured to convert the AC voltage from the emergency power generator to a DC voltage; and wherein the rectifier is configured to output the DC voltage to the DC bus; a fuel cell; a DC-DC converter coupled to the fuel cell; wherein the DC-DC converter is coupled to the DC bus; and wherein the fuel cell is configured to provide power to the DC bus via the DC-DC converter; and a controller configured to activate the emergency power generator upon the failure of the one or more engines, wherein the controller is structured to control power outputted from the emergency power generator and the fuel cell to power the critical load. 
         [0057]    In a refinement, the critical load includes at least one of an AC load and a DC load. 
         [0058]    In another refinement, the apparatus further comprises a DC-AC inverter configured to convert the DC voltage on the DC bus to another AC voltage and to provide the other AC voltage to the AC load. 
         [0059]    In yet another refinement, the apparatus further comprises a second DC-DC converter configured to convert the DC voltage on the DC bus to another DC voltage and to provide the other DC voltage to the DC load. 
         [0060]    In still another refinement, the apparatus further comprises an electric motor-driven hydraulic pump powered by the emergency power generator. 
         [0061]    In yet still another refinement, the apparatus further comprises a control power supply coupled to the DC bus. 
         [0062]    In a further refinement, the controller is structured to control an amount of power drawn from the emergency power generator and the fuel cell to maximize a duration of provision of emergency power. 
         [0063]    In a yet further refinement, the apparatus further comprises a battery coupled to the DC bus and configured to supply power to the DC bus. 
         [0064]    In a still further refinement, the emergency power generator is structured to provide three-phase AC power. 
         [0065]    In a yet still further refinement, the emergency power generator includes a ram air turbine coupled to a generator. 
         [0066]    In another further refinement, the emergency power generator includes an air driven generator. 
         [0067]    In yet another further refinement, the emergency power generator includes a variable speed generator. 
         [0068]    In still another further refinement, the controller includes a fuel cell controller and an energy management controller. 
         [0069]    Embodiments of the present invention include a method, comprising: determining an emergency power requirement for an aircraft, wherein the emergency power requirement includes a critical loads power requirement and an other load power requirement; providing one or more fuel cells, wherein the one or more fuel cells is configured to satisfy the critical loads power requirement; and providing an emergency power generator configured to satisfy the critical loads power requirement alone; wherein the emergency power generator and the fuel cell are configured to jointly satisfy the emergency power requirement. 
         [0070]    In a refinement, the emergency power generator is not capable of satisfying the emergency power requirement alone. 
         [0071]    In another refinement, the one or more fuel cells are not capable of satisfying the emergency power requirement alone. 
         [0072]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.