Patent Publication Number: US-2023142953-A1

Title: Heating Control System and Method for Unpressurized Aircraft

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Patent Application No. 63/278,177, entitled Heating Control System And Method For Unpressurized Aircraft and filed on Nov. 11, 2021, the disclosure of which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     1. Field 
     Embodiments of the invention relate generally to the field of aircraft temperature control systems, and more specifically to systems for controlling heating in unpressurized aircraft. 
     2. Related Art 
     Unpressurized aircraft require temperature control of the cockpit and cabin for comfort and safety of the passengers, or for maintaining optimal temperatures for temperature-sensitive cargo. As part of reaching this objective, bleed air is typically extracted from the engine and provided to the occupied compartments to heat said compartments. 
     Temperature control systems have been provided in a variety of ways in prior aircraft, albeit typically in reference to pressurized aircraft. For example, U.S. Patent Publication 2018/0057170 to Sautron discloses a system of mixing bleed air with a cold air source for an environmental control system. U.S. Patent Publication 2020/0391872 to Bruno et al. discloses a system to regulate cabin air in an aircraft by mixing outside air and bleed air. U.S. Patent Publication 2018/0312262 to Wiegers et al. discloses a pneumatic flow-control system and method to regulate ambient air temperature. U.S. Pat. No. 10,752,366 to Fernandez-Lopez et al. discloses a system for heating an auxiliary power unit compartment of an aircraft. U.S. Patent Publication 2021/0061476 to Van Den Ende et al. discloses a system and method for increasing bleed air flow to a heat exchanger. U.S. Pat. No. 6,848,652 to Palin et al. discloses a heating system that uses bleed air to heat a cabin of an aircraft. U.S. Pat. No. 8,985,966 to Sampson et al. discloses a jet pump apparatus. 
     SUMMARY 
     This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. Other aspects and advantages of the invention will be apparent from the following detailed description of the embodiments and the accompanying drawing figures. 
     In an embodiment, a heating system for an unpressurized aircraft includes: a first ram air source configured to provide ram air to a heat exchanger via a first valve; a bleed air source from a turbine engine configured to provide bleed air to the heat exchanger via a second valve, wherein the heat exchange uses the ram air to cool the bleed air; an ejector fluidly coupled downstream of the heat exchanger to receive cooled bleed air from the heat exchanger; a second ram air source configured to provide ram air to the ejector via a third valve, wherein the ejector mixes the second ram air source with the cooled bleed air; a controller operatively connected to the first valve, the second valve, and the third valve; a control panel operatively connected to the controller, including: a heating enable switch, wherein the heating enable switch includes an on configuration and an off configuration; and a temperature selection control, wherein the temperature selection control is configured to receive a desired temperature range; and the controller is configured to regulate air temperature in the unpressurized aircraft by controlling the first, second, and third valves based on the temperature selection control when the heating enable switch is in the on configuration. 
     In another embodiment, a method for heating an unpressurized aircraft includes: receiving, via a controller, a desired air temperature from a control panel; calculating, via the controller, a target duct air temperature based on the desired air temperature; determining, via the controller, an actual duct air temperature via a duct air temperature sensor disposed in an air duct; calculating a target modulation of one or more ram air valves based on a difference between the target duct air temperature and the actual duct air temperature; modulating one or more of the ram air valves via the controller based on the target modulation; introducing a bleed air from a turbine engine to a heat exchanger; introducing a temperature control air from one of the one or more ram air valves to the heat exchanger for cooling the bleed air to provide a temperature-controlled air; mixing the temperature-controlled air from the heat exchanger with an ejector ram air in an ejector; and providing air from the ejector to an occupied compartment of the unpressurized aircraft via the air duct. 
     In yet another embodiment, a method for heating an unpressurized aircraft includes: providing a desired air temperature to a controller via a control panel; calculating, via the controller, a target duct air temperature based on the desired air temperature; determining, via the controller, an actual duct air temperature via a duct air temperature sensor; determining a temperature error based on a difference between the actual duct air temperature and the target duct air temperature; calculating a target ejector ram air valve position based on the temperature error; determining a measured ejector ram air valve position from a position sensor; determining a valve error based on the difference between the target ejector ram air valve position and the measured ejector ram air valve position; maintaining a position of an ejector ram air valve when the valve error is less than a predetermined value; and adjusting the position of the ejector ram air valve based on the valve error when the valve error is greater than the predetermined value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
       Embodiments of the invention are described in detail below with reference to the attached drawing figures, wherein: 
         FIG.  1    is a diagram showing an environmental embodiment in an aircraft having a turbine engine and occupiable compartments as shown; 
         FIG.  2    is a schematic diagram showing one embodiment of a heating system for an unpressurized aircraft; 
         FIG.  3    is a schematic diagram showing another embodiment of a heating system for an unpressurized aircraft; 
         FIG.  4    is a front view of one embodiment of a user-operated temperature selection control for the heating system; 
         FIG.  5    is a block diagram illustrating a control architecture for controlling components of the systems of  FIGS.  2 - 4   , in an embodiment; 
         FIG.  6    is a process-flow diagram illustrating a heating method performed using the system of  FIGS.  2 - 4   , in an embodiment; and 
         FIG.  7    is a process-flow diagram illustrating a heating method performed using the system of  FIGS.  2 - 4   , in an embodiment. 
     
    
    
     The drawing figures do not limit the invention to the specific embodiments disclosed and described herein. The drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the invention. 
     DETAILED DESCRIPTION 
     The following detailed description references the accompanying drawings that illustrate specific embodiments in which the invention can be practiced. The embodiments are intended to describe aspects of the invention in sufficient detail to enable those skilled in the art to practice the invention. Other embodiments can be utilized, and changes can be made without departing from the scope of the invention. The following detailed description is, therefore, not to be taken in a limiting sense. The scope of the invention is defined only by the appended claims, along with the full scope of the equivalents to which such claims are entitled. 
     In this description, references to “one embodiment,” “an embodiment,” or “embodiments” mean that the feature or features being referred to are included in at least one embodiment of the technology. Separate references to “one embodiment,” “an embodiment,” or “embodiments” in this description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and/or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, act, etc. described in one embodiment may also be included in other embodiments, but is not necessarily included. Thus, the technology can include a variety of combinations and/or integrations of the embodiments described herein. 
     Unpressurized aircraft require that the cabin be ventilated, and temperature controlled to maintain a comfortable environment for the passengers, crew, or temperature-sensitive cargo. Bleed air may be extracted from one or more of the engine&#39;s compressor stages to provide a source of high temperature air. Based on the compressor stages used, a range of available bleed air pressures and temperatures may be provided depending on engine power and ambient air conditions. However, extraction of highly compressed bleed air from the later engine compressor stages causes increased engine fuel burn and decreased available thrust. A temperature control system may be used to regulate pressure, flow rate, and temperature of the bleed air that is provided to the aircraft cabin for heating or cooling. The architecture and sizing of the bleed air extraction assembly directly affects engine fuel burn, aircraft performance, and the amount of cooling required from the temperature control system. 
     A typical turbine engine powered aircraft heating system uses a pressure regulating valve, temperature control valve, and heat exchanger to provide and control heat to the crew and passenger compartment. The temperature of the air is varied by modulating ambient ram air across the cold side of the heat exchanger. For a small cabin, the amount of bleed air extracted off the engine is relatively small, but for a large cabin the amount of bleed air required can be higher than what a turbine engine is able to provide. Even if an engine can provide the amount of bleed air required, as more bleed air is extracted off the engine, the specific fuel consumption increases and the overall aircraft efficiency decreases. As a result, heating systems are typically designed to extract as little bleed air as possible resulting in insufficient heating capability. 
     For a typical aircraft heating/cooling system, ambient ram air is used to provide a cross flow for a heat exchanger, which allows for acceptable cooling performance in flight. However, when the aircraft is on the ground, ambient ram air is not available for cooling the heat exchanger. The lack of cooling flow can cause the heating system to quickly exceed its operating temperature while heating a stationary aircraft. This is another downside of the simple heating system. 
     An ejector may be used to reduce the impact of extracting excess bleed air. By mixing ambient or lower pressure bleed air with high pressure bleed air, the overall heating flow rate may be increased while reducing the detrimental effect on engine specific fuel consumption. These ejector systems are typically controlled to a fixed mass flow schedule which allows for a constant cabin pressurization system. However, a fixed mass flow schedule does not adapt to changes in ambient temperature and bleed air temperature, which causes the resultant heating capacity to vary. These types of systems locate the ejector upstream of the heat exchanger so that the air flow quantity can be managed independently from the air temperature. 
       FIG.  1    shows an aircraft  10  containing a cabin  20  and a cockpit  30 , which collectively may represent an occupied compartment  60  (see  FIG.  2   ). The occupied compartment  60  may be occupied by one or more of passengers or cargo. In embodiments, aircraft  10  is an unpressurized aircraft such that occupied compartment  60  is unpressurized. Unpressurized aircraft are typically operated up to altitudes of about 10,000-feet above sea level such that sufficient oxygen is available for crew and passengers without providing pressurization. The aircraft  10  is propelled forwards by one or more turbine engines, (e.g., turbine engine  40 ). The turbine engine  40  generates bleed air by compressing air as it travels through the engine. The turbine engine  40  may be, for example, a turbofan, turbojet, turboprop, or turboshaft engine. Bleed air temperature and pressure may be regulated based on the type of turbine engine  40 , as well as a compression ratio and a compression stage of the engine from which the bleed air is provided. 
       FIG.  2    depicts a heating system  50  which may control the air temperature of the occupied compartment  60  of the aircraft  10 . The heating system  50  has three sources of input air: 
     1) a bleed air  42  from the turbine engine  40 ; 2) a temperature control air  112 , which enters the system through a temperature control air inlet  110 ; and 3) an ejector ram air  122  that enters through an ejector ram air inlet  120 . 
     Bleed air  42  from the turbine engine  40  and temperature control air  112  from the temperature control air inlet  110  flow through a heat exchanger  130 . The heat exchanger  130  may be a cross flow type of heat exchanger with two primary flow paths, wherein the bleed air  42  flows through a first path and the temperature control air  112  flows through a second path. The cooling air introduced into the heat exchanger  130  from inlet  110  exits the system, e.g., at an aircraft exit duct  131  and into the ambient environment. 
     The temperature-controlled air  132 , now at a reduced temperature, is introduced into an ejector  140 . The ejector  140  is a fixed geometry device that operates as a jet pump using the temperature-controlled air  132  from the heat exchanger  130  as a motive flow to induce ambient flow from ejector ram air inlet  120 . The temperature-controlled air  132  passes through a fixed nozzle located within the ejector  140  at a high velocity, which results in a low-pressure zone in the ejector ram air  122  from the ejector ram air inlet  120 , thereby causing a motive force and flow in the ejector ram air  122 . The mixing of the temperature-controlled air  132  with ejector ram air  122  increases the overall ventilation flow while moderating the temperature of the air. Duct air  142  is subsequently distributed to occupied compartment  60  of the aircraft  10 . In one embodiment, the occupied compartment  60  comprises the cabin  20  and the cockpit  30 . In another embodiment, the occupied compartment  60  comprises the cockpit  30 . Alternatively, other occupied spaces might also include the cabin  20  only, or even other occupiable spaces within the aircraft such as a storage compartment. The occupied compartment  60  may be occupied by one or more of passengers or cargo. 
       FIG.  3    shows that the heating system  50  can, in embodiments, be generally regulated by a controller  210 . The controller  210  of the heating system  50  receives information from multiple sources to regulate air temperature of the occupied compartment  60 . An exemplary controller  210  is described below in connection with  FIG.  5   . Sources of information may include data related to temperature of the air. Another source of information the controller  210  may receive is data relating to the aircraft&#39;s flight stage (e.g., ground, takeoff, cruise, or landing). Other sources of information may include data reflective of altitude, air pressure, speed of the aircraft, etc. 
     In one embodiment, the controller  210  is fed information on a plurality of different air temperatures. This may include the temperature of the duct air  142  through a duct temperature sensor  162 . The controller  210  may receive information on the temperature of the air in the occupied compartment  60  from a compartment temperature sensor  164 . The controller  210  may receive information on the temperature of the outside air from an ambient temperature sensor  166 . Temperature sensors  162 ,  164 ,  166  may each be a thermocouple or a resistive thermal type of device such as a resistive temperature detector (RTD). The controller  210  may also receive information regarding an aircraft status  168  via a wired or wireless communications connection. The information may be provided by a flight computer or aircraft avionics and include data regarding all stages of flight, such as grounded, taxiing, takeoff, cruise, and landing. The controller  210  may also receive information on the aircraft status  168  including turbine engine fire or bleed air leak. 
     The controller  210  may also receive information on the desired air temperature of the occupied compartment  60  by a control panel  170 . The control panel  170  may be operated by a user within the aircraft  10  during any flight stage. The control panel  170  may comprise a heating enable switch  172 . The heating enable switch  172  may comprise an on/off function in which, in the off configuration the heating system  50  is not active, whereas in the on configuration the heating system  50  is active. The user, via the control panel  170 , may direct the controller  210  to alter air temperature of the occupied compartment  60  when the heating enable switch  172  is in the on configuration. The control panel  170  may include a temperature selection control  174 . The temperature selection control  174  is shown as a variable rotary knob but may also be a variable linear input or a variable touch screen selection. In one embodiment, the temperature selection control  174  comprises a potentiometer. A person skilled in the art will appreciate that the temperature selection control  174  may also be any form of variable input in which a range of selection is possible, and the heating enable switch  172  may be any user selection device for controlling a switch. For example, a touch screen or other graphic-user interface (GUI) may be used to provide heating enable switch  172  and to receive a temperature selection from the user. 
     Referring now to  FIG.  4   , the temperature selection control  174  may comprise a display for displaying a range of desired temperatures, ranging from a full cold selection  176  to a full hot selection  178 . In one embodiment, selecting the full cold selection  176  or the full hot selection  178  may be used to provide a safe range of cabin air temperature for passengers or cargo via the heating system  50 . For example, the temperature range may be between 65 degrees Fahrenheit to 85 degrees Fahrenheit for passenger comfort. In another embodiment, the temperature range may be between 33 degrees Fahrenheit to 95 degrees Fahrenheit for safely transporting temperature-sensitive cargo. 
     In an embodiment, the temperature selection control  174  may further comprise predetermined temperature ranges. The predetermined ranges may comprise a cool temperature range  171 , a warm temperature range  173 , and a hot temperature range  175 . In one embodiment, the cool temperature range  171  may be between about 60 to 68 degrees Fahrenheit; the warm temperature range  173  may be between about 68 to 75 degrees Fahrenheit; and the hot temperature range  175  may be between about 75 to 85 degrees Fahrenheit. In one embodiment, the cool temperature range  171  may be between about 70 to 106 degrees Fahrenheit; the warm temperature range  173  may be between about 106 to 142 degrees Fahrenheit; and the hot temperature range  175  may be between about 142 to 185 degrees Fahrenheit. 
     The temperature selection control  174  may further comprise a warm outside air temperature control input  177  and a cold outside air temperature control input  179 . The warm outside air temperature control input  177  and the cold outside air temperature control input  179  are selected by the controller  210  based on the outside air temperature and predetermined temperatures inputted into the controller  210 . In one example, the predetermined temperature range for the cold outside air temperature control input  179  may be any temperature below or up to 0 degrees Fahrenheit. In one example, the predetermined temperature range for the warm outside air temperature control input  177  may be any temperature above 0 degrees Fahrenheit. The cool temperature range  171 , the warm temperature range  173 , or the hot temperature range  175 , in combination with the warm outside air temperature control input  177  or the cold outside air temperature control input  179 , may direct the controller  210  to select target valve positions and/or valve duty cycles as described below in controllable heating methods  300 / 400  and shown in  FIGS.  6  and  7   . 
     When setting a target temperature of the air in the occupied compartment, via the temperature selection control  174 , the controller  210  may calculate a target duct temperature. The heating system  50  is used to adjust the temperature of the occupied compartment  60  via the controller  210  based on the target duct temperature, the target occupied compartment temperature, or both, as described below. 
     Returning to  FIG.  3   , the controller  210  may receive input from the duct temperature sensor  162 , the compartment temperature sensor  164 , the ambient temperature sensor  166 , the aircraft status  168 , and the control panel  170  to subsequently regulate the air temperature of the occupied compartment  60 . The controller  210  regulates the temperature of the occupied compartment  60  by controlling a plurality of valve-actuators. In embodiments, each of the valve-actuators includes a valve actuated by an electric motor. As depicted in  FIG.  3   , a bleed air motor  46  is configured to actuate a bleed air valve  44  that regulates the air flow of the bleed air  42  from the turbine engine  40 , a temperature control air motor  116  is configured to actuate a temperature control valve  114  that regulates the flow of the temperature control air  112  from the temperature control air inlet  110 , and an ejector ram air motor  126  is configured to actuate an ejector ram air valve  124  that regulates the ejector ram air  122  from the ejector ram air inlet  120 . The plurality of valve-actuators each have a plurality of positions ranging from fully open (e.g., positioned at 90 degrees) to fully closed (e.g., positioned at 0 degrees). Said another way, the valves may be quarter-turn valves operable to any angle between 0 degrees to 90 degrees to provide fully closed, fully open, or partially open positions. The valves used to regulate air flow from each inlet may take the form of a ball, butterfly, poppet, or gate-type valve. The valves may also be controlled via different mechanisms. In one embodiment, a valve may be pneumatically actuated open by upstream pressure. For example, bleed air valve  44  may be pneumatically controlled without a feedback loop. In one embodiment, a valve may be electrically actuated using a downstream pressure transducer for pressure feedback. In one embodiment, a valve may be a brushed or brushless electrical motor driven valve. In one embodiment, a valve may be pneumatically actuated by a torque motor. Furthermore, in one embodiment a valve may have position feedback via a resolver. In one embodiment, a valve may have position feedback via a rotary variable differential transformer (RVDT). A person skilled in the art will appreciate that numerous other types of valves used to modulate airflow through an orifice may be used. 
       FIG.  5    shows an exemplary control architecture  200  for controlling air mixing using the heating system  50 . Control architecture  200  includes a controller  210  communicatively coupled to the devices of the heating system  50 . The devices may include components of the heating system  50 , including the duct temperature sensor  162 , ambient temperature sensor  166 , compartment temperature sensor  164 , aircraft status  168 , control panel  170 , bleed air valve  44 , temperature control valve  114 , and ejector ram air valve  124 . Controller  210  is typically a microcontroller, a microprocessor, or programmable logic controller (PLC), but could also be a computer (e.g., the aircraft flight control computer or a separate computer), having a memory  230 , including a non-transitory medium for storing software  240 , and a processor  220  for executing instructions of software  240 . In certain embodiments, some, or all of software  240  is configured as firmware for providing low-level control of devices of the heating system  50 . Communication between controller  210  and devices of heating system  50  may be by one of a wired and/or wireless communication media. 
     Controller  210  determines the temperature of the duct air  142 , the occupied compartment  60 , and the outside ambient air based on data received from the duct temperature sensor  162 , compartment temperature sensor  164 , and ambient temperature sensor  166 , respectively. Controller  210  receives aircraft information via the aircraft status  168 . The user will direct the controller  210  via the control panel  170 , to alter the air temperature of the occupied compartment  60 . Controller  210  will then alter the configuration of one or more of the bleed air valve  44 , temperature control valve  114 , and/or ejector ram air valve  124  to achieve the desired air temperature within the occupied compartment  60  as set by the user. The controller  210  may alter the configuration of the valves by various mechanisms. For example, the controller  210  may set a valve position that is maintained until a new valve position is instructed by the controller. In another example, the controller  210  may enact a duty cycle in which the valve is modulated towards the open or closed direction for a specified amount of time over a certain period of time. For instance, the valve may be moved in the open direction for two seconds and held in place for one second, which may repeat for a period of ten minutes. 
     In one embodiment, the desired air temperature may be obtained by determining a target valve position of the ejector ram air valve  124  and a duty cycle for the temperature control valve  114  based on information input into the controller  210 , such as depicted in  FIG.  6   . In this embodiment, the controller  210  may operate a closed loop control system in which one or more of the duct air  142  temperature or the occupied compartment  60  temperature may affect the controller&#39;s  210  calculation of the target valve position or the duty cycle. In one embodiment, the desired air temperature may be obtained by determining a target valve position of the ejector ram air valve  124 , such as depicted in  FIG.  7   . In this embodiment, the controller  210  may configure a closed loop system, wherein one or more of the duct air  142  temperature or the occupied compartment  60  temperature may affect the controller&#39;s  210  calculation of the target valve position. The response of the plurality of valves is determined using one or more valve sensors for each valve. Determining a response via the valve sensor may include for example determining an instantaneous position or a rate of response of the valve. In an embodiment, the valve sensors comprise one or more of a resolver or a RVDT. Controller  210  may include any type of suitable controller, including analog or digital, for controlling the plurality of valves. 
     Controller  210  executes control algorithms that may include a feedback mechanism which depends on a difference or error term between a desired air temperature and a measured air temperature from one or more of the duct air  142  or the occupied compartment  60 . In an embodiment, the controller  210  includes a proportional-integral-derivative (PID) control algorithm in which the proportional term adjusts the position of the valves in proportion to the magnitude of the error term, the integral term adjusts the position of the valves in proportion to both the magnitude and the duration of the error term by integrating over time to account for any cumulative error, and the derivative term adjusts the position of the valves in proportion to the rate of change of the error term over time. The terms are weighted based on gains (e.g., coefficients), which may be tuned to provide a stable valve position with a minimal error term. In another embodiment, the controller  210  is a proportional-integral (PI) controller in which the derivative term is not used (e.g., set to zero). In another embodiment, the controller  210  is a proportional (P) controller in which the derivative term and the integral term are not used. In certain embodiments, the valve position feedback may be used as a surrogate for rate feedback (e.g., derivative controller action). 
     The controller  210  reduces the error term based on feedback from the temperature sensors  162 ,  164 , and  166 , as well as the valve sensors, which may be used to improve performance of the heating system  50  in addition to avoiding unsafe deflection of the valves. 
       FIG.  6    is a process flow diagram illustrating an exemplary controllable heating method  300  in an embodiment, performed using, for example, the heating system  50  of  FIG.  3   . 
     In a step  309 , the controllable heating method  300  starts. 
     Step  310  is a decision to determine whether heating has been enabled. For example, if in step  310  the heating enable switch  172  is in the off configuration, then the controllable heating method  300  proceeds to step  312 . If in step  310  the heating enable switch  172  is in the on configuration, then controllable heating method  300  proceeds with step  314 . 
     In a step  312 , the valves are automatically positioned. In embodiments, the valves  44 ,  114 ,  124  are automatically positioned based on predetermined criteria instead of input from temperature selection control  174 . In an example of step  312 , if in step  310  the heating enable switch  172  is in the off configuration, the controller  210  directs the ejector ram air motor  126  to position the ejector ram air valve  124  to fully closed (e.g., at 0 degrees), the controller  210  directs the bleed air motor  46  to position the bleed air valve  44  to fully closed (e.g., at 0 degrees) and the controller  210  directs the temperature control air motor  116  to position the temperature control valve  114  to fully open (e.g., at 90 degrees). The valves remain as such until the heating enable switch  172  is changed to the on configuration. In some embodiments, the controller  210  periodically returns to the start step  309  and then rechecks whether heating has been enabled in step  310 . 
     In a step  314 , the outside air temperature is determined. In an example of step  314 , the controller  210 , via the ambient temperature sensor  166 , determines that the outside air temperature is 30 degrees Fahrenheit. 
     In a step  320 , a desired temperature input is received. In an example of step  320 , the controller  210  receives a desired temperature input from the temperature selection control  174 . The temperature selection control  174  may be operated by a user to, for example, increase the temperature by adjusting the knob away from the full cold selection  176  and towards the full hot selection  178 . Controllable heating method  300  may proceed to step  330  and step  350  concurrently, and optionally to step  351  in some embodiments as described below. 
     In a step  330 , information is acquired about the unpressurized aircraft via various steps. In an example of step  330 , steps  331  and  333  are performed by the controller  210  to acquire various information. In an example of step  330 , the controller  210  may receive information continuously. In another example of step  330 , the controller  210  may acquire information on a predetermined schedule (e.g., once a second, once a minute, etc.). 
     In a step  331 , the aircraft flight position is determined. In an example of step  331 , the controller  210 , via the aircraft status  168  of  FIG.  3   , determines the flight position to be on the ground. In another example of step  331 , the controller  210 , via the aircraft status  168 , determines the flight position to be in air. For the in air flight position, the controller  210  may automatically override method  300  and direct the ejector ram air motor  126  to position the ejector ram air valve  124  in the flight position. The flight position of ejector ram air valve  124  may be a set angle to avoid conflict with the temperature control valve  114 . For example, the flight position of the ejector ram air valve  124  may be a set angle to provide a constant inflow to the occupied compartment  60  that varies with altitude, which avoids undesirable interaction with control of the temperature control valve  114 . In some embodiments, the flight position may be between about 10 degrees to about 40 degrees. In some embodiments, the flight position may be between about 15 degrees to about 35 degrees. In some embodiments, the flight position may be about 25.5 degrees. 
     In a step  333 , the engine fire status is determined. In an example of step  333 , the controller  210  determines there is no engine fire. In another example of step  333 , the controller  210  determines there is an engine fire. In the case of an engine fire, the controller  210  may automatically override method  300  and direct the ejector ram air motor  126  to position the ejector ram air valve  124  at fully closed (e.g., 0 degrees). 
     In a step  340 , the target ejector ram air valve position is calculated. In an example of step  340 , the controller  210  determines the target ejector ram air valve  124  position for controlling an amount of ejector ram air  122  that enters through ejector ram air inlet  120 . In embodiments, the controller  210  determines that the target ejector ram air valve  124  position is one-third open (e.g., about a 30 degree angle). This target position is calculated by the controller  210  based on the input from steps  314 ,  320 , and  330 . For example, if in step  320  the temperature selection control  174  is directed towards the warm temperature range  173 , and in step  314  the outside air temperature is determined to be within the predetermined range for the cold outside air temperature control input  179 , then a target position is calculated for the ejector ram air valve  124  based on these inputs to provide a target amount of ejector ram air  122  that enters through ejector ram air inlet  120 . This target position may be the same or different for any other combination of the cool temperature range  171 , the warm temperature range  173 , or the hot temperature range  175 , and the cold outside air temperature control input  179  or the warm outside air temperature control input  177 . Calculations in step  340  may also comprise computations for determining a speed at which to open the ejector ram air valve  124 . 
     In a step  349 , the actual valve position of the ejector ram air valve is determined. In an example of step  349 , the controller  210 , based on a signal from a resolver or a RVDT, determines the actual position of the ejector ram air valve  124  is about 40 degrees. 
     In a step  341 , the ejector ram air valve position error is calculated. The valve position error is the difference between the target valve position from step  340  and the actual valve position from step  349 . In an example of step  341 , the controller  210  calculates that the valve position error is about 10 degrees. 
     Step  343  is a decision to determine if the position of the ejector ram air valve matches the target position calculated in step  340 . If in step  343  the controller  210  determines the error term of the position of the valve is greater than a predetermined absolute value, then controllable heating method  300  proceeds to step  347  to adjust the position of the ejector ram air valve  124 . If in step  343 , the controller  210  determines the position of the ejector ram air valve  124  matches the target position (i.e., the error term is below the predetermined absolute value), then controllable heating method  300  proceeds to step  345 . 
     In a step  345 , the position of the ejector ram air valve  124  is maintained. In an example of step  345 , controller  210  directs the ejector ram air motor  126  to maintain the position of the ejector ram air valve  124  at one-third open (e.g., at an angle of 30 degrees) for a predetermined duration. Step  345  may also continuously monitor method  300  for a new desired temperature input. Alternatively, step  345  may monitor method  300  at a predetermined rate or following a predetermined duration to determine if a new desired temperature input has been received. 
     In a step  347 , the ejector ram air valve is adjusted based on the error term. In embodiments, the ejector ram air valve  124  is adjusted based on an amount that is proportional to the size of the error term. In an example of step  347 , the controller  210  directs the ejector ram air motor  126  to position the ejector ram air valve  124  at one-third open (e.g., about an angle of 30 degrees). 
     Controllable heating method  300  then proceeds back to step  349 . By proceeding back to step  349 , the controller  210  forms a closed control loop in which steps  341 ,  343 ,  347 , and  349  are repeated to adjust the position of the ejector ram air valve  124  until the error term is below a predetermined value. The closed control loop may be a PID control loop, for example. In one embodiment, the closed control loop may be a PI control loop. In one embodiment, the closed control loop may be a P control loop. 
     In a step  350 , the target duct air temperature is calculated. In an example of step  350 , in one embodiment, the controller  210 , using the information from step  320 , and optionally from step  355 , calculates that the target temperature of the duct air  142  is 120 degrees Fahrenheit. In some embodiments, the target temperature of the duct air  142  is higher than the desired temperature inputted in step  320 , therein allowing efficient heating of the occupied compartment  60 . 
     In a step  352 , the temperature of the duct air is determined. In an example of step  352 , the controller  210 , via the duct temperature sensor  162 , determines that the duct air  142  temperature is 130 degrees Fahrenheit. 
     In a step  354 , the duct air temperature error is calculated. In an example of step  354 , based on steps  350  and  352 , the controller  210  calculates the difference (i.e., error) between the target temperature (e.g., 120 degrees Fahrenheit) and the actual temperature (e.g., 150 degrees Fahrenheit) of duct air  142 . 
     Step  356  is a decision to determine if the duct air temperature is at the target temperature. In an example of step  356 , the controller  210 , using information from step  350  and step  354 , determines that the actual temperature is not at the target temperature of the duct air  142  (i.e., the error term is above a predetermined value). In this case, controllable heating method  300  proceeds to step  358  to calculate a duty cycle for the temperature control valve  114 . If in step  356 , the controller  210  determines the actual temperature of the duct air  142  matches the target temperature (i.e., the error term is below a predetermined value), then controllable heating method  300  proceeds back to step  352  to continue monitoring the temperature of the duct air  142 . This way, if there is an alteration in the temperature of the duct air  142  such that it falls outside of the error term, controllable heating method  300  may then proceed with the closed control loop described above to adjust the temperature of the duct air  142  accordingly. Such feedback may proceed indefinitely unless otherwise directed by a change in input to the controller  210 . 
     In a step  358 , the duty cycle for the temperature control valve is calculated. In an example of step  358 , the controller  210 , based on the temperature error of the duct air  142  calculated in step  354 , determines the duty cycle of the temperature control valve  114  to be moved in the open direction for two seconds and held in place for one second (e.g., a 2:1 duty cycle), which will be repeated for a predetermined period of time (e.g., one minute). In step  358 , the calculated duty cycle of the temperature control valve  114  may be any number of possible combinations of open or closed commands for specified periods of time. The controller  210  calculates the duty cycle that efficiently adjusts the temperature of duct air  142  to the target temperature determined in step  350 . 
     In a step  360 , the temperature control valve is modulated. In an example of step  360 , based on the calculated duty cycle from step  358 , the temperature control valve  114  is modulated by means of the controller  210  directing the temperature control air motor  116  to move the temperature control valve  114  in the open direction for two seconds then hold it in place for one second. This opening and closing is set to repeat for a predetermined period of time or until otherwise adjusted by the controller  210 . It is contemplated that other methods of opening and closing the temperature control valve  114  (e.g., specific angles) may be used to regulate the amount of temperature control air  112  that reaches the heat exchanger  130 . Controllable heating method  300  then proceeds to back to step  352  to determine the temperature of the duct air  142 . By proceeding back to step  352 , the controller  210  subsequently repeats step  354  to determine the error between the target temperature and actual temperature, step  356  to determine the temperature of the duct air  142 , step  358  to calculate a duty cycle for the temperature control valve  114 , and step  360  to modulate the temperature control valve  114 ; the controller  210 , therein, forms a closed control loop in which steps  352 ,  354 ,  356 ,  358 , and  360  are repeated to adjust the duty cycle of the temperature control valve  114  until the error term is below a predetermined value. The closed control loop may be a PID control loop, for example. In one embodiment, the closed control loop may be a PI control loop. In one embodiment, the closed control loop may be a P control loop. 
     The controllable heating method  300  may repeat continuously or on a predetermined schedule (e.g., once a second, once a minute, etc.) to reach and maintain the desired temperature. 
     In some embodiments, optional steps  351 ,  353 , and  355  are performed in which an occupied compartment temperature is used to inform the calculation of the target duct air temperature in step  350 . These optional steps may be used to provide a more accurate temperature control for the compartment  60  compared to only measuring the duct air temperature. 
     In an optional step  351 , the target occupied compartment temperature is calculated. In an example of step  351 , the controller  210  calculates that the target occupied compartment  60  temperature is 75 degrees Fahrenheit. The controller  210  may calculate this based on the positioning of the temperature selection control  174  in step  320 . 
     In an optional step  353 , the occupied compartment temperature is determined. In an example of step  353 , the controller  210  via the compartment temperature sensor  164  determines that the measured temperature of the occupied compartment  60  is about 65 degrees Fahrenheit. 
     In an optional step  355 , the occupied compartment temperature error is calculated. In an example of step  355 , based on steps  351  and  353 , the controller  210  calculates the difference between the target temperature (e.g., 75 degrees Fahrenheit) and the actual temperature (e.g., 65 degrees Fahrenheit) of the occupied compartment  60 . If optional step  355  is performed, controllable heating method  300  provides the occupied compartment temperature error value to step  350 . 
     Optional steps  351 ,  353 , and  355  may be performed continuously while controllable heating method  300  is ongoing. In this embodiment, it may be advantageous for the temperature of the occupied compartment  60  to be measured and used for calculating the target duct air temperature, thereby indirectly affecting the modulation of the temperature control valve  114  in step  360 . For example, if the temperature of the occupied compartment  60  is approaching the desired temperature received in step  320 , controllable heating method  300  may adjust the calculations of the target temperature of the duct air  142  in step  350  (e.g., lowering the target temperature of the duct air  142 ). As such, controllable heating method  300  may help to prevent overshooting the desired temperature and therefore requiring a readjustment. Thus, optional steps  351 ,  353 , and  355  may not be required for the proper functioning of controllable heating method  300  but may offer advantages as described above. 
       FIG.  7    is a process flow diagram illustrating an exemplary controllable heating method  400  performed using, for example, the heating system  50  of  FIG.  3   . 
     In a step  409 , the controllable heating method  400  starts. 
     Step  410  is a decision to determine whether heating has been enabled. For example, if in step  410  the heating enable switch  172  is in the off configuration, then the controllable heating method  400  proceeds to step  412 . If in step  410  the heating enable switch  172  is in the on configuration, then the controllable heating method  400  proceeds with step  420 . 
     In a step  412 , the valves are automatically positioned. In an example of step  412 , if in step  410  the heating enable switch  172  is in the off configuration, the controller  210  directs the ejector ram air motor  126  to position the ejector ram air valve  124  at fully closed (i.e., 0 degrees) and the controller  210  directs the temperature control air motor  116  to position the temperature control valve  114  at fully open (i.e., 90 degrees). The valves remain as such until the heating enable switch  172  is changed to the on configuration. In some embodiments, the controller  210  periodically returns to the start step  409  and then rechecks whether heating has been enabled in step  410 . 
     In a step  420 , a desired temperature input is received. In an example of step  420 , the controller  210  receives a desired temperature input from the temperature selection control  174 . In one embodiment, the temperature selection control  174  is the same as the embodiment shown in  FIG.  6   . In one embodiment, the temperature selection control  174  is different than the embodiment shown in  FIG.  6    in that the options for outside air temperature control inputs  177  and  179  are not included. The temperature selection control  174  may be operated by a user to, for example, increase the temperature by adjusting the knob away from the full cold selection  176  and towards the full hot selection  178 . In embodiments, controllable heating method  400  may then proceed to step  422 . In one embodiment, controllable heating method  400  may concurrently proceed to an optional step  450  as described below. 
     In a step  422 , the target duct air temperature is calculated. In an example of step  422 , in one embodiment, the controller  210 , using the information from step  420 , and optionally from step  454 , calculates that the target temperature of the duct air  142  is 120 degrees Fahrenheit. In one or more examples, the target temperature of the duct air  142  is higher than the desired temperature inputted in step  420 , therein allowing efficient heating of the occupied compartment  60 . 
     In a step  430 , information is acquired about the unpressurized aircraft via various steps. In an example of step  430 , steps  431 ,  433 , and  435  are performed by the controller  210  to acquire various information. In an example of step  430 , the controller  210  may receive information continuously. In another example of step  430 , the controller  210  may acquire information on a predetermined schedule (e.g., once a second, once a minute, etc.). 
     In a step  431 , the engine fire status is determined. In an example of step  431 , the controller  210  determines there is no engine fire. In another example of step  431 , the controller  210  determines there is an engine fire. In this example, the controller  210  may automatically override method  400  and position the ejector ram air valve  124  at fully closed (i.e., 0 degrees). 
     In a step  433 , the temperature error of the duct air is determined. In an example of step  433 , the controller  210 , via the duct temperature sensor  162 , determines that the actual temperature of the duct air  142  is 100 degrees Fahrenheit. Controller  210  then calculates the difference between the actual temperature (e.g., 100 degrees Fahrenheit) and the target temperature (e.g., 120 degrees Fahrenheit) calculated in step  422 . 
     In a step  435 , the flight position is determined. In an example of step  435 , the controller  210 , via the aircraft status  168 , determines the flight position to be in air. In another example of step  435 , the controller  210 , via the aircraft status  168 , determines the flight position to be on the ground. 
     Step  440  is a decision step to determine if the plane is on the ground. If in step  440 , the controller  210 , via the aircraft status  168 , determines the plane is on the ground, then controllable heating method  400  proceeds to step  442 . If in step  440 , the controller  210 , via the aircraft status  168 , determines the plane is in the air, then controllable heating method  400  proceeds to step  444 . 
     In a step  442 , the temperature control valve is opened. In an example of step  442 , the controller  210  directs the temperature control air motor  116  to position the temperature control valve  114  to fully open (i.e., at 90 degrees). This step is directed to allowing as much temperature control air  112  in through the temperature control air inlet  110  to reach the heat exchanger  130  while the plane is on the ground. 
     In a step  444 , the temperature control valve is modulated. In an example of step  444 , the controller  210  directs the temperature control motor  116  to adjust the temperature control valve  114  by means of moving the valve towards the open direction for 1 second and holding the valve in place for 2 seconds. This duty cycle may repeat for a predetermined amount of time. Additionally, this duty cycle may be adjusted by the controller  210  if different input is received. 
     In a step  460 , the target ejector ram air valve position is calculated. In an example of step  460 , if in step  435  the controller determines the flight position to be in the air, then the controller  210  determines the target ejector ram air valve  124  position for controlling an amount of ejector ram air  122  that enters through ejector ram air inlet  120 . In embodiments, the controller  210  determines that the target ejector ram air valve  124  position is one-third open (e.g., about a 30 degree angle). This target position is calculated by the controller  210  based on the input from steps  420 ,  422 , and  430 . For example, if in step  435  the controller  210  determines the flight position to be on the ground, then controller  210  uses the duct air temperature error determined in step  433  to calculate the target ejector ram air valve  124  position. Controller may then proceed to step  468 . Calculations in step  460  may also comprise computations for determining a speed at which to open the ejector ram air valve  124 . 
     In a step  468 , the actual valve position is determined. In an example of step  468 , the controller  210 , via a signal from a resolver or a RVDT, determines the actual position of the ejector ram air valve  124  is about 40 degrees. 
     In a step  462 , the ejector ram air valve position error is calculated. This error is the difference between the target position from step  460  and the actual position of the ejector ram air valve from step  468 . In an example of step  462 , the controller  210  calculates that the position error of the ejector ram air valve  124  is about 10 degrees. 
     Step  464  is a decision to determine if the position of the ejector ram air valve matches the target position. If in step  464  the controller  210  determines the error term of the position of the valve is greater than a predetermined absolute value, then controllable heating method  400  proceeds to step  466  to adjust the position of the ejector ram air valve  124 . If in step  464 , the controller  210  determines the position of the ejector ram air valve  124  matches the target position (e.g., the error term is below the predetermined absolute value), then controllable heating method  400  proceeds to step  470 . 
     In a step  466 , the ejector ram air valve is adjusted based on the error term. In embodiments, the ejector ram air valve  124  is adjusted based on an amount that is proportional to the size of the error term. In an example of step  466 , the controller  210  directs the ejector ram air motor  126  to position the ejector ram air valve  124  at one-third open (e.g., about an angle of 30 degrees). 
     Controllable heating method  400  then proceeds back to step  468 . By proceeding back to step  468 , the controller  210  forms a closed control loop in which steps  462 ,  464 ,  466 , and  468  are repeated to adjust the position of the ejector ram air valve  124  until the error term is below a predetermined value. The closed control loop may be a PID control loop, for example. In one embodiment, the closed control loop may be a PI control loop. In one embodiment, the closed control loop may be a P control loop. 
     In a step  470 , the ejector ram air valve position is maintained. In an example of step  470 , controller  210  directs ejector ram air motor  126  to maintain the position of the ejector ram air valve  124  for a predetermined duration (e.g., 1 minute). 
     In a step  472 , the temperature of the duct air is determined. In an example of step  472 , the controller  210 , via the duct temperature sensor  162 , determines that the duct air  142  temperature is 100 degrees Fahrenheit. Controllable heating method  400  then proceeds back to step  433  to calculate the temperature error of the duct air  142 . By proceeding back to step  433 , the controller  210  forms a closed control loop in which steps  433 ,  460 ,  462 ,  464 ,  466 ,  468 ,  470 , and  472  are repeated to adjust the position of the ejector ram air valve  124  until the error term of the duct air temperature is below the predetermined value. The closed control loop may be a PID control loop, for example. In one embodiment, the closed control loop may be a PI control loop. In one embodiment, the closed control loop may be a P control loop. 
     The controllable heating method  400  may repeat continuously or on a predetermined schedule (e.g., once a second, once a minute, etc.) to reach and maintain the desired temperature. 
     In some embodiments, optional steps  450 ,  452 , and  454  are performed in which an occupied compartment temperature is used to inform the calculation of the target duct air temperature in step  422 . These optional steps may be used to provide a more accurate temperature control for the compartment  60  compared to only measuring the duct air temperature. 
     In an optional step  450 , the target occupied compartment temperature is calculated. In an example of step  450 , the controller  210  calculates that the target occupied compartment  60  temperature is 75 degrees Fahrenheit. The controller  210  may calculate this based on the positioning of the temperature selection control  174  in step  420 . 
     In an optional step  452 , the occupied compartment temperature is determined. In an example of step  452 , the controller  210 , via the compartment temperature sensor  164 , determines that the measured temperature of the occupied compartment  60  is about 65 degrees Fahrenheit. 
     In an optional step  454 , the occupied compartment temperature error is calculated. In an example of step  454 , based on steps  450  and  452 , the controller  210  calculates the difference between the target temperature (e.g., 75 degrees Fahrenheit) and the actual temperature (e.g., 65 degrees Fahrenheit) of the occupied compartment  60  to determine the temperature error. If optional step  454  is performed, controllable heating method  400  provides the occupied compartment temperature error value to step  422 . 
     Optional steps  450 ,  452 , and  454  may be performed continuously while controllable heating method  400  is ongoing. In this embodiment, it may be advantageous for the temperature of the occupied compartment  60  to be measured and used for calculating the target duct air temperature, thereby indirectly affecting the modulation of the temperature control valve  114  in step  444 . For example, if the temperature of the occupied compartment  60  is approaching the desired temperature received in step  420 , controllable heating method  400  may be able to adjust the calculations of the target temperature of the duct air  142  in step  422  (e.g., lowering the target temperature of the duct air  142 ). As such, controllable heating method  400  may help to prevent overshooting the desired temperature and therefore requiring a readjustment. Thus, optional steps  450 ,  452 , and  454  may not be required for the proper functioning of controllable heating method  400  but may offer advantages as described above. 
     Controllable heating methods  300 / 400  greatly improve the comfort and safety of passengers in said unpressurized aircraft, while optimizing efficiency of heating an aircraft while the aircraft is performing other energy required processes. Controllable heating method  300 / 400  and heating system  50  improve efficiency of heating an unpressurized aircraft by first allowing bleed air  42  and temperature control air  112  to flow through the heat exchanger  130  and then through the ejector  140 . Placement of said ejector  140  downstream of said heat exchanger  130  allows the greatest difference in temperature between the bleed air  42  and temperature control air  112  received by the heat exchanger  130 , resulting in a more efficient heat transfer between the bleed air  42  and the temperature control air  112 . Furthermore, this reduces required size and weight of said heat exchanger  130 , therein enhancing efficiency of the unpressurized aircraft. 
     Controllable heating method  300 / 400  and heating system  50  improve the flexibility of regulating the temperature of the occupied compartment  60 . For instance, in one scenario the occupied compartment  60  may be occupied by passengers. Said passengers may desire a minimum air temperature of 75 degrees Fahrenheit, which may be achieved by the controllable heating method  300 / 400  and heating system  50 . In another example, the occupied compartment  60  may be occupied by temperature-sensitive cargo. Said temperature-sensitive cargo may require a minimum air temperature of 45 degrees Fahrenheit and a maximum air temperature of 95 degrees Fahrenheit, which may be achieved by the controllable heating method  300 / 400  and heating system  50 . 
     Although the invention has been described with reference to the embodiments illustrated in the attached drawing figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.