Abstract:
A method of controlling the flight of an aircraft by automatically controlling the descent phase of an aircraft using a Flight Management System and Flight Guidance System (FMS &amp; FGS) to control the air speed of the air craft and respond to an over speed condition.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
       [0001]    This invention was made with government support under Contract No. DTFAWA-10-C-00046 awarded by the United States Federal Aviation Administration. The Government has certain rights in this invention. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The descent of an aircraft from a cruise phase to a landing phase may be controlled for a variety of reasons, which may have contradictory goals. When fuel conservation is the primary goal, it is common to perform an idle descent, where the engine is set at idle, i.e. minimum thrust, and controlling the path of descent using control surfaces. During an idle descent, the aircraft may encounter an over-speed condition, which is currently solved by the pilot deploying speed brakes, generating a great amount of noise, which many passengers do not like. For aircraft without speed brakes, other solutions, typically much less desirable, may be used. 
         [0003]    Alternatively, the pilot can apply a pitch input into the aircraft, which change the trajectory and consumes additional fuel and defeating the purpose of the idle descent. Another alternative solution is to utilize one or more of the aircraft avionics, like the Flight Management System and/or Flight Guidance System (FMS &amp; FGS), and leave the engine throttle above idle, at approximately 10% and decrease the throttle when an over-speed condition occurs, which also consumes additional fuel and defeats the purpose of an idle descent. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0004]    The invention relates to a method of automatically controlling the descent phase of an aircraft using aircraft avionics executing a descent algorithm. The aircraft avionics repeatedly receives aircraft airspeed input and compares said airspeed with a first reference airspeed to determine if an over-speed condition has occurred. If an over-speed condition has occurred, the aircraft enters a slip maneuver. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0005]    In the drawings: 
           [0006]      FIG. 1  is a perspective view of the aircraft in data communication with a ground system, and which provide an illustrative environment for embodiments of the invention. 
           [0007]      FIG. 2  is a basic illustration of an aircraft avionics systems and its surrounding environment for use in controlling the aircraft. 
           [0008]      FIG. 3  is an exemplary altitude profile of a flight plan. 
           [0009]      FIG. 4  is a pictorial view of an aircraft in a forward-slip. 
           [0010]      FIG. 5  is a pictorial view of an aircraft in a side-slip. 
           [0011]      FIG. 6  is a flow chart of an aircraft system for controlling the flight of the aircraft in accordance with an exemplary embodiment. 
           [0012]      FIG. 7  is a schematic block diagram of a controller to control the flight path of an aircraft according to an exemplary embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0013]      FIG. 1  illustrates an aircraft  10  that may execute embodiments of the invention using aircraft avionics  100 , such as a Flight Management System and Flight Guidance System (herein after referred to as “FMS &amp; FGS”). While it is within the scope of the invention for dedicated or specialized aircraft avionics  100  to carry out the different embodiments of the invention, currently practical implementations of the embodiment can use the FMS &amp; FGS currently residing on contemporary aircraft. The FMS &amp; FGS may be programmed to carry out the embodiments of the invention. For purposes of this description the aircraft avionics  100  will be described in the context of the FMS &amp; FGS  100 . However, it should be understood that the particular avionics system is not limiting to the invention. 
         [0014]    The aircraft  10  may include a fuselage  12 , a nose  26 , one or more propulsion engines  16  coupled to the fuselage  12 , a cockpit  14  positioned in the fuselage  12 , and wings  30  extending outward from the fuselage  12 . The aircraft  10  may further include control surfaces  18  on the wing  30  and empennage  32 . The control surfaces  18  further comprise ailerons  22  which roll the aircraft  10 , rudder  20  which turns the aircraft  10  in the yaw direction, engine throttles which can turn the aircraft  10  in the yaw direction if applied asymmetrically, e.g., differential thrust, and speed brakes  24  to slow the airspeed  40  of the aircraft  10 . There are many different types of control surfaces and their use may depend on the size, speed, and complexity of the aircraft  10  on which they are to be used. 
         [0015]    A ground system  404  may communicate with the aircraft  10  and other devices including an interface device  400  via a wireless communication link  402 , which may be any suitable type of communication such as satellite transmission, radio, etc. The ground system  404  may be any type of communicating ground system  404  such as an airline control or flight operations department. 
         [0016]      FIG. 2  schematically illustrates a FMS &amp; FGS  100  with its surrounding environment. The FMS &amp; FGS  100  acquires input from flight instruments  140 , avionics  150 , and interface device  400  in order to control a flight plan  124  (shown schematically as a box) for an aircraft  10 . The flight instruments  140  include, but are not limited to, an altimeter, attitude indicator, airspeed indicator, compass, heading indicator, vertical speed indicator, course deviation indicator, and/or a radio magnetic indicator. The avionics  150  comprise an electronic systems including, but not limited to, communications, navigation, and the display and management of multiple subsystems. The interface device  400  may comprise any visual display which collects input from an operator  410  and presents output to the operator  410  and may comprise a control display unit which incorporates a small screen and keyboard or touchscreen. 
         [0017]    The FMS &amp; FGS  100  may be used for any aircraft  10  including commercial or military use with single or multiple engines  16 . The aircraft  10  may include but is not limited to a turbine, turbo prop, multi-engine piston, single engine piston and turbofan. 
         [0018]    The FMS &amp; FGS have the primary function of in-flight management of a flight plan  124 . Using various sensors, such as GPS (global positioning system) and INS (inertial navigation system), to determine a position of the aircraft  10 , the FMS &amp; FGS  100  can guide the aircraft  10  along the flight plan  124 . The flight plan  124  is generally determined on the ground, before departure either by the pilot or a professional dispatcher. The flight plan  124  is entered into the FMS &amp; FGS  100  either by typing it in, selecting it from a saved library of common routes or via a link with the airline dispatch center. Once in flight, a principal task of the FMS &amp; FGS  100  is to determine the aircraft&#39;s position and the accuracy of that position, especially relative to the flight plan. Simple FMS &amp; FGS  100  use a single sensor, generally GPS, in order to determine position. 
         [0019]      FIG. 3  illustrates an exemplary altitude vs distance profile for a flight plan  124  which includes a takeoff phase  330 , ascent phase  340 , cruise phase  300  typically between 30,000 and 40,000 feet above sea level for contemporary commercial aircraft, then enters a descent phase  310  before a landing phase  320 . The descent phase  310  may be any time that the aircraft  10  descends in altitude other than the landing phase  320 . In most cases the descent phase  310  is the transition from the cruise phase  300  to the landing phase  320 . For purposes of this description, the descent phase  310  does not include the landing phase  320 . The landing phase  320  comprises a final approach phase  324 , landing flare  322 , touchdown  326 , and roll-out phase  328 . The landing flare  322  is a maneuver or stage during the landing phase  320  of an aircraft  10  and follows the final approach phase  324  and precedes the touchdown  326  and roll-out phases  328  of landing  310 . In the flare  322  the nose  26  of aircraft  10  is raised, slowing the descent rate, and the proper attitude is set for touchdown  326 . In the case of conventional landing gear-equipped aircraft  10  the attitude is set to touch down on all three wheels simultaneously or on just the main landing gear  34 . In the case of tricycle gear-equipped aircraft  10  the attitude is set to touchdown  326  on the main landing gear  34 . 
         [0020]    The descent  310  may comprise a normal, rapid, stair-step, continuous, powered, unpowered descent, idle, or nominal thrust, or any combination of the preceding or any other known descent methods. An idle descent may be utilized where the engine  16  is set at idle, i.e. minimum thrust, then descending the aircraft  10  in altitude towards a landing area or ground  54 . A nominal thrust descent may also be implemented during the descent phase  310  where the engine  16  is set at approximately 10% thrust above idle. The idle descent or the nominal thrust descent may be part of a continuous approach descent wherein the altitude of the aircraft  10  changes at a steady rate. 
         [0021]    In the current market, cost pressures are driving aircraft operators to seek fuel, environmental and maintenance savings. Accordingly, idle descent has become the preferred method during the descent phase  310  as the idle descent provides the most efficient utilization of fuel while reducing noise and increasing the life of the engines  16 . A detriment to an idle descent is that at least one degree of freedom of flight control is lost in that the pilot can no longer use thrust to control the rate of descent. The use of thrust increases fuel consumption, which negates the fuel-saving benefit of an idle descent. Unfortunately, during an idle descent, it is common for the aircraft  10  to encounter an airspeed over-speed condition  120 . The current solution is to pitch up the aircraft  10  and increase the thrust to slow the airspeed  40  of the aircraft  10 , which negates the fuel savings benefits of the idle descent. An embodiment of the invention addresses this over-speed condition  120  by placing the aircraft  10  into a slip maneuver  200 , which increases aerodynamic drag to slow the aircraft, instead of using thrust and pitch. The slip maneuver  200  increases the aerodynamic drag of the aircraft  10 , which reduces the airspeed  40 . Applying the slip maneuver  200  during the descent phase  310  may be accomplished by the FMS &amp; FGS  100  repeatedly obtaining an airspeed input  116  which corresponds to the airspeed  40  of the aircraft  10 . When the aircraft  10  encounters an over-speed condition  120  due to gravitational forces, the FMS &amp; FGS  100  will enter the aircraft  10  into a slip maneuver  200  in order to slow the airspeed  40  of the aircraft  10 . Once the slip maneuver  200  is completed and the airspeed  16  is reduced as desired, the descent phase  310  continues as before, prior to entering the slip maneuver  200 . The slip maneuver  200  can be used to control the airspeed  40  in alternate descents  310  described above. 
         [0022]    Referring to  FIGS. 4 and 5 , specific implementations of the slip maneuver  200  may be at least one side-slip  202  or forward-slip  204  maneuver. Looking first at the forward-slip maneuver  204 , the aircraft  10  enters the forward-slip maneuver  204  by the FMS &amp; FGS  100  outputting control surface settings to adjust one or more control surface  18  of the aircraft  10 . More specifically, the FMS &amp; FGS will control the aircraft  10  such that the aircraft  10  banks and applies opposing rudder or throttle  20  and aileron  22  in order to keep moving straight along the ground track  52 . The nose  26  of the aircraft  10  will point in an alternate direction than the direction of the ground track  52 , altered by a slip angle  212 . The effect of the slip maneuver  204  is to rotate the aircraft  10  by the slip angle  212 , which is a fraction of a degree, in order to increase the aerodynamic drag to decrease the airspeed  40  of the aircraft  10 . In one embodiment, the slip angle  212  of the forward-slip maneuver  204  is 0.2-0.3 degree, although the slip angle  212  may be larger or smaller in alternate embodiments. 
         [0023]    The slip angle  212  is the angle between the heading  50  and the ground track  52 . Heading  50  is the direction which the nose  26  is pointed. Ground track  52  is the path on the surface of the Earth directly below an aircraft  10 . In the forward-slip maneuver  204 , while the heading  50  of the aircraft changes, the ground track  52  remains the same as before the maneuver. 
         [0024]    Referring to  FIG. 5 , a side-slip maneuver  202  is when the heading  50  of the aircraft  10  remains the same but the ground track  52  changes due to the movement of control surfaces  18 , particularly by adjusting rudder or throttle  20  and ailerons  22  in the opposite directions. The horizontal component of lift forces the aircraft  10  to move sideways toward the low wing, creating an angled ground track  52 . As the slip angle  212  is a fraction of a degree and the slip maneuver is normally short lived such that the aircraft  10  will not substantially go off the predetermined course. The amount of off track travel can be easily corrected after exiting the slip maneuver  202 . 
         [0025]      FIG. 6  illustrates a flow chart of exemplary operation of a specific implementation of the FMS &amp; FGS  100  executing the descent algorithm  110 . The airspeed input  116  is repeatedly sent to the FMS &amp; FGS  100  in order to determine if an over-speed condition  120  has occurred. The over-speed condition  120  occurs if the airspeed  40  of the aircraft  10  is greater than or equal to a predetermined first reference airspeed  112 . An exemplary first reference air speed  112  is a threshold air speed  118  for the given conditions, i.e. a maximum operating speed limit (Vmo)  122 . In this embodiment, the first reference airspeed  112  equals five knots less than the maximum operating speed limit (V mo )  122 . If the airspeed input  116  is less than the first reference airspeed  112 , the descent phase  310  continues as planned without a slip maneuver  200 . If the airspeed input  116  is equal to or greater than the first reference airspeed  112 , then a slip maneuver  200  is entered. Once the aircraft  10  is in the slip maneuver  200 , the airspeed input  116  continues to be repeatedly send to the FMS &amp; FGS  100  and compared to a predetermined second reference airspeed  114 . Once the airspeed input  116  is determined to be below the second reference airspeed  114 , the aircraft  10  will exit the slip maneuver  200 . The second reference airspeed  114  is equal to fifteen knots less than V mo    122  in this embodiment. At that time the descent  310  will continue as before the slip maneuver  200 . 
         [0026]    The first reference airspeed  112  is greater than the second reference airspeed  114 . The range between the first  112  and second reference airspeed  114  is ten knots. In alternate embodiments, the range may be larger, in order to prevent the aircraft from entering and exiting the slip maneuver  200  many times during the descent phase  310 . The range may be selected as appropriate for a particular aircraft  10  and its intended operation Inherently after the slip maneuver  200  is exited, the airspeed  40  of the aircraft  10  would naturally increase again, it is contemplated that the aircraft  10  may enter a slip maneuver  200  multiple times. 
         [0027]      FIG. 7  illustrates an exemplary block diagram of a controller  130  for the FMS &amp; FGS  100 . The airspeed input  116  is repeatedly sent to the FMS &amp; FGS  100  and is compared via a relational operator to the first reference air speed  112 . If the airspeed input  116  is equal to or greater than the first reference air speed  112 , a slip maneuver  200  is activated. When the airspeed input  116  is determined to be less than the second reference air speed  114 , the slip maneuver  200  is deactivated. A slip input  206  and slip maneuver  200  is input to the FMS &amp; FGS  100  then a slip error  210  is calculated from a summing point. The slip error  210  determines the forward gain  132  which is summed with a damping gain  134  from the slip rate input  208 . The sum of the forward gain  132  and damping gain  134  results in the scaling gain  136  and thus the control surface  18  command is determined. The illustrated exemplary controller  130  is in no way limiting to the invention disclosed. 
         [0028]    In any of the previously described embodiments, the slip maneuver may be entered into prior to reaching the over speed condition. The descent algorithm being executed by the FMS &amp; FGS to control the descent may be programmed to monitor the aircraft&#39;s speed and at a predetermined value (percentage, threshold, delta, rate of change, etc.) before reaching the operational speed limit, such as Vmo, the FMS &amp; FGS initiates the sending of the appropriate control signals to the appropriate control surfaces, such as rudder or throttle and aileron, to perform the slip maneuver and put the aircraft into the slip condition. The FMS &amp; FGS could also be programmed to project if/when the aircraft is likely to reach an over speed condition based on the acceleration of the aircraft and the current airspeed. In response to this projection, the FMS &amp; FGS can execute the slip maneuver. 
         [0029]    This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.