Abstract:
An axillary airfoil located as far forward as practicable on the fuselage of an airliner. During high speed cruise, the airfoil can be adjusted to provide supplemental lift to move the center of pressure forward, thereby reducing the amount of downforce needed to be produced by the vertical stabilizer. This would result in saving fuel. Spoilers mounted on the airfoils would be programmed to automatically deploy to return the center of pressure rearward whenever flight conditions require greater longitudinal stability.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    Provisional Patent Application No. 61/957,085 filed on Jun. 24, 2013 
     
    
     BACKGROUND-FIELD OF THE INVENTION 
       [0002]    Even though, modern airliners have very sophisticated, computer controlled autopilots, these aircraft must have sufficient aerodynamic characteristics of pitch, roll, and yaw stability that they can be hand flown by a pilot throughout a wide range of flight conditions and maneuvers in the event of computer or autopilot failure. 
         [0003]    An important consideration when designing s longitudinally stable airplane is the balance between the center of gravity and the center of pressure of the wing. The center of pressure or CP is a point along the wing chord line where lift is considered to be concentrated. To achieve longitudinal stability, a conventional airplane is designed with its center of gravity or CG far enough forward of its CP so it is nose heavy in all phases of flight. 
         [0004]    Hypothetically, the CP can be considered a fulcrum and the distance between the CG and the CP a lever arm. A horizontal stabilizer, located at the tail of the aircraft, offsets this nose heavy tendency of an airplane by being designed with a negative angle of attack with respect to the relative wind to produce a downward force called the tail-down force. Its distance from the CP can also be considered a lever arm and is the balancing force in most flight conditions. 
         [0005]    The stabilizer will cause the aircraft to self correct. If the nose is pitched up, the negative angle of attack of the tail is reduced, so it generates less tail-down force, allowing the nose to drop. On the other hand, if the nose is pitched down, the tail creates more tail-down force, raising the nose. 
         [0006]    If the CP and the CG are too close together, the aircraft is not sufficiently nose heavy to be stable in pitch for all conditions of flight. With insufficient aerodynamic longitudinal self correcting force, when turbulence or a control input changes the aircraft&#39;s pitch, the nose could continue to pitch up or down, unless there is an immediate control correction. 
         [0007]    The further aft the CP is relative to the CG, the greater the aircraft&#39;s stability; however, the greater the tail-down force required of the stabilizer. If the CG and CP are too far apart, it will adversely affect the aircraft&#39;s maneuverability and reach the limits of the horizontal stabilizer&#39;s and elevator&#39;s ability to control the aircraft&#39;s pitch. Thus the CG must be located within a limited range forward of the CP. This is referred to as the CG limits. 
         [0008]    An example of one of the possible conditions that must be taken into consideration when calculating an aircraft&#39;s CG limits is that occasionally, an aircraft might have to slow down to its maneuvering speed, a speed slow enough that it will stall before extreme turbulence can cause structural failure. This slow speed results in a very high angle of attack. In the unlikely event of such a stall, it is important that the airplane is nose heavy so that the nose will drop, which will increase airspeed and help the airplane to recover from the stall. 
         [0009]    Although the tail-down force created by the horizontal stabilizer is necessary for longitudinal stability and balance, it is aerodynamically inefficient. The wings must support the negative lift created by the tail-down force, which increases induced drag. Both the increased negative angle of attack of the stabilizer and positive angle of attack of the wing increase parasitic drag. These drags, in turn, increase the power required of the engines, and increase fuel consumption. 
         [0010]    The CG limits for an aircraft are established during design, initial testing, and airworthiness certification of each airplane to provide sufficient longitudinal stability for safe operation. These limits are based on worse case scenarios such as extreme turbulence and low airspeeds. 
         [0011]    The CG limits represent a range of locations where the CG can occur. It will vary with the amount and type of the cargo and must be calculated before every flight. Once an airliner is loaded, the CG will remain fixed except for minor variations, such as people walking up and down the aisles. 
         [0012]    During flight, the exact location of the CP of an aircraft varies with airspeed. It is furthest forward at the stall speed and, as airspeed increases, aerodynamic forces cause the CP to shift to the rear, increasing the tail-down force required. 
         [0013]    Most of a commercial airliner&#39;s operating time and fuel consumption occurs at medium to high speed cruise. If the distance between the CP and the CG could be adjusted in flight so that the distance between them is just enough that the aircraft remains stable for the flight environment at the time it would result in substantial reduction in fuel consumption, For example, during routine cruise through smooth air with all control systems, such as a computer controlled autopilot, functioning correctly, the CP could be adjusted to be adjacent to and directly to the rear of the CG and the tail-down force would then be minimal. 
         [0014]    This would be feasible for an airliner if it had a controllable means of decreasing the distance between the CG and CP during flight when it is safe to do so; and a means of increasing this distance as rapidly as needed to not compromise safety when greater stability is warranted. 
         [0015]    Occasionally, due to other design parameters, aircraft can be too nose heavy. One way to alleviate this problem is to install additional small horizontal airfoils well forward of the main wing. There are aircraft in use today that have auxiliary airfoils exerting lift forward of the CG to obtain a desired location for the CP, either as a part of the aircraft&#39;s original design or as a modification. 
         [0016]    An example of forward mounted auxiliary airfoils included in the original design of the aircraft is the PIAGGIO AERO INDUSTRIES S.p.A. “P 180 AVANTI” business turboprop. This aircraft&#39;s main wing is located aft of the passenger cabin so it doesn&#39;t intrude on space for passengers. With the wing so far aft, the balancing loads from a high negative angle of attack of the horizontal tail would be huge and that would add excess drag. So a small forward wing adds lift to relieve loads on the horizontal tail, which then can be smaller in size. The AVANTI is a three surface airplane with the conventional horizontal T-tail providing all the pitch controls while the forward surface adds lift and reduces the load on the horizontal tail. The only thing that is adjustable on the AVANTI&#39;S forward wing is a small flap that extends in concert with the main wing flap to balance the pitch changes caused by the extension of the main flap at low airspeeds during takeoffs and landings. 
         [0017]    A second example of a forward mounted airfoil currently in use as a modification to a previously manufactured aircraft is one for a CESSNA 182, a four passenger, single engine light aircraft. This particular aircraft, with a large, six cylinder engine, is relatively nose heavy. This is due to the fact that the 182 has a high wing that has to be mounted in a position far enough back that the pilot can see where he or she is going when the plane is banked in a turn. Without modifying the main wing or the horizontal tail, PETERSON&#39;S PERFORMANCE PLUS INC, of El Dorado, Kans. installs a small rigid airfoil near the nose of the 182. The rigid airfoil moves the CP forward, but still allows a useful load between the fore and aft CG limits. 
       SUMMARY OF THE INVENTION 
       [0018]    The objects of the invention are: 
         [0019]    (a) to provide a means to controllably shift the CP forward as the angle of attack of the main wing decreases at high airspeeds, and shift the CP rearward as the angle of attack increases at lower airspeeds; 
         [0020]    (b) to provide a means to return the CP rearward to its original position in a sufficiently rapid and dependable manner whenever necessary thereby increasing the amount of tail-down force immediately in the event of an unexpected incident such as encountering clear air turbulence. 
         [0021]    The invention is comprised of mounting an airfoil on the fuselage of an aircraft as far forward of the aircraft&#39;s main wing and CG as practicable. Each airfoil would be capable of exerting a lifting force that would supplement the lifting force of the main wing. Each airfoil would have at least one spoiler mounted on its upper surface to rapidly reduce that lift and return the CP to its original rearward position should an unexpected destabilizing event occur. 
         [0022]    The embodiments that follow will also show means to adjust the airfoils to reduce their parasitic and induced drag during portions of the aircraft&#39;s flight when a forward shift of the CP is not desired. During takeoff and climb, if the airfoils are in a low lift position, spoilers on the airfoils are retracted. As the aircraft approaches its cruise altitude and speed, the airfoils can be adjusted in flight by the aircraft&#39;s autopilot control system to create enough additional lift to temporarily move the aircraft&#39;s CP forward, closer to the aircraft&#39;s CG. Whenever necessary for safety, the spoilers could be quickly extended. During routine operation, for example the decent and landing phase, the airfoils would gradually be returned to their neutral lift position. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1A  is a schematic plan view of a commercial transport aircraft with airfoils forward of the main wing. 
           [0024]      FIG. 1B  is a partial schematic plan view of the aircraft showing a forward airfoil with spoilers and a flap mounted thereon. 
           [0025]      FIG. 1C  shows a partially retracted forward airfoil and spoiler. 
           [0026]      FIG. 2  diagrams an angle of attack. 
           [0027]      FIG. 3A-3C  are schematic, cross sectional views of a forward airfoil having a flap and a spoiler as shown in  FIG. 1B . 
           [0028]      FIG. 3D  is a view of an airfoil having a spoiler as shown in  FIG. 1C . 
           [0029]    FIG.  4 A,B are partial views showing details of the airfoil depicted in  FIG. 1B  and  FIGS. 3A-3C . 
           [0030]    FIGS.  5 A,B show details of an articulating airfoil. 
           [0031]    FIGS.  6 A,B are detailed views of an airfoil with a flap. 
           [0032]      FIGS. 7A-7C  show an airfoil fully retracted, partially extended, and fully extended, respectively. 
           [0033]      FIG. 8  is an isometric view showing two positions of the airfoil depicted in  FIGS. 5  A,B. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0034]    A commercial transport aircraft  100  of conventional design shown in  FIG. 1A  is comprised of a fuselage  102  and a pair of main wings  104  located amidships. Ailerons  105  are mounted on the trailing edges of wings  104  respectively. A horizontal stabilizer  106  is located near the tail of fuselage  102 . Attached to the rear of stabilizer  106  is an elevator  110 . A trim tab  112  is mounted on elevator  110 . An airfoil assembly, comprised of a pair of airfoils  108  and mechanisms for configuring them, have been retrofitted near the nose of fuselage  102 . Points representing a CG  114  and a CP  116  are located amidship. 
         [0035]      FIG. 1B  shows spoilers  118  mounted on the top surface of airfoils  108  Articulating flaps  120  are an integral part of airfoils  108 . 
         [0036]      FIG. 1C  shows retractable airfoils  108  with spoilers  118  mounted thereon, fully extended and partially retracted into fuselage  102 . 
         [0037]      FIG. 2  is a vector diagram showing the angle of attack  140  between the longitudinal cord line  142  of an airfoil and the direction of the relative wind  144 . Chord line  142  is an imaginary straight line drawn from the leading edge to the trailing edge of an airfoil. Relative wind is the airflow that is parallel to and opposite the direction of the flight path of aircraft  100 . The combined surface areas of airfoils  108  are substantially smaller than the surface areas of either stabilizer  106  or main wings  104 ; therefore, stabilizer  106  and wings  104  determine the direction of the relative wind  144  for aircraft  100 . Increasing angle of attack  140  increases lift. A change in chord line  142  relative to aircraft  100  will create a corresponding change in the angle of attack of airfoil  108 . 
         [0038]      FIGS. 3A-3C  are cross sectional views showing spoiler  108  with flap  120  attached by means of a flap hinge  122 . Spoiler  118  is installed on airfoil  108 . Relative wind  140 , chord line  142 , and angle of attack  144  for airfoil  108  are also shown. 
         [0039]    In  FIG. 3A , spoiler  118  and flap  120  are retracted. In  FIGS. 3B , spoiler  118  is retracted into airfoil  108 , and flap  120  is extended. In  FIG. 3C , spoiler  118  and flap  120  are extended. 
         [0040]      FIG. 3D  shows airfoil  108  with spoiler  118  retracted and extended. Angle of attack  144  for airfoil  108  is fixed. 
         [0041]    Taken together,  FIG. 3A  and  FIG. 4A  represent airfoil  108  with spoiler  118  and flap  120  retracted. In this configuration, chord line  142  and relative wind  140  are nearly parallel. Angle of attack  144  is nearly zero. 
         [0042]    FIGS.  4 A,B are enlarged partial cross sectional views showing details of operation of airfoil  108  depicted in  FIGS. 3A-3C . Referring to FIGS.  4 A,B, an electronic input signal from the flight deck can be transmitted to a controller  124 . Controller  124  can process command signals from the flight deck, including commands from a pilot, computerized auto pilot, or sensors such as accelerometers and also contain a backup computer dedicated to processing “fail safe” signals. Controller  124  is connected by means of a spoiler signal link  126  to a spoiler actuator  130 . Spoiler actuator  130  is comprised of a direct current push type solenoid. Since it is a direct current solenoid the polarity of the electric signal positively controls the solenoid&#39;s motion in either direction. 
         [0043]    Spoiler actuator  130  is coupled to spoiler  118  by means of a spoiler push pull rod  134  which can extend or retract spoiler  118  in a variety of intermediate positions 
         [0044]    A flap  120  is pivotally mounted on airfoil  108  by means of a hinge  122 . Controller  124  is coupled to flap actuator  132 . Flap actuator  132  can be actuated and controlled by in a manner similar to that described above with reference to spoiler actuator  130 . Flap actuator  132  is an electric servo motor typically used for the extension and retraction of flaps and is coupled to flap  120  by a flap push pull rod  136 . 
         [0045]      FIG. 1C , and FIGS.  7 A,B,C, show aircraft  100  with retractible airfoils  108  fully retracted, partially extended, and fully extended horizontally out of fuselage  102 . Angle of attack  144  is fixed. The amount of lift generated by airfoil  108  is determined by the surface area of airfoil  108  extended into relative wind  140 . 
         [0046]    Referring to FIGS.  7 A,B,C. Airfoil  108  with spoiler  118  mounted thereon has a fixed angle of attack as shown in  FIG. 3D . Airfoil  108  can extend and retract through an opening in fuselage  102 . By means of a control transmission link  125 , controller  124  can signal a hydraulic pump  154  to pump hydraulic fluid through either a hydraulic extension line  156  or a hydraulic retraction line  158  to an airfoil extension actuator  150  which is comprised of a hydraulic cylinder, can cause an actuator push pull spar  152  to extend or retract. Spar  152 , rigidly attached to airfoil  108 , can extend and retract airfoil  108  through the opening in fuselage  102 . 
         [0047]    FIGS.  5 A,B show airfoil  108  at two different positions with respect to relative wind  140 . Controller  124  can send a command signal by means of a spoiler signal link  126  to a spoiler actuator  130 . Spoiler actuator  130  is coupled to spoiler  118  by means of a spoiler push pull rod  134  which can extend or retract spoiler  118  in a variety of intermediate positions. 
         [0048]    Referring to FIGS.  5 A,B and  FIG. 8 , airfoil  108  is attached to fuselage  102  by means of main spar  160 , that is rotatable on the lateral axis of aircraft  100  A spar arm  166  is rigidly connected to spar  160  and has an articulating connection to a piston rod  164 . Piston rod  164  is operated by a n airfoil tilting actuator  162  comprised of a hydraulic cylinder. 
       Operation of the Invention   
       [0049]    In the first embodiment, as shown in  FIGS. 1A and 1B , a conventional aircraft  100  has been retrofitted with airfoil  108  mounted on fuselage  102  ahead of main wings  104  and ahead of both the CG  114  and CP  116 . As shown in  FIGS. 3A and 4A , during take off and climb, spoiler  118  and flap  120  are both in the retracted position. Retrofitting aircraft  100  with the airfoil assembly comprised of airfoil  108  and control wiring together with materials necessary to reinforce fuselage  102  have added weight in that area, so airfoil  108  has been rigged so that at cruise speeds in this configuration, airfoil  108  will generate sufficient lifting force on fuselage  102  at the location where airfoil  108  is mounted to neutralize this added weight thus leaving the distance between CG  114  and CP  116  virtually unchanged. 
         [0050]    As shown in  FIGS. 3A ,  3 B,  4 A and  4 B as aircraft  100  reaches its cruise altitude and speed, and is being flown by autopilot, if the pilot determines that the prognosis for the flight conditions are suitable, i.e. little or no anticipated turbulence, the pilot can input a command to the autopilot to extend flap  120 . When signaled from the autopilot, controller  124  sends a command through flap signal link  128  to flap actuator  132 . Actuator  132  retracts push pull rod  136  to extend flap  120  to a predetermined position causing chord line  142  to increase angle of attack  144  of airfoil  108  as shown in  FIG. 3B . The increase of angle of attack  144  increases the coefficient of lift which increases the lifting force of airfoil  108 . When this lifting force increases, CP  116  is moved forward on fuselage  102 . At the same time as CP  116  is moved forward the autopilot controls elevator  110  and adjusts trim tab  112  to maintain the flight attitude of aircraft  100 . 
         [0051]    Should flight conditions suddenly change, e.g. unexpected clear air turbulence, partial malfunction of the autopilot, pilot overriding the autopilot, a signal from an accelerometer, an automatic command from the autopilot, or a loss of signal from the flight deck; controller  124  would send a signal through spoiler signal link  128  to spoiler actuator  130  causing spoiler  118  to extend in a rapid manner as shown in  FIGS. 3C and 4B . This will result in the immediate dumping of the additional lifting force created by airfoil  108 . Later, if flight conditions permit, controller  124  can be directed to signal spoiler actuator  130  with a reverse polarity current to retract spoiler  118 . 
         [0052]    Spoiler  118  and flap  120  could be any of numerous standard designs known to those versed in the art. They would be empirically adapted to this application so that the amount of lift dumped when spoiler  118  is fully extended is in close approximation to the amount of lift previously created by the increase of angle of attack  142  caused by the extension of flap  120  and lifting force will revert to the amount that is generated when spoiler  118  and flap  120  are fully retracted. This would result in the immediate rearward shift of CP  116 . During this transition period, unless previously disengaged by the pilot, the autopilot will simultaneously exert pressure on elevator  110  as it adjusts trim tab  112  to compensate for a rearward shift of CP  116 . 
         [0053]    If the pilot estimates that the cause of the deteriorated flight conditions is probably going to be brief, the pilot can continue to fly with spoiler  118  and flap  120  extended. Then, when the need for greater stability, such as a brief period of turbulence, is passed, the pilot can turn off the “Fasten Your Seatbelt” sign and retract spoiler  118  which would return CP  116  to its forward position. On the other hand, if the pilot estimates that the cause might continue for a longer period of time, he or she can send a signal to controller  124  in order to reduce both the induced and parasitic drag of airfoil  108 ,. Controller  124  would issue a simultaneous command to spoiler actuator  130  and flap actuator  132  causing spoiler  118  and flap  120  to retract in a synchronized manner so that the lifting force and CP  116  remain unchanged. 
       Additional Embodiments 
       [0054]    In the second embodiment, airfoil  108  has a fixed angle of attack as shown in  FIG. 3D . As shown in  FIG. 7A ,  7 B,  7 C, airfoil  108  can be fully retracted and controllably deployed horizontally from fuselage  102  to numerous positions. 
         [0055]    While aircraft  100  is at the gate, airfoil  108  would be fully retracted as shown in fig  FIG. 7A  in order to not interfere with access to fuselage  102  by ground service trucks or the airway ramp extended from the terminal. 
         [0056]    As aircraft  100  taxies for takeoff, the pilot extends airfoil  108  for takeoff and climb by sending a command to controller  124 . Controller  124  sends a signal through transmission link  125  to hydraulic pump  154  to pump hydraulic fluid through extension line  156  to actuator  150 . At the same time, retraction line  158  allows hydraulic fluid to return to pump  154 . actuator  150  extends push pull rod  152  to partially extend airfoil  108  to the position shown in  FIG. 7B  which represents the point where lifting force  148  would approximately equal the additional weight of the retrofitted airfoil assembly. 
         [0057]    As the aircraft becomes airborne, the exact intermediate position of airfoil  108  beyond the position shown in  FIG. 7B  can be adjusted by computer to compensate for the weight of the airfoil assembly at various airspeeds. Spoiler  118  is mounted on the outboard portion of airfoil  108  so that it will function at any point of extension of airfoil  108  beyond the position shown in  FIG. 7B  in the same manner as described in the first embodiment. 
         [0058]    As aircraft  100  reaches cruise altitude and speed, the pilot can cause airfoil  108  to extend to the position shown in  FIG. 7C . Spoiler  118  can be deployed at any time during this transition if necessary. Before or during decent for landing, the pilot causes airfoil  108  to be retracted to the position shown in  FIG. 7B  when hydraulic pump  154  pumps fluid through retraction line  158  and fluid returns to pump  154  by means of extension line  156 . 
         [0059]    After landing, while taxiing to the gate, the pilot can fully retract airfoil  108  as shown in  FIG. 7A . 
         [0060]    In a third embodiment, airfoil  108  can be articulated from a position where chord line  142  is as shown in  FIG. 3A  to the position as shown in  FIG. 3D . 
         [0061]      FIGS. 5A , B, and  FIG. 8  show airfoil  108  mounted on fuselage  102  by means of a airfoil main spar  160 . Spar  160  and airfoil  108  together rotate along a lateral axis of aircraft  100 . Airfoil tilting actuator  162  is mounted on fuselage  102 . A floating piston (not shown) in tilting actuator  162 , is linked by a piston rod  164  to a spar arm  166  that is rigidly attached to spar  160 . 
         [0062]    During takeoff, climb and decent airfoil  108  is in the low lift configuration shown in  FIGS. 3A ,  5 A and  8 , and the angle of attack  144  between between the relative wind  140  and chord line  142  is minimal. As shown in  FIG. 5B and 8  during high speed cruise in smooth air, the pilot can cause tilting actuator  162  to retract piston rod  164  causing spar arm  166  and spar  160  to rotate airfoil  108  to the high lift position shown in  FIG. 3D. 5B  and  8 . Should unexpected turbulence make it necessary, spoiler  118  can be quickly extended at any time to eliminate the additional lift. Extending piston rod  164  will return airfoil  108  to the position shown in  FIG. 5A  for decent and landing. 
         [0063]    In a fifth embodiment, airfoil  108  is in a fixed high lift position as shown in  FIGS. 1C ,  3 D and  6 A,B. Spoiler  118  would be normally extended during takeoff, climb, decent, and landing as shown in  FIG. 6B  wherein airfoil  108  is in the low lift mode.. When conditions permit, a command from the flight deck is sent to controller  124 , Controller  124  sends a command to retract spoiler  118  by means of spoiler signal link  126  to spoiler actuator  130  causing spoiler  118  to retract as shown in  FIGS. 3D and 6A . When spoiler  118  is retracted, airfoil  108  is in the high lift mode. To return to the low lift mode, controller  124  sends a command to extend spoiler  118  by means of spoiler signal link  126  to spoiler actuator  130  causing spoiler  118  to extend as shown in  FIG. 6B . 
         [0064]    While the embodiments discussed above assume that the airfoils  108  mounted on either side of fuselage  102  are identical and at similar locations, the reader can see that they could be offset, of unequal size, or a single airfoil on one side only. For example, a single airfoil  108  could be mounted on the starboard side of aircraft  100  so as not to interfere with the main passenger door. When airfoil  108  exerts lift on the starboard side of aircraft  100 , the pilot or autopilot would compensate for this asymmetrical lift by adjusting ailerons  105 . 
         [0065]    Some airliners are equipped with a stabilator, rather than a horizontal stabilizer and elevator as shown in the embodiments. These aircraft might particularly benefit from these improvements since the stabilator would self align when less tail-down force is needed to minimize parasitic drag. 
         [0066]    Although the embodiments illustrate a specific condition, namely high speed cruise, it will be obvious to the reader that there may be other situations where some additional lift on an optional basis would be advantageous, for example during an aircraft&#39;s takeoff and climb. 
         [0067]    An adjustable CP would also allow a greater flexibility in the loading of cargo. Currently, for greater fuel efficiency, both airliners and air freighters try to load cargo so that the CG is as close to its aft limit as practicable. 
         [0068]    The several embodiments illustrate different ways to routinely increase and decrease the lifting force of forward airfoils to adjust the CP during flight; however, how far forward the CP can be safely moved for any aircraft depends on how rapidly the CP can be returned to its original rearward position at anytime. The use and deployment of spoilers provides a superior means of doing so. Spoilers have low mass so they can be deployed quickly to immediately convert laminar flow to turbulent flow, thereby “spoiling” the lift of the airfoils 
         [0069]    A spoiler system can be designed to be deployed automatically in the event of a control computer malfunction, unexpected turbulence, or any sudden maneuver by the pilot. As such, it represents a “Fail Safe” means of assuring an aerodynamically stable aircraft at all necessary times 
         [0070]    Some military aircraft are so unstable that they can only be flown by its human pilot with (redundant) computer assistance. While feasible, it is doubtful that the flying public would accept that condition in commercial airliners in the foreseeable future. 
         [0071]    Tail-down force represents dead weight that has to be compensated for by fuel burn. Having an adjustable Center of Pressure with a reliable and rapid means to restore it to its original rearward location, takes advantage of computer stabilized flight to minimize tail-down force when practicable, without compromising the safety of an aerodynamically stable aircraft capable of being flown by a pilot whenever necessary.