Patent Publication Number: US-9429401-B2

Title: Passive stability system for a vehicle moving through a fluid

Description:
FIELD OF THE INVENTION 
     The invention is in the field of stability systems for vehicles moving through a fluid, such as air vehicles moving through air, or submersibles moving through water. 
     DESCRIPTION OF THE RELATED ART 
     Aerodynamic stabilization of flight vehicles is required to prevent loss of control or degraded performance. Stabilization is traditionally performed aerodynamically with fixed, large stabilizing aerodynamic surfaces located aft of the vehicle center of gravity. Active stabilization is achieved with high bandwidth inertial measurement units (IMUS) and control actuation systems. Such systems add to vehicle size, weight, and cost, and require power to be operational. 
     SUMMARY OF THE INVENTION 
     A passive stability system affects the stability of a vehicle, such as an air vehicle or a vehicle submersed in a liquid, without the need for power or active control. The stability system uses deflection of drive surfaces, which have a tendency to align with the fluid stream perceived by the vehicle, to position control surfaces, which provide a stabilizing moment on the vehicle. The drive surfaces and the control surfaces are operatively coupled together by one or more linkages, such that torque produced by lift forces on the drive surfaces are used to position the control surfaces. 
     According to an aspect of the invention, a stability system for a vehicle moving through a fluid includes: a drive surface pivotable relative to a fuselage of the vehicle; and a control surface pivotable relative to the fuselage. The drive surface passively pivots relative to the fuselage in response to changes in fluid flow external to and relative to the vehicle. The drive surface is mechanically coupled to the control surface by the mechanical linkage, such that pivoting of the drive surface relative to the fuselage causes pivoting of the control surface relative to the fuselage 
     According to another aspect of the invention, a vehicle includes: a fuselage; a drive surface pivotable relative to the fuselage; and a control surface pivotable relative to the fuselage. The drive surface passively pivots relative to the fuselage in response to changes fluid flow external to and relative to the vehicle. The drive surface is mechanically coupled to the control surface such that pivoting of the drive surface relative to the fuselage causes pivoting of the control surface relative to the fuselage. 
     According to yet another aspect of the invention, a method of passively stabilizing a vehicle includes the steps of: passively aligning a drive surface of the vehicle toward an external fluid flow relative to the vehicle, by pivoting the drive surface relative to a fuselage of the vehicle; and passively positioning a control surface that is operatively coupled to the control surface by a linkage, using fluid forces on the drive surface, acting through the linkage, for pivoting the control surface. The positioning control surface provides stability to the vehicle. 
     According to still another aspect of the invention, a method of passively stabilizing a vehicle includes the steps of: passively aligning drive surfaces of the vehicle toward an external fluid flow relative to the vehicle, by pivoting the drive surfaces relative to a fuselage of the vehicle; and passively positioning control surfaces that are operatively coupled to the control surfaces by linkages, using fluid forces on the drive surfaces, acting through the linkages, pivot the control surfaces. The positioning control surfaces provides stability to the vehicle. 
     To the accomplishment of the foregoing and related ends, the invention comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The annexed drawings, which are not necessarily to scale, show various aspects of the invention. 
         FIG. 1  is a side view of a vehicle according to an embodiment of the invention. 
         FIG. 2  is an first oblique view of a stabilizer of the vehicle of  FIG. 1 . 
         FIG. 3  is another oblique view of the stabilizer of  FIG. 2 . 
         FIG. 4  is a side view of a vehicle according to another embodiment of the invention. 
         FIG. 5  is an first oblique view of a stabilizer of the vehicle of  FIG. 4 . 
         FIG. 6  is another oblique view of the stabilizer of  FIG. 5 . 
         FIG. 7  is a side view of a vehicle of yet another embodiment of the invention. 
         FIG. 8  is a side view showing details of forward stabilizers of the vehicle of  FIG. 7 . 
         FIG. 9  is a side view showing details of aft stabilizers of the vehicle of  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION 
     A stability system for a vehicle moving through a fluid includes stabilizers each having a drive surface that follows the position of the fluid stream perceived by the vehicle. The movement of the drive surface positions control surfaces of the stabilizers, which are coupled to the drive surfaces by mechanical linkages. Lift forces on the drive surfaces provide the force that is used in positioning the control surfaces. The deflection of the control surfaces provides a force on the vehicle that affects stability of the vehicle, for instance in making an inherently unstable vehicle more stable. The stability system may work completely passively, without any active control, and without the need for power to operate it. 
     Referring initially to  FIG. 1 , a vehicle  10  that moves through a fluid, such as an air vehicle or an underwater vehicle, has a fuselage or other structure  12 , and a pair of stabilizers  14  and  16  that are mechanically coupled to the fuselage  12  as part of a stability system  20 . The vehicle  10  may be inherently unstable, with a center of pressure  22  of the vehicle  10  forward of a center of gravity  24  of the vehicle  10 . The stabilizers  14  and  16  act to provide stability to the vehicle  10 , passively providing stabilizing force to the vehicle  10  in response to changes in angle of attack of the vehicle  10 . 
     The stabilizer  14  includes a drive surface  32  and a control surface  34 . The stabilizer  16  includes a drive surface  36  and a control surface  38 . As explained further below, the drive surface  32  is mechanically coupled to the control surface  34 , and the drive surface  36  is mechanically coupled to the control surface  38 . The drive surfaces  32  and  34  are configured to passively stay pointed in substantial alignment with the direction of free stream fluid flow relative to the vehicle  10 . Thus the drive surfaces  32  and  36  change position as the angle of attack of the vehicle  10  changes. The drive surfaces  32  and  36  are mechanically coupled to the control surfaces  34  and  38 , respectively. The coupling is such that the rotation or pivoting of the drive surfaces  32  and  36  in response to a change of vehicle angle of attack is used as a driving force to position the control surfaces  34  and  38  to produce a stabilizing moment on the vehicle  10 . The stabilization may be completely passive, without any input from a pilot, without any action from an active control system, and without any sort of power input, relying simply on lift forces (aerodynamic forces in the case of an air vehicle). 
     With reference now in addition to  FIGS. 2 and 3 , details of the stabilizer  14  are described. The stabilizer  16 , on an opposite side of the fuselage  12 , may have a similar configuration and mode of operation. The mechanical connection between the drive surface  32  and the control surface  34  is a mechanical linkage  50 . Lift forces on the drive surface  32  operate to maintain the drive surface  32  closely oriented with the direction of perceived external fluid motion  51  relative to the vehicle  10 . As the vehicle  10  changes its angle of attack, a lift force is produced on the top or bottom surface of the drive surface  32  at a drive surface center of pressure  52 . The drive surface center of pressure  52  is at a distance  54  from a drive surface axis or pivot point  56  about which the drive surface  32  can rotate relative to the fuselage  12 . Thus any lift force produces a moment on the drive surface  32  that rotates the drive surface  32  back toward with the direction of perceived fluid motion  51  relative to the drive surface  32 . That moment is used as the driving force, transmitted through the linkage  50 , to also pivot or rotate the control surface  34  to produce a stabilizing force on the vehicle  10 . 
     To that end, the drive surface  32  is connected to a bell crank  62  of the linkage  50 . Rotation or pivoting of the drive surface  32  about the drive surface axis  56  rotates the bell crank  62  as well. The drive surface  32  is attached to a center part of the bell crank  62 . An end of a connecting rod  66  is connected to one end of the bell crank  62 . The other end of the connecting rod  66  is mounted on a crank pin of a crank  68 . The control surface  34  rotates about the crankshaft of the crank  68 , the rotation being about a control surface axis or pivot point  70 . The crank  68  is rotated to turn the control surface  34 , even against the moment on the control surface  34 . This moment on the control surface  34  is provided by a lift force acting at a control surface center of pressure  72 , at a distance  74  away from the control surface rotation axis  70 . The distance  74  may be less than the corresponding distance  54  of the drive surface  32 . This allows the drive surface  32  to provide a sufficient torque to dictate the position of the control surface  34 . Even though the control surface  34  may have a greater surface area than the drive surface  32 , the difference in the distances  54  and  74  may be such that for a given deflection angle of the surfaces  32  and  34 , the moment provided by the lift forces for rotation of the drive surface  32  is greater than the moment from the control surface  34  opposing the rotation. The drive surface  32  thus acts as the driver to position the control surface  34 , with the moment from a small deviation of the drive surface  32  from the relative fluid motion direction  51  used to produce a larger deviation of the control surface. The ratio of torque delivered by the drive surface  32  to the torque required to deflect the control surface  34  may vary based on the requirements of a given system. This ratio may be tailored over a large range, for example from 0.1 to 10.0, which gives the significant latitude in optimizing a system to meet any of a variety of different performance characteristics. A non-limiting range of the ratio of drive fin torque to control fin torque is from 2 to 5. A non-limiting range of ratio of drive surface to control surface size (area) is 0.2 to 0.4. 
     A damper  80  may be coupled to the other end of the bell crank  62 , to damp motion of the linkage  50  in response to changes in angle of attack, or other events changing the perceived flow direction  51 . The damper  80  is also coupled at its opposite end to a pin  84  that is fixed to the fuselage  12 . The damper  80  may be any of a variety of inertia damping devices, for example devices filled with a viscous fluid or a ferrofluid to provide resistance to and dampening of motion. The damper  80  may be used to prevent oscillations in the movement of the surfaces  32  and  34 , and the characteristics of the damper  80  may be selected to achieve desired characteristics in the operation of the linkage  50 . 
     Similarly, other parts of the linkage  50  may be selected and configured to achieve desired operating conditions. The parts of the linkage  50 , and the surfaces  32  and  34  themselves, may be configured to make the movement between the surfaces  32  and  34  proportional at any desired proportion, for example producing an angular deflection (or rotation or pivoting) of the control surface  34  that is greater in magnitude than the angular deflection of the drive surface  32  that drives movement of the control surface  34 . To give one example, the surfaces  32  and  34  and the linkage  50  may be configured so that a deflection of the drive surface  32  produces twice that deflection in the control surface  34 . More broadly, the surfaces  32  and  34  and the linkage  50  may be configured so that a deflection of the drive surface  32  produces at least 1.1 times the deflection in the control surface  34 . The configuring may include suitable selection of any of a variety of features of the linkage  50  and the surfaces  32  and  34 , including (for example) combinations of areas of the surfaces  32  and  34 , the distances  54  and  74 , the dimensions and layouts of the bell crank  62  and/or the crank  68 , and/or the placement of the various parts relative to one another. 
     The linkage  50  in the illustrated embodiment is only one example of many possible suitable mechanical linkages (mechanical connections). Alternatives may include a wide variety of suitable elements, including for example rods, cranks, chains, gears, cables, pulleys, sliders, cams, springs, dampers, elastics, plastics, magnets, hydraulics, pneumatics, electromagnetic and/or hinges. It is also possible for there to be a mechanical connection between different stabilizers, for example with a single drive surface able to control multiple control surfaces, or with elements of different stabilizers linked in other suitable ways. The term “mechanical linkage” is used herein broadly to refer to passive (not actively driven by a powered system or by volitional control) linking together of movement of the drive surface and the control surface, without regard to the actual type of mechanism accomplishing the linkage. 
     In the illustrated embodiment stabilizer  14  has a triangular shape, with the drive surface  32  adjacent to the control surface  34  when the surfaces  32  and  34  are not deflected from their neutral central positions. The surfaces  32  and  34  alternatively may have any of a variety of other suitable shapes. In addition the surfaces  32  and  34  need not be adjacent to one another, and may be placed at longitudinal locations along the fuselage that are well separated. However, the illustrated configuration has the advantage of reducing drag when the surfaces  32  and  34  are coplanar, in their neutral central (undeflected) positions. 
       FIGS. 2 and 3  show the stabilizer  14  in operation. The drive surface  32  has pitched downward in response to a change in fluid flow perceived by the vehicle  10  (the apparent fluid flow relative to the vehicle  10 ), for example by a downward pitch of the nose of the vehicle  10 . The drive surface  32  passively moves toward alignment with the direction  51  of fluid flow perceived by the vehicle  10 , due to the drive surface axis  56  being so far forward on the drive surface  32 . The drive surface  32  therefore may move to a location where it receives a minimal lift force, pitching up in the illustrated operation. The rotation or pivoting of the drive surface  32  about the drive surface axis  56  causes a larger deflection of the control surface  34 , due to the mechanical action of the linkage  50 . Thus the control surface  34  deflects less than the amount necessary to align itself with the perceived fluid flow direction  51 . This results in the control surface  34  receiving an upward lift force, in the situation shown in  FIGS. 2 and 3 . Since the control surface  34  is forward of the center of gravity  24  ( FIG. 1 ), this upward force on the vehicle  10  acts to pitch the nose of the vehicle  10  up, counteracting the downward pitching of the vehicle nose that initiated the chain of events. The action of the stabilizer  14  therefore tends to increase the stability of vehicle  10 . If properly configured, with the control surface  34  having sufficient surface area, and deflecting far enough in response to deflections by the drive surface  32 , an inherently-unstable vehicle can be transformed by use of the stabilizers  14  and  16  into a stable vehicle in which changes in pitch are automatically reduced without any need for active control. The operation of the stabilizer  14  is fully passive, without any active control required, and without any external power applied. The stabilizing affect is fully a function of the configuration of the surfaces  32  and  34 , and the linkage  50  that allows the drive surface deflections to be multiplied to larger (perhaps proportionally larger) control surface deflections, which aids in stabilizing the vehicle  10 . 
     The surfaces  32  and  34  may have shapes with top and bottom symmetry, for example having substantially flat top and bottom surfaces. Alternatively, the surfaces  32  and  34  may have other suitable cross-sectional shapes to take advantage of different fluid dynamic properties from highly viscous mediums to incompressible, supersonic and hypersonic flight regimes. A bias torque can be designed into the drive or control fin (camber for example) to induce a force at zero perceived fluid motion  51   
     The stabilizers  14  and  16 , and their parts, may be made of any of a variety of suitable materials. Non-limiting examples include steel, aluminum, titanium, and composite materials. 
     In the illustrated embodiment the stability system  20  has two stabilizers  14  and  16 , on opposite sides of the fuselage  12 . More stabilizers may be added if desired, for example to have four stabilizers spaced around the fuselage  12 , with two pairs of stabilizers providing stabilization in two perpendicular directions. 
     The fuselage  12  is shown as having a circular cross section. As an alternative the fuselage  12  may have any of a wide variety of other suitable shapes and/or configurations. 
     As noted above, the vehicle  10  may be any of a variety of vehicles that move in a fluid. The vehicle  10  may be an air vehicle, such as a missile, an airplane, or an unmanned aerial vehicle (UAV), to give a few broad examples. Alternatively the vehicle  10  may be a water vehicle, such as a submersible. 
     In one example, the vehicle  10  is a missile that is launched from an aircraft. It is desirable from a safety standpoint that the missile control system and any sort of active controller (like a computer) not be powered up during the launching. The stability system  20  does not require any sort of power or active control to achieve an increase in stability. 
     The vehicle  10  may have additional features not shown in the illustrated embodiment, for performing other functions. For example it may have control surfaces for steering, lift-producing surfaces such as wings for producing lift, fixed or movable fins, rudders, and/or canards for course stabilization, and/or a propulsion system, such as a rocket motor, jet engine, or propeller. Additional control surfaces can be in place before flight and/or can be deployable during flight. Further, the stabilizers  14  and  16  may be disconnected, such as being separated from the linkage, and/or repurposed for other functions during flight, if desired. 
     The stability system  20  is described above as a way to passively increase stability of the vehicle. As an alternative, the stabilizers  14  and  16  may be configured to passively decrease stability, such as by moving the control surfaces in opposite directions from the drive surfaces  32  and  36 . Decreasing stability may have benefits, such as improving maneuverability of a vehicle. Terms such as “stabilizer” and “stability system” are used herein broadly to indicate change in stability, whether that change is an increase in stability or a decrease in stability. 
       FIGS. 4-6  show an alternate embodiment, a vehicle  110  that has stabilizers  114  and  116 , parts of a stability system  120 . The stabilizers  114  and  116  are coupled to a fuselage  112  aft of a center of gravity  124  of the vehicle  110 , which in turn is aft of a center of pressure  122  of the vehicle  110 . The stabilizers  114  and  116  act to provide additional stability to the vehicle  10 , passively providing stabilizing force to the vehicle  110  in response to changes in angle of attack of the vehicle  110 , or in response to other changes in perceived external fluid flow direction (flow relative to the vehicle  110 ). 
     Many aspects of the stabilizers  114  and  116  are similar to those of the stabilizers  14  and  16  ( FIG. 1 ), and discussion of some similar features will be omitted below. However, since the stabilizers  114  and  116  are aft of the center of gravity  124 , control surfaces  134  and  138  of the stabilizers  114  and  116  must pivot (rotate) in the opposite direction from drive surfaces  132  and  136  of the stabilizers  114  and  116 . This is unlike the stabilizers  14  and  16 , for which the drive surfaces  32  and  36  ( FIG. 1 ) caused the control surfaces  34  and  38  ( FIG. 1 ) to rotate in the same direction as the drive surfaces  32  and  36  (but at a greater magnitude). 
     This difference in rotation may be accomplished by differently configuring a mechanical linkage  150  for linking the surfaces  132  and  134 . A similar mechanical linkage (not shown) links together the surfaces  136  and  138 . With reference to  FIGS. 5 and 6 , the parts of the linkage  150  (a bell crank  162 , a connecting rod  164 , a crank  166 , and a damper  180 ) may all be similar to corresponding parts of the link  50  ( FIG. 2 ). The difference in rotation may be accomplished by changing the orientation of the crank  166  when connecting the rod  164 , relative to how the crank  66  ( FIG. 2 ) is connected to the rod  64  ( FIG. 2 ). This change makes the control surface  134  rotate in the opposite sense from the rotation of the drive surface  132 . 
       FIGS. 5 and 6  illustrate operation of the stabilizer  114 . The nose of the vehicle  110  has pitched up, with the drive surface  132  pitching down in response, to move toward alignment with a direction  151  of the fluid flow relative to the vehicle  110 . The movement of the drive surface  132  is transmitted through the linkage  150  to cause the control surface  134  to pitch upward. Again, as with the stabilizer  14  ( FIG. 2 ), the magnitude of the deflection of the control surface  134  may be greater than the deflection of the drive surface  132 . The lift on the vehicle  110  from the deflection of the control surface  134  produces a nose-down pitch, tending to stabilize the vehicle  110  with regard to pitch. 
     The various variations discussed above for the vehicle  10  are applicable to the vehicle  110  as well. As a further alternative, a vehicle may have stabilizers both forward of and aft of its center of gravity. An example of this further alternative is the vehicle  210  shown in  FIGS. 7-9 . The vehicle  210  has four stabilizers  214  along a fuselage  212  forward of a vehicle center of gravity  224 , and four stabilizers  216  aft of the center of gravity  224 . The forward stabilizers  214  have respective drive surfaces  232  and control surfaces  234  that rotate in the same direction, as shown in  FIG. 8  and in a manner similar to that described above with regard to the stabilizer  14  ( FIGS. 1-3 ) of the vehicle  10  ( FIG. 1 ). The aft stabilizers  216  have respective drive surfaces  236  and control surfaces  238  that rotate in opposite directions, as shown in  FIG. 9  and in a manner similar to that described above with regard to the stabilizer  114  ( FIGS. 4-6 ) of the vehicle  110  ( FIG. 4 ). Other details of the vehicle  210  may be similar to those described above with regard to the vehicles  10  and  110 . 
     The vehicles  10 ,  110 , and  210  provide advantages in the ability to passively affect vehicle stability through simple mechanical linkages, without any volitional action or active control, and without requiring any power source. Such a stability system, using fluid forces for its driving power, provides stability control in situations where it would be undesirable to use active or powered stability control. 
     Although the invention has been shown and described with respect to a certain preferred embodiment or embodiments, it is obvious that equivalent alterations and modifications will occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein illustrated exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several illustrated embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.