Abstract:
Control surface assemblies have a torque tube base. In one embodiment, a method includes moving an aerospace vehicle through a medium; and moving at least a portion of a control surface assembly to generate a force for controlling the vehicle.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application is a continuation of copending U.S. Ser. No. 12/038,319 filed Feb. 27, 2008, which is a divisional of U.S. Ser. No. 11/043,918 entitled “Control Surface Assemblies with Torque Tube Base” filed on Jan. 21, 2005, now U.S. Pat. No. 7,410,120. 
     
    
     GOVERNMENT LICENSE RIGHTS 
       [0002]    This invention was made with Government support under U.S. Government contract F33615-98-9-2880 awarded by United States Air Force. The Government has certain rights in this invention. 
     
    
     FIELD 
       [0003]    This invention relates to structures for flight vehicles, and more specifically, to control surface assemblies having a torque tube base. 
       BACKGROUND 
       [0004]    Many types of aerospace vehicles include one or more control surfaces that project outwardly from a main body of the vehicle to enhance or to enable proper control of the vehicle. Typically, such control surfaces are designed to meet anticipated load requirements associated with control of the vehicle. Among the considerations involved in the design of such control surfaces is the stiffness of the control surface to avoid flutter. More specifically, to avoid flutter of a control surface (e.g. a control fin) it is typically necessary to increase the fundamental mode shape frequencies. 
         [0005]    For example,  FIGS. 1 and 2  show simplified cross-sectional views of control surface assemblies in accordance with the prior art. In  FIG. 1 , a control surface assembly  100  includes an outwardly-projecting control surface portion  102  coupled to a flat flange portion  104  that attaches to an aerospace vehicle  106  (e.g. a missile, an aircraft, etc.). Typically, the control surface assembly  100  is efficient in bending stiffness, but is relatively less efficient in providing torsional stiffness. In  FIG. 2 , a control surface assembly  200  includes a non-uniformly tapered outwardly-projecting control surface portion  202  coupled to a base portion  204  having a solid support member  205 . The base portion  204  is coupled to a fuselage (or body)  206 . The control surface assembly  200  is typically less efficient in bending stiffness than the control surface assembly  100  having the flat flange portion  104  however, the control surface assembly  200  may exhibit improved torsional stiffness over the control surface assembly  100  due to the stiffness of the solid support member  205 . 
         [0006]    Although desirable results have been achieved using the prior art control surface assemblies shown in  FIGS. 1 and 2 , there may be room for improvement. For example, for at least some applications, the prior art assemblies may exhibit undesirable weight and heat transfer characteristics. Therefore, improved control surface assemblies that at least partially mitigate these undesirable characteristics would have utility. 
       SUMMARY 
       [0007]    The present invention is directed to control surface assemblies having a torque tube base. Embodiments of the present invention may advantageously provide a desired degree of bending and torsional stiffness, with improved weight and heat transfer characteristics in comparison with the prior art. 
         [0008]    In one embodiment, a method includes moving an aerospace vehicle through a medium; and using a tubular arcuate base and a control surface projecting outwardly from the base as a control surface assembly to generate a force for controlling the vehicle. 
         [0009]    The features, functions, and advantages that have been discussed can be achieved independently in various embodiments of the present invention or may be combined in yet other embodiments further details of which can be seen with reference to the following description and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments of the present invention are described in detail below with reference to the following drawings. 
           [0011]      FIG. 1  is an end cross-sectional schematic view of a control surface assembly in accordance with the prior art; 
           [0012]      FIG. 2  is an end cross-sectional schematic view of another control surface assembly in accordance with the prior art; 
           [0013]      FIG. 3  is an end cross-sectional view of a control surface assembly in accordance with an embodiment of the present invention; 
           [0014]      FIG. 4  is an isometric view of the control surface assembly of  FIG. 3  coupled to a vehicle in accordance with another embodiment of the invention; 
           [0015]      FIG. 5  is an isometric view of the control surface assembly of  FIG. 3  in an inverted position; and 
           [0016]      FIG. 6  is an isometric view of an aircraft having a plurality of missiles in accordance with further embodiments of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    The present invention relates to control surface assemblies having a torque tube base. Many specific details of certain embodiments of the invention are set forth in the following description and in  FIGS. 1-6  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the present invention may have additional embodiments, or that the present invention may be practiced without several of the details described in the following description. 
         [0018]      FIG. 3  is an end cross-sectional view of a control surface assembly  300  in accordance with an embodiment of the present invention.  FIG. 4  is an isometric view of the control surface assembly  300  of  FIG. 3  coupled to a vehicle fuselage  306 . In this embodiment, the control surface assembly  300  includes an outwardly-projecting control surface portion  302  coupled to a hollow, shell-like base portion  304  having a thickness t. The outwardly-projecting control surface portion  302  may be tapered (uniformly or non-uniformly) as shown in  FIG. 3 , or alternately, may be of uniform thickness or width, or any other suitable combination thereof. 
         [0019]    In one embodiment, the base portion  304  includes a rounded (or arcuate) member  314  ( FIG. 3 ) that forms a substantially hollow (or tubular) section. In some embodiments, the rounded member  314  may have a semi-circular (or partially semi-circular) cross-sectional shape, and may be completely enclosed, as shown in  FIG. 3 , or alternately, it may be only partially closed. As best shown in  FIG. 4 , the rounded member  314  comprises an elongated main portion  308  having a pair of tapered end portions  310 . The base portion  304  further includes a plurality of attachment flanges  312  for coupling the base portion  304  to the aircraft  306 . The control surface portion  302  is coupled to the rounded member  314  and projects outwardly from the fuselage  306  by a height H. As further shown in  FIG. 3 , the base portion  304  has a width W. 
         [0020]      FIG. 5  is an isometric view of the control surface assembly  300  of  FIG. 3  in an inverted position. As shown in  FIG. 5 , the base portion  304  may further include a plurality of span members  318  that span between opposing lateral sides of the rounded member  314 , and which are formed between a plurality of gaps  320  having a gap width G. In this embodiment, the base portion  304  includes multiple attachment flanges  312  suitable for fixed aero-surface configurations such as strakes or fences. In alternate embodiments, the base portion  304  may include only a single attachment point, such as for rotating control surface configurations. 
         [0021]    In operation, the control surface assembly  300  provides increased fundamental mode shape frequencies to avoid flutter. Because the base portion  304  of the control surface assembly  300  is a hollow, shell-like structure, the base portion  304  advantageously provides suitable torsional stiffness characteristics by increasing the frequency of multiple mode shapes (e.g. plate bending and plate torsion) while also providing improved weight characteristics. In one particular aspect, the substantially-hollow main portion  308  may provide a highly efficient structure for meeting the desired torsional stiffness characteristics. In addition, the hollow base portion  304  may provide suitable bending stiffness. 
         [0022]    In some embodiments, the base portion  304  of the control surface assembly  300  may provide a substantial weight savings over comparable prior art assemblies. In one particular embodiment, for example, a 30% or higher weight savings may be achieved. Substantial weight savings may be achievable for both metal and composite control surface assemblies. Furthermore, for high temperature applications, the base portion torque tube feature between the attach points, allows a reduced amount of contact area required for attachment. This may advantageously reduce or minimize the amount of heat transfer from the control surface portion  302  into the fuselage  306  compared with prior art apparatus. 
         [0023]    For applications that require enhanced stiffness of control surface assemblies, prior art methods of adding bending stiffness included simply thickening the outwardly-projecting portion and the base portion. It has been determined, however, that there is a point of diminishing returns for blade thickening because the added mass offsets the increased blade/plate bending stiffness. Furthermore, in one particular embodiment, the hollowed base portion  304  of the control surface assembly  300  provides a lowest natural frequency of a plate bending mode of approximately 120 Hz, and approximately 150 Hz for a first plate torsion mode, as compared with a lowest natural frequency of 60 Hz for the plate bending mode and approximately 90 Hz for the first plate torsional mode for the flat flange  104  of the assembly  100  shown in  FIG. 1 . These data demonstrate that embodiments of the invention may simultaneously increase the frequency of multiple mode shapes. Furthermore, the control surface assembly  300  may be substantially lighter than the flat flange assembly  100  of the prior art. 
         [0024]    It will be appreciated that control surface assemblies in accordance with the present invention may be used on a variety of vehicles and systems, including but not limited to any suitable type of aerospace vehicles. For example,  FIG. 6  is an isometric view of an aircraft  1000  having a plurality of missiles  1050  in accordance with further embodiments of the present invention. The aircraft  1000  includes a variety of known components, including a fuselage  1002 , lift generating surfaces  1004  (e.g. wings), a propulsion system  1006 , a control system  1010 , and a host of other systems and subsystems that enable proper operation of the aircraft  1000 . The aircraft  1000  also includes a tail assembly  1020  having a pair of vertical fins  1022  and a pair of horizontal fins  1024  (only one visible). The fins  1022 ,  1024  may suitably be control surface assemblies in accordance with embodiments of the present invention. 
         [0025]    In addition, each of the missiles  1050  may include a variety of known components, including a fuselage  1052 , a plurality of control surfaces (or fins or strakes)  1054  coupled to the fuselage  1052 , a propulsion system  1056 , a control system  1062 , and other systems and subsystems that enable proper operation of the missile  1050 . Each of the control surfaces  1060  may suitably be control surface assemblies in accordance with embodiments of the present invention. 
         [0026]    In one embodiment, the aircraft  1000  may be a fighter aircraft, such as, for example, an F/A-18E Super Hornet manufactured by The Boeing Company of Chicago, Ill. However, it will be appreciated that embodiments of control surface assemblies in accordance with the present invention may be included in any other suitable aircraft. For example, in alternate embodiments, the aircraft may be a fighter aircraft, a rotary aircraft, a bomber aircraft, or any other suitable type of manned or unmanned aircraft, including those described, for example, in The Illustrated Encyclopedia of Military Aircraft by Enzo Angelucci, published by Book Sales Publishers, September 2001, and in Jane&#39;s All the World&#39;s Aircraft published by Jane&#39;s Information Group of Coulsdon, Surrey, United Kingdom, which texts are incorporated herein by reference. Similarly, the missiles  1050  may be any suitable type of missiles that include a movable or non-movable control surface assemblies, including but not limited to Harpoons, HARMs, Sparrows, AM RAAMs, or any other suitable missiles, including those described in the above-referenced texts.