Abstract:
Testing apparatus, systems and methods are provided to obtain measurements pertaining to aircraft control surfaces mounted to stationary aircraft structures for displacements about a hinge axis. A support structure and an actuator carried by the support structure may be provided, the support structure including attachment assemblies for positionally fixing the testing apparatus to the stationary aircraft structure. The actuator carried by the support structure includes a rectilinearly movable actuator shaft which contacts the aircraft control surface when the support structure is positionally mounted to the stationary aircraft structure. Actuation of the actuator will thereby cause the actuator shaft to apply a load to the movable aircraft control surface to cause deflection thereof about the hinge axis.

Description:
FIELD 
       [0001]    The embodiments disclosed herein relate generally to testing apparatus, systems and methods for obtaining measurements pertaining to aircraft surfaces, especially measurements pertaining to the free play and backlash characteristics of aircraft control surfaces. 
       BACKGROUND 
       [0002]    The free play of an aircraft&#39;s control surfaces physically introduces decreased rigidity effects into the aeroelastic system. Such decreased rigidity effects attributable to such free play may in some cases be sufficiently large to cause limit cycle oscillations (LCO) in the surfaces that use surface rigidity to suppress flutter. The LCO can in turn reduce the aircraft fatigue life or, in certain extreme cases cause catastrophic failure. A free play test is therefore required to be conducted on an aircraft&#39;s control surfaces before an aircraft can be released for conducting a Flight Flutter Test (FFT) so that the free play is characterized and the aircraft safety is warranted. 
         [0003]    Once the free play of a control surface is determined, according to the MIL 8870C standard (incorporated by reference hereinto), other tests are necessary in order to monitor free play evolution during the aircraft service life. These other monitoring tests of free play are known as backlash tests which are performed by the manufacturer before aircraft delivery and by the operators during aircraft service life. 
         [0004]    In order In guarantee the aircraft safety, both the military and the FAA have published standards that define the amount of free play allowed on different aircraft control surfaces for the aircraft service life. In addition, these standards provide set points at intervals throughout the aircraft service life in which backlash must be tested. 
         [0005]    Free play of an aircraft control surface can be tested statically or dynamically. Dynamic free play testing involves the placement of accelerometers in or on control surfaces with the surfaces thereafter being vibrated by shakers or actuators so that the free play can be monitored by a computer system. However, this type of dynamic free play testing system is generally applied to control surfaces of larger aircraft and allows for the correlation of the vibration frequency and the free play of the control surfaces which is not possible to obtain with smaller and medium sized aircraft. One such conventional dynamic free play testing system is known from U.S. Pat. No. 7,933,691 issued on Apr. 26, 2011 (the entire content of which is expressly incorporated hereinto by reference). 
         [0006]    Because of the deficiency noted above with respect to dynamic testing, smaller and medium sized aircraft must have free play statically tested. Currently, however, static testing of the control surfaces is performed by applying a known load to the control surface and then measuring the corresponding deflection (linear measurement or angular displacement). In this regard, a typical static free play test is started a zero load and increased to some percentage of ultimate load. During testing, the moment or applied load is plotted versus displacement, i.e., to provide a L/D plot. For a control surface with no free play and a linear spring stiffness, the L/D plot is a straight line with the slope of the line being the measured spring stiffness. As free play is introduced into the system, a discontinuity in the curve occurs near the zero load range. For larger displacement values the slope increases and is more representative of the effective stiffness without the free play. As hysteresis is introduced into the system, the L/D plot forms a known type of curve. 
         [0007]    The conventional static free play test method is timely, expensive and not very accurate. Moreover, the static test setup is relatively complex since the loading device must be fixed physically to the control surface without damaging the aircraft. Loading is typically executed with lead baskets of known mass which may in turn require certain system accommodations during each loading step thereby resulting in a very time consuming (and thus costly) process. 
         [0008]    What has been needed therefore are improved systems and methods whereby static free play and backlash data may be obtained for control surfaces associated with small and medium sized aircraft. It is towards fulfilling such a need that the embodiments herein are directed. 
       SUMMARY 
       [0009]    In general, the embodiments disclosed herein are directed toward testing apparatus, systems and methods for obtaining measurements pertaining to aircraft control surfaces mounted to stationary aircraft structures for displacements about a hinge axis. According to some embodiments, the testing apparatus may include a support structure and an actuator carried by the support structure. The support structure includes attachment assemblies for positionally fixing the testing apparatus to the stationary aircraft structure. The actuator carried by the support structure includes a rectilinearly movable actuator shaft which contacts the aircraft control surface when the support structure is positionally mounted to the stationary aircraft structure. Actuation of the actuator will thereby cause the actuator shaft to apply a load to the movable aircraft control surface to cause deflection thereof about the hinge axis. 
         [0010]    A load cell may operatively be connected to the actuator shaft to sense applied loads to the aircraft control surface and output a load signal indicative thereof. A displacement transducer may also be operatively connectable to the aircraft control surface to output a deflection measurement signal indicative of the aircraft control surface. 
         [0011]    Each of the attachment assemblies includes an adjustable stem and an attachment suction cup attached to an end of the stem for placement against a surface of the aircraft structure. Additionally or alternatively, the actuator may include an actuator suction cup attached to a terminal end of the actuator shaft for placement against a region of the aircraft control surface. A swivel joint may attach each of the attachment and/or actuator suction cups. A vacuum line may be attached operatively to each of the attachment and actuator suction cups and in turn attached to a vacuum source for drawing a vacuum within each of the attachment and actuator suction cups. 
         [0012]    According to some embodiments, the displacement transducer may include a transducer support extending laterally of the transducer towards the aircraft structure for mounting the displacement transducer in an operative position relative to the aircraft control surface. At least one mounting foot may be provided with the transducer support for contacting the surface of the aircraft structure. 
         [0013]    Systems for determining free play of a movable aircraft control surface mounted to a stationary aircraft structure for displacements about a hinge axis will include a testing apparatus as briefly described above, and a control system operatively connected to the testing apparatus. The control system thus receives the load and deflection signals from the load cell and displacement transducer, respectively, to provide a load versus displacement diagram therefrom and thereby determine free play of the aircraft control surface. 
         [0014]    The free play of a movable aircraft control surface mounted to a stationary aircraft structure for displacements about a hinge axis may therefore be determined by positionally fixing the testing apparatus to a surface of the stationary aircraft structure such that the actuator shaft and the displacement transducer are in contact with respective regions of the movable aircraft control surface. The testing apparatus may be operatively connected to a control system to receive the bad and deflection measurement signals output by the bad cell and the displacement transducer, respectively. Operating the control system will thereby actuate the actuator and thus cause the actuator shaft to apply repetitive loads to the aircraft control surface. 
         [0015]    Simultaneously with the actuation of the actuator, the bad and displacement measurement data associated with the repetitive applied loads are collected from the bad and deflection measurement signals output by the bad cell and the displacement transducer. A bad versus displacement curve based on the collected bad and displacement data may be determined from such collected data. The free play of the aircraft control surface may thereby be determined from the load versus displacement curve. 
         [0016]    These and other aspects and advantages of the present invention will become more clear after careful consideration is given to the following detailed description of the preferred exemplary embodiments thereof. 
     
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
         [0017]    The disclosed embodiments of the present invention will be better and more completely understood by referring to the following detailed description of exemplary non-limiting illustrative embodiments in conjunction with the drawings of which: 
           [0018]      FIG. 1  is a schematic view of a system according to an embodiment disclosed herein for the static testing of free-play and backlash associated with an aircraft control surface; 
           [0019]      FIG. 2  is a schematic block flow chart diagram of an operational sequence that may be employed in the system depicted in  FIG. 1 ; and 
           [0020]      FIG. 3  is an exemplary Load-Deflection data plot that may be obtained with the system depicted in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Accompanying  FIG. 1  schematically depicts a testing system  10  for statically testing free play and backlash of an aircraft control surface ACS which is operatively associated with an aircraft airfoil structure AAS. Specifically, the aircraft control surface ACS is capable of controllable deflections about a hinge axis HA relative to the stationary aircraft airfoil structure AAS. In general, the testing system  10  according to the embodiment depicted schematically in  FIG. 1  includes an electromechanical testing assembly  10 - 1  physically and operatively attached to the aircraft control surface ACS and the aircraft airfoil structure AAS, and a control system  10 - 2  operatively connected to the testing assembly  10 - 1  to control the test parameters and collect the test data. 
         [0022]    The testing assembly  10 - 1  is provided with a support structure  12  which includes a plurality of attachment assemblies  14  to physically attach the support structure  12  to the aircraft airfoil structure AAS. Each attachment assembly is provided with an attachment suction cup  14   a  connected to an adjustable stem  14   b  by a swivel connector  14   c.  The adjustable stem  14   b  is in turn coupled to the support structure  12  to allow it to be reciprocally linearly adjusted to allow its associated attachment suction cup  14   a  to be moved towards or away from the aircraft airfoil structure AAS. The stem  14   b  may in some embodiments be threadably connected to the support structure  12  to allow such adjustable movements. The swivel connector  12   c  assists to ensure proper positioning of the attachment suction cup  14   a  onto the curved airfoil surface of the aircraft airfoil structure AAS. 
         [0023]    In such a manner therefore the attachment suction cups  14   a  associated with each of the stems  14   b  may be moved into direct physical contact in a slightly compressed state with the aircraft airfoil structure AAS so as to permit the support structure  12  to be mounted in a fixed spaced relationship thereabove. The attachment suction cups  14   a  are connected to a vacuum source  16  by vacuum lines  16   a  which operates to draw vacuum within the cups  14   a  to ensure that each is positionally fixed to the aircraft airfoil structure AAS and thereby provide positional stability to the support structure  12 . 
         [0024]    The support structure  12  supports an electrically operated actuator  18  having a rectilinearly movable actuator shaft  18   a  terminating with an actuator suction cup  18   b.  The actuator suction cup  18   b  is connected to the terminal end of the actuator shaft  18   a  by a swivel joint  18   c  in a manner similar to the attachment suction cups  14   a  and support stems  14   b  to allow a direct fixed connection between the suction cup  18   b  and the aircraft control surface ACS. The actuator suction cup  18   b  is likewise operatively connected to the vacuum source  16  by the vacuum line  16   a.  A load cell  20  is operatively associated with the actuator shaft  18   a  of the actuator  18  to sense the deflection forces during testing. 
         [0025]    A linear displacement transducer  22  is provided with a lateral transducer support structure  22   a  with mounting feet  22   b,    22   c  which allow for operatively positioning relative to the movable aircraft control surface ACS. In such a manner, the linear displacement transducer is fixed to the stationary aircraft airfoil structure AAS to allow the transducer  22  to be placed in operative contact with a portion of the movable aircraft control surface ACS. The extent of angular deflection of the movable aircraft control surface ACS relative to the stationary aircraft airfoil structure AAS during testing will therefore be sensed by the linear displacement transducer  22 . 
         [0026]    The control system  10 - 2  includes a conventional personal computer  24  having suitable non-volatile memory which may include data storage media, a data entry keyboard and a display. A data conditioner  26  is provided to collect the angular deflection data and the force data sensed by the load cell  20  and the linear displacement transducer  22  and transmitted thereto. The data conditioner  26  is operatively connected to the computer  24  so the conditioned data may be stored and/or further manipulated thereby. A servo-driver  28  operatively interconnects the transducer  18  and the computer  24 . 
         [0027]    Accompanying  FIG. 2  is a block diagram depicting an exemplary operational procedure for conducting a free play and backlash test using the system shown in  FIG. 1 . In this regard, it will be observed in block  100  that the test will initially be set up for the particular movable aircraft control surface ACS being tested and involves the initial positioning of the testing assembly  10 - 1  relative to the movable aircraft control surface ACS and the stationary aircraft airfoil structure AAS. Once the testing assembly  10 - 1  has been properly positioned, the vacuum system including the vacuum source  16  is operated in step  102  to thereby positionally fix the testing assembly  10 - 1  relative to both the movable aircraft control surface ACS and the stationary aircraft airfoil structure AAS. 
         [0028]    After setting up the test in step  100 , data from the load point arms of the hinge axis of the aircraft control surface ACS is input into the computer  24  in step  104 . The computer  24  comprises software stored in its non-volatile memory that manages the test and computes the free play. The computer  24  also allows the parameters (load and displacement) to be set to zero in step  106  before the start of the actual free play test. Following step  106 , the free play test may be started in step  108 . In this regard, the computer  24  executes a loading command via the servo-driver  28  and the data acquisition for three subsequent repetitions is obtained via the data conditioner  26 . The loading command thus causes the transducer  18  to operate so that compression and tension forces are sequentially exerted onto the movable aircraft control surface ACS by means of the actuator shaft  18   a  and the suction cup  18   b.  The resistance forces acting in response to these compression and tension forces are thus sensed by the transducer  20  and acquired simultaneously with the angular deflection data sensed by the displacement transducer  22 . Both the loading and the data acquisition are performed in a continuous manner over a specified cycle time which increases the test speed with no detrimental effects on the data quality. 
         [0029]    According to one embodiment, after the third repetitive loading and data acquisition cycle is completed, the computer  24  automatically stops the test and the data acquisition in step  110 . However, at any time during testing the loading and data acquisition cycles may be stopped in step  110   a  should there be a need. 
         [0030]    Data is saved from the test in step  112  and a load versus deflection (L/D) curve is obtained as depicted in accompanying  FIG. 3 . The L/D curve or parts of the L/D curve are then selected in step  114  by fitting a tangent line to each of the associated upper and lower curve parts associated with each of the tension and compression force cycles. Free play may then be computed by algorithms stored in the computer  24 , specifically by computing the difference of the derivatives of the upper (tensile loading—Free Play A) and lower (compression loading—Free Play B) loading curves as shown in  FIG. 3 . The free play for the tested aircraft control surface ACS is considered to be the greatest value obtained from the calculation and is thereby input as the free play test result in step  116 . 
         [0031]    Following the determination of the free play test result, the vacuum system, including the vacuum source  16 , may be turned off in step  118  and the testing assembly  10 - 1  removed from the aircraft airfoil structure AAS and the aircraft control surface ACS and reattached to other similar structures for testing. 
         [0032]    It will be understood that the description provided herein is presently considered to be the most practical and preferred embodiments of the invention. Thus, the invention is not to be limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope thereof.