Abstract:
A system and method for adjusting the orientation of trim tabs on a helicopter rotor blade includes a gage, a bender and a calibrator plate. The gage is secured to the calibrator plate which holds the gage in an orientation that simulates a rotor blade with trim tabs at zero degrees so that the gage can be zeroed. The gage is then removed and positioned on a rotor blade. Because the gage is supported on the blade by rollers, it is free to roll along the length of the blade and may thereby be positioned and repositioned quickly. Once in position, the bender is applied to the trim tabs adjacent to the gage and tightened using thumb screws. The handle of the bender allows the trim tabs to be adjusted while verifying that the amount of adjustment indicated by the gage dial indicator matches the preselected angle.

Description:
FIELD OF THE INVENTION 
     The present invention relates to maintenance of helicopters in general and to adjusting trim tabs of helicopter rotor blades in particular. 
     BACKGROUND OF THE INVENTION 
     Helicopter rotor blades vary in thickness from leading edge to trailing edge. Their trailing edges are tapered to be very thin compared to the balance of the blade, defining what are called “trim tabs.” Trim tabs are designed to be bent slightly up or down to reduce low frequency vibrations that would otherwise occur when the rotor blades are rotating. Adjusting the degree of bend in the trim tabs is part of routine helicopter maintenance. Instruments in the helicopter provide information about which rotor blades and which parts of each blade need to be adjusted and the amount of adjustment needed. 
     There are few devices available to adjust trim tabs, such as those described in U.S. Pat. No. 5,111,676 issued to Ruzicka Jr. et al, and U.S. Pat. No. 2,422,042 issued to Roberts. The device used most often requires considerable time to set up and use. Therefore, there remains a need for an improved system for adjusting trim tabs of helicopter rotor blades. 
     SUMMARY OF THE INVENTION 
     According to its major aspects and briefly recited, the present invention is a system and method for adjusting helicopter rotor blade trim tabs. The system permits accurate bending of the tabs. 
     In particular, the system includes the following major components: a gage with a folding arm, a bender, and a gage calibration plate. The gage arm is folded and then clamped to the gage calibration plate for calibration. The gage calibration plate is formed to simulate a rotor blade with trim tabs oriented at zero degrees, so that the gage, when clamped in place to it, can be zeroed. Once calibrated, the gage is removed from the plate, unfolded, and then placed on the rotor blade. Unlike prior art trim tab bending systems, the present gage is designed to roll freely along the length of the blade so that the operator can easily position it where it is needed. Once the gage is in position, the bender is applied to the trim tabs at that particular location. The gage will indicate to the operator the precise angle at which the tabs are bent. By grasping the bender handle, the operator can bend the trim tabs up or down while observing the degree of bend on the gage. When the trim tabs have been adjusted to the desired angle, the bender is removed and the gage rolled to a different position on the rotor blade for adjustment at the new position. 
     An important feature of the present invention is the capability of the gage to roll freely along the length of the rotor blade. This feature has the corresponding advantage of allowing the user to position and reposition the gage quickly and easily at any position along the rotor blade. 
     Another important feature of the present invention is the method of calibration of the gage. This method is simple enough to do prior to adjustment of each blade. Simply by placing the folded gage on the gage calibration plate, locking the gage in place, dropping the depth rod to the plate, and then rotating the gage dial to zero it, the gage is calibrated. 
     Still another feature of the present invention is the use of a gage that measures bend to ½ of a degree. This allows very accurate adjustments. 
     Related to this feature is the use of manual bending. With a little experience and keeping an eye on the gage indicator, an operator can quickly develop the skill to accurately adjust the trim tabs using a simple bender. 
    
    
     These and other features and their advantages will become readily apparent to those skilled in helicopter maintenance techniques and equipment from a careful reading of the Detailed Description of Preferred Embodiments, accompanied by the following drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, 
     FIG. 1 is a perspective view of the a helicopter rotor blade trim tab adjustment device undergoing calibration, according to a preferred embodiment of the present invention; 
     FIG. 2 is a front view of the dial indicator of the trim tab adjustment device shown in FIG. 1; 
     FIG. 3 is a perspective view of the trim tab adjustment device in place on a rotor blade, according to a preferred embodiment of the present invention; 
     FIG. 4 is a front view of a dial indicator of the adjustment device as shown in FIG. 3; and 
     FIG. 5 is a side view of the trim tab adjustment device in place on a rotor blade, according to a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention is a system and method for adjusting the trim tabs of helicopter rotor blades. The system includes a gage  10 , a bender  12  and a gage calibration plate  14  that, together, are used to calibrate gage  10  and then apply it and bender  12  to a rotor blade  16  for accurate bending trim tabs  18  on the trailing edge  20  of blade  16 . The method is for using the system for calibrating and bending operations. Although the present system and method is applied to a helicopter rotor blade, the rotor blade is not part of the present invention; it is the work piece on which the system operates. 
     Trim tabs are a feature of the rotor blade (and thus not the present invention) beginning when the trailing edge has tapered to a uniformly thin band running along the trailing edge of the rotor blade. 
     Referring now to the figures, the present invention includes gage  10  with a folding arm  30 . Gage  10  includes an indicator dial  32  housed within a protective indicator guard  34  that is preferably fluted to fit comfortably the hand of a user. Indicator dial  32  is secured in an indicator adjustment block  38  that is in turn main tool plate  44 . Indicator rod  46  depends from indicator dial  32 . The relative vertical position of the end of indicator rod  46  determines the angle indicated on indicator dial  32 . 
     This is an important feature. Indicator dial  32  is calibrated in degrees but actually measures distance from indicator dial  32  to the top surface  50  of trim tabs  18 . This is possible because the present system is engineered for the particular type of helicopter rotor blade  16  with which it will be used. A modest amount of engineering can be used to adjust indicator dial  32 , gage  10  and bender  12  for other types of helicopter rotor blades. Importantly, however, the user, who needs to adjust trim tabs  18  by a known angle, can read that angle directly from indicator dial  32  and does not need to convert distance to angles. 
     Main tool plate  44  is supported by the upper surface of rotor blade  16  using a remote wheel support arm  54  that carries a roller  58 . Roller  58  is adapted to engage top surface  50  of rotor blade  16  and roll freely when gage  10  is moved along the major dimension of rotor blade  16  (running from rotor hub to blade tip). Main tool plate  44  has a second end  60 , opposing first end  40  to which indicator dial  32  is attached, that also carries a roller  64  for engaging rotor blade  16 , when gage  10  is applied to the rotor blade  16 . 
     First end  40  of main tool plate  44  also has two guide pins  66  depending from indicator guard  34 . Guide pins  66  extend below trim tabs  18  of rotor blade  16  on either side of indicator rod  46  when gage  10  is placed on rotor blade  16 . Indicator rod  46 , between them, rests on trailing edge  20  of trim tabs  18  when guide pins  66  are pushed against trailing edge  20 . 
     Hingedly attached to main tool plate  44  is an extension arm  70  having a first end  72  that carries a hinge  76  and opposing second end  78  that carries a leading edge roller support  82  with two rollers  86 ,  88  mounted so as to a engage leading edge  90  of rotor blade  16 . One of these rollers  86  is mounted in a cutout portion  94  of leading edge roller support  82  so that both can be in direct engagement with the highly radiused leading edge  90 . Specifically, leading edge  90  has a small radius of curvature. It is important that these rollers engage the surface of rotor blade  16  directly and from different parts of leading edge  90  including a part of leading edge  90  just around the forwardmost edge  98 . Hinge  76  on first end  72  of extension arm  70  is pivotally connected to main tool plate  44  and rigidly connected to first end  72  of extension arm  70 . Hinge  76  straddles roller  64 . 
     Leading edge roller support  82 , guide pins  66  and hinge  76  cooperate to allow a user to position gage  10  on rotor blade  16 . When extension arm  70  is placed on rotor blade  16 , leading edge roller support  82  wraps around leading edge  90  so that rollers  86 ,  88  engage it on either side of forwardmost edge  98 . Then main tool plate  44  is pivoted down onto rotor blade  16  so that guide pins  66  swing into engagement with trailing edge  20  and trim tabs  18 . Gage  10  is supported entirely by five rollers  58  (two rollers),  64 ,  86 ,  88 , made of materials such as TEFLON so as not to mar the surface of rotor blade  16 . 
     Finally an elongated hole  100  is formed in extension arm  70  so that, when gage  10  is folded, indicator rod  46  can pass through hole  100 . This is the configuration required to calibrate indicator dial  32 . Extension arm  70  is pivoted under main tool plate  44 , with indicator rod  46  passing through hole  100 , and then gage  10  is placed on gage calibration plate  14 . Note also that remote wheel support arm  54  has a notch  106  formed therein dimensioned to accommodate extension arm  70  when gage  10  is folded. 
     Gage calibration plate  14  has a rear wall  110  with a clamp  112 . Remote wheel support arm  54  of main tool plate  44  of gage  10  is placed against rear wall  110  of gage calibration plate  14  and clamp  112  is applied to second end  60  of main tool plate  44  to hold gage  10  in position on gage calibration plate  14 . Indicator rod  46  is lowered to engage the top surface  116  of gage calibration plate  14 . The arrow  118  on indicator dial  32  will then indicate a value that maybe other than zero. Preferably, dial ranges from −7.0 degrees to +7.0 degrees. The dial  122  of indicator dial  32  may be rotated so that the zero indication corresponds with the position of the arrow  118  to “zero” indicator dial  122 . Gage  10  is thus calibrated. 
     When gage  10  is applied to a rotor blade  16 , and indicator rod  46  is lowered to the tip of trim tabs  18  at a location along rotor blade  16 , the position of the arrow  118  on indicator dial  32  will then indicate the angle of trim tab  16  at that location with respect to the horizontal. Clearly, for indicator dial  32  to be calibrated as thus described, gage calibration plate must be formed to simulate a rotor blade with trim tabs oriented at zero degrees, so the height of rear wall  10  of gage calibration plate  14  must be related to the thickness of the particular type of rotor blade  16  with which gage  10  will be used; i.e, rear wall  110  must hold second end  60  of main tool plate  44  at the same height it would be held when gage  10  is mounted to a rotor blade of the type for which gage  10  is engineered. Also, modest re-engineering would be required to change the height of rear wall  110  for use in calibrating a rotor blade  16  with a different leading edge-to-trailing edge profile. 
     Note that gage  10  does not have to be folded to be calibrated; it is only convenient to do so and allows indicator dial  32  to be held at a slightly upward angle for viewing rather than a downward angle if not folded. 
     To bend trim tabs  18 , bender is applied at the point where gage  10  is positioned. Bender has a broad set of jaws  126  and a narrow, thin handle  128 . Jaws  126  assure an even bend along trailing edge  20  of rotor blade  16 . Handle  128  provides convenient leverage for adjusting the metal trim tabs  18 . 
     Jaws  126  have notches  130 ,  132  formed to receive guide pins  66  and indicator rod  46 , respectively because jaws  126  are wide enough to grip the full width of trim tabs  16  (width in this case is measured from the trailing edge toward the leading edge as far as the trim tabs extend). 
     Jaws  126  are held in closely spaced relation by jam lock nuts  136  and thumb screws  138  so that jaws  126  will separate only wide enough to receive trim tabs  16 . Also, one jaw  126  or the other or both have a flange  140  at the rearward extreme end to serve as a stop for trailing edge  20  in order to prevent application of clamp too far onto rotor blade  16 . 
     In use, gage  10  is folded so that extension arm  70  is brought under and against main tool plate  44 . Gage  10  is then placed on gage calibration plate  14  and secured thereto by clamp  112 . Indicator rod  46  is lowered onto the top surface  116  of gage calibration plate  14 . If the arrow  120  on dial  122  of indicator dial  32  is not pointing to a zero indication, dial  122  is rotated to align the zero with arrow  120 . 
     Clamp  112  is then opened to release gage  10 , and gage  10  is unfolded. Gage calibration plate  14  is set aside and gage  10  is then applied to a rotor blade  16  having trim tabs  18  that require adjustment. Extension arm  70  of gage  10  is extended (unfolded) and applied to leading edge  90  of rotor blade  16  so that its two rollers  86 ,  88  are engaging leading edge  90 . Then, main tool plate  44  is rotated down unto top surface  50  of rotor blade  16  so that guide pins  66  are just touching trailing edge  20  and indicator rod  46  is resting on trim tabs  18 . The arrow  120  on dial  122  of indicator dial  32  will indicate the angle trim tabs  18  depart from horizontal. 
     Bender is then slid onto trim tabs  18  where gage  10  is located until trailing edge  20  meets jaw flange  140  and then jaws  126  of bender are tightened with thumb screws  138 . Using handle  128  of bender, trim tabs  18  are bent by the desired angle either up or down. A slight overbend is desired because of resilience in the metal trim tabs  18 . 
     Except for the coating on jaws  126 , and rollers  58 ,  64 ,  86  and  88 , gage  10 , bender, and gage calibration plate  14  are preferably made of a light-weight but dimensionally stable materials, such as an aluminum alloy. 
     It will be apparent to those skilled in the art of helicopter maintenance and trim tab adjustment in particular that many modifications and substitutions can be made to the preferred embodiments just described without departing from the spirit and scope of the present invention, which is defined by the appended claims.