Fine Tuning the Wing


 There are four sets of criss-crossing drag wires in each wing. Each wire is a 3/16 inch heavy duty stainless steel wire threaded on each end.  The wires are used to literally tune and square the wing.  A trammel point tool is used for this process which is basically a measuring device that measures the “X” distance where the wires attach to the spars.  These trammel points are drawn on the top of the spar connection points and the object is to measure all the wire connection points until they measure the same. This is done by adjusting the threaded drag wires back and forth until the trammel points are equal by turning a nut against a block. When everything is squared a couple of jam nuts are used to fix the drag wires into final position. Where the two wires cross in the middle a nylon cable tie is used to keep the wires from rattling against each other. The drag wires help tune and square the wing but their most important role is to keep the wing spars parallel and prevent the spars from sweeping or parallelograming.  

At this point in the construction the wings need to be squared and finished because the next step will be to attach the leading and trailing edge sheet metal across the length of the wing. Once this sheet metal is attached it will fix the shape and squareness and prevent the wing from twisting. Before the leading edge sheet metal is attached the concealed aileron pulley and cable transit had to be completed because soon it would be mostly covered over by the sheet metal.  Fairlead brackets also had to be attached along the spar to keep the aileron cable inline and away from interfering with the ribs.  It will be important to remember that when the wing is later covered in fabric that inspection holes be located below these fairleads so they can later be replaced due to wear.

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