Fabric Covering Wing 3 of 8

fabric top wing A

The fabric attachment process for the top of the wing is the same as the bottom side with exception that you overlap the bottom edge fabric by 2 inches on the leading edge and one inch on the trailing edge.  The photos above show the fabric after the 3rd of three heat shrinking temperature settings. The fuel tank cover was reattached to make sure the holes of the cover still aligned with the anchor nut attachments on the wing.  They did and there was no deformation due the fabric shrinking process.

Before moving on to the next step the fabric was scrubbed down with full strength MEK to remove any drips of glue while carefully keeping the MEK off any glued edges.

 

Attaching the Leading & Trailing Edges

Image

 With the drag wires squared up and firmly tightened, it was time to lock the wing into place. The Trailing Edge sheet metal came in preformed “S” shaped sheets approximately four feet wide.  The first sheet was attached at the root end and then each subsequent sheet was added with a slight over lap.  The preformed “S” shaped profile fit nicely against the shape of the trailing edge of the ribs and the predrilled holes allowed an easy way to back drill through the ribs and into the sheet metal.  As holes were drilled, Clecos were attached to keep the sheet in position.   Before  final riveting, the sheets were removed, holes were deburred and dimpled to receive countersunk Avex rivets. 

The Northstar Wing uses .020 for the Leading Edge and is designed to extend further down  creating a firmer and truer airfoil shape.  The Leading Edge sheet metal also came in preformed sheets and were also attached starting at the wing root however they had to be stretched over the wing in tension to assure that the sheet metal came in contact with the edges of the ribs.  This was done by first attaching the sheet metal on the underside of the ribs with a set of Clecos and then using tension straps and racheting the sheet down in place.  When the sheet metal was in place holes were back drilled and Clecos held the sheet in place. The sheet was later removed, holes were deburred and dimpled and countersunk Avex rivets were installed for final assembly  

The tip of the wing Leading Edge  ends with a raked wing tip bow and tip rib covered with a wrap around fiberglass termination cover that is also attached with Avex rivets. With the Leading and Trailing edges firmly attached the wing no longer twists and is permanently locked into shape.

 

Fine Tuning the Wing

Image

 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.