Fabric Covering Wing 4 of 8

wing fabric rivet

One of my reasons for selecting the Northstar Wing Kit was the use of fabric rivets.  They are so much easier to use than stitching the ribs and they make for a stronger attachment and are easy to replace or repair. Northstar fabricates the ribs with predrilled 1/8th inch holes that are equally spaced along the centerline of each rib cap. After the fabric is attached and shrunk, a line of Polyester Twill reinforcement tape is attached along the top and bottom of each rib cap.  After the tape was attached, I used an auto inspection light and placed it below the wing to back light the rib which then showed where the holes were located. I used a sharp pointed hot soldering iron and poked a hole through the reinforcing tape and fabric into the predrilled hole. This seals (melts) the surrounding edge of the hole. The Northstar wing kit includes special Avex Pull Rivets and .016 X 1/2″ thin aluminum washers that connect the fabric directly to the ribs.

Attaching the Tapes and Gussets was the next step but before that, I used a pencil and straight edge and drew on the fabric exactly where tapes were to be located such as over the riveted ribs, leading and trailing edges, around openings, and where inspection covers would be located. After the lines were drawn I then brushed on the Poly Brush over the entire fabric wing area. The Poly Brush is a very rubbery material and you cannot draw a pencil line over it.

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Fabric Covering Wing 2 of 8

Fabric bottom wing B

With the wing turned upside down, the first length of fabric was draped over and glued on the trailing edge with a one inch glued turnover section on the topside of the wing. The bottom trailing edge of the Northstar Wing incorporates a very gracefully formed “S” shaped aluminum profile. The fabric in the “S” shaped profile must be glued down along it’s entire shape otherwise the fabric would stretch across the curves after shrinking. Before gluing down the trailing edge, the fabric was precisely cut out to fit over the large aileron and flap protrusions.  Also, prior to gluing the fabric down, a pencil centerline was drawn on the leading edge where the top and bottom pieces of fabric would eventually meet and overlap each other for a glued two inch overlap. After the trailing edge fabric was attached and dried,  glue was then applied on numerous edges where inspection covers occurred and around the tank cover openings. The photos above show the fabric as it was glued over these edges. Please note the fabric is loose and was not shrunk down yet. Poly Fiber instruction suggest one inch of fabric slackness after the fabric is glued down prior to shrinking.  On the upper left photo there is a protrusion that was not cut out. This is an eye bolt used for a flying rope connection for the aircraft when on floats.  The protrusion was only an inch or so above the surface allowing the fabric to be cut out after the fabric was shrunk.

While the fabric attachment was fairly routine on the trailing and leading edges it was quite different on the wing tip edges.  This was especially true on the compound curves where fabric would otherwise bunch up. To avoid this, the iron was heated up to a low heat setting and the fabric was dry formed (without glue) which included clamping, heating the fabric, pulling the fabric around and repeating this until the fabric was shaped to follow the curve.  Excess fabric was then trimmed away and the fabric was clamped and glued in place until dry.

Before starting on the topside of the wing, you use your iron on the fabric edges where the bottom and top fabric glued edges will overlap to take out any wrinkles or imperfections.

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Fuel Tank Installation

Image

 The Northstar wing kit includes two custom TIG welded fuel tanks.  The tanks hold 52 gallons in total or 312 pounds of fuel.  That quantity of fuel will give the aircraft approximately a 6 hour/ 600 mile range.  The fuel tanks were crafted to form the airfoil shape of the wing and were held tightly in place with three stainless steel tensioning straps.  Inside the tanks were three baffles to reduce sloshing of fuel.  After the tanks were installed in the wing a set of “X” braced drag wires were inserted through the fluid tight internal tubes in the tank.  

Using the Northstar wing made it unnecessary to use a header tank.  Piper aircraft and many Piper replicas require a header tank which is a small fuel tank mounted in the cockpit just above the Pilots feet. The header tank purpose is to ensure consistent fuel flow during climbs, dives and maneuvering. I did not like the idea of highly combustible 100 octane racing/aviation fuel just above my feet. The Northstar wing plumbing and fuel line routing provides positive fuel flow during steep climbs or dives making the header tank unnecessary. The fuel system is gravity fed from a forward port and a rear port that feed together to a central fuel selector. The head pressure is sufficent to also eliminate the need of an electric fuel pump.

One last feature of the Northstar fuel tanks are the fuel sight gauges in the root of each wing. These sight tubes provide the pilot an honest indication of remaining fuel on the ground and in the air.