Finishing Tapes, Gusset Tapes and Inspection Rings were attached per the pencil line locations by first coating the affected area with a brush coat of Poly Brush, then brushing the tape and the affected area with more Poly Brush while pressing the fabric tape into the wet glued zone. Wet tapes are essential and it is easy to see when a tape is wet or has areas not wet. The Poly Fiber Instructions are excellent and this Blog is not meant to replace them or even supplement them. Needless to say, their instructions include much greater detail on how the process works. The tape attachment was followed by heat smoothing the pinked edges of the tape down into the Poly Brushed surface until they were smoothed out and there were no standing ears or rough edges.
When the brushing and heat smoothing process is finished then you move to the spraying process. This required me to relocate both wings to a spray booth which is my garage with a lot of drop cloths. I used my wing rotator fixtures (Harbor Freight Engine Stands) to rotate the wings with the other end attached to a sling contraption. When any of the Poly Fiber coatings came in contact with a plastic drop cloth they make for a very sticky floor. When I tried to walk across the plastic drop cloths my feet would stick to it. The solution was to use a cotton drop cloth on the floor. Another item that needed protection before spraying the wings were the aileron and flap brackets, the wing strut connection brackets and any other protrusions – so these were carefully taped off.
After two spray coats of Poly Brush the wings took on a very ruby red glossy appearance. The next phase is the protection coat of Poly Spray which is the UV silver coat that protects the fabric from the damaging effects of the sun.
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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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Attaching large sheets of sticky medium weight Polyester fabric to the sticky Poly Tak edges of the fuselage frame became a two person job. The objective is to attach the fabric before the Poly Tak glue starts to set up and dry while also leaving enough time to get the right amount of slack in the fabric for shrinking allowance. Too little slack could deform the metal frame during shrinking and too much slack could result in a saggy skin.
Side walls of the fuse were covered first, then shrunk and trimmed. The Belly panel was attached next and overlapped the side walls. The roof panel was attached last. Fabric tapes were attached on the edges and over the stringers using Poly Brush as the glue. Poly brush coats were then brushed on next over the entire fabric surface. Poly Brush coats were then sprayed on as seen in the photos above.
The Turtle deck had its own spray booth and is shown with tapes attached. There is no “Red Tint” on the fabric finish since the “Untinted Poly Brush was used.
The next step will be the Silver Coats using Poly Spray for UV Protection.
The sides of the Turtle Deck were fabric covered first and heat shrunk and then the top fabric was attached and shrunk down. The above photo shows the fabric before tapes were attached. Because the inside of the Turtle Deck can be seen when it is raised, I used the “Untinted” Poly Brush which is basically a clear finish product. The regular Poly Brush has a red tint and as you brush it on before, during and after the taping stage the brush marks and runs all begin to show. The red tint is there so you can see where you have brushed and where you haven’t. Theses brush marks will all be coated over with the sprayed on silver and color finishes but they will always be seen from the back side of the fabric. That’s not a problem when it’s inside the fuselage and can’t be seen but any fabric that can be seen from the back side such as fabric that faces the cockpit or in my case is seen when the turtle Deck is raised is an area where you would want to use the “Untinted” Poly Brush product