My Blog is a bit behind. I have not put any posts out for the last year since I was busy assisting in the installation of my Clamar Amphibious Floats. I will describe this in more detail in future posts. Although I live in Grand Rapids Michigan USA this airplane has almost total Canadian content. The fuse started out in Canada, the wing Kit is from Northstar in Canada, the Clamar Floats are from Canada and even the ventral fin was from a Canadian Pilot. – Thanks Canada!
Update; If you would like see a short 3 minute video of this aircraft on floats – check out this link; https://vimeo.com/198351351
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The final step was applying the classic #146 J3 OEM Cub Yellow. There are many yellows out there but this yellow was my favorite. I was very pleased on how it turned out. While it was not as glossy as Ceconite, Butyrate or Polyurethane finishes it still had a nice gloss level and most important to me is that it’s very easy to repair, which I needed to do many times. The Poly Fiber System is a beautifully conceived product as long as you follow their instructions. If you do, you end up with a project that’s hard to believe you did!
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Yellow airplanes need an extra step.
You cannot go directly to a yellow Poly Tone color with out first coating the wing in Poly Tone White. If you skipped this step and painted it yellow after the silver you would end up with a really ugly greenish color. The Poly Tone White goes on the same as the silver but it’s not designed to be sanded like Poly Spray. If you wanted white wings you would be done but I wanted yellow so I have one more step to go.
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Spraying the silver Poly Spray makes a real change to the wings. Three coats are applied until there is no obvious light showing through. An auto inspection light was placed beneath the wing and the lights were turned off in the garage. If any light penetrated the fabric then it had to be recoated again. Between coats, Poly Fiber advises to use their special “Paint Cleaning Chemical” which is wiped on and off. This removes any sanding residue, dust or dirt before the next coat is applied without harming the base finish.
The silver finish is actually fine granules of aluminum suspended in a clear Poly Based mixture. The sprayed aluminum needs to be very lightly sanded between coats until smoothed out before the final paint color is sprayed. If the pinked ears of any tapes stand up or if any taped edge is rough the fabric can be lightly sanded and the fabric recoated.
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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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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.
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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The photos above show the top view of the left wing as it stands vertical to make it easier to work on. The long piece of wing fabric is temporarily attached from the trailing edge and was for the moment just draped down. The Northstar plans called for two 2 inch strips of fabric tape to be stretched over the top of the fuel tank area to reinforce the ribs so they won’t deform when fabric is attached and shrunk over the the whole wing. I also did this to the bottom of the wing fuel tank area since I decided to have a removable cover there too. This was also the time to add the Inter Rib Bracing material which is basically a preshrunk ribbon-like material. Poly Fiber instructs you how to zig zag this between the ribs and how to knot them at each crossover point. The bracing is designed to keep the ribs from deforming during the fabric shrinking process.
The left wing also had an Angle of Attack Probe which was located 12 feet out from the root. This device had a plumbing line in the form of a tube that brings ram air pressure to a reporting module behind the instrument panel. Location of the probe on the leading edge of the wing is critical to it’s reliability so I was not sure if the location I decided on was the best. In view of possibly having to change it during flight testing, I chose to use a conduit that I could access to retrieve and re-route the air line. I used a very light weight fluorescent bulb tube sleeve as the conduit for this purpose. One last thing was attaching Anti-Chafe Tape to any sharp or protruding item that could puncture or fray the fabric. There were very few places where this was necessary.
It was now time to turn the wing upside down and start the wing fabric attachment on the bottom of the wing.
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Before the fabric covering process was started, I attached the control surfaces (aileron and flap) tank cover, and inspection covers to check fit and control movement. Aircraft cables were routed through pulleys and fairleads to check clearances. This was also the time to route the strobe and navigation wires from the wing tip to the root through the the trailing edge. Battery power confirmed their operation.
The Northstar wings are a work of art and engineering. It was time to admire the structure before covering it all up.
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