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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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 most important finish of a fabric covered airplane is the sprayed on silver finish. These multiple coats of silver are basically aluminum particles suspended in the vinyl chemistry to protect the fabric from the harmful effects of the Sun. There is usually a minimum of three coats of the Poly Spray material needed to bury the fabric in metal. A work light is placed behind the fabric to inspect if enough silver has been applied to totally eliminate any light penetration through the fabric. The silver/fabric material is carefully sanded with 320 / 400 grit sandpaper between coats.
The next spray coats will be a White Poly Tone Color that is used as a base finish prior to spraying the final classic 146 J3 Yellow. The White is needed to cancel the gray tone of the silver otherwise the Yellow color would be a greenish and hideous color.
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 Poly Fiber Instruction manual warns about over tensioning the fabric during the three stage Ironing process as it can deform metal parts. I was deeply concerned that this may occur on the Turtle Deck since it is an open ended frame so a Test Fit was in order to check for proper fit on the Fuselage. Luckily there was no deformity and as I gained expierence I found that it was next to impossible to deform parts, even light weight aluminum parts. The only caveat is, if you glue the fabric too tightly around the part to begin with then it is entirely possible to deform it as the fabric pulls itself together. The best practice is to leave a little slack in the fabric when it is first glued to the frame, then as it shrinks it will not deform the part it is covering.
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
With the Fuse painted, it was now ready to fabric cover. However before I tackled the largest fabric covered component I decided to first test my skills on some smaller parts. The Turtle Deck was my first experiment in learning the fabric cover process. I researched various covering methods and products and decided on The Poly Fiber System. I liked the Instruction Manual and I also attended a two day class which helped me gain some confidence. But the most important aspect was the product itself. The Poly Fiber System is durable, easy to install and easy to repair.
In the photo above the fabric has been glued to one side of the Turtle Deck and is in the process of being heat shrunk. The next ironing at the highest temp setting will smooth the wrinkles away.