Fabric Covering Wing 5 of 8

poly brush wing

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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Wing Test Fit

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With the right wing structure completed, it was time to fit it to the fuselage and check for spar and fuse fitting alignment and see how the bird cage of the fuse lined up with the wing root profile.  This was also the first time I could actually see how the all the plumbing terminations (fuel ports, fuel vent line, and fuel site gauge ports) fit between the bird cage structure.  With the wing in position I could also finish weld the upper pulley entry mount for the wing and evaluate where the aileron cross over balance line fairleads run through the upper head area of the cockpit. Because I was adapting a Northstar wing to a Wag Aero 2+2 Fuselage I knew there would be issues for locations of these aforementioned items but luckily I really had only one problem and that was the aileron balance line fairleads on the fuse that did not line up with the fairleads on the the Northstar wing.  I got the torch out and burned the paint off the proposed affected weld area and welded new 4130 fairlead barrels to line up with the wing. Instead of removing the old fairleads I adapted them as a crossover visor bracket.

It was also at this time I needed to make a small temporary addition on my pole barn so I could attach both wings at the same time. The photo above is when I had only enough space to attach one wing at a time. I had the wings on and off the fuselage a few different times as it was necessary to design how the flaps would function and how to trim out the wing root with the side of the fuselage.  The Northstar wing has flaps and the Wag Aero plans only used spoilers, thus I was on my own to design the pulley and cable locations between a Johnson flap bar between the seats to transit the underside of the fuselage and activate the raising and lowering of the flap system. I left the wing struts off during this process and used a temporoary brace to hold up the wings in order to expedite the design of the flap system.

 

Miscellaneous Wing Projects

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A number of various plumbing, electrical, and access issues needed to be completed before covering the wing with fabric.  Fuel vent lines were installed on both wings, fuel ports, sump drains, and site guage fittings were terminated through the wing root for future connections.  The wing tip nav/strobe light wiring was fished through the trailing edge void and operationally tested.  Any electrical problem occuring inside the wing will become a lot more troublesome to fix after the fabric is attached. Inspection covers were also fabricated for aileron and flap operations along with wing strut connection locations.  I elected to use 8/32 machine screws and anchor nuts for all covers which took a little longer than the conventional sheet metal screws. Northstar provides the templates for these covers and also explains on their video a very clever method to bump out the aluminum as needed to go around a protruding aileron pulley.

Finishing the Wing Tip

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The Northstar wing has a very elegant wing tip shape.  Instead of the popsicle stick end found on the Piper wing,  the Northstar wing tapers down and back into a graceful rake. The wing tip extends the leading edge and maximizes the aspect ratio by  increasing the effective wing span, this according to it’s designer. The kit includes a custom shaped fiberglass leading edge element, a tip rib, a wing bow, and a preformed trailing edge sheet metal piece. The fiberglass part is firmly attached with Avex rivets to the end of the leading edge sheet metal and along the top and bottom sides of the wing bow.  The trailing edge metal is preformed and temporarily held in place with strapping tape to keep it positioned for drilling rivet holes.  The holes are then cleco’d down and a stiffener channel that runs diagonally is placed on top for locating rivet holes.  The stiffener channel is then placed inside the trailing edge piece and attached using  flush Avex rivets. Northstar also welded the mount on the wing bow for the attaching the standard Whelen nav/strobes light fixture.  The design of the wing tip is especially appreciated when fabric is attached making the finished tip an extraordinarily beautiful shape.

Preparing the Wing Build

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 Unlike other Experimental Aircraft Plans I had a choice on what wings to build.  I could build the Wag Aero 2+2 Sportsman Wings per the plans or select other wing options.  The Wag Aero Wings  are wood construction with square tips and wing spoilers instead of flaps. At the time I did not have a high confidence level for fabricating wood parts and I really wanted flaps so my attention turned to a wing kit made in Canada and available for use on the Sportsman 2+2.  

The Northstar Wings are made by Custom Flight Limited of Perkinsfield Ontario. The Northstars airfoil is the same as the Proven Piper USA 35B and is totally adaptable to fitting my Wag Aero Fuse.  Morgan Williams is the owner and Chief Engineer for Custom Flight Limited and is the brightest and most knowledgable person in Aviation that I have ever met.  His company (http://www.customflightltd.com) makes the Northstar Bush Plane Kit which is a Super Cub type airframe and they sell the same wings for Sportsman builders like me.  In the next several posts I will describe a lot more about this fantastic wing kit and what a joy it was to build such an extraordinary piece of engineering.

However before proceeding I always like to point out misguided ideas I had as a novice homebuilder.  Early in the process I read somewhere the need to build an absolutely flat wing table needed to fabricate the wings.  That seemed so logical to me that I did not hesitate to build a huge 4 foot wide by 16 foot long wing table.  Later on, after purchasing the Northstar wing kit I discovered that they are assembled on a simple pair of saw horses. The Northstar instructions provide all the necessary methods for keeping things square and true.  The wing table I built would actually have been a hindrance but it was a nice work bench for other things including the installation of Micro Vortex Generators on the wings during the time of flight testing.