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.

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Finalizing Projects in the Forward Fuse

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The effort was to finalize every item in the fuse that would eventually get covered by fabric. One of those regrettable decisions was to accommodate an AM/FM Stereo CD player and all the necessary wiring, speakers, etc. This was the result of having too much time on my hands and not thinking like a pilot.  Yes, it would have been nice to listen to my favorite music while relaxing on a lake in my float plane but now that can be done with an iPod, an iPhone, or many other modern devices.  To this day I have yet to use it and it all goes along for a ride consuming space, adding to the weight of the airplane and reminding me how behind the times I was to ever consider such an item. 

To secure all the interior sheet metal panels of the passenger compartment I used # 6 sheet metal screws that affixed to Tinnerman nuts attached to welded tabs on the fuse.  Another item that was not in the plans is the simple idea of what to grab on to when you have to climb up to refuel the airplane. In a truck part catalog I found a unique 90 degree entry/egress handle. This would allow a good handle to grab on when you have to climb on the wheels to gain access to the wing tanks and the 90 degree turn in the handle would also provide a very useful way of climbing into the cockpit. 

While I was getting closer to starting the fabric cover project for the fuse I was also reminded of the severe limitation of the width of the cockpit and it became time to take a detour and research the method for designing and fabricating a set plexiglas bubble doors to widen the cockpit.

 

Finalizing Projects in the Vertical Stabilizer

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 Efforts were concentrated on finishing anything that would eventually get buried behind fabric. In the vertical stabilizer area I had a couple of mis-guided ideas that would later be abandoned. The first was a “Helper Spring” I found described in a Cub Club newsletter and at the time it sounded like a worthy idea.  The spring and cable were designed to attach to the top lug of the elevator bell crank and be adjusted so as to keep the elevator in a neutral position with no stick pressure.  Without the helper spring the elevator would otherwise deflect downward with the stick forward in the cockpit as with most airplanes.  The point of the helper spring was to reduce any tendency for the airplane to nose over while parked on a very windy day.  The bottom line is that I found no good way to terminate the cable to an adjustable turnbuckle in an area that would later be accessible. 

Another misguided effort was to install a VOR antenna in the upper vertical stabilizer.  At the time it seemed logical – it was how we navigated back then.  It was not a lot of work to install the antenna and associated wiring but by the time I was done with the aircraft the use of VOR navigation was quickly being replaced with GPS.  The antenna and part of the wiring remains but for all intents and purposes it is useless to me. 

The last and somewhat amusing story of the vertical stabilizer is the use a long push/pull control for adjusting the trim tab on the left elevator.  The Wag Aero plans actually called for this mechanism which is basically the same as the Vernier control as used for the throttle.  The problem is that this push/pull cable had to be nearly twenty feet long to reach the adjustment arm on the trim tab.  I called a company known to make such a cable and explained how long it needed to be and proudly announced it was for my “Homebuilt Airplane”!  The conversation suddenly shifted to, “WE CAN’T HELP YOU – Thank You Very Much!”  I called the next week and said it was for a bus and it was sent out promptly!  This was not the last time I had to be less than truthful of what I was using a part for. 

Another remaining item I needed to finish was the rudder strobe wiring that went from the power supply under the turtle deck to the bottom of the rudder and up to the strobe.

 

Rear End of Rotisserie

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 The forward end of the fuselage was easy to attach to the rotisserie fixture.  Several metal strap clamps were formed over the fuse tubes and simply attached with wood screws to the plywood panel that was used to spin the frame.  The rear end of the fuselage was more problematic.  Several protruding parts such as the rudder stops and hinge bushings were in the way of trying to flush mount the tail end of the fuse to the spinning plywood disk.  I discovered that a drill press vise had a sizable clamping area and was already “V” grooved for tubing.  A good snug turn on the vise handle kept the fuse nicely attached to the rear rotating disk of the rotisserie.

Motorized Rotisserie

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The fuse became noticeably heavier to turn as I continued to attach more parts.  Without redesigning the rig I attached a hoist motor at the base of the rotisserie and strung the winch cable to a pulley at the top of an 8 foot aluminum mast. I then redirected the cable downward and attached it to an “L” channel that spans the rotating plywood panel. This arrangement allowed me to spin the fuselage from zero to ninety plus degrees in one direction.  To spin the other direction all I needed to do was disconnect the cable and reattach it to the other side.  This proved to be very helpful especially when it came to the Poly Fiber Fabric attachhment and painting process.

Later, after the airplane was completed I used the same motorized mast to help raise the tail for tailwheel repairs, weight and balance computations and adjusting wing dihedral angles. In this case, I attached the hook and cable directly to the welded lift handles on the fuselage.

Back to the Belly Panels

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With the fuselage painting completed, it was time to reattach it to the rotisserie and it would stay that way for the next two years.  Over that time I would complete the belly panel installation, floorboard project, interior sheet metal attachment and the complete fabric attachment  and painting process.  

The belly project continued with the trimming and fitting of the fixed and removable belly panels. The fixed sheet metal panels were attached with Avex pop rivets to the “Z” channels. The removeable panels were designed to slip fit into a forward slot created by an overlap of the adjacent fixed sheet metal panel and secured to the sides and rear edge of the openings with #8-32 machine screws that connected to fixed anchor nuts on the “Z” channels.  It was at this time that I made a deliberate decision to standardize on #8-32 machine screws and anchor nuts on all detachable sheet metal skins versus using sheet metal screws.  This would add time to the project since anchor nuts are time consuming to install but for as many times as I had to take these panels on and off it has been well worth the effort.  Sheet metal screw holes would have enlarged and become an unreliable means of connection over time.

The forward belly panel was fabricated with clear Lexan.  I originally tried clear acrylic (Plexiglass) but it turned out to be too brittle.  The Lexan is very tough but is easily scratched and is not as optically clear as the acrylic.  The clear Lexan panel is located just below the control sticks and my thought at the time was to have a glass port in the floorboard that could be used for targeting a belly camera or for general observation of the passing landscape below. During flight testing I quickly discovered the oil from the breather line would cover the Lexan belly panel and make it useless to see through, even with an Air/Oil Separator.  This was more likely to occur when I filled the crankcase with over 6 quarts of oil.  If I maintained a maximum of 6 quarts there was no oil blow back on the belly.

Another very useful purpose for the clear Lexan panel was for preflight inspection of components that would otherwise be unobservableable. I could easily inspect from above and below the torque tube, push-pull tube, aileron pulleys, brake line connections, hydraulic lines, fuel lines and fuel selector valve.

Fuselage Painted

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Cascoat did an outstanding job and all the metal was evenly coated with no runs and a beautiful overall sprayed finish. Careful preparation and professional finishing should result in a 100 year airframe without rust or corrosion.  The two part urethane epoxy paint system is well suited for the attachment of the Poly Fiber Fabric system.  The Poly Fiber Fabric system utilizes solvents  that range from the mild 2210 fabric cleaner to the very aggressive MEK (methyl ethyl keytone) all of which have no effect on the Randolph epoxy finish.  You can brush MEK on the Randolph coatings all day long without ever damaging the finish.  The only way to really remove the paint is a torch.  During the build project I found it necessary to add a bracket or tab or make a repair on the painted tubes and the easiest way to do this was to burn off the paint in the weld zone, clean it with MEK and repaint it with the same Randolph coatings. It was almost impossible to see where these repairs were made.

Fabricating the Belly Panels

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I decided to experiment with a material used in the display business called Alucabond.  It is a 6mm panel consisting of two .020″ aluminum skins thermo bonded to a solid polyethylene core with an overall thickness of 6mm or 1/4″.  It is a very durable material and easy to form. I chose the 6mm thickness to fit the standard 1/4″ set back of the “Z” channels however in retrospect I should have used the 3mm thickness and remade custom 1/8″ “Z” channels instead. The thinner panel would have been easier to form and be less weight. 

My shop was not equipped with a metal forming machine so I designed my own contraption to form the bends.   I used a cardboard tube from my local Home Depot that is used for making footings for decks.  These come in various diameters and I used a slightly smaller diameter to compensate for springback. I filled the tube with concrete to make it as ridgid and hard as possible. A 1.5″ thick plywood panel was hinged at the edge of the work bench and was used for bending the Alucabond around the concrete filled tube.  As crude as it sounds, this fixture worked amazingly well.  There were of course a few R & D bends that did not fit right but I eventually developed a method that worked.  Fitting the panels to the airframe was also a trial and error process.  My only regret was that I did not make an extra set of panels. Ground looping the airplane during flight testing damaged two of the panels that I would later replace using an altogether different material and forming method that I will describe in a later post.

Removable Belly Panels

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The plans called for a fabric encased belly which means that once the fabric is attached, I would have to cut it open to get inside the belly or tear out the complete interior and remove the floorboards to get at what I need to, which is an equally bad idea . . . and there’s no way I’m going to use inspection rings in the fabric because I’ll never place them exactly where they should be and they are just too small to ever get any work done.

Because it’s the belly, it’s an area that is likely to get a lot of abuse including water, dirt, stones, rocks and worse. I decided to divide the belly up into four removable panels with fixed sections between them. At each fuse tube crossover point I welded a pair of channels approximetely 10 inches apart.  These channels would be used to rivet fixed aluminum skins to.  In-between these fixed sections I would fabricate removable panels shaped with the same belly contour as the fixed sections. Using the rotisserie, I welded the channels and pre fitted the fixed skins.  The channels were actually “Z” channels that had an edge that would provide the removable belly panels a lip to fit up against.  The next question was, what material should I use to make the belly panels from. They have to be sturdy, light weight, follow the contour shape of the belly and be easily fastened.  On my next post I’ll describe what I used.

Seaplane Preparation / Part 4 of 5

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Taking 13 years to build this airplane came with a price.

Have you heard of an AM/FM CD player, a VOR antenna, and a hydraulic pump to raise and lower the landing gear?  By the time I was done building the airplane all of these items were obsolete and replaced with something newer and better!  The tape deck was replaced with a tiny MP3 Player.  The VOR was replaced with GPS and the hydraulic pump was replaced with an electric motor system.  For seaplane preparation I made an extensive installation of a hydraulic pump, oil line network and electric plug and play set-up.  The hydraulic system is used to raise and lower the two main gear wheels and the castering forward gear.  I made the pump demountable so it would only be carried when floats were attached. The wiring harness and all the gear warning lights were all pre-wired with easy plug-ins.  All I needed were the floats.  As with the other afore-mentioned items I  became aware that my extensive accommodation for hydraulically operated floats was no longer needed.  The float company now uses an electrically driven motor system.  They did offer to buy back the pump if I purchase the new floats but how about all the oil lines and electrics I installed previously.  Oh well, I’m just too slow a builder to keep up with technology!

PS; The Clamar floats pictured above are on Larry Bauers seaplane and use the same hydraulic system as described above.