Flap Mechanism

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The Wag Aero Sportsman 2+2 is designed as a four place aircraft, however the “+2” refers to two children or one adult for the back seat. When determining the routing of the flap cables, consideration had to be given on the location of these cables to keep clear of the back seat passengers, thus a side mounted cable system was needed.  The flaps are engaged by pulling a Johnson Bar Lever between the front seats that pulls the cable that run down the centerline under the floorboards until they reach behind the baggage panel and are then directed upward and over to the right side of the fuse where they terminated to a pivoting bell crank.  The bell crank cable was attached to a “Y” connection from cables routed from each wing.  As my previous post described, I found that this cable geometry limited the flap travel and it was later greatly simplified by removing the bell crank and using only one cable from the Johnson Bar.  The return springs in the wings provided the means of retraction and are assisted greatly by the thrust of the airstream.

The Northstar Wing instructions advise to set the maximum deployment angle to 52 degrees down. While that seemed extreme, the actual angle was between 40 to 45 degrees when the air load was applied.  The Northstar flaps are massive and one difficulty is being able to pull on that much flap. Your airspeed is very important and the slower the aircraft, the easier it will be to get that last notch of flaps engaged. The larger wing area and the Fowler like flaps help the aircraft fly much slower, so it takes some getting use to  as when you can pull on that last notch of flaps.

Finishing the Bubble Doors

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 I used a black spray to finish the inside face of the Plexiglas called “Lacryl” which is a specially formulated Lacquer used in the sign business.  It has a very nice eggshell appearance on the sprayed side and a very glossy black look on the outside.  I used a metal reinforced black plastic edge to finish the plexiglas flange that extended beyond the door frame and I attached the plexiglas to the steel door frame using special black sheet metal screws with a waxed black plastic washer.  A Plexiglas drill bit was used to drill slightly oversized holes in the plexiglas to eliminate cracking or splitting when the sheet metal screws were attached and tightened.

The Forming Secret

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 The Fabricator basically uses a big pizza oven to heat up an oversized sheet of Plexiglas. When it arrives at the correct forming temprature it is removed from the oven and draped over the lower part of the mold.  The upper plywood frame is then clamped over the Plexiglas sheet and air is immediately pumped in from the center of the lower mold.  There is a “Secret” as to how the air is introduced to the lower mold. If you just attach an air hose nozzle the result of the form will look very localized around the air nozzle location. The preferred shape is a balanced uniform inflation of the bubble around the entire frame shape.  The way this is done is amazingly simple and crude.  A piece of cardboard approximately 12 inches square is stapled on the corners over the air inlet and that’s it. That is enough air diffusion to uniformly lift the heated sheet of acrylic to its lofty formed shape.

The Photos above show the finished parts trimmed and reclamped in the mold. For Insurance, I had the Fabricator make two sets just in case I broke one later and that’s exactly what happened a few years later when I ground looped the airplane and shattered the left door with a safety cable flinging off the landing gear!

Fabricating the Bubble Doors

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 The Bubble Doors utilize the same fabrication method as Plexiglas Skylights – the same skylights as typically seen in school gymnasiums and factory spaces.  Luckily I had a local company who made these Skylights.  They had the equipment and know how to make my Bubble Doors and instructed me on how to make the tooling.

The first thing was to weld together a steel door frame that followed the contour of the airframes door opening.  I used a 1″ square 4130 steel tube and carefully tack welded the door frame inside the airframes frame.  With one of the wings attached I could determine if the future Gull Wing type Bubble Doors would interfere with the bottom side of the wing when it was raised.  I also  designed the latching method and gas lift spring locations needed to open and close the doors.   After I finish welded both left and right steel door frames I then began to build the wooden molds around the front and back sides of each door frame.

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.

 

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.

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.

Engine Mount Installation

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Before proceeding further with the Belly Panel project, I decided to move on to the Engine Mount installation.

There are certain welds on the airframe that deserve more attention and respect. These include the wing spar brackets, wing strut brackets, spar crossover tubes,  landing gear brackets, tail feather attachments and the Engine Mount Brackets.  Every weld is important but a a bad weld on the engine mount can ruin your day. 

This project starts by first taking the fuse off the rotisserie to expose the front end of the airframe.  The four airframe connection points must be accurately welded to agree with the chosen engine mount holes and the engine mount must agree with the engine you plan to use. My future plan was to use a Lycoming or Superior 180HP Engine and for now all I needed to do was decide on which type of Engine Mount to use.  There are basically two types of mounts – conical or Dynafocal.  The Dynafocal Mount is said to reduce noise and vibration inside the cockpit and the swing out feature sounded good in theory. The installation needed for the swing out feature will require careful alignment of the top and bottom brackets on each side so that the hinges will not bind and stay in alignment. There is no means of adjustment for a misaligned hole so careful tack welding and trial fitting is necessary to assure proper fit of the Engine Mount. 

In later years I would discover that the swing out Engine Mount is not as practical for servicing the engine as it sounds.   As you can imagine, the throttle cable, mixture cable, carb heat cable, magneto cables, oil lines and numerous electrical connections disallow any means of hinging the engine away from the firewall without first disconnecting everything.  Only during a major service event will the swing out Engine Mount feature be utilized.

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.