Heat Shrinking the Fabric

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 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

Time for Fabric

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 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. 

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.

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.

Seaplane Preparation / Part 5 of 5

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The wings, tail surfaces, turtledeck, and fuselage were fabric covered at different times and each horizontal lower fabric covered  surface required the installation of drainage grommets. They are intended to drain away any water collected by condensation or otherwise from the lowest point in the airframe.  As an example, each pair of ribs in the wings has it’s own grommet on the bottom lowest portion of each rib bay.  An ordinary drainage grommet is the size of a quarter with a hole in it and is glued to the fabric.  Then you glue a larger diameter fabric dollie  over the grommet and then  take a soldering iron and burn a hole through both fabrics and through the hole of the grommet. If your going to put your aircraft on floats the Poly-Fiber Fabric Instructions advise you to use “Seaplane Grommets” which have a molded shroud that is open on one side.  These are mounted so the open hole or drain port points backwards thus avoiding the collection of water during take-offs and landings.

Another item unique for seaplane operations are flying dock ropes. These ropes are usually two to three feet long and hang below the leading edge of the wing tips. They help manipulate the seaplane while docking by providing a rope to grab and pull the seaplane to the dock. I reinforced the metal wing understructure and mounted 1/4 inch eyelets for the later attachment of the flying dock ropes.

The last and perhaps most costly item needed for seaplane preparation is a “Seaplane Prop”.  My 80 X 44 wood Sensenich will not survive the severe duty of water operations.  Water spray is like gravel and will quickly harm the soft wood surface. My hope is to use a Catto Composite 86 X 38 climb prop that is light weight with reinforced nickel edges .

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.

Seaplane Preparation / Part 3 of 5

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Other considerations needed beyond welding mounts and rudder retract tubes included attachment of the interconnect pulleys that connect the air rudder to the two water rudders. I purchased a set of EDO float installation drawings from Kenmore Air along with the specified pulley hardware. There’s a pulley on each side of the lower rear longerons and another balance pulley mounted between them on a crossover tube that completes the cable circuit. The brackets remained attached during the fabric skin assembly but the pulleys were removed and stored until needed for the later float installation.

Seaplane doors are basically gull wing doors that open up and away from the prop wash.  Additionally, it allows the pilot and/or passenger to quickly depart the cockpit to grab a rope or a dock.  A conventional side hinged door would be deflected by the prop wash making it difficult to open and quickly depart the cabin.

During the building process I had talked with other builders and seaplane pilots about the necessity of using a ventral fin for the float installation.  The fixed ventral fin fits on the rear underside of the fuse and adds to the overall rudder surface area giving the airplane more directional stability.  The problem is that not every pilot agrees and not every seaplane needs it.  I decided to cover my bases just in case and found  a ventral fin for sale in Canada.

In the early building stage it was difficult to think ahead of the day how I would actually raise the aircraft, remove the wheel gear and install the floats.  Luckily, the wing kit I built  had a very simple solution on how this would be done. It basically consists of a pair of “U” shaped metal fittings that fit over the wing spar bracket using the same through bolt. The top of the “U” has a welded shoulder nut that permits a large 3/8″ threaded eyebolt to attach to.  You only attach the eyebolts when their needed for lifting thus no need to fly around with them. Also this is the perfect place to lift the airplane since it is common with the center of gravity location of the complete airframe.

Seaplane Preparation / Part 2 of 5

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The floats are attached using the same forward attach points as the main wheel gear but requires a special “Aft” fitting for the rear float attach points. The aft float fitting assembly is available from Atlee Dodge of Anchorage Alaska who specialize in Cub type parts.  The fitting is a heavy duty steel plate that is welded over the cluster of  longeron, crossover and vertical tube intersections.  It is designed to attach the rear float struts and float brace wires. While welding these fittings on I also welded on the front seat belt retractor mount plates.

Another item on my seaplane welding prep list was the provision for mounting a tube below the aircrafts belly that is used to pull a cable through that allows the water rudders to be retracted after a water take-off. The tube would only be attached when the floats are installed so I needed to weld a larger tube insert in the cockpit for the cable retract tube to attach to. The water rudders  are located on the stern of each float and are interconnected with the air rudders and rudder pedals. They assist steering the seaplane while on water and are manually retracted by the pilot with a cable attached chain that attaches to a hook below the instrument panel.