Wing Test Fit

MVC-007S

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.

 

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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. 

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.

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.

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 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 .

Floorboards and Re-Welded Seats

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While my main effort was to complete all the welding on the fuselage I had to re-focus my attention to the wood floorboards and seating attachment issues.  That’s because metal tabs and seat mounts had to be welded on the fuse to hold them down.  I chose 5/16″ exterior grade plywood and carefully cut it out to fit around tube joints and around the control sticks.  This was not to be the final finished floorboard.  In fact I ended up fabricating three different floorboard patterns until I ended up with a suitable design that evolved with other changes I made along the way.

During this early phase of construction I was reminded of the labor intensive method used for annual inspections for my Cessna Skyhawk.  My A&P (Airframe & Powerplant) Mechanic at the time had the complete cockpit interior removed including the seats and carpeting and all the floorboard inspection panels were also off.  This close up inspection is to check for airframe corrosion, control cable integrity, pass through wiring integrity, fuel line integrity, etc. But my mechanic also found a large mouse nest which certainly did not belong there!

This led me to think how easy or difficult it would be to inspect my homebuilt when it was finished. The plans specified that all interior sidewall sheet metal panels have a lip or 90 degree edge to be used to attach to the wood floorboards.  This would require me to completely remove all the metal sidewalls just to get to the floorboard removal and that would be incredibly difficult and time consuming.  The plans also specified a fabric belly and Yes, I could have added several removable inspection rings but they are very small and difficult to get into. Thus I decided in the months ahead to design a system of easily removable full width belly panels and omit the fabric belly altogether.

During this phase of building was the time I also purchased and modified a pair of Cessna 172 seats and removed the upholstery and removed 3 inches of metal frame width and re-welded them back together.

Learning to Weld

Welding ProjectsWith the fuselage securely attached to the rotisserie it was time to learn to weld the 4130 steel tubing.  Using a oxygen/acetylene gas rig and jewelers torch I test welded several scrap pieces together but it was’nt until I got expert instruction from Chuck & Craig Garret from my local EAA Chapter 145 that I finally gained some confidence.

I started welding on the fuselage lift handles and then the wing spar brackets, elevator bell crank assembly, floorboard mounts, rudder pedal mounts, engine mounts and landing gear and wing strut brackets.  They say the best way to test a weld is to try to tear or break it apart.  Unfortunately that destroys your weld.  Sadly, a few years later I put some of my welding to a real world test during a bad landing/ground loop event.  The good news is, the welds survived – the bad news is, the landing gear did not.

I will post more about that event in a future post including photos of the damage and the repairs made to the aircraft.

Preparing the Fuse

Fuselage on RotisserieThe newly purchased fuselage was attached to a homemade rotisserie fixture on wheels.  The fixture supported the fuse and allowed it to be turned and held in place for welding parts on, attaching floorboards, installing components, and for fabric covering and painting.

The fuselage stayed on the rotisserie for 4 years until it was removed for sand blasting and painting.  It was then re-attached and the rotisserie was motorized for easier turning. It stayed attached for another two years for fabric covering and painting until it was finally removed and let to stand on its own wheels.

The Starting Point

Trip To Orillia, OntarioEvery Project has a starting point and N728DC started with a trip to  Orillia, Ontario to inspect a Sportsman 2+2 fuselage that was for sale.  In November of 1995 we packed up the family, rented a trailer and headed to Canada to inspect and possibly buy a former builders uncompleted project.  A set of color coded plans were used to inspect tube diameters and a thorough set of measurements were also taken to confirm if the fuselage fabrication was done correctly.

It turned out that everything was spot on.  The frame was square and true, the welds looked good, and there was no corrosion.  In fact it also turned out that the fuselage was actually fabricated by Wag-Aero and sold as a kit in their catalog for a much higher price.

There was still a lot of welding to complete but this fuselage would provide a huge head start to a long and complicated project.