Rear End of Rotisserie

Image

 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.

Seaplane Preparation / Part 3 of 5

liftringphotos-1

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

aft float fitting

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.

Re-Fitting, Sandblasting, Priming and Storing the Tail Parts

Preparing Tail Parts for Covering
With the tail parts re-attached to the fuse it was time to re-check control movement of the elevators, trim tab and rudder.  When this checked out, the elevators and horizontal stabilizers were removed for sandblasting and priming.  A strobe light bracket from Univair was welded on the top of the rudder and later wired with a quick link harness prior to fabric cover.

The vertical stabilizer remained attached to the fuse and all the remaining tail parts were then hung from the rafters until the rest of the fuse was ready to cover.

Welding the Elevators, Trim Tab, Stabilizers, and Rudder

Welding Tail partsMaking the tail parts require accurate welding fixtures.  Plywood panels were purchased and painted flat white.  Then a 2″ pencil grid was drawn on the entire face of the panels.  I then transposed the full size shape of the stabilizer, elevator and rudder on the plywood panels and located  each rib location, hinge knuckle, cross brace etc. per the plan. The tubing was bent using a spring and soft rubber hammer and plenty of hand persuasion.  Gradually I got the metal to agree with my curvy drawing.  The horizontal stabilizer had a tricky leading edge taper that required spliting the last outboard length a few inches from the end and then removing sufficient material and then squeezing the ends together and re-welding the seam back together.  The seam was then ground smooth.

The metal tubes and ribs were cut to size and fitted tightly together on top of the plywood pattern. Wood blocks were used to keep everything in their place during welding.  Only tack welds were used to temporarily hold parts together.  The assembly was then removed and finish welded on a welding table.

Welding the thick hinge knuckles and bushings was the most difficult due to the differental thickness of the knuckle and the parent tube.  It was important to keep the heat directed to the heavier wall tubing and avoid burning through the adjoining thinner parent tube.  Also keeping the hinge knuckles aligned  was done with sacrificial bolts that sometimes became unknowingly welded to the finished assembly.

The plans also called for small 1/8″ rods in certain end locations.  This was used as a anti bending brace to avoid end deformation during the later fabric cover and shrinking process.

Finishing the Turtledeck

Fabricating the Turledeck 3 of 3After the metal fabrication and system testing of the lift and lock mechanism was complete it was time to finish and protect the metal.  A backyard sandblasting set up was used to clean and prepare the metal for paint.  This set up was used for all smaller parts like tail pieces, rudder, landing gear legs, etc.  I found out that sandblasting is very messy and its impossible to recover used blasting material when you do it outside. All future sandblasting was done by Southwest Sandblasting in Grand Rapids who do an outstanding job.

After the turtledeck was sandblasted it was cleaned with MEK and hand brushed with a 2 part epoxy primer from Randolph Coatings quickly followed by a 2 part epoxy J-3 yellow finish color.  The 2 part epoxy paint protects the metal from corrosion and is impervious to MEK and all other Poly Fiber chemicals used for fabric attachment and finishing.

Because the inside fabric of the turtledeck can be seen when it is raised I used untinted Poly Brush to avoid having pink brush marks visible.