Exhaust, Boot cowl, NACA ducts

The left front exhaust had previously been only tacked in place, so all seams were fully welded.  A couple of stainless hooks for attaching the springs were then carefully positioned and welded onto the exhaust.  Once the welding was completed, the exhaust was pressure tested to check for leaks.  Two small pinhole leaks were found near the ball end, and these areas were ground down and touched up with the TIG welder.  After this touchup, the exhaust passed the pressure test.

All exhaust tubes were then wrapped with a fiberglass cloth material to protect nearby hoses and wiring, which was clamped at both ends with stainless straps. 

Spring hooks welded in place

Completed exhaust.  Fits perfectly!

Exhaust tubes with heat wrap

We had previously repositioned the boot cowl slightly, and the bottom edge was now a little long, so this was trimmed down with a Dremel tool.

Bottom edge of boot cowl trimmed

Work began to add two small NACA ducts.  These openings will be used to feed fresh air into the cabin through two adjustable vent ducts, one for the pilot and one for the passenger.  A template was made from the plastic NACA duct parts, and holes were cut in the aluminum side panels by using nibblers and a Dremel tool.  These panels were previously painted, so I'm trying to be careful to protect the paint while doing this work. Hours: 21

New NACA duct hole in the side panel

Top Cowl and Firewall work

 The Silicone/Fiberglass baffle seal was received from Aircraft spruce and cut to the desired shape.  We chose 2" of overlap as our starting point but later trimmed it down to about 1", which worked much better at contouring to the boot cowl shape.  The backer bracket was used to locate the holes and the holes where punched in the silicone with a hand bunch.  Currently the baffle seal is cleco'd in place awaiting rivets.

The firewall was finally riveted to the fuselage, replacing the clecos that had been holding it in place.

Baffle Seal Cleco'd in Place

We decided we wanted an access door in the top cowl so that we could quickly check the oil level in the oil tank.   Michael had some left-over Hartwell latches from his previous project that fit the bill perfectly. We also ordered a hidden hinge from Aircraft Spruce.  The access door needed to be large enough  to reach down and remove the oil tank lid.  Once that was determined, an extra lip was needed for the door to close against.  We chose a 1/2" lip.  The access door was marked on the top cowl and cut out with a Dremel tool.  A new door was fashioned out of 0.040" aluminum and it was coaxed into shape since the top cowl is curved.  To create the needed lip for the door to seal against we needed to use fiberglass/epoxy.  The original piece of fiberglass that was cutout of the top cowl was coated with packing tape, which epoxy doesn't stick to. It was taped back into its position on the top side.  Some modeling clay was put in the cut gap to create a smooth inside surface.  Four layers of fiberglass was layed up and allowed to dry.  Once cured, the old door was removed.  The 1/2" lip was drawn and the excess fiberglass was cutout with a Dremel.  The cutout for the Hartwell latches with made on poster board and transferred to the metal access door.  The holes were cutout and each latch were installed with 4 solid rivets.  Next the hinge location was set. The holes were drill in the cowl and access door and then riveted in place  with solid rivets.

Oil Access Door with Fiberglass Lip

Oil Access Door with Latches and Hinge Installed

The throttle cable pass-thru on the firewall was installed.  We bought a "eyeball" firewall pass-thru from Aircraft Spruce that worked out nicely.  Once tightened, it provided a nice sealed port for the throttle.

Hours: 20

Cabin Side of Throttle Cable Eyeball Port

Engine Side of Throttle Cable Eyeball Port

Exhaust update

Progress was made on the left front exhaust, which needed to be rerouted around the radiator.  As mentioned in a previous post, a mock-up was first made using plastic pieces that were 3d-printed.  Thought we had one we liked, but later decided we wanted more clearance from the radiator and a straighter entrance to the muffler.  Once we were happy with the general design, the old exhaust tube was cut to reuse some of the stainless pieces.  We also bought a new stainless flange, donut, and temperature probe bung from Lockwood.  

Stainless tubing was measured and cut to duplicate the plastic prototype.  They were then sanded and cleaned, and carefully tacked to duplicate the prototype that we made in plastic.  

Welding stainless has some of its own challenges as heat control is more important than standard steel, and purging the inside of the tube with argon during welding is also necessary to avoid oxidation on the backside of the weld.  I purchased a dual-regulator for the argon supply and fitted a silicone tube to it which runs to a silicone plug inserted into one end of the exhaust.  The other end has another plug with a small hole to allow argon to flow through the exhaust.

Ed prepping to tack up another piece of the exhaust

Plastic prototype held next to final tacked tube

After several adjustments (had to grind some tacks and re-tack to get the shape right), the new pipe shape looks and fits great.  The temperature probe bung still needs to be attached, and then full welds around all joints need to be made.  Loops for the exhaust springs will be welded on last.

Hours: 18

Top Cowl Work

Work continued on the top cowl propeller hub fairing.  Four layers of fiberglass were added with West System Epoxy.  A peal ply was added to help removed excess epoxy.

Fiberglass added with peal ply on top

Once the fiberglass cured the top cowl was sanded to get a good transition to the top cowl.  Since the surface had some pin holes and imperfections a layer of micro (micro-balloons and epoxy) was applied to the surface.  Once the micro cured a good sanding was done to get the final shape.  A layer of sanding/filler primer was applied and then the top cowl was sanded with 400 grit sandpaper.  Additional cleanup work will be done during the final preparations for paint.

Top Cowl with Prop hub fairing

The top of the firewall is sealed to the boot cowl with a silicone fiberglass baffle seal.  A backer plate for the rivets was made from 0.025 aluminum.  Pilot holes were first drilled in the backer plate and then the backer plate was clamped on the firewall and the holes were match drilled to the final 1/8" rivet size.  Once the baffle seal arrives from Aircraft Spruce it will be cut to size, holes punched, and finally riveted to the firewall.

Hours: 12

Rivet Backer Plate for Boot Cowl Baffle

Holes in Firewall for Boot Cowl Baffle.

 

Fuel filter and fuel hoses

The fuel filter was installed, and several AN6 fuel hoses were made.  Three of these hoses are forward of the firewall.  One connects from the firewall to the fuel filter, one goes from the fuel filter to the fuel rail (inlet side), and one connects from the fuel outlet to back to the firewall (fuel return).  These hoses are sleeved in a blue firesleeve to provide additional protection. 

Fuel filter and fuel hoses (blue)

Fuel Hose (return side)

Two additional hoses were made for the other side of the firewall, one of which connects to the supply fuel side, and one is for the return that heads back to the header tank.  The hoses will be secured later with adel clamps.

Some additional planning was done on the exhaust to provide better separation from the radiator, and some parts have arrived so work can begin on this soon.  

Hours: 16

Firewall Forward Work

Starting to knock off some of the miscellaneous items firewall forward.  Based on the Rotax 912iS installation manual, the engine ECU must be mounted inside the cockpit.  That means that some fairly large electrical cables will need to be passed through the firewall into the cockpit.  After measuring the connectors and cables a 3"x1.5" hole was cut in the firewall.  This will later be covered and sealed.  Temporarily, some edge protecting plastic was added to prevent any cable damage.  It was a tight fit, but the ECU, HIC and Fuel Pump cables were passed through the hole. 

3"x1.5" hole in the Firewall

The coolant overflow bottle was mounted to the firewall.  A titanium strap was made and riveted to the firewall.  A screw and nut was used to secure the bottle in its holder.  Finally a hose from the coolant reservoir tank was installed with clamps. 

Coolant Overflow Bottle Installed

We discovered that we need a little more clearance at the oil cooler to prevent rubbing on the oil cooler hose lines.  We didn't need much about 10mm (a little over 3/8").  The four lower cowl attach holes were moved giving us the needed space.  The boot cowl will need some modification to fix this.

Started work on the upper cowl modification.  We wanted to add a fairing behind the propeller hub back plate.  We started with clay to get close to the shape we wanted.  Once it was close, some dimensions were taken and the clay was removed.  Now we need to add some foam and shape it so we can add some fiberglass.  A containment chamber for the 2-part foam was constructed out of cardboard and packing tape   Once all the seams were covered the 2-part foam was mixed and poured into the area.  After allowing the foam to cure excess pieces were removed and a rough shape was carved.

Hours 10

Modeling Clay Fairing

2-part Expanding Foam

Expanding Foam in cardboard containment

Foam carved to rough shape