Working on the fuselage interior

I'll try to be fairly prompt in reporting my build progress. I plan to follow the sequence in the kit build manual, expanding here with additional information that may be useful to other builders.

The factory support has been excellent. An e-mail to the support staff is always answered by the next day with detailed explanations, accompanied by additional drawings and photos where they are needed to help explain something.

The first thing I ran into is that the location of various holes and openings where components are to be installed were not marked on my fuselage as indicated in the kit manual. In retrospect, I'm not sure how helpful those markings would be, since they are relatively easy to wipe off the slick gel coated interior surfaces, and because I always think mounting holes should be match-drilled to the component to be mounted.

The real problem is that the manual is not specific about the locations and sizes of the various holes and openings. I sent an e-mail to the factory and got what I needed on the following day, in the form of drawings with the necessary dimensions.

One point of confusion was the opening in the rear cockpit bulkhead through which the flap handle linkage extends. When I placed the flap handle in position as indicated by the drawing in the manual, the shape of the bulkhead opening in the supplied sketch didn't make sense. The hole shown above seemed complete adequate. I asked the factory about this, and they replied with some photos that clarified things and revealed an error in the flap handle drawing in the kit manual.

The photo from Tomaz, showing the flap handle in the jig they use to mark the bulkhead opening

The problem was that the mounting angles at the aft end of the flap handle assembly needed to be rotated 180 degrees, such that the assembly itself protrudes through the bulkhead, not just the linkage. With that clarification, the shape of the opening made complete sense, so I corrected it as shown here.

I masked off the front part of the fuselage, as indicated in the kit manual, and painted the interior lip of the windscreen opening with spray "bumper paint", supplied with the kit. This is a very nice, flat black paint that goes on very smoothly without forming runs, and seems very durable. I also painted the bare composite interior surfaces below the windscreen with black Nitro paint.

At first I was not clear on what the kit manual wanted me to paint, but after examining the cockpit and looking at the manual photos for awhile, I decided that the idea was to paint all of the interior surfaces that are not the slick gray gel coat. I'm trying to follow the manual sequence, so some of the sufaces will get painted later.

I masked off and painted both sides of the cockpit. The area that needs to be painted black is the section that is not gel coated surrounding the door opening. This includes a narrow strip running up the edge of the forward door post. I sprayed sections below the top of the door opening with bumper paint, and used black nitro to paint a few inches above each door opening. The rest of the upper section and the top of the cockpit will be painted after I invert the fuselage.

Here is the left side of the cockpit after masking and painting with bumper paint. After this picture was taken, I painted the section above the door opening with black nitro paint.

Next, I mounted the rudder pedal assemblies. Here is the sequence that I favor in order to get components match-drilled reliably:

Hold the assembly in the desired position (this is pretty easy for nearly all of the kit assemblies, because everything fits very well). Mark one mounting hole of the four holes in the aft end of the rudder assembly. Drill that hole to the size of the bolt (6 mm), insert a bolt through the assembly into that hole and secure the assembly temporarily with a washer and nut on the bottom side of the cockpit floor.

Ensuring that the rudder pedal assembly is level side-to-side, drill a second 6 mm hole in the diagonally opposite hole in the aft end of the assembly. Put a bolt through that hole to keep things lined up.

Disconnect the rudder pedal return springs so that you can lay them back out of the way. Center the forward mounting flange of the assembly on the mounting pad at the forward bulkhead, and mark the lower mounting hole with a fine Sharpie pen.

Remove the assembly and as carefully as you can, drill a 6mm hole where you marked the mounting pad. Put the assembly back in place and ensure that you can easily slip mounting bolts into the three holes that you have drilled so far.

Having confirmed the proper position for these three bolts, remove the assembly again and enlarge the forward mounting hole to 8mm using a metric step drill. Then, using your nutsert installation tool (see the page on tools), install a 6mm nutsert in the forward hole.

Mount the pedal assembly again using bolts, nuts and washers in the two rear holes, and a 6mm bolt screwed into the forward nutsert.

Now drill the two remaining holes for the rear flange. Put bolts through these just to help ensure that things are aligned and stay that way while you finish the holes for the front flange.

To drill the two remaining holes for the front mounting flange, I used an angle drill attachment, because it has a small chuck and avoids interference with the assembly structure.

A careful scan of the kit manual and the separate file of photo details allowed me to determine where the rudder cables penetrate the firewall, fuselage floor and the bulkheads on their route to the tail section. I also confirmed that all the penetration holes are 6 mm diameter. The forward ends of the rudder cables are swaged to 6 mm diameter threaded rods, and the tubing that is used for routing the cables is also 6 mm diameter. I also measured the left-to-right distance between the rudder cable S-tubes on the rudder pedal assembly. That measurement is 5 cm, which establishes the lateral distance between the rudder cable penetration pairs at the firewall and under the front seats.

I sanded some rough fiberglass edges around the roof of the cockpit, then painted all the bare glass surfaces with black Nitro paint.

After the black Nitro paint dried, I did a trial fit of the cockpit lining material in the cabin roof. I then brushed contact cement onto the roof (using a disposable brush and wearing my organic vapor face mask) and sprayed contact cement on back side the lining material. Both types of contact cement are included in the kit. The cement is left to dry until it is no longer tacky to touch.

With Mary's help, I positioned the lining material on the roof of the cockpit and pressed it into place, working from center out and back to front. The contact cement was easy to use. It didn't grab until the cloth was pressed into place, so it was straightforward to position the cloth first, then carefully press it down for a good bond and a smooth cloth surface. The lining material supplied with the kit fit perfectly.

I then repeated this process for the sections of lining material that cover the sides of the cockpit above the doors at the wing root. These pieces of lining had to be slit where they fit over the brackets that mounts the fuel valves. I cut these slits while trial-positioning the lining pieces before applying the contact cement. Again, everything fit nicely.

One of the next steps is to mount the fuel valves on the brackets above the door openings. I discovered that the fiberglass layup over the brackets was built up high enough to interfere with the mounting of the valves. Even removing the cockpit lining material under the valves will not create sufficient clearance. It would be easy enough to grind down the material with my rotary tool, but I've asked the factory for their suggestion on how to address this.

Also, I could not identify the two washers that are used in mounting the valves to the brackets, so I've asked the factory to clarify which part to use.

Tomaz of Pipistrel answered my e-mail and sent this picture for clarification of the fuel valve installation. He agrees that it is permissible to remove a small amount of fiberglass over the valve bracket, and also suggested enlarging the hole slightly.

I also noted that the fuel hose attached to the bracket appears different from that shown in the manual, but matches what was delivered with the kit. I'm still waiting for my order of Loctite to arrive, so it will be a couple of days before I complete the valve installation.

I couldn't locate a source for long (30 cm or so) metric drill bits at a reasonable price, which I needed to drill the holes for mounting the airbrake center bracket. So I found a workaround in the form of a flexible angle drill from Aircraft Spruce that would accept my small angle drill chuck and allow me to get underneath the mount to drill the holes.

I measured carefully to get the bracket located 1 mm right of the fuselage center line, per the kit manual, drilled the holes (one at a time, inserting a bolt temporarily in each hole before drilling the next), and left the bolts in place temporarily until my order of Loctite arrives.

Note that positioning the bracket as called for in the manual places it well to the right of the space between the two openings cut in the bulkhead. Referring to the pictures in the kit manual, this appears to be correct.

I assembled the fuel valve components using Loctite 542, capturing the bracket between the valve body and one fuel nipple. After tightening the fittings, there was still some play between the valve and the bracket, but after the Loctite hardened, the valve was securely held in place and felt pretty solid.

I also permanently installed the nuts onto the mounting bolts for the airbrake lever center bracket, using Loctite 262.

This is a picture from Tomaz at Pipistrel, showing the fuel valve and fuel line installation on the completed aircraft. The fuel line material is different from that in the photos in the kit manual, but matches the material in the kit. Similarly, the photo shows the use of zip ties to secure the fuel line to the valve stem, rather than the metal hose clamps shown in the kit manual. The kit comes with the zip ties as shown in the photo from Tomaz.

I installed the fuel lines with the quick disconnect fittings. The fuel line is very difficult to push over the stem on the fuel valve, so I boiled some water, poured that into a cup and held the end of the fuel line in the hot water for a minute or so. That softened it enough to get it onto the stem with some coaxing. I then used two zip ties on each connection, cinched up as tight as I could, using pliers to apply the tension.

The manual next mentions an aluminum fitting for the fuel return line that penetrates the bulkhead above the pilot. I don't have that piece in the kit, and it's not in the inventory, so there is a change to investigate here.

That completes the work to be done while the fuselage in inverted. Now it's time to turn it upright again.

With the help of three people interested in the Pipistrel, arranged by Scobie Puchtler, a local pilot and RC model designer (see www.liftworx.com), we carried the fuselage out of the garage, turned in upright again and repositioned it for the next steps in construction. We also spent an hour or so looking through the kit contents and talking airplanes. Thanks, guys!

Scobie had already been watching Pipistrel on the web, and all were impressed with the kit and the utility of this airplane. Chalk up some more enthusiasts for the Sinus.

Here is the velcro on the rear cockpit bulkhead for attaching the headrests.

To install the velcro, I first cleaned the surface with acetone, then marked where the velcro is to be mounted. Then I painted the special primer on the marked location. The kit manual says this is a 3M primer. I found a .5 litre plastic bottle labeled Primer, but saying nothing to indicate it is a 3M product. I couldn't find any other reference to primer in the manual, and the placement of this item in the kit inventory eventually convinced me that this is the correct material. So, as instructed, I painted it onto the surface for one strip to see how it works. After letting it dry for 5 or 10 minutes, I applied the adhesive-backed velcro strip. I must say that the resultant bond is very strong. I am sure that the velcro strip would have to be destroyed to remove it. I also noted that you had best be careful when placing the velcro strip, because once it comes in contact with the primed surface, it's there to stay.

Being thus satisfied with the materials and the process, I proceeded with the remainder of the velcro installation.

First, I put the seats and carpet in place and marked the location of the ends of the sewn-in velcro strips where they contacted the fuselage floor. I then positioned the loose matching velcro strips at appropriate spots on the floor, guided by the kit manual photos, and marked around them with a thin felt marker. I painted the primer inside these marked locations, let it dry and applied the velcro strips.

These are the velcro strips that will secure the cockpit carpet beneath the rudder pedals.

Here are the seat and headrest installed temporarily. The headrest is sewn into the black panel that surrounds it. The headrest is held in place by velcro strips on the back of that panel. The seat and seatback upholstery and paddding is all sewn in one piece, with velcro strips under the seat padding. The back is later supported by nylon webbing across the opening in the bulkhead behind the seat.

At this point, being satisfied with the velcro installation, I covered all the velcro strips in the fuselage with blue painter's tape to protect it during the remainder of the construction.

Using dimensions provided by Tomaz at Pipistrel, I cut the prescribed hole in the firewall, using a 7/8" hole saw two cut two adjacent holes as described in the kit manual. I then positioned the 3-piece fuel line assembly with the T-connector behind the aft fuselage bulknead and ran the center line forward under the cockpit floor through the hole in the firewall. After that, I ran the fuel return line forward under the floor and through the same hole.

This is the hole in the lower firewall with the fuel delivery and return lines emerging from under the cockpit floor. The large openings will later be filled by fire sleeve material that will protect the fuel lines inside the engine compartment.

I then riveted plastic straps to the back of the aft fuselage bulkead and routed the fuel delivery lines form the T connector through the straps to the left and right fuel valves. I routed the fuel line with its quick-connect fitting to the left side. Under the floor, I tied the delivery and return lines together with plastic zip ties and taped them to the fuselage floor as instructed in the kit manual. Tomaz said to use fabric-backed tape for this, which sounds like what we call duct tape. I used a product called Gorilla Tape, manufactured by the same company that makes Gorilla Glue. I have found Gorilla Tape superior to duct tape for adhesion and longevity.

I installed the carpet on the sides of the cockpit. I painted liquid contact cement on the fuselage and sprayed aerosol cement on the back side of the carpet. After both surfaces were dry to the touch, I pressed the carpet in place. Because the carpet did not adhere consistently, I brushed some liquid cement on the backside of the carpet at the edges, which then secured it well.

I unpacked the door frames, lexan windows and door parts. The door assembly and mounting is not covered in the kit manual, but it appears very straightforward.

After familiarizing myself with the parts and determining how they will be assembled, I checked the fit of the lexan windows in the frames to confirm that they match. I also confirmed that the frames match the door openings in the fuselage, and that the hinge recesses in the doors match the hinge recesses in the fuselage. Then I painted the recessed mounting surface of the door frames with the same black Nitro paint that I used for the windshield and top window mounting surfaces.

The next step is to prepare the lexan windows for mounting in the door frames. For that step I will follow the directions provided in the kit manual for the windshield and top window.

I received the photos below from Dave Clark showing reference dimensions for the positions of the holes in the cockpit floor through which the throttle cable, choke cable and various electrical cables are routed.

After marking the hole positions, I measured the rubber grommets and determined that the two larger holes are 3 cm diameter and the smaller hole is 2 cm diameter. I cut the holes slightly undersize using hole saws, then opened them to the final dimension with my rotary grinding tool. Then I installed the rubber grommets in the holes.

I drilled a 10 mm hole for the brake line near the center of the cockpit floor forward of the rudder cables at the position specified in the kit manual. Then I inserted a rubber bushing in the hole.

The cable ends have to be soldered to keep them from unraveling while sliding through the cable housings and end fittings. Once a strand comes free, there really is no alternative but to cut off the cable end until you get to a clean section.

A solder pot comes in handy to solder cable ends. I found one on eBay. To use it, I first coat the cable end with past flux, then dip the cable end in the molten solder. Sometimes it helps to add more flux and dip it again until the cable is saturated. The result is a nicely coated cable end that won't unravel and will slide through the cable housing easily.

First, I had to drill two new holes in the firewall for the cables, aligned with the opening in the electrical panel. The holes that I drilled at the positions indicated by the measurements from Pipistrel were about 1 cm too high. Then I routed the throttle cable housing through the firewall, through the electrical panel, through the smaller of the three grommeted holes in the cockpit center tunnel, and up through the fuselage floor at the lower end of the throttle lever.

The shorter of the two cables in the kit is the throttle cable. This cable comes with a hex-shaped stop at one end and bare cable at the other.

I decided to take advantage of the cable end already installed on the throttle cable and use it to anchor the cable at the throttle lever. This freed up the 6.5 mm steel barrel to use for the choke cable. The 6.5 mm barrel fits the choke lever anchor point better than the 5.5 mm brass barrel supplied in the kit.

I soldered the end of the throttle cable to keep the strands from unraveling. Then I removed the throttle cable from the housing, and lubricated the cable and housing with spray lithium grease. I removed the threaded cable bushing from the bottom of the throttle lever to make it easier to thread the cable back through the throttle handle and into the cable housing.

I threaded the cable through the top of the throttle lever, from front to back, then around the groove in the handle and out the bottom of the lever assembly. Then I slid the threaded bushing over the cable and screwed it back into the throttle assembly, using Loctite 243 on the threads.

Note the steel barrel that is used to anchor the end of the cable in the choke lever

The choke cable is the longer of the two cables, with the cable bare on both ends. It goes through the left hole in the firewall, through the electrical panel, through the grommeted hole in the cockpit center tunnel, then loops under the floor behind the throttle quadrant and comes up through the left side of the quadrant from the rear, ending at the choke lever.

Having decided to use the larger steel barrel on the end of the choke cable, I first drilled the 6.5 mm hole for the barrel all the way through the choke lever. As delivered, this hole is only on the right side of the lever, but it needs to be extended through to permit the cable to line up with the hole through the barrel.

I slid the barrel into the choke lever, then lubricated the choke cable and housing, threaded the cable through the hole in the barrel and tightened the hex bolt in the barrel to secure the end of the cable. Then I pulled the slack out of the cable until it was seated in the groove around the choke lever and pushed the cable housing into the opening at the bottom of the choke lever assembly.

That completes the throttle and choke cable installation until the engine is mounted on the firewall.