The Independence Project: We Start the Finish Kit

Little systems mean big projects on the RV-12.



At the end of the Finish Kit process, with its completed canopy removed, the RV-12 airframe is nearly ready for the addition of the avionics and power packages.

When last visited, the Van’s RV-12 project looked like an airplane—minus a few necessities such as landing gear and canopy. Also missing were the engine, propeller and avionics. They still are.

This time we will tackle the RV-12 Finish Kit, which includes everything else to complete the airframe itself, from the wheels and tires to pre-made upholstered seats in the builder’s choice of trim colors. In the order noted in the building instructions, tasks this time include wing attachment, wiring harnesses, flight controls, seat parts plus crew restraints, the canopy, landing gear, fuel tank and the engine cowl. Following the procedure recommended by the manufacturer, we began this segment with an inventory of the parts. A few things were omitted but they soon arrived, and we were ready to proceed.

Initial fitting of the wings onto the fuselage is one of the first steps in this fourth segment of the Van’s RV-12 kit.

Winging It

A major feature of the RV-12 is easily removable wings so that the airplane may be trailered and kept at home instead of in a hangar. Two people can install or remove the wings in less than 5 minutes. Two large steel pins hold the crossing wingspar root ends to each other and to the fuselage. Sailplanes have used this configuration for more than 40 years.

The RV-12 includes an electrical system to guarantee the pins are in place before the engine can be started, and that is where Finish Kit construction begins. A magnet is epoxied in the handle on each wing pin, and a reed switch installed in the side canopy rail detects the magnet in each handle, closing its switch. The two switches are in series, and the circuit must be complete to start the engine, though there is an override in case the system does not work. The wingpin detection system, by the way, has no effect on engine ignition, just on the starter.

Receiving one of the first Finish Kits, I had a problem getting the reed switches to close. The fix was a slight repositioning of the magnets in each handle, and a resulting change to the kit instructions. First wing attachment also required trimming the inboard end of the flaperons to clear the fuselage sides.

Wiring It

The kit comes with wiring harnesses mostly made up. There’s a lot of wire, and some of the bundles require attaching a connector at one end. The builder will experience crimping wires to tiny pins that are inserted in some of the connectors, and a tool is supplied to detach pins that have been inserted incorrectly. I used the tool a few times.

Two large hollow steel pins, each with a small handle containing a magnet for sensing correct pin placement, hold the wings to the fuselage and to each other.

The wiring for several RV-12 options is in the harness set, including a cable for the Dynon autopilot option. Consisting of seven color-coded wires twisted together, the cable was described in the manual as 75 inches long, which it was. The problem was that 85 inches of cable is needed. The joy of being an early builder reared its head again; my discovery resulted in a change to the cable and a two-week wait for a replacement, which was no problem as there was plenty more to do.

Supplied wiring includes the automatic wingroot connections for optional wingtip lighting and strobes. Overall wiring instructions require 15 pages in the manual and took more than a week to complete. Dual headset jacks and dual push-to-talk switch wiring on the ends of the temporarily installed control sticks are in this package. Getting wires through the control sticks was a challenge, because both sticks have a 90° turn followed by a U-shape curve. After unsuccessful attempts to push a slightly flexible wire through, I succeeded by using a string with several split-lead fishing line weights on one end. An even easier way suggested by one builder is to tie a small cloth to the end of a string and suck it through using a vacuum cleaner.

Flight Controls

This easiest part of this section requires installing the brake cylinder reservoir forward of the firewall and hooking up the plastic brake lines to it. Strings previously taped into the tail cone make it easy to pull pre-made rudder and stabilator cables through the airframe.

Not so easy was fabrication of the flaperon system including a mixer, the flap handle with its position-locking device, five pushrods and flaperon torque arms that drive the inboard ends of the flaperons. Routing wire bundles so they would not interfere with the flaperon system and adjusting everything to work reliably and smoothly took more than a few minutes.

To set the angle of the flaperon torque drive tubes, the wings were attached. Flaperons were held neutral with spring clamps while a pilot hole was drilled in the left and right tubes that telescope into the flaperon drive system. A bolt installed temporarily in the flaperon drive holds the sticks neutral laterally while the pilot holes are drilled. Much of this system is disassembled for final drilling to bolt size, and I bought a small 3⁄8-inch, variable-angle ratchet wrench (Pittsburgh Professional brand at Harbor Freight). This tool greatly eased the left and right side “put-together, take-apart, put-back-together” chore.

Stabilator cable turnbuckles are adjusted separately for length and together for proper tension, 35 to 45 pounds.

Connecting rudder cables between the pedal fittings and the rudder horn was easy, but the stabilator cables require more effort. A pair of pulleys is installed in the stabilator cable circuit, and the cables are tensioned to 35 to 45 pounds using turnbuckles accessible through inspection holes on the fuselage bottom. Cable tension is important, and professional tension meters are expensive. I was fortunate and borrowed one. Other options are EAA chapters or renting one from an airframe shop.

Getting hands and arms up through the inspection holes to attach, tension and lock the cables with their turnbuckles can be uncomfortable. I positioned a small lamp inside the tail cone, wore a long-sleeve flannel shirt and thin gloves to minimize blood loss and fabricated the recommended tool for this operation. The manual shows how to use coat hanger wire to form a tool that keeps the two ends of the two-part stabilator cable from turning while tensioning the turnbuckle barrel with a short stiff wire or tool. Lying on a comfortable pad (furniture blankets in my case), expecting this process to take more than an hour because you had better work slowly, and programming some soothing music should get you through this.

It’s time-consuming because there are two sets of cables to attach and then test. Full stick throw in pitch must cause the stabilator to reach its up and down stops before the control stick torque tube gets to its stops. If a stick stop is reached before the stabilator stops, one cable will have to be loosened and the other tightened. Tension will have to be rechecked and probably adjusted after achieving the stabilator-stop requirement.

With everything tensioned and set, pairs of stainless-steel locking clips are inserted into the turnbuckle ends to prevent their rotation. I did most of this by feel rather than sight, but the clips snapped into place more easily than I thought they would. I managed to suppress shouts of joy when each clip clicked into place.


My opinion is that portions of this next section are best left until the airframe is essentially complete, which is a couple of major steps away. For example, cockpit and wingwalk nonskid should probably be delayed, especially if the wings are going to be painted. I also delayed installation of the shoulder harnesses, knowing the fuel tank would sit below the right occupant’s harness. As it turned out, the tank goes in and out easily, so the seatbelt system might as well be attached at this point.

On the other hand, installing the seat upholstery before completing the landing-gear attachment makes little sense, but you could set the custom-color, nicely finished seat components in place temporarily for “cockpit familiarization,” also known as sitting there making airplane noises.

One of the tasks is to attach the wings and mark the fuselage for applying wingroot air seal foam tape. By this point, you and a helper will be getting good at installing and removing the wings. With wing-attach skills in top form, invite and amaze your aviation friends. Expect a yawn from glider pilots, however.

This section includes screwing floor and rear bulkhead panels in place, and I complied. However, it’s likely that whoever does the compliance inspection for licensing will want to look at all the work under and behind those panels, so my electric screwdriver is likely to get another workout or two.

With control sticks temporarily installed, the area under the seats becomes crowded. Note the flap handle on the left. The wood fixture holds rudder pedals for proper cable routing.

The Canopy

Every experienced RV homebuilder, it seems, dreads canopy installation because it is fraught with drudgery and danger. The danger is that you will crack the canopy, destroying a really expensive part that is also pricey to ship. Yet I don’t know anyone who admits to having broken one.

Unlike most canopies for Van’s aircraft, the RV-12’s bonnet comes nearly trimmed to final shape, and the welded aluminum frame requires little preparation. It is placed in position on the fuselage using supplied wood spacers between the aft canopy frame and the roll-bar leading edge, and corrugated cardboard is used on the sides of the frame to maintain clearance from the cockpit rails.

For trimming the aft edge of this canopy, with trepidation I used a 3-inch cutting wheel at medium speed on a pneumatic die grinder. It worked. A set of Plexiglas (acrylic) drills that I tried on a scrap of thin acrylic also made perfect holes without cracking. Confidence built.

Doug Davis reacts to noisy yet successful separation of the fiberglass canopy fairing from the metal cowl, thanks to the packing tape/paste wax parting agent.

Many steps took us from this point to the smooth fiberglass leading-edge canopy fairing made of a 20-piece glass cloth layup. I’ll spare a lot of detail here except for two exciting procedures: First, bottom canopy sides are drilled while a volunteer not likely to have a claustrophobic attack (the manual cautions) is locked inside to back up the drilling with a wood block. I volunteered, and my helpers decided to release me shortly after completion of this 5-minute step.

Second, the fiberglass fairing made of 20 pieces of builder-supplied glass cloth is bonded to the leading edge of the acrylic canopy and formed tightly against the top of the metal cowl forward of the instrument panel. Separating the wet fiberglass layup from the metal cowl is a layer of clear plastic packing tape that is waxed with ordinary paste car polish—the parting agent in this process. If, after the fiberglass cures, the parting agent fails and the fiberglass sticks to the metal cowl, there’s a major glitch, close to a personal version of “Houston, we have a problem.” But as advertised, the fairing popped free with quite a noise as we raised the canopy on its hinges. Be still, my heart!

Altogether, more than a week of work went into the manual’s 15 pages of canopy building. Epoxy resin and flox or microballoons followed by quick-curing, easily sanded light auto body putty, and several hours of sanding had the fairing ready for primer and paint. The canopy project also included fitting its latch. At one point in the process, the latch handle got stuck with the canopy down. Panic was only momentary, however. Removing the outside handle with a Phillips screwdriver allowed a reprieve and further adjustments.

Landing Gear

All three RV-12 tires are 5.00×5, six ply. Two-piece wheels and Matco hydraulic brakes make up the differential braking and steering system. Landing-gear legs are bolted to the carry-through I-beam, and aluminum-tube brake lines are formed by hand, flared for hydraulic fittings and routed down each maingear leg. Two tries per side at filling the brake lines with fluid resulted in air-free hydraulics. Get those bubbles out!

The powder-coated nosegear unit comes ready to bolt in place. Sharp edges on the factory-made nosegear fork were smoothed with a file, and swivel tension was adjusted by the large bottom nut that compresses two concave washers. A fish scale found among my late father’s tools goes to 50 pounds and allowed adjustment of the fork to the required 26 pounds of side force to move it. I’d be surprised if Dad ever caught a fish weighing more than 2 pounds.

Fuel Tank

As I write this, the 20-gallon RV-12 fuel tank solution is to be revealed later. Made of sheet metal, it is easy enough to build, but it involves using tank sealant (not supplied because of short shelf life) often called Pro-Seal, a particular brand.

Experienced RV builders (referred to as repeat offenders at the factory but given a 3% kit discount for their loyalty) have criticized the tank, many preferring a manufactured unit, maybe made of plastic. I’ve defended the do-it-yourself metal version as complying with primary RV-12 goals: lightness and low cost. Cost, however, is beginning to add up if you include builders’ time and frustration.

The tank contains two fuel-measuring devices: an electric float gauge that varies resistance with the level of the in-tank float and an acrylic-window sight gauge that could be used to calibrate the electric gauge during initial fill-up. However, the sight gauge (on the left rear corner of the tank) can’t be seen in flight from either seat, and it also cannot be viewed during fueling.

Van’s supplies special closed-end pulled rivets for tank construction and good instructions for sealing. An air pressure test kit is also supplied, but not the party balloon or rubber glove that can be used to gauge air tightness. My first air test of the system indicated a leak-free tank. But putting 17 gallons of gasoline in the tank revealed a tiny leak at the bottom of the acrylic sight gauge. The test gasoline went into cars, and application of tank sealant to the outside of the bottom sight gauge holes fixed the leak. A five-day air pressure test and more test gasoline confirmed that we had a sealed tank.

Then came word from Van’s that acrylic on the year-old red RV-12 prototype’s sight gauge was crazing in the presence of gasoline, and a new solution was being sought. I’ll reveal the solution in a subsequent installment.

Finally, the Engine Cowl

Several friends helped with various parts of the two-piece fiberglass engine cowl project, including the oil door installation and trimming along the scribe lines. From that perspective, cowl construction has been far easier than I anticipated. That’s due to really high-quality fiberglass parts and accuracy of the scribe lines.

Piano hinge halves riveted to cowl edges and a handful of nutplates completed the mechanics of attaching the upper and lower cowl parts to the airplane and to each other. Unfortunately, I mounted the left and right nutplates closest to the propeller too far inboard; their screws will be covered by the spinner. Problems of this sort are easy to correct in fiberglass parts, however, and the evidence has been eliminated with some tiny pieces of fiberglass cloth, resin and filler.

At the end of this section, the cowl isn’t quite complete because the factory recommends not priming or painting it until engine systems are installed. The translucent cowl parts will allow positioning some power-system parts easily.

Only two people are needed to attach or detach the wings, but supervision the first time by many friends is comforting.

What’s to Come?

In the next installment, we’ll find out whether the Rotax 912ULS engine and Sensenich propeller package became available. Or was it the avionics suite complete with the Dynon FlightDEK-D180 EFIS/engine monitor, switches, fuse block, transponder, transceiver, intercom and ELT that came next? In either case, we are at the point of anticipating a big dig into the wallet.

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Dave Martin
Dave Martin served as editor of this magazine for 17 years and began aviation journalism evaluating ultralights in the early ’80s. A former CFI (airplanes, gliders, instruments), he'd flown more than 160 aircraft types plus 60 ultralights (including a single-seat, no-basket hot air balloon). Dave passed away in June, 2021.


  1. Hi Dave,

    Great article. By chance did you have a project schefule that was followed for this project. Is this something you would mind sharing? I am involved in an RV12iS build that will start as soon as the kit arrives.

    Please let me know if you can help.


    Dan McCarthy


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