Quickbuild: Behind the Scenes

As an amateur builder of a quickbuild airplane kit, I’ve always been interested in knowing more about the factory workers who assembled the rest of our airplane. I was recently able tour the Bearhawk kit factory in central Mexico, where Bearhawk Aircraft produces quickbuild kits for three different models: the Bearhawk 4-Place, Bearhawk Patrol, and Bearhawk LSA.

The factory was initially set up to make kits for the Bearhawk 4-Place, the oldest and largest of the three designs. Think of it as a modern-day replacement for a Cessna 170-180 class of airplane, depending on the builder’s engine choice. Later came the more recently designed Bearhawk Patrol, which is loosely categorized as a two-place Super Cub/Scout/Citabria alternative. The Bearhawk LSA is the newest design, a modern version of the lightweight two-place category of airplanes that were popular in the late 1940s like the Cub and Champ. All three are tailwheel airplanes with sheet-aluminum wings and fabric-covered steel tube fuselages.

This stack of ribs is in line for receiving lightening holes. Bob Barrows does not design planes based on ease of factory setup, and the lightening holes are of varying diameters, each requiring a different hole saw.

Builders are able to purchase plans for any of these aircraft directly from designer Bob Barrows, and then source raw materials to build a fine airplane. However, scratch building is a monumental investment of time and effort, and that is why there is demand for the quickbuild kits made by Bearhawk Aircraft.

While Bearhawk Aircraft and Bob Barrows’ R&B Aircraft are two separate companies, Bob is frequently involved with kit manufacturing as a consultant and advisor, and he has licensed Bearhawk Aircraft to build from his designs.

These shelves hold parts for flaps and ailerons in various stages of completion.

From Drawings to CNC

To understand how Bearhawk kits come together, it is best to start with how the Bearhawk types were designed in the first place. Bob did not design his planes to be built by automated CNC machinery in a factory production environment. He knew he was going to build them in his own shop. Airplanes are like any other tangible product—they must be designed with a fabricating strategy in mind. One can’t just sit down to the drawing board and draft an airplane without having some idea of what materials it is going to be made from or how they are going to go together.

Drill jigs like the ones on this wall help ensure correct hole alignment, both to minimize mistakes, and to make parts interchangeable.

Bob’s design priorities were minimizing weight, maximizing performance, and using construction techniques that he could execute with the tools in his shop. That shop doesn’t include a CNC milling machine or a huge forming press, so his designs do not require these tools. Instead, they go together with the builder’s hands, combined with a few fixtures that can be made in a modestly equipped shop.

This is the right wing of a Bearhawk Patrol in the jigging table that workers use to assemble a wing skeleton. The white vertical members hold the ribs in the correct position and location while workers match-drill the attaching angles at the front and rear spar.

Knowing that, it’s not surprising that the Bearhawk kits are made in Mexico. The kit factory is a facility that relies primarily on skilled manual labor, which is available for a much lower price in Mexico. This keeps the price of the finished kit much lower, which is a key to ensuring that the value exceeds the price. If the same results were to come from a factory staffed with workers in the U.S., the factory would need to get much more productivity out of the workers, likely by using computer-controlled machinery and more expensive tooling. This is problematic for a recreational aviation venture where sales volume is often far too low to justify such expensive production investment. In the case of the Bearhawk, high-volume production would require design changes that would compromise the original performance goals.

This orange jig is for the horizontal stabilizer on the Bearhawk Patrol. A leading edge tube is already in place, and the jig is ready for the chordwise ribs, which are formed to an airfoil shape out of 4130 steel. The slots in the top of the orange square tubes will receive the airfoil-shaped ribs and the tabs will hold the ribs vertical.

Quickbuilds Built From Scratch

Before my factory visit, I differentiated Bearhawk scratch builders from Bearhawk kit builders. But after the visit, I realized that all Bearhawks are built from scratch. Kit-built Bearhawks are just made from major assemblies that have been built by skilled professionals with access to tools and jigs. Bearhawk kit builders pay an additional investment for this service in the price of a kit, but interestingly, that cost premium is similar to the additional resale value that kitbuilt Bearhawks have been able to command over scratch-built Bearhawks.

Agustin Limon stands to the left of the black Bearhawk Patrol fuselage floor jig. The green cage in front of Jose Luis Martinez at the grinding wheel is also for the Bearhawk Patrol fuselage.

When new customers hear that the kits are made in Mexico, quality control is sometimes a concern. The old adage, “You get what you pay for,” is often true, and the workers in Mexico are certainly paid less than they would be paid if they were working in the U.S. However, the adage isn’t entirely true in this case. While the workers are paid less in Mexico, they are paid fairly well for what they do, where they are doing it. The factory is in an area of Mexico with a healthy manufacturing economy, and working in an airplane factory is a matter of pride for the employees. Turnover is very low, and the success of the operation depends heavily on the personal relationships and frequent communication between Mexico and the United States.

Mark Goldberg, owner of Bearhawk Aircraft, says, “There is no way I’d just go down to Mexico and hire strangers to build airplanes.” Mark has known the managers of the factory since 1971, long before they were working for him. This personal connection is the “secret sauce” that makes it possible for him to keep such a large foreign investment safe.

This chart above the steel tube storage rack shows the color coding for the wall tube thickness, along with a chart of arbitrarily-named “T sizes” that correspond to sizes referenced in the Bearhawk 4-Place plans.

The Quickbuild Team

The patriarch of the managing family is Angel Limon. Angel worked in a copper wire and electrical component factory for most of his career, in charge of fixing the production machinery. When a machine would break in that factory, they didn’t call the manufacturer or order parts. Instead, Angel would first determine what was wrong with a machine and then go to work in the machine shop fabricating what he needed to make the repair. His resourcefulness-by-necessity approach is visible in all parts of the Bearhawk factory, too, though his age and failing health limit his time in the factory these days. Angel’s sons, Agustin and Luis, manage the day-to-day operations of the factory. These are the guys that direct the hands-on workers on which tasks to complete in the short term, though with it being such a small operation, they also occasionally spend time working on the factory floor.

There are eight full-time front-line workers that report to Agustin and Luis. Most of these are some of the 200 employees that worked for Agustin in a furniture factory, which closed shortly before the Bearhawk factory opened. These front-line workers are fairly specialized. For example, Juan Vazquez makes flaps and ailerons. Oscar Gonzalez is the lead welder, and he handles the limited TIG welding, which includes aluminum fuel tanks, tail-feather finish welding, and a few other small parts. He is also an experienced fabricator and handles some of the tooling construction. The factory relies heavily on tooling and jigs, which make tasks easier for the workers. This isn’t because they aren’t smart or capable, but rather to minimize mistakes that might be costly to fix or dangerous if not noticed. Even in this type of repetitive production environment, the workers still rely on the corresponding set of plans and detailed notes.

These clever tube marking guides greatly expedite tube fitting. Notice how each of the oversized tubes has the correct fishmouth, allowing for an easy scribe mark transfer onto the tubing stock.

Tooling and Jigs

Tooling and jigs are a key ingredient to the factory’s success. The Bearhawk designs use a mix of welded-steel construction and riveted-aluminum construction, and the factory is organized to reflect this. All of the steel parts are tack-welded in heavy, rigid fixtures to ensure that they are dimensionally accurate. A scratch builder might, for example, make an engine mount by welding it in place on the fuselage. This method will generate a single accurate engine mount, but the mount will not necessarily be interchangeable with another Bearhawk. The factory tooling eliminates these sorts of problems, giving the kit customer some added value. First, he knows that the parts will be straight. Second, if he should need new parts in the future, he can get replacements from Bearhawk Aircraft and know that they will fit.

Notice how small the gap is on these fitted fuselage tubes. The semicircular gap at the top is to account for a vertical tube that will join the structure in the next jig.

Here is another fishmouth example, also showing a relieved area that will accept a vertical tube in the next jig. These tubes are fit very tightly, especially for a welded structure.

Each part, for each Bearhawk type, has a jig. This means that there are literally tons of tooling on the factory floor, mostly made from locally sourced mild steel. Production metals and hardware come from aerospace suppliers in the United States. Mark sources them as the factory needs them and orchestrates periodic shipments across the border. Some parts use a single simple jig and complexity goes up from there. A structure like the fuselage requires several. The floor and ceiling are each tack-welded in separate flat jigs, and then transferred to a large outer cage that will hold them in place while workers fit the vertical and diagonal tubes. Jose Luis Martinez, steel tube specialist, cuts the fishmouth on each tube as he builds up a part in its jig. A scratch builder would probably custom-cut each tube to length and slowly adjust the length and angle of the fishmouth for a tight fit. Jose Luis has the benefit of marking guides, which are made from two short lengths of tubing that have the same inside diameter as the outside diameter of the production part. These two short lengths are welded to a piece of square tube to position them parallel to each other and spaced to define the length of the finished tube. When he’s ready to make a particular tube, Jose Luis puts the raw material into this marking guide, clamps the material to the square tube near the middle, then scribes the ends to match the fishmouths on the guide. From there he visits the bandsaw and bench grinder to produce the final shape. The cut tube will usually not require any additional trimming or fitting before tack welding.

Lead welder Oscar Gonzalez is checking the alignment of a flap cable pulley mount. He has installed temporary pulleys and a short length of control cable to verify that the mount is at the correct angle.

Ruben Maravilla prepares the mainspar for a Bearhawk Patrol.

Tubing Selection

The biggest threat with tubing selection is mistaking the wall thickness. It will be pretty obvious if the worker selects the wrong outside diameter of tubing because it will not fit properly in the marking guide. But a wall thickness error will not be obvious in this case, so the folks who set up the factory knew that they would need a system to keep it all straight.

Whenever a new shipment comes into the factory, each piece of tube is checked for wall thickness with a caliper. They never trust the stamp on the tube. The verified stock is then painted with a temporary color code that will provide the first line of defense in construction. When a worker goes to the tubing stock rack to select a piece of material, he’ll still check it again with a caliper to make sure it is correct. The temporary marking paint will be removed during sandblasting, though much of it also burns off in finish welding.

The same jigging concept applies to other steel parts, such as seats, control sticks, tail feathers, landing-gear legs, and more.

Take note of the quality of these weld beads. While appearance of the weld bead alone is not a sufficient indicator of weld quality, these beads certainly show good craftsmanship.

Welding

Once the parts have been tack-welded in the jig with a MIG wire welder, someone like Jose Luis will begin finish welding. He’ll use the same techniques that a scratch builder would use, skipping around the areas of the part to minimize distortion. The finish weld bead will consume the small MIG-welded tackbeads. Almost all finish welding is by oxy-acetylene (O/A) flame torch. This method is slower than TIG, but with the factory’s business model, O/A welding makes better economic sense. There is a never-ending debate among homebuilders about which method is better, but I doubt many folks would be able to tell these factory O/A weld beads from TIG weld beads by sight. Look at the close-up pictures and see if you agree.

There are several quality control checks as the steel parts are welded, and the final check involves assembling all of the welded parts to verify proper alignment. After this check, the workers take everything apart and prep for paint. Steel parts are sandblasted and painted with a strontium chromate epoxy primer, then a topcoat epoxy paint. Customers of quickbuild kits will not need to do any further welding or painting, unless they attempt to modify the original configuration of the parts, such as by adding a skylight to the Bearhawk 4-Place, for example. This epoxy topcoat is suitable to accept any of the common fabric covering processes.

Working With Aluminum

The aluminum parts require an entirely different skill set and mindset. For structural parts, the factory only works with 2024-T3 alloy, which is heat treated and cannot be welded. The wings begin life on the spar table, where Ruben Maravilla starts with a spar web blank. The spar web is the portion of the spar that runs span-wise, oriented vertically. Each wing has two spars, a forward and rear, for a total of four per airplane. These are bent to a C shape, where the top and bottom of the C are riveted to the wingskin. These bends must be precisely located, since they determine the thickness of the wing, along with the height of the ribs. This bend requires a very large and heavy brake, which can be hard for a scratch builder to find. While scratch builders usually make ribs by hammering blanks over a wooden form block, the kit factory outsources rib production to a hydro-forming plant in the USA. Bearhawk Aircraft also sells these pre-bent spar webs and pre-formed ribs to some scratch builders, just because they save so much time and difficulty.

Here is what Oscar Gonzalez’s TIG welding looks like on a 5052 aluminum fuel tank destined for a Bearhawk LSA.

Ruben consults the plans for the appropriate airplane type and builds a “spar sandwich” that includes several cap strips of 1/8-inch thick aluminum. The sandwich is thickest at the wingroot and where the external strut joins the wing. In the outermost rib bays, there are not any layers at all since the tip section of the wing carries very little load. Ruben will locate and match-drill these and other pieces, then, just like a builder would have to do at home, he takes the whole assembly apart and deburrs all of the holes. Then the parts are prepped for paint, including Alumiprep etching, Alodine, and finally a coat of yellow epoxy strontium chromate primer. Only spar parts are Alumnipreped and Alodined, with the wingribs and wingskin interiors just receiving a clean scrub and primer treatment.

Riveting

When all of the spar parts are back from painting, Cesar Barojas and Pedro Maravilla set up the parts at the spar riveting table. They attach the spar to a table-based jig in the same orientation it will be in the wing and assemble the parts with clecos. Then they rivet the parts together in a systematic way, skipping around to minimize shifting and distortion. It takes most of an afternoon to get a painted spar riveted. Those two do almost all of the riveting, and they do it well. Watching them work was, well, riveting. They have been a team for over five years so, to the casual observer, it seems like they are communicating by radio waves.

Cesar Barojas (L) and Pedro Maravilla (R) prepare a section of wing top skin for the Bearhawk Patrol wing. The skins on the Bearhawk 4-Place are left unriveted on the top of the wing, but the bottom skins are left unriveted on the Bearhawk Patrol and Bearhawk LSA.

Pedro (L) and Cesar (R) attach nose ribs to the wing skeleton after it has been aligned in the wing skinning jig. Note the measuring strings that run spanwise.

Once the spar is riveted, Pedro and Cesar begin building a wing skeleton structure on a specially designed table. This assembly table holds the ribs and spars vertically, and then the parts are match-drilled, disassembled, deburred, and then reassembled with rivets. The factory floor includes a separate table for left and right wings for this step, and for each step thereafter.

After the skeleton structure is riveted, it is transferred to a very heavy vertical skinning jig. This jig suspends the structure in a way that workers can stretch strings and plumb lines to carefully align the parts. Here they attach nose ribs on the front of the mainspar and wrap 4-foot-wide skin sections that go from one side of the mainspar all the way around the leading edge and back to the rear spar. A shorter piece of skin will connect the remaining wing section from the mainspar to the rear spar. This section is match-drilled, deburred, and dimpled, but not riveted. The intent is for the end customer to rivet these sections after he or she has finished a few plumbing tasks inside of the wing.

Ruben Maravilla carefully trims rib spacer strips. Much of the spar’s strength is derived from the tight fit of parts like these. He checks each part and gently removes material as needed.

Juan Vazquez is the flap and aileron specialist. Here he is preparing the leading edge skin of a Bearhawk Patrol aileron. The kit customer will cover this aluminum structure with fabric and will only need to make minor adjustments to the trailing edge alignment before doing so.

Experience Counts

The workers in the factory benefit from all of these jigs and tools, but they also benefit from their own experience. Most homebuilders will say after their first airplane that they could build a second airplane to a higher quality in less time. Imagine how the average homebuilder would do if he had built over 100! Bob Barrows himself is an experienced builder, and he built the prototype Bearhawk LSA with 0.016 aluminum wing skins. Such thin material is very difficult to work with and make look nice with its tendency for oil canning. When Bob saw the first set of factory-riveted wings for a Bearhawk LSA kit, he commented that he wished he could make his own turn out that smooth.

There are many other steps and many other parts, but the techniques are mostly similar for those discussed.

The nearly completed fuselage is a surprisingly complex assembly, bristling with tabs, stringer standoffs, and various mounting plates. Here Jose Luis Martinez adds stringer standoffs on the left side of a Bearhawk Patrol fuselage.

This Bearhawk Patrol fuselage will be serial number 32. Fuselages are serialized, as are wings. After blasting and painting, this fuselage will receive a small oval-shaped brass plaque with a stamped serial number.

Ready for Shipping

Once all of the parts for a kit are ready, workers assemble a kit package, starting with a pair of wings that are secured in a set of custom-made steel boxes. These boxes protect the wings and also support the fuselage, which is packed on top. The many small parts including the tail feathers, control mechanisms, floorboards, and cowling metal are carefully packaged inside of the fuselage, and then the whole stack is stored in a warehouse until it is time to send a truck to Texas. Kits are stored in Texas until they are delivered by road to customers in the U.S., or packed into oceangoing shipping containers for customers around the world.

To date, Bearhawk Aircraft has sent kits to six continents, and all have originated from the same factory. As I stood next to the Bearhawk 4-Place fuselage jig, I knew that my own fuselage #60 was made in that very jig. There have been many other fuselages made since then, and they have found homes far and wide. I’m always interested in touring manufacturing facilities, but it was especially worthwhile to see the birthplace of parts that have in some ways become a part of our family. Someday I would love to participate in a group flight of Bearhawks to visit the factory and offer rides to the guys who built so much of our airplanes.

Augustin Limon consults with Mark Goldberg about a shipment of parts that is destined to be in stock in Texas, ready to ship to scratch builders who buy some of the more complicated parts, but do not buy whole kits.

Mark Goldberg shows off three Bearhawk LSA kits ready to ship to Texas, along with a set of Bearhawk 4-Place wings. In several instances, Bearhawk Aircraft has shipped new wings to customers with flying aircraft that have been damaged.