Building a Bearhawk
Each of the Bearhawk airplanes has a fabric-covered steel tube fuselage, with skinned aluminum wings. Bob Barrows designed the airplanes intentionally with these characteristics. The steel tube fuselage structure provides the most favorable combination of strength, durability, light weight, and crashworthiness. The wings are fully sheeted with aluminum for the same reasons, but also because of dimensional accuracy. Bob knows that small changes to the shape of an airfoil can make a big difference, and usually not for the better. Aluminum skin keeps the wing shape constant when compared to a fabric wing, especially at the higher cruise speeds the Bearhawk is capable of.
Building a Bearhawk from a Quick-Build kit is a big job, but it’s a great source of education and recreation. You can build a Bearhawk without a kit, and while so many of the tedious and repetitive tasks are already completed at the factory, there is still plenty of building to do. Airplanes built from Quick-Build kits are straight, and the builder doesn’t require any jigs to finish. The fuselage and other steel parts are fully welded in heavy fixtures, which means that the parts match the plans, but it also means that the parts match each other. If the need should arise for a replacement part in the future, those parts will match too. The wing structure is complete, and the skins are riveted from the bottom of the main spar, up around the leading edge, and back to the top of the rear spar. The remaining section of lower skin is not yet riveted, but the holes are drilled to final size, deburred, and dimpled. As are the ribs underneath. This allows the builder easier access to install the aileron and flap mechanisms (the Bearhawk LSA omits the flaps), along with optional auxiliary fuel tanks, and any wires or plumbing the builder desires. The wing attach fittings have been carefully match-drilled to the fuselage, and the wing struts have been custom made to length, ensuring that the dihedral and incidence are correct from the factory.
There are several starting points in the project, depending on the builder’s work space and priorities. If starting with the wings, steps include adding nutplates for the wing inspection panels and fuel tank bay covers, installing the ailerons and flaps, and a few small sheet metal tasks around the trailing edge and wing root. Once the process is far enough along, it’s time to rivet the remaining section of the wing skin closed, install the tips, and prep for paint. The wing control surfaces are fabric-covered to save weight, and they can be covered now, or later on when covering the fuselage and tail parts.
In the factory, the fuselage is fully welded, including the primary 4130 steel tube structure, and also key structural points like the wing and main landing gear attach points, plus a myriad of various mounting tabs for the fuselage stringers, floorboards, firewall, and more. Once welded, the steel parts are media blasted down to clean, bare metal, then primed with a MIL spec epoxy strontium chromate primer. Then on steel parts the epoxy primer coat is top coated with a gray epoxy paint which can be left as-is, or top-coated if the builder would like to have a particular color on the few exposed tubes in the cabin. The gray top coat paint is compatible with all known fabric covering systems, so the tail surfaces can be covered without any additional paint. The builder will spend time bolting on the landing gear legs and oil-dampened spring shock struts. If space allows, it only takes a few hours to get the fuselage on its wheels, though some builders prefer to make a rotisserie for working on the fuselage, postponing the landing gear installation. If building in a single car garage bay, this latter strategy will probably be necessary. Several parts bolt onto the fuselage, including the horizontal stabilizer, elevator, rudder, and trim mechanisms. The control stick, flap handle, rudder pedals, brake pedals, windows and doors, all bolt in place, along with a few other parts. These come completely welded and painted, just like the fuselage and tail surfaces.
The area between the instrument panel and the firewall is called the boot cowl. This area is made from aluminum sheets, and a section of stainless steel on the bottom, where the exhaust pipes exit the cowling. Once the firewall and instrument panel are installed, this boot cowl section can be fabricated from the slightly oversized pieces that are provided with the kit. From there, the engine and prop can be mounted, then the builder constructs the cowl from the nosebowl aft, ensuring a good fit between the cowl and spinner.
It is advantageous to build as much as possible before covering the fuselage, because once the covering goes on, access requires more acrobatics on the part of the builder. Depending on the covering process that the builder selects, the fuselage may have a sewn fabric envelope, or may be covered from large pieces. Many builders also cover the interior of the cabin with the same type of fabric, which makes for a lightweight and clean interior. Polyfiber, Stewart System, Air Tech, and Oratex are all popular choices for fabric systems.
After covering and paint, it’s time to move to a hangar for final assembly. Seats will need covers and foam. There are companies we can connect you with who can provide turn-key seat covers and foam, or you can make them yourself.
Similarly, some builders install their own avionics and instrument panel, and some hire a specialist. The Bearhawk airplanes are renowned for their versatility, being anything from a sturdy off-road airplane to a luxury cross-country machine. Simple instrument panels provide lightweight utility, while modern integrated avionics systems provide features and utility that run circles around the options available for “store bought” Type-Certificated airplanes.
Once the airplane is ready for flight, a meeting with the local FAA FSDO or a DAR will complete the paperwork, and Phase 1 of the flight testing period begins. In this period, the test pilot will validate and document the performance and capabilities of the airplane, completing at least the minimum number of hours specified by the regulator. Often this is 25 or 40 hours, depending on the type of engine and propeller used. Once in Phase 2, the airplane is ready to use! Load it up with gear and folks for a weekend to somewhere inaccessible, take it to a pancake breakfast or a fly-in, or just take a short hop in those last few minutes of the day, when the air gets smooth and the light gets soft.