Bucker Bu-133 Jungmeister

Model Airplane News, Mar 2000 by Allen, Gary

A classic 1/3-scale aerobatic biplane

With two wings and a round engine, the Bucker Bu-133 Jungmeister, designed as an advanced aerobatic single-seat trainer, is truly the epitome of an aerobatic biplane. This masterpiece of Carl Bucker's German company, Bucker Flugzeugbau GmbH, rolled out of the factory in early 1935, two years after the introduction of the company's highly successful two-seat biplane trainer, the Bu-131 Jungmann.

The design of these legendary aircraft resulted from Bucker's collaboration with his brilliant young Swedish engineer, Anders J. Andersson. The two aircraft were very similar in design and construction, and they shared many jigs and components. Both aircraft were commercially successful and certainly provided a major inspiration for Curtis Pitts' design of the Pitts Special.

The only intended deviation from scale in my design is the wing airfoil. I elected to use a semisymmetrical section rather than the scale, flat-bottom section. All other outlines and sections are intended to be exact scale.

My design features standard balsa and aircraft ply construction and uses standard hobby shop and hardware store items. All the fittings are fabricated by hand from brass sheets. The cabane struts are fashioned from hardware store aluminum, and the interplane struts from hobby shop streamlined tubes. I actually built two identical models simultaneously. One is intended for fun scale and is relatively undetailed; the other is covered with fabric, painted and fully detailed. The fun scale version weighs 21 pounds, and the fully detailed version weighs an additional 9 ounces.

CONSTRUCTION

Construction is reasonably straightforward, and the expeperienced builder shouldn't require detailed, step-by-step instructions. It's important that the steps be performed in sequence, however.

Make two fuselage sides directly over the plans. Note that the longerons are 1/4 x 3/8-inch spruce. Be sure to add the vertical-grain-1/4 inch balsa fill, and use epoxy to attach the various 1/4-inch ply parts, for example, the nose piece, F-15; the cabane mounts, F-18 and F-19; and the lower wing mount, F-21. Making a right and a left side, add the 1/16inch ply doublers and gussets, then epoxy F-20 into place to finish the rear cabane strut mount.

Fabricate the landing-gear mounts out of 1/4-inch ply as shown. Cut, and drill the 1/16-inch brass landing-gear straps, then, using as guides, drill the landing-gear mounting holes to accommodate 6-32 bolts. Install the blind nuts at this time. Fabricate the F-3 and F-6 for mer assemblies as shown in the cross-sections.

Using slow-setting epoxy, assemble the two fuselage sides with for mer assemblies F-3 and F-6 and the front and rear landing- gear assemblies. Check to ensure everything is square and properly aligned. After the epoxy has set, add the 1/4-inch-square spruce cross-members between F-3 and F-6. Epoxy the four F-22 formers into place, then epoxy the identical top and bottom nose pieces, F-16, and the two firewall mount pieces, F-17, as well. Use clamps to hold everything in place while the epoxy sets. Again, it is important to ensure that everything is properly aligned. For easy reference, I marked the centerline on all top members. After the epoxy has set, hammer in the small reinforcement nails as shown. Add 1/4-inch cross-grain balsa fil from F-15 to F-3, from the fuselage top to the front landing-gear mount on the bottom.

Pull the Tear fuselage sides together and glue the tail post into place Add the V4-inch-square balsa cross-members and gussets as shown. In the plans. Add a 3-inch length of 1/4-inch cross-grain balsa fill by the rear landing-gear mount as shown. Add the nose former F-4 and F-5. and add the stringers. Then add the rear formers, F-7 to F-14. Note that F-8 and F-9 are glued together. Next, add the stringers, but don't add the N-inch balsa sheeting at this point. Install the tailwheel mount bracket (a 1/2A steerable nose-wheel mount) on F-24, then glue the former in the fuselage and add the 1/4-inch balsa gussets. Epoxy into place the stabilizer mounts, F-25 and F-26, and add the 1/4inch-square balsa fill as shown in the plan top view. Add the 1/8-inch balsa sheeting, cut out the exits for the elevator and rudder pushrods, then set in place the 1/2inch-square, 1/8-inch ply pieces to accept the tail-shroud mounting screws.

Epoxy the 1/4-inch ply tail-brace mount to the bottom of the tail post, then fabricate the removable bottom tail hatch from balsa and 1/16-inch ply as shown. Removal of this hatch from the finished model provides access to the steerable tailwheel mechanism, the stabilizer mounting bolts and the pushrod exits.

Now fabricate the bottom wing center section. In preparation, stack pairs of the top and bottom 1/8-inch ply end ribs (two W-5 and W-6 pairs for the top wing and two W-511 and W-613 pairs for the bottom wing). Mark and drill the front and rear holes for the 5/16-inch fiberglass arrowshaft, wing-mounting studs as shown in the plan. Keep the rib pairs matched for the remainder of the construction.