Texan II
by Bob Isaacks
Rubber-scale modelers are always in search of the “perfect subject.” The modeled airplane must be charismatic, well documented, and, most important, possess good areas and moments to assure successful flight performance. Additionally, the aircraft must offer some promise of ease of construction as the plans are developed. The Raytheon/Beechcraft Texan II, a turbo-powered trainer currently in use by the U.S. Air Force, meets all of these requirements.
I live in Katy, Texas, and own a ranch near Del Rio, Texas, home of the 47th Flying Training Wing at Laughlin Air Force Base. Texan IIs are constantly in the air around Del Rio, and I spent several hours watching the sleek trainers shoot approaches and practice touch-and-gos at Laughlin. I made contact with Captain Ken Hall, chief of public affairs at Laughlin, and Kent Cummings, chief of community and media relations, who allowed me to take photos of a Texan II on the flightline for authentication of the model I present here. My thanks to the personnel at Laughlin—especially Carl Riordan, T‑6 maintenance work leader, and Mark Escobar, aircraft sign painter—who were very cooperative in helping me obtain some details not currently available on the Internet.
The Texan II is a development/redesign of the Pilatus PC‑9, a trainer several countries currently use. With slight modifications to the fins and canopy framing, the model in this feature can be built as a PC‑9; a Google search will yield a myriad of appealing PC‑9 color schemes. While researching the Texan II, I found references indicating that the Pilatus is a direct descendant of the Arado Ar.96 German World War II trainer. My last article in Model Aviation (December 2005) was about an Ar.96—the design similarities are astonishing, and the Arado was conceived in 1938.
CONSTRUCTION
A quick glance at the Texan II’s plans reveals low wing placement, ideal for conversion to an RC electric-powered park flyer. There is plenty of room for miniature servos, and the rudder and elevator surfaces can be hinged by simply doubling their respective spars. For rubber-power enthusiasts, the CG sits almost exactly halfway between the model’s rear peg and nose—perfect for a long motor.
- Type: Scale rubber-powered free flight
- Skill level: Intermediate
- Wingspan: 25.25 inches
- Wing area: 120 square inches
- Airfoil: Wing, modified Neelmeyer; stabilizer, 5% cambered
- Length: 25 inches
- Weight without rubber: 50 grams
- Motor: Three loops of 1/8-inch Tan Super Sport, 40 inches long, braided
- Construction: Primarily balsa with 1/32-inch plywood reinforcement
- Propeller: Hand-carved balsa with 1:1-1/4 pitch-to-diameter ratio
- Finish: Esaki tissue, dope for color
- Trim: Right/right
Fuselage
The fuselage build is based on the conventional box/former method. All components are constructed from 1/16-inch balsa except for the nose blocks. Pin down and build one fuselage side on top of the other so that symmetry is assured; note that all verticals on the box are the same length. I made a stop on a miter box and cut all the verticals at one time. The rear peg support can be cut at the same time as the 1/16 uprights.
The fuselage longerons are straight except for the rear of the top longeron; it can be notched and “cracked” to match the fuselage/rudder rear line. After the sides are completed and separated, pin them to the top view on the plans and add the crosspieces in the cabin area. Use a square to keep the sides vertical and true. When the cement is dry on the crosspieces, glue the tail and front crosspieces in place, making sure the nose and tail are square and centered on the plans. Add the remaining crosspieces, front and rear, checking for squareness at each station.
At this point spray the completed structure with a mist of water while it is still pinned down to relieve any built-in stresses in the balsa construction. This results in a true fuselage.
When the stress-relieved structure is dry, add the bottom formers, front to rear. The formers are purposely slightly oversize. I typically make a copy of each former on bond paper and use rubber cement to attach the copy to the appropriate thickness of balsa sheet. After cutting the formers from the sheet, peel off the paper copy and rub away any rubber cement residue.
Center the oversize formers on each station, allow them to dry, then sand them to blend perfectly with the fuselage sides and each other. Add the center stringer, ensuring it is straight front to rear, then add the remaining stringers, alternating from side to side and measuring to assure symmetry. I use a small Swiss file to notch the formers for a perfect fit.
After the bottom stringers are in place and dry, remove/unpin the fuselage from the plans and add the top formers in the same manner as the bottom. The cockpit flooring is made from extremely light 1/32-inch balsa, applied cross-grained to the box. Laminate 1/8-inch balsa for the nose block and add it and the bottom chin block to the fuselage. Leave these components slightly oversize, add the 1/32-inch plywood nose ring to the front of the assembly, and carefully sand/blend them to the fuselage, using the plans and photos for correct side and top profile.
I drilled the initial undersized hole for the nose plug using a router bit with a Dremel tool, then finished/sized the hole using a sandpaper-wrapped dowel.
The exhaust stacks are made from scrap balsa as thick as the widest portion of the exhaust. Make copies of the top view of the exhausts on bond paper, rubber-cement them to the scrap balsa, and jigsaw them to shape. Carve and sand away anything that does not look like an exhaust stack; use a Dremel cutter to hollow out the stacks’ interior. The stacks are a signature feature of the Texan, so take time to shape them correctly. I used a circle template to inscribe a ring on the inner portion of the exhaust where it attaches to the fuselage; carving/sanding to that circle yields the desired profile.
Spinner: Use a Dremel tool. Cut a piece of 1/32-inch plywood slightly larger than 1 3/8 inches in diameter. Mount it on a Dremel arbor (the abrasive-disc arbor) and sand it to exactly 1 3/8 inches. Add an oversized balsa block to the plywood disc using Ambroid or Duco cement (you will need to rout out a small recess in the center of the block to clear the arbor screw). Give the glue plenty of time to dry. Rough-shape the spinner block with an X-Acto before spinning it up, then use a sanding block and light pressure to shape the spinner, comparing its profile to the plans. Wear eye protection.
Nose plug: Make from laminated 1/8-inch sheet. I made an oversize lamination and used it for both the nose block and the nose plug. The nose plug is made the same way as the spinner: spin/sand a plywood disk to size (3/4 inch), glue the oversized laminated balsa plug to the disk, and spin it to size while checking fit to the nose block. Fit a 1 3/8-inch-diameter 1/32-inch plywood disk to the front of the plug and glue it.
Drill the nose plug on center with the other end of the plug resting on a 4 1/4° wedge. When rotated correctly, the plug will yield the desired 3° of downthrust and right thrust. Install a brass tubing bushing with an ID matching the propeller-shaft OD in the drilled hole, and the nose plug is complete.
Wing
Make a rib template from 1/16-inch plywood by copying the root rib on bond paper, rubber-cementing the reproduction to the plywood, jigsawing the template, and carefully sanding it to the exact profile. Drive two straight pins through the template so they project 1/16 inch below the bottom surface, secure them with CA, and cut them off above the top surface. These pins hold the template to the balsa thicknesses so you can carefully cut around the template with an X-Acto.
Cut every rib using the same template. Make smaller/shorter ribs by rotating the template TE-down to achieve the length measured from the plans; the point of rotation is the center of the LE notch.
Pin down the TE along its entire length and add the ribs, making sure they are square to the building board. Add the LE in the fish-mouth front of the ribs and the wingtips. When that assembly is dry, remove it from the building board and sight over the top of the ribs to ensure a uniform taper from root to wingtip.
Use a long sanding block to remove high spots in the upper camber of the wing. Mark the spar locations with a steel straightedge and notch the ribs for the spars with a small Swiss file. Glue the spars in place except for the bottom spar on the outer wing sections. To ensure washout (TE high at the wingtips) is permanently built into the structure, pin the LE down and raise the TE using the wedge shown on the plans. Glue the bottom spar in place.
Sand a bevel on the outer wing-panel LE, TE, and spars to allow for the 2-inch dihedral on each panel. Glue the outer wing panels in place, measuring to ensure equal dihedral on each side. Add dihedral braces and gussets, give the wing a final touch-up sanding, and the wing is finished.
Tail Feathers
Build the tail surfaces similarly to the wing, with one exception: the rudder has a symmetrical airfoil, so shim the LE and TE off the building board before adding the ribs. The stabilizer is flat-bottomed and can be pinned directly to the board. After gluing in the ribs, airfoil the stabilizer (top surface only is cambered) and airfoil the rudder on both sides. Cut the stabilizer strakes and rudder forward fin, sand the appropriate edges, and the tail surfaces are ready to cover.
Propeller
Carve the propeller by hand using the profile shown on the plans. Jigsaw the top “bowtie” profile and drill a 3/32-inch-diameter hole in the center. Jigsaw the side profile. Begin carving with the back of the propeller, carefully moving across corners; go slowly and ensure both undersides are carved to match. Use a small balsa sanding block with a 5% arc on its upper surface to sand in a slight undercamber on the blades.
Carve a camber on the top surface by feel to attain the same thickness on both blades. Spin/sand a 1 3/8-inch-diameter 1/32-inch plywood backplate and enlarge the center hole to 3/32 inch. Install the propeller on the backplate using 3/32-inch OD brass tubing to bush both backplate and propeller, then install a larger brass-tube “clutch” over the bushing.
Add the hollowed-out balsa spinner or a vacuum-formed version after finishing the propeller, backplate, nose plug, shaft, and bearing assembly. See the plans/sketches for reference.
Finishing
The traditional nitrate dope and Esaki tissue method was used to finish the Texan. Prepare all surfaces by coating every area that will contact the tissue with several coats of nitrate dope, sanding after the first coat. Apply enough dope so the surfaces appear glossy.
Apply white Esaki tissue wet, using 70% alcohol as the wetting agent. Use thinner brushed through the tissue to adhere it to the airframe, applying thinner only to the periphery of the surface being covered. This allows the wet tissue to shrink evenly and yields a superior, wrinkle-free covering. Tissue overlaps require a second coat of dope on the overlapped surface to get the added tissue piece to adhere properly.
After the tissue is stretched and dry, brush it with a coat of nitrate thinned 50%. The red stripe on the fuselage is a piece of red Esaki applied with thinner and given a coat of the 50/50 nitrate. The blue fuselage bottom, wing underside, top chevrons, and stabilizer were airbrushed using the pigment from Dark Blue Floquil model-train paint mixed into nitrate thinner and added to clear nitrate dope. The wing, stabilizer, and rudder LEs were airbrushed with Old Silver Floquil in the same manner. Use frisket paper to mask surfaces for all airbrushing.
Trim the canopy and attach it to the finished model with Pacer Formula 560 Canopy Glue. The spinner, vacuum-formed from .030-inch Vivak, was airbrushed on the inside with chrome enamel designed for model-car bodies, then coated with flat-black enamel for a deep polished look. Glue the spinner to the propeller backplate with Formula 560.
Give the propeller several coats of clear nitrate mixed with talc to fill the balsa grain. Airbrush it with flat-black enamel and paint the tips flat white.
I have vacuum-formed canopies, spinners, and water-slide decals for the Texan, as well as a tissue-covering DVD for aeromodellers. I will also provide construction assistance via e-mail—please preface all correspondence with "Texan II" in the subject line.
Flying
My Texan flew "off the board" with little adjustment required. Remove the propeller and add clay to the nose to get the CG correct. Test-glide the Texan over high grass by pointing it at a spot about 50 feet ahead and giving it a firm toss toward that spot. Cure diving or stalling with small adjustments to the stabilizer decalage. Cure unwanted turning/spiraling by adding small bits of clay to the wingtip opposite the turn.
When satisfied with the glide, add the rubber motor (three loops of 1/8-inch Tan Super Sport, 40 inches long, braided). Recheck the CG and wind in 450 turns. When released, the model should climb and turn right; make all adjustments by shimming the thrustline.
As the airplane begins to behave, add turns until you reach approximately 1,750 turns. At this point have binoculars available and a reliable way to retrieve your model.
Good luck with your Texan II.
Bob Isaacks [email protected]
Transcribed from original scans by AI. Minor OCR errors may remain.
