With radio, engine, fuel systems already installed, this RTF trainer could be built in 20 minutes. Spending longer on construction will yield a model that may last 1,000 flights with no problem.

THINGS ARE CERTAINLY different today for the aspiring model pilot. Gone, and surely not greatly lamented, are the days when a new modeler had to spend several months building a trainer from a wood kit. He or she usually made a few mistakes along the way; sometimes the kit directions were not very clear or helpful. Sometimes the instructor spotted these mistakes, such as poorly or incorrectly mounted control horns, before the first flight.

   However, other problems, such as using the wrong adhesive to join the wing spars and the parts that strengthen the wing's center joint, were undetectable and often fatal to the model when flown. Even minor damage then often meant weeks of downtime while repairs were made. A total loss could mean missing a whole flying season.

    We should all be properly grateful to those pioneers of yesterday for their talent, patience, and perseverance. Without them, none of us would have the reliable radios, great engines, and ready-built aircraft we enjoy today.

    Today's new model pilot has a wide choice of ARF and RTF basic trainers. Last month I wrote about the differences between RTF and ARF aircraft and how best to choose between them.

    This month I will explore assembling an RTF basic trainer. Along the way, I might have a suggestion or two about how to improve the aircraft's function and durability without much experience or building skills. Next month I'll build a complete ARF trainer—the Hobbico HobbiStar 60 Mk III—and include improvements and performance enhancements.

    Shown is a typical RTF "kit" as it comes out of the box: the Hangar 9 Alpha 60. Where there are differences, I'll use additional aircraft for illustration. All of the RTF basic and advanced trainers available are finely engineered systems. Their production quality is outstanding and the costs seem magically low.

    But the "real world" requires some compromises, such as wings that cannot be fully assembled and fuselages without attached rear surfaces because of shipping restrictions. There is also the need to make every assembly step as simple as possible so that even the newest modeler will have little difficulty assembling a good, flyable aircraft. The cost of this simplicity can sometimes be a loss of durability.

    In theory, there are five major steps to construct an RTF trainer: assemble the wing, bolt on the tail feathers, connect the rear control rods, bolt the main landing gear in place, and mount the spinner/propeller assembly. Total building time could be less than 20 minutes!

    The Hangar 9 Arrow RTF advanced trainer was completely assembled in 17 minutes. You can read more about this aircraft on MA's Sport Aviator Web site: www.masportaviator.com.

    What you get after 20 minutes of assembly is a model that usually lasts for an even shorter period once airborne. Why? RTF trainers remain complex aircraft with many subsystems that require checking before flight. There have been durability problems past the 50-flight mark that are best addressed before final assembly.  

Wing Assembly: I like to start on the wing since it is the biggest and the easiest part to finish. It makes me feel as though I have accomplished a whole lot in a short time. All RTF trainers use metal spars to align the wing halves and to ensure a strong wing center-section. There is usually a smaller rear metal pin to further align the wing halves. If the wing has a plastic center rib, as the Hobbico NexSTAR does, the rear pin is omitted.

The Hangar 9 Alpha-series RTFs use light aluminum tube spars and a rear alignment pin to join the wing halves.

The Hobbico NexSTAR employs solid-steel rods to join wing halves and a full-length plastic center rib for alignment.

    Slide the metal spar into place and attach the second wing half. Each center wing rib is coated to make it fuelproof. Sometimes this coating flows into the spar and rear pin holes. Tolerances of the spar-to-rib hole are tight to ensure a stiff wing. The smallest amount of coating inside the hole can prevent the spar from sliding in.

    If that happens, use a fine, medium-size, round file—a rat-tail file—to gently remove only the coating. Never enlarge the hole itself.

    Hobbico wing halves usually screw in place, as on the Avistar 40 advanced trainer. Hangar 9 wings are secured using clear tape. Either method is good for approximately 200 flights; after that, the constant flexing, sudden pullouts, and "difficult" landings take their toll, and the wing spar begins to wear its wing rib mounting holes, allowing the wing to get sloppy. Both methods allow perfect wing alignment, so that is not a problem.
 
    Use an extra-sharp hobby knife to remove only the covering that overlaps the wing center-section. Lightly block-sand the wing halves. Brush a thin film of 30-minute epoxy onto one wing's center rib. Assemble the wings as in the directions, hold them together with masking tape, make sure the LEs and TEs are aligned, and allow to dry.

    This RTF wing will never loosen and will stay true throughout the most strenuous maneuvers. Hold off on connecting the aileron control rods for now.  

Hobbico RTFs use screws to lock wing halves in place.

Hangar 9 RTFs use fuelproof clear tape. Screws and tape are adequate methods, but adding epoxy is the most durable.