project pattern
and reinforcements and bubble wrap padding. Removing all the bits, the weight of each component was checked. And to es- tablish a weight “budget” for Yuri, the weight of all major components was also checked. The maximum takeoff weight allowed in
Y
FAI F3A is 5000 grams (11 pounds) with a 50-gram tolerance (for measurement or cal- ibration errors). For AMA Masters, the weight limit is 5000 grams and in Advanced, Intermediate, and Sportsman the limit is 5115 grams (with a 50-gram allowance if calibration weights are not available). With the all-up weight of the bits for Yuri totaling 4915.7 grams (10 pounds, 13.4 ounces), this would initially seem to leave very little room under the 5000-gram limit. However, during the construction/assem-
bly of Yuri a number of weight savings mea- sures will be employed; after all, lighter flies better. It is also worth noting Yuri arrived fully painted and minimal construction is needed, in particular for the wings, stabs, and rudder. And a final note: since the pro- duction of Yuri in May of 2011, RC-Composit has been hard at work refining their manu- facturing process and has substantially re- duced the airframe weight by approximate- ly 10% (240 grams, 8.5 ounces). I opted to start construction/assembly
with the installation of the aileron and ele- vator servos and linkages. Within the hollow molded wings and stabilizers, ribs with ser- vo cutouts are pre-installed by RC-Compos- ite. Servos are installed through the root ribs with the output shafts facing the wing/stabilizer tips. Hardpoints are also pre-installed in the control surfaces. The lo- cations of the hardpoints and linkage slots can be easily determined with the help of a bright light. With a bright light on one side of a wing or stabilizer panel, the “shadows” of the hardpoint and rib can easily be seen on the opposite side of the panel, allowing lo-
PHOTOGRAPHY: DAVE LOCKHART
Arriving safely from RC-Composite pre-painted with all major construction complete, the remaining construction/assembly of Yuri begins with installation of the servos and linkages for the ailerons and elevators. A number of weight savings measures will be employed during construction/assembly.
cations to be marked with a non-permanent marker (dry erase markers work well). In the control surfaces, either “blade”
style or threaded stud control horn styles can be used. For the ailerons and elevators, I prefer the stud style as it allows more pre- cise adjustment of control throws and accu- rate installation is easily accomplished with the help of a drill press. I use 6–32 all thread rod for the control studs as I’ve found this material is less prone to snapping from fa- tigue, in comparison to hardened cap screws. With a Dremel fiberglass cutting wheel, I cut several angled grooves at the base of each stud to provide additional glu- ing area. Total length of the elevator studs are 1.75 inches with the aileron studs at 2.25 inches (dimensions are critical to en- sure correct throw). When marking the locations for the con-
trol horn studs, it is important to mark the locations relative to the hingelines and con- trol surface edges, not within the center of the hardpoint location itself. Symmetrical control surface throw is dependent on the lo- cation of the control horn, not the hardpoint itself (which may vary slightly). The control horn stud locations are drilled using a drill press, taking care to set the drilling depth to not punch through the top wing/stabilizer skins.
Drilling occurs from the bottom, with the
drill bit perpendicular to the top skin. This results in the stud leaning forward, towards the hingeline. Ideally, the linkage attach- ment will be exactly perpendicular to the hingeline (to provide equal throw in each di- rection), however, as long as the attach- ments are close to the hingeline, it is more important that the studs are installed symmetrically. With the “live” top skin hinges used by
Yuri, the control surfaces will actually re- quire greater movement “down” than “up” to have equal control authority as the control surface area is effectively reduced when moving “down” (hiding within the wing/stab). The drilled hardpoints are then tapped for the 6–32 studs, again taking care to not break through the top skins. The studs are installed into the hard-
points using slow cure epoxy. It is very im- portant to fill the hardpoints with epoxy pri- or to installing the studs to ensure that the full length of the stud is glued into the hard- point. “Poking” the epoxy into the hard- points with a small T-pin is my preferred technique to keep the epoxy from bridging and eliminating air bubbles within the hard- point.
While the control studs are drying, it is
time to prepare the servos. In the past, JR offered “sa” versions of several servos which utilized a metal output gear with internal
Redux
uri has arrived! Within a single heavy duty cardboard box, Yuri ar- rived undamaged, packaged in a maze of shaped foam block cradles
by dave lockhart with algirdas ungulaitis You can reach Dave Lockhart via e-mail at
davel322@comcast.net
Mounting ribs for the aileron and elevator servos (above) are pre-installed by RC-Composit. Text describes techniques to easily mount the servos and complete linkages. Servo mounting ribs (at right) and control horn hard points can easily be located using a strong light source on the opposite side of the surface.
60 OCTOBER 2012
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