To ensure accuracy and symmetry, control horn stud locations are drilled (above left) using a drill press with the depth set to not puncture the top skin.
nylon gears. The use of nylon gears reduces weight and improves precision, both a pri- ority for Pattern planes. Using part num- bers JRPSG3025 and JRPSG911, I respec- tively replaced the full gearsets for the 3517 elevator and 9411 aileron servos. The most difficult part of this procedure is freeing the ball bearings from the output gears. I gen- erally accomplish this task with an assort- ment of flat blade jeweler screwdrivers to gently pry the bearings loose. Leaving the metal output gear is certainly an option; however, the greatest weight savings is not realized. The additional modification I complete is reducing the lead length on the 3517s to 3 inches such that the plugs extend just out- side of the stabilizer halves. This avoids having either extra wiring coiled up inside the stabilizer halves, or a junction with the elevator extension leads occurring in the middle of the fuselage (inaccessible, unless the full leads are removed). With the modi- fications described, approximately 7.5 grams are saved on the pair of 3517s; and 8 grams are saved on the pair of 9411s. Cutting the linkage slots in the wing and stabilizer skins is a classic scenario of mea- sure twice, cut once. I rest the servo on the wing/stabilizer skins, aligned with the mounting ribs, and mark the locations for the linkage slots. Using very light pressure with an 1⁄8-inch carbide bit, I Dremel under- sized linkage slots in the skins. I then install the servos to verify the accuracy of the link- age slots, and then complete cutting the
Component
Left Stab Right Stab Stab Tube
Rudder (with hinge pin) Canopy
Belly Pan Fuselage
Landing Gear Legs Wheelpants Left Wing Right Wing Wing Tube Accessories
(linkages, wheels, axles, tailwheel assembly)
Airframe Total Weight FLYING MODELS 2450.2 86.4
Airframe Weights Weight
(grams) 102.1
105.8 12.2 83.7 72.4 72.0
840.0 157.5 21.0
403.5 403.5 63.5
113.0
Short, direct linkages (above right) provide positive control and eliminate trim changes associated with longer pushrods and temperature variations.
linkage slots. I use an assortment of fine tooth files to clean up the edges. Cutting the linkage slots is best done slowly with light pressure to avoid delamination of the com- posite skins. As the aileron and elevator servos are mounted with the output shafts facing the wing/stabilizer tips, the output arms must be installed first. Servo arms should be in- stalled symmetrically on the servos, using a minimum of subtrim. For the elevator ser- vos, I use the largest DuBro Super Strength standard size (Cat No 674) arm, with the linkage attached to the outermost hole (ap- proximately 0.75 inch from the center). For the aileron servos, I use the medium DuBro Super Strength large size (Cat No 671) arm, with the linkage attached to the outermost hole (approximately 1 inch from the center). This combination of servo arms and con-
trol horn stud lengths provides approxi- mately 22 degrees of elevator throw (each di- rection) and 25 degrees of aileron throw (each direction) when servo endpoints are adjusted to approximately 130% (default is 100% for JR, with 150% being maximum). This combination provides good mechanical advantage to the servos and good resolution for precise control. Prior to installing the arms, I tap the holes in the arm for a 2mm screw, which will be used to attach the linkages.
Installing the elevator servos is simple enough, as they are close enough to the root ribs such that standard tools can be used. As the aileron servos are installed approxi-
Weight (ounces)
3.6 3.7 0.4 3.0 2.6 2.5
29.6 5.6 0.7
14.2 14.2 2.2 4.0
Component JR DS8711 (rudder) JR DS9411 (2, ailerons)
JR DS3517MG (2, elevators) JR 921X (receiver)
HD Servo Extension Leads
Tech Aero Voltage Regulators (2) Thunder Power 2s1p480 RX Lipos (2) Neu 1513/2Y F3A-1 Neu Prop Adapter Hyde Softmount
RC-Composite Spinner PT Models 22x12
Castle Creations Phoenix ICE2 80HV Thunder Power 5s5000 G6 Lipos (2) Castle Creations Phoenix ICE2 80HV
Total Equipment Weight
mately 6 inches into the wing, I fabricated an extra long ball driver by taping an “L” wrench to a 12-inch long piece of 3⁄8-inch dowel. #2 socket washer head screws (part number STW0207) from MicroFasteners
www.microfasteners.com further eases the installation, as the screws can be “pinched” onto the ball driver. “Pinching” is accom- plished by placing a small piece of paper towel between the ball driver and the sock- et, resulting in the screw staying attached to the ball driver until the fastening is completed. Recently defunct, MK Model Products for
many years produced a number of quality hardware bits for Pattern planes, including my favored ball bearing linkages. F3A Un- limited has largely filled the void, and is now my source for ball bearing clevises (con- trol surface end, “34mm Aluminum Control Horn with Bearing Clevis”) and ball bearing connectors (servo end, FH5002). A bit pricey, but well worth it in my opinion as they are slop free and will last for thousands of flights. The required length of pushrods between
the aileron servo arms and control horn studs was well suited for the Hangar 9 3.5- inch 4–40 titanium Pro-Links (HAN 3554). Another option for turnbuckle style pushrods is the rather extensive line from Secraft (available at F3A Unlimited). Alter- nately, custom length pushrods can be made from the extensive variety of carbon pushrod tubes and titanium pushrod ends available from Central Hobbies.
Equipment Weights
Weight Weight (grams)
68.0 79.4 51.0 83.7 45.4 28.0 60.0
532.0 53.0 50.0 40.0 77.0
120.0
1180.0 120.0
2465.5
2.8 1.8 3.0 1.6 1.0 2.1
18.8 1.9 1.8 1.4 2.7 4.2
41.6 4.2
87.0 61
(ounces) 2.4
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