Carbon fiber blade style control horns (above left) (32 mm size) from F3A Unlimited were modified slightly to provide the ideal size for the desired control throw with maximum resolution. A Dremel with a 3⁄32-inch carbide bit is used to cut slots (above center) into the pre-installed hardpoint into which the control horns are installed. The path (above right) of the rudder cables from the rudder servo arm to the rudder control horns is mapped out to allow accurate cutting of the rudder cable exit holes in the fuselage. The exit (below left) of the rudder
cables through the fuselage sides occurs after the former at the stabilizer leading edge. A sharpened brass tube (below center) is used to cut a hole in the tailpost, and then in the former at the stabilizer leading edge for the passage of the rudder cables. Initial cable exit slot (below right) is cut with a 2-inch diameter cutoff wheel. Final dimensions are completed after trial fitting the rudder cables. This is also a good time to use the Dremel tool to cut round holes for the elevator servo leads.
The rudder cable is doubled onto itself (above left) before being tied with a simple overhand knot to the eyelet. After tying the rudder cable and checking the length, the knot (above center) is heated to the point of melting the vinyl jacket,
movement of the cables through the deflec- tion range of the rudder.
Trial fitting the rudder cables will require relieving the former in the fuselage located at the front of the stabilizer. This is easily done with a sharpened 1⁄2-inch piece of brass tubing. The tubing is used to drill a hole in the rudder post, and then on each side of the former at the locations where the cables will pass. The hole in the rudder post doubles as a useful access point to assist with feeding rudder cables and elevator servo extensions through the fuse, as well as feeding in glue for the front stabilizer adjuster rod. A brief note about crossed/straight rudder cables. Some kits have the rudder exit slots already cut, in which case it is extremely critical to accurately mount the control horns and rudder servo such that the exit slots will be in the correct location. Some kits are set up for straight cables; i.e., a ca- ble connects the left side of the servo arm to the left rudder horn. I prefer to cross the ca- bles as this increases the angle at which the cables exit the fuselage sides, reduces the length of the exit slots needed, and reduces the amount of exposed cables as the exit point shifts further aft.
When cutting the rudder exit slots, it is
also a good time to cut holes in the fuselage for the elevator servo leads. Again using the Dremel, I use a conical or round bit to cut round holes for the elevator servo leads, and slightly chamfer the holes to remove any sharp edges that might cut the leads over time.
FLYING MODELS
and then additionally secured with a drop of thin CyA. Save the carbon fiber control horns (above right), Nothing exotic is evident in the completed installation of the rudder.
Back to the rudder cables themselves; to
avoid fraying in the long term, I use the aforementioned Sullivan eyelets to connect the cables to the clevises. The round cross- section of the eyelets eliminates kinking/ cutting of the cables. I pass the cable through the eyelet, and tie the doubled cable in a sim- ple overhand knot.
To permanently secure the knot, I pass the knot through the flame of a lighter (while under tension) to melt and fuse the vinyl jacket. And then I put a drop of thin CyA on the knot, which bonds the Kevlar strands together. The overall length of the cable will increase slightly as the vinyl jack- et is melted, so I “target” the initial length of the cables such that only 1–2 threads of the eyelets will engage the clevises. The elevator extension leads are an op- portunity to save weight. The ideal exten- sion length for Yuri’s elevator servos is about 40 inches. In the case of JR exten- sions, extensions are available in 36- and 48- inch lengths. A pair of standard 22 AWG 48- inch extensions weighs approximately 27 grams, while a pair of heavy duty 20 AWG 48-inch extensions weighs approximately 41 grams.
In my January 2012 column, I presented some testing data regarding voltage losses attributable to connectors, wiring length, and differing wire sizes (20 vs 22 AWG). For Yuri, I made a custom harness consisting of a pair of 30 AWG magnet wire signal leads (one for each elevator servo) and a shared pair of 20 AWG magnet wire (1 positive; 1
negative) for the power leads. Magnet wire is solid strand wire using enamel coating (vs silicone jacket) for insulation and is found in the windings of electric motors. The finished custom harness (at 40-inch
length) has the same current capacity as a pair of 22 AWG 36-inch extensions, but at a weight of only 13 grams, for a weight sav- ings of 14 grams. The downside to magnet wire is that it is not as flexible as tradition- al extensions, so I leave a balance of silicone wire at the ends to accommodate bending near the receiver and fuselage exits. I have not used such a harness on a glow powered plane, and would not do so for concern of the effects of vibration on the magnet wire.
Elevator servo harness custom made to the exact length saves weight with common power leads and the use of lighter weight magnet wire.
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