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Dave's RV-7A Builder's Log
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Date: 2-19-2017
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Number of Hours: 6.00
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Manual Reference:
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Brief Description: Misc firewall forward work
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Today I focused on finishing various firewall forward tasks, including the following:
• Attached right side GPS antenna tray, installed BNC & TNC connectors, and installed GPS antenna.
• Wired left and right magnetos by stripping associated leads, attaching a solder sleeve with wire pigtail for shield ground, terminating both leads and then attaching terminals to the appropriate location on each magneto. Since I am using a keyed switch similar to those used on production aircraft, the ground for the magneto is accomplished through the switch, rather than through a separate magneto switch with a ground in the circuit. An interesting (and essential) feature of a magneto is that it is designed to be “hot” regardless of the aircraft electrical system. Since the magneto generates a spark due to the rotation of the engine, there is no direct connection to any part of the electrical system. The only way to deactivate a magneto is to ground it—exactly the opposite of most electrical circuits. This grounding can be accomplished in several ways, and like some of the debates in the home building community, this one can be a bit divisive. The biggest issue is that with a single failure of grounding, the magneto is hot, so…like a firearm; you always assume the magneto is “loaded” and treat it as hot. Simple enough for me.
• Organized the lower right section of the firewall where main power distribution is located. This included adding a current limiter to the standby alternator circuit, terminating the main power amperage shunt (which displays alternator amps on the G3X), tightening all connections and adding wire ties to secure the bundles.
• Added two Adel clamps to the upper engine mounts to secure the magneto harness as it crossed under on the way to the upper spark plugs. These two locations are the only place where the magneto harness is connected to the engine mount.
• Reinstalled the throttle and mixture cables and associated hardware. Still needs final adjustment after the panel is back in.
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G3X antennas installed and top wire bundle finished
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Main power distribution location on lower right firewall
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Right side wiring
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