Tuesday, February 9, 2016

Installed More Wiring Harnesses & Modification Of Pitot Tubing

Moving thorough the plans, the WH-00062 power wiring harness was the next wiring harness that needed to be installed. This harness brings in the power to the AV-50001 switch module. Van’s has made a change to the plans regarding the routing of wire WH-P156 … older versions of the plans route the WH-P156 wire(s) through the firewall grommet and into the engine compartment to the Ducati voltage regulator, however newer versions of the plans show the WH-P156 wire(s) routed down under the instrument panel base to the new home for the Ducati regulator. Not wanting a high current device such as the Ducati regulator with a history of smoky failures inside the cockpit, the decision has been made to keep the regulator somewhere in the engine compartment. So all the wires in the WH-00062 wiring harness were routed through the firewall grommet and into the engine compartment.

The next wiring harness tackled was the WH-RV12-EGT harness. This harness consists of only two wires that are routed into the engine compartment through the firewall grommet. The wires will connect to the exhaust gas probes on each side of the engine that measure exhaust gas temperature. The DB-25 connector on the WH-RV12-EGT wiring harness attaches onto the SkyView EMS-220 engine monitoring module. The DB-25 connector comes without a housing attached so it was necessary to open a bag containing the clam-shell housing for the DB-25 connector, screw down the strain relief and snap the clamshell halves together. Initially, I thought the connector may receive more wires which is why the housing was not attached … but a quick look at the wiring schematic showed only the two EGT probe wires going to the connector.
Installing the strain relief on the housing for the DB-25 EGT connector.
Fishing the WH-RV-12-EGT wiring harness through the firewall grommet.

The connector housing did not have a label as most all of the other connectors do, so used the label maker to make an EGT label to stick onto the connector's housing.
The WH-RV12-EGT harness’s DB-25 connector attached to the SkyView EMS-220 engine monitoring module.

The next step in the plans instructs the builder to route a 54 1/2" piece of what appears to be a form of vinyl or poly tubing through the firewall grommet and on into the engine compartment … this becomes the FF-1216 forward Pitot tube.  Here is where the DOG Aviation RV-12 will make a tiny modification and deviate from the plans … normally a 4" piece of vinyl tubing is used to splice the forward Pitot tubing coming from the engine compartment to the aft Pitot tube going to the ADAHRS mounted in the tail cone.
My finger is pointing to the piece of 4” vinyl that normally would be used to splice the forward Pitot line to the aft Pitot line … this will not be done because of the need to tap into the Pitot line for the backup airspeed indicator.

Because the DOG Aviation RV-12 will have a backup airspeed instrument, it is necessary to tap into the Pitot line. So in lieu of using a piece of vinyl tubing to splice the forward and aft Pitot lines together, a "Y " designed for tubing will be used to split the Pitot line coming from the engine compartment so one leg can head aft to the ADAHRS module in the tail cone and the other leg of the "Y" can connect to the Pitot port on the UMA backup airspeed indicator.
The "Y" fitting will allow the Pitot tubing from the engine compartment to be split so the backup airspeed instrument can also receive Pitot air.

At this point in time, will wait to install the Pitot line going to the UMA Backup airspeed indicator until the instrument is installed in the panel and the best routing for the tubing can be determined.

For those builders interested, the Y fitting was obtained from Stein Air. They have many types to choose from such as manifolds, T, elbow and straight fittings. Most of the fittings are also available with or without pipe threads so they can be connected directly to instruments.