Here is a sketch and some photos of the system. Sorry for the quality, not my strong point. Tubing is 3/16 Nylaflow. Ram air is collected with a tube near the aft end of the nose gear door, on the side away from the exhaust. The lower cowl provides shielding from bugs and ice,
the warm cooling air may help as well. Ram air flow is delivered to the reference legs from a manifold behind the instrument panel through orifice passages (about .028 from memory) to prevent condensation. The airflow through the reference log produces a small pressure drop that causes the sight gauges to read about 2 gallons low in cruise. Reducing the size of the orifice will reduce this error, however the reference leg provides an alternate supply of vent air if the tip vent gets plugged, so I would not make it any smaller. A thin red pinstripe is mounted under each tube of
the sight gauge. The gas magnifies the stripe as in a thermometer. On a level ramp it is easily readable to ½ gallon. While under the plane I took a picture of the mechanical nose door actuator.
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