Mike wrote: >>The author suggests that static pressure will fluctuate due to vents being opened or closed. I don't open and close vents randomly and nobody else does either <<
I've done that test, as I've moved my static port from the wing to the back of the fuselage to the interior of the plane and then to the front of the fuselage in an effort to get my airspeed to read right (airspeed indicator was already calibrated as shown at http://www.n56ml.com/airspeed_calibration/ ). [that was a nasty sentence structure!] Apparently the wing location was very corrupted by a leak in the static line, and a constant vacuum being pulled on the inside of the wing...probably the hole where the aileron bellcrank pushrod operates through the aft spar. Seal those static lines with silicone and shrink tubing or something before you seal the wing up! Once I move up to the front of the fuselage, I found very little difference between the front ports and porting internal, although it was measurable to a mph or two if I opened the vents wide open as opposed to closing them. Using the front ports, which is a port on each side of the fuselage connected by a T in the middle. I even used a very sensitive differential pressure gauge to quantify it, and there was a real difference to be had by opening and closing the vents. But you're right, that wouldn't cause a fluctuation on the mode C unless you fiddled around with them constantly, and even then it would be minor, at least on my plane. This kind of stuff is why I can build the next plane so much faster...I know exactly how to build that system, where to put it, and have all parts required located in one place in the mezzanine of my hangar... Mark Langford ML at N56ML.com website at http://www.N56ML.com --------------------------------------------------------
