The altimeter on a FC measures the pressure within the cockpit not true static pressure. If the air pressure in the cockpit increases or decreases with throttle or airspeed the altitude reported will be off. I believe this is at least part of the altimeter drift problem reported by many people.
Building a static port on the aircraft that provides the barometric source would eliminate the cabin pressure problem. Connecting the static source to the FC with no leaks could also present a problem. I considered using a secondary barometric source connected directly to the static port, thereby eliminating the plumbing issue.
So far I can find no data at all on building a static port for RC aircraft and connecting it to the baro. I would appreciate any help/advice from people who have worked on the problem.
I’m not aware of any off the shelf flight controllers that have a ported static pressure sensor. At my UMN lab we did something similar (with our own internal ecosystem) using an AMS 5915 static pressure sensor: https://www.analog-micro.com/en/products/pressure-sensors/board-mount-pressure-sensors/ams5915/
Physically we Y’d the static port off the pitot tube to feed the static pressure sensor and the static side of the differential sensor.
These communicate via a straightforward i2c protocol. From a quick check I don’t see any ardupilot support of these devices and I don’t know the areas of the ardupilot ecosystem for adding new i2c devices so not sure how easy/hard this would be?
My subjective 2 cents is that you still don’t achieve perfect altitude sensing (for all the different reasons including bias drift (hysteresis?) and adc noise, integration variations, small weather changes during flight,etc.), but it does help reduce the overall effect of change in airspeed/cabin pressure. So it is a win, but maybe not enough for people to demand ported static pressure sensors on their economy flight controllers?