Where does one place the barometer in a plane setup? If placed inside the fuselage (for example flight controller with integrated barometer) and if the fuselage has an opening or scoop to the outside (for ventilation, cooling airflow), the pressure inside the fuselage is going to be influenced by the airspeed. If using external gps/barometer/compass combination and placed underside wing, if the cavity has opening to outside, then airspeed and pressure under wing is going to change barometer readings. If barometer is sealed from the outside air, then it defeats the purpose of barometer. What am I missing?
Ideally, the barometer would be installed on the outside of the airframe in a location with stable, clean airflow, and not affected by the ram air of forward flight. Many static ports on manned airplanes and helicopters are on the side of the fuselage, 90 degrees to the airflow in forward flight (However there are plenty of examples of alternate locations).
All that said, in many cases you don’t have much of a choice. For most flight controllers the barometer is mounted on the board, and you aren’t going to mount that outside your airframe. Components need cooling so the airflow inside the fuselage is needed. It may not be the most accurate, but it should be consistent.
When using a compass/GPS/barometer combination then I mount that on the top of the fuselage, if possible away from the curvature of the wing. It’s worked well, but again sometimes I don’t have enough choices, or the position has been more dictated by keeping the compass away from electrical interference over possible barometer error.
If precision altitude is needed then I recommend you look at a range finder over just a barometer.
Wow, so its an actual problem. I was hoping it was just my ignorance, and someone would post a 1 line solution.
Speaking of GPS/barometer combination, can we blend barometer as we do GPS? Mount 2 barometers left/right(or top/down) sides of fuselage, so any wind/yaw/pitch effects cancels out through blending?
Well, how accurate do you need it? If you’re flying VLOS then don’t worry. If your barometer is 10m off at 100m AGL is that going to be a really big deal? For some users, absolutely it’s a big deal and they need rangefinders or RTK GPS or both. For most users, nope. What kind of flying are you planning to do? If you’re flying FPV or recreationally, then I wouldn’t get too worried about it.
I don’t know of blending barometers. Again, if that’s the needed accuracy, a range finder is going to be better bang for the buck.