Upgrade from Plane 3.7.1

I use my flying wing with 3.7.1, if I upgrade to 3.8 I will lost settings ?

It should auto-convert your settings, but it is a complex conversion, so please do careful ground tests after updating to ensure it is correct.
See this document for more details

Its possible to downgrade… ?

downgrade has a problem that is being tracked here:

After upgrade, I have lose compass and gyro calibration, its normal ?

gyro cal happens on every boot, so you don’t need to save it.
compass cal will be lost if you use a hmc5883 compass, as we changed the way that sensor is scaled. Other compasses will keep their calibrations.

Tridge…tonight Sept 18, I upgraded from 3.7.1 to 3.8.2 and was doing some elevon testing. I need to go back to 3.7.1 but when I select that as a “previous version” the only version it shows underneath the “plane” icon is 3.6. So it appears to not find actual 3.7.1 files even though “AP 3.7.1” is listed in the previous versions drop down list. I have also tried the other tricks listed like setting FORMAT_VERSIONS to 0 and installing Rover then trying to install Plane 3.7.1 and they don’t work…I believe it’s because the install files for 3.7.1 aren’t found. Can you please help those of us who need to fall back to 3.7.1? Thx
PS: For what it’s worth, I’m not trying to reverse “migrate” back to 3.7.1 or save any parameter settings. I just want to install 3.7.1 and its default parameters just like I was installing it for the first time.