Originally Posted by Brantel
Question about the xTreme, I see that it will provide GPS derived bank angle when used without the AHRS, what does it do for pitch?
It provides somthing we like to call "flightpath". It is not attitude or AHRS. However, for most flight regimes, it behaves very similar.
The display is based on your flight path in 3D and it assumes that you are flying a three axis aircraft or something that behaves similar. The XTreme has a pretty good GPS which provides some interesting data beyond the normal and this is what we are using.
It shows you a bank angle based on velocity and rate of turn (assuming you will fly more or less a balanced turn). The Pitch angle is based on your true vertical flight path (i.e. forward velocity vs vertical velocity).
Where are the differences to a normal, gyro based AHRS ?
It can't tell if you are upside down (it shows flightpath, not attitude).
It will not show a point roll (your flightpath does not change).
It has a very slight lag, just noticable. We need to use historic data to assemble where you came from and where you are going.
If you stall with high nose up attitude the pitch will show nose down - that is because you are going down !
Other than that it is a valuable reference if used correctly. You can absolutely fly an aircraft with zero external reference with this. This kind of system is "absolute". It does not suffer from gyro drift, rate limitations and never topples.
It's most valuable contribution is as a reference for gyro based AHRS systems. It is a true reference that you can trust as a check on your AHRS and it is much more valuable in that role as a second gyro based AHRS as you would need at least three as a tie breaker if one starts showing a deviation.
Essentially a true gyro AHRS and the GPS based "fake" complement each other in many ways - the weaknesses of one are the strenghts of the other.
CEO MGL Avionics