gmcjetpilot said:
No debate that the new autopilots have more capability than the Navaid and are digital vs analog, but why do the digital autopilots need a GPS signal to keep the wings level?
The Navaid does NOT req a GPS signal to work. It has the classic small spinning mass, driven by an electric motor, to provide the "gyroscopic platform." The new Gen electronic platforms have some need to resolve their "attitude" by getting GPS ground track, as I understand it.
What if the GPS signal is lost? I realize these are VFR/experimental autopilots and gps is very reliable. What is the opinion of those in the know?
I know some EFIS do use GPS to resolve a solution to display attitude while other EFIS do not. I have a Navaid and wounder if the digital autopilots will improve so they can independently operate from the GPS.
Any comments, or insight?
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The digital autopilots have good performance for a reasonable period of time without GPS input. Your question is valid and is one I had great interest in when I first started foolin' around with solid state EFIS's and autopilots. When the DigiTrak first hit the market, I had an extended email discourse with one of TruTrak's engineers about this very matter. And one of the first tests I posed to my new EZ-Pilot was to force it to fly without GPS. The results of that test are here:
http://home.hiwaay.net/~sbuc/journal/EZ_Pilot.htm
Since that original test, the EZ-Pilot has been enhanced with new sensor orientation and new software to make the unit even more stable without GPS input. The unit should be able to keep the plane upright for quite an extended period of time, the exact amount I don't know. Even when the unit starts to satuarate, it won't go belly up, it just starts to slowly drift off course. The trim switch can be used to "educate" the platform and correct for the drift.
Yes, the Navaid doesn't require GPS. But providing GPS data to the new units allows them to have features that were never possible with the mechanical Navaid. I am comfortable with the digital devices because of the reliability of GPS and the satisfactory non-GPS performance they deliver.
The idea of depending on GPS for an EFIS's AHRS platform is more controversial. Those who go to the bank with GPS's reliability are ok with basing the AHRS on a system that needs GPS for full functionality. Personally, I would prefer the AHRS be autonomous, and no doubt this is the way of the future. Like the autopilots, many of the new, inexpensive (!?!) EFII will continue to function with loss of GPS, but not at full speed.
That is why there is still a place for backups!
Sam Buchanan (RV-6, Dynon, EZ-Pilot, AlTrak, uEncoder, AnyWhereMap, Lowrance and Garmin GPS's.......and a sectional!)