Originally Posted by AndyWW
Thanks very much Steve. From your post can I infer that I could get a G5 to drive some GSA28 servos directly without needing a GMC307? That might be another possibility for us.
I think I may have failed to be clear enough on my other question. I was asking how many times per second the G5 outputs the GPS position. The Trutrak autopilot documentation (but I guess it's true for all autopilots) said that to get the best performance the refresh rate needs to be better than once per second.
You are welcome.
While the G5 and GSA 28 servos are the main part of this autopilot, there is no user interface on the G5 for moding the autopilot (for good reason!), so you do need the buttons/knobs/wheel provided by the GMC 307/507 to have an operational autopilot.
The G5 internal WAAS GPS updates at several Hz and the NMEA output is updated at 1 Hz, but again, it is somewhat irrelevant what the update rate of the G5 NMEA output is since you would want to drive an external autopilot with a navigator, not the G5.
Besides, an autopilot should not be dependent on the update rate of the navigator (within reason) to fly the plane smoothly. The GPS TRK, XTK, and speed provided by the navigator are only parts of the flight director solution which incorporates high speed attitude and air sensor data to constantly derive the gain filtered pitch/roll rate used to fly the required heading, track, course, altitude, climb, pitch, roll, etc.
High end IFR navigators like the GNS/GTN provide roll angle steering data over A429 which gives the autopilot more to work with, but VFR navigators providing NMEA data over RS-232 do not provide roll steering data, but this is no problem for the G5 autopilot.
The Aera 660 also outputs NMEA data at 1Hz, which is plenty fast enough for the G5 autopilot to smoothly fly the plane and track a flight plan both laterally and vertically.