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Garmin introduces retrofit autopilots (GFC500 and GFC600)

My understanding , remembered from 8 months ago (when I had twin G5’s fitted) is you can fit a Garmin pitch trim servo but it’s optional. I am guessing that it needs to be fitted for the “straight and level” button to work properly.

My understanding is you can use it just on the G5’s and steer it with the DI bug. That’s what I do with the Piper autopilot at present. I use the Analogue to Digital GAD29B which allows the G5 to talk to the legacy autopilot.

I fly VFR with Sky Demon and the display/map is better than any Navigator I’ve seen so for my mission profile, why buy a Navigator?

Last Edited by Archer-181 at 15 Apr 14:04
United Kingdom

Airborne_Again wrote:

I went to the Garmin presentation about the GFC500 in Friedrichshafen. Quite interesting. You have to use a G5 AI with the GFC500 because the A/P computer is actually in the G5!

Did you ask what a GFC500 does on an ILS approach if it looses GPS? :)

EPKP - Kraków, Poland

tmo wrote:

Did you ask what a GFC500 does on an ILS approach if it looses GPS? :)

I suppose that without a heading source it is dependent on the GPS to maintain track? But with a heading source (e.g. a magnetometer) I don’t see why loss of GPS should be a problem.

ESKC (Uppsala/Sundbro), Sweden

Generally, in aviation, whether flying manually or with autoflight, you always fly a heading. This is then adjusted according to the error relative to the chosen navigation source: VOR, LOC, GPS, INS, TACAN, etc.

The heading comes from a compass system. One uses a fluxgate sensor to get it from the earth’s gravity. Or one could get it from an INS system; presumably this is done on jets flying over the poles where the mag field is not usable. You can get it from GPS too but you need to be moving to do that. Esoteric solutions have been developed which use a GPS at each end of a long aircraft and you work out the heading from their relative positions.

So, in light GA, if GPS fails, and you don’t have a fluxgate compass, you lose the ability to fly an approach.

Does the GFC500 require a G5? I thought it integrates with a G500 / TXI. These systems must have a fluxgate input; the Q is whether this is optional.

Shoreham EGKA, United Kingdom

The G5 contains an AHARS. How would a glass DG and AI and autopilot system work without one?

Last Edited by JasonC at 16 Apr 08:52
EGTK Oxford

In general you need a DG (directional gyro) because the fluxgate signal jumps around by 1-2 degrees. In old systems this would be say a KG102A which takes in the fluxgate input and gives you a stabilised heading. In modern systems it is an AHRS module (like my Sandel SG102) and this also takes in the fluxgate input and gives you a stabilised heading, as well as pitch and roll data which can be used for stuff like KI256 replacement (if “certified”, via EA100/GAD43 converters), radar antenna pitch/roll stabilisation, reversionary AI synthesis (like I have on the Sandel SN3500), etc.

You still do need a fluxgate magnetometer and that may be what tmo above is getting at. If there is an option to not have that, then they are using GPS to get the heading; obviously this gives you track, not heading, but it can be used because you just need a stable lateral reference which you then adjust according to the nav error. And it means that if you lose GPS you can’t fly say an ILS, because an AHRS (with a drift of the order of 1 degree per minute) isn’t going to do you much good.

But until somebody who installs these, posts, or somebody has the time to go through the installation manuals, we are just speculating on the options

Shoreham EGKA, United Kingdom

Peter wrote:

Does the GFC500 require a G5? I thought it integrates with a G500 / TXI.

Yes it does. The G500 (Txi) docs on the Garmin web site are clear that to use the GFC500 you also need a G5. And the Garmin presentation at AERO made clear that the A/P computations are actually done by the G5. I don’t know if the G3X can also serve as A/P computer for a GFC500 system, but the Garmin web site makes no mention of a requirement to use a G5 with the G3X so I guess it can.

Last Edited by Airborne_Again at 16 Apr 12:06
ESKC (Uppsala/Sundbro), Sweden

With the G3X (certainly in experimental aircraft) you definitely don’t need the G5 for the autopilot.

Avionics geek.
Fairoaks. EGTF
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