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Rick_A
11-11-2009, 08:18 PM
I've got a TT Digiflight II VSG (GPSS but no GPSV) connected via a switch to a GRT Horizon and a GNS 480. I've been driving the AP directly from the 480 which works great for lateral guidance and altitude hold. I can't really see the benefit of switching the AP to use the EFIS as the input.

Am I missing something? Since the AP doesn't have GPSV, are there any benefits to letting the EFIS drive the AP?

Brantel
11-11-2009, 08:26 PM
- If you want to use an internal EFIS flightplan to drive the AP
- If you want to follow one of them synthetic approaches
- If you want to drive the AP from the EFIS bugs
- If you want the EFIS to be a translator for a NAV data source by converting VOR/LOC/GS data to GPSS and GPSV steering commands.

The later lets you get NAV capability on a cheaper TT AP.

You can get your AP upgraded to the GPSV capable model for a good price.

Ironflight
11-12-2009, 05:57 AM
Everything that Brian said!

I have the same switch Rick (EFIS/GNS), and it almost never leaves the EFIS position. It is really nice in "Heading" mode to be able to tun the knob on the map page until the cursor line is just tangent to some airspace I want to avoid, and watch the airplane follow it obediently....

Paul

Rick_A
11-12-2009, 07:52 AM
Brian, I presume the AP will only follow the lateral commands of the synthetic approach without having the GPSV feature. Right?

Paul, good idea about using the heading bug to skirt an airspace. I hadn't thought to do that.

Since I've been using the 480 to drive to AP, I've not used the AP features of the GRT. I noticed that there are 3 options on the GRT for AP: HDG, ENAV, GNAV. I presume GNAV is GPSS.

What is ENAV? I guessing it might be VOR/LOC heading used as input. If it is, does that mean that I can dial in a VOR radial on the HSI page and track a heading/radial?

Upgrading to GPSV is a good idea but I don't have much service clearance to remove it. It's not a job that I want to tackle unless I'm really motivated.

breister
11-12-2009, 08:13 AM
What the others said, plus one additional feature.

The GRT will "convert" the ILS steering commands to GPS steering commands - or so I am led to believe. Thus you could get lateral steering on a Localizer approach.

I am mystified, however, that you did not spend the extra bit for the VSGV since you have a GNS 480. That baby will fly your airways; GPSS-V approach; and if you don't break out you can punch the button and it will fly the missed approach and put you in holding. I've only recently started flying with that combo, and am looking forward to learning all the "tricks" the GNS 480 will do.

Two final tidbits. Yes, you might as well have a DPDT switch to allow you to drive the AP from the GRT. Personally I think I'd be more inclined to drive it from the 480 most days, but everyone has a preference. Second, if you have a hand held or secondary GPS, hook it up to the TT using the serial connection. That way if the WIRES fail or primary GPS dies you can still drive the AP from the hand held / backup.

Radomir
11-12-2009, 08:13 AM
Brian, I presume the AP will only follow the lateral commands of the synthetic approach without having the GPSV feature. Right?


Not Brian.. but yes.. it'll follow lateral only. For GRT's synthetic approach, you don't even need GPSS for lateral.. regular "NAV" will work too..



I noticed that there are 3 options on the GRT for AP: HDG, ENAV, GNAV. I presume GNAV is GPSS.


Yes.. kinda... GNAV is pass-through mode where EFIS just passes through GPSS and GPSV steering commands from a GPS (eg. 430W or 480) to the AP..



What is ENAV? I guessing it might be VOR/LOC heading used as input. If it is, does that mean that I can dial in a VOR radial on the HSI page and track a heading/radial?


ENAV is "EFIS NAV" -- that's the mode you'd be in if you want your AP to follow EFIS-generated navigation/steering commands. Example would be ILS approach -- a radio sends signal to EFIS and then EFIS generates appropriate commands to follow the loc/gs...



Upgrading to GPSV is a good idea but I don't have much service clearance to remove it. It's not a job that I want to tackle unless I'm really motivated.

My humble opinion.. once you experience full integration, you'll be wondering why you didn't upgrade to VSGV sooner.. :)

Rick_A
11-12-2009, 10:45 AM
So now I have 2 things that I wish I had spent the money on while I was building - GPSV and the Garmin 330. It was just hard to justify even bigger checks then the ones I wrote when I was buying my avionics.

I guess the GPSV will come next. :)