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Cheapest & Smallest Certified GPS for VNAV

Hi,

In the RV-10 I’m building, i’m going for all dynon gear, and this was all purchased and installed in the panel some time ago – it has Skyviews, Autopilot, Twin Dynon COMs and Dynon XPD.

It has WIFI and you can send a flight plan from SkyDemon direct to the Skyviews and the autopilot will fly the route.

I’ve just learned that the autopilot cannot do any vertical navigation without a certified GPS source. Seems a bit odd… but there you go.

Whilst i know it’s not essential or even terribly important, it does sound like a bit of fun to have vertical nav – so i’m wondering what my purchasing options are. I don’t think a fully integrated GTN is the solution here as it’d have to remodel the whole panel and flog half of what i’ve bought.

Is there a nice neat, small, certified GPS receiver, that can feed the Dynon lovely VNAV information?

-C

EGKL, United Kingdom

A cheap-ish option today would probably be a 430W. But I do believe the old 300XL is certified and it’s also still supported, as far as I know. That would be even cheaper. They can be had for about $2K.

Last Edited by AdamFrisch at 05 Jan 06:17

The 300XL is non-WAAS, so if you mean LPV or LNAV/VNAV or LNAV+V by “VNAV” – it cannot do that. You would need at least a 430W

Last Edited by Flyer59 at 05 Jan 06:36

Not sure what might be meant by “vertical navigation”.

Any GPS should offer a screen which can be used to calculate a descent rate to a waypoint.

However, in the context of an autopilot discussion it can mean only flying an ILS, LNAV+V or LPV approaches, and the cheapest GPS for that will be a GNS430W. That also contains an 8.33 capable VHF radio/NAV which does ILS.

Whether one should choose a GNS430W or the more modern GTN650 is another matter. Both have tiny screens… I would rather install a GNS530W than a GTN650.

The 430W and 530W are both discontinued but there are plenty used ones.

Administrator
Shoreham EGKA, United Kingdom

I’m still trying to get to the bottom of what i mean by “vertical navigation” …. It all started when i read this, written by Dynon Technical Support:

Without wading too deep into the techncials, here’s the short list:

If you have a GTN or GNS 430W/530W, you get vertical guidance on the GPS side when you’re on a GPS approach that provides vertical guidance (LPV, LNAV+V), and on the radio side when you’re on a glideslope. This data comes across via ARINC.

If you have a Garmin SL30 or the new radios, you get glideslope information via Garmin’s proprietary serial format.

If you have a Garmin portable x96 GPS, there is a proprietary Garmin sentence (not NMEA technically) that outputs the handheld’s vertical nav feature as a glideslope.

Any of those will show up as a glide slope on the SkyView HSI, and, as of 6.0, can be flown by the autopilot in VNAV mode.

My current aircraft with a Trio autopilot is pretty simple 2D autopilot that can follow the magenta line, all climbs and descends are manual.

It would be great for me if the new aircraft with skyview could do a bit more. (in order of importance to me)

1. A 3D flight plan, descending and climbing over/under controlled airspace as per the flight plan i send it over WIFI or set directly into the skyview

2. Do a circuit pattern and GPS approach, home made is fine, but that would be the perfect autopilot ending to a flight if it could fly the pattern and set the aircraft on approach to the runway.

EGKL, United Kingdom

You must have a certified GPS in the following situations:

  • for LPV – because none of the uncertified units do LPV
  • for flying instrument approaches using GPS – because none of the uncertified units contain the Jeppesen database, and Jeppesen is the only game in town for the database
  • for Eurocontrol IFR (as distinct from "UK-style IFR in Class G which is usually a VFR flight with nobody looking )

Your point 1.

A 3D flight plan, descending and climbing over/under controlled airspace as per the flight plan

is damn clever and no certified equipment does it. I don’t think even any airliner has a capability to climb and descend in a programmed way (that came to light in the MH370 discussion). AFAIK no autopilot will do it, unless you use it in approach mode and feed with a faked glideslope signal. Is there any certified GPS which has a vertical profile config i.e. a different altitude at each waypoint?

Your point 2.

I don’t think you would fly a circuit using GPS/autopilot

An approach does not involve flying a circuit. It is a specific horizontal and vertical profile. The database of these is owned by Jeppesen, but only for published approaches. Various avionics (certified and not) can be configured to fly a DIY approach to a waypoint, however.

Administrator
Shoreham EGKA, United Kingdom

Peter you are correct about airliner 3D flight profiles, it is posable to have a degree of 3D in a progmed flight plan but it can’t work without Some manual intervention.

As to the subject of the GTN 650 screen size, as a stand alone unit I would agree it is too small, but used as a control head for something like a G500 it would seem like an economic use of panel space especially if you also use the remote transponder option.

Is there any certified GPS which has a vertical profile config i.e. a different altitude at each waypoint?

Of course there are. Most all FMS systems and integrated systems can do it to some extent. Garmin G1000 will fly a VNAV profile in descent. G3000 can fly VNAV climbs and descents. In the Gx000 cases you still need to move the altitude select as they will never climb/descend through that in VNAV mode. And you also need to adjust power (unless you have auto throttles).

I also agree with @A_and_C, the 650s work well as FMS controllers for a system with an MFD of some sort. In the Mirage I had them with the Avidyne Entegra and loved them.

Last Edited by JasonC at 05 Jan 10:15
EGTK Oxford

Of course there are

Which system can have a programmed vertical profile comprising of multiple waypoints, each with a different level, and fly it hands-off?

That’s the obvious context here, because if you allow a manual intervention, any GA system with altitude capture (e.g. my ancient 1990s one) can do this.

but used as a control head for something like a G500 it would seem like an economic use of panel space especially if you also use the remote transponder option.

Agreed, but what “MFD” options are there for an uncertified aircraft for say a GTN650? A G500 is extremely pricey. That was my drift in the GNS530W reference; if that is to be your only box in the panel, at least you get a decent size screen.

Administrator
Shoreham EGKA, United Kingdom

Peter, in G1000 the system will fly a full STAR complying with all level and crossing restrictions hands off other than throttles (assuming you set the ALT select to the final ALT on the arrival or below). It will also continue to fly you down the steps in a procedural ILS or GPS approach until you are on the final approach track.

EGTK Oxford
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