Altitude Reference: Stratus 2 WAAS or Altimeter?

[FastEddieB]

My autopilot definitely uses GPS for heading.

You sound pretty definite!

Maybe show me a reference, and I'll be convinced.

I've just never seen a GPS that provided heading information - that traditionally had to come from a compass somewhere.

If there's a way a GPS can actually figure heading without compass input, I'll consider myself educated.

Like I said, even the Cirrus with modern stuff have a compass in the wing (magnetometer below) that hooks up to the PFD for heading info.



Of course the autopilot uses GPS info for NAV info, but that's different from heading info. In the Cirrus it gets its heading info through the PFD, but the source is the magnetometer, not the GPS. I know this because with failed GPS you still have heading info, both displayed and available to the autopilot.

Are you sure your setup isn't similar? If you turn off your GPS does your autopilot lose its ability to fly a heading?

And finally, if a 496 knows your magnetic heading, why does it need you to input it on the E6B page?

[CharlieTango]

The GPS and EFIS magnetometer are usually within 1°-3° of each other, but I have observed errors up to 6°.

Do you mean error or crab angle?

[MrMorden]

The GPS and EFIS magnetometer are usually within 1°-3° of each other, but I have observed errors up to 6°.

Do you mean error or crab angle?

Could be either, I have no way to be sure.

Edit: almost certainly crab angle difference between heading and ground track.

[MrMorden]

My autopilot definitely uses GPS for heading.

You sound pretty definite!

Maybe show me a reference, and I'll be convinced.

I've just never seen a GPS that provided heading information - that traditionally had to come from a compass somewhere.

If there's a way a GPS can actually figure heading without compass input, I'll consider myself educated.

Like I said, even the Cirrus with modern stuff have a compass in the wing (magnetometer below) that hooks up to the PFD for heading info.



Of course the autopilot uses GPS info for NAV info, but that's different from heading info. In the Cirrus it gets its heading info through the PFD, but the source is the magnetometer, not the GPS. I know this because with failed GPS you still have heading info, both displayed and available to the autopilot.

Are you sure your setup isn't similar? If you turn off your GPS does your autopilot lose its ability to fly a heading?

And finally, if a 496 knows your magnetic heading, why does it need you to input it on the E6B page?

Don't get too breathless, Eddie. I just meant that the AP uses the 496 for directional control (I believe). It's probably actually ground track, not heading. I believe there is a magnetometer in the AP itself for heading info, it requires the airplane to not move while it calibrates on startup.

I know it doesn't use the EFIS though, Lockwood told me I could not use EFIS heading bugs to make changes to the AP because there is no direct connection between the EFIS and the AP.

[FastEddieB]

Got it.

We know how some can twist meaning, so the exact terms are important.

If your autopilot really has a compass/magnetometer built in, I'd be curious to see that.

[3Dreaming]

If your autopilot really has a compass/magnetometer built in, I'd be curious to see that.

That is what TruTrak says in the manual.

[CharlieTango]

If your autopilot really has a compass/magnetometer built in, I'd be curious to see that.

That is what TruTrak says in the manual.

Its got to come from somewhere. True TruTrak could get heading info from an EFIS but that thinking limits it to EFIS equipped planes. Including a self calibrating magnetometer makes it good EFIS or no.

[3Dreaming]

If your autopilot really has a compass/magnetometer built in, I'd be curious to see that.

That is what TruTrak says in the manual.

Its got to come from somewhere. True TruTrak could get heading info from an EFIS but that thinking limits it to EFIS equipped planes. Including a self calibrating magnetometer makes it good EFIS or no.

From their manual.
When the GPS track is not available TRK will be replaced by HDG, which means the autopilot now uses an internal source of magnetic information for direction.

[CharlieTango]

From their manual.
When the GPS track is not available TRK will be replaced by HDG, which means the autopilot now uses an internal source of magnetic information for direction.

That works for CRS, GPS, VOR modes but not for HDG mode

[3Dreaming]

From their manual.
When the GPS track is not available TRK will be replaced by HDG, which means the autopilot now uses an internal source of magnetic information for direction.

That works for CRS, GPS, VOR modes but not for HDG mode

I think you are talking about a different autopilot than Andy and myself are.

[FastEddieB]

From their manual.
When the GPS track is not available TRK will be replaced by HDG, which means the autopilot now uses an internal source of magnetic information for direction.

That's cool, and a new one on me!

Never too late to learn something.

[CharlieTango]

From their manual.
When the GPS track is not available TRK will be replaced by HDG, which means the autopilot now uses an internal source of magnetic information for direction.

That works for CRS, GPS, VOR modes but not for HDG mode

I think you are talking about a different autopilot than Andy and myself are.

True but my statement remains true.

Whenever you have a HDG bug, or are in a HDG mode the AP should steer the magnetic heading, otherwise it should stear the course, whatever the source.

[BrianL99]

[quote="CharlieTango"
From their manual.
When the GPS track is not available TRK will be replaced by HDG, which means the autopilot now uses an internal source of magnetic information for direction.[/quote]

That works for CRS, GPS, VOR modes but not for HDG mode[/quote]

I think you are talking about a different autopilot than Andy and myself are.[/quote]

True but my statement remains true.

Whenever you have a HDG bug, or are in a HDG mode the AP should steer the magnetic heading, otherwise it should stear the course, whatever the source.[/quote]

***************

If I understand my TruTrak Owner's Manual, IF there's a GPS attached and sending data, it can only fly the GPS heading. If the GPS signal is interrupted, it will then get heading information from the 'internal magnetic source'.

I'm curious about my TruTrak ADI, which supposedly has a "built in ground track DG". How is that possible? Is there an electronic way to derived actual ground track without using GPS ?

[MrMorden]

Whenever you have a HDG bug, or are in a HDG mode the AP should steer the magnetic heading, otherwise it should stear the course, whatever the source.

The TruTrak DigiFlight IIVS I have has two modes, HDG and GPS. The first uses its internal magnetic gizmo to set a pilot selectable heading, and the latter uses the GPS flight plan to steer.

I believe this is consistent with what you said.

[drseti]

FWIW, both the Dynon D100 EFIS I have in my plane and the Dynon Skyviews I've flown in other people's planes have a magnetic heading indication available as a tape across the top of the screen. And, in both cases, the magnetic heading information comes from a flux gate magnetometer installed in the aircraft. The Dynon EFIS units work just fine with all GPS units turned off, and display magnetic heading, not ground track. So, if an autopilot is being driven by an EFIS, it should certainly be possible to select heading mode, to follow a magnetic pointing direction (properly known as a HEADING).

And, yes, to those of you who have Private Messaged me to keep this thread going, I'm fine with that, as long as we're discussing something useful like how particular equipment functions, and not arguing about the meaning of terms that are already very clearly defined in the AIM.