Autopilot + 496 Question

[FlyingMonkey]

Hey guys, in the next month or two I will be installing a Trutrak Digiflight II VS in my 2007 CTSW equipped with a 496.  The autopilot is capable of vertical speed select (though not altitude pre-select).  My question is:

 

If I set up a VNAV profile in the 496, for example a descent to pattern altitude within 3 miles of the destination airport, will the Trutrack use the vertical speed capability to fly the VNAV profile, or will I still need to manually dial in the appropriate descent rate on the autopilot based on the 496 prompts?  Inquiring minds want to know.

[S3flyer]

Nope.  None of the portable Garmin's output VNAV data in the NMEA data stream.

[FlyingMonkey]

That's what I expected, but was curious...thanks Dave!

[Rich]

Hi Andy,

 

If it's not cost prohibitive, the TT APIII will give you altitude pre-select and a few other features. I find this very useful.

It's pre-select up and down so it comes in handy if you'd like to do approaches. Set it and forget it gives you more time looking out the window.

[FlyingMonkey]

Hi Andy,

 

If it's not cost prohibitive, the TT APIII will give you altitude pre-select and a few other features. I find this very useful.

It's pre-select up and down so it comes in handy if you'd like to do approaches. Set it and forget it gives you more time looking out the window.

 

Hey Rich...I got the Digiflight II VS Wm.Ince took out of his 2007 CTSW when he upgraded to a Skyview system with integrated AP.  His airplane only had 83hrs on it, and he made me an offer I could not refuse.  

 

My understanding from Trutrack is that the Digiflight series can be upgraded to their new Vizion series (with alt pre-select and GPSS if desired) by sending the head unit to them (along with $1200)...that might happen in the future, but I'd probably also want to upgrade the 496 before doing that or at the same time.

[Anticept]

Gentlemen,

 

I am pretty sure that garmin portables DO output the VNAV info in the NMEA stream when configured properly (at least starting with the 496). When you select one of the "NMEA out" functions in the serial data format configuration window, make sure that box is still highlighted, then press MENU. It will bring up a configuration menu with an option "Advanced NMEA setup". Press enter to go to the new screen. You need to set the NMEA output rate to NORMAL. Additionally, you need to make sure your VNAV is set up too in the Setup > vnav subtab.

 

D series dynon units, nor the autopilot, do not have a use for GPS status (reports satellite information), waypoint information (this might be useful for skyview), or the proprietary garmin format (very specialized for specific garmin interfaces, you won't use this unless you have a garmin unit that needs it).

[S3flyer]

Oops -- my bad :-(

 

The Garmin portables definitely do output VNAV as one can see that on the D100.  What they cannot do is output ALT information for a coupled approach.

 

Several years ago when I was researching APs, neither Trutrak nor Dynon (D100) APs would accept vertical guidance from a Garmin portable.  That is still true today for Dynon's D100 AP.  Don't know about later Trutraks or Skyview.

[Anticept]

It should output altitude too. That's part of the GPGGA sentence, which is always transmitted. It may also be affected by the advanced NMEA setup too.

 

I need to build a debugger, I am curious as to exactly what the 496 sends. Looks like this is good software to test with: http://www.navmonpc.com

[FlyingMonkey]

Thanks Anticept!

 

So...does this mean that an AP with vertical speed would fly down on the selected descent path, then level at the selected altitude?  Or would you need altitude pre-select for the AP to be able to level out at the bottom?  I would guess that the VS select could do it by just zeroing out at the bottom, but I'm not sure.

[Anticept]

That's dependent on the autopilot system. Pretty much the outputs of the GPS system act a lot like physical steam gauges. It just reports current status and route information, it is up to the autopilot to figure out what to do with it.

[FlyingMonkey]

Got it, makes sense.  Thanks again.

[FlyingMonkey]

The answer from Trutrak (at least as regards the TT Digiflight series) is, no, the autopilot will not follow a 496 VNAV profile.  Specifically the support guys said: "The 496 doesn't actually output this information as any form of steering signal."

 

So it looks like to fly the VNAV profile I'll have to look at the queues on the 496 and manually adjust the vertical speed rate to match what the 496 indicates.  Not a big deal, but it would have been nice to have this happen automagically.  Once I get everything installed I will play with it to see if I can make it work despite the response from Trutrak, but I am not hopeful.

[S3flyer]

Andy,

 

It's not really a practical issue for us VFR flyers. I have my AP defaulted to a 500fpm decent so I just dial in pattern altitude when the GPS displays 500fpm to reach my target.

[FlyingMonkey]

Andy,

 

It's not really a practical issue for us VFR flyers. I have my AP defaulted to a 500fpm decent so I just dial in pattern altitude when the GPS displays 500fpm to reach my target.

 

 

Sure, but it's nice when traveling long distances at relatively higher altitudes (6000-10,000ft) to have the VNAV profile tell you when and how fast to work your descent to get you at pattern height smoothly just a couple of miles from the airport.  If the AP would start and end that descent that would be pretty cool, but this is definitely just a convenience thing.

[S3flyer]

We're probably talking past each other but the Garmin does tell you that information based on the VNAV profile (I'm pretty sure the 496's VNAV is similar to the 79x).  The missing part is actually linking it.  Of course, you need to have the fpm match in the AP and GPS for this to work.

[FlyingMonkey]

We're probably talking past each other but the Garmin does tell you that information based on the VNAV profile (I'm pretty sure the 496's VNAV is similar to the 79x).  The missing part is actually linking it.  Of course, you need to have the fpm match in the AP and GPS for this to work.

 

Right.  The "missing piece" as you said is the ability for the 496 to pass the descent profile to the AP,  to manage the descent without intervention by the pilot by using the vertical speed select function.

[Ed Cesnalis]

Sure, but it's nice when traveling long distances at relatively higher altitudes (6000-10,000ft) to have the VNAV profile tell you when and how fast to work your descent to get you at pattern height smoothly just a couple of miles from the airport.  If the AP would start and end that descent that would be pretty cool, but this is definitely just a convenience thing.

 

I don't think the 496 tells you when and how fast to descend.  It tells you when based on how fast you tell it in the set-up, e.g. 500fpm.

 

On most flights, on my outbound leg I am descending from 10,000' to near sea level.  I have never missed the bar that appears when I first approach the vertical profile.  It takes a few minutes for the bar to descend to the middle and as that is about to happen I use a big throttle reduction to get to 500fpm.

 

Because I cruise at 5,500 if the AP put the nose down for me I would still have to reduce the throttle to keep from over speeding the engine.  The descent takes a power reduction or if you want to go fast a pitch and power reduction so your TruTrak couldn't fly the vertical profile on its own anyway.

[Doug G.]

I am wondering if it is necessary to use the HSI, or if the map display will give you a required v-speed message without it. I have a 696. Thanks.