S-Tec 3100

[donv]

I guess I can post about it, since it's on the Twin Commander website now...

It's pretty nice, I have to admit. Compared with the AP-106, at least as mine was configured, it has some real advantages, especially in the vertical modes. The big one is altitude preselect, which my AP-106 didn't have. The 3100 also has a very nice vertical speed mode, which works off the bug on the G-600 vertical speed, so it's very easy to control.

It does require some slightly different thinking than I'm used to. It always wants to capture whatever altitude is set on the G-600... I'm used to autopilots where you have to choose an "Altitude Select" mode or something like that, but the 3100 just always wants to level off at the selected altitude by default. Nothing wrong with that at all, just takes a bit of getting used to.

The lateral modes are pretty much the same as any other autopilot. Unlike the analog AP-106, it doesn't need a "GPSS Steer" mode, so you can choose HDG or NAV just like in the old days. It also has a half bank mode, which I always find to be a nice thing.

It gives me some nice redundancy. The 3100 has it's own AHRS built into it, so if the AHRS for the G-600 fails, the 3100 will still fly the airplane. Alternatively, if the 3100's AHRS fails, it will use the G-600 AHRS.

The next update to the 3100 will include VNAV coupling, which will be nice. Although, since the GTN-750 generates a vertical speed bug for the required vertical speed to make the crossing, all you have to do now is put the autopilot's VS bug on top of that and you'll get there at the right time.

Apparently they resolved the yaw damper issues of the 2100, and also provide better integration with the G-600. The 3100 reads the selected altitude straight from the G-600.

My AP-106 had two annoying glitches, both of which seem to be pretty common to other AP-106s that I've flown. Mine always crept up 100 feet in cruise, and at low com frequencies, it would pitch down when you keyed the mic. The good news is that the 3100 eliminates both of these glitches, so that is nice.

All in all, I'm quite happy with it.

[SKYFLYER]

So is the STC now valid and it it good for the fleet or just your model?

[donv]

Yes, the STC is all approved. Valid for all the turbine models, for sure, and I think at least the 500s if not most of the piston models.

[Adam Frisch]

Congrats!

And glad to see I'm not the only one that has condensation on some of the gauges...

[kent4142]

That is great news!  I am fascinated that you say the S-Tec 3100 is good for the whole fleet now.  In discussions with Garmin, I was told every single model of Commander would have to be certified individually.  ie 1000 series first, 900, 9980, 840, 690, 500 etc.  Unless of course I did not understand them correctly.  (This guy from Garmin probably did not understand the Commander line as well.)  690's, 695's etc.

My 81 840 had the same pitch issues on low frequencies as well.  Everett Macarthur helped me find a weak ground in the avionics bay that fixed that.  I was delighted!

My biggest issue with the AP-106 is that the altitude pre-select does not seem to work well at high descent rates.  My climb rates are never severe enough to cause the issue.

I am getting a G600 txi installed presently in Peoria.  I am sad to lose the steam gauges - but I am excited to join the "tv screen" crowd, in order to have all the advantages that the new technology provides.

[donv]

The 3100 will do up to 4000 fpm, I believe. That is the sort of stuff they looked at during flight testing.

[donv]

It covers pretty much all of the Commander models, piston and turbine.

[Steve binnette]

Don, what does it cost. Any idea

[donv]

It really depends on what you already have in your airplane. I think the basic unit is about $25-26k, and if you already have an S-Tec 2100, that might be all you need, since the servos are the same. If you have an AP-106 or some other analog autopilot, they will have to put new servos in, and the installation becomes a big deal. I think around $65-70k all in.

[donv]

One other nice thing the 3100 does is stall protection when the autopilot is engaged. Basically, if it hits a preset speed on the low side (which is higher in icing conditions, as denoted by the prop heat being on), it pitches down to maintain speed rather than trying to maintain altitude.

This is great because in my experience, the real world stall situations happen because the airplane is leveling off (altitude capture), and you are distracted by ATC or doing something, and don't advance the power. This scenario almost always happens with the autopilot on.

It also has an overspeed protection feature, which does the same thing on the high end (but, fortunately for the 980, it uses a set speed and ignores the barber pole, so not a big issue).

[Popeye]

Sarasota Avionics and Stec quoted around $30K installed on my 680F. Did not take the deal at the time. Right now I have other priorities, like props annual, and finding a honest shop.

[JMA]

Thanks Don- can I ask was this what needed to be 'hush hush', and if so, why?  Wouldn't the publicity be a positive?

[donv]

I think they just wanted to make a big announcement that it was available on the Commander.

Thanks Don- can I ask was this what needed to be 'hush hush', and if so, why?  Wouldn't the publicity be a positive?

[donv]

This is an excellent article about autopilot use, which applies in particular to the 3100:

https://flightlevelsonline.com/2021/control-column-automation-isnt-automatic/?fbclid=IwAR2jshlfE6smXjTkQLJEg7E47c0bEkrt1vKuVR9_ZCAfxRiNispWNRh-7eA

Making sure that it is programmed correctly BEFORE you turn it on is the important point. You don't have to operate an AP-106 that way, but you do need to operate the 3100 that way.

[donv]

I finally got my 3100 upgraded to the 1.4 software yesterday! I think I might have been the last airplane in the fleet running 1.3, mostly due to circumstances-- since S-Tec did my install, I didn't have a dealer to work with for updates, but I was finally in the Dallas area and able to stop in to Mineral Wells and get it updated.

1.4 flies the airplane much more smoothly, and seems to have largely done away with the porpoising in smooth air that 1.3 had. And you can use go-around mode on takeoff.