GPSS - STEC ST-901 vs Garmin G5

Discussion in 'Avionics and Upgrades' started by DesertNomad, Aug 16, 2018.

  1. DesertNomad

    DesertNomad Pattern Altitude

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    I have an STEC-30 and have an ST-901 GPSS unit with it. I am considering adding dual G5s to my Dakota which have GPSS. Is there any difference between the quality of the GPSS in the ST-901 vs the G5?

    A friend has a Twin Comanche with dual Aspens and and S-TEC 55x. I believe he uses the GPSS in the Aspen as he thinks it is a bit more aggressive than the one in the 55x.

    Thoughts?

    Also - with my ST-901 I have a GPSS/HDG toggle button to switch modes. Is there a similar button on the G5?
     
  2. WannFly

    WannFly En-Route

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    yes, you push the knob, turn and push again to choose between GPSS and HDG. dont know about the quality and have no baseline for comparison, but you can adjust the roll steering gain if need be if you are overshooting or undershooting (?) the life line .. er..magenta line

    EDIT: i might be wrong, but i believe the aggressiveness of a turn depends mostly on the GPS anticipation
     
    Last edited: Aug 16, 2018
  3. James331

    James331 Touchdown! Greaser!

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    Are you talking the G5?

    On my stec I have a GPSS/HDG button, i always have by heading bug snapped to my heading, so if I’m flying on nav and I’m given a turn left 15 degrees, or start getting vectors to final, I just push the GPSS/HDG button and turn the knob to the assigned heading, or left or right XYZ degrees.

    Can’t speak for the garmin, but the stec does a pretty good job and is fast enough to switch IMO. The only thing mine doesn’t have, which I would like is a arm mode for nav, where say you’re given “turn left heading 330, maintain 300’ until established on the localized, clearered the ILS RWY 31”, in that example I would turn the plane in heading mode to 330, have the ILS all set up, hit nav but since the CDI isn’t on it would just arm approach/nav, once I started to come into the loc it would switch over to nav/aprch mode, capture and fly the ILS.
     
  4. WannFly

    WannFly En-Route

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    yes. i do the same thing, fly on GPSS, keep the heading bug on my assigned heading, then when getting vectors, switch to HDG mode. pushing one button is lot better than 3 steps though.
     
  5. teejayevans

    teejayevans Pattern Altitude

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    I had both, functionally the same, you can sell the 901 for $400 to recoup some of the update costs.
     
  6. Clip4

    Clip4 En-Route

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    “We’re pleased to announce the G5 electronic flight instrument will soon be compatible with a wide-range of third-party autopilots available on the market. Utilizing the new GAD 29B adapter, the G5 directional gyro (DG)/horizontal situation indicator (HSI) can interface with a variety of autopilots to provide heading and course error to drive the autopilot. With a compatible navigation source, the G5 can also interface with select autopilots for coupled flight in heading and navigation modes. Additionally, when interfaced with a GTN 650/750 or GNS 430W/530W, the G5 can provide GPSS roll steering navigation from the navigator to the autopilot. Pilots can simply select GPSS on the G5 and heading mode on the autopilot and the autopilot will fly smooth intercepts, holding patterns, procedure turns and more.”
     
  7. DesertNomad

    DesertNomad Pattern Altitude

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    Which STEC do you have? Is this a STEC-30 and ST-901 GPSS combo? I guess you kept the 901 when adding the G5s so the GPSS in the G5 is not used?

    I think I may keep the 901 as it is made by STEC (so maybe a bit better to have the GPSS and AP built by the same people) and it is one button vs push-twist-push.
     
  8. teejayevans

    teejayevans Pattern Altitude

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    There seems to be no difference, and it may be better to have the GPSS and the GPS be made by the same people.
    How often do you have to switch between heading and GPSS modes?
     
  9. James331

    James331 Touchdown! Greaser!

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    30 ALT hold with GPSS
     
  10. DesertNomad

    DesertNomad Pattern Altitude

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    So did you keep the ST-901 even after adding the G5-HSI?

    I guess you just leave the G5 in HDG mode all the time, as well as the STEC-30 and use the 901 button to toggle HDG/GPSS?

    How does that work with regard to the blue heading bug on the G5 - it is always solid, or always an outline?
     
  11. bnt83

    bnt83 Final Approach

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    James has a G5 HSI lol! Good one. He's still flying Sandel incandescent lightbulb inlumated LCD.

    the G5 HSI interface couldn't be any simpler, just read the airplane flight manual supplement. The autopilot needs to be in heading mode because that's the only channel hooked to the G5 HSI system. The G5 itself is where you switch between heading and GPSS modes.
     
  12. DesertNomad

    DesertNomad Pattern Altitude

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    Unless I keep my STEC-901 GPSS and bypass the one in the G5. With that method I think the heading indicator on the G5 will remain solid even when I am in GPSS mode since the G5 won't know GPSS exists.
     
  13. bnt83

    bnt83 Final Approach

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    So you are willing to give up autopilot tracking heading bug on the G5 just to keep an older GPSS adapter? Why? It makes no sense to me. Or I'm not seeing the whole interface.
     
  14. DesertNomad

    DesertNomad Pattern Altitude

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    I don't think I am giving anything up. The heading bug will stay solid all the time and the autopilot will follow it. If I engage GPSS on my ST-901, the G5 won't know this has happened (because it is always in HDG mode) and will keep the heading bug solid, but the AP will us GPSS to follow the course in the GTN750. Right?
     
  15. teejayevans

    teejayevans Pattern Altitude

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    You could sell the 901.
     
  16. DesertNomad

    DesertNomad Pattern Altitude

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    I see prices on eBay all over the place: $335, $850, $1,450. It's not worth the hassle for $335, but for $1K it is. My main thought is that I will have to recut my lower AP panel if I remove it and I like the one button control without push-twist-push.
     
  17. bnt83

    bnt83 Final Approach

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    IDK, and couldn't find a wiring diagram for the ST-901, typical proprietary nonsense.
     
  18. teejayevans

    teejayevans Pattern Altitude

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    $850, $1450? They are on drugs...
     
  19. James331

    James331 Touchdown! Greaser!

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    Apologies if I miscommunication, yeah, it’s a 30 alt hold GPSS with a 3308, which IMO is a far better, and a real, eHSI, G5 is a little basic on its display.
     
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  20. DesertNomad

    DesertNomad Pattern Altitude

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  21. teejayevans

    teejayevans Pattern Altitude

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  22. chartbundle

    chartbundle Line Up and Wait

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    And that's what the sold items button is for, looks like they're actually selling for an average of about $450
     
  23. teejayevans

    teejayevans Pattern Altitude

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    I’d be willing to bet a cold beverage that next year that average will be less.
     
  24. DesertNomad

    DesertNomad Pattern Altitude

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    Which is why I am considering keeping it. I gather that the G5 just won't know the difference.
     
  25. Russell MacDonald

    Russell MacDonald Filing Flight Plan

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    I have an S-Tec 30, and two G5's installed in my C177RG, and I removed the ST901 GPSS. The G5 GPSS tracking works fine except I now find the autopilot very slowly hunts left and right about 1 degree each way as it tracks a straight line course using GPSS from the G5. It is barely noticeable and I can only detect it when in perfectly smooth air, but I never noticed any 'hunting' when I had the ST901 driving the autopilot. I have been told that the G5 GPSS tracking function is adjustable on the Master G5 in the 'Flight Controls' area in the Configuration settings. There is a number for 'GPSS Scale Factor', which is recommended to start at 1.0 setting. I will check this today to see what mine it set to and try changing it. I think that this number adjusts the sensitivity of the GPSS function and maybe reducing it will correct my problem.

    Russ
     
  26. DesertNomad

    DesertNomad Pattern Altitude

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    I've had my ST901 removed so hopefully the G5s won't hunt like that. My 901 GPSS was rock solid.
     
  27. Russell MacDonald

    Russell MacDonald Filing Flight Plan

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    I just got back from checking my G5 'scale factor' setting at my hangar, and found it was set to 2.0. I reduced it to 1.5 but there is too much wind to flight check it today. Now, we have hurricane Michael headed our way, so it might be a week or so before I will get a really calm day to check it.
     
  28. Arrow76R

    Arrow76R Filing Flight Plan

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    Interesting! I have a dual G5 setup in my Arrow with the GMU 11 magnetometer and GNS 530W all interfaced with the S-Tec 30. The scale factor on the G5 HSI is set to 1.0 and my avionics shop said that if the G5 doesn't "track well" let them know. So far the only slight thing I have noticed is (perhaps) a little lag in making course changes using GPSS which leads to a slight overshoot coming back on course but that damps out almost immediately. Like Russell said, though, the winds have been to strong and gusty to get definitive data. I will share further test data once the winds calm down a bit.
     
  29. Russell MacDonald

    Russell MacDonald Filing Flight Plan

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    After reducing it to 1.5, I found it was still 'hunting' while tracking a GPSS course, only noticeable in very calm air. So, I reduced it to 1.0. Now it no longer hunts, but it is a bit sluggish when intercepting a GPSS course, and it takes a long time to get perfectly centered on the course, which makes me think I went too far. Next I will try increasing it to 1.25.

    I'll update after I find out.
     
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  30. Arrow76R

    Arrow76R Filing Flight Plan

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    Russell,

    Good data point. Now you (and I) know which direction to move the scale factor...just a matter of how much. I think I will nudge mine to 1.25 to see if that tightens up the GPSS course capture.

    Jim
     
  31. Arrow76R

    Arrow76R Filing Flight Plan

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    Russell,
    Just thought of another consideration. How much of a heading change was your GPSS trying to make. Obviously you should try the same amount of course change when you adjust the scale factor to remove that variable.

    Jim
     
  32. SbestCFII

    SbestCFII Line Up and Wait

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    That’s likely more an STEC issue than the G5. The STEC 20,30,40 units have never been know for their solid CDI capture like the Century APs which are pretty brisk at the task.
     
  33. Arrow76R

    Arrow76R Filing Flight Plan

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    Agreed because the S-Tec units are rate based vs attitude based autopilots which, I believe, include the Century units.

    Russell, Today I changed the GPSS scale factor in my G5 AI to 1.25 from the initial 1.0 value and noticed what I believe to be a much more rapid course acquisition with little overshoot. My heading change was almost 90 degrees with 140 knots TAS. It wasn't really feasible to see if any "hunting" occurred during course tracking because there is NO SUCH THING as calm winds here in Colorado!! But it appeared to be a smooth track.
     
  34. DesertNomad

    DesertNomad Pattern Altitude

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    My shop got the G5s installed with my S-TEC 30 (ST-901 is gone). Now my AP only seems to turn at half rate. The STEC was reconfigured to a KI-525 for the G5. Any ideas? Could the AP be misconfigured as something other than a KI-525? My shop still has the plane and I did not see this - only going on what they told me.
     
  35. Arrow76R

    Arrow76R Filing Flight Plan

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    My shop said they had to "re-do settings" in the S-TEC 30 that I have when they installed a G5 HSI to replace a vacuum DG. You might compare the GPSS rate of turn with just changing the heading bug (in heading mode, of course), both of which should result in a full standard rate turn. If not, then some settings need to be tweaked. Have you checked to see what the GPSS "Scale factor" is as mentioned above?
     
  36. DesertNomad

    DesertNomad Pattern Altitude

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    The slow (about 1/2) rate turn happens in bot GPSS and HDG mode (by moving the bug). The scale factor is 1.0 but that should not affect turns with the bug. They had to send the STEC-30 out for the reconfiguration so it looks like that part was not done right.
     
  37. bnt83

    bnt83 Final Approach

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    The Garmin STC Installation Manual is extremely lacking IMHO regarding these issues. Basically "here's ur wiring diagram and basic config"... "troubleshooting??? HAHAHAHA."
     
  38. bnt83

    bnt83 Final Approach

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  39. mr_happyland

    mr_happyland Pre-takeoff checklist

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    I have a STEC 50 in my plane. If I want to add GPSS, is the STEC ST-901 all I need to add that functionality? (I have a GTN 650 as well). Those eBay prices seem pretty reasonable to gain that xtra function.
     
  40. teejayevans

    teejayevans Pattern Altitude

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    Yes, I had 901 before G5 upgrade, it works well.
    Caveat: 901 must be configured by factory for specific HSI, make sure you get one that matches what you have. It’s stamped on the box, ask for picture to be sure.