I've ordered an STEC-20 for my Cherokee and have been talking to some other pilots. One told me that the STEC-20 tends to wander back and forth while navigating on a GPS track from the CDI, especially with a crosswind (tends to overcorrect). As my budget doesn't include a GPSS, I'd be interested to hear from others with experience with STEC-20s and 30s. I already thought about increasing the sensitivity on the GPS to make the CDI more sensitive and running the STEC in High Sensitivity mode. Would these strategies help? What has been your experience? Any suggestions would be welcomed.
Gary, you are probably not going to like my suggestion ... 'cause it's going to dent your budget. Sorry. Here goes. I have an STec-30 with GPSS coupled to a Garmin 430. In GPS tracking and with the GPSS engaged, the STec30 tracks like a dream. Wonderful. It will fly the magenta line on the 430 like it's on rails. Ok,ok maybe not quite that great, but really terrific.
If, however I select HDG rather than GPSS on the selector and change the 430 from GPS tracking to VLOC, the the STec is not terrific. Not wonderful. Not even average. It will wander and it does not handle cross winds well at all. Bummer. I have thought that this relates to the radio beam from a VOR or Localizer but it maybe just the capabilities of the STec.
Ok here is the money comment. Spend the money and get GPSS. If you have an IFR GPS, the GPSS will fly what you have loaded into the flight plan: departure procedure, enroute with turns, STAR and approach (everything except procedure turn and the first part of the missed approach procedure). GPSS so impressed me when I got it for my Arrow 3 years ago. My company used to fly a 1986 Dassault Facon 50 with a Universal FMS and Collins A/P. And my little setup in my little Arrow came close to being as capable as that in the Falcon. Yes, yes, the FMS had greater reduncancy and could do vertical navigation better than my simple altitude hold. But to transition from enroute to STAR to IAP you had to steer the plane to the next segment and engage. No need with the GPSS set up. Waaaay cool.
I read your comment on the S-Tec 30 we have a 74 Arrow with the piper auto pilot and thinking about installing the S-tec 30 you said it tracks the gps signal great but when you put to vloc you were saying that it wonders a bit. We have the garmin 430 we have not upgraded it yet to the wass and the gpss. Does the S-Tec 30 fly the ILS aproaches good and follow the heading bug and are you pleased with the S-Tec?
What kind of price are we looking at installing the 30 and would you recommend this one.
Kyle, sorry to take so long to respond. I just wasn't checking the forum with any frequency.
Let me respond:
Yes, I'm very pleased with the S-Tec 30 with altitude hold and GPSS. It is very good value for the money. It is not a full featured King 225 with altitude pre-select, etc, but it is a lot less expensive. It is a rate based a/p that tracks very well when driven by a gps signal. The altitude hold is a wonderful tool, but it is just a hold unit and does not have an automatic trim feature. I do not find this to be a problem and there is both an audible and visual alerter for out of trim conditions. Can be a little annoying on a bumpy day.
ILS approaches using the Garmin 430, S-TEC, GPSS and Alt Hold are a snap. I generally use the following procedures for an ILS approach. Kyle, I have found that most of my ILS's are vectors so that is what I'll use here.
When about 50 miles out at still at altitude I listen to get the approach in use or just ask the final approach controler what approach to expect. If it is the ILS, then I load in the approch from the list in the Garmin 430. Once the vectoring for aligning to intercept the localizer begins, I use the Heading bug and Alt Hold. Descent instructions are complied with by disconnecting the Alt Hold and descending. Once I've be vectored to the 45 deg intercept to the localizer, I activate the ILS approach and engage the GPSS. The "magenta" line in the Garmin display is the desired track and once the GPSS is engaged it will fly the airplane to the inbound localizer course. Once on the localizer outside the OM and at the appropriate altitude I engage the Alt Hold. Now the airplane is tracking the localizer and holding altitude. I switch the sensing in the Garmin 430 from GPS to VLOC. With GPSS still on, the a/p is tracing the gps final course line while the OBS is displaying the localizer beam - so the a/p is still flying the gps line but I can see and monitor the localizer beam capture and track on the oBS indicator. I review the approach plate for the 8th time! Just before the FAF, I lower the gear, slow and put in flaps. At the FAF, I disconnect the Alt Hold and begin flying the plane down the glidepath. I'm manually controling pitch and the resultant alitude, but the a/p is flying the localizer. I complete the approach and land. But if I need a go around, the combination 430, S-Tec 30 and GPSS become a handy tool again. Once the 430 cycles through to the missed approach course line I am about ready to take the unit our of suspense and put in HDG mode. I fly the runway heading and climb. At the appropriate point I switch to gps on the 430 and engage the GPSS. This means that the a/p will follow the steer directions from the 430 and track the missed approach line. That is a life saver when you are tired in IMC at night. Let the a/p earns it's keep.
Frank, I don't believe that it can be silenced. Yes, it can be annoying, on the other hand, I do want more than the visible alert that trim forces are getting high.
In fact, most, if not all current biz jets have audible alerts when the trim is in motion. That alert it so insure that the pilot has knowledge of trim movement so that the a/p won't unintentionally drive an unstable condition due to trim. But the point is that it is annoying. I guess we have to live with trim annoyance!
FYI---if you upgrade your 430 to WAAS, you won't be able to couple the A/P to the GPSS if the the 430 is in the VLOC mode. A relay has to be installed to disconnect the serial data to the roll steering computer whenever the 430/530 is in VLOC mode. This is IAW the Garmin installation manual.
Granby - are you there? Can anything be done to an STec 30 ALT to either silence the audio alert or control the volume? I had heard about this before and it has kept me from installing one.
verry interesting! I am about to add an S-TEC 30 and GPSS to my Warrior (already equipped with a GNS430) but I really do not understand your explanation.
How can fly an ILS and GPSS at the same time? If you select an ILS approch from the data basa and activate it, then the CDI follows the radio singals of the LOC, right? But you say that the AP will still follow the magenta line of the LOC...
Ok, I have 4 weeks unbtil the AP is installed, so there's time to learn :-)
