RNAV with 430W Stec30 GPSS Roll

[MyassisDragon]

I have noticed on when flying GPS approach with this configuration in a Grumman Tiger the Autopilot doesn't seem to lock onto the track until after I blow thru it the first time. I have talked to one other pilot who described something similar with a 530 and Century AP and I was wondering if this was a common thing?

Here is the my procedure (yes I normally fly the approach without AP but it would be nice to get it to work)

Example : Vectors from ATC bring me in on 20-30 degree angle to the track and I have the AP on track and GPSS on HDG.

When I get close and shallow out my turn to 10-15 degrees I switch the STEC to APP mode HI and switch the GPSS from HDG to GPS.

This is when the AP will not lock on until I muscle the plane back on track, then it seems to catch and all is good.

Any ideas?

 

[poadeleted20]

Don't use the autopilot TRK mode at all. -- the only time you want to use that mode on an S-Tec 20/30 is when actually tracking a VOR radial or LOC course. Do the vectors in HDG mode on the a/p with HDG on the GPSS. When you're cleared for the approach, hit the GPSS button to shift the GPSS to GPS, and it should handle the interception and tracking just fine after that.

 

[MyassisDragon]

Don't use the autopilot TRK mode at all. -- the only time you want to use that mode on an S-Tec 20/30 is when actually tracking a VOR radial or LOC course. Do the vectors in HDG mode on the a/p with HDG on the GPSS. When you're cleared for the approach, hit the GPSS button to shift the GPSS to GPS, and it should handle the interception and tracking just fine after that.

I just read what I typed, an made an error, I have the AP in HDG mode for the vectors and changed it to TRK for the approach.

Regardless, next time I am out I will leave it in HDG mode and just switch the GPSS to GPS.

Thanks for the help, I will let you know if it works better.

 

[N9552K]

The manual for the GPSS unit will have instructions for how to make it work properly. I was having trouble until I went through those instructions which tell you how to make the GPSS, AP and GPS all work together properly.

 

[poadeleted20]

I just read what I typed, an made an error, I have the AP in HDG mode for the vectors and changed it to TRK for the approach.

That's the problem. TRK bypasses the GPSS roll steering output from the 430, and reads only needle position. Once it does that, it won't start turning until the needle starts moving, and that's how you overshoot. As I said before, the only time you want to use TRK is when tracking a VOR or LOC signal.

Regardless, next time I am out I will leave it in HDG mode and just switch the GPSS to GPS.

Bingo.

Thanks for the help, I will let you know if it works better.

You might want to read this and this, especially the latter. They will help you understand your autopilot better. And you can even download them onto your iPad for inflight reference.

 

[MyassisDragon]

You might want to read this and this, especially the latter. They will help you understand your autopilot better. And you can even download them onto your iPad for inflight reference.

Actually I have the first one in my ipad and this is what confused me

3.1.4.2
GPS Course Tracking
Program a predefined course into the GPS Navigation Receiver, comprised of
course segments connected by waypoints.
Maneuver the aircraft to within ±1 CDI needle width and ±10° heading of each successive course segment.
Engage the high track mode. The HI TRK lamp alone will be illuminated as
shown in Fig. 3-4, to acknowledge that this mode is engaged. The autopilot will
track the selected course segment with maximum authority

I guess I was thinking if it worked En route with Maximum authority it would be used with approaches as well. I did not have the second one so I will do some more reading.....Thanks!!!

 

[poadeleted20]

Actually I have the first one in my ipad and this is what confused me

3.1.4.2
GPS Course Tracking
Program a predefined course into the GPS Navigation Receiver, comprised of
course segments connected by waypoints.
Maneuver the aircraft to within ±1 CDI needle width and ±10° heading of each successive course segment.
Engage the high track mode. The HI TRK lamp alone will be illuminated as
shown in Fig. 3-4, to acknowledge that this mode is engaged. The autopilot will
track the selected course segment with maximum authority

I guess I was thinking if it worked En route with Maximum authority it would be used with approaches as well. I did not have the second one so I will do some more reading.....Thanks!!!

GPSS changes everything. Read the second manual, and you'll see.

And note that "±1 CDI needle width and ±10° heading" bit regarding TRK mode -- if you were getting vectors to final, you were probably cleared for the approach with about a 30-degree angle to the final approach course and the needle likely still pegged. If you were to use TRK mode for a GPS approach (i.e., if you didn't have a roll steering adapter), you'd have to use the heading bug to fly yourself within those parameters before punching over to TRK.

 

[MyassisDragon]

GPSS changes everything. Read the second manual, and you'll see.

Wow I see that now, didn't realize the little button did that much (its not my plane so I dont get to play with it all the time)

you'd have to use the heading bug to fly yourself within those parameters before punching over to TRK.

This is what I was actually doing, not knowing how the GPSS worked, thats where I would get the over shoot and big turn back. So when it didn't work, I just flew the approaches by hand.....Feel kinda human now that I read it (dumb, dumb)

 

[poadeleted20]

Wow I see that now, didn't realize the little button did that much (its not my plane so I dont get to play with it all the time)



This is what I was actually doing, not knowing how the GPSS worked, thats where I would get the over shoot and big turn back. So when it didn't work, I just flew the approaches by hand.....Feel kinda human now that I read it (dumb, dumb)

One of the cool things about the 21st century is that the manuals for pretty much everything are available on the internet and downloadable onto your iPad. Every time I get an assignment involving an unfamiliar system, I grab the manual the week before so I can study it before arriving on the job. More times than not, I know more than the client by the time I get there. If clients did the same, I wouldn't appear so smart to them. :wink2: