Lil' help please. UAvionics vertical navigation

[Chip Sylverne]

We're installing uAvionics AV30, hsi, mag and apa into the Comanche. I have an STEC 60-2 which for lateral navigation is supposed to be seamless with the APA, GPS 175 and SL30, the AV system is supposed to handle nav/gps switching internally. Cool. Problem is arising with coordinating vertical nav. The STEC requires 5 analog inputs to follow a glideslope; vertical deviation +/-, Flag +/-, and ILS activate, which is a low input to kick the a/p into appch mode sent from either the gps or by tuning in an ILS.

I need the be able to switch between the gps and sl30 for the a/p to recieve the correct vnav signals. The problem here is that ils arm signal ground. Has anybody dealt with this in a good clean way? I have an Eaton switch I used for the GPSS unit, but it's only 4 poles, and I haven't found a dpst toggle that will control 5 circuits. Installing an avionics relay is kinda overkill. And expensive.

Thoughts appreciated.

 

[plsmt]

Have you confirmed whether the AV30/APA already handles the GS source switching internally? My understanding is that it was designed to feed legacy autopilots like the S-TEC, so you may not need to switch all five signals yourself. If it doesn't, a small avionics relay tied to the NAV source select is probably the cleanest solution.

 

[Chip Sylverne]

Have you confirmed whether the AV30/APA already handles the GS source switching internally? My understanding is that it was designed to feed legacy autopilots like the S-TEC, so you may not need to switch all five signals yourself. If it doesn't, a small avionics relay tied to the NAV source select is probably the cleanest solution.

Spent most of the day poring over the manuals. Yes, it does switch internally, and after going over the RS-232 data output from the SL30 and Arinc 429 from the 175, all the analogue vdi/flag signals should be redundant and unecessary. The only open question I have is which unit should be pinned directly to the ILS arm pin on the STEC so it will fly a glideslope. I understand two units controlling one low pin leads to backfeed issues. And secondly, whats "pass through" configuration for the APA mean operationally. I've been living with lpv only, but it would be nice to have an a/p on an ils again.

 

[Ed Haywood]

Try calling uAvionix. I've spoken to their tech support folks before at SnF and they are very helpful.

 

[Chip Sylverne]

Try calling uAvionix. I've spoken to their tech support folks before at SnF and they are very helpful.

Thier answer was basically the following:

The problem here is trying to mate 1980's and 21st century technology. The APA does support the stec, but lateral only. The 60-2 A/P requires vertical analog inputs from a navigator in Nav mode to capture and fly a glideslope, either ILS or LPV. The uAvonics APA converts digital inputs and outputs to analog lateral, but not vertical, so when you push the A/P nav button to capture, it fails glideslope. Not much can be done.about it. So while it will display the needles, the stec can't fly them.

Given the time and expense of screwing around, trying to make something work, i think the way to go is to use the analog outs of the 175 for both lateral and vertical coupled lpv's and overlays, and just hand fly the occasional ILS.

The KCS 55A had to go. Just not up for installing a full Arinc 429 autopilot right now.