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  #11  
Old 09-25-2018, 01:46 PM
lr172 lr172 is offline
 
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Originally Posted by airguy View Post

I'm curious about this because, today when manually switching the PFD HSI source from GPS to NAV side, it does NOT carryover the course direction. It must be something in the automatic switching that carries that over?
As I mentioned above, 430 does not provide a magnetic course in VLOC mode. I believe the TSO specifies that guidance on the ILS or LOC approach must be CDI and therefore th3 430 stops sending it in VLOC mode. The course on your HSI can be a situational awareness aide, but cannot be used as official LOC guidance, therefore the 430 doesn't provide it. The LOC course must therefore be manually entered or determined by the EFIS if it has access to IAP's or runway headings.

Larry
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Last edited by lr172 : 09-25-2018 at 01:57 PM.
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  #12  
Old 09-25-2018, 03:15 PM
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Carefully reading through the documentation, it appears that only the CDI deviation data switches from the GPS to the NAV side on the 430W, and the 430W utilizes something they call an "OBS resolver" that apparently, from what I can ferret out of the docs, acts as a "target" for lack of a better term for the autopilot to go toward and then take CDI deviation from that target. In theory, given enough time, it would finally correct itself just like a GPS course with a massive crosswind would, but on initial startup (like when manually switching to NAV source) it will turn toward the target course immediately and then start making corrections. Using the CRS knob on the Skyview to set the course to the proper runway alignment should communicate that OBS back to the 430W through the ARINC-429 and feed that into the OBS resolver, which then will send appropriate-magnitude corrections to the autopilot, if it works the way I think it does.

The Bendix-King KLN94/KMD550/KAP140 GPS/autopilot installed in late-model C-172's will do the same thing now that I think about it, you needed to dial in the "DTK" readout from the KLN94 display into the HSI for it to capture quickly - otherwise it would hunt drunkenly around the compass for several minutes before settling down into somewhat the correct direction.

It's starting to make a little sense now, but it will be tomorrow afternoon before I get a chance to test it.

In all fairness I'll point out that this agrees completely with all the advice given by Larry, Ted, and Carl - I'm just trying to figure out the "why" behind the "what".
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Last edited by airguy : 09-25-2018 at 03:31 PM.
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  #13  
Old 09-25-2018, 06:12 PM
lr172 lr172 is offline
 
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Originally Posted by airguy View Post
Carefully reading through the documentation, it appears that only the CDI deviation data switches from the GPS to the NAV side on the 430W, and the 430W utilizes something they call an "OBS resolver" that apparently, from what I can ferret out of the docs, acts as a "target" for lack of a better term for the autopilot to go toward and then take CDI deviation from that target.
OBS only works on VOR navigation. OBS doesn't apply to LOC signals, as they are designed only to allow navigation down the preset course, unlike the Onmibearing VOR, that allows the pilot to select the course to or from the VOR (it effectively broadcast all 360 segments). The 430, or any Nav receiver, will ignore the OBS selector data when tuned to a LOC freq.

The 430 will not provide any bearing or course data for LOC guidance, beyond the deviation data that is receiving over the air, when in VLOC. No DTK or similar. It only provides course deviation, derived from the broadcast signal. Only your HSI or EFIS can establish a desired magnetic course indication for you, with no help from the 430.

The why is the TSO. The FAA makes it very clear that LOC/ILS approaches are to be flown based upon deviation data from the broadcast signal and not from magnetic course.

Unfortunately I can't answer WHY the Dynon wants course data to fly a LOC approach. It should be flying off CDI data. Though I fully understand how the course data will help with intercept. I think most AP's want you inside of full scale deflection and asssumes you are pointed at the airport, so don't need course data. These are usually limits that must be met before an armed mode will switch to active.

Also, remember that the 430 isn't driving the AP. It is only providing basic data that an AP can use to fly. Nav data is far more limited than GPS data. It provides no direction to help the AP intercept. This excludes GPSS data which is specifically designed as instructions for the AP.

The 430 does help with intercept by flying in VNAV GPS mode up until intercept before switching to VLOC, so that it can be more involved in intercept for the AP.

Larry
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Last edited by lr172 : 09-25-2018 at 06:30 PM.
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  #14  
Old 09-30-2018, 01:49 PM
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Circling back on this thread - all is well. I figured out the buttonology and it works as advertised, shot three coupled ILS approaches today intercepting at various point and it was all happy-happy.
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Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.
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  #15  
Old 09-30-2018, 04:42 PM
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Originally Posted by airguy View Post
Circling back on this thread - all is well. I figured out the buttonology and it works as advertised, shot three coupled ILS approaches today intercepting at various point and it was all happy-happy.
OK, so what "buttonology" did you wind up using? Inquiring minds want to know.
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  #16  
Old 10-01-2018, 09:15 AM
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airguy airguy is offline
 
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Originally Posted by GalinHdz View Post
OK, so what "buttonology" did you wind up using? Inquiring minds want to know.
Well the core of it, once I identified and fixed a broken wire feeding from the NAV side of the 430W to the 429, was enabling the autoswitching on the Dynon and then STOP TRYING TO do the job of switching from GPS to VLOC. I was not understanding just how easy it was to allow the 430W to switch the Dynon, and how well the Dynon accepted that. My IFR instructor cautioned me several times about making sure the 430W was in VLOC mode on an ILS approach, calling it the "$500 button" (for the cost incurred if I failed to switch during the checkride), and that had me in the mindset that I had to make a forced switchover.

With the wiring corrected, and in autoswitch mode, all you have to do is select the approach on the 430W, and set the autopilot for heading/altitude to intercept somewhere on the approach with NAV armed and it will capture like a charm. Once established inbound and the glideslope comes alive, arm the VNAV and enjoy the ride. I was trying to make it harder than it needed to be.
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N16GN flying! http://websites.expercraft.com/airguy/
Built an off-plan 9A with too much fuel and too much HP. Should drop dead any minute now.

Last edited by airguy : 10-01-2018 at 09:19 AM.
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