INS System Depth Questions

[Joshua Green]

1. Are the INS systems triple mixing the position information?  If not, is it coming? If so, is the mode configurable?

2. Is remote mode planned so that waypoints and position data can be set simultaneously across all three?

3. Is there an inflight position update process either available or planned? DME/DME or even just a manual update at a known position?

Edited 13 hours ago by Joshua Green
addition

[MD82]

I read somewhere that triple mix as well as remote will come at a later date. Regarding the LTN-72 (Not the RH models) I believe only manual updating was possible and described in the manual. Search RNAV 5 or RNAV 10, I believe it's mentioned somewhere there.

[richboy2307]

1. The LTN-72 is not capable of triple-mixing IRL, so not simulated by design. The AP on this equipment configuration can be driven by INS-1 or INS-3 only. At the moment, only INS-1 drives the autopilot in the simulator. Team is investigating feasibility of coupling INS-3 in a future update.

2. Remote functionality is planned for a future update.

3. INS-Drift is simulated, and is a user-configurable option via the PFB Aircraft Settings (Note: Further refinement of drift-rate is in progress).
As MD82 mentioned above, there is no automatic position updating on the LTN-72 (manual excerpt attached). The manual position-updating procedure is explained starting Page 105 in the manual which can be obtained here.

[Joshua Green]

Thank you for that information. However, there are some aspects of it that I find confusing.

A few follow-up questions about the nuances of the update procedure:

1. All the info about the DME/DME fix and intersection fix accuracy are relevant for systems like the CIVA, which can compute position corrections based on it, but it sounds like the LTN-72 can't do that.  Also, the pilot can't manually derive lat/long coordinates from a DME/DME fix either, without a lot of math. 

So it seems like directly overflying a radio navaid with known coordinates is the only way to do this update procedure. Am I right?

If so, that leads to the next question:

2. The aircraft is moving at multiple miles per minute, and tends to sequence to the next waypoint slightly before arriving at any particular one. How do you indicate to the INS that it should overfly the fix rather than cutting the corner, so that you fly precisely over the coordinates you intend to update? (Manual mode? or is their an OVFLY function?)

3. Does pressing the "hold" key, as indicated in the procedure, cause any newly entered position apply a correction to a) where the INS thought it WAS at the moment you pressed the "hold" key or b) does that entered position become where the INS thinks it is RIGHT NOW?  I'm hoping it's the first option. Otherwise, any delay in typing the corrected position in would cause miles of error given the aircraft's speed. 

 

Edited 3 hours ago by Joshua Green

[richboy2307]

1 hour ago, Joshua Green said:

1. All the info about the DME/DME fix and intersection fix accuracy are relevant for systems like the CIVA, which can compute position corrections based on it, but it sounds like the LTN-72 can't do that.  Also, the pilot can't manually derive lat/long coordinates from a DME/DME fix either, without a lot of math. 

So it seems like directly overflying a radio navaid with known coordinates is the only way to do this update procedure. Am I right?

The information provided applies to navigation in general. The key difference is that the Delco Carousel IV-A (CIVA) can perform these calculations automatically, while the LTN-72 requires the crew to calculate positions manually using navigational charts.

These updates are usually planned in advance during flight planning. In practice, they’re often done during a VOR-to-VOR segment, where radio navigation is used temporarily while updating the INS. Full flight navigation via random fixes only was very uncommon at the time, so there would typically be a suitable cruise segment to carry this out.

Overflying a radio navaid with known coordinates would be the most straight-forward way. Alternatively it would be the procedures detailed in the manual with the help of navigational charts. These days you could use something like SkyVector or LittleNavMap for guidance.

1 hour ago, Joshua Green said:

2. The aircraft is moving at multiple miles per minute, and tends to sequence to the next waypoint slightly before arriving at any particular one. How do you indicate to the INS that it should overfly the fix rather than cutting the corner, so that you fly precisely over the coordinates you intend to update? (Manual mode? or is their an OVFLY function?)

There is no OVFLY function as far as I'm aware but I'll ask the developer regarding that too. The way to go about it is manual flight, or reverting to radio navigation / heading hold temporarily during a VORDME-to-VORDME segment ideally.

1 hour ago, Joshua Green said:

3. Does pressing the "hold" key, as indicated in the procedure, cause any newly entered position apply a correction to a) where the INS thought it WAS at the moment you pressed the "hold" key or b) does that entered position become where the INS thinks it is RIGHT NOW?  I'm hoping it's the first option. Otherwise, any delay in typing the corrected position in would cause miles of error given the aircraft's speed. 

I believe it is the former. You are telling the INS what the *actual* coordinates were for the position which you told it to hold, thereby correcting the drift/error that was present in the system. However, I will confirm with the developer as well. 

Thanks!