Felix448

INS precision loss way too fast

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Hi, just a short question, might it be that the INS precision is decreasing too quickly?

 

I´ve done a couple of flights now and am loosing precision from 0 to 8 in just about 10mins after departure. Also, the INS DME update with a nearby VOR station doesnt help improving it much, maybe reaching 7 at best. 

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From the manual:

 

DISCUSSION OF INDICATION OF NAVIGATION PERFORMANCE The displayed PI number during NAV (the second digit from the right in the CDU right hand data display when the C/DU data selector is at DSRTK/STS) has been made representative of predicted navigation performance. During NAV, this digit, sometimes referred to as the Accuracy Index (AI) number, will range from 0 to 9, with 0 being the best accuracy. The computer forces this number to 0 when the NAV mode is entered. The number progresses toward 9 as time in NAV increases. As DME updating is being performed, the AI number decreases towards 0 but will not go below 2 if altitude information is invalid. The rate of increase or decrease of this number is dependent on time in NAV, DME station geometry, length of time of DME acquisition, and whether dual or single DME updating. The AI number can be roughly approximated to a worst case estimate of radial error in nmi. The AI number is limited to "9" which is reached after a three hour flight with no DME updating . THE INS PERFORMANCE MAY BE BETTER THAN THAT INDICATED BY THE AI NUMBER. It is intended to provide a measure of the 3 δ, or worst case estimate, of navigation performance considering the effects of flight duration and DME updating.

 

It looks like it should take 3 hours to get to 9, so maybe a bug there.  I will ask Tom (the INS author) to look at it. But remember, the AI number is only a function of time passing; it doesn't mean the actual loss of precision is that bad.  

 

I have done a number of DME updates that brought the AI down to 2. It takes a fair amount of time and results will vary with the DME position relative to your track.  So it's best to select one well out in front and I believe also significantly offset from your track. 

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Hi Michael,

I appreciate that you / Tom take a look at it. I think there´s some kind of oddity with it decreasing too fast and therefore also not recalibrating the way it should. Also even with accuracy rated at 9 it still flies the entered route without issues, so at least it´s not completely breaking the experience for the moment. 

 

I´ve been flying Concorde as well as a couple of other INS supported birds in the sim, so I got some experience with the system. 

If I can assist you with anything just let me know. 

 

Best Regards,

Felix

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same here after 10 minutes the INS is in 9, and i always try to recalibrate but not successful the best number of recalibration I had is 7

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