F-15E Aircraft Additional Settings in the Mission Editor ?s

[Wrecking Crew]

F-15E Aircraft Additional Settings in the Mission Editor ?s

In this Mission Editor screenshot of a Cold Start F-15E, there are four settings in the Aircraft Additional Settings (I guess it's Settings,,, can't read the full text).  I'm looking for info and recommendations.  What do these do?  Is there documentation?

1. Equip AN/AVS-9 NVG and NVG Fil (text is cut off)

2. Cold Aircraft needs GC Alignment

3. Time Airborne (minutes),,, when does this setting apply?

4. Cold Aircraft is in ALERT status

 

Thanks!

[Despayre]

1) Add night vision goggles to helmet instead of sunvisor

2) I believe means you can't use a Stored Heading alignment, you have to wait for a full alignment

3 and 4, not sure.

[Rainmaker]

1.  As above

2.  Its used to set the accuracy of starting PP coords when you enter the jet. Unselected, coords will be accurate.  Can still be flown with either alignment method, but there will be pos errors if full alignment in not completed 

3.  Is predetermined INS drift. Used to add drift error at mission start. 
 

4.  Old. Will probably eventually get removed or repurposed. Serves no function currently. 

[Avio]

For Point-3, if GPS is in use all the time, there shouldn't be any INS drift IRL right? Since the correction will be coming from the GPS.

 

[Rainmaker]

24 minutes ago, Avio said:

For Point-3, if GPS is in use all the time, there shouldn't be any INS drift IRL right? Since the correction will be coming from the GPS.

 

INS is still its own system. But, yes, since EGI is there, you wont really notice unless you select it. 

[SloppyDog]

10 hours ago, Wrecking Crew said:

F-15E Aircraft Additional Settings in the Mission Editor ?s

In this Mission Editor screenshot of a Cold Start F-15E, there are four settings in the Aircraft Additional Settings (I guess it's Settings,,, can't read the full text).  I'm looking for info and recommendations.  What do these do?  Is there documentation?

1. Equip AN/AVS-9 NVG and NVG Fil (text is cut off)

2. Cold Aircraft needs GC Alignment

3. Time Airborne (minutes),,, when does this setting apply?

4. Cold Aircraft is in ALERT status

1) Helmet equipped with night vision goggles instead of sun visor

2) Aircraft needs full alignment before taxiing

3) When using INS only (not corrected by GPS) determines the amount of drift the system will have as soon as the mission starts. Let's say you want to start at an air start, you could set the INS drift to 30 minutes, for instance. If you have set up offset points for waypoints in the mission, you would see them way out of place and a Precision Velocity Update (PVU) in the radar would be needed, as well as a INS update to reset the INS. It adds a layer of realism for the older systems. Of course, you can set the INS drift at 0 minutes, like you just had made an update and are good to go.

4) ALERT Status means that the aircraft is shutdown but already with INS aligned. So crews can go in, start it up and don't need to wait for the INS to align. That was common practice during the Cold War, before GPS was widely available. EDIT: It works in game. In the kneeboard there is a message in red that says: SH Align Ready. When you start the jet, you can go to the INS knob and set it to SH (Stored Heading). It will take a while to align, but it is faster than the GC align. I tested it, and once you have power to the Right Gen (always starting the #2 engine first), you can start the alignment with Stored Heading. Way faster.  

P.S.: About 3, if you wanna know more, you can check pages 258-259 in the manual and the video by Notso in the Razbam channel, that explains a whole lot about Offset points, PV updates, etc:

 

  

Edited September 13, 2023 by SloppyDog

[Avio]

So if INS drift set to 30 min, I take it that it means the system gradually drifts over every block of 30 minutes counting from the last reset?

What is the average normal drift like in the real jet, that we may use in the sim setup?

 

 

[Rainmaker]

1 hour ago, Avio said:

So if INS drift set to 30 min, I take it that it means the system gradually drifts over every block of 30 minutes counting from the last reset?

What is the average normal drift like in the real jet, that we may use in the sim setup?

 

 

You essentially start the mission with 30 minutes of drift already in place. Really only effective if you are starting missions in flight, which is what it was designed for. 

[SloppyDog]

1 hour ago, Avio said:

So if INS drift set to 30 min, I take it that it means the system gradually drifts over every block of 30 minutes counting from the last reset?

What is the average normal drift like in the real jet, that we may use in the sim setup?

 

 

No, no. Without the GPS the INS will drift ad eternum, with the errors being accumulated over time.  To the best of my knowledge the INS erros accumulate, getting worse and worse. I really don't know it this accumulation is linear or nonlinear.

To answer your second question, in page 270 of the manual it is stated that the INS drift is 0.8 nm per hour. And NotSo in the Discord channel has confirmed that as well. 

What this means is that for every hour the INS will distance itself 0.8 nm from the aircraft real position. So, within two hours, you would be 1.6 nm off from the real position that you should be. And that accumulates over time. 

So, to answer your first question, if you setup the INS drift to 30 min at the start of the mission, it means that the system position will already be 0.4 nm from the real position. And this error will get bigger and bigger as the time passes. There is no automatic reset. The radar operator will have to do a PVU, and then a INS update using offset points from time to time, as NotSo shows in the video.

For older systems, or non radar equipped aircraft, the INS update was made using ground reference points or other navigation equipment (VOR/TACAN). Way more difficult, much imprecise, but that's the way they were going to fight a nuclear war. 

I had made a mission to test the effects of iNS drift and this option in the system. The Mission is attached below, if someone want to test it.

If you look at the map picture in the mission editor, for Waypoint 01 (for the air start aircraft) I created two offset points: 1.2 at the runway intersection at Creech Airbase, and other, 1.1, at the hangar closer to the runway intersection. Now compare these points to the HRM map of the same region. You will see the Offset points in the radar map image way off to where they should be.  And that's with 30 min INS drift setup in the mission editor.

 

 

 

F-15SE-NEVADA - NO EGI Practice.miz

F-15SE-NEVADA - NO EGI Practice.miz

Edited September 13, 2023 by SloppyDog

[Rainmaker]

2 minutes ago, SloppyDog said:

No, no. Without the GPS the INS will drift ad eternum, with the errors being accumulated over time.  To the best of my knowledge the INS erros accumulate, getting worse and worse. I really don't know it this accumulation is linear or nonlinear.

To answer your second question, in page 270 of the manual it is stated that the INS drift is 0.8 nm per hour. And NotSo in the Discord channel has confirmed that as well. 

What this means is that for every hour the INS will distance itself 0.8 nm from the aircraft real position. So, within two hours, you would be 1.6 nm off from the real position that you should be. And that accumulates over time. 

So, to answer your first question, if you setup the INS drift to 30 min at the start of the mission, it means that the system position will already be 0.4 nm from the real position. And this error will get bigger and bigger as the time passes. There is no automatic reset. The radar operator will have to do a PVU, and then a INS update using offset points from time to time, as NotSo shows in the video.

For older systems, or non radar equipped aircraft, the INS update was made using ground reference points or other navigation equipment (VOR/TACAN). Way more difficult, much imprecise, but that's the way they were going to fight a nuclear war. 

I had made a mission to test the effects of iNS drift and this option in the system. The Mission is attached below, if someone want to test it..

If you look at the map picture in the mission editor, for Waypoint 01 (for the air start aircraft) I created two offset points: 1.1 at the runway intersection and Creech Airbase, and other, 1.2, at the hangar closer to the runway intersection. Now compare these points to the HRM map of the same region. You will see the Offset points in the radar map image way off to where they should be.  And that's with 30 min INS drift setup in the mission editor.

 

 

F-15SE-NEVADA - NO EGI Practice.miz 1.43 MB · 0 downloads

 Thats not how drift really works. In addition, the drift rates are not that much. 

[SloppyDog]

6 minutes ago, Rainmaker said:

 Thats not how drift really works. In addition, the drift rates are not that much. 

How does it drift though? 

I believe it will get to a limit and stop. I agree that the rates are not that big, and commercial aircraft lived fine with that, with fewer and farther updates over time. 

But in game, it seems to drift faster than it should. in the same mission, when getting to Creech, I make a position update, to attack the targets at Waypoint 2. but 5 minutes later the waypoint and offset are way off than they should be. Maybe a DCSism. 

[Galinette]

Drift rates ARE that much. Commercial aircraft do have several NM of drift after a transcontinental flight. They don't need more precision though, landing is not performed using INS. Without GPS, they use radionavigation beacons (VOR, ILS...) and ATC radar. INS is just a fully autonomous backup way of roughly knowing where on earth they are.

What SloppyDog explained above is a simplified version, but he is mostly right.

Drift will NOT get to a limit and stop.

A more complex picture : drift is not linear but a stochastic process. It will randomly drift in continuously variable directions over time. The advertised rates are not a constant, but a confidence interval (aka n.sigma). So it says that after one hour, there is a good chance (95% if this is 2sigma) that your drift is lower than 0.8NM. It can be zero if you are very lucky, or more if you are very unlucky.

Even more complex picture : the drift rate variance is not even constant over time, it follows a 84min oscillation. It's about zero after ground alignment, then increases to twice the advertised value after 42min, and back to nearly zero after 84min and this cycle starts again. On average over 84min it's the advertised value. A perfect velocity update resets this cycle. The 84min is related to earth gravity and radius.

Now yes excessive drift rates have been reported, there is likely a bug. It will be addressed at some point

 

Edited September 13, 2023 by Kercheiz

[Rainmaker]

5 hours ago, Kercheiz said:

Drift rates ARE that much. Commercial aircraft do have several NM of drift after a transcontinental flight. They don't need more precision though, landing is not performed using INS. Without GPS, they use radionavigation beacons (VOR, ILS...) and ATC radar. INS is just a fully autonomous backup way of roughly knowing where on earth they are.

What SloppyDog explained above is a simplified version, but he is mostly right.

Drift will NOT get to a limit and stop.

A more complex picture : drift is not linear but a stochastic process. It will randomly drift in continuously variable directions over time. The advertised rates are not a constant, but a confidence interval (aka n.sigma). So it says that after one hour, there is a good chance (95% if this is 2sigma) that your drift is lower than 0.8NM. It can be zero if you are very lucky, or more if you are very unlucky.

Even more complex picture : the drift rate variance is not even constant over time, it follows a 84min oscillation. It's about zero after ground alignment, then increases to twice the advertised value after 42min, and back to nearly zero after 84min and this cycle starts again. On average over 84min it's the advertised value. A perfect velocity update resets this cycle. The 84min is related to earth gravity and radius.

Now yes excessive drift rates have been reported, there is likely a bug. It will be addressed at some point

 

 

This has been discussed before.  I dont know why ‘commercial’ aircraft are being brought into the discussion here. 
 

The drift rate quality number is not an absolute, as it was commented above before, and just as you restated in your post. The numbers are not absolute, and the jet does not give you absolutes in terms of a defined drift over time. So, what I was commenting on is the time = x distance comment.  The drift error is not near as simple as it was being made to be.  You cant just solve the math by going X time equals X distance in error away from the original location. Everything you pretty much put in your post, is why I commented that the system does not work in the fashion that was posted in the original post. 
 

Beyond that point but also of note, the INS and EGI systems are separate.   They are not inclusive as the other post suggested they were. 
 

Edit: I do see that part of your post may have been directed more at SD than at my post. The lack of quotes just muddied the water a little bit.  

Edited September 13, 2023 by Rainmaker

[SloppyDog]

6 hours ago, Kercheiz said:

Drift rates ARE that much. Commercial aircraft do have several NM of drift after a transcontinental flight. They don't need more precision though, landing is not performed using INS. Without GPS, they use radionavigation beacons (VOR, ILS...) and ATC radar. INS is just a fully autonomous backup way of roughly knowing where on earth they are.

What SloppyDog explained above is a simplified version, but he is mostly right.

Drift will NOT get to a limit and stop.

A more complex picture : drift is not linear but a stochastic process. It will randomly drift in continuously variable directions over time. The advertised rates are not a constant, but a confidence interval (aka n.sigma). So it says that after one hour, there is a good chance (95% if this is 2sigma) that your drift is lower than 0.8NM. It can be zero if you are very lucky, or more if you are very unlucky.

Even more complex picture : the drift rate variance is not even constant over time, it follows a 84min oscillation. It's about zero after ground alignment, then increases to twice the advertised value after 42min, and back to nearly zero after 84min and this cycle starts again. On average over 84min it's the advertised value. A perfect velocity update resets this cycle. The 84min is related to earth gravity and radius.

Now yes excessive drift rates have been reported, there is likely a bug. It will be addressed at some point

 

 

Thank you. That's what I meant. What I said is a very simplified explanation to help answer Avio questions. 

And I understand that the advertised rates are only an average, a ball park, to help understand system drift. 

By the way, the oscillation you mentioned is Schuler tuning. Just another layer of complexity in a already complicated system.

And I don't know if the game simulates that. I don't think it does.

Edited September 13, 2023 by SloppyDog

[Galinette]

2 hours ago, SloppyDog said:

Thank you. That's what I meant. What I said is a very simplified explanation to help answer Avio questions. 

And I understand that the advertised rates are only an average, a ball park, to help understand system drift. 

By the way, the oscillation you mentioned is Schuler tuning. Just another layer of complexity in a already complicated system.

And I don't know if the game simulates that. I don't think it does.

 

Yes it does

Edited September 13, 2023 by Kercheiz

[Wrecking Crew]

Thank you, all!  That was most interesting

[Home Fries]

INS drift could be a topic all its own.  It's definitely not linear and it is cyclical.  Some inertials also incorporate a Kalman filter which dampens the level of drift and tries to make it as linear and predictable as possible.  Bottom line: that amount of drift advertised is really your radius of trust.  I've had inertials stay within a mile after 10 hours and we could match them to the TACAN when we got near home plate.

There's also a school of thought that you don't update the position on the inertial because you don't know where you are within the Kalman cycle, e.g. if you update when the drift is at its maximum, then you've just recentered your confidence radius on a fringe point.  Of course, if you're getting ready to put weapons on target, you don't care about your position in the Kalman cycle, but rather your accuracy over the next few minutes.  This is the classic reason you have Initial Points: they're used to update navigation as well as line up on the target.  IPs are classically something you can identify either visually or on radar (with radar they're called RUPs) so you can update your inertial prior to run-in.

Edited September 18, 2023 by Home Fries
technical correction

[Rainmaker]

53 minutes ago, Home Fries said:

INS drift could be a topic all its own.  It's definitely not linear and it is cyclical.  Some inertials also incorporate a Kalman filter which dampens the level of drift and tries to make it as linear and predictable as possible.  Bottom line: that amount of drift advertised is really your radius of trust.  I've had inertials stay within a mile after 10 hours and we could match them to the TACAN when we got near home plate.

There's also a school of thought that you don't update the position on the inertial because you don't know where you are within the Kalman cycle, e.g. if you update when the drift is at its maximum, then you've just recentered your confidence radius on a fringe point.  Of course, if you're getting ready to put weapons on target, you don't care about your position in the Kalman cycle, but rather your accuracy over the next few minutes.  This is the classic reason you have Initial Points: they're used to update navigation as well as line up on the target.  IPs are classically something you can identify either visually or on radar (with radar they're called RUPs) so you can update your inertial prior to run-in.

 

Or a separate set nav function, like MN in this case, so you dont necessarily worry about trashing the INS. 
 

cant imagine that would be an enjoyable event. 

Edited September 18, 2023 by Rainmaker