What is the Rationale behind System Deltas (besides confusing the pilot)?

[GrEaSeLiTeNiN]

The manual says

“System deltas are X and Y values which reflect the horizontal difference between the SPI position and the currently selected Steerpoint’s original position. The SPI position is initially locked on the STPT position and once SPI is moved (by slewing the FCR or TGP) system delta values change. These delta values are applied to all STPTs, even though the original steerpoint positions (including Bullseye) will still be displayed on the FCR and HSD pages. This means that when slewing the SPI in A-G mode, your current STPT position is changing too and following the SPI position. You’ll see the STPT diamond on the HUD following the SPI position. This change in STPT position affects all navigation STPTs, so even if choosing a different STPT the position will be different than it was originally, as system delta values will have been added to it.”

Why must all the steerpoints move when you slew/target in A-G?

Cheers

[Agave_Blue]

One of the answers is likely, “Ask Lockheed-Martin.”

Someone might have something more substantive than that, but that’s what it comes down to, LM system design.

[Cik]

the reasoning is probably classified

[GrEaSeLiTeNiN]

They probably have a good reason as l’m sure they have the pilot and his mission objective in mind but I couldn’t figure out why and the other manual also says it’s a confusing thing.

[GrEaSeLiTeNiN]

To make sense of the table, I think the rationale is that the SPI being, as the name implies, a System Point of INTEREST, takes so much precedence that it redirects everything to itself in A-G mode but only the Steerpoint diamond cues in A-A and NAV modes. In A-G mode, this is understandable since the objective is finding and destroying ground targets and the SPI ‘leads the way’. In A-A and NAV modes, much less so.

[Red Dog]

Remember the old 4.32 days where different sensors where looking at different location, and we needed a lot of time when it was required to acquire target from one sensor to the other

• TGP, radar, wpn LOS, steerpoint could all be different and it was pretty confusing and time consuming

SPI addresses just that making them all common and resettable at a click of a button
it’s now much more efficient and faster to coordinate sensors to a target, share it required, and bring weapon to bear on them fissa.

All you need to do to get used to it is as the manual says:

• TMS down, wide FOV, Cursor zero

and remember now when there is a SPI, the CZ mnemonic is highlighted, clearing some confusion we had left with 4.33

It’s all a question to get accustomed to it and learn the new system, just like any new thing

[Cik]

system delta is confusing (as a concept) but like red dog says, it’s far better now as a usable system

the TGP itself is absolutely magnificent now, and it’s displaced everything else as my primary sensor for A-G. finally i don’t have to deal with the radar’s really obnoxious FOV limits and can use it just for initial acquisition which is what it’s good at.

give it some effort and you’ll see what a wondrous advance a working SPI system actually is.

[Frederf]

SPI is a different concept than system deltas. It’s perfectly possible to have the SPI concept without the system delta concept (e.g. A-10C).

The concept of system deltas is based on the fallibility of INS as the main source of targeting error. Back in the day your INS might be wrong to reality but the relative positions of your known points was reliable. As such your system deltas being global made sense because any INS position error was similarly global. When you applied a delta by slewing the radar over a known object that fixed aligned that objects true and assumed position and by extension all other assumed positions. There are updates which can be done but it takes a deliberate step. When you roll in and out to attack your bridge or depot having the FCR over the target absolutely ensures that the rest of your flight plan is exactly where you wanted it to be.

Another reason is that framing targeting positions as steerpoints it greatly simplifies the programming complexity and pilot understanding or interaction required. If you start to imagine the design without the system delta concept it quickly gets hard to work with.

[deep]

Thanks Frederf. When you know why it was done, it all makes sense.

[Habu_]

The F-16 relies on 2 main navigation systems to follow a flight plan: INS and GPS. INS relies on mechanical components like gyroscopes and accelerometers; thus the INS accumulates positional errors over the time of a flight. The GPS is satellite based and maintains much better positional accuracy, resulting in an increasing divergence over time of the INS and GPS reported global positions (system delta). Flight plans should include a Sighting Point, a fixed geographic feature that can be observed by sight or sensors, somewhere near the target, so that the aircraft position displayed to the pilot and weapon systems can converged on a known earth position.

[GrEaSeLiTeNiN]

@Frederf:

SPI is a different concept than system deltas. It’s perfectly possible to have the SPI concept without the system delta concept (e.g. A-10C).

The concept of system deltas is based on the fallibility of INS as the main source of targeting error. Back in the day your INS might be wrong to reality but the relative positions of your known points was reliable. As such your system deltas being global made sense because any INS position error was similarly global. When you applied a delta by slewing the radar over a known object that fixed aligned that objects true and assumed position and by extension all other assumed positions. There are updates which can be done but it takes a deliberate step. When you roll in and out to attack your bridge or depot having the FCR over the target absolutely ensures that the rest of your flight plan is exactly where you wanted it to be.

Another reason is that framing targeting positions as steerpoints it greatly simplifies the programming complexity and pilot understanding or interaction required. If you start to imagine the design without the system delta concept it quickly gets hard to work with.

System deltas to correct possible INS errors makes sense. Let me see if I understand this correctly. Let’s say there is a digital map that is accurate. And Target A is a bridge and say Steerpoint 5 is marked right over Target A. Everything is good and accurate but when it’s ‘ported’ over (or whatever, not sure how it works) to the INS, you may get offset errors. So when you fly over Target A and find it’s not directly on Steerpoint 5, you designate Target A as SPI and the system drags Steerpoint 5 over Target A, and applies the same x and y displacement corrections to all the other Steerpoints, and that supposedly brings the Steerpoints back to their correct positions as originally marked out in the digital map. Is that the idea? If so, what if you are just designating a random target? Then wouldn’t all the Steerpoints get adjusted but not for the right reasons?

Cheers

[Darkman]

Not exactly. As Frederf explained system deltas were originally used to make up for INS drift over time, in the days before GPS.

This is why steerpoints are set up at clearly visible landmarks, so the pilot can more easily compare where the INS thinks the jet is and where the pilot knows the jet is. The pilot uses system delta to compensate for any difference, i.e. for the distance and direction that the INS has ‘drifted’ from reality.

[Dee-Jay]

… And it is not because now we have GPS that INS becomes obsolete. What is great with INS is that it is autonomous. GPS is not and can be easily be jammed. Even the military GPS working on L1 and L2 with anti-spoofing can be jammed and you will simply lost the reception.

Not implemented in game, but IRL, trusting blindly the GPS availability can be disastrous.

[Frederf]

@GrEaSeLiTeNiN:

System deltas to correct possible INS errors makes sense. Let me see if I understand this correctly. Let’s say there is a digital map that is accurate. And Target A is a bridge and say Steerpoint 5 is marked right over Target A. Everything is good and accurate but when it’s ‘ported’ over (or whatever, not sure how it works) to the INS, you may get offset errors. So when you fly over Target A and find it’s not directly on Steerpoint 5, you designate Target A as SPI and the system drags Steerpoint 5 over Target A, and applies the same x and y displacement corrections to all the other Steerpoints, and that supposedly brings the Steerpoints back to their correct positions as originally marked out in the digital map. Is that the idea? If so, what if you are just designating a random target? Then wouldn’t all the Steerpoints get adjusted but not for the right reasons?

Cheers

The target of opportunity is usually handled by CCIP or snow plow CCRP which creates a pseudo steerpoint. I’m not sure if snowplow slews contribute to normal system deltas or if they are temporary system deltas that vanish at the end of snow plow use. In any case the ToO system deltas which are not necessarily INS corrections are an acceptable downside to the design. That’s why the “CZ” button exists. Having a fixed target strike following an off flight plan target is quite rare in any case. There are specific INS updating fixes processes to align INS to the world (at zero delta) so any required system deltas on top of that should be minor and flying “CZ’d” should be no big issue.

[Tiffy]

@Dee-Jay:

… And it is not because now we have GPS that INS becomes obsolete. What is great with INS is that it is autonomous. GPS is not and can be easily be jammed. Even the military GPS working on L1 and L2 with anti-spoofing can be jammed and you will simply lost the reception.

Not implemented in game, but IRL, trusting blindly the GPS availability can be disastrous.

NATO used to conduct a Yearly Exercise in the North Sea where GPS was routinely jammed over an area. They had to post a notice to the local fishermen to warn them before the exercise.

Come a conflict with a major power GPS will only be available while it is of more benefit to them than the enemy. A fight between NATO and Russia/ China would almost certainly loose GPS quite quickly.

[Dee-Jay]

@Tiffy:

Come a conflict with a major power GPS will only be available while it is of more benefit to them than the enemy. A fight between NATO and Russia/ China would almost certainly loose GPS quite quickly.

This is why I do also take my GNS2000 and my tablet with me so I can enjoy the GLONASS constelation when I loose the GPS. … But still have to pay a deeeep attention and I can tell you that I take care about my IRS’s health. …

[macieksoft]

@Tiffy:

Come a conflict with a major power GPS will only be available while it is of more benefit to them than the enemy. A fight between NATO and Russia/ China would almost certainly loose GPS quite quickly.

But GPS can be encrypted so enemy would not be able to use it! They can shut down civilian GPS (unencrypted one) while maintaining encrypted GPS available to ones who have correct crypto keys!

[Dee-Jay]

@macieksoft:

But GPS can be encrypted so enemy would not be able to use it!

The information provided by a military GPS “can not” be distorded. BUT … it is relatively easy to jam all frequencies by making radio noise in a big area making the GPS signal unavailable. And it happens …

Edit:

They can shut down civilian GPS (unencrypted one) while maintaining encrypted GPS available to ones who have correct crypto keys!

Encryption (Y code) does affect the location’s accuracy (dilution of precision), not the GPS availability.

[Tiffy]

Don’t forget the ultimate in jamming your GPS. If your satellites aren’t there anymore then your GPS ain’t going to be working. The USA, Russia and China have all demonstrated the ability to shoot down satellites and to degrade you GPS they don’t even need to get them all :???:

[rmax]

Read Vipers in the Storm. He describes how he corrects the INS drift by moving the SPI over a crossroads.