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INS only CCIP in the Hornet


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Does anybody have a solution on how to effectively employ the Hornet in A/G without GPS?

I find it practically impossible, when flying the blue flag 80's server, to drop bombs. By the time I get to the AOB the INS has drifted so much that the CCIP + is completely off.

 

I have tried to update via TACAN, but still not precise. Tried all kinds of update, but usually just makes matters worse.

 

EDIT: Edited to be more clear.


Edited by Svend_Dellepude

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CCIP and Auto should still be pretty accurate since its only really using AGR and own ship present velocities. Same goes for Auto if the designation is refined .. I mean that was the only option in the early pre GPS Hornet days 🙂. Any INS errors would be very slight and would hardly effect weapons solution. Pre GPS days in the A model  INS drift post flight un updated after say 1 hrs flight were only in the order of 1nm max with perhaps 3Kts residual ground speed.... and these with analog INS systems not the laser system in the updated C.

 

As to TACAN update .. forget it you are biasing the INS position on an incredibly inaccurate source. Not forgetting you must have the TACAN station you are using both tuned and in the TACAN station update data base.

 

Only updates worthwhile are the Overfly or perhaps Radar update using Expand modes. Any update has to be carefully decided on a Dud one might very well make your issue worse.

 


Edited by IvanK
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INS drift and attitude errors are grossly over-represented in the DCS Hornet. The Tomcat and the Mirage offer a much better idea of what it's supposed to be like.

Anyway, if you have a TACAN station's coordinates in your navigation database, you can use it to fix the position and you can use PVU Sea or PVU Ground with the INS knob to IFA. PVU is a radar mode that will update velocities and is invoked when the INS knob is set to IFA, without GPS.

Remember that, if you don't have GPS available, you need to set the knob to NAV for navigation, not IFA.

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Ok just had a look at INS drift over 30 mins POS INS only. after 30 mins the Drift was as shown in attached screen shot. So not to bad. However CCIP release resulted in bombs impact as shown by the X. I then attempted another CCIP release on a heading 90 degrees from the first ... same issue. Then landed GS showed 0 when parked. So something is very wrong imo. The Drift exhibited(though I consider ok)  should not have resulted in the CCIP bomb errors seen.

 

Progtgt.jpg

 

 

Impact.jpg

Doing an IFA is a not in real world a real option just to improve things ... it wont your original alignment will always be way better than any IFA. IFA is a last chance type thing to try and get something back after after say an INS crash etc.  A vel update using PVU might be a thought .... though again should not be required.... and it doesn't look like its implemented.

 

Either way the CCIP release impact errors seen after just 30 mins of flight are completely wrong. I tried an Auto release but need to try again after refing the designation to see where the bombs go.

 

Anyway its a major issue imo ... good pick up Svend.


Edited by IvanK
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Looking further. Noted Nil wind then had a look at the DIL line on 4 different headings all around 90 degrees apart (Standard diagnostic thing in the last century on non GPS aircraft).

Heading East or West DIL is is normal and vertically below the VV. But on Northerly and southerly headings it always leans towards the EAST !! ... Why ? If there was some unkown wind the DIL would be displaced downwind regardless of heading.

 

In balanced flight nil wind DIL should be vertically under the VV.  When I bombed with CCIP on the target weapon impacts were WEST of the CCIP cross.

 

CCIPdrift.jpg

 

Take Off point Batumi, Tgt Novorssiysk so a fairly large change in Latitude .. about 3 degrees worth. Dist about 252nm.   Is this some Earth transport error being reflected in a false vertical ?

 

Update:

Tested again over 250nm East West track  no latitude change .... same issue with CCIP DIL and bomb impacts.

 

Then reflew the first mission with POSAINS no issue DIL was good weapon impacts good.


Edited by IvanK
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8 hours ago, IvanK said:

Doing an IFA is a not in real world a real option just to improve things ... it wont your original alignment will always be way better than any IFA. IFA is a last chance type thing to try and get something back after after say an INS crash etc.

 

As far as I understand the manuals, the IFA in the F/A-18 is not to be confused with the last resort In-flight-alignments you are mentioning. I also at first hesitated to accept IFA as the regular in flight regime for the Hornet's INS at first, as in my civil aviation life I know an in-flight alignment to be the least desired.

Yet it seems in the Hornet the IFA is just an unlucky wording, in fact meaning an in-flight update. So the IFA dial position doesn't do an In-flight-alignment the way you intend to avoid, but essentially only presents the normal operating mode of your INS after doing the GND or CV alignment. You then make use of the HSI settings to specify, how the in-flight updating is processed.

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To my understanding, the IFA position on the INS knob has these main functions:
- commanding Aided INS (AINS) position-keeping mode after INS alignment with GPS
- complete in-flight alignment after an INS shutdown (with or without GPS)
- partial ground/CV alignment completion (with or without GPS)

 

If the INS has been shut down mid-flight, and GPS available, IFA should command IFA GPS for position and velocity. On completion, the system should automatically return to AINS. Without GPS, IFA should command IFA RDR, and enables the CONT PVU option for the radar to provide velocities. Position-keeping is performed dead-reckoning by the ADC, and POS/TCN is recommended to be used if available. If the aircraft has taken off with a partial alignment (at least without the 'NO ATT' caution), IFA can complete the alignment the same way as the complete in-flight alignment with radar PVU and position-keeping, but with less time.


Edited by Tholozor
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Thanks for looking into this @IvanK . 

There are a few reports in the bug section that are related to the CCIP fall line. 

As you noted there are no issues when GPS is available. Bombs will be spot on. It seems that the bomb cross is somehow tied to the ground and not the aircraft it self.

 

It would be nice to get this one sorted.

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I don't really understand the relationship between ccip and GPS availability... It should feed from the AGR or, if not available, the radio altimeter.
Except that, in DCS, you can get a solution with both the radar and the radalt off, and without a TPOD for laser ranging. And we presumably do not have DTED either (TAMMAC in general), given our HSI.

So, I don't know how the jet calculates a CCIP solution without at least one of the above. Kinda magic...

Would it be possible to get a solution based on the INS alone and doing ranging calculations based on your attitude (as determined by the INS) and barometric altitude? It'd probably be horribly inaccurate, I'm just wondering if it's feasible. Even like that though, the GPS would not be useful for attitude calculation, but merely for getting GPS altitude, which again, I don't know how accurate it is.
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2 hours ago, amalahama said:

I don't really understand the relationship between ccip and GPS availability... It should feed from the AGR or, if not available, the radio altimeter.

Considering the newer block Hornets should have a DTED, your current position compared with your current attitude (i.e. the LOS of the CCIP piper) should be correlated with the DTED to give you an accurate computed impact point. So basically both are linked.

 

It should feed from the AGR when telling it to though (via SSS Fwd), so there's definitely a bug. But at the end of the day your GPS/INS position is indeed used for CCIP.

3 minutes ago, Harker said:

Except that, in DCS, you can get a solution with both the radar and the radalt off, and without a TPOD for laser ranging. And we presumably do not have DTED either (TAMMAC in general), given our HSI.

So, I don't know how the jet calculates a CCIP solution without at least one of the above. Kinda magic...

Would it be possible to get a solution based on the INS alone and doing ranging calculations based on your attitude (as determined by the INS) and barometric altitude? It'd probably be horribly inaccurate, I'm just wondering if it's feasible. Even like that though, the GPS would not be useful for attitude calculation, but merely for getting GPS altitude, which again, I don't know how accurate it is.

The HSI situation is actually wrong. Our HSI is not what the jet should have, since it is a TAMMAC equipped jet and thus should have a DTED.

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Considering the newer block Hornets should have a DTED, your current position compared with your current attitude (i.e. the LOS of the CCIP piper) should be correlated with the DTED to give you an accurate computed impact point. So basically both are linked.
 
It should feed from the AGR when telling it to though (via SSS Fwd), so there's definitely a bug. But at the end of the day your GPS/INS position is indeed used for CCIP.
Except we don't have DTED. AFAIK it came as part of the TAMMAC upgrade, which we should have, but we don't.

The DCS A-10C, however, indeed uses INS/GPS, attitude and DTED.

So ED should either implement TAMMAC or should remove the DTED functionality we appear to have out of nowhere.

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10 minutes ago, Harker said:

Would it be possible to get a solution based on the INS alone and doing ranging calculations based on your attitude (as determined by the INS) and barometric altitude? It'd probably be horribly inaccurate, I'm just wondering if it's feasible. Even like that though, the GPS would not be useful for attitude calculation, but merely for getting GPS altitude, which again, I don't know how accurate it is.


This is exactly how it does it without AGR and Laser ranging. It uses either your BARO altitude combined with known Target elevation (or current waypoint elevation, in CCIP) to calculate height above target. Your dive angle / attitude completes the triangle to determine slant range. 
Obviously it can use rad alt without a known target elevation over flat terrain. 
 

It’s not rocket science or magic at all, and has been the basis of most advanced attack aircraft since the 1960’s. There’s no need for a DTED if using a planned target, or one near a waypoint with known elevation. 
 

Notice the A, R and B under the altitude box on HUD? AGR, Rad alt, and BARO respectively. They tell you the ranging source. Real Hornet can have G and L as well I think. GPS or Laser. 

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This is exactly how it does it without AGR and Laser ranging. It uses either your BARO altitude combined with known Target elevation (or current waypoint elevation, in CCIP) to calculate height above target. Your dive angle / attitude completes the triangle to determine slant range. 
Obviously it can use rad alt without a known target elevation over flat terrain. 
 
It’s not rocket science or magic at all, and has been the basis of most advanced attack aircraft since the 1960’s. There’s no need for a DTED if using a planned target, or one near a waypoint with known elevation. 
 
Notice the A, R and B under the altitude box on HUD? AGR, Rad alt, and BARO respectively. They tell you the ranging source. Real Hornet can have G and L as well I think. GPS or Laser. 
Ok, but how can it provide an accurate CCIP solution anywhere right now, regardless if it's near a waypoint or not? We're not talking about pre-planned targets.

The limitation here would be that the elevation the system considers is the waypoint's elevation, so if it's not set to ground level or if the intended target's elevation is not the same as the WP's elevation, the solution should be wrong.

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8 minutes ago, Harker said:

Ok, but how can it provide an accurate CCIP solution anywhere right now, regardless if it's near a waypoint or not? We're not talking about pre-planned targets.

The limitation here would be that the elevation the system considers is the waypoint's elevation, so if it's not set to ground level or if the intended target's elevation is not the same as the WP's elevation, the solution should be wrong.


Yeah I guess DCS uses it’s magic to fake a solution that wouldn’t be possible in the case when using BARO Ranging and wrong waypoint elevation. This is going be particularly obvious when using CCIP, as you say. I’ve not tested it recently, but Iremember CCIP being ‘magic’.

 

Have you tried AUTO bombing with a WP DSG and completely wrong Elevation? I’ve not tested that for some time, can’t remember if this works or not. (It shouldn’t provide a valid solution…)

 

I was describing how it works IRL, rather than excusing DCS. Cheers. 

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Have you tried AUTO bombing with a WP DSG and completely wrong Elevation? I’ve not tested that for some time, can’t remember if this works or not. (It shouldn’t provide a valid solution…)


Last time I had the wrong elevation, with WPDSG, AUTO worked as I expected it, in that it gave me a solution for the point in the air.

In general, it's fine if we're talking about pre-planned targets, where there is a point of reference for the elevation. The problem appears when elevation data and ranging aren't available and we're still getting good solutions.

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In my tests I have the exact elevation for the waypoint pre programmed. Wypt elevation is not however a player in CCIP.

 

As to using Auto with the wrong elevation... not a big  deal ... the diamond obviously wont be on the actual TGT so refine the designation in the HUD ... as soon as you stop slewing AGR takes a range sample and uses that for the calculation. If you didnt have AGR working then yes it would be an issue.

 

The issue here is why is the DIL line and CCIP +  leaning over after 30 mins flight time in nil wind? This only happens if you are not using AINS. If in the ME you set the date to pre GPS times  (e.g. 1985) you only have POS INS (INS in NAV rather than IFA) . Flying the same mission with a date say 2020 with POS AINS you dont have the issue.

 


Edited by IvanK
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Some more testing. Again DIL line always seems to be displaced to the east after 30 odd mins flying POS INS. AGR display indicates 0 Vel error. Again nil wind.

Images depict CCIP and subsequent impact point (x). Interestingly Impact point lies directly under the VV adjacent the CCIP + position ... i.e. about were the CCIP + should be if it and the DIL weren't leaning over to the East.

 

CCIPImpact.jpg

 

 


Edited by IvanK
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Looks to me like the CCIP pipper is attached to the coordinate system that is drifting, instead of aircraft velocity vector and inertial rates like it should be. Think absolute coordinates and the pipper doesn’t know about the drift, so it goes to those absolute coordinates, but the aircrafts INS has drifted. 
whatever’s going on that’s pretty screwed up.

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It seems like it "should" work for CCIP like the INS knows its at XYZ with vector ABC. Then using the AGR radar the FCS knows "relatively the target is xdeg down and slant range Y for CCIP (in some modes, I get that you can use alt to solve for range in backup modes) and thats it, it shouldn't matter where the INS thinks it is in CCIP since the coordinate system should be relative. an INS bombing mode is a whole other can of worms. 


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Another test this time using AUTO and looking at a Manual designation and what happens after 26 mins flying. Interestingly the ASL is displaced to the South. The top image is immediately after the HUD designation. The Designated point has drifted 041 for about 151m i.e easterly.  Which for an un updated raw INS system is pretty good imo and works out about 300m per hour.

 

However given this is Nil wind I would have expected the ASL to be running through the Designation diamond ?

 

Auto-drift.jpg

 

 


Edited by IvanK
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Another test. Same mission 1985 no GPS POS INS no wind. Initially did a Point Blank HUD designation (flt time 2 mins), ASL appeared centered on the designation diamond as expected.

Then flew for 30 odd mins. INS drift as in previous post much the same. So Undesignated.

Came around and did another Point Blank (HUD) designation (33 mins flt time). ASL pops up displaced to the left.?? why given its a new designation and nil wind it should be through the designation diamond. ... Something is off and it relates to Flight time.

 

 

Pointblank.jpg

 

Came around again and did a CCIP pass, DIL and CCIP was leaning out to the right (East again).


Edited by IvanK
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