Bad INS alignment influences RWR

[Kang]

I just noticed that if you start your flight with a rather bad INS alignment (or simply deliberately don't wait for it to finish) the RWR system displays threats in relation to where the INS believes the plane to be, rather than the correct bearings. For example a single enemy plane I can clearly see off my nose might get displayed as behind, despite no possible emitter being in that direction.

 

In my opinion that seems rather bizarre, since the two systems should work independent from one another.

[dorianR666]

On 8/27/2021 at 11:58 PM, Kang said:

since the two systems should work independent from one another.

they are interconnected actually IIRC. when you rotate the plane in azimuth, rwr contacts rotate too according to whats fed to it by ins. the rwr refresh delay is too long and youd notice them not rotating smoothly otherwise (as it is currently, incorrectly, in dcs hornet).

 

but what you say definitely sounds like a bug.

jf-17 had the same exact bug actually, the rwr code was using the drifted ins own position instead of real in-game own position to compute azimuth to emitter. which results in azimuths being more off with more drift.

Edited August 31, 2021 by dorianR666

[Aries144]

Yeah, this may be something that got overlooked. RWR sensors use information from the antennae on the exterior of the aircraft. INS shouldn't have any connection with that.

[Naquaii]

9 hours ago, Aries144 said:

Yeah, this may be something that got overlooked. RWR sensors use information from the antennae on the exterior of the aircraft. INS shouldn't have any connection with that.

 

No, that's incorrect. The INS is used as a correlation reference in the RWR, otherwise the aircraft wouldn't know to associate the same threat with the same emitter when the aircraft turns, it'd spew out new multiples of the same thread indicator as the aircraft banked as it wouldn't know to associate them to the same threat. This is however not a perfect process so there might still be sporadic doubles, esp as the rear quadrant sensors are located on the stabilators that themselves move (which the RWR can't compensate for) but without INS it would be much worse.

[sLYFa]

2 minutes ago, Naquaii said:

 

The INS is used as a correlation

Is it really the INS or AHRS?. And if the former is the case does it fall back to AHRS in case of an INS failure?

[Naquaii]

26 minutes ago, sLYFa said:

Is it really the INS or AHRS?. And if the former is the case does it fall back to AHRS in case of an INS failure?

 

Afaik, yes. I'll ask Grover to elaborate.

[Super Grover]

Yes, the RWR is 'stabilised' by the INS, and should automatically switch from the IMU to the AHRS when the IMU fails. This uses only the angular part of the INS, so the alignment quality shouldn't affect it that much, as long as the pitch ladder looks ok and the heading isn't completely wrong. I remember I tested the RWR against the INS failures and they worked but it was long ago , so I'll check it again. However, depending on the geometrical situation, under certain circumstances, some threats appearing at unexpected angles can be normal and not a bug.

 

[Aries144]

On 9/14/2021 at 12:19 PM, Naquaii said:

 

No, that's incorrect. The INS is used as a correlation reference in the RWR, otherwise the aircraft wouldn't know to associate the same threat with the same emitter when the aircraft turns, it'd spew out new multiples of the same thread indicator as the aircraft banked as it wouldn't know to associate them to the same threat. This is however not a perfect process so there might still be sporadic doubles, esp as the rear quadrant sensors are located on the stabilators that themselves move (which the RWR can't compensate for) but without INS it would be much worse.

That makes perfect sense. Thank you for being on top of the subject and thank you very much for taking the time to explain.