Viper INS alignment issue with autopilot

[littlewing]

Hi,

 

In Syria on cold start with normal alignment at '6', I found that when I'm in the air and set the autopilot to STRG SEL the autopilot flies to the steerpoint and when it levels out towards the steerpoint the tadpole is offset and not inside the FPM marker.

 

I watched the videos on how to align the INS and at the beginning I just clicked ENTER on the ICP on the LAT, LONG, ALT. Afterward, when I saw it didn't work (tadpole not inside the FPM when A/P is on) I inserted the LAT,LONG, ALT manually - Still tadpole is not inside the FPM).

 

I took off from the runway (assuming the script made the INS align correctly) and still tadpole is not inside the FPM.

 

 

 

Has anyone else experienced this?

 

Thanks.

Edited September 4, 2020 by littlewing

[RuskyV]

Not sure if the AP would account for wind But did you have any weather settings in your mission?

[littlewing]

Hi,

 

Thanks for the quick reply Blade,

 

Yeah I did have around 10 m/s, But if I compare it to BMS I don't think the wind affected the AP there.

[Frederf]

There is an error with F-16 avionics. With crosswind and nose pointed at waypoint FPM is on leeward side which is fine and correct. But heading = bearing to waypoint causes FPM and GCSC to be lined up which is wrong. Instead FPM and GCSC should only line up when ground track = bearing to waypoint.

 

This is the picture that autopilot is trying to fly and it's wrong. GCSC (tadpole) should not be aligned with FPM in this case because you're not flying toward the steerpoint.

 

This is what autopilot should fly and also when tadpole should be aligned with FPM. So I don't think it's really autopilot's fault really, it's trying to make the steering error zero (align GCSC with FPM) but the problem is steering error calculation is wrong so it is successfully doing the wrong thing. Once steering error calculation is fixed autopilot will be fixed automatically.

[littlewing]

Hi frederf, thanks for the detailed reply!

 

So its a bug? (known bug)?

Should I fly towards the steerpoint diamond? (asusuming lat/lan are corect)?

 

Thanks