Unusual INS pointer drift

[Bestandskraft]

Observe the attached track which was recorded in a no-wind mission.

Entering the aircraft, I'm programming ESERI (a waypoint southwest of Cyprus) into the INS and steer towards it.

With true heading selected, the indicated course to ESERI is initially 300°.

I deliberately command the autopilot to fly a heading of 305°, expecting that the head of the TACAN/waypoint needle will fall off to the left, which would lead to a passage to the right (northeast) of ESERI.

Instead, the indicated bearing to ESERI initially remains constant at 300°, and as we approach the point, actually starts to fall off to the right, passing the heading bug. The aircraft ends up missing ESERI approximately 1.3 nm to the left (southwest) of the point.

To precisely overfly ESERI, a constant adjustment of heading to the right (homing) would have been required.

Without knowing precisely how to RL F1EE's INS worked, the above behaviour is highly unexpected and unusual, which leads me to believe a bug in the INS modelling might be involved.

Note that I'm getting the same basic result when ground starting the aircraft.

Note also that if I instead navigate to ESERI off of PHA TACAN using the VA function, the needle behaves as expected (heading set right of course causes the needle to fall off to the left, heading set left of course causes the needle to fall off to the right).

 

ESERI.trk

Edited August 6, 2023 by Bestandskraft

[Proper Charlie]

Yeah, I too get the feeling that the wide needle is pointing a few degrees off course when in INS mode.

[Loukuins]

AFAIK there is no true heading on the F1EE since the HSI only works with gyro

[Proper Charlie]

2 hours ago, Loukuins said:

AFAIK there is no true heading on the F1EE since the HSI only works with gyro

Yes, you can change between true and magnetic bearings.  It is the switch labeled "3" here:

[Loukuins]

14 hours ago, Proper Charlie said:

Yes, you can change between true and magnetic bearings.  It is the switch labeled "3" here:

My bad then, didn't know that, thanks for correcting me 

[fausete]

Hi, will be reviewed. The INS is undergoing an overhaul right now but work is proceding in parallel with the BE, so you might have to wait a bit before seeing the second phase of the INS overhaul.