investigating [desync bug] L-39C Multicrew Desync

[Zweistein000]

Me and a friend of mine just tried to have a multcrew pilot-in-training/instructor flight across the Caucasus. The L-39C we set up as instructor priority with the gunsight removed. After starting up and getting taxi clearance it quickly became obvious that we are desynced. It looks like aircraft remains synced to the instructor server side and instructor will not see any movement on his end. The damage however remains synced and any failure caused by one of the pilots is felt by both (note felt, not seen, visually damage does not transfer). If instructor takes control after the pilot is instantly moved to instructors location. On pilots side te game begins vibrating hard to the point that it shakes itself apart form continuous bashing into the ground. Instructor only sees his annunciator light light up until aircraft becomes inoperable. We have noticed that instructor jumping out of the aircraft does not resync the pilot. Instructor rejoining the aircraft does not resync the pilot. In both cases Server-side aircraft remains on the parking. 

 

Currently we have managed to reproduce this bug 100% times using the following steps:

1) Place L-39C, make sure instructor has priority, remove gunsight, make sure 3D NS430 is ticked.

2) Have instructor launch a multiplayer server. Make sure pilot joins aircraft, then instructor joins.

3) Perform startup according to L-39C manual/quick start guide.

4) Have pilot begin to taxi. Confirm with pilot that aircraft is taxying. Observe instructor and F-10 map to confirm aircraft is standing still.

5) Have instructor take control. Confirm with pilot, that pilot has teleported to instructors location. 

 

We have reproduced this 3/3 times. 

I am unable to attach a track file. 

Edited February 5, 2021 by Zweistein000

[Zweistein000]

I have 3 additional pieces of information:

1) Setting the L-39 to either player or client in editor doesn't matter. 

2) This issue also happens with hot-startsd L-39

3) THIS ISSUE IS RELATED TO CONTROL PRIPRITY BEING SET TO INSTRUCTOR! 

 

To elaborate: This issue can be reproduced by setting the control priority to instructor. In this case instructor will not see any movement pilot does (though control surface deflection, switches and damage will still sync). Even if aircraft is being flown by the instructir, as soon as pilot takes iver, the aircraft will slowly stop in mid air for the instructor while the pilot keeps flying. If the instructor then takes control the pilot will again be teleported to instructirs location and the aircraft will stall and fall from thy sky due to having no speed (and therefore no lift).

 

WORKAROUND: Make sure that aircraft control priority is set to equal control by both pilot and instructor. In this case the server will correctly sync both players and L-39 multicrew will work as intended. 

Edited February 7, 2021 by Zweistein000

[Justin Case]

On 2/7/2021 at 2:13 PM, Zweistein000 said:

WORKAROUND: Make sure that aircraft control priority is set to equal control by both pilot and instructor. In this case the server will correctly sync both players and L-39 multicrew will work as intended. 

I tested this yesterday and it worked very well! This was a pleasant surprise, thank you for sharing!

Edited April 30, 2021 by Justin Case