FENIX A320 jumping on pushback end

[Barnes]

Hi Umberto. Any ideas on a solution to this issue ?

There are two issues, which are not exactly the same:

- A small bump after disconnecting the towbar. This will happen regardless of the airplane, but it changes depending on the scenery, and it's due to the fact almost every airport in MSFS has some kind of elevation difference.

The way GSX pushback works, it freezes the airplane, but it doesn't disable the simulation, otherwise the airplane and the tow truck would proceed in a straight line, always at the same initial altitude MSL, because with the simulation disabled, they won't "feel" the terrain underneath. Also, disabling the simulation would disable almost all systems so, clearly, that's not an option. Instead, when the airplane is just freeze, it won't move during the pushback, so there will be no jittery due to fight between the flight model and GSX controlling it, but when the terrain changes elevation during the path, the airplane inertia system will register it so, at the end of the pushback, when it gets unfrozen, the altitude difference will catch up, causing that bump. We use some mitigation feature, like setting all the accelerations variable to 0 just before and just after unfreezing, but couldn't manage to remove it entirely. The issue is, if we didn't freeze the airplane during pushback, it you start engines, it's likely that just the movement caused by idle thrust might be enough to cause jitters, because two vectors forces would be fighting at each frame, the tow truck would likely slide as if was on ice, etc. We found that kind of bump to be a minor nuisance, compared to the alternatives.

An alternative might have been using the default Left/Right pushback events, like other default-based systems do, but that's not precise enough for what we need, since we couldn't control the position and especially the heading as finely as we can do now (small decimals of a degree), we would have a coarse Left/Right control that, since input events are processed only at 6hz, would probably always chasing the line, in addition of course to the aggravation of spamming simconnect with events, instead of setting data variables, which is way gentler to the simulation.

Having the option to raise the gear or not in Towbarless truck doesn't make any difference, once the airplane is frozen, it doesn't really matter if it's pitched up or not. We have a custom value that has been tuned manually to show just the right amount of pitch up, depending on the airplane, they don't react the same, it depends on their payload and the shockers compression value.

- Some reaction in the airplane custom systems.

That's a completely different issues, and it can be fixed completely once you'll see the first developers integrating GSX. They can detect when GSX is pushing and change any assumptions affected system about the airplane status, so it won't trigger any specific alarms.

Thanks for your detailed explanation of how the pushback system in GSX works, however I also see this bump at the beginning of pushback, as well as at the end when disconnecting the towbar.
It's not really a small bump either - If I were to guess a relative height, I would say the entire aircraft (in my case the Fenix A320) is being raised about one foot at the start of push and then being dropped about the same amout when disconnecting the towbar. It's really quite a violent effect.

[virtuali]

It changes depending on the altitude difference in the scenery. These might be realistic or not, it really depends.

There are some sceneries we found (even default) where the parking *itself* is visibly sloped, I think pushback there wouldn't even be allowed from that position in real life, if the slope were really like that, surely a towbar would break, and I have no idea what will happen with the towbarless arms either. I guess that, at least from the parking stands to the typical pushback positions for that area, the apron should be reasonably flat, but the problem is in MSFS almost invariably isn't.

[Guenseli]

However,

with MSFS default pushback that does not happen ...
Whats the difference?

[virtuali]

with MSFS default pushback that does not happen ... Whats the difference?

The plane is not frozen, which is not required, because the default flight model *knows* the plane is being pushed.

[AUA9085]

Can/will this be solved sometimes?

I tried it with other Pushback tools too (Toolbar pushback for example is also raising the AC and lowering it) without this bumping effect.

[virtuali]

Can/will this be solved sometimes? I tried it with other Pushback tools too (Toolbar pushback for example is also raising the AC and lowering it) without this bumping effect.

Have you read the previous posts ? It might be solved if we made the default pushback as an alternative way of pushing, which of course will result in less accuracy, and possibly more impact on the system.

We'll can try it, but it's not a quick "fix", and we'd rather check better ways, for example finding if there's some better solution to nullify the inertial system.

[ycristia]

So I guess this issue has not been solved yet? I too get the bump when pushback starts and tug disconnects.

[rsaberi]

Every once in a while I also get a crash out of the pushback with Fenix-GSX Pro. So basically the pushback system with Fenix is useless right now. Hope you fix it.

[virtuali]

Every once in a while I also get a crash out of the pushback with Fenix-GSX Pro. So basically the pushback system with Fenix is useless right now. Hope you fix it.

GSX pushback works perfectly fine and it's hardly "useless". Sure, there's a minor bump, but nothing like you are describing. Have a look at these two channels:

https://www.youtube.com/c/CptCanada

They fly regularly with GSX and the Fenix, and they use GSX mostly for Pushback.

[silvera]

I had this issue for a long time but after using the setting "raise the nose" from aircraft options of GSX it disappeared  on pmdg 737. I no longer have jumps at the end of pushback!