General Question Complex flight model

[gamer19]

hi everyone.

As the title says, this is about Complex flight model - a option under Parameters/Realism section in Orbiter.
Don't know is it important but I'm talking about 2016 version, since I fly 99% in that game version. At least for now

Didn't even thinking about this before, for me it was always ON, since I prefer realism (as long it doesn't kill all the fun)
But a couple days ago I've noticed that with this option ON can crash the game. And it's not like Orbiter need any help.
I would say (except AMSO which have it's own folders) I got roughly 50% crashes on any scenario I start in Orbiter 2016.
That being said, I firmly believe I have ALL the files I need for these scenarios. But alas... it still crashes. A lot.

So one day I stumble on this scenario "Venus descent" in Delta-glider folder. You all got it, it comes with the vanilla game.
Game crashes once again and I opened .scn file with notepad and, to my surprise, I read this part

BEGIN_DESC
You are descending into the thick atmosphere of Venus.

If you have selected the complex flight model, then the high atmospheric pressure at lower altitudes will render your engines ineffective,
and below an altitude of about 40km they will stop producing thrust altogether.
So if you want to keep airborne, you need to stabilise your orbit soon.
END_DESC

similar text was in "Venus takeoff" scenario:

BEGIN_DESC
Launch the delta-glider from Venus and see how it handles under extreme dynamic pressures.

Warning: You must disable the complex flight model for this scenario, otherwise your engines will not work under the enormous atmospheric pressure at the
Venus surface.
END_DESC

First time I've heard about this possibility - crashes with this option on.

So, my question(s) for all of you would be:
Do you have "Complex flight model" option ON ?
Do you experience a vast amount of crashes ?
Do you think game would be more stable with it on OFF ?
Does that option worth the effects this option have on game physics ?

Thank you for reading
and looking forward to some constructive comments

 

[Thunder Chicken]

hi everyone.

As the title says, this is about Complex flight model - a option under Parameters/Realism section in Orbiter.
Don't know is it important but I'm talking about 2016 version, since I fly 99% in that game version. At least for now

Didn't even thinking about this before, for me it was always ON, since I prefer realism (as long it doesn't kill all the fun)
But a couple days ago I've noticed that with this option ON can crash the game. And it's not like Orbiter need any help.
I would say (except AMSO which have it's own folders) I got roughly 50% crashes on any scenario I start in Orbiter 2016.
That being said, I firmly believe I have ALL the files I need for these scenarios. But alas... it still crashes. A lot.

So one day I stumble on this scenario "Venus descent" in Delta-glider folder. You all got it, it comes with the vanilla game.
Game crashes once again and I opened .scn file with notepad and, to my surprise, I read this part


similar text was in "Venus takeoff" scenario:


First time I've heard about this possibility - crashes with this option on.

So, my question(s) for all of you would be:
Do you have "Complex flight model" option ON ?
Do you experience a vast amount of crashes ?
Do you think game would be more stable with it on OFF ?
Does that option worth the effects this option have on game physics ?

Thank you for reading
and looking forward to some constructive comments

Do you get anything in the Orbiter.log that suggest a bug?

There are a host of physical models that, in certain circumstances, can cause instabilities. A lot of simplifications of physical models are implemented simply to side-step these unstable modes. Getting accurate physics AND a stable model can be nigh impossible in some cases. It's just the nature of the universe. Complex models frequently become non-linear.

Another common issue is with the simulation time step size used for time propagation. If you enable any physics (drag, contact forces, anything) that rapidly changes forces on time scales shorter than that time step, you are going to get non-physical forces that will likely grow exponentially fast until you get punted into solar orbit or crash the simulations. The only real fix would be to make the time step smaller than the timescale, but this may require hundreds or thousands (or more) time steps to resolve the simulation and the computational effort becomes astronomical very quickly.

Orbiter was really developed algorithmically to handle spaceflight where there were no drag forces to speak of. But in atmospheric flight, drag and lift forces become important, and so how fast you can go depends on how fast you are going (i.e. it becomes non-linear). As long as the forces change slowly the propagation routines can cope with it. However, if you plow into the Venusian atmosphere at high Mach number, things are going to get crazy really fast.

Realism costs.

 

[Urwumpe]

Generally, complex flight model is just a on/off-flag that gets passed to the ovcInitVessel function for creating a new vessel. Most add-ons actually ignore it.