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Having issues with FPS and getting disconnected from VATSIM because of it


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Hello VATSIM community. I am having an issue with FPS staying above 20 to prevent getting disconnected from the network. I am running X-Plane 11 on a laptop with a Intel Core i3 5005U processor and a GeForce 930M graphics card. My X-Plane is also running on the lowest settings possible. There are addons that are installed for the Zibo Mod though. I am also running the 3jFPS script to increase the frames but probably because of the specs the script can't do wonders. The frame rate on the ground is around 20 FPS. In cruise, the FPS is around 10 for more than 20 seconds. Nvidia Settings are optimized from a Youtube guide i followed online. I got X-Plane 11 for the updated airports but looks like I just have a frame rate issue on VATSIM. I am not going to spend money on a new computer because I do not have the money for it. Any help to get the average framerate to atleast 30 during cruise and on the ground would be nice. Any configs I can mess with to increase the FPS? Any help would be nice!

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Well, as you're already using 3jfps, there's only so much you can do. Your PC's specifications have seen its better days, and you can only optimize and squeeze out extra frames so much before you need to start looking at upgrading... There are some performance boosting scripts out there, but I am not sure there is any script available that will bring your frames up to the level VATSIM requires... Sorry!

Mats Edvin Aarø
General Manager - Member Engagement
Supervisor Team Lead: Team 4
[email protected]

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At the end of the day, you may just be attempting to run software that is too complex for the hardware you have to run it with. However, you may still be able to get some enjoyment out of VATSIM by running FSX or P3D and the PMDG 737.  Prior to my latest PC purchase I ran those quite happily on pretty substandard hardware without any issues.   When FSX or P3D suffers from low framerates, it does not dilate time, either -- aircraft control becomes difficult in such cases, but, you still progress across the ground at normal speed. 

Cheers,

-R.

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The problem isn't FPS itself, but the fact that XP11 (unlike all the other sims) will slow down simulation rate when FPS drops below 20.

VATSIM doesn't really care if you're seeing a slideshow on your end; what we do care about is that when you report 240 knots, you will cover roughly 4 miles per minute - but XP11 running at 10 fps will slow down sim time by 50%, so your airspeed indicator will still show 240 knots, while you're really moving at 120 knots, 2 miles per minute.

Now, that hardware isn't exactly top notch; but it being a laptop, just buying, say, a used GTX1050Ti is not really an option. This leaves you with:

  • Flying (much) simpler aircraft models. A 737 is very common, but it's still an airliner, and as such, it has complex systems and instruments that need to be simulated. Maybe try a simple steam-gauge light aircraft, like a Cessna or a PA-28, and see if that helps any.
  • Rule out other applications eating into your system resources.
  • See if you can obtain a copy of FSX, or try FlightGear. You won't see significantly better performance, possibly even worse, but unlike XP11, these sims don't dilate time to keep up.
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7 hours ago, Reece Arcinas said:

I have FSX and I might use that because it is not that demanding. What happens if Laminar Research did not slow down the sim if the FPS goes below 20?

Then the sim would break and the plane would be unfliable. Their whole physics engine is based on something called Blade Element Theory, which very dumbed down runs the aircraft through a fictional and invisible wind tunnel, calculating how the physics affect the aircraft, how the gravity, thrust, drag and lift impact the plane's aerodynamics.

When you max out the performance limit your PC can handle, it starts stuttering, and it can no longer compute these aerodynamic impacts as fast as it needs to in order for the plane to fly as you expect it to. You can see this happening if you try to speed up the simulation rate a bit. The whole plane will likely start to wobble and might absolutely lose control.

To prevent this, X-plane slows down the simulation rate as much as it needs in order to process these calculations properly.

Therefore, that feature isn't going to go away unfortunately..

Mats Edvin Aarø
General Manager - Member Engagement
Supervisor Team Lead: Team 4
[email protected]

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Table lookup, pretty much they have made a model based on real life aircraft performance characteristics and recorded airspeed, AoA, V/S and a ton of other telemetry at specific altitudes, power settings, flap angles etc. in order to interpolate this into a flight model. There are pro's and con's with both solutions.

Mats Edvin Aarø
General Manager - Member Engagement
Supervisor Team Lead: Team 4
[email protected]

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The physics simulation algorithm is not actually all that relevant. There is no reason why you couldn't perform two or three updates of that Blade Element algorithm for each rendered frame - even a complex simulation like this is usually limited on rendering, not physics, which means that frame skipping would be a perfectly viable way of sacrificing perceived performance (number of frames shown per second) for correctness (accuracy and stability of physics simulation).

Yes, XP11's physics simulation relies on the time step delta to be small enough, but the same also applies to literally every other viable integrator - aerodynamics are way way way too complex to boil it all down into a continuous-time formula that you can just interpolate without introducing any errors. And then we haven't even started to consider floating-point errors, which is yet another can of worms.

The real reason why they do it this way is because they chose to run physics and rendering in strict lock-step: exactly one physics update per screen update, no exceptions. There is a lot to say for this approach, especially with a physics engine that allows for variable time delta: it makes things a lot simpler, and it avoids jitter due to interference effects between the screen update rate and the logic update rate (e.g.: if you run the logic at 60 fps and the renderer does 59 fps, then there will be one frame skip per second, and that frame skip will amount to approx. 1/60th second of sim time; this is going to be noticeable as a tiny little jump at a regular 1-second interval). Strict lock-step with variable delta takes care of that: each frame receives a world state that matches the simulated time *exactly*, down to the limits of what the computer can represent. But still, variable or not, the delta cannot become too large, so when render frame rate drops below a certain critical value, the time delta will exceed the critical value, and the numeric calculations become unstable. And in order to keep things simple, what they did is they simply put a hard limit on the time delta: whenever the renderer takes longer than 50 milliseconds, the time delta is capped to 50 ms, and thus the simulation is no longer advanced in real time, but in steps of 50 ms per rendered frame. So if you're doing 10 fps, then you get 10 x 50ms = 0.5s of sim time per 1s of wall-clock time: you're running the sim at half the rate.

Other sims adopt a different approach: they run the renderer at whatever rate it can achieve, and then do as many physics updates as needed to catch up. I'm not sure how FSX does it, but at least for FlightGear, I know that the FDM runs at a constant 120 fps; if the renderer runs at 60 fps, then the FDM runs twice per frame, at 20 fps it'll run 6 FDM updates per frame, and you can go all the way down to 1 fps, literally a slideshow, and the FDM just updates 120 times per frame.

Oh, and the "tables vs. blade physics" thing is largely irrelevant, because the problem is not how you come up with forces and moments, but how you get from forces and moments at a discrete point in time to a good approximation of their continuous-time dynamics - in other words, approximating continuous-domain integrals using discrete-time sums. A more sophisticated physics algorithms is less dependant on a good integrator, but the fundamental problem, and viable solutions, remain.

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