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Prepar3d input lag

Peter Pukhnoy

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Peter Pukhnoy

I tried P3D once but uninstalled it because I found an issue which for me ruined the whole simming experience. There was a very noticeable inverse relationship between mouse and joystick input lag and the frame rate. The input lag in FSX remains the same at any frame rate. I was surprised that I'd never seen this issue brought up before and the general agreement seems to be that P3D overall is a better sim. Maybe it only happens on my system for some reason? Can someone try comparing the input lag with unlimited FPS and FPS locked at 20 on their PC?

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This isn't that uncommon with P3D I believe. i've experienced it with PMDG and the FSL A320 in V3. I read before that Its to do with the BIOS clock. It means a hungry 'sim-minute' versus a real minute can be out by as much as 100%. So starting engines, extending flaps, moving control services etc can easily take twice the time they are programmed  to. Bizarrely, ground speeds and flight speeds seem to not be affected, so you can fly a 2 hour flight in 2 hours.

I've never been able to fix it, I think its mostly down to how powerful your computer is. I have run on the lowest possible settings and still had it. I've not tried V4 yet so don't know if it still exists. Time will tell when the A320 is released! But its caused me go back to FSX for now.

If you want to test it, run the chrono in your aircraft cockpit and measure 30s with your own watch or similar. If it's the BIOS clock misbehaving or unable to keep up, your chrono/timer in the cockpit will fall quite short of reading 30 seconds in that time. For me a it takes an actual minute to reach 20 or 30s in the sim.

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Peter Pukhnoy

@Tom Redsell I don't know much about computers but I don't think it's that. First, why would this issue only be present in P3D if it's an issue with some global clock? Second, why does the lag vary with the frame rate, which is my whole point. I've done some measurements in the last couple of days which I think are pretty accurate and I'm going to post them on the P3D forum. According to the measurements, the input lag at 20 fps and 30 fps is about 100 ms and 50 ms higher, respectively, than it is at 60 fps.

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I'm not suggesting its definitely down to the BIOS clock, but thats what was suggested as a fix on other forums. If I recall correctly, there was a change in the way 'events' are linked to system time in P3D compared to FSX. 

In my experience, it was nothing to do with the FPS I was getting, if I ran P3D with its lowest settings with no addon scenery and loaded up the FSL A320, I would get a pretty steady 40fps and yet time would progress in the sim at around 50% of real time, the flaps took twice as long to extend, engines/apu took twice as long to start etc.  If I flew into dense scenery and the FPS dropped, the aircraft would perform at the same slow speeds but no worse.

I'm not a tech guru, I certainly don't claim to know much about computers but what I could tell you was that for me, the sim time was progressing far slower than reality and that corresponded with the slow 'reactions' of many aspects of the aircraft within it. My suggestion is, don't just focus on input lag, but look at if the sim time (not the UTC because that can be locked to reality through FSUIPC) generated by a timer in the cockpit (chrono/ET) is lagging behind over a few minutes, I suspect that could explain the input lag you are experiencing. After all, an immensely clever product like the FSL A320  is making thousands of calculations a second to produce those events and I imagine nearly all of them have a time component in them that is in some part taken from the sim.

Like I said, I never did find a fix unfortunately, but I've stopped looking until V4 is released anyway.

Best of luck and hopefully someone else might chip in with some advice.


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