[Closed] Excessive Fuel Consumption when FPS is Low

[2Fat2Fly]

Hi,

I noticed that when the FPS drops below 20 and causes the sim to slow down, the fuel consumption rate would increase, causing the estimated FOB at destination drops significantly.

This behavior is especially obvious when the sim freezes during scenery loads. Yesterday when I passed by the scenery-heavy area near New York (New York Airports XP v2 & New York City by Drzewiecki Design edit: after another test it turned out that overlapping overlay installed in the same area is the culprit, not DD's), the sim freezed for ~10 mins, and the EFOB at dest dropped from 1800 lbs to 1300, which made it dangerous to continue the planned trip.

 

To reproduce this, simply slow the sim down and observe the decrease of the EFOB at DEST.

Here's a test I've done:

The first screenshot was taken before the test was carried out. The EFOB at DEST was 1840 lbs.

Then I used a script to force XP to run under 5 FPS for 16 minutes.

Notice the widget on the top-right of the screen, where "ST" means the in-Sim Time (measured by dataref "sim/time/total_flight_time_sec"), and "RT" means Real Time (measured by LUA's "os.clock()"). In this screenshot it means 19:15 minutes were passed in reality, but only 7:15 minutes were passed in the simulator. Also the chrono below the widget tells the same story: the FLT time advanced by 16 minutes, but the UTC clock only advanced by 4 minutes from the last screenshot.

Since there was a 12-minutes discrepancy, the EFOB dropped from 1840 to 1450, which matches the fuel burnt during 12 mins (~450 lbs). So it means that the fuel consumption is calculated based on the actual time elapsed, regardless of the sim being actually running slow.

(The auto-pilot also struggled to maintain a level flight under low FPS, but I'll leave that for now.)

When I lifted the limit to the FPS, the EFOB behaved normal again, proving that it wasn't the wind caused the drop in the EFOB.

 

I know the aircraft is meant to be used when the FPS is at least 20. But it's hard to guarantee that X-Plane won't freeze when flying across the scenery-heavy areas due to X-Plane's poor scenery loading mechanism. Fix for this issue would be appreciated!

Edited January 27, 2022 by 2Fat2Fly
Changed title to avoid confusion

[EGT]

Get a faster hard disk or more memory.

I fly over high-res ortho (I have terrabytes of the stuff). The hard disk is non-stop over those areas but XPL never hiccups.

[Rodeo]

A 10-minute freeze is uncommon, but occasional drops below 20 fps may happen even with powerful systems. Might be interesting for the Challenger to adjust fuel flow based on the sim speed (which I suspect they already do for time acceleration, but maybe they're not using the one that accounts for time dilation)?

sim/time/sim_speed	int	y	ratio	This is the multiplier for real-time...1 = realtime, 2 = 2x, 0 = paused, etc.
sim/time/sim_speed_actual	float	n	ratio	The actual time-speed increase the sim has achieved - takes into account fps limiting.
sim/time/sim_speed_actual_ogl	float	n	ratio	The actual time-speed increase the sim has achieved - takes into account fps limiting and time dilation if fps<19.

…with the last one probably being able to work around the issue?

Regards,

Tim

[bumbak]

I have that problem propably...Its my 8 flight where everytime I finish with half amonut of fuel at destination compared what was planned in simbrief ( first I used NOAA wether plugin and I thought that this is a reason, but after few flights with default x-plane 11 weather updater its the same) I have low end PC and that why i always used autospeed plugin to solve time acceleration problems with X-plane. Since this autospeed causes IRS to lose their aligment in CL60 I have to add at least 500 kg of fuel for 5 hours of flight to actually be able to land with some fuel reserve.

 

[2Fat2Fly]

5 hours ago, EGT said:

Get a faster hard disk or more memory.

I fly over high-res ortho (I have terrabytes of the stuff). The hard disk is non-stop over those areas but XPL never hiccups.

My X-Plane installation and scenery packs are already installed on a separate SSD. So far I have this issue only with DD's New York City packs, while orthos, TrueEarths etc. are just fine. Indeed it's major pain when flying over New York with that installed. But since I mostly fly offline this should not bother much (with the fuel consumption issue solved) and I don't want my money wasted either.

Edited January 16, 2022 by 2Fat2Fly

[ois650]

Hello, 

Unfortunately this isn't really a Challenger issue - this is an issue with the machine you are running your simulator on. There are minimum requirements for X-Plane 11 and minimum requirements for the Challenger 650 that must be abided by. The real time aspects of the Challenger are not designed to run at 5fps and especially not for a 10 minute freeze (this is not normal - something is wrong with your scenery perhaps?)

Kind regards

[2Fat2Fly]

13 hours ago, oisin650 said:

Hello, 

Unfortunately this isn't really a Challenger issue - this is an issue with the machine you are running your simulator on. There are minimum requirements for X-Plane 11 and minimum requirements for the Challenger 650 that must be abided by. The real time aspects of the Challenger are not designed to run at 5fps and especially not for a 10 minute freeze (this is not normal - something is wrong with your scenery perhaps?)

Kind regards

Hi oisin650,

Thanks for the reply!

 

While I understand it's no easy task to fix such thing in such a complex simulation of an aircraft, and truely appreciate your work that brought such an amazing addon to the X-Plane community, I have to emphasize that IT IS a Challenger issue. Please let me explain why:

First, the issue only exists in this particular addon. I have more than a dozen of aircraft addons for XP11 but it seems the CL650 is the only one that doesn't obey with the "law of X-Plane".

Second, my computer spec is i9-9900k + RTX 2080ti + 32GB DDR4 3600MHz RAM, plus my X-Plane copy and sceneries are installed on a 2T WD Blue SSD, which is well above the required spec. Even with this spec XP still freezes & drop below 20fps occasionally. Therefore it is still necessary to provide consistency even when the sim runs slowly.

And third, I believe X-Plane has already provided several ways to provide such consistency. For example, the "sim/time/total_flight_time_sec" and "sim/time/sim_speed_actual_ogl" datarefs mentioned before. Also, most other parts of the Challenger 650, including the simulated IRS positions and error accumulations (which should be more sensitive to time decelerations), works fine when FPS is low. Which makes it strange it is the fuel consumption model alone, that doesn't behave normally when such deceleration occur.

 

I still wish the issue will be fixed though. If so I can fly long distances at ease without worrying about higher fuel consumption than expected. Which will make the overall experience better for long haul flights IMHO.

Regards.

[ois650]

12 hours ago, 2Fat2Fly said:

First, the issue only exists in this particular addon. I have more than a dozen of aircraft addons for XP11 but it seems the CL650 is the only one that doesn't obey with the "law of X-Plane".

The 650 does not obey "the law of X-Plane" - it obeys the laws of physics. The entire systems simulation occurs outside of X-Plane, only the flight model, weather, visuals etc. are dependent on the base simulator. 

12 hours ago, 2Fat2Fly said:

Second, my computer spec is i9-9900k + RTX 2080ti + 32GB DDR4 3600MHz RAM, plus my X-Plane copy and sceneries are installed on a 2T WD Blue SSD, which is well above the required spec. Even with this spec XP still freezes & drop below 20fps occasionally. Therefore it is still necessary to provide consistency even when the sim runs slowly.

There is something else going on there, check out Plugin Admin to see what's actually slowing you down. 

[2Fat2Fly]

24 minutes ago, oisin650 said:

The entire systems simulation occurs outside of X-Plane

This makes sense and conform to my observation to this aircraft so far. It would be a nice addition to cross check and ensure the consistency between the simulated systems and X-Plane.

34 minutes ago, oisin650 said:

There is something else going on there, check out Plugin Admin to see what's actually slowing you down. 

I believe it is the scenery as it only occurs in certain areas. I'll check this out myself.

Again thanks for your patience in reading and answering the questions!