I flew a 9hr with preset weather light clouds and no wind, used x4 …i had insufficient fuel warning whilst on the ground at EGLL despite loading what SB suggested.before i had started the engines so i added another 10KG and that was enough for the flight, i landed with 9.7 and the temps stayed consistent with SB.
I have done 2 flights both using 2X (EHAM-VHHX-EHAM) and both fuel on arrival were pretty consistent with SimBrief.
I am suspecting that anything above 2X creates a problem with fuel consumption.
And for the brake temperature it seems like doesn’t increase after landing for some reason. On the last flight I tested the brakes while taxiing before departure and there was a temperature increase so I am not sure why that happens.
If you are in climb, change your altitude cruise in vnav page.
I think the T7 wants to step to the next altitude, so put your cruise altitude in vnav page to cancel that
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Thank you all for these reports, but without knowing if the weather (more specific, temperature) is correct, they are not very useful. We know for a fact the sim can deliver incorrect temperatures at cruise levels and that this causes serious abnormal fuel burn.
Mathijs Kok
PMDG
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For the folks who are flying on a SimBrief flight plan uploaded to the FMC while flying with a weather preset in MSFS instead of live weather, it might be interesting to see how the winds and temperatures aloft during the flight compare to the operational flight plan. I found the suggestion above to use the DAL OFP format in SimBrief helpful for this kind of comparison. If the differences in the winds and temperatures aloft are great enough between the forecast SimBrief used and the values the MSFS weather preset generates, what then is the impact on fuel burn during the flight?
One might take a look at this on any flight, short or long haul, with or without time compression. If the comparisons are close, then maybe planing with a little extra fuel solves for FOB? OTOH if there are big differences in the winds/temperatures aloft between the OFP uploaded to the FMC and what MSFS is simulating for the preset, then the discrepancy should impact fuel burn, possibly adversely? Could be interesting to observe as this discussion about the sim delivering incorrect temperatures at cruise levels impacting fuel burn, continues. Good flying today!
There is outside temperature, with wind data, shown in the Position Reports.
The TAT (Total Air Temperature) is being calculated - but who is doing that calculation - PMDG, or the Sim?
In my screen shot the TAT and outside temperatures look correct (TAT is outside temp plus “ram rise” of friction, which can be as much as 30 degrees C), as -50C + 30C = roughly -20C…
The issue of fuel burning faster than expected seems to be occuring with sim rate, so not just a temperature issue, but a sim rate calculation issue.
So perhaps with a sim rate increase of x4 or x8, the calculation is mistakenly calculating a ram rate friction increase of x4 or x8 which would artificially raise the TAT, and increase fuel burn?
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I agree with your assessment. As per my KSFO-EGLL flight above (Completed successfully), I believe Temp and TAT are calculated & displayed correctly.
Good job!! With how much fuel did you land comparing with the SB predicted?
Yes, I think that when you increase Simrate, x4 or x8 or whatever, it might be mistakenly calculating a x4 or x8 increase in friction, so the TAT goes up, burning more fuel - just a guess on my part, but obviously there is faulty logic in the fuel burn calculation at icreased simrate.
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Can that be fixed?
Did beta tester have already made a long haul flight on X BOX, without fuel issue, without adding fuel in flight with auto sim rate x 4 x 8..?
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Mathijs,
I don’t think it is the temperature. On Xbox X with default livery, default settings, I just flew from CYVR to CYYZ.
At cruise, both fuel burn and fuel prediction were stable until I enabled Auto Time Compression via the EFB (which resulted in SimRate of 4x).
TLDR: The fuel is burning about 20 to 25% faster than the “FF” Fuel Flow value on the Engine page would allow, when SimRate is x4. Example: FF says 7.5 but fuel burn rate is about 10. See below:
After only 30 minutes of flying time (sim time) at Simrate 4x, the fuel burn seemed to increase by about 25% (calculating difference of fuel on board after 30 minutes of sim time at simrate x4). So the fuel on board and fuel prediction both decrease more than expected…
Yet the “Fuel Flow” (FF) indicated on the Engine page decreased, so the increased fuel burn should not be possible and somehow out of sync. And it wasn’t caused by temperature, because TAT temperature also decreased at the same time.
Simbrief: CYVR ALNOD IKNIX YQL ZOMTA AGLIN OTNIK BOXUM7 CYYZ
Time and weather: live
Block Fuel: 78,520 lbs
Fin Res + Alt: 15.3
Landing Fuel predicted: 19.6
Landing Fuel actual: 10.7
- I took off, climbed to FL380 cruise and flew with no Time Compression for about 100 NM.
- Predicted Fuel remained stable at 19.6 for CYYZ destination.
- At 233 NM from YQL Fuel on Board was 63.9.
- I enabled Time Compression via EFB, it increased SimRate to 4x.
- At YQL, Fuel on Board had dropped to 53.2
- That’s a burn rate of approx 10,000 lbs in 30 minutes flying time (sim time)
- Equivalent to 20,000 lbs per hour, or Fuel Flow (FF) of 10 per side per hour
- … But the Fuel Flow FF Engine Synoptic had dropped from 7.5 to 7.4 per side per hour.
- So a Fuel burn rate of 10 is roughly 25% more than the 7.4 indicated on the Engine page.
- TAT had also dropped from -17 to -18 C so it is not caused by temperature.
- Predicted Fuel for CYYZ dropped from 19.6 to 16.0 in that short time.
I left Time Compression on until TOD, where TAT continued to decrease to -24 C and the landing fuel was only 10.7, far below the Finres + Alternate of Simbrief.
It is obvious that with Time Compression, there is something wrong with the fuel burn calculations, especially since the Fuel Flow engine synoptic remains stable, but the fuel on board decreases at a faster pace than indicated. Perhaps the plane is calculating more clock cycles than the sim? Or something?
Here are 4 sceenshots, starting with the fuel loaded on the ground (via Simbrief):
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I landed within a few hundred Kgs of plan actually! (I was lower). No danger of running out. I am not sure what is deemed acceptable.
I plan to do LGAV-WSSS next. I suspect I won’t have a problem if I do a real time cruise and weather set up again. If I do I will report back.
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Did you use Time Compression / SimRate increase?
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@GimbalAxis thanks for your detailed reports.
I believe the fuel burn issue is tied to Time Compression / SimRate. The times I’ve had this happened was while using it. I literally watched as my fuel just evaporated. Every flight at 1x has not had this issue. At least for me.
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Yes, and if you notice, the “FF” (Fuel Flow) on the Engine Page doesn’t change enough to match the amount of fuel that is disappearing from the tanks.
The FF value is units (lbs or kg) per hour, per side.
example FF 7.5 is 7,500 lbs per hour, per engine, or 15,000 total per hour.
When time allows I will do a simple 2 hour flight with 1 hour each of no Time Compression and with Time Compression, and compare the FF and rate that fuel disappears from the tanks.
If fuel was really being burned, then the FF value would match the amount disappearing from the tanks. But currently it’s very different.
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I just flew from HK to Zurich in serious headwinds and ran out of fuel by the time i got to turkey had to top up numerous times totalling over 50% of fuel so there is something going on.
I was on cruise up to x8 simrate
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No - all at 1x
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We use the simVar for that.
Mathijs Kok
PMDG
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Hmmm, sounds a little like the fuel disappearing problem discussed during beta testing the v2 (and perhaps continuing in the v2 after SU15 was released)? And so this may be a core sim issue affecting other add ons and not the T7 specifically? Of course it is of high interest here for long haul and auto time compression functionality; that said if it is an underlying defect in MSFS, perhaps our end user conversation now turns to how to fully understand the defect and how to compensate for it? For example, is the increased fuel burn predictable, and if so how much extra to plan for? Are the increases in fuel burn rates between 1x, 4x, 8x, etc. linear or geometric (perhaps this question is already answered above)? So until there is a fix in the sim (or 3rd parties can program around the defect) we need to figure out a few rules of thumb to manage burn by way of more FOB? Just how much more then becomes the problem to solve?
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