Time acceleration and fuel burn

[United744]

Hi,

I used 4x time compression in cruise, and found that by the time I reached the end of an 11 hour simulated flight, that I had only burned half the fuel predicted (before the time acceleration, it was predicting 60000 lbs at destination). I arrived with around 160000 lbs of fuel remaining, and some 20000 lbs over MLW.

Is fuel computed during time acceleration? I'm using Beta 4.

[Hardy Heinlin]

Hi,

yes.

Just park on the ground, set max thrust, and watch the tanks while playing with the time acceleration slider.


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Note that the totalizer fuel intentionally lags behind the calculated fuel. The lag may increase due to rounding errors at high time acceleration. Push "Reset lag" on Service page if necessary.

[United744]

Hmm... well in that case it doesn't appear to be working properly.  :?

I was cruising at FL340 for 10 simulated hours, at 4x acceleration. I should have burned the best part of 200000 lbs of fuel (5000 lbs/hr/eng), but only burned off 100000 lbs (2500 lbs/hr/eng).

[Hardy Heinlin]

I'm currently testing it at factor x16 and all predictions are correct.

Are you sure you did everything correctly in your test?

Look at your CALC fuel. The difference to TOTAL will be huge when using time acceleration over a long time. Perhaps I should disable the lag effect for time acceleration. But the problem is the timing in the fuel system logic: no human can push the pump switches so quickly!

Push "Reset lag" on the Service page from time to time.

[United744]

Note that the totalizer fuel intentionally lags behind the calculated fuel. The lag may increase due to rounding errors at high time acceleration. Push "Reset lag" on Service page if necessary.

Let me try that now.

[United744]

I'm currently testing it at factor x16 and all predictions are correct.

Are you sure you did everything correctly in your test?

Yes, AFAIK? I planned a flight, which required 260000 lbs of fuel (approx. 11 hours flight time). FMC was predicting 50000 lbs on board at destination (winds had been up-linked at this point).

I took off, climbed to cruise in real-time, prediction was showing 55000 lbs at top of climb. I then set acceleration to 4x. By the time I arrived at destination (actually, I flew past it by 200 nm due to being AFK), I still had 160000 lbs on board and was over max landing weight. I dumped 6000 lbs of fuel, then landed.

I just reset lag, and it still shows 152000 lbs fuel on board.

[Hardy Heinlin]

See my edits above.

[United744]

Read, but how does that prevent it burning the fuel? If I reset lag it still shows 152000 lbs fuel on board, suggesting that it didn't actually burn that fuel?

[United744]

If I look in the Service tab, it shows:

Total fuel qty: 152537 (lbs)

[Hardy Heinlin]

I see. I will go a bit deeper and check ...

[United744]

The sensor lag appears to be working - the stabilizer fuel quantity took some time to fall after it alerted to low pump pressure (it was still displaying 1.5 at this time). Shortly afterwards the value reduced towards zero.

I see. I will go a bit deeper and check ...

Thanks!

[Hardy Heinlin]

Fixed in Beta 5.

[United744]

Great! Thanks!