Just an idea, file a support question/suggestion to Autorouter logged in on their website.
Piotr_Szut wrote:
But how accurate is the G1000 LFOB? I suppose it assumes a constant fuel flow and speed till overhead.
In my DA42 it’s precise within 1-2 liters range (0.5 USG or less error when refueling). FF information comes from FADEC and FOB is calculated from the quantity you entered at the beginning of the flight – it’s not related to what fuel gauges for main tanks show. On old engines it was 10% off, showing more fuel than actually was in tanks.
Piotr_Szut wrote:
When I fly a more sophisticated aircraft, I’ll need something else that would take into account the performance model, and the altitude and speed on the STAR and APP. I thought that Autorouter would do that.(And why adding useless numbers on the plog anyway, I thought the Autorouter team wouldn’t do such a thing)
How do those of you who fly complex airplanes manage your fuel in flight?
As I wrote above, if you enter correct FF data to AR, it will present sufficiently precise fuel quantity data in PLOG. If you spend enough time in one aircraft you’ll know FF by heart and, by tracking time spent in different flight regimes (climb, cruise and descent), you’ll be able to have pretty precise guess on fuel quantity. However, for longer flights, fuel totalizer is very useful and reassuring tool, especially when empirically proven to be precise.
A totaliser, once adjusted correctly against a known-good pump, should be within a few litres.
This is a graph of the errors in mine, from 2006 to present, in percent. A lot of the fills are small, say after a 1hr flight, and these obviously show more of a variation. I should have disregarded these small fills. There is also a summer to winter variation, clearly due to different evaporation losses. I posted this previously a few years ago but can’t find it.
Peter wrote:
There is also a summer to winter variation, clearly due to different evaporation losses.
Or difference in fuel density?
Emir wrote:
Piotr_Szut wrote:
But how accurate is the G1000 LFOB? I suppose it assumes a constant fuel flow and speed till overhead.
In my DA42 it’s precise within 1-2 liters range
I have no doubt that the totaliser is pretty accurate.
My understanding was that LFOB meant meant “Fuel that the computer thinks will be on board at landing”. And I think that the computer assumes that the fuel flow and the airspeed will remain constant till overhead the destination, without taking into account the fact that the speed and Fuel flow will vary during the descent, and during the procedure which will be flown at a low level.
During an IFR flight you never fly the planned flight, so your LFOB will never be the one planned. The aim in making several checks during the flight is
1 to make a gross error check, so that you know if something is wrong (faulty totaliser or totally wrong planning)
2 to monitor the fuel saved thanks to a shortcut or wasted due to a long taxi, or by having been kept at a low level for an unusually long time. It’s important to know how much extra you have to make several approaches or to wait for a thunderstorm to go away.
Autorouter I hope does take the flight profile (descent speed and fuel flow) into account, but does it take into account the length of the planned procedure?
And why does it not show directly on the plog the planned fuel on board at each waypoint as Skydemon does?
During an IFR flight you never fly the planned flight, so your LFOB will never be the one planned
The LFOB is recalculated continuously, based on the current GS and the current remaining loaded route. So unless the wind changes a lot, or you get some massive detour later, it is a good number.
On most flights I find that the displayed LFOB at the top of the climb, once settled in cruise, is within 1-2 USG of what I land with a few hours later.
Autorouter I hope does take the flight profile (descent speed and fuel flow) into account, but does it take into account the length of the planned procedure?
Not always because planned route includes what it claims to be included – sometimes directs, sometimes SIDs and/or STARs are included.
And why does it not show directly on the plog the planned fuel on board at each waypoint as Skydemon does?
Just different approach to showing same data. That’s the question for AR designers.
BTW G1000 shows estimated R(emaining)FOB at each point in flight plan including LFOB so you can track it all the time and see how they are charging as the flight progresses and estimate if it fits your expectations.
An issue that I have with my Garmin GTNs and fuel calculation is that on a direct leg to a point in the FPL, they seem to ignore that direct leg (count it as zero fuel), and thus overstate the “fuel on landing” by the fuel necessary from current position to end of direct leg.
Autorouter profile for Mooney M20K 231
I’m looking for an Autorouter profile / share code for a plain Mooney M20K 231 (no intercooler, stock wastegate). The public template is for a 252, which significantly outperforms a stock 231… TIA!
Sorry, I only have a 201 and 252.
But it only takes about 25 minutes to create from the POH.
