Author Topic: dash fuel planning  (Read 5441 times)

Gert Visser

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dash fuel planning
« on: Sat 12 Mar 2016, 14:57 »
Hello all,
I have run into something.
I use simbroef for generating the plog.
After some 30+ flights I get the inpression that something is amiss with the fuel planning.
I  allways use considerably less fuel than simbrief advises.
When using the climb, cruise and descend profiles from the intercity SOP, I arrive ath the following figures:
Climb, ff 1440 kg/hr, 185kn up to fl100, afterwards 210 kn
cruise ff 950 kg/hr cruise abt 225-230 kn
descend ff 450 kg /hr , 1800 ft/min at 230kn
On average flights I use some 20% less than simbrief indicates.
Hwever, the 45 min flight reserve of some 750 kg is fairly accurate considering the fuel consumption in cruise.
On the fuel page of the q400 fmc the final reserve is calculated considering the actual fuel consumption of the moment. It doesn't take into account the much lower fuel burn in descend. So, the FMC doesn't help in fuel planning.
My question.
Am I doing something wrong OR is the fuel planning in simbrief not correct?
In simbrief I have entered the correct profiles for climb, cruise and descend, fuel factor P20.
I hope somebody can help out.

Gert

Gert Visser

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Re: dash fuel planning
« Reply #1 on: Sun 13 Mar 2016, 14:41 »
In respect to tis subject, I have some other queations:
In the dash sop it says climb at 185 kn tot fl100, then accellerate to 210 and continue climb.
Is this climb with a constant ias of 210kn, or with a constant vertical speed??
I have read the operations manual and the bombardier fuel planning manual and I can't figure out exactly what the differend climb profiles mean
Some help appreciated, also in connection with accurate fuel planning.

Gert

Gert Visser

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Re: dash fuel planning
« Reply #2 on: Sun 22 May 2016, 11:31 »
After some flights it seems to me that simbrief calculates the necessary fuel to be overhead at flightlevel on the destination airfield.
It doesn't take into account the considerably less fuel burn while descending. But this raises the question how the fuel  to reach your alternate airport is calculated. If its done by taking the overhead point on the destination airport at flight level, then the fuel to reach the alternate field is too little, because you need to climb again.
Hope somebody can shed light on this.

Gert

Chris Liu

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Re: dash fuel planning
« Reply #3 on: Mon 23 May 2016, 11:28 »
In the dash sop it says climb at 185 kn tot fl100, then accellerate to 210 and continue climb.
Is this climb with a constant ias of 210kn, or with a constant vertical speed??
I have read the operations manual and the bombardier fuel planning manual and I can't figure out exactly what the differend climb profiles mean
Sorry Gert I must've missed this post! It's a constant IAS climb (use IAS hold on the autopilot) although occasionally you may need to revert to VS or pitch angle at some point above FL200.

There's a fuel efficiency manual at http://commercialaircraft.bombardier.com/content/dam/Websites/bca/literature/q400/Q400_Fuel-Efficiency-manual.pdf and the three different climb types are shown on page 18. As you said, Intercity SOP is currently Type II (185 KIAS) until FL100, then Type I (215 KIAS) climb, all at 900 prop rpm.

...simbrief calculates the necessary fuel to be overhead at flightlevel on the destination airfield. It doesn't take into account the considerably less fuel burn while descending. But this raises the question how the fuel  to reach your alternate airport is calculated. If its done by taking the overhead point on the destination airport at flight level, then the fuel to reach the alternate field is too little, because you need to climb again.
AFAIK, SimBrief's Q400 fuel planning is broadly correct, more so than PFPX according to some forum posts! However, I haven't gone in to the minutiae of how it reaches its figures nor attempted a diversion. I believe diversions are based are typically based on a set fuel flow for maximum range.
« Last Edit: Mon 23 May 2016, 17:03 by Chris Liu »

Chris Hulme

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Re: dash fuel planning
« Reply #4 on: Mon 23 May 2016, 15:22 »
I've never had an issue with fuel planning and sim brief. Always seem to land with a little more than it plans for like you said but I'm happy to do this as it gives you extra to play with when it's busy on VATSIM and incase of go around/divert and all 3 if it's a bad day!
Wouldn't say it's hugely over though a couple of hundred kilos at most?

Chris Hulme

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Re: dash fuel planning
« Reply #5 on: Mon 23 May 2016, 15:24 »
Just a further thought, I assume sim brief gets the winds and calculates fuel based on cruise wind but this can differ depending on sim settings and weather engine and also that the wind could change from what was forecast as time of planning. So lots of variables to play with!