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Driver170

PFPX fuel dilema

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Having some trouble with figures here.

 

In PFPX i set my 737 800 W taxi fuel burn to 5kg/min in the editor window, i have a taxi time of 20mins so that only gives me 100kg of taxi fuel.

 

I'm at the gate FOB is 3865 kg and my MIN TO fuel is 3765. but i'm finding my taxi fuel very short for that amount of time and to taxi to the active.

 

basically my acft is burning more than its calculating and 5kg per min is the ball park figure to work with so whats going on? 


Maybe 5kg/min is per engine?


I got these figures from a pilot

 

Roughly 40kg per minute holding (eg 30 min final reserve fuel is ca 1200kg) Expect to use about minimum 600kg extra for a go-around and second approach without additional delay and depending on the length of the missed approach procedure. APU uses about 150kg/hour ballpark figure For remote de-icing with engines running with no extra delay add about 300kg, if deicing on stand, see APU burn figure for about 15 min extra if no delay.

 

 

Can someone let me know is that 600 kg per engine on a go around?

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It may not be the most realistic method but why not pull up your fuel page and use the stopwatch function of the aircraft for a minute and then pause the sim and note what was used?, that will probably get you a lot closer to what the sim is actually using. Not so sure how closely real world data matches the sim on this. 

 

Out of practicality I usually end up adding about 2k LBS of extra fuel unless I'm parked right by the departure runway....but thats just me as I'm not the fastest at getting everything setup.

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Sorry to hear you're having problems because when I use PFPX with the 737 the figures are absolutely spot-on. I can't help with the RW fuel burn figure I'm afraid but sure Kyle will know it

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Hi guys just to get something across my fuel figures are spot on every time for a whole year since getting PFPX. but my trouble was i changed my taxi fuel to kg/min to 5kg but i wasn't sure if this is per engine or 2?

 

But the looks of it and googling it seems the 737 uses about 10kg per minute. so i have technically found my own answer! Now i have about 200kg for taxi for 20 minutes.

 

Another thing where does the APU fuel get added to if you require this at the gate?

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The APU burn is normally included as part of the taxi figure.

 

I find that in general aircraft in FSX burn far more fuel on the ground than their real world counterparts -- I'm not entirely sure why but I suspect it's partially to do with the MS atmosphere and partially to do with developers having to add extra thrust on the ground to overcome the FSX friction model (and also the fact that higher thrust levels are generally needed to overcome the same when taxiing around).

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I have added the lua friction through FSUIPC ? So not sure if that sorts FSX limitation?

 

End of the day its a sim and will never be close to the real thing and maybe i need to realise that and just have a fixed 200kg taxi fuel - well most airliners do go with this fixed amount for the 737.

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Hi guys just to get something across my fuel figures are spot on every time for a whole year since getting PFPX. but my trouble was i changed my taxi fuel to kg/min to 5kg but i wasn't sure if this is per engine or 2?

 

But the looks of it and googling it seems the 737 uses about 10kg per minute. so i have technically found my own answer! Now i have about 200kg for taxi for 20 minutes.

 

Another thing where does the APU fuel get added to if you require this at the gate?

APU is fed from the left main tank unless you have center tank or are cross feeding.

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Try 13kg/min ... you favourite EU operator uses this & plans with a standard 15 mins of TAXI Fuel which gives them 195kgs INCLUSIVE of APU usage which is normally kept to a minimum ... if the OAT is ABOVE +5'C & BELOW +25'C they discourage the use of the APU altogether in lieu of Ground Power until it is time to close the doors.

 

Whilst you are at it I have noticed that you have been using some very crap cfgs for 'your favourite EU operator' from various screenies you have been posting.

 

Can I suggest you follow this shameless plug & get these 'paints' by Christian Mohr as the cfgs are as spot on as they can be within the confines of what PMDG currently offers for the NGX (I did the cfgs):

 

http://library.avsim.net/esearch.php?CatID=fsxacrp&DLID=186747

 

Happy Flighting

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APU is fed from the left main tank unless you have center tank or are cross feeding.

 

Matt, ever since I read this on the FCOM I always leave the Left FWD fuel pump on during ground ops while the APU is running and engines are on cutoff. I can't remember where but I read that you could theoretically leave the pump off and the APU would still be getting its fuel but that it's good practice to leave that particular pump on for APU operations. Could you corroborate this? Thanks

 

Edit: 

 

And just to comment on the OP's issues: like many, I've also found out long ago that FSX birds use way more fuel and thrust than their real world counterparts when taxiing. I have found that 220-280 kgs is what I end up using for my usual 5-12 minute taxi. I have thus edited PFPX to always assume a 240kg taxi fuel. This always works for me. Although I'm inclined to change it to 13 kg/min to nail it 

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This is from the NG pilot i know but is now on the bus

 

APU use depends on local regulations and temperatures. On most airports we have to use the GPU if available and do that wherever possible. However if temperatures are lower than 10°C or higher than 20°C we should give consideration to cabin temperatures. At some airports we do get automatically pre-conditioned air from the airport and do not have to use the APU to cool down or warm up the cabin, on some it is available on request and on most it is not usually available.

 

In general: wherever possible we try not to use the APU although we always switch it on during arrival. If we can use other means it gets switched off again once GPU/Air is connected.

 

Taxi fuel is planned on a statistical basis, based on average taxi times per airport/filed runway and aircraft type. It is usually somewhere around 110 to 250 kgs, mostly in the lower 100s. We usually round it up to the nearest 100kg for easier fuel calculation.

Try 13kg/min ... you favourite EU operator uses this & plans with a standard 15 mins of TAXI Fuel which gives them 195kgs INCLUSIVE of APU usage which is normally kept to a minimum ... if the OAT is ABOVE +5'C & BELOW +25'C they discourage the use of the APU altogether in lieu of Ground Power until it is time to close the doors.

 

Whilst you are at it I have noticed that you have been using some very crap cfgs for 'your favourite EU operator' from various screenies you have been posting.

 

Can I suggest you follow this shameless plug & get these 'paints' by Christian Mohr as the cfgs are as spot on as they can be within the confines of what PMDG currently offers for the NGX (I did the cfgs):

 

http://library.avsim...crp&DLID=186747

 

I havent downloaded that file yet, what exactly is it?

 

Thanks for the figures :)

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I havent downloaded that file yet, what exactly is it?

Read the file description on the Avsim page. If that is not enough info, download the file, unzip it, and read the README. If you don't want it you can delete the whole mess of files. Downloading the zip file does not install it.

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I can't remember where but I read that you could theoretically leave the pump off and the APU would still be getting its fuel but that it's good practice to leave that particular pump on for APU operations. Could you corroborate this? Thanks

 

Running the APU without positive pressure will reduce the life expectancy of the APU fuel pump. It will run without a main pump.

 

Those pumps are AC-powered and won't run if you don't have AC on the aircraft. The 737 does come with an option for a DC boost pump. I flew some in Korea and IIRC, we didn't run the main tank pump.

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Running the APU without positive pressure will reduce the life expectancy of the APU fuel pump. It will run without a main pump.

 

Those pumps are AC-powered and won't run if you don't have AC on the aircraft. The 737 does come with an option for a DC boost pump. I flew some in Korea and IIRC, we didn't run the main tank pump.

 

So you should have the fuel pump on when at the gate and running the APU as this saves cost on the apu pump?

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So you should have the fuel pump on when at the gate and running the APU as this saves cost on the apu pump?

 

Exactly, I thought that was mentioned in either the Intro or one of the Tutorials, which is where I gained the habit of left pump on for APU.

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Found this -

 

Sounds right as access to the FWD boost pump is via deployed LE FLAPS and access to the AFT boost pump is via the wheel well.

 

So in that case,using the AFT one would make more sense as servicing access would be easier.

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