Fuel Tankering Economy
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Disgusted of Tunbridge
Disgusted of Tunbridge
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I'm afraid your reply is too simple and ridiculous! What sector length are you talking about? Do you only fly one particular rotation? What about tanking 30 mins. Or 14 hours? Both cost 10% in fuel? Daft mate. Because that is what you have said!
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Fine tuning
Dear BOAC,
Fuel service, delay, parking fee... Previous replies mentioned some situations were those factors may have an impact, even if it is almost impossible to build up an equation with those parameters for all our network (17 AC, 450 different stations during the year).
Regarding heavier weights, I was not meaning it regarding fees.
We use a software to compute Take off and landing data. This allows us to optimise thrust reduction for take off with large savings regarding engine maintenance. (plus: datas are far more accurate and improved than the results from books...).
Tankering = heavier weight = more thrust required = less engine saving... even if this extra thrust is used to carry less expensive fuel, we should consider it in the global economy (I may look insane now... engineering studies perhaps).
Regarding landing, structural loads increase with heavier weights (even if below certified limits).
More over, my belief with tankering fuel practice is you fill more fuel than requires just to guarantee you will not need more... Finally, you carry fuel that you do not really need... B737, around 35kg per ton per flight hour from each extra ton carried !-( Large amount of fuel burn wasted for nothing... (I speak about the extra fuel from the extra fuel)
Well, after lot of thinking, I may make a single change to the current situation : I will present ECO fuel recommendation for 5 extra tons in stead of 1.
Why? For 737, when you evaluate carrying more fuel for cost reasons, you will try to take more than one single extra ton.
Therefore, the result for 5t will represent a more accurate data to be used than the one extrapolated from the first ton until reaching the desired amount. Hope it makes sense for you too.
Again, thanks for your contribution.
Best regards,
Fin
Fuel service, delay, parking fee... Previous replies mentioned some situations were those factors may have an impact, even if it is almost impossible to build up an equation with those parameters for all our network (17 AC, 450 different stations during the year).
Regarding heavier weights, I was not meaning it regarding fees.
We use a software to compute Take off and landing data. This allows us to optimise thrust reduction for take off with large savings regarding engine maintenance. (plus: datas are far more accurate and improved than the results from books...).
Tankering = heavier weight = more thrust required = less engine saving... even if this extra thrust is used to carry less expensive fuel, we should consider it in the global economy (I may look insane now... engineering studies perhaps).
Regarding landing, structural loads increase with heavier weights (even if below certified limits).
More over, my belief with tankering fuel practice is you fill more fuel than requires just to guarantee you will not need more... Finally, you carry fuel that you do not really need... B737, around 35kg per ton per flight hour from each extra ton carried !-( Large amount of fuel burn wasted for nothing... (I speak about the extra fuel from the extra fuel)
Well, after lot of thinking, I may make a single change to the current situation : I will present ECO fuel recommendation for 5 extra tons in stead of 1.
Why? For 737, when you evaluate carrying more fuel for cost reasons, you will try to take more than one single extra ton.
Therefore, the result for 5t will represent a more accurate data to be used than the one extrapolated from the first ton until reaching the desired amount. Hope it makes sense for you too.
Again, thanks for your contribution.
Best regards,
Fin
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a % does not depend on length of sector as it will be a % of the fuel burn not a number per hour a this would go up or down based on how much you weigh. thus we use %. 10% might be high but that is what we ue as a rule of thumb. for the 737-400. it is simple becuase it is a rule of thumb not percise but the pilots are the ones who make the decision on wether or not to tanker and a we all know us pilots are not to good at math. there is just too many numbers to remember. 
it is just what we use not supposed to be a hard fact. if it is wrong then oh well at least it isn't my money we are wasting.
it is just what we use not supposed to be a hard fact. if it is wrong then oh well at least it isn't my money we are wasting.
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here you go.
MATHEMATICS OF TANKERING
To determine the ' break-even cost difference' (Cbe), use the formula:
Cbe = ( (RFCh + CmT) / F(1-R) ) x ($/gal)
Where:
R is the percentage of the fuel carried which is consumed due to carrying its own weight. The percentage is expressed as a decimal. Here 10%, that is .1, is assumed.
F is the quantity of tankered fuel in gallons.
Ch is the price per gallon at home base.
Cm is the maintenance cost, including engines, per minute of flight.
T is the additional flight time incurred by the added fuel weight, in minutes.
Assuming 600 gal are tankered, the formula shows that the break-even figure is $0.069/gal. This means that the price of fuel would have to be about 7 cents per gallon more than at home base, just to break even. Obviously, the price difference would have to be much higher than the 7 cents per gallon to make it logical to tanker the 600 gal.
The savings per average trip can be expressed by the following formula: S = F(Cd - RCh - RCd) - CmT. Cd is the cost per gallon difference between home and destination.
Assuming a 600-gal tankering load, at 35 cents difference in price ($.52 at home base and $.87 at destination) and a $2.92/min maintenance cost, the savings comes to $151.96 per trip. The formula: S = 600[$.35 - (.1 x $.52) - (.1 x $.35) - $2.92/min x 2 min] = $151.96 per trip.
If many trips were made to this destination, an operator could reap considerable annual savings in fuel costs.
MATHEMATICS OF TANKERING
To determine the ' break-even cost difference' (Cbe), use the formula:
Cbe = ( (RFCh + CmT) / F(1-R) ) x ($/gal)
Where:
R is the percentage of the fuel carried which is consumed due to carrying its own weight. The percentage is expressed as a decimal. Here 10%, that is .1, is assumed.
F is the quantity of tankered fuel in gallons.
Ch is the price per gallon at home base.
Cm is the maintenance cost, including engines, per minute of flight.
T is the additional flight time incurred by the added fuel weight, in minutes.
Assuming 600 gal are tankered, the formula shows that the break-even figure is $0.069/gal. This means that the price of fuel would have to be about 7 cents per gallon more than at home base, just to break even. Obviously, the price difference would have to be much higher than the 7 cents per gallon to make it logical to tanker the 600 gal.
The savings per average trip can be expressed by the following formula: S = F(Cd - RCh - RCd) - CmT. Cd is the cost per gallon difference between home and destination.
Assuming a 600-gal tankering load, at 35 cents difference in price ($.52 at home base and $.87 at destination) and a $2.92/min maintenance cost, the savings comes to $151.96 per trip. The formula: S = 600[$.35 - (.1 x $.52) - (.1 x $.35) - $2.92/min x 2 min] = $151.96 per trip.
If many trips were made to this destination, an operator could reap considerable annual savings in fuel costs.
Prof. Airport Engineer
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hoover1
Many thanks for that formula - I'd been trying to find that one without success.
Just a thought, but is there anyone that can make an HTML page with this formula in (as a javascript I guess), and send it to me so I can stick it on the web for us to use (and to reference here and in the TechLog stickies).
Cheers
OverRun
Many thanks for that formula - I'd been trying to find that one without success.
Just a thought, but is there anyone that can make an HTML page with this formula in (as a javascript I guess), and send it to me so I can stick it on the web for us to use (and to reference here and in the TechLog stickies).
Cheers
OverRun
R is the percentage of the fuel carried which is consumed due to carrying its own weight. The percentage is expressed as a decimal. Here 10%, that is .1, is assumed.
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The formula doesn't include the total flight time as a factor so it will not be able to differentiate between tanking over 30 mins or 14 hours. If you always fly sectors of roughly the same time you have no need to take account of this as it can be accommodated in the 10% figure, i assume in this case it has.
Exactly. That's where it gets interesting. For an aircraft flying under approximately similar conditions over the same distance, the ratio of its take-off weight to landing weight is constant. So for any given sector you can use representative values of landing weight / take-off weight to work out what fraction of excess fuel you get to keep, or conversely fuel burn / take-off weight to work out how much fuel is burnt carrying it.
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this is from boeing so hopefully they can answer the question
http://www.iata.org/NR/ContentConnec...Cons_Nov04.pdf
http://www.iata.org/NR/ContentConnec...Cons_Nov04.pdf
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Posters mentioned 4% fuel burn per hour per pound of additional weight carried for a 737.
Used to be 3% for 757/767.
Using 777 and 737NG performance data appeared to indicate 2.5%. IMO 3% is close enough.
Maybe advancement in fuel efficiency has changed the percentage?
Used to be 3% for 757/767.
Using 777 and 737NG performance data appeared to indicate 2.5%. IMO 3% is close enough.
Maybe advancement in fuel efficiency has changed the percentage?
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earn or loss in $ = Store tons x(Arr [$ / ton] / 1.04 ↑ hrs– Dep [$ / ton])
earn or loss in tons = Store / (1.04 ↑ hrs) –Store / (Arr$/Dep$)
Fuel Price $ / ton = 26.42 * (c/Gal) / SG(lb /Gal) if(kg / L ) / 8.3454
1.04 =1+ [4 % loss per hour]/100 , 3% etc. as per aircraft
earn or loss in tons = Store / (1.04 ↑ hrs) –Store / (Arr$/Dep$)
Fuel Price $ / ton = 26.42 * (c/Gal) / SG(lb /Gal) if(kg / L ) / 8.3454
1.04 =1+ [4 % loss per hour]/100 , 3% etc. as per aircraft
Last edited by Green Guard; 13th Mar 2012 at 16:33.
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Penalty for tankering
My recollection for the B747 Classic is that it cost 6% of tankered fuel per hour and it was not uncommon to carry fuel for up to three sectors, e.g. Hong Kong-Taipei - Taipei-Seoul - Seoul-Taipei.
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Penalty for tankering
I recall reading that it's 4%/kg/hr for moder twin turbo fans and 6% for multi-engine turbo fans of the 80s..perhaps a little higher for the turbo jets/low by-pass ratio turbofans/duct fans of the 70s and earlier.
I imagine prevailing fuel price is incorporated in the algorithm.Current fuel prices are on the high side...which disfavours tankering.Low fuel prices favour tankering.
Also availability of fuel or lack-there-of might influence the decision to tanker...tanker cost not withstanding!
I stand to be corrected.
I imagine prevailing fuel price is incorporated in the algorithm.Current fuel prices are on the high side...which disfavours tankering.Low fuel prices favour tankering.
Also availability of fuel or lack-there-of might influence the decision to tanker...tanker cost not withstanding!
I stand to be corrected.
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My believe is fuel tankering should be done only for operational reasons and not be driven by economic consideration.
One of those situation is positionning flights (no load).
Here you can uplift from the beginning the fuel for the 2 next flights (without having to call for fueller at the next station). You will in this case (if the fuel is cheaper at the first station) uplift much more than 1t.
The indicated information of gain or loss for 1 extra ton is then erroneous as you will extrapole from 1t to 5 or 6 or even more... but the gain is not linear...
Thanks for your contribution
Fin
One of those situation is positionning flights (no load).
Here you can uplift from the beginning the fuel for the 2 next flights (without having to call for fueller at the next station). You will in this case (if the fuel is cheaper at the first station) uplift much more than 1t.
The indicated information of gain or loss for 1 extra ton is then erroneous as you will extrapole from 1t to 5 or 6 or even more... but the gain is not linear...
Thanks for your contribution
Fin
Don't you contradict yourself on this one???
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It's moot. You guys don't know what the company is paying at point A and B, any more then you know what the overhaul cost is that forces you guys to run it to the end with de-rated power.
That said, if you want to have a conversation about flight planning, efficiencies, costs, etc, then you need to be able to pick optimal altitudes, power settings, routes etc..if you cant, or are not able, then taking on a few thousand pounds of fuel here or there, saving $20 on the contracted price at destination A or B is really just academic and has little real consequence to the overall flight operation.
That said, if you want to have a conversation about flight planning, efficiencies, costs, etc, then you need to be able to pick optimal altitudes, power settings, routes etc..if you cant, or are not able, then taking on a few thousand pounds of fuel here or there, saving $20 on the contracted price at destination A or B is really just academic and has little real consequence to the overall flight operation.