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keesje
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Costs of 1kg extra / year for NB, WB, on average.

Wed Oct 17, 2018 6:33 pm

Hi, does anybody have an indication on the costs per year of flying around 1kg extra?

Of course this would depend on e.g. flight hours, flights, operations, specific aircraft type and fuel prices.

Are there any rules of tumb airlines use making trade-off? E.g. when buying cheaper, but heavier interiors?
"Never mistake motion for action." Ernest Hemingway
 
kalvado
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Re: Costs of 1kg extra / year for NB, WB, on average.

Wed Oct 17, 2018 7:09 pm

I suspect there is no single answer. Biggest uncertainty would be if you need that extra last kg for other purposes. Can you sell it as cargo? Do you need last mile of range?
Otherwise, only extra expense I can think of is fuel. Extra brakes and engine wear are tricky for me..
Fuel:
For a 738, payload fuel chart shows 2000 mile flight needs 30 klb of fuel for 110klb ZFW, and 35 klb fuel for 140 klb ZFW - or about 1/6 of extra weight in fuel. Crude analysis from the graph, but maybe reasonable guestimate.
 
LH707330
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Re: Costs of 1kg extra / year for NB, WB, on average.

Wed Oct 17, 2018 9:36 pm

Horseshoes and hand grenades: $100-200 per kilo per annum, based on an A330 weighing 200t and burning 6t/hr. Assumptions and math below:

Item Value Unit
A330 weight 200 t
fuel burn 6 t/h
FB/t/hr 0.03 t/t/hr
Fuel price $1,000 $/t
Price/t/hr $30 $/hr
Daily utilization 13 hrs
Annual utilization 4745 hrs
Annual cost/t $142,350 $
Annual/kg $142.35 $
 
frmrCapCadet
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Re: Costs of 1kg extra / year for NB, WB, on average.

Thu Oct 18, 2018 2:10 pm

I suspect that the best metric to do this is 50KG for 1000 and 5000KM, and it would be interesting to know. Possibly a better weight could be 35 pound, the maximum in the US for a person to be lifting.
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WIederling
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Re: Costs of 1kg extra / year for NB, WB, on average.

Thu Oct 18, 2018 5:36 pm

frmrCapCadet wrote:
I suspect that the best metric to do this is 50KG for 1000 and 5000KM, and it would be interesting to know. Possibly a better weight could be 35 pound, the maximum in the US for a person to be lifting.


why 50kg when the question was 1kg?
( If you've got one number you've got any other small, relative weight too.)

set up the equation for fuel use as a function of payload or overall weight.
create the first derivative.
Murphy is an optimist
 
frmrCapCadet
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Re: Costs of 1kg extra / year for NB, WB, on average.

Thu Oct 18, 2018 7:35 pm

One pound packages are likely too small to overcome all of the variables in a typical plane. A friend tried to calculate how much it cost him to make one pancake at his restaurant. He could calculate how much it cost to sell breakfasts for the morning, but 999 pancakes or 1000 - no statistical difference possible to discern.
Buffet: the airline business...has eaten up capital...like..no other (business)
 
kalvado
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Re: Costs of 1kg extra / year for NB, WB, on average.

Thu Oct 18, 2018 9:53 pm

frmrCapCadet wrote:
One pound packages are likely too small to overcome all of the variables in a typical plane. A friend tried to calculate how much it cost him to make one pancake at his restaurant. He could calculate how much it cost to sell breakfasts for the morning, but 999 pancakes or 1000 - no statistical difference possible to discern.

Of course 1 kg will not be apparent.
But then you add another one and another one and another one.... and at some point you're suddenly over MTOW.
Normalizing things per unit weight is completely normal, as well as assigning error margin that is more than the single unit.
There is a company which offers 4 kg (9lb) titanium frame seats for 737 Y class - compared to 11 kg (25 lb) regular seat. Of course, the difference is way below spread in regular pax weight. But once you consider 150 seats in 737 make as much difference as 10-12 passengers... And you really need to do the math to see if lighter seat worth it, or cheaper (and heavier) one makes sense.
 
LH707330
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Re: Costs of 1kg extra / year for NB, WB, on average.

Thu Oct 18, 2018 10:51 pm

frmrCapCadet wrote:
One pound packages are likely too small to overcome all of the variables in a typical plane. A friend tried to calculate how much it cost him to make one pancake at his restaurant. He could calculate how much it cost to sell breakfasts for the morning, but 999 pancakes or 1000 - no statistical difference possible to discern.

Well with the flapjacks you have the fixed costs of running the joint, the variable costs of flipping the last flapjack, and the marginal cost of the batter. In the plane example, even if the percentages are small, the math is easy, here's the logic:

Weight=lift
Di=k*lift ceteris paribus
Di=35% of Drag in cruise
Thrust=drag in level flight
Fuel burn scales with thrust (linear scaling assumption is ok at these infinitesimal amounts)
Ergo Δ weight = ~.35 Δ fuel burn for small changes

So update to my math above, those numbers are 3x too high.

For the chairs example, take Δ weight per chair leg * chair legs for your total Δ weight, then perform that same operation to figure out if/when they'd pay for themselves. Obviously the airlines have more sophisticated ways of modeling that, with other assumptions baked in, like how much revenue they could get from additional payload due to the lower OEW, etc.
 
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Starlionblue
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Re: Costs of 1kg extra / year for NB, WB, on average.

Fri Oct 19, 2018 12:10 am

Length of sector makes a massive difference:
- A350 on a 12-hour sector. 1 extra ton of weight results in 250-280kg extra fuel burn.
- A350 on a 90-minute sector. 1 extra ton of weight results in 20-30kg extra fuel burn.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
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lightsaber
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Re: Costs of 1kg extra / year for NB, WB, on average.

Fri Oct 19, 2018 11:03 pm

Rule of thumb is $50/kg at today's oil per year.

But be careful, that is for adding 1kg that does nothing of benefit.

The A330NEO gain 6,000kg of more fuel efficient engines and wings. Airbus knows it will cost less to fly than the A330CEO.

The 777x adds 800kg for folding wingtips and tons for more fuel efficient engines.

Useful weight undergoes a trade study. For example, adding 3 inches (7.5 cm) of fan diameter adds 200 to 350kg to each engine. Doeing so increases the optimal mission length by an hour. Shorter missions add cost, longer missions are cheaper. This is part of the trade study. The A320NEO's optimal mission is 2 hours. The -8 max is closer to 75 minutes. Both can fly shorter or much longer missions.

But in simplicity, adding 1kg costs $50/yr. It is fuel, wear and tear (tires,brakes, engines not derated as much thus more wear, ATC fees, lost payload).

Lightsaber
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LH707330
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Re: Costs of 1kg extra / year for NB, WB, on average.

Sat Oct 20, 2018 4:05 pm

lightsaber wrote:
Rule of thumb is $50/kg at today's oil per year.

But be careful, that is for adding 1kg that does nothing of benefit.

The A330NEO gain 6,000kg of more fuel efficient engines and wings. Airbus knows it will cost less to fly than the A330CEO.

The 777x adds 800kg for folding wingtips and tons for more fuel efficient engines.

Useful weight undergoes a trade study. For example, adding 3 inches (7.5 cm) of fan diameter adds 200 to 350kg to each engine. Doeing so increases the optimal mission length by an hour. Shorter missions add cost, longer missions are cheaper. This is part of the trade study. The A320NEO's optimal mission is 2 hours. The -8 max is closer to 75 minutes. Both can fly shorter or much longer missions.

But in simplicity, adding 1kg costs $50/yr. It is fuel, wear and tear (tires,brakes, engines not derated as much thus more wear, ATC fees, lost payload).

Lightsaber


$50/year, thanks for confirming that. Now I can pat myself on the back for the revised 142.35*.35 coming out to $49.82 on the back of a napkin. My assumption all along with that was that it was just a kilo being taken out, obviously a kilo replaced by payload, or a kilo doing something useful, as in your examples, gets more complicated.
 
Winterapfel
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Re: Costs of 1kg extra / year for NB, WB, on average.

Sun Oct 21, 2018 2:04 pm

Interesting to add in this threat are the savings I'd shaving 28 grams if each in-flight magazine.

https://www.foxnews.com/travel/united-a ... -paper.amp
 
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Horstroad
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Re: Costs of 1kg extra / year for NB, WB, on average.

Mon Oct 22, 2018 3:11 am

A few years back Lufthansa had a weight savings program, where everything not necessarily needed was removed from the aircraft. On the cargo aircraft for example magazines, documents, coat hangers, polar survival kits, the life raft etc. were removed. Each kilo less would amount to fuel savings of about 3t per year. There's a video on YouTube "MD-11 Clear Out made by Rhein Main TV". It's in German though.
For the whole Lufthansa fleet, the savings were supposed to be €30.000 per year for each kilo that could be removed from the entire fleet.
 
WIederling
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Re: Costs of 1kg extra / year for NB, WB, on average.

Tue Oct 23, 2018 11:20 am

LH707330 wrote:
My assumption all along with that was that it was just a kilo being taken out, obviously a kilo replaced by payload, or a kilo doing something useful, as in your examples, gets more complicated.


The question was "cost of 1kg extra". i.e. the cost differential for 1kg.
Murphy is an optimist
 
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keesje
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Re: Costs of 1kg extra / year for NB, WB, on average.

Thu Nov 01, 2018 4:56 pm

Horstroad wrote:
A few years back Lufthansa had a weight savings program, where everything not necessarily needed was removed from the aircraft. On the cargo aircraft for example magazines, documents, coat hangers, polar survival kits, the life raft etc. were removed. Each kilo less would amount to fuel savings of about 3t per year. There's a video on YouTube "MD-11 Clear Out made by Rhein Main TV". It's in German though.
For the whole Lufthansa fleet, the savings were supposed to be €30.000 per year for each kilo that could be removed from the entire fleet.


Does LH have 30.000 / 50 = 600 aircraft than?

The $50 (for a NB I presume) per year is low. $2500 per kg on an aircraft life time.

:arrow: Out with the ultra light carbon seats, we can start using heavier but much cheaper metals !
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