ultrapig
Topic Author
Posts: 566
Joined: Fri Dec 12, 2003 11:38 pm

Additional Fuel Brun Per Additional Weight

Thu Oct 13, 2011 7:37 pm

Its pretty obvious to us novice airline users that an airplane has a maximum takeoff weight which is the total of the empty plane, plus fuel plus cargo plus passengers (okay I missed something). Thus I understand that a plane packed with passengers and cargo might not be able to fill its tanks with fuel and might not be able to travel for as many hours as the same plane with no passengers. That seems to be a pretty simple calculation.

But lets take a regular mainline plane like a 737. Say its half full of passengers and cargo and its going 1k miles. Can the airline calculate the additional fuel it would take if the plane was two tons heavier-or is it like my car-I know that it probably uses more fuel when I have five passengers and the trunk full but its virtually impossible to tell.

I ask this because of all of the whining about baggage charges. Obviously there is labor cost in loading an processing bags but is the system sophisticated enough to calculate the extra fuel cost of flying x pounds of cargo y miles.

If there is such a formula what would it cost in fuel to fly on 40 pound bad on a 2400. mile flight? and how does it compare to the charge for taking a bag?
 
OldAeroGuy
Posts: 3183
Joined: Sun Dec 05, 2004 6:50 am

RE: Additional Fuel Brun Per Additional Weight

Thu Oct 13, 2011 7:55 pm

Quoting ultrapig (Thread starter):
If there is such a formula what would it cost in fuel to fly on 40 pound bad on a 2400. mile flight? and how does it compare to the charge for taking a bag?

Yes, it's easy for the airlines to calculate the additional fuel burn for carrying the weight of a bag on a flight of any length.

However, this has nothing to do with checked baggage fees. A bag of a given weight increases burn by the same amount if it's unchecked (in an overhead bin) or checked (in a cargo hold).

The bag fee offsets the costs of handling a checked bag and provides the airline with another source of revenue.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
kalvado
Posts: 476
Joined: Wed Mar 01, 2006 4:29 am

RE: Additional Fuel Brun Per Additional Weight

Thu Oct 13, 2011 10:48 pm

I asked more or less similar question to myself a few times. Maybe I'm completely wrong here, and any corrections are more than welcome - however here is my uneducated understanding:
let's look at Boeing performance charts, http://www.boeing.com/commercial/airports/acaps/737sec3.pdf
For the sake of certainty, I'll be talking about chart 3.2.10, (p.12 pdf document) chart for 737-700.

for a 1000 mile trip,
OEW+ payload=90k lb correspond to brakes release weight of just over 105 k lb ( ~15k lb fuel), and
OEW+ payload~112.5k lb correspond to brakes release weight of about 130 k lb ( ~17.5k lb fuel)

Sounds to me as if extra 22.5 k lb of payload result in 2.5 k lb extra fuel burn, or 1 lb of fuel for 9 lb extra weight.
(for a 777 on a 5000 mile mission, looks like it's 0.4 lb fuel per extra pound of weight, calculated same way)

conversion factors are: 6.79 lb/gallon of Jet-A and $5.5/gallon of Jet-A at local airport
With those, extra 40 lb bag comes to extra $3.60 in fuel; (and extra 200 lb person on board - $18)

Disclaimers:
As mentioned before, this is just extra fuel - bag handling, customer service etc. are extra.
Apparently, flying empty plane also incurs fuel costs; I'm not talking about fair allocation of that cost on per- ticket or per-pound basis, that is completely different story. This is about incremental fuel burn only.

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