So I'm looking at my OKA-IAH route, where I have a340-200 and 777-200er flying.
A340-200 has 4 engines, each with a fuel flow of 39,936, and the per-flight fuel cost is $283,404
777-200er has 2 engines, each with a fuel flow of 45,203, and the per-flight fuel cost is $325,084
How in the world is the a340 cheaper? By my estimation it should use almost twice as much fuel, especially considering it travels slower than the 777.
This is also a good example that these raw engine datas are misleading to calculate the actual fuel consumption of an aircraft.
Here are the raw datas:
engines: 4 x CFM56-5C2
thrust: 4 x 31200 lbs
Fuel flow: 4 x thrust x TFSC-> 39936
engines: 2 x Rolls-Royce Trent 877
thrust: 2 x 80720 lbs
Fuel flow: 2 x thrust x TSFC-> 45203
As you can see Fuel Flow Rate calculated from the efficiency and the maximum thrust of the engines.
But in the real world this maximum performance won't be used even in take off, climb out conditions the engines will operate at a much lower thrust. During the majority of the flight time, the engines will operate in cruise mode.
This cruise mode is used for 80-90% of a flight, and this depends on much more parameters, than the above mentioned raw engine datas:
-aerodinamics of the aircraft (wingspan, design, engine cross section, winglets)
-weight of the aircraft (passengers, baggage, cargo, aircrafts own weight, fuel and reserves, engine weight)
-engine parameters (cruise SFC)
In this example, these aircrafts required to handle the fault of an engine at take off. This is why the two engine equipped Boeing required to use a much higher maximum thrust engine vs. the four engine equipped Airbus. Also all two engine equipped aircraft has a certification, which determines how long it can fly with one engine. When you assign a route to a two engine aircraft you have to calculate with this one engine max. operation time, to always have a diversion airfield within that one engine operation range.
In real world normal operating conditions Boeing 777-200ER's huge 160000lbs thrust won't be used (this is a built in spare performance for take off and ETOPS), and this misleads the fuel calculations here. In this metrics the four engine aircraft have better raw engine data.
Actually the Boeing 777-200ER has a better fuel consumption here, but the A340-200 also good.
You can compare the datas here with a 6000nm example: http://theaviationsp...ion_dataset.gif
(burn off fuel, passenger only)
Also to give an example about the cruise fuel consumption you can check this picture:
This is an actual fuel flow measurement during a flight of a Fokker F100 aircraft where both engines measured separately (blue/red dots). The fuel consumption measured in KG/hours (1kg/hour means 2,2 pounds/hour)
You can clearly see the three main stages of the flight:
- take off / climb out,