11 replies to this topic

[Chernobyl]

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.

[**OLT@22.Hrvatska**]

I've always liked the A340 for that reason. But I believe that the maintenance costs are considerably higher then the 777

[Superman]

Yeah data error...

[Nexus8]

Yeah data error...

Data error....I see...I didn't notice that one cause I got so stunned when I found out  A340sflying domestically.

[mxax-ai]

Actually the fuel flow is not per engine but per plane.
And those CFMs are more efficient than the Trents of you have to run them at full thrust all the time. Now, in real life the A340 will need about 75% of that and the 772 about 50%. Now multiply the TSFC with the actual needed thrust and you'll see quite different results.

[the DOC]

I would always have considered it impossible for the A340 to be more efficient but I can't work it out

[Yuxi]

And those CFMs are more efficient than the Trents of you have to run them at full thrust all the time. Now, in real life the A340 will need about 75% of that and the 772 about 50%. Now multiply the TSFC with the actual needed thrust and you'll see quite different results.

Yep, the issue here lies in the fuel flow calculations and not the data itself (I checked the max thrust, TSFC, etc and they are correct). We are looking at different options to get better fuel consumption numbers without fudging the raw data. Depending on how we bridge the gap, the solution may get backported to AE 3, and in that case we'll try not to affect existing worlds in progress.

[dzsoki]

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:

A340-200

engines: 4 x CFM56-5C2

thrust: 4 x 31200 lbs

TSFC: 0,32

Fuel flow: 4 x thrust x TFSC-> 39936

 

777-200ER

engines: 2 x Rolls-Royce Trent 877

thrust: 2 x 80720 lbs 

TSFC: 0,28

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)

-service ceiling

etc. etc.

 

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.

ETOPS certification

 

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,

- cruise, 

- descent,

[Chernobyl]

That still doesn't explain how the a340 uses less total fuel than the 777. It's common knowledge that the 777 is more fuel efficient and that is why the a340 isn't nearly as successful in terms of units sold.

[**OLT@22.Hrvatska**]

The game can not always be !00% accurate. Just go with it.

[X-Wing @Aliciousness]

That still doesn't explain how the a340 uses less total fuel than the 777. It's common knowledge that the 777 is more fuel efficient and that is why the a340 isn't nearly as successful in terms of units sold.

 

That explanation states exactly why the A340 uses less fuel than the 777 in game in a detailed, scientific manner. What more do you want?

 

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.

 

In this specific example you also need to keep in mind that the A340-200 is smaller than the 777-200. In fact, even though they have the same maximum capacity, the A340-300 is also slightly smaller than the 777 and is usually outfitted with less seats than a comparable T7 as a result.

[Mobeer]

That still doesn't explain how the a340 uses less total fuel than the 777. It's common knowledge that the 777 is more fuel efficient and that is why the a340 isn't nearly as successful in terms of units sold.

 

Short version is that the smaller difference between cruising and maximum thrust benefits the A340.