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Author Topic: The fuel cost is way off... is it intended or a bug?  (Read 578 times)

Online tititaka

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The fuel cost is way off... is it intended or a bug?
« on: July 11, 2019, 05:30:00 AM »
I found the fuel consumption is way off according to my calculation. Is there anything I'm missing?

Taking this route as an example (EDDF-ZBAA) section:

Load is ~40 pax, way less than maximum of 88 pax. The fuel cost is ~$3380. The highest fuel cost is $63 in the last few weeks - no discount is applied as EDDF-ZBAA is inbound from foreign airport. This implies the segment consumes 53tonnes of fuels. The return trip is 14H38M roughly 14.5Hours. This comes down to 53000/14.5=3650kgs of fuels per hour. However my starliner's average burn is 2890kgs per hour. This is a difference of 30% extra fuel.

I understand the average burn is a thereotical value based on a number of assumptions but this 30% is hard to explain with fluctuation.

I have also calculated this on a few routes in ~2000-3000 routes but the difference is still more than 20%. Is this a bug or I have missed something in calculation?

Offline MikeS

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #1 on: July 11, 2019, 10:42:34 PM »
Hi,
We had this before. It is simply not possible to reverse calculate the figures, they will always be off by quite a bit. Just take the stated average figures as a guideline.
(unfortunately due to this, we cannot really find a bug when there might be one)

Cheers!
Mike

Online tititaka

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #2 on: July 11, 2019, 10:52:51 PM »
they would be off but not by 30%. i tried on gw4 and most of them are very very close. i guess there is unknown component of the airplane performance system in the work. Can Sami confirm?

Offline schro

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #3 on: July 11, 2019, 11:59:07 PM »
they would be off but not by 30%. i tried on gw4 and most of them are very very close. i guess there is unknown component of the airplane performance system in the work. Can Sami confirm?

Fuel burn is calculated based upon the fuel used in initial climb, cruise and descent. Each plane has different values for burn amount during each of those stages as well as how much flight time is needed to reach those stages. The fuel burn presented to us is simply an average of those amounts that is impossible for us to derive based upon a given flight profile.

What your findings tell me is that the Starliner is likely a very slow climber and burns a lot of fuel climbing to cruise levels before leveling off. This would explain the differences in average burn that you're seeing.

Another way you can test this is comparing the 727-200Adv and the A320-200 fuel burn. When you look at 300nm flights, they will have near identical fuel burn numbers, yet, on a 1600nm flight, the 727 will burn twice the fuel.....

Online tititaka

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #4 on: July 12, 2019, 03:44:01 AM »
Fuel burn is calculated based upon the fuel used in initial climb, cruise and descent. Each plane has different values for burn amount during each of those stages as well as how much flight time is needed to reach those stages. The fuel burn presented to us is simply an average of those amounts that is impossible for us to derive based upon a given flight profile.

What your findings tell me is that the Starliner is likely a very slow climber and burns a lot of fuel climbing to cruise levels before leveling off. This would explain the differences in average burn that you're seeing.

Another way you can test this is comparing the 727-200Adv and the A320-200 fuel burn. When you look at 300nm flights, they will have near identical fuel burn numbers, yet, on a 1600nm flight, the 727 will burn twice the fuel.....

I understand this is an estimation, and quote from the manual

Quote
The calculation of the displayed Average Fuel Burn reference value depends on the aircraft size class and each aircraft model in the same size class are directly comparable. The value is calculated by placing the aircraft into a flight of defined length (Size class Small: 200 NM, Medium 450 NM, Large 1000 NM, Very Large 4000 NM) with zero wind and approximately 80% loaded aircraft. The system then calculates the entire flight's fuel usage and flight duration, and dividing these two will give the average hourly fuel burn. The true and actual fuel burn depend on the aircraft, route, winds, weight and other factors and is always unique for each route and aircraft combination.

The starliners are large planes therefore the fuel displayed is probably for routes with 1000nm. Assuming the same climbing time for 1000nm and 4000nm, that leaves 4000nm routes significant longer cruising time, which theoritically should make the average consumption less not more. Unless 4000nm route meaning significantly longer climbing phase

Offline groundbum2

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #5 on: July 12, 2019, 06:41:54 AM »
are the new winds aloft in GW2? That would affect the numbers with headwinds and tailwinds etc..

I had a KLAX-LTAC route, the shortest route was a tech stop in EKCH. But some reason I looked at EINN which was way out the way and the flight was an hour less going there, even though it was 300nm further, and there was a huge tailwind to EINN and a headwind to EKCH. Weird!

Simon
« Last Edit: July 12, 2019, 06:30:08 PM by groundbum2 »

Offline Talentz

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #6 on: July 12, 2019, 08:37:15 AM »
Hmm.. new winds yes. But I think tititaka's concerns come from the new weight-fuel calculations. While they effect Jets more then Props, there is still an effect on Props.

The further you fly, the more fuel you need and thus the weight increases, causing a higher burn. This we know in RL, but starting with GW2, its more effective (for lack of a better term). Since your flying at the edge of your range, trading payload for a ton of fuel, your burn rate is higher then "avg" sector length displayed. This is what's causing the numbers to look off vs your typical mission figures.

Basically, flying at the edge of your aircraft's range (or beyond) will cost you alot and will make routes less economical viable moving forward.


BTW, I see this to a degree with my airline and the DC10. On a 2300nm route the -10 burns about 41k avg/Wk. However, on a 3300nm route, the -10 burns upwards of 70k fuel/Wk. Huge increase just for 1000nm more. Why? Cause on a 2300nm, the aircraft's overall mission weight is low compared to flying 33000nm where it needs MTOW with less then typical payload for more fuel. Alot of fuel to burn....


Still cheaper then a 707 though... lol. Least, for this GW2. Those GW1 numbers are crazy low I tell you...


Talentz
Co-founder and Managing member of: The Star Alliance Groupô - A beta era, multi-brand alliance.

Offline dandan

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #7 on: July 12, 2019, 09:58:00 AM »
BTW, I see this to a degree with my airline and the DC10. On a 2300nm route the -10 burns about 41k avg/Wk. However, on a 3300nm route, the -10 burns upwards of 70k fuel/Wk. Huge increase just for 1000nm more. Why? Cause on a 2300nm, the aircraft's overall mission weight is low compared to flying 33000nm where it needs MTOW with less then typical payload for more fuel. Alot of fuel to burn....

if thats the case, we certainly need more information on aircrafts v2 data. what use is there in a complex system to determine fuel usage if all we know about it is one value called "average fuel costs".

Online tititaka

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #8 on: July 12, 2019, 01:08:11 PM »
Hmm.. new winds yes. But I think tititaka's concerns come from the new weight-fuel calculations. While they effect Jets more then Props, there is still an effect on Props.

The further you fly, the more fuel you need and thus the weight increases, causing a higher burn. This we know in RL, but starting with GW2, its more effective (for lack of a better term). Since your flying at the edge of your range, trading payload for a ton of fuel, your burn rate is higher then "avg" sector length displayed. This is what's causing the numbers to look off vs your typical mission figures.

Basically, flying at the edge of your aircraft's range (or beyond) will cost you alot and will make routes less economical viable moving forward.


BTW, I see this to a degree with my airline and the DC10. On a 2300nm route the -10 burns about 41k avg/Wk. However, on a 3300nm route, the -10 burns upwards of 70k fuel/Wk. Huge increase just for 1000nm more. Why? Cause on a 2300nm, the aircraft's overall mission weight is low compared to flying 33000nm where it needs MTOW with less then typical payload for more fuel. Alot of fuel to burn....


Still cheaper then a 707 though... lol. Least, for this GW2. Those GW1 numbers are crazy low I tell you...


Talentz

if this is the case, then the range is more important than ever as it does not only affect where you can reach but how economical it is as well. a 20-30% increase on fuel when flying at 6000nms meaning a330/340 may be more economical than 762er

Offline MikeS

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #9 on: July 12, 2019, 04:22:53 PM »
Hmm.. new winds yes. But I think tititaka's concerns come from the new weight-fuel calculations. While they effect Jets more then Props, there is still an effect on Props.

The further you fly, the more fuel you need and thus the weight increases, causing a higher burn. This we know in RL, but starting with GW2, its more effective (for lack of a better term). Since your flying at the edge of your range, trading payload for a ton of fuel, your burn rate is higher then "avg" sector length displayed. This is what's causing the numbers to look off vs your typical mission figures.

Basically, flying at the edge of your aircraft's range (or beyond) will cost you alot and will make routes less economical viable moving forward.


BTW, I see this to a degree with my airline and the DC10. On a 2300nm route the -10 burns about 41k avg/Wk. However, on a 3300nm route, the -10 burns upwards of 70k fuel/Wk. Huge increase just for 1000nm more. Why? Cause on a 2300nm, the aircraft's overall mission weight is low compared to flying 33000nm where it needs MTOW with less then typical payload for more fuel. Alot of fuel to burn....


Still cheaper then a 707 though... lol. Least, for this GW2. Those GW1 numbers are crazy low I tell you...


Talentz

I wasn't aware AWS did such complex fuel burn calculations. Makes it all the more interesting.
I remember IRL how airlines were asking Boeing for a little more range from the 757 but it appeared any attempt to add more fuel to the aircraft would have resulted in such an increase in fuel burn during the trip (due to higher weight) that it was not worth it. You have to "carry" that extra fuel to the edge of the aircraft's performance before you can actually start burning it..... I wonder how Airbus keeps getting more range out of it's A321 neos

Mike

Offline Tauge

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #10 on: July 12, 2019, 05:02:05 PM »
It's been 30 years since the introduction of the A320. Engines are more efficient, wings are more efficient, winglets are more efficient. I wouldn't be surprised to learn that there were other ways they've reduced drag on the airframe.

Offline Talentz

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #11 on: July 12, 2019, 06:39:07 PM »
if thats the case, we certainly need more information on aircrafts v2 data. what use is there in a complex system to determine fuel usage if all we know about it is one value called "average fuel costs".

True Dan. The v2 data likely refers to updating existing performance data (ala 707/DC8/CV880/990 in GW1). Since now the calculations for fuel usage differ based off length of mission, those figures become more relevant(?). But how to present this data without confusing or overwhelming the player... Well actually, Sami is already working on it right? (https://www.airwaysim.com/forum/index.php/topic,58864.msg480609.html#msg480609).

So in the future, we won't be completely in the dark...

if this is the case, ...

Yes indeed. Were still learning how these changes effect our understood aircraft choices from prior GWs and years. Does the new calculations really change the dynamics of these old school battles? Choosing the aircraft that for years, was understood as being the "better" choice... is it really the better choice now?

Case in point: A333 vs 772(non-ER) - For 10+ years, the AWS community says A333 is the better LH aircraft. With Cargo added, the 772 gets some merit, but still under most missions, the A333 is better. Now with the new wind/fuel Cals, @ 5200nm... is the A333 still, hands down better over the 772? A333 starts running into payload restrictions before the 772...

This and other aircraft comparisons come into question. It's still to early to say for sure, but I think our 10 year understanding of AWS is going to need a 2019 update.


Talentz
Co-founder and Managing member of: The Star Alliance Groupô - A beta era, multi-brand alliance.

Offline groundbum2

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #12 on: July 12, 2019, 07:28:35 PM »
the Britannia used to be a 707/DC8 killer now.... makes nice tin cans  :,( :,( :,( :,( due new winds aloft and 30% reduction in fuel for the big American boys

S

Offline MikeS

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #13 on: July 12, 2019, 10:00:29 PM »
It's been 30 years since the introduction of the A320. Engines are more efficient, wings are more efficient, winglets are more efficient. I wouldn't be surprised to learn that there were other ways they've reduced drag on the airframe.
Yup, especially the new engines, but the wing, I'm surprised they could get that much performance out of it. It seems quite small for the A321XLR now that it flies double the range of the original A321-100.

Offline spiff23

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #14 on: July 14, 2019, 02:58:23 PM »
if thats the case, we certainly need more information on aircrafts v2 data. what use is there in a complex system to determine fuel usage if all we know about it is one value called "average fuel costs".
This seems like a lot of analyzing when it's pretty simple in real life.  The father you fly theplane, the more fuel you need with a significant proportion of that fuel used just to get the plane off the ground. A 747-8 on PEK-SHA literally rockets off the ground without using much runway or fuel vs the same plane used on a flight to the US where it's rolling down a good portion of the runway and then slowly climbing as it's burning massive amounts of fuel to get just to cruising altitude.

Not sure if true or not but a pilot told me a TPAC 747 burns 1/2 it's fuel by the time the plane is 1/3 of the way and then as the weight becomes less the fuel burn become more optimized and hence the reason the plane doesn't run out of fuel by the time it is 2/3 of the way there.  IM sure the real algorithm is more complex, but something like that is probably a good rule of thumb.

Offline gazzz0x2z

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Re: The fuel cost is way off... is it intended or a bug?
« Reply #15 on: July 14, 2019, 06:29:36 PM »
A few years ago, before the ticket prices(cargo and pax) & winds overhauls, I did use A148Es in big numbers. Their range limit is around 2100NM; Already in those times, they were very juicy on 1800NM routes, and not at all on 2100NM routes. Because taking off with max fuel is punitive for this plane.

 

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