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majano
Posts: 183
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Re: 787 vs A350 range

Sun Sep 29, 2019 9:08 pm

Vladex wrote:
AECM wrote:
Eyad89 wrote:

And as he said, 6.2 tons is the fuel consumption of the full one hour flight, including take off, climb and cruise.
According to FR24 the recorded data from this "flight" starts at 13:31 UTC and goes until 15:00 UTC. If we account that the total fuel consumption from engine start to engine shutdow was 6,2 tons and that the engines were running for arround 1h30 the average fuel burn per hour is ~ 4,14 ton.


That would be world record and would allow it to fly more than 20 hours but he said before the takeoff that 1 hour burns 6.2 tonnes not the flight itself which is higher than reported here. However the flight was almost full of employees, no children

I am not sure what to make of this. Firstly you claimed that there were "about 250 persons onboard", yet the video states from 13:43 that "... every seat is filled" . The aircraft itself seats 324 passengers. Now you claim that "he said before the takeoff that 1 hour burns 6.2 tons, not the flight itself. The captain states from 7:32 of the video that"...it will take us one hour to reach Paris, with a fuel consumption of 6.2 tons of petrol, which is very low..... "

Please understand that I am not trying to defend the 4.14 calculation you are questioning. Just curious about the claims you made.
 
Vladex
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Re: 787 vs A350 range

Mon Sep 30, 2019 12:16 am

majano wrote:
Vladex wrote:
AECM wrote:
According to FR24 the recorded data from this "flight" starts at 13:31 UTC and goes until 15:00 UTC. If we account that the total fuel consumption from engine start to engine shutdow was 6,2 tons and that the engines were running for arround 1h30 the average fuel burn per hour is ~ 4,14 ton.


That would be world record and would allow it to fly more than 20 hours but he said before the takeoff that 1 hour burns 6.2 tonnes not the flight itself which is higher than reported here. However the flight was almost full of employees, no children

I am not sure what to make of this. Firstly you claimed that there were "about 250 persons onboard", yet the video states from 13:43 that "... every seat is filled" . The aircraft itself seats 324 passengers. Now you claim that "he said before the takeoff that 1 hour burns 6.2 tons, not the flight itself. The captain states from 7:32 of the video that"...it will take us one hour to reach Paris, with a fuel consumption of 6.2 tons of petrol, which is very low..... "

Please understand that I am not trying to defend the 4.14 calculation you are questioning. Just curious about the claims you made.


I think I heard earlier in the video that it was 250 passengers but it looks more than 300 . So considering it was almost full occupancy and a takeoff and climb , it makes sense that the fuel burn was little more than usual as stated here.
 
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Stitch
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Re: 787 vs A350 range

Mon Sep 30, 2019 1:33 pm

Even with 300+ passengers, for a block time of under two hours the plane would have been going out at her Basic Weight plus ~30,000kg of payload (passengers only, likely, so no cargo) and fuel (combined). So I could very well see such a "low" trip fuel value.
 
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zeke
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Re: 787 vs A350 range

Tue Oct 01, 2019 1:54 am

majano wrote:
I am not sure what to make of this. Firstly you claimed that there were "about 250 persons onboard", yet the video states from 13:43 that "... every seat is filled" . The aircraft itself seats 324 passengers. Now you claim that "he said before the takeoff that 1 hour burns 6.2 tons, not the flight itself. The captain states from 7:32 of the video that"...it will take us one hour to reach Paris, with a fuel consumption of 6.2 tons of petrol, which is very low..... "

Please understand that I am not trying to defend the 4.14 calculation you are questioning. Just curious about the claims you made.


The 6.2 tonne number makes sense.

I ran a plan from TLS to CDG at FL350 with ORY as an alternate. Routing LFBO14R FISTO5R FISTO UY156 FOUCO UT181 POI UT182 KEPER KEPER7W LFPG27L which is a ground distance of 413 nm, ISA deviation is +5, planned flight time 1:06.

The 6.2 tonnes makes total sense, 500 kg would be for taxi before departure, 3.3 tonnes to climb to FL350, 1.5 tonnes for cruise, and 900 kg for descent and landing.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
majano
Posts: 183
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Re: 787 vs A350 range

Tue Oct 01, 2019 2:40 pm

zeke wrote:
majano wrote:
I am not sure what to make of this. Firstly you claimed that there were "about 250 persons onboard", yet the video states from 13:43 that "... every seat is filled" . The aircraft itself seats 324 passengers. Now you claim that "he said before the takeoff that 1 hour burns 6.2 tons, not the flight itself. The captain states from 7:32 of the video that"...it will take us one hour to reach Paris, with a fuel consumption of 6.2 tons of petrol, which is very low..... "

Please understand that I am not trying to defend the 4.14 calculation you are questioning. Just curious about the claims you made.


The 6.2 tonne number makes sense.

I ran a plan from TLS to CDG at FL350 with ORY as an alternate. Routing LFBO14R FISTO5R FISTO UY156 FOUCO UT181 POI UT182 KEPER KEPER7W LFPG27L which is a ground distance of 413 nm, ISA deviation is +5, planned flight time 1:06.

The 6.2 tonnes makes total sense, 500 kg would be for taxi before departure, 3.3 tonnes to climb to FL350, 1.5 tonnes for cruise, and 900 kg for descent and landing.

Thanks. Because of the short flight duration, every kilogram makes a difference. If the discussion was an 18 hour flight, the 500 kg required for taxiing would not matter, but it matters greatly in this context.
 
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Starlionblue
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Re: 787 vs A350 range

Wed Oct 02, 2019 4:46 am

Eyad89 wrote:
Vladex wrote:
According to the capetan, Air France A350-900 delivery flight with about 250 people on board burns 6.2 tonnes for one hour .
https://youtu.be/DqmViXCyVKA?t=433


And as he said, 6.2 tons is the fuel consumption of the full one hour flight, including take off, climb and cruise.


Don't forget taxi fuel, which could be half a ton.
"There are no stupid questions, but there are a lot of inquisitive idiots." - John Ringo
 
WIederling
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Re: 787 vs A350 range

Wed Oct 02, 2019 7:40 am

Starlionblue wrote:
Don't forget taxi fuel, which could be half a ton.

To quote
zeke wrote:
I ran a plan from TLS to CDG at FL350 with ORY as an alternate. Routing LFBO14R FISTO5R FISTO UY156 FOUCO UT181 POI UT182 KEPER KEPER7W LFPG27L which is a ground distance of 413 nm, ISA deviation is +5, planned flight time 1:06.

The 6.2 tonnes makes total sense,
. 500 kg would be for taxi before departure,
3,300 kg tonnes to climb to FL350,
1,500 kg tonnes for cruise, and
. 900 kg for descent and landing.


:-)
Murphy is an optimist
 
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lightsaber
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Re: 787 vs A350 range

Sat Nov 02, 2019 4:04 pm

IgorD wrote:
Thomas, I appreciate your critique! But let me explain some things where we differ.

First, FCOM is an official document. It provides datapoints on fuel burn at certain weights and altitudes. When I put these datapoints into a regression, it looks like x = ab + c, where x is fuel burn, a is a coefficient, b is weight and c is a constant. What I found is that a is around 1/38 and c can be set to 0 without a substantial increase in inaccuracy. The model gives R2 in excess of 0,99. In other words, there is a constant fuel burn to weight ratio, which is logical, given that L/D should be more or less constant for the optimal altitude and constant speed. I sufficiently trust these data: the hard work has been done by Boeing in providing the data points, my job was just to find a linear law behind them.

With Airbus it is more tricky, as I don't have access to a nice FCOM with data points. Those I collected from photos. I agree that these data are messier, where speed and temperature play a role (speed can be corrected, as 10 degrees above / below ISA lead to 3% extra or 3% less fuel burn respectively). But again, if one plots the data, there could found an simple law behind them. The deviation from the average of 1/38 to 1/39 is around 2,5%, not 5%, which is the difference between the extremes. I think the difference between specific airframes and engines within the same type can be even larger. This data driven approach is alternative to the engineering one you propose -- and of course I am interested in feedback on it, as my interest is in model validation and not in a discussion on which type is better (I know they are more or less equal, otherwise the market would kill one program over another :)) By the way, both 77W and A346 burn the same for a given weight, circa 1/35 per hour. We know why 77W won -- it is lighter and has some more capacity (deck floor space).

Concerning the argument on a larger wing of A350, I am considering that it is heavier and has more wetted area. So the overall impact on the fuel burn in less clear cut, otherwise the industry would go to the designs with very long wings, which has not happened yet (yes I am aware about gate space issue too :)).

Wings are always optimized for a mission shorter than average. Optimizing for long missions does more to dame short range economics as the climb penalty is huge. Only at cruise does one benefit.

The worst penalty is weight, that is why material changes are key. But with newer underside laminar flow, longer wingspans will happen.

There is a huge gate space cost for wingspan. Folding wingtips mitigate that cost. I could see a new A350 with folding wingtips.

Lightsaber
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Sokes
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Re: 787 vs A350 range

Wed Nov 06, 2019 5:54 am

lightsaber wrote:

Wings are always optimized for a mission shorter than average. Optimizing for long missions does more to dame short range economics as the climb penalty is huge. Only at cruise does one benefit.
Lightsaber



Interesting. I always assumed longer is better beside really short flights. I guess that was my thought: Longer wings enable a plane for a given weight to fly slower. Turboprops are really light, but wingspan is not so little. So even if there is a climb penalty for 20 min, doesn't the rest of the flight compensate for this?
And doesn't the extra lift along the wing during climb help to "lift" the plane?
And why would the A330 NEO add wingspan? It's meant for medium range.

lightsaber wrote:

There is a huge gate space cost for wingspan. Folding wingtips mitigate that cost. I could see a new A350 with folding wingtips.
Lightsaber



We had this discussion earlier with narrowbodies.

7 m/ 64.8 m = 0,108. So the folding mechanism increases the span by 11%.
1.11 * 1.11 = 1.2321. Lift increases roughly 23%.
I thought folding wingtips are too complicated. But one really needs only a "tiny" extension for a lot more lift.
Maybe I should submit to your judgement.
I guess it's not yet out in the open how much extra weight the folding mechanism adds?

https://www.boeing.com/777x/reveal/vide ... g-Wingtip/
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xwb565
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Re: 787 vs A350 range

Wed Nov 27, 2019 11:20 am

slide 40- SQ stating that the 787-10 has 26 % better fuel productivity vs a333 on medium haul and the a350 has 29% better fuel productivity vs the 772 on long haul.

https://www.singaporeair.com/saar5/pdf/ ... fy1920.pdf
 
majano
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Re: 787 vs A350 range

Fri Nov 29, 2019 3:26 pm

xwb565 wrote:
slide 40- SQ stating that the 787-10 has 26 % better fuel productivity vs a333 on medium haul and the a350 has 29% better fuel productivity vs the 772 on long haul.

https://www.singaporeair.com/saar5/pdf/ ... fy1920.pdf

Do you happen to know what the LTK / AG is? Or anyone else for that matter?
 
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zeke
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Re: 787 vs A350 range

Fri Nov 29, 2019 4:51 pm

majano wrote:
Do you happen to know what the LTK / AG is? Or anyone else for that matter?


I posted this on another thread recently as people keep repeating the same junk without knowing what it means

viewtopic.php?t=1435781&p=21822077

“ Garbage in = garbage out. Those figures are based upon a little used LTG/AG basis.

They A333 is 285 seats, 78J 337 seats, 772 266 seats, and 359 medium haul 303 seats.

The Load Tonnes Kilometre (LTK) as computed as a product of network distance (based on Great Circle Distance) and payload, we don’t know what routes they are basing the figures over for each fleet. The seat disparity between types obviously makes up for a lot of the difference. Cargo payload is weighed, hence the weight is known. Passenger weight is the product of passenger numbers and nominal weight, for different classes (J,Y), they have different ratios between types. The American Gallon of fuel (AG) is obtained from fuel receipt as signed by Flight Crew, which is highly dependent of the routes being served.”
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
majano
Posts: 183
Joined: Sun Oct 14, 2018 10:45 am

Re: 787 vs A350 range

Fri Nov 29, 2019 6:07 pm

zeke wrote:
majano wrote:
Do you happen to know what the LTK / AG is? Or anyone else for that matter?


I posted this on another thread recently as people keep repeating the same junk without knowing what it means

viewtopic.php?t=1435781&p=21822077

“ Garbage in = garbage out. Those figures are based upon a little used LTG/AG basis.

They A333 is 285 seats, 78J 337 seats, 772 266 seats, and 359 medium haul 303 seats.

The Load Tonnes Kilometre (LTK) as computed as a product of network distance (based on Great Circle Distance) and payload, we don’t know what routes they are basing the figures over for each fleet. The seat disparity between types obviously makes up for a lot of the difference. Cargo payload is weighed, hence the weight is known. Passenger weight is the product of passenger numbers and nominal weight, for different classes (J,Y), they have different ratios between types. The American Gallon of fuel (AG) is obtained from fuel receipt as signed by Flight Crew, which is highly dependent of the routes being served.”

Thank you very much.
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