According to Boeing and Airbus websites, the A350 has more range than the 787. 787-9 has a range of 14,100km while the A350-900 has 15,000km and the A350-1000 has a range of 15,557km. So why is it that the 787 is praised as a game changing aircraft that opens up the ability for ultra long routes (such as Perth to London) when the A350 has more range and can carry more passengers?

And to be clear, I'm not trying to start an Airbus vs Boeing war. I like both aircraft.

NYPECO wrote:

According to Boeing and Airbus websites, the A350 has more range than the 787. 787-9 has a range of 14,100km while the A350-900 has 15,000km and the A350-1000 has a range of 15,557km. So why is it that the 787 is praised as a game changing aircraft that opens up the ability for ultra long routes (such as Perth to London) when the A350 has more range and can carry more passengers?

And to be clear, I'm not trying to start an Airbus vs Boeing war. I like both aircraft.

Perhaps partly because the first 787 delivery was in 2011. And the first 350 delivery was in 2014.

cerealspiller wrote:

NYPECO wrote:

According to Boeing and Airbus websites, the A350 has more range than the 787. 787-9 has a range of 14,100km while the A350-900 has 15,000km and the A350-1000 has a range of 15,557km. So why is it that the 787 is praised as a game changing aircraft that opens up the ability for ultra long routes (such as Perth to London) when the A350 has more range and can carry more passengers?

And to be clear, I'm not trying to start an Airbus vs Boeing war. I like both aircraft.

Perhaps partly because the first 787 delivery was in 2011. And the first 350 delivery was in 2014.

Both are game changing. All other widebodies are now obsolete.

The 787 has a lower cost per flight. It has less capacity. What do you want to pay for? The A350 is more optimized for longer flights and short field performance.

If someone would post the payload/range charts, it would generate better discussion.

Lightsaber

The efficiency of the 787 is what made it a game changer on longhaul routes. I've seen a payload/range chart somewhere that has a 342, 343, 77E, 77L, 345, 789, and 359 on it, looking at that you wouldn't think either the 789 or 359 is particularly remarkable. What makes them interesting, though, is that they move the "tankering wall" (my term for the range at which the cost of tankering fuel on ULH hockey sticks and the flight becomes unprofitable so airlines don't do it) out by a sizable chunk. Look at the real-world max flight times (excluding the few weird exceptions) for the planes below, and you'll see why the 789 is a game changer:

707-300B: 11 hours
742: 12-13 hours (not counting 741 because it was engine-constrained)
74SP: 14 hours (sales flop)
744/343/77E: 14 hours
A345/77L: 16-18 hours (sales flop)
789/359: 15-16 hours

Overall efficiency is the only way the wall moves out. Almost all cases where OEMs tried to brute-force their way to ULH flopped because they were too heavy and their CASM was awful. Examples include the 747SP, A342 (lunch eaten by 343 MTOW boost within 3 years), 345, and 77L.

LH707330 wrote:

789/359: 15-16 hours

That does not reflect their relative performance. At the longer ranges the Airbus, more optimized for long flights, carries a lot more payload. Where the A359 stops being useful, the 789 carries about half its payload.

Best regards
Thomas

lightsaber wrote:

If someone would post the payload/range charts, it would generate better discussion.

That will not help on the A350 as the payload range chart published are for WV000.

LH707330 wrote:

The efficiency of the 787 is what made it a game changer on longhaul routes. I've seen a payload/range chart somewhere that has a 342, 343, 77E, 77L, 345, 789, and 359 on it, looking at that you wouldn't think either the 789 or 359 is particularly remarkable. What makes them interesting, though, is that they move the "tankering wall" (my term for the range at which the cost of tankering fuel on ULH hockey sticks and the flight becomes unprofitable so airlines don't do it) out by a sizable chunk. Look at the real-world max flight times (excluding the few weird exceptions) for the planes below, and you'll see why the 789 is a game changer:

707-300B: 11 hours
742: 12-13 hours (not counting 741 because it was engine-constrained)
74SP: 14 hours (sales flop)
744/343/77E: 14 hours
A345/77L: 16-18 hours (sales flop)
789/359: 15-16 hours

Overall efficiency is the only way the wall moves out. Almost all cases where OEMs tried to brute-force their way to ULH flopped because they were too heavy and their CASM was awful. Examples include the 747SP, A342 (lunch eaten by 343 MTOW boost within 3 years), 345, and 77L.

I question this chart. I do not think the 707 in any form was ever used for 11 hour flights. And I have flown a 77W between JFK and TPE or HKG, both of which are very close to 16 hours.

SEPilot wrote:

LH707330 wrote:

The efficiency of the 787 is what made it a game changer on longhaul routes. I've seen a payload/range chart somewhere that has a 342, 343, 77E, 77L, 345, 789, and 359 on it, looking at that you wouldn't think either the 789 or 359 is particularly remarkable. What makes them interesting, though, is that they move the "tankering wall" (my term for the range at which the cost of tankering fuel on ULH hockey sticks and the flight becomes unprofitable so airlines don't do it) out by a sizable chunk. Look at the real-world max flight times (excluding the few weird exceptions) for the planes below, and you'll see why the 789 is a game changer:

707-300B: 11 hours
742: 12-13 hours (not counting 741 because it was engine-constrained)
74SP: 14 hours (sales flop)
744/343/77E: 14 hours
A345/77L: 16-18 hours (sales flop)
789/359: 15-16 hours

Overall efficiency is the only way the wall moves out. Almost all cases where OEMs tried to brute-force their way to ULH flopped because they were too heavy and their CASM was awful. Examples include the 747SP, A342 (lunch eaten by 343 MTOW boost within 3 years), 345, and 77L.

I question this chart. I do not think the 707 in any form was ever used for 11 hour flights. And I have flown a 77W between JFK and TPE or HKG, both of which are very close to 16 hours.

Thanks for pointing out the omission, I missed the 77W, that one deserves to be on the list. It would probably go in as a 14-15 hour plane by that list. Again, not looking at the longest ever routes, but the ones that were commonly flown with economic payloads. Regarding the 707s, there's ample evidence of them doing 11-12 hour flights, like Europe-West Coast:

viewtopic.php?t=528161
viewtopic.php?t=686457

tommy1808 wrote:

LH707330 wrote:

789/359: 15-16 hours

That does not reflect their relative performance. At the longer ranges the Airbus, more optimized for long flights, carries a lot more payload. Where the A359 stops being useful, the 789 carries about half its payload.

Best regards
Thomas

I'm not talking about the no-longer-useful range, I'm talking about the realistic ranges for pax+bags and maybe a few t of cargo. When you look at their spec pax+bags ranges, the 789 shows 7635 nm for 28C/262Y and the 359 shows 8100 nm 48C/267Y. 500nm works out to roughly an hour of flight time, hence the 15-16 I quoted.

LH707330 wrote:

tommy1808 wrote:

LH707330 wrote:

789/359: 15-16 hours

That does not reflect their relative performance. At the longer ranges the Airbus, more optimized for long flights, carries a lot more payload. Where the A359 stops being useful, the 789 carries about half its payload.

Best regards
Thomas

I'm not talking about the no-longer-useful range, I'm talking about the realistic ranges for pax+bags and maybe a few t of cargo. When you look at their spec pax+bags ranges, the 789 shows 7635 nm for 28C/262Y and the 359 shows 8100 nm 48C/267Y. 500nm works out to roughly an hour of flight time, hence the 15-16 I quoted.

By conveniently replacing 3.5t of fuel with pax and seats....
If I recall correctly the MZFW range of the A350-900 was 600-700 nm longer than the 789s, and that probably was before the new wingtips and last MTOW bump.

For example from here
viewtopic.php?t=1352139&start=550

Best regards
Thomas

NYPECO wrote:

According to Boeing and Airbus websites, the A350 has more range than the 787. 787-9 has a range of 14,100km while the A350-900 has 15,000km and the A350-1000 has a range of 15,557km. So why is it that the 787 is praised as a game changing aircraft that opens up the ability for ultra long routes (such as Perth to London) when the A350 has more range and can carry more passengers?

And to be clear, I'm not trying to start an Airbus vs Boeing war. I like both aircraft.

Mostly a difference in PR and Astroturfer language and culture.
Overstating facts or not.
Like "Step to full laminar flow nacelle" where laminar flow
has just been extended a couple percent further.
Tagging things as quantum step absolute firsts that are anything but. ..

Both the 789 and the 359 are game changers. The endlessly rehashed payload argument doesn't fit because it is not an apples to apples comparison because each is optimized in different ways.

For example....I think the 359 is perfectly optimized for DL's TPAC network while the 789 is a better fit for AA.

Each is a highly capable frame....It really boils down to what works best for each individual airline.

For me what's remarkable about the 787 is the 'family' and the multitude of different roles it achieves so well.
The 788 has been and will be a phenomenal 767 and 330 replacement aircaft.
The 789 as discussed above has -via its range and economics,opened up a host of new P2P routes
The 7810 - well I just didn't see that one coming! It is a mid range 777! How that wing/engine combo does it is frankly surprising.

I do wonder whether Airbus saw it either.
Having said that the 350 is also a great aircaft that much is clear.But I worry about Airbus planners.
Did they really think ( They must have) that a 358 was going to 'cut it'? Very worrying.
And the 3510.A great plane no doubt but veeery late in the day they were forced to make some major changes that certainly put RR in a jam.
Had they understood from the outset that the 358 was a non starter perhaps this could have been avoided.Sloppy planning imho.
But things change and today perhaps the enhanced 1000 may be just what the doctor ordered.The 777x is looking awfully dicey right now.
The reason Boeing is having a hard time closing the 797 business case imho is because the 788 is such a good and versatile aircaft.

parapente wrote:

The reason Boeing is having a hard time closing the 797 business case imho is because the 788 is such a good and versatile aircaft.

How many 788 have been sold recently? How many A332/8

In view of the A359 besting the 789 in a similar way the A330 bested the 767
An A358XWB built to the original specs would have been like dynamite fishing in the 787 pond.

so what kind of reasoning drove Airbus to discontinue the effort?

WIederling wrote:

An A358XWB built to the original specs would have been like dynamite fishing in the 787 pond

Any factual basis for this opinion statement, or is just part of your usual partisan/nationalistic take on any matter that involves comparing these two manufacturers?

The A350-900's cabin area is half way between the 787-9 and 787-10. However lets compare the two most popular models the 787-9 to the 280T A358-900.

The A350-900 can carry 10% more payload and fly it 10% further. That is the A350-900's advantage.

The 787-9 when flying the same payload the same distance burns nearly 10% less fuel on the trip. That is the 787-9's advantage.

If you had to pick only one aircraft it would depend if you had any routes that required the extra range of the A350.

The big advantage the 787 has is what parapente pointed out. As a family it is stronger. The 787-10 gains an even bigger fuel burn efficiency advantage over the A350 models but trades significant range. The 787-8 offers a size well below the A350 family. This provides lower trip costs and allows more long thin routes to open up, routes that would struggle to fill a 787-9 or A350-900.

There is no 10% difference in fuel burn between the 787-9 and A350-900 when looking at the same payload over the same distance, the A350-900 is capable of carrying more than 10% additional payload. For shorter ranges on the same airframe Airbus offers lower MTOWs to take advantage of lower costs. The A350-900 can be configured as a medium range high density, or long range medium density aircraft with the same aircraft.

RJMAZ wrote:

The A350-900's cabin area is half way between the 787-9 and 787-10. However lets compare the two most popular models the 787-9 to the 280T A358-900.

The A350-900 can carry 10% more payload and fly it 10% further. That is the A350-900's advantage.

The 787-9 when flying the same payload the same distance burns nearly 10% less fuel on the trip. That is the 787-9's advantage.

If you had to pick only one aircraft it would depend if you had any routes that required the extra range of the A350.

The big advantage the 787 has is what parapente pointed out. As a family it is stronger. The 787-10 gains an even bigger fuel burn efficiency advantage over the A350 models but trades significant range. The 787-8 offers a size well below the A350 family. This provides lower trip costs and allows more long thin routes to open up, routes that would struggle to fill a 787-9 or A350-900.

My model shows that if the B789 takes off at MTOW (254t), by the time it has reached 5469nm it has burned 67521kg of fuel.
When the A359 takes off at MTOW (280t), by the time it has reached 5469nm it has burned 72688kg of fuel.

The A359 appears to burn 7.6% more fuel. You determine whatever pax/cargo you want to put in them.

Fred

zeke wrote:

There is no 10% difference in fuel burn between the 787-9 and A350-900 when looking at the same payload over the same distance.

The difference is 10%.

Cross section area.
787 - 29,700 cm2
A350 - 31,600 cm2
A350-900 cross section is 6.5% larger..

Length:
787-9 - 62.8m
A350-900 - 66.8m
A350-900 length is 6.5% longer.

The A350-900 has a 12-13% greater fuselage wetted area than the 787-9. That is massive. Extra wetted area means extra drag. Extra drag means extra thrust. Extra thrust means extra fuel burn.

There is a reason the A350-900 has 18% more thrust than the 787-9 it is bigger and heavier.

The A350-900 definitely burns 10% more fuel than the 787-9 carrying the same load the same distance.

The A359 does have more wetted area than the 787-9, it is also slightly heavier.

However the A359 climbs higher, flies slightly faster, has a slightly newer engine, which are offsets.

It has more thrust for takeoff and can use thrust to fly a lot further, or in addition to the better wing to achieve better hot and high performance.

No “definite” facts to show 10%.

RJMAZ wrote:

zeke wrote:

There is no 10% difference in fuel burn between the 787-9 and A350-900 when looking at the same payload over the same distance.

The difference is 10%.

Cross section area.
787 - 29,700 cm2
A350 - 31,600 cm2
A350-900 cross section is 6.5% larger..

[/quote]
6.5% cross sectional are is a 3.1% difference in circumference.

RJMAZ wrote:

Length:
787-9 - 62.8m
A350-900 - 66.8m
A350-900 length is 6.5% longer.

The A350-900 has a 12-13% greater fuselage wetted area than the 787-9. That is massive. Extra wetted area means extra drag. Extra drag means extra thrust. Extra thrust means extra fuel burn.

9.8% greater surface area in the fuselage. The wing has an additional 17%.

RJMAZ wrote:

There is a reason the A350-900 has 18% more thrust than the 787-9 it is bigger and heavier.

it does not mean it has 18% more drag and fuel burn.

RJMAZ wrote:

The A350-900 definitely burns 10% more fuel than the 787-9 carrying the same load the same distance.

My numbers still say 7.6% more and this is when both take off at MTOW. this will reduce the overall fuel burn gap as the A359 would only need to be getting off the ground at 260-265t. The part you may be missing is the reduced induced drag because of a reduced spanwise loading.

Fred

zeke wrote:

The A359 does have more wetted area than the 787-9, it is also slightly heavier.

However the A359 climbs higher, flies slightly faster, has a slightly newer engine, which are offsets.

It has more thrust for takeoff and can use thrust to fly a lot further, or in addition to the better wing to achieve better hot and high performance.

No “definite” facts to show 10%.

@Zeke,

We can do a comparison. I have 787 flight planning data from the manual, I guess you can provide A350 numbers. It would be interesting to see what comes out of it.

Below are 787 trip fuel figures @LRC:

I assumed 40T payload and ~8T reserve fuel at landing

4000Nm -44T
5000Nm - 54T
6000Nm - 70T
7000Nm - 84,5T*
* Above MTOW, can’t carry 40T payload that far

Can you look up A350 fuel burn data for the same conditions?

What was the landing weight you were working on to generate the above numbers ?

Are you looking at the trip fuel and time required table in performance dispatch?

I cannot look the numbers up in a manual as they are not published, I would need to do some calculations with the performance application on the OIS.

zeke wrote:

What was the landing weight you were working on to generate the above numbers ?

Are you looking at the trip fuel and time required table in performance dispatch?

I cannot look the numbers up in a manual as they are not published, I would need to do some calculations with the performance application on the OIS.

I was using Boeing's equivalent of Flight planning tables in FCOM PER-Dispatch. Does the A350 have similar tables, or did it go digital? The A330 still had them...

My assumptions were:
DOW 127T
Res fuel 8T
Payload 40T
Landing weight 175T
still air
LRC

It is still a bit of 'back of the fag pack' calculations, but should give a rough idea of fuel required to carry same payload for a given distance.

I chose 40T payload as it is pretty much 'full house' plus some cargo for the 787. It is still below MZFW, but I think quite representative for a 300 pax flight.

The A350 is all digital the FCOM refers to the performance program.

Our worst A359 will do over 57 tonnes and worst 35K over 73 tonnes of payload.

I have the 787-8 manuals so I was trying to see what you were using. I guessed it was performance dispatch.

8 tonnes reserve is a lot, I can land with less than 5 tonnes with my alternate and final reserve fuel intact.

As I said, this is just an assumption of a 'typical' flight. The 787 can do ~54T payload, but I hardly ever see more than 40 in day-to-day ops for a full-ish plane. Perhaps other carriers normally carry more cargo. Likewise the reserves - 8-10T is what I usually see after landing, which normally includes un-burnt contingency fuel. I'm sure it can be 'shaved off' by another tonne, or two with less conservative flight planning. It won't change the big picture much, though....

I was trying to compare fuel burn for typical flights with ~300 pax, far from the edges of performance envelope. This is where missions of bot planes overlap.

Okay the numbers I got from an early version of the performance program that I used during my initial training (new version is better now they have more data).

Assumed a DOW of 135 tonnes, Landing weight of 183 tonnes.

4000 nm - 45.2
5000 nm - 57.5
6000 nm - 70.3
7000 nm - 83.9

I think it would carry that payload out to around 8000 nm.

Given what I see when I plot the two series, your 5000 nm number looks to be in error, should be around 57 tonnes.

The coninued interest in range is fascinating to me. I don't have the data in front of me, but IIRC, the very large proportion of long haul flying is between 8 and 13-14 hours.

Why the fascinatiin with extreme ranges?

SteelChair wrote:

Why the fascinatiin with extreme ranges?

Seems to me the arrival of the 787 and the A350 is producing a step change in realistic long haul ranges compared to the 744 era. It's being led by the 77W/77L/A380 but clearly the 787 and A350 are transforming the economics of 16 hour+ flights. And more to come: eg SQ re-launching NYC, QF and NZ wanting to launch non-stop to ORD, NYC, not to mention Project Sunrise. Extreme ULH is now a commercial reality.

tealnz wrote:

SteelChair wrote:

Why the fascinatiin with extreme ranges?

Seems to me the arrival of the 787 and the A350 is producing a step change in realistic long haul ranges compared to the 744 era. It's being led by the 77W/77L/A380 but clearly the 787 and A350 are transforming the economics of 16 hour+ flights. And more to come: eg SQ re-launching NYC, QF and NZ wanting to launch non-stop to ORD, NYC, not to mention Project Sunrise. Extreme ULH is now a commercial reality.

My guess for the extreme long range is the relative efficiency of the engines giving a less steep slope from the MZFW portion of the payload range curve. If two aircraft have identical MZFW range and identical typical pax capacity but differing TSFC then that with the lower TSFC will have the higher pax range.

Fred


Sent from my iPhone using Tapatalk

zeke wrote:

Okay the numbers I got from an early version of the performance program that I used during my initial training (new version is better now they have more data).

Assumed a DOW of 135 tonnes, Landing weight of 183 tonnes.

4000 nm - 45.2
5000 nm - 57.5
6000 nm - 70.3
7000 nm - 83.9

I think it would carry that payload out to around 8000 nm.

Given what I see when I plot the two series, your 5000 nm number looks to be in error, should be around 57 tonnes.

Good catch, it should be 56.3. Did some quick’n’dirty interpolations and must have gotten this one wrong...

Thanks for the 350 data. Looks like the fuel burn delta is on order of 2%, rather than 10%...

Depends on sector length, looks like the A350 burns about 1% less at longer ranges, and easily carries the same payload too far.

Bring back solar powered aircraft.

zeke wrote:

Depends on sector length, looks like the A350 burns about 1% less at longer ranges, and easily carries the same payload too far.

Bring back solar powered aircraft.

That confirms what we’ve already known - that the A350 is optimised for higher stage lengths and payloads. Now, however, we were able to quantify it to some extent...

So basically, if an airline chooses an A350 over the 789, they have a more capable a/c payload-range wise, at the expense of approximately 1 ton fuel burn/sector on shorter stage lengths. Then there’s of course a difference in lease rates, navigation charges stemming from higher MTOW of the 350 etc.

We could try to repeat this exercise for a range of payloads (say 20 to 50 tons) and plot it, to get a bigger picture - I can do calcs for 788, 789 and could even throw in A330 data as comparison with previous gen aircraft. You’d have to provide the 350 numbers...


What I think is interesting to see is how these airplanes compare on typical ‘bread and butter’ LH sectors of 4-5000 NM, as that’s where they operate majority of flights and are often interchanged with each other.

I used the data you sent me via PM to come up with more refined numbers for the 787-9, the 787-9 looks like it will beat the A350-900 by 0.6% on average. That is not a lot of penalty for the additional payload and range the A350-900 beings to the table.

I also plotted the fuel burns for the 787-8, A330-200, 777-200ER (286.9 MTOW), and 777-200LR for the same payload. The 787-8, 787-9, and 777-200ER were unable to carry 40 tonnes 7000, near identical maximum range for the same payload.(maximum of 6663 nm for the 787-9 and 6688 nm for the 777-200ER) ,

Thanks Zeke, great stuff. Got your PM, but haven't had the time yet, to have a closer look... I will try to post data for other payloads later.

It's interesting to see how close in terms of fuel burn the 789 and 359 are.

Also, I was quite surprised to see how the 788 fares in the big picture - I was expecting it to be much closer to the 789.

IMO this data defies the prevailing A.net opinion, that the 788 is now obsolete and that 789 does the same thing for a small fuel penalty. 4-5 tons fuel per trip is quite a significant difference...

If Boeing was able to increase the MTOW of the 788 it would be a formidable LR plane...

P.S. You're A332 data seems to be optimistic in terms of range. Even at 242T MTOW, with 40T payload, you have around 80T for fuel. If you subtract reserves, you'll max out the MTOW at approximately ~5700NM...

When I get a chance I’ll send you the 788 and A332 data, straight from FCOM to see if I have made any obvious mistakes.

What surprised me about the A332 is it is only around 8% above the 789/359, the 338 was supposed to have a drop of more than that.

zeke wrote:

When I get a chance I’ll send you the 788 and A332 data, straight from FCOM to see if I have made any obvious mistakes.

What surprised me about the A332 is it is only around 8% above the 789/359, the 338 was supposed to have a drop of more than that.

Will gladly have a look and will try to throw in the A333 into the picture - tomorrow probably, as today I only have a cellphone with me, which is not optimized for number crunching

What DOW did you assume for the 332 and 788?

Thank you pinkmachine and Zeke you have made this thread brilliant injecting facts in to his often emotive topic.

I hope you guys realise this thread will be referenced a lot in the future.

Fred


Sent from my iPhone using Tapatalk

Without wishing to be rude in any way whatsoever.Re Zeke's numbers.Are we very confident they are right.I also was astounded on how low the 788 numbers were relative to the 789.Are we confident that it's right?
If they are ,it's gonna squeeze any 797 programme into a very small box.
The 788 seats nearly an identical number of pax to the proposed 797 and will fly the stated range (5,000 nm) very nicely.Indeed if you loaded it up with cargo (as the Asian carriers want anyway) it does that range almost perfectly.So where's the gap?.

I could very well be wrong on some accounts, I have sent the source data and the data I have derived from that to pinkmachine to have a look at.

Pinkmachine did correctly spot an error in the A332 numbers I had checking for MTOW limit.

The only difference I had with the 787-8 numbers were the source numbers were in lbs, the rest were kg. For that I did the numbers all in lbs and one last conversion into kg.

I also added A340-300 data into my spreadsheet yesterday.

If it's correct then the A350 has a very small fuel burn penalty for the extra capability.

Zeke has sent me a significant amount of data, including a detailed description of his methodology and asked for a review. All I can say, it seems completely correct according to my knowledge. It is all based on FCOM Flight Planning data, so it is as accurate as it gets - the FCOM tables are good enough to be used for real-world flight planning eg. in case of un-availability of a computerized flight-planning system.

Having said that, the following caveats apply:

- The A359 fuel burn has been derived from official Airbus in-flight performance software. I expect it to be the most accurate.

- Other airplanes' figures were derived from tables, with quite a bit of linear interpolation. I expect it to be of slightly lower accuracy, and probably the manufacturer has made these figures a bit more conservative, to allow for interpolation inaccuracies. There is no harm if the plane burns slightly less than planned. It could spell trouble for the manufacturer if it was otherwise

- In view of the above, I suspect the 787 burn figures might be slightly better than on the plot and the advantage over the 359 higher. Still, that's just my guess and the numbers are accurate enough for real-world use. I'd love to have access to perf software for the 787, but at the moment - I don't. Stay tuned, though…

- The flight profile is simplified. Real airline flight planners use things like cost index, individual airframe performance factors, etc. Having said that, since all our FCOM data is based on LRC (long range cruise, or 99% of max range), I think it is a good way of comparing various types.

- All data is based on our best guess of Dry Operating Weight and Reserve fuel remaining at the end of the flight. The former may vary from airline to airline and frame to frame, the latter from flight to flight and on airline policy. I have operated airplanes of the same type and variant with as much as 5 tons difference in DOW. Fuel remaining upon landing on a widebody may be as low as 4 tons, or as high as 11 tons. To quantify possible error - we re talking about 200-300kg of fuel per ton of weight per sector, depending on model and sector length. Again, close enough for the purpose of A.Net discussions.

All in all, it is a fascinating thread and some very interesting results

It's always better to have data for this type of discussion rather than relying on verbal discussions.

That being said, the increment between the 788 and 789 looks a bit suspect. The 789 in Zeke's chart is shown to be burning about 10% more fuel than the 788. Since the wing and engines are the same for these airplanes, the fuel burn difference would come from the OEW difference and the additional drag of the 789 body stretch.

If the OEW difference between the 788 and 789 is about 9t, that would increase 789 fuel burn by about 4% relative to the 788. The 789 body stretch drag would increase fuel burn by 1% - 2%.

For the 40t payload scenario shown in Zeke's plot, I suspect the 789 burns about 5% - 6% more fuel than the 788, not 10%.

OAG,

I have sent you a PM with the method used to derive the numbers, would appreciate if you can see any obvious errors.

Range 787-9 787-8
4000 44.73 41.31
5000 56.98 52.44
6000 70.00 64.03
7000 83.73 76.21

I was of the understanding that the 787-8/9 are not that common, only about 30% commonality.

Zeke's data confirms one fact that has been floating around for a while. That is the 789 is more fuel efficient on a typical payload mission (assume 40t) up to 6000 nm where the advantage swings to the A359. This makes perfect sense to me.

What i find surprising is how small the 789 advantage is considering it is quite a bit lighter and has a smaller surface area ( i.e. less drag). Some UA pilots gave fuel burn numbers for the 789 on an ULH fight SFO-MEL and there numbers were quite different.

I am not saying the numbers presented here are wrong....particularly for the A359....I just can't square the difference.

Thank you every body
All the number are for 40t payload?
40t payload is a lot for a 787-9 ?
And not so much for A350-900 in the real life
How does it change the analysis when you go with "typical payload ?" Wha is the usual penalty (rule of thumb) for 1t more of weight ?

Aviaponcho wrote:

Thank you every body
All the number are for 40t payload?
40t payload is a lot for a 787-9 ?
And not so much for A350-900 in the real life
How does it change the analysis when you go with "typical payload ?" Wha is the usual penalty (rule of thumb) for 1t more of weight ?

The penalty is highly dependent on sector length. On a 350-900, for a 12-hour sector an extra ton means 250-280 kg more burn. On a 1.5-hour sector more like 25-30 kg.

zeke wrote:

OAG,

I have sent you a PM with the method used to derive the numbers, would appreciate if you can see any obvious errors.

Range 787-9 787-8
4000 44.73 41.31
5000 56.98 52.44
6000 70.00 64.03
7000 83.73 76.21

I was of the understanding that the 787-8/9 are not that common, only about 30% commonality.

Thanks for the data Zeke. I agree with the interpolations you made for the 788 and 789 mission fuel tables you provided.

I still have some questions about the relative 787 fuel burn levels. Let's take 5000 nm as an example.

The data you provided show the 789 will burn 8.7% more fuel (56.98 / 52..44 = 1.087) relative to the 788.

As I said earlier, part of this is the 7t DOW difference between the 788 and 789. This can be adjusted by using the 788 LW (168t) to compute a 789 mission fuel burn.

The result is a mission fuel burn of 55.0t. The 789/788 fuel burn difference would drop to 4.9% (55.00 / 52.44 = 1.049)

While commonality between the 788 and the 789 has been reduced to improve weight and producibility, the primary external geometry change is the body stretch. The 789 is 6.1m longer than the 788 (62.8m - 56.7m = 6.1m).

It's unlikely a 6.1m body stretch would increase overall 789 drag by 4.9% relative to the 788. I suspect that part of the difference in mission fuel shown in the 788 and 789 tables is engine related.

Are both tables for the same engine manufacturer and the same bill-of-materials? The later is particularly important since both GE and RR have PIP'd the GEnx-1B and Trent 1000 for better fuel burn.

I agree that using 8t of reserve fuel for all models is very conservative. It skews mission fuel burn at shorter ranges for all airplanes and disadvantages the modern airplanes (A350 & 787) relative to the older models.

My guess is it the additional mass of the 787-9 is giving it a very different verticle profile in addition to the other items you addressed.

I think the 787-8 and A350-900 would climb straight to FL370 after takeoff with that payload, then the 787-9 maybe limited to FL330. Every change of 1000 could change that fuel burn by 1%.

If you do as I did and use the 788 landing weight with the 789 mission data, that will eliminate the weight effect on initial cruise altitude. In terms of landing weight, the mission profile doesn't differentiate between DOW, Payload and Reserve Fuel.

The 5% fuel burn difference between the 788 and 789 shown in the table has to be due to something else and the body stretch drag increment won't explain it all.