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patrickjp93
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Re: 787 vs A350 range

Mon Aug 26, 2019 5:10 pm

WIederling wrote:
patrickjp93 wrote:
There's additional weight in the airframe beyond the engines, mainly from wing and wing box strengthening with Titanium.


Titanium?

I'd expect the machined Al parts to be slightly resized.

patching up parts with different materials is the perfect way to increase weight more than strength.


By that logic the A380 would never have come to be. It's essentially a mutt of composite and Aluminum paneling, but all-aluminum would have been lighter?

Regardless, we're way off topic now.
 
flipdewaf
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Re: 787 vs A350 range

Tue Aug 27, 2019 11:47 am

patrickjp93 wrote:
flipdewaf wrote:
Let’s assume 14% of a total 125t frame is composite and 2 6t engines are 10% each. That means 17.5t total composite with 1.2t of that in the engines so the airframe is 16.3t.

In the new engine that is ~1ton heavier there is still ~10% composite so a total of 1.4t in the engine for a required 17.78t total in the aircraft or 16.38 in the airframe. A whopping 80kg of composites! Just stick some hefting great wing tips and you’re there!

Fred


Sent from my iPhone using Tapatalk


The A330-900 is also the same composite percentage by weight. And RR engines are less than 10% composites. 10 is probably high-balling them. And we don't even know if Airbus would be counting the composites in the engines to begin with, as that's a factor they can't control. But regardless, your math is still off. There's additional weight in the airframe beyond the engines, mainly from wing and wing box strengthening with Titanium. Even if 10% is spot on and Airbus includes the engines in their calculations, you're looking closer to 800kg as a lowball estimate of additional composite materials included.


Lol, 800kg! and maintaining the 14% by weight of composites. this suggests that the 800kg must be 14% by weight of the increase in total suggesting that the overall weight increase is (0.8/0.14) tons? None of your links showed that, only media pieces with pretty pictures. Show where the empty weight increase for the NEO is 5.7t and you'll look more credible.

A+ for looking convincing at a cursory glance, C- for providing evidence.

Fred
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patrickjp93
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Re: 787 vs A350 range

Thu Aug 29, 2019 1:01 am

flipdewaf wrote:
Lol, 800kg! and maintaining the 14% by weight of composites. this suggests that the 800kg must be 14% by weight of the increase in total suggesting that the overall weight increase is (0.8/0.14) tons? None of your links showed that, only media pieces with pretty pictures. Show where the empty weight increase for the NEO is 5.7t and you'll look more credible.

A+ for looking convincing at a cursory glance, C- for providing evidence.

Fred


https://airwaysmag.com/airlines/first-a ... ivery-tap/

Airbus says 4-5 tonnes. It's 5.7.
 
WIederling
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Re: 787 vs A350 range

Thu Aug 29, 2019 7:27 am

patrickjp93 wrote:
https://airwaysmag.com/airlines/first-a330neo-delivery-tap/

Airbus says 4-5 tonnes. It's 5.7.


foot stamping is not evidence.
( can't find the 4--5 t numbers either in the article.)
Murphy is an optimist
 
flipdewaf
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Re: 787 vs A350 range

Thu Aug 29, 2019 8:12 am

patrickjp93 wrote:
flipdewaf wrote:
Lol, 800kg! and maintaining the 14% by weight of composites. this suggests that the 800kg must be 14% by weight of the increase in total suggesting that the overall weight increase is (0.8/0.14) tons? None of your links showed that, only media pieces with pretty pictures. Show where the empty weight increase for the NEO is 5.7t and you'll look more credible.

A+ for looking convincing at a cursory glance, C- for providing evidence.

Fred


https://airwaysmag.com/airlines/first-a ... ivery-tap/

Airbus says 4-5 tonnes. It's 5.7.

... Maybe they do, but certainly not in that article.

Fred
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patrickjp93
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Re: 787 vs A350 range

Thu Aug 29, 2019 11:13 am

flipdewaf wrote:
patrickjp93 wrote:
flipdewaf wrote:
Lol, 800kg! and maintaining the 14% by weight of composites. this suggests that the 800kg must be 14% by weight of the increase in total suggesting that the overall weight increase is (0.8/0.14) tons? None of your links showed that, only media pieces with pretty pictures. Show where the empty weight increase for the NEO is 5.7t and you'll look more credible.

A+ for looking convincing at a cursory glance, C- for providing evidence.

Fred


https://airwaysmag.com/airlines/first-a ... ivery-tap/

Airbus says 4-5 tonnes. It's 5.7.

... Maybe they do, but certainly not in that article.

Fred


Yes they do. 11,000 pounds is how much in metric tonnes...?

Then there's the MZFW up by 6 tonnes exactly, max landing weight up by 4 tonnes exactly. The data's right there.
 
flipdewaf
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Re: 787 vs A350 range

Thu Aug 29, 2019 12:44 pm

patrickjp93 wrote:
flipdewaf wrote:
patrickjp93 wrote:

... Maybe they do, but certainly not in that article.

Fred


Yes they do. 11,000 pounds is how much in metric tonnes...?

Then there's the MZFW up by 6 tonnes exactly, max landing weight up by 4 tonnes exactly. The data's right there.


I can see a graphic where they say that the A339NEO weight is 4-5t higher than the 787-9. I cannot see 11000lb anywhere in the linked article.

Fred
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xwb565
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Re: 787 vs A350 range

Thu Aug 29, 2019 2:58 pm

AECM wrote:
xwb565 wrote:
thepinkmachine wrote:

Care to share some numbers? I have flown both the 330-ceo and 787, would love to see how they compare.


4.8t-5.0t/hour depending on trip length. I am somewhat skeptical but perhaps you have a better idea.


Hi,

Any new figures for payload / fuel burn regarding A339 or A35K? :scratchchin: :spin:


New frame a359- full payload(i.e mzfw), 13.5hrs and 5.9t/hr.
 
tommy1808
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Re: 787 vs A350 range

Mon Sep 02, 2019 11:30 am

flipdewaf wrote:
patrickjp93 wrote:
flipdewaf wrote:
... Maybe they do, but certainly not in that article.

Fred


Yes they do. 11,000 pounds is how much in metric tonnes...?

Then there's the MZFW up by 6 tonnes exactly, max landing weight up by 4 tonnes exactly. The data's right there.


I can see a graphic where they say that the A339NEO weight is 4-5t higher than the 787-9. I cannot see 11000lb anywhere in the linked article.

Fred


And even if, what is that supposed to mean anyways, as the A330neo has 4 metres more wing and would be even heavier if absolutely everything was the same...

And how does an A330neo get into the "787 vs A350 range" thread at all...

best regards
Thomas
This Singature is a safe space......
 
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AECM
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Re: 787 vs A350 range

Wed Sep 04, 2019 11:08 am

xwb565 wrote:
AECM wrote:
xwb565 wrote:

4.8t-5.0t/hour depending on trip length. I am somewhat skeptical but perhaps you have a better idea.


Hi,

Any new figures for payload / fuel burn regarding A339 or A35K? :scratchchin: :spin:


New frame a359- full payload(i.e mzfw), 13.5hrs and 5.9t/hr.


:D How about Qatar A35K in IAH and DFW flights?
 
xwb565
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Re: 787 vs A350 range

Wed Sep 04, 2019 11:40 am

AECM wrote:
xwb565 wrote:
AECM wrote:

Hi,

Any new figures for payload / fuel burn regarding A339 or A35K? :scratchchin: :spin:


New frame a359- full payload(i.e mzfw), 13.5hrs and 5.9t/hr.


:D How about Qatar A35K in IAH and DFW flights?


I only have general figures for the a35k. No idea about the QR frames on those sectors.
 
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AECM
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Re: 787 vs A350 range

Wed Sep 04, 2019 12:28 pm

xwb565 wrote:
AECM wrote:
xwb565 wrote:

New frame a359- full payload(i.e mzfw), 13.5hrs and 5.9t/hr.


:D How about Qatar A35K in IAH and DFW flights?


I only have general figures for the a35k. No idea about the QR frames on those sectors.


I see, do you have some figures for a MZFW flight of an A35K?
 
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Stitch
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Re: 787 vs A350 range

Sat Sep 07, 2019 11:25 pm

UA 807 (787-10) averaged 5.1t/hr on IAD-PEK over a similar flight time, but she was nowhere near MZFW (32t short) nor TOW, for that matter (17t short) and I fully expect that has to be taken into effect when looking at the fuel burn. At MZFW, an A350-900 should be lifting north of 53t, which is double what UA807 was hauling across that same timeframe so factor that, the higher OEW, the higher fuel load and higher TOW and that it burns around 15% more does not strike me as overly surprising.
 
WIederling
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Re: 787 vs A350 range

Sun Sep 08, 2019 9:02 am

Stitch wrote:
UA 807 (787-10) averaged 5.1t/hr on IAD-PEK over a similar flight time, but she was nowhere near MZFW (32t short) nor TOW, for that matter (17t short) and I fully expect that has to be taken into effect when looking at the fuel burn.

Where was that datum sourced?
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Stitch
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Re: 787 vs A350 range

Sun Sep 08, 2019 3:21 pm

WIederling wrote:
Where was that datum sourced?


It was posted on this site (possibly even up-thread). The flight in question occurred on 14 February 2019.

The specifics posted:

TOW: 237,520kg
Payload: 26,000kg (226 passengers + 3800kg cargo + 3900kg bags)
ZFW: 161,090kg
Flight Time: 13:41h
Trip Fuel: 71,440kg (1678kg worse than plan due to ATC altitude holds)
Block Fuel: 76,430kg
Average Fuel Burn per Hour: 5103kg
 
patrickjp93
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Re: 787 vs A350 range

Sun Sep 08, 2019 8:21 pm

But going back to the original question of the thread: The 787 was first to market and a very bold move in technology by Boeing to do it. Without that push, the A350 wouldn't be flying either, and the A330 NEO wouldn't be quite as good as it is either.

Now, long-term, I think what we'll see is another 25-30% range increase after 2-3 more generations of the 787, and at that point, every other adjustment will be an effort to reduce fuel usage and improve range economy.

We may even get our 787-3 idea back. Thinner, smaller wings, much smaller central tank (maybe no central tank, just plumbing to route fuel between wings if an engine fails?), maybe different wing tips to improve climb performance, remove the equivalent weight from the MTOW, and she'll be able to fly 6 hours no issue at that point.
 
IgorD
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Re: 787 vs A350 range

Sun Sep 08, 2019 8:28 pm

Stitch wrote:
WIederling wrote:
Where was that datum sourced?


It was posted on this site (possibly even up-thread). The flight in question occurred on 14 February 2019.

The specifics posted:

TOW: 237,520kg
Payload: 26,000kg (226 passengers + 3800kg cargo + 3900kg bags)
ZFW: 161,090kg
Flight Time: 13:41h
Trip Fuel: 71,440kg (1678kg worse than plan due to ATC altitude holds)
Block Fuel: 76,430kg
Average Fuel Burn per Hour: 5103kg

These data imply an average fuel flow of 5,222 tonne per hour (71,440 / 13,68). That is very well within the estimation that the 781 burn 1/38 of its weight per hour (that's for the LRC speed).
 
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zeke
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Re: 787 vs A350 range

Tue Sep 10, 2019 1:44 am

Stitch wrote:
WIederling wrote:
Where was that datum sourced?


It was posted on this site (possibly even up-thread). The flight in question occurred on 14 February 2019.

The specifics posted:

TOW: 237,520kg
Payload: 26,000kg (226 passengers + 3800kg cargo + 3900kg bags)
ZFW: 161,090kg
Flight Time: 13:41h
Trip Fuel: 71,440kg (1678kg worse than plan due to ATC altitude holds)
Block Fuel: 76,430kg
Average Fuel Burn per Hour: 5103kg


So that is 4990 kg in tanks after landing.

If you look at what jayunited posted in viewtopic.php?t=1422657

"Take for example today's 5/29/2019 UA85 TLV-EWR flight the MTOG for the 78X is 560,000 today's TOG was 559,235. Now before you said I told you so lets take a look at what is on that aircraft. First and foremost the aircraft went out full with 318 passengers and 326 bags and 26,089 pounds of cargo. Lets break it all down the OEW is 300,563 the weight of all 318 passengers is 60,903, the weight of their 326 bags is 9780 pounds and there was 26,089 pounds of cargo add those number together we get a ZFW of 397,335 out of a MXFW of 425,000. The cleared fuel was 161,900 so when you add the cleared fuel to the ZFW you get a TOG of 559,235.

The block time for UA85 is 11 hours 9 minutes"

for this UA TLV-EWR flight, block fuel of 161900 lb (73450 kg) assuming it has 4990 kg in tank after landing makes a trip fuel of 68460 kg, and flight time of 11:19, average burn 6223 kg/hr with a payload of 43903 kg.

The ZFW you have stated at 161,090 kg minus a real UA OEW of 300563 lb (136359 kg) only gives a payload of 24730 kg, which isnt even a 788 load.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
moyangmm
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Re: 787 vs A350 range

Tue Sep 10, 2019 1:58 am

zeke wrote:
If you look at what jayunited posted in viewtopic.php?t=1422657

"Take for example today's 5/29/2019 UA85 TLV-EWR flight the MTOG for the 78X is 560,000 today's TOG was 559,235. Now before you said I told you so lets take a look at what is on that aircraft. First and foremost the aircraft went out full with 318 passengers and 326 bags and 26,089 pounds of cargo. Lets break it all down the OEW is 300,563 the weight of all 318 passengers is 60,903, the weight of their 326 bags is 9780 pounds and there was 26,089 pounds of cargo add those number together we get a ZFW of 397,335 out of a MXFW of 425,000. The cleared fuel was 161,900 so when you add the cleared fuel to the ZFW you get a TOG of 559,235.

The block time for UA85 is 11 hours 9 minutes"

for this UA TLV-EWR flight, block fuel of 161900 lb (73450 kg) assuming it has 4990 kg in tank after landing makes a trip fuel of 68460 kg, and flight time of 11:19, average burn 6223 kg/hr with a payload of 43903 kg.

The ZFW you have stated at 161,090 kg minus a real UA OEW of 300563 lb (136359 kg) only gives a payload of 24730 kg, which isnt even a 788 load.


Why did you assume it had the same 4990 kg in tank after landing? If the actual remaining fuel is 10000 kg, the average burn would be 5.6 kg/hr, much less than an A359 could possibly do.
 
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zeke
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Re: 787 vs A350 range

Tue Sep 10, 2019 2:10 am

moyangmm wrote:
Why did you assume it had the same 4990 kg in tank after landing? If the actual remaining fuel is 10000 kg, the average burn would be 5.6 kg/hr, much less than an A359 could possibly do.


because the SAME assumption was made further up
Stitch wrote:
Trip Fuel: 71,440kg (1678kg worse than plan due to ATC altitude holds)
Block Fuel: 76,430kg


"much less than an A359 could possibly do" again is pure Boeing fanboy comment.

Those fuel burns are perfectly in line with what the 359 does at comparable payload mass. Even the UA 787-10 OEW stated by jayunited is slightly heavier than our A359.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
moyangmm
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Re: 787 vs A350 range

Tue Sep 10, 2019 2:24 am

zeke wrote:
moyangmm wrote:
Why did you assume it had the same 4990 kg in tank after landing? If the actual remaining fuel is 10000 kg, the average burn would be 5.6 kg/hr, much less than an A359 could possibly do.


because the SAME assumption was made further up


I know, but these are two different flights. Do all UA flights land with the same amount of fuel? Certainly not. You picked a particular data point, and assumes it landed with the same amount of fuel as another one on a different route.

zeke wrote:
Those fuel burns are perfectly in line with what the 359 does at comparable payload mass. Even the UA 787-10 OEW stated by jayunited is slightly heavier than our A359.


6.1 t/hr is probably in line with what the A359 does, but 5.6 t/hr is not.
 
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Stitch
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Re: 787 vs A350 range

Tue Sep 10, 2019 3:32 am

WIederling wrote:
Where was that datum sourced?


Found the thread: viewtopic.php?f=3&t=1415561

Data provided by jayunted in Post #27. He uses Imperial, but I converted to Metric since that is what we seem to normally use for measurements.
 
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zeke
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Re: 787 vs A350 range

Tue Sep 10, 2019 4:30 am

moyangmm wrote:
I know, but these are two different flights. Do all UA flights land with the same amount of fuel? Certainly not. You picked a particular data point, and assumes it landed with the same amount of fuel as another one on a different route.


Both UA flights, one IAD-PEK the one Stitch mentioned, the other TLV-EWR. For IAD-PEK they would use TSN as the alternate, for TLV-EWR, JFk would be used. JFK os closer to the destination an TSN, so alternate fuel would be less.

These are the same aircraft, in the same airline, operating under the same fuel policy.

zeke wrote:
6.1 t/hr is probably in line with what the A359 does, but 5.6 t/hr is not.


5.6/hr is defiantly in line with the A359 at light payloads like the IAD-PEK example.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
moyangmm
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Re: 787 vs A350 range

Tue Sep 10, 2019 5:10 am

zeke wrote:
5.6/hr is defiantly in line with the A359 at light payloads like the IAD-PEK example.


Ok. I was referring to MZFW fuel burns. At light payload on IAD-PEK, A359 probably burns 5.6 t/hr as you said, but Stitch’s data shows 787-10 burns 5.1 t/hr. Still, 787-10 is more efficient.
 
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zeke
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Re: 787 vs A350 range

Tue Sep 10, 2019 11:30 am

moyangmm wrote:
Ok. I was referring to MZFW fuel burns. At light payload on IAD-PEK, A359 probably burns 5.6 t/hr as you said, but Stitch’s data shows 787-10 burns 5.1 t/hr. Still, 787-10 is more efficient.


Just to clarify something, this is not data Stitch has, it is a something he has posted based upon what someone else has posted in the viewtopic.php?f=3&t=1415561.

The source "United B78X IAD-PEK" thread does not have the flight time in it, according to FR24 "AVERAGE FLIGHT TIME 13:03"

But I do understand you are saying the 787-10 is efficient at flying empty ?

http://pic.twitter.com/qev7HnSHow

Now that something to boast about.

Meanwhile the A359 would do that flight with full passengers and cargo, they do those sector lengths and greater flight times every day. It is not a remarkable achievement for the A359, it does not get a special thread.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
IgorD
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Re: 787 vs A350 range

Tue Sep 10, 2019 1:03 pm

Zeke, my point is that both types (B787 and A359) burn around 1/38 of their gross weight per hour in flight at LRC speed, optimum altitude and ISA temps. Speed or temperature deviation or change would affect both types equally. Assuming same DOWs of 781 and 359 (which is reasonable giving your datapoint for UA OEW), they will burn more or less the same per hour for the same payload. As both frames are M.85 frames they will burn the same per nm and ton-km payload. What differs between the frames is that 781 will hit the payload wall distance-wise earlier, as it has much smaller MTOW. That is where 781 lacks the longer range capability of 359, especially so if airline aims at a payload of +-50 ton (which is reasonable to assume for both frames)

Where 781 may have an edge is in a higher max payload (57 ton vs 53 ton for A359 according to Wikipedia), it may also have an edge in slightly lower OEW, engine choice and fleet commonality. But purely on fuel burn it should not (tonne-for-tonne) outperform A359. And all these advantages of B781 can only be realized on segments of up to 9 flight hours – this is the flight length where my model shows that B781 hits MTOW with max payload (57 ton) and a reserve of 8,5 ton.
 
IgorD
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Re: 787 vs A350 range

Tue Sep 10, 2019 1:13 pm

My model estimates an average fuel burn for B781 of 5,9 ton/hour for a payload of 57 ton and a flight length of 9 hours (circa 4290 nm still air, ISA conditions, landing with 8,5 ton reserves). Takeoff at 254 and landing at about 201 ton.

The 781 will burn 5,1 ton per hour on a 9 hour flight with full pax (32 ton payload)
 
tommy1808
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Re: 787 vs A350 range

Tue Sep 10, 2019 2:04 pm

IgorD wrote:
Zeke, my point is that both types (B787 and A359) burn around 1/38 of their gross weight per hour in flight at LRC speed, optimum altitude and ISA temps.


And what makes you think it is 1/38th for both? Airbus did stick some 15 feet more wing onto for a reason, i would think they did so to burn less fuel. I would also assume that effective wingspan wise that should even be more of a difference.

Plus of course, from the publicly available data OEW may be pretty much the same between the two.

best regards
Thomas.
This Singature is a safe space......
 
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zeke
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Re: 787 vs A350 range

Tue Sep 10, 2019 2:09 pm

IgorD wrote:
Assuming same DOWs of 781 and 359.....

Where 781 may have an edge is in a higher max payload (57 ton vs 53 ton for A359 according to Wikipedia)


From the TCDS

787-10 MZFW 192777 kg
A350-900 MZFW 195700 kg (some W/V have a MZFW of 192 tonnes).

IgorD wrote:
Speed or temperature deviation or change would affect both types equally.


I think that is not valid, 787-10 seems not to have the same altitude capability of the 787-9. When light at the end of a flight or on shorter sectors the A359 optimum will push to FL430, the 787-10 is not certified that high.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
IgorD
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Re: 787 vs A350 range

Tue Sep 10, 2019 2:32 pm

tommy1808 wrote:

And what makes you think it is 1/38th for both? Airbus did stick some 15 feet more wing onto for a reason, i would think they did so to burn less fuel. I would also assume that effective wingspan wise that should even be more of a difference.

Plus of course, from the publicly available data OEW may be pretty much the same between the two.

best regards
Thomas.


1/38 is a factor that I collected from Boeing's FCOM and A359 cockpit photos in flight. There is of course an error margin, but I think it should be within a couple of percent (i.e. between 1/37 and 1/39).
Those 5 meter longer wing comes handy at weights above 254 ton, that's why I believe it should be comparable between the two frames.
A larger wing will allow A359 fly higher at the same weight, having a different balance between induced and parasitic drag -- though I stick to regression models that I understand -- fine aerodynamics is not my expertise :)

zeke wrote:

I think that is not valid, 787-10 seems not to have the same altitude capability of the 787-9. When light at the end of a flight or on shorter sectors the A359 optimum will push to FL430, the 787-10 is not certified that high.


For the same weight, 781 and 789 should have the same optimum altitude. Or do I see it wrong, as 781 has a larger wetted area, so may have a higher optimum for the same weight -- wonder if that relevant from the safety (buffet onset) point of view?

From the modelling point of view it is important that L/D ratio does not change much with continuously decreasing weight in flight, assuming a/c flies at the optimum FL (or roughly optimum with a step clime).
 
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zeke
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Re: 787 vs A350 range

Tue Sep 10, 2019 2:36 pm

IgorD wrote:
Or do I see it wrong, as 781 has a larger wetted area, so may have a higher optimum for the same weight -- wonder if that relevant from the safety (buffet onset) point of view?


I would suggest the 787-10 has more drag than the 787-9, hence a reduced excess thrust margin.
Human rights lawyers are "ambulance chasers of the very worst kind.'" - Sky News
 
tommy1808
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Re: 787 vs A350 range

Tue Sep 10, 2019 3:24 pm

IgorD wrote:
tommy1808 wrote:

And what makes you think it is 1/38th for both? Airbus did stick some 15 feet more wing onto for a reason, i would think they did so to burn less fuel. I would also assume that effective wingspan wise that should even be more of a difference.

Plus of course, from the publicly available data OEW may be pretty much the same between the two.

best regards
Thomas.


1/38 is a factor that I collected from Boeing's FCOM and A359 cockpit photos in flight.


You can not use that methodology and expect to get valid data out of it. You can compare FCOM to FCOM or (lots and lots) of cockpit pictures with other cockpit pictures, but not one with the other. In the FCOM this magical place where optimum cruise speed, optimum climb profile and optimum cruise altitude at ISA exist for a flight, in the real world of cockpit pictures it rarely ever does.

There is of course an error margin, but I think it should be within a couple of percent (i.e. between 1/37 and 1/39).


There is a 5% difference between 1/37th and 1/39th. That's hundreds of Kg of fuel per hour. Airlines pay for 0.x% PIPs on their engines.
Depending on the numbers you believe, that is 77W killed A346 territory.

Those 5 meter longer wing comes handy at weights above 254 ton, that's why I believe it should be comparable between the two frames.


A longer, larger wing will always help. At lower weight you can climb to a higher ICA faster for example.

It would be truly odd if two aircraft with pretty much the same engines, but one is ~10 years newer, and companies can throw some 20 to 30 times more computing power at their designs to optimise aerodynamics a decade later, and that has a longer wing, would have the same fuelburn/weight.

Best regards
Thomas
This Singature is a safe space......
 
IgorD
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Re: 787 vs A350 range

Tue Sep 10, 2019 3:54 pm

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 :)).
 
tommy1808
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Re: 787 vs A350 range

Tue Sep 10, 2019 4:05 pm

IgorD wrote:
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 :)).


Oh they do. Other than the 787 and the MRJ, everything recent seems to max out the available Gate space to get a wing as long as possible. Even in the E2 as a regional airliners stretches them almost to the limit. Boeing puts folding wingtips on the 777x. That slightly stretched A330neo wing shaves 4% of the fuel bill, and the A330 wing was already longer than the 787s and a wing that had aged really well....

Best regards
Thomas
This Singature is a safe space......
 
patrickjp93
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Re: 787 vs A350 range

Tue Sep 10, 2019 4:35 pm

tommy1808 wrote:
IgorD wrote:
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 :)).


Oh they do. Other than the 787 and the MRJ, everything recent seems to max out the available Gate space to get a wing as long as possible. Even in the E2 as a regional airliners stretches them almost to the limit. Boeing puts folding wingtips on the 777x. That slightly stretched A330neo wing shaves 4% of the fuel bill, and the A330 wing was already longer than the 787s and a wing that had aged really well....

Best regards
Thomas
The 787 really is an interesting case study in reseting the dial on wing specs while achieving its fairly unique capabilities. Some people say the wing is still too big to make it a decent successor to the 767F, but I don't know if I buy that.

What do you think they'll do for the NG? Keep the current length with new wingtips/winglets, max out the 65m wingspan limit, or go farther beyond with folding wingtips?
 
LH707330
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Re: 787 vs A350 range

Tue Sep 10, 2019 5:35 pm

patrickjp93 wrote:
tommy1808 wrote:
IgorD wrote:
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 :)).


Oh they do. Other than the 787 and the MRJ, everything recent seems to max out the available Gate space to get a wing as long as possible. Even in the E2 as a regional airliners stretches them almost to the limit. Boeing puts folding wingtips on the 777x. That slightly stretched A330neo wing shaves 4% of the fuel bill, and the A330 wing was already longer than the 787s and a wing that had aged really well....

Best regards
Thomas
The 787 really is an interesting case study in reseting the dial on wing specs while achieving its fairly unique capabilities. Some people say the wing is still too big to make it a decent successor to the 767F, but I don't know if I buy that.

What do you think they'll do for the NG? Keep the current length with new wingtips/winglets, max out the 65m wingspan limit, or go farther beyond with folding wingtips?

Given that the 787 was supposed to be much lighter, I think the wing was designed correctly at the time for the 216t/228t MTOWs they had in mind. Seeing as the -9 and -10 selling today are at 254t, the wing seems a bit small, and 20/20 hindsight would probably have led them to a slightly larger span. That said, if a new set of engines comes along in another 5-10 years, it'll be back in the sweet spot and the 350 will be overbuilt by comparison.

Another factor to consider is that the plastic planes don't fatigue the same way as metal planes do, so A and B might have issues selling newer copies down the line because the current-gen models don't age out as quickly.
 
patrickjp93
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Re: 787 vs A350 range

Tue Sep 10, 2019 5:41 pm

LH707330 wrote:
Given that the 787 was supposed to be much lighter, I think the wing was designed correctly at the time for the 216t/228t MTOWs they had in mind. Seeing as the -9 and -10 selling today are at 254t, the wing seems a bit small, and 20/20 hindsight would probably have led them to a slightly larger span. That said, if a new set of engines comes along in another 5-10 years, it'll be back in the sweet spot and the 350 will be overbuilt by comparison.

Another factor to consider is that the plastic planes don't fatigue the same way as metal planes do, so A and B might have issues selling newer copies down the line because the current-gen models don't age out as quickly.

I've heard some on here say the fuselage of the 787 is overbuilt, so maybe they can save a couple tonnes there, fix up some plumbing, tweak the resin used for the composites, and then tweak the landing gear for the final weight reduction of, say, 6 tonnes? Every tonne of weight taken out of the frame though can go into cargo capacity though, so maybe keeping the MTOWs as they are is better. You can always restrict pax and cargo to extend range for ULH if needed after all.
 
flipdewaf
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Re: 787 vs A350 range

Wed Sep 11, 2019 12:34 pm

So I had some geek fun putting this together derived from my models. Based on the 2 aircraft we have been debating in the last few posts, 787-10 and the A359. I have put up some varying SFCs in the document, the 781 has 0.51 and 0.52 for cruise and the A359 has 0.5 and 0.51 (the A359 should have better SFC I believe but I decided to add the option to look at identical SFC in this instance)

The spreadsheet is a bit scruffy, I havent locked any cells out so technically you can edit whatever you like but the ones in yellow are the ones that I would expect people to tinker with. The SFC is not a linked cell but simply indicates what was used in the model for deriving the data.
You can edit hold time at 1500ft (in minutes)
DOW
Payload
Mission Range (still air)

https://drive.google.com/file/d/1TIiP99 ... sp=sharing

Any questions please ask.

Fred
Image
 
IgorD
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Re: 787 vs A350 range

Wed Sep 11, 2019 1:09 pm

Hi Fred, thanks, very interesting! Your model predicts a 2% fuel burn diffence for equal weights and SFCs, which is in agreement with my model, where I have an error margine of a few percent.

Once the models are calibrated & validated it is rather easy to answer essentially all questions on what frame is better and under what conditions.
 
Eyad89
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Re: 787 vs A350 range

Wed Sep 11, 2019 4:45 pm

flipdewaf wrote:
So I had some geek fun putting this together derived from my models. Based on the 2 aircraft we have been debating in the last few posts, 787-10 and the A359. I have put up some varying SFCs in the document, the 781 has 0.51 and 0.52 for cruise and the A359 has 0.5 and 0.51 (the A359 should have better SFC I believe but I decided to add the option to look at identical SFC in this instance)

The spreadsheet is a bit scruffy, I havent locked any cells out so technically you can edit whatever you like but the ones in yellow are the ones that I would expect people to tinker with. The SFC is not a linked cell but simply indicates what was used in the model for deriving the data.
You can edit hold time at 1500ft (in minutes)
DOW
Payload
Mission Range (still air)

https://drive.google.com/file/d/1TIiP99 ... sp=sharing

Any questions please ask.

Fred


That is in line with what I have always thought. A359 consumes slightly less per trip, but the higher floor area of 787-10 gives it a slightly lower CASM.
 
tealnz
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Re: 787 vs A350 range

Thu Sep 12, 2019 2:11 am

patrickjp93 wrote:
I've heard some on here say the fuselage of the 787 is overbuilt, so maybe they can save a couple tonnes there, fix up some plumbing, tweak the resin used for the composites, and then tweak the landing gear for the final weight reduction of, say, 6 tonnes? Every tonne of weight taken out of the frame though can go into cargo capacity though, so maybe keeping the MTOWs as they are is better. You can always restrict pax and cargo to extend range for ULH if needed after all.

6 tonnes would be a huge reduction. Remember after the torments of the early-build 788s Boeing put an immense effort into cleaning up the design for the 789, with particular focus on weight reduction as well as streamlining manufacture. They had a further opportunity to make refinements in developing the -10. From everything we read on a.net the structural differences between the -9 and -10 are minimal apart from those required for the extra length – so it doesn't look as if there was a lot of additional scope for weight reduction beyond what was achieved with the -9. What makes you imagine Boeing could get a further 6t out of the aircraft at this stage in its development?
 
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SQ22
Moderator
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Re: 787 vs A350 range

Thu Sep 12, 2019 10:20 am

Please discuss possible 787 improvements in the specific thread:

viewtopic.php?f=5&t=1411693

Thanks.
 
tommy1808
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Re: 787 vs A350 range

Thu Sep 12, 2019 4:49 pm

Eyad89 wrote:
flipdewaf wrote:
So I had some geek fun putting this together derived from my models. Based on the 2 aircraft we have been debating in the last few posts, 787-10 and the A359. I have put up some varying SFCs in the document, the 781 has 0.51 and 0.52 for cruise and the A359 has 0.5 and 0.51 (the A359 should have better SFC I believe but I decided to add the option to look at identical SFC in this instance)

The spreadsheet is a bit scruffy, I havent locked any cells out so technically you can edit whatever you like but the ones in yellow are the ones that I would expect people to tinker with. The SFC is not a linked cell but simply indicates what was used in the model for deriving the data.
You can edit hold time at 1500ft (in minutes)
DOW
Payload
Mission Range (still air)

https://drive.google.com/file/d/1TIiP99 ... sp=sharing

Any questions please ask.

Fred


That is in line with what I have always thought. A359 consumes slightly less per trip, but the higher floor area of 787-10 gives it a slightly lower CASM.


I don't think that hauling ~3% more cabin floor area around for ~3% more fuelburn gives you lower CASM....

Best regards
Thomas
This Singature is a safe space......
 
WIederling
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Re: 787 vs A350 range

Thu Sep 12, 2019 5:10 pm

tommy1808 wrote:
I don't think that hauling ~3% more cabin floor area around for ~3% more fuelburn gives you lower CASM....

787 math is different. ( Like "German Physics" :-))

What is the expectable delta from 789 to 7810 ( how much more drag has the -10 ? )
Murphy is an optimist
 
flipdewaf
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Re: 787 vs A350 range

Thu Sep 12, 2019 5:30 pm

WIederling wrote:
tommy1808 wrote:
I don't think that hauling ~3% more cabin floor area around for ~3% more fuelburn gives you lower CASM....

787 math is different. ( Like "German Physics" :-))

What is the expectable delta from 789 to 7810 ( how much more drag has the -10 ? )

A.net maths says a fuselage is approximately 20% of MTOW but heaven forbid should we think MTOW is 5x fuselage weight.

Fred


Sent from my iPhone using Tapatalk
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tommy1808
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Re: 787 vs A350 range

Thu Sep 12, 2019 5:33 pm

WIederling wrote:
tommy1808 wrote:
I don't think that hauling ~3% more cabin floor area around for ~3% more fuelburn gives you lower CASM....

787 math is different. ( Like "German Physics" :-))


Must be. Just look at 787-9 vs A330-300. Same cabin floor area to within 1/1000th, the 787 has 9-abrest economy, yet VS somehow has the same number of seats in a more premium heavy configuration on the Airbus.....

But that's truly off topic....

Best regards
Thomas
This Singature is a safe space......
 
Vladex
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Re: 787 vs A350 range

Sat Sep 28, 2019 1:45 pm

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
 
Eyad89
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Re: 787 vs A350 range

Sat Sep 28, 2019 4:07 pm

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.
 
majano
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Re: 787 vs A350 range

Sat Sep 28, 2019 4:47 pm

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.

A take-off run plus climb up to FL 350 probably account for the lion's share of the time (1 hour) and fuel (6.2 tons) of this flight. Those in the know could enlighten us perhaps.
 
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AECM
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Re: 787 vs A350 range

Sat Sep 28, 2019 5:01 pm

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.
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.
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