Which Frame Will Be More Efficient....The A35J or the 779?

Eyad89 · Wed Aug 22, 2018 9:49 pm

VV wrote:
We know that the target sfc for the GE9X is about 10% better than that of the GE90-115B.

Does anyone know what the expected overall L/D of the 777-9 compared to 777-300ER?

My wild estimate is between 5% to 8%, but the range is too large and it's only based on the aspect ratio deduced from the planform geometry found in the airport compatibility document.

I need a more accurate estimate.

Thanks.

While 779 has a considerably higher aspect ratio than 77W, its Cl should be lower than 77W at a certain altitude and speed. This should bring down the gap quite a bit.

But I guess you range of 5-6% sounds about right .

Taxi645 · Wed Aug 22, 2018 9:50 pm

Taxi645 wrote:
Matt6461 wrote:
@Taxi645 - moving lift inboard increases induced drag.
For example, when one models wingtip devices as extensions to span, one is just tracking the effect of the revised (outward) lift distribution versus a wing of equal span with the baseline distribution.
There's not much point to building a longer wing and then moving lift inboard to avoid the weight implications of your longer wing.
The only plane I know that did this is the A380.

flipdewaf wrote:
That almost all move the lift distribution somewhat inboard, it isnt something we have started doing recently. Just a trade off like any other. The trick is to only do it when required i.e at the limit cases. I would expect as the 779x is aimed at super long haul/heavy work then it is more highly outboard loaded than would otherwise be the case.

Fred

I'm referring to this: ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20160003578.pdf

But I have no idea if any of this has much relevancy in relation to modern airliner wing design.

I'll repost the question again as many seems more interested in b*tch fighting and chest thumbing. Is there a remote possibility that Boeing is using new insights on span load distribution (bell shaped rather than the conventional elliptical shape) in the design of the 777x wing as it's span and aspect ratio is quite a big leap from it's predecessor and other recent designs?

https://www.youtube.com/watch?v=w-dk1NpVNNI

smartplane · Wed Aug 22, 2018 9:52 pm

mjoelnir wrote:
For the A350-1000 the provisional numbers are there. For the 777-9 all the projected numbers but the projected OEW are there in the ACP for the 777-9 on Boeing´s website. Boeing must be operating with some numbers regarding OEW and payload when discussing the frames with the customers. That is were the ideas about a possible OEW are starting to leak out. It is of course the question, if Boeing will hit the projected specs.

If Boeing don't yet have the confidence to contract on the published / leaked numbers, and by inference ink guarantees and penalties, comparisons are 'pie in the sky' fun.

Yet there are contributors with real numbers for real aircraft whose contributions seem to be dismissed.

I overheard a client comment the 777X will climb like an A340, unless operators are willing to incur PBTH penalties. How would they know? They haven't ordered the 777X and don't operate the A340.

Which makes following these threads highly enjoyable, whether on the merits of cellos, new models just a glimmer in the eye of an OEM, writing off damaged air frames..............

Some will be right some of the time, but no-one will be right all of the time. Even those who 'know' have to stay silent, or tell porky pies from time to time, to avoid losing their livelihood.

zeke · Thu Aug 23, 2018 12:13 am

Matt6461 wrote:
You can't keep the same wing strength and increase MZFW, regardless of what you do with MTOW.

That can and has been done numerous times by Airbus. This has been achieved a number of ways, firstly through modifications to the wing load, through the flight control system they can use the FBW to unload the wing, Airbus calls the load alleviation function. Secondly when the wing is designed they assume a load spectrum at the design phase to calculate the actual loads, through in service experience they use in service loads to refine the spectrum. Then there is additional analysis that can be performed, until the wing is actually tested the designers are not sure exactly how much reserve load factor they have in their wing, after testing the wing they can through applying the measured loads in testing to the models change the maximum load.

Matt6461 wrote:

First there's no such thing as efficiency, next there's no such thing as design constraints.

My comments were directly related to your 40 : 60 influence of area and span on the weight of the wing being a design constraint. That is not a certification limit, while it might be a historical trend of previous designs, it does not mean that new materials, new design techniques etc result in designs that exceed that ratio.

RJMAZ wrote:
I'm not quite as conservative as you. If you combine a 3% SFC advantage to that 165T weight estimate you get a 777-8 that will outclimb the A358-1000. In a previous thread I estimated the 777-8 will take off at 326T when the A350-1000 is at 316T..

Is 165 tonnes reasonable for the 777-8 ?

To my understanding the main difference between the 777-9 and 777-8 is the 6.9 meters in fuselang length, wings and engines are common, similar to the 77W to the 77L. 777/77X share the same fuselage cross section.

Can you check to see if the following seems realistic ?

Difference in OEW 77W-77L, 167829-145150=22679 kg
Difference in length 77W-77L, 73.08-62.94=10.14 m
Average fuselage mass per meter 22679/10.14=2236 kg/m

Difference in length 779-778, 76.7-69.8 = 6.9 m
Projected mass drop based on previous average = 6.9x2236=15432 kg

Boeing projected in that previous document an OEW range of 184.6 to 188.2 tonnes for the 777-9, using the 15.4 tonne difference based upon the calculated average 777 fuselage mass per meter would place the 777-8 in the range of 169.1 to 172.7 tonnes.

strfyr51 · Thu Aug 23, 2018 12:30 am

So why is this Really a concern?None of you is going to influence whether any airline buys a B777-8 or-9 or the A350. This is purely academic. The A350 No matter How good they claim it is isn't going to affect the B778 or B779 sales one bit. Those whom Airbus can convince to buy their airplane will live and Die with their decision because it only depends on the Bottom line Just as the B778 or B779 will depend on the support that Boeing and GE gives them. And Boeing can discount their airplane every bit as much as Airbus if not more.

Matt6461 · Thu Aug 23, 2018 12:39 am

zeke wrote:
Matt6461 wrote:
You can't keep the same wing strength and increase MZFW, regardless of what you do with MTOW.

That can and has been done numerous times by Airbus. This has been achieved a number of ways, firstly through modifications to the wing load, through the flight control system they can use the FBW to unload the wing, Airbus calls the load alleviation function. Secondly when the wing is designed they assume a load spectrum at the design phase to calculate the actual loads, through in service experience they use in service loads to refine the spectrum. Then there is additional analysis that can be performed, until the wing is actually tested the designers are not sure exactly how much reserve load factor they have in their wing, after testing the wing they can through applying the measured loads in testing to the models change the maximum load.

Matt6461 wrote:

First there's no such thing as efficiency, next there's no such thing as design constraints.

My comments were directly related to your 40 : 60 influence of area and span on the weight of the wing being a design constraint. That is not a certification limit, while it might be a historical trend of previous designs, it does not mean that new materials, new design techniques etc result in designs that exceed that ratio.

RJMAZ wrote:
I'm not quite as conservative as you. If you combine a 3% SFC advantage to that 165T weight estimate you get a 777-8 that will outclimb the A358-1000. In a previous thread I estimated the 777-8 will take off at 326T when the A350-1000 is at 316T..

Is 165 tonnes reasonable for the 777-8 ?

To my understanding the main difference between the 777-9 and 777-8 is the 6.9 meters in fuselang length, wings and engines are common, similar to the 77W to the 77L. 777/77X share the same fuselage cross section.

Can you check to see if the following seems realistic ?

Difference in OEW 77W-77L, 167829-145150=22679 kg
Difference in length 77W-77L, 73.08-62.94=10.14 m
Average fuselage mass per meter 22679/10.14=2236 kg/m

Difference in length 779-778, 76.7-69.8 = 6.9 m
Projected mass drop based on previous average = 6.9x2236=15432 kg

Boeing projected in that previous document an OEW range of 184.6 to 188.2 tonnes for the 777-9, using the 15.4 tonne difference based upon the calculated average 777 fuselage mass per meter would place the 777-8 in the range of 169.1 to 172.7 tonnes.

Nothing in your reply relates to a direct MTOW/MZFW tradeoff. As usual, you're confused about the topic in dispute.

StTim · Thu Aug 23, 2018 1:01 am

Is it possible to respond without being snide? No wonder professionals are leaving this board.

zeke · Thu Aug 23, 2018 1:22 am

Matt6461 wrote:
Nothing in your reply relates to a direct MTOW/MZFW tradeoff. As usual, you're confused about the topic in dispute.

Your statement as I quoted was “You can't keep the same wing strength and increase MZFW, regardless of what you do with MTOW“, Airbus has done that many times. For example the basic A350-900 has a MTOW of 268 tonnes, and a MZFW of 192 tonnes. W/V 001 has a MTOW of 275 tonnes with a MZFW of 195.7 tonnes with the same airframe. Both an increase in MTOW and MZFW.

Reference section 2-1-0 page 1 in this document https://www.airbus.com/content/dam/corp ... 0-1000.pdf

I do not think I am “confused” at all, it is a full time job keeping up with your factual inaccuracies.

RJMAZ · Thu Aug 23, 2018 2:46 am

zeke wrote:
Can you check to see if the following seems realistic ?

Difference in OEW 77W-77L, 167829-145150=22679 kg
Difference in length 77W-77L, 73.08-62.94=10.14 m
Average fuselage mass per meter 22679/10.14=2236 kg/m

Difference in length 779-778, 76.7-69.8 = 6.9 m
Projected mass drop based on previous average = 6.9x2236=15432 kg

Boeing projected in that previous document an OEW range of 184.6 to 188.2 tonnes for the 777-9, using the 15.4 tonne difference based upon the calculated average 777 fuselage mass per meter would place the 777-8 in the range of 169.1 to 172.7 tonnes.

That is similar to how I did my calculation but I assumed the 777-9 was lighter so my 777-8 was then lighter.

If the 777-9 is 188T and the 777-8 172T then the 777-8 would probably have a fractionally higher fuel burn per hour compared to the A350-1000. The 777-8 would fly two full hours longer with the same payload weight but it would struggle to do Sydney to London.

If the 777-8 weighs only 165T it will probably have equal fuel burn per hour as the A350-1000. The 777-8 would fly 3 hours longer with the same payload weight. That extra hour flight time will probably be the difference to allow Sydney to London.

My weight estimates I also double checked by working backwards. Using published payload/range figures and using the predicted engine fuel burn to determine the fuel load required. If the 777-9 weighs 188T it probably couldn't reach the published payload range as it wouldn't be able to tank enough fuel. The wing and engine combo would need to perform better than expected.

In summary the engine SFC and OEW numbers make or break the program. If both miss by 1% then the performance will be clearly inferior to the A350-1000 across the board. If they beat the design goals by 1% then the 777X will sell in massive quantities.

I assume Qantas has not ordered the 777-8 for this reason. The closer we get to the first flight the more accurate fuel burn and weight numbers they will get.

I personally think the weight numbers posted here for the 777X are too high. These numbers would be accurate only if Boeing failed to hit the design target weight.

Matt6461 · Thu Aug 23, 2018 3:10 am

zeke wrote:
Matt6461 wrote:
Nothing in your reply relates to a direct MTOW/MZFW tradeoff. As usual, you're confused about the topic in dispute.

Your statement as I quoted was “You can't keep the same wing strength and increase MZFW, regardless of what you do with MTOW“, Airbus has done that many times. For example the basic A350-900 has a MTOW of 268 tonnes, and a MZFW of 192 tonnes. W/V 001 has a MTOW of 275 tonnes with a MZFW of 195.7 tonnes with the same airframe. Both an increase in MTOW and MZFW.

Reference section 2-1-0 page 1 in this document https://www.airbus.com/content/dam/corp ... 0-1000.pdf

I do not think I am “confused” at all, it is a full time job keeping up with your factual inaccuracies.

Once again nothing in your reply relates to a MZFW/MTOW tradeoff - the dynamic that mjoelnir claims is a basic feature of wing design.

Citing variations around a mean between different subvariants actually cuts against mjoelnir's case, as the two values move upwards together in the examples you cite, rather being traded off against each other as mjoelnir claims is the case. In any event, weight variants come with different maintenance schedules and/or reinforcement.

Try to understand the issue, then reply. You're still confused.

novarupta · Thu Aug 23, 2018 4:22 am

Matt6461 wrote:
zeke wrote:
Matt6461 wrote:
Nothing in your reply relates to a direct MTOW/MZFW tradeoff. As usual, you're confused about the topic in dispute.

Your statement as I quoted was “You can't keep the same wing strength and increase MZFW, regardless of what you do with MTOW“, Airbus has done that many times. For example the basic A350-900 has a MTOW of 268 tonnes, and a MZFW of 192 tonnes. W/V 001 has a MTOW of 275 tonnes with a MZFW of 195.7 tonnes with the same airframe. Both an increase in MTOW and MZFW.

Reference section 2-1-0 page 1 in this document https://www.airbus.com/content/dam/corp ... 0-1000.pdf

I do not think I am “confused” at all, it is a full time job keeping up with your factual inaccuracies.

Once again nothing in your reply relates to a MZFW/MTOW tradeoff - the dynamic that mjoelnir claims is a basic feature of wing design.

Citing variations around a mean between different subvariants actually cuts against mjoelnir's case, as the two values move upwards together in the examples you cite, rather being traded off against each other as mjoelnir claims is the case. In any event, weight variants come with different maintenance schedules and/or reinforcement.

Try to understand the issue, then reply. You're still confused.

What you keep saying can’t happen is precisely what Airbus did with regards to the A340 vs the A330 (particularly the -200/300 variants).....those extra pairs of engines provided bending relief on the wings, allowing for an increase of MZFW and MTOW without any additional strengthening of the basic wing structure (if I recall correctly).

Sent from my iPhone using Tapatalk Pro

zeke · Thu Aug 23, 2018 4:44 am

RJMAZ wrote:
If the 777-8 weighs only 165T it will probably have equal fuel burn per hour as the A350-1000. .

I like your optimism, however 165 tonnes is not going to happen, that is below the 77W. The 777-8 will be heavier than the 77W.

RJMAZ wrote:
The 777-8 would fly 3 hours longer with the same payload weight. That extra hour flight time will probably be the difference to allow Sydney to London.

Boeing is quoting 8690 nm for 365 pax, and Airbus with the A350-1000 8400 nm with 366 passengers, 290 nm difference, I know the A350 will cover its distance faster but it will not be 3 hours.

RJMAZ wrote:
If the 777-9 weighs 188T it probably couldn't reach the published payload range as it wouldn't be able to tank enough fuel. .

They increased the fuel volume over the 77W.

RJMAZ wrote:
If they beat the design goals by 1% then the 777X will sell in massive quantities.

Neither the Boeing of Airbus market forecasts would support a prediction of "massive quantities" for aircraft at the big end of town.

Matt6461 wrote:
Once again nothing in your reply relates to a MZFW/MTOW tradeoff - the dynamic that mjoelnir claims is a basic feature of wing design.

I quoted and corrected your inaccurate statements in that post and the previous one, no one else.

Eyad89 · Thu Aug 23, 2018 5:30 am

RJMAZ wrote:

Some examples. The 787-8 can go straight to 36,000ft at MTOW. The 787-9 can only go up to 32,000ft, same wing, heavier MTOW. The 777W can only go to 30,000ft it is underwinged.

Singapores A350-900 to north americas initial cruise is only 31,000ft. After 4 hours it climbs to 34,000ft and gets to 39,000ft after 8 hours.

We can’t conclude based on a single flight on a certain route. On the 16th of August, SQ’s A359 climbed straight away to 34,000 ft on the SIN-SFO route, and it spent roughly the last 40% cruising at 41,000 ft.

And on the 22nd of August, SQ’s A359 climbed immediately to 37,000 on the MAN-SIN route, 35 mins after takeoff. This takeoff isnt at MTOW, but it’s close enough.

RJMAZ wrote:
I would expect the A350-1000 to not reach 30,000ft at MTOW.

Well, we don’t have many A35Ks flying around, the longest I’ve found is QR16 from LHR to DOH, and on the 20th of August it climbed straight away to 39,000 ft half an hour after takeoff. As for QR’s 77W, it climbs immediately to 35,000 ft in the same route (QR 8). I would be really surprised if 77W gets a higher initial climb than A35K, so I think your guess of A35K not being able to even get up to 30,000 ft at MTOW is a bit too much. A35K has a pretty low wing loading and power loading.

zeke · Thu Aug 23, 2018 5:51 am

Eyad89 wrote:
We can’t conclude based on a single flight on a certain route. On the 16th of August, SQ’s A359 climbed straight away to 34,000 ft on the SIN-SFO route, and it spent roughly the last 40% cruising at 41,000 ft.

The 359 will go to FL350 departing at MTOW, I haven’t flown the 35K anywhere near max weights year, regionally it is performing line the 359. I suspect on long haul it will 200 ft below initially and joining the same profile as the 359 as fuel is burnt off.

The A350 does not like high ISA temperatures at cruise, eg ISA+15-20

VV · Thu Aug 23, 2018 6:44 am

zeke wrote:
Eyad89 wrote:
We can’t conclude based on a single flight on a certain route. On the 16th of August, SQ’s A359 climbed straight away to 34,000 ft on the SIN-SFO route, and it spent roughly the last 40% cruising at 41,000 ft.

The 359 will go to FL350 departing at MTOW, I haven’t flown the 35K anywhere near max weights year, regionally it is performing line the 359. I suspect on long haul it will 200 ft below initially and joining the same profile as the 359 as fuel is burnt off.

The A350 does not like high ISA temperatures at cruise, eg ISA+15-20

In which part of the world do you find ISA+15C ISA+20C at A350's cruise altitudes?

Thanks

RJMAZ · Thu Aug 23, 2018 7:08 am

Eyad89 wrote:
We can’t conclude based on a single flight on a certain route. On the 16th of August, SQ’s A359 climbed straight away to 34,000 ft on the SIN-SFO route, and it spent roughly the last 40% cruising at 41,000 ft.

And on the 22nd of August, SQ’s A359 climbed immediately to 37,000 on the MAN-SIN route, 35 mins after takeoff. This takeoff isnt at MTOW, but it’s close enough.

I did look at around 100 samples of 777, 787, A350's. Its very hard to find an aircraft taking off at MTOW to see the worse case climb profile. Granted the data is probably too rough to get a solid conclusion.

If the route is only 4000-5000nm the aircraft could be taking off 20+T below maximum takeoff weight which would allow it to have a high initial cruise altitude. I did find enough transpacific flights to get a rough idea.

Eyad89 wrote:
I would be really surprised if 77W gets a higher initial climb than A35K, so I think your guess of A35K not being able to even get up to 30,000 ft at MTOW is a bit too much. A35K has a pretty low wing loading and power loading.

The A35K will definitely out climb the 77W. The 77W has a very low initial cruise altitude as it has a high wing loading. I was talking about the 777X it will have much better climb performance than its predecessor and maybe slightly better climb performance than the A35K on a similar flight. At MTOW the 778 may climb slower than the A35K but the 778 doesnt need to take off at MTOW to match a maxed out A35K.

flipdewaf · Thu Aug 23, 2018 9:48 am

Matt6461 wrote:
flipdewaf wrote:
Basics

Quick reply from phone:
On the basics you present the A380's wing should be ~11x heavier than 737's. [ (262/118)^3 ]

Obviously that's not the case. It's more like 7x.

So something must account for your model's 70% overshoot.

Matt6461 wrote:
flipdewaf wrote:
for a distributed load the maximum bending stress will rise with the third power of the length of the cantilevered beam.

That statement assumes that the force per distance remains the same for the distributed load as you extend the beam's length.

If, on the other hand, the the total magnitude of the resultant of the distributed force vector is constant before and after extending the beam, then the bending moment caused by the resultant vector of the distributed load increases only linearly with the length of the beam.

That's the case with lift: keeping wing area and Cl constant and merely extending span results in linear escalation of the bending moment (resultant vector is equal in magnitude, lever arm moves with span).

Of course that doesn't mean a merely linear escalation of material required because we have to consider the moment of inertia of our now-thinned wing as well as the greater.length of the beam.

But then we need to consider the position and magnitude of the resultant bending moments (i.e. the bending relief) caused by our longer, heavier beam.

...all of this is to say that yes span costs a lot but, as my A380/737 example shows, it's far more complicated than simple cubic escalation of wing weight with span.

As a correction from my previous statement the bending stresses do only infact increase with the square of the span, it is the mass that is required to carry those loads that increases with the cube of the span.

Bending moments do increase as the square of the span for a distributed load but the mechanism of carrying those loads is compression in the top surface and tension in the bottom.
Imagine that you are carrying a compressive load of X on a rod of length Y. If you now make the Rod 2*Y and increase the compressive force by 4 (imitating the increase in bending moment) how much must your rod weigh to carry those new forces?

You ask why the A380 isnt 11 x the 737? well interestingly my models put the A380 at about 10x that of the A320 but as the A380 has a very big chord length then it also has a correspondingly large thickness and therefore stiffness due to the high second moment of area.

I have no reference for the 737 wing weight so it is difficult to judge and understand. I did in the past have some reference breakdowns of weight but cant seem to find them at the moment. Do you have any reference?

When I build a quick model of the bending stresses on a wing box I get the scales almost exactly as I mentioned previously. A320 about 5t for the top and bottom skins, assuming that there is good design of stiffening and the A380 comes out at about 50t.

Fred

tommy1808 · Thu Aug 23, 2018 9:50 am

SomebodyInTLS wrote:
Second; a circle is mathematically the most efficient way to enclose a cross-sectional area - so a cyclinder will always have the smallest surface area of any tube enclosing a given volume. I'm not exactly sure what Zeke is getting at... unless he's hinting that the rounding at nose and tail means a typical fuselage has less surface area that a fully cylindrical fuselage would have.

Yes and no. A cylinder will have the smallest surface area for a given volume, but airliners are not designed for a volume, they are defined to enclose two LD3 and a 9/10 abreast seating with the optimum combination of surface area and structural weight.
Steeper side walls and flatenend out top reduce surface area to enclose that, and the steeper walls give the fuselage more strength for a given amount of material against vertical bending forces.

If that wasn't the case, am aircraft would have circular fuselages.

Best regards
Thomas

SomebodyInTLS · Thu Aug 23, 2018 11:59 am

zeke wrote:
SomebodyInTLS wrote:
Second; a circle is mathematically the most efficient way to enclose a cross-sectional area - so a cyclinder will always have the smallest surface area of any tube enclosing a given volume. I'm not exactly sure what Zeke is getting at... unless he's hinting that the rounding at nose and tail means a typical fuselage has less surface area that a fully cylindrical fuselage would have.

The shape of the A350 fuselage I have seen referenced as a double-lobe ovoid design. To get 9 seats across in economy you need a dimension at parallel to the floor at shoulder height to fit passengers in, you need a different dimension for two containers in the cargo hold, and at floor level you really only need a similar dimension as the shoulder level to fit the base of the seats in. If you base a circular cross section upon the width parallel to the floor for shoulder room there is an waste of space at floor level. The optimum shape is for flatter sides, not circular, which has less surface area, and less material, i.e. less drag, and less weight.

Okay, gotcha (now that you've qualified what you meant).

zeke · Thu Aug 23, 2018 1:21 pm

VV wrote:
In which part of the world do you find ISA+15C ISA+20C at A350's cruise altitudes?

Thanks

I have seen it around HKG and MNL normally associated with large weather systems, in China around jetsteams, coming out of TLV, over the North Pole.

VV · Thu Aug 23, 2018 2:22 pm

zeke wrote:
VV wrote:
In which part of the world do you find ISA+15C ISA+20C at A350's cruise altitudes?

Thanks

I have seen it around HKG and MNL normally associated with large weather systems, in China around jetsteams, coming out of TLV, over the North Pole.

Oh I didn't know it happens all over the world very frequently.

RandWkop · Thu Aug 23, 2018 5:43 pm

zeke wrote:
Eyad89 wrote:
We can’t conclude based on a single flight on a certain route. On the 16th of August, SQ’s A359 climbed straight away to 34,000 ft on the SIN-SFO route, and it spent roughly the last 40% cruising at 41,000 ft.

The 359 will go to FL350 departing at MTOW, I haven’t flown the 35K anywhere near max weights year, regionally it is performing line the 359. I suspect on long haul it will 200 ft below initially and joining the same profile as the 359 as fuel is burnt off.

The A350 does not like high ISA temperatures at cruise, eg ISA+15-20

Can you expand on why the 350 doesn't like these temperatures?

Matt6461 · Thu Aug 23, 2018 6:12 pm

flipdewaf wrote:
my models

If it's true, as you suggest, that increasing wing area for a given span should *reduce* wing weight, then the ascending weight rank of the following 65m wings would be:

Lightest: 747-400
Next Lightest: 777-300ER
Heaviest: A330NEO

...because wing area decreases as we go down that list.

That doesn't pass the smell test, IMO. I get what you're saying about material versus bending moment for a distributed load, but I'd guess you're discounting wing factors beyond the max bending moment on the vertical plane at MZFW. The torsional moment, for example, increases with the length of the wing root. Wing ribs and other load paths along the fore/aft axis have to strengthened as their cantilevered distance from the wing spars increase (recall that these ribs failed in the A380 and some weight had to be added).

flipdewaf · Thu Aug 23, 2018 7:36 pm

Matt6461 wrote:
flipdewaf wrote:
my models

If it's true, as you suggest, that increasing wing area for a given span should *reduce* wing weight, then the ascending weight rank of the following 65m wings would be:

Lightest: 747-400
Next Lightest: 777-300ER
Heaviest: A330NEO

...because wing area decreases as we go down that list.

That doesn't pass the smell test, IMO. I get what you're saying about material versus bending moment for a distributed load, but I'd guess you're discounting wing factors beyond the max bending moment on the vertical plane at MZFW.

yes, in simple terms. I built a quick model during my lunch break at work today and I’ll send you it tomorrow if I remember. It demonstrates the phenomenon we speak of. The part that you say doesn’t pass the smell test is because the MZFW plays a role in the wing weight too.

Matt6461 wrote:
The torsional moment, for example, increases with the length of the wing root. Wing ribs and other load paths along the fore/aft axis have to strengthened as their cantilevered distance from the wing spars increase (recall that these ribs failed in the A380 and some weight had to be added).

I have some more models I built at uni that help locate and size the stiffening ribs and takes torsion effects into account from the engines the sweep and the moment from lift but my memory does not serve me well enough to drive them at the moment but by far and away the biggest driver of wing weight is the stiffness required for the bending moment.

Fred

Edit:remember to think of span of the length of the wing, 37degrees of sweep make a difference.

rheinwaldner · Fri Aug 24, 2018 5:37 am

Matt6461 wrote:
If it's true, as you suggest, that increasing wing area for a given span should *reduce* wing weight, then the ascending weight rank of the following 65m wings would be:

Lightest: 747-400
Next Lightest: 777-300ER
Heaviest: A330NEO

...because wing area decreases as we go down that list.

I could imagine, that a number of other key parameter should stay constant, for these models to be applicable: e.g. MTOW, number of engines, design and arrangement of gears and HLD and others. If these things change from wing to wing, I am quite sure that the resulting absolute weight does not depend so much on Freds model.

Hence the discrepancy between 737 and A380.

I assume we can expect a much higher accuracy of the model, if we study different wing options for the same aircraft (e,g, 777X wings vs 77W wing) or at least very similar configurations (A350 wings vs 777 wings).

keesje · Fri Aug 24, 2018 7:11 am

I think in the end Boeing will be forced to use the 777X to its maximum potential, a stretch with 120k lbs engines placing it at some distance from even a pumpep up A350-1000R. With all respect the current 777-8/9 does not look superior to do A350 family. The high empty weight isn't compensated enough with extra usefull capability.

I'm convinced such a large heavy version is already baked into the massive wings, engines and landing gears.

WIederling · Fri Aug 24, 2018 7:40 am

Matt6461 wrote:
(recall that these ribs failed in the A380 and some weight had to be added).

That was not structural but a materials mismatch ( and some other design detail things ) issue.

If you feel bored out you could plot MTOW vs span on a logarithmic scale(s).
( and you'll find that the A380 is pretty in line with other frames.)

SteinarN · Fri Aug 24, 2018 10:10 am

I have not seen much mentioning of the effect of wing thickness on the wing weight. Clearly a thick wing, especially thickness inboard or closer to the fuselage, will make for a lighter wing when keeping the other geometric parameters constant. Ofc, you cant add thickness as you wish as it (hugely) affects the air flow over the wing. But isn't one reason for the A330 (neo) beeing so close in efficiency to the B787 that the A330 wing is fairly thick and by that it is relatively lighter than it would have been if it was thinner like the B787 wing is?

flipdewaf · Fri Aug 24, 2018 10:49 am

SteinarN wrote:
I have not seen much mentioning of the effect of wing thickness on the wing weight. Clearly a thick wing, especially thickness inboard or closer to the fuselage, will make for a lighter wing when keeping the other geometric parameters constant. Ofc, you cant add thickness as you wish as it (hugely) affects the air flow over the wing. But isn't one reason for the A330 (neo) beeing so close in efficiency to the B787 that the A330 wing is fairly thick and by that it is relatively lighter than it would have been if it was thinner like the B787 wing is?

Absolutely, that's why when you increase chord with the same t/c your weight reduces and why higher ARs are so expensive in terms of weight.

My understanding on the Airbus vs Boeing wing design philosophy (at least historically) is that Airbus use a ticker wing (detrimental to compressibility effects) to be able to manage the torsion from the outer wing better meaning that the twist from the outer ailerons doesn't induce control reversal and so cutting out the need for an inboard high speed aileron as on a Boeing giving a cleaner flap line for increased effectiveness on the flaps, the norm for a long time was single slotted continuous on airbus with double slotted with a high speed aileron on the Boeings. Its a trade off as ever.

Fred

SteinarN · Fri Aug 24, 2018 12:30 pm

flipdewaf wrote:
SteinarN wrote:
I have not seen much mentioning of the effect of wing thickness on the wing weight. Clearly a thick wing, especially thickness inboard or closer to the fuselage, will make for a lighter wing when keeping the other geometric parameters constant. Ofc, you cant add thickness as you wish as it (hugely) affects the air flow over the wing. But isn't one reason for the A330 (neo) beeing so close in efficiency to the B787 that the A330 wing is fairly thick and by that it is relatively lighter than it would have been if it was thinner like the B787 wing is?

Absolutely, that's why when you increase chord with the same t/c your weight reduces and why higher ARs are so expensive in terms of weight.

My understanding on the Airbus vs Boeing wing design philosophy (at least historically) is that Airbus use a ticker wing (detrimental to compressibility effects) to be able to manage the torsion from the outer wing better meaning that the twist from the outer ailerons doesn't induce control reversal and so cutting out the need for an inboard high speed aileron as on a Boeing giving a cleaner flap line for increased effectiveness on the flaps, the norm for a long time was single slotted continuous on airbus with double slotted with a high speed aileron on the Boeings. Its a trade off as ever.
Fred

Interesting. I am aware of the consept of aileron control reversal, but I hadnt thought abou this aspect regarding thickness and weight considerations. But it makes completly sense when you bring it up.

I have seen a number somewhere, but I dont know where, comparing the thickness to span ratio of the B787 wing and the A330 wing, and the B787 wing had only about 80% or something like that of the thickness to span ratio of the A330 wing. I dont know how the B777W and B777X wing compares to the A330 wing, but it would have been very interesting to know.

par13del · Fri Aug 24, 2018 12:49 pm

keesje wrote:
I think in the end Boeing will be forced to use the 777X to its maximum potential, a stretch with 120k lbs engines placing it at some distance from even a pumpep up A350-1000R. With all respect the current 777-8/9 does not look superior to do A350 family.

The question would be which A350 are you talking about, the one initially proposed, the one that went into service or the revisions that have since taken place?
The 777X is not yet flying, the process mandates a design freeze, once that occurred, anything that the competitor does cannot be addressed until the frame is flying, in which case, we still have time to wait and see what the initial product can do in testing.

VV · Fri Aug 24, 2018 4:57 pm

According to my estimates, that I already mentioned in my blog, the A350-1000 and 777-9 would be in the same ballpark if the fuel burn is expressed on per seat basis. This is obtained using the airframers' seat count.

The 777-9 is normally much heavier than the A350-1000. However, the difference of capacity compensate the fuel burn on per trip basis.

So it depends on how you want to express the "efficiency".

I ran the estimates several times and always end up with fuel burn on per seat basis that is still within the uncertainty at this stage.

If you don't need the capacity, then obviously the A350-1000 matches better your need. If you need that capacity for long haul flights then 777-9 seems to be more interesting.

Of course it is not always about cost on per seat basis, you also need to bake in the revenue.

OldAeroGuy · Fri Aug 24, 2018 6:51 pm

VV wrote:
According to my estimates, that I already mentioned in my blog, the A350-1000 and 777-9 would be in the same ballpark if the fuel burn is expressed on per seat basis. This is obtained using the airframers' seat count.

The 777-9 is normally much heavier than the A350-1000. However, the difference of capacity compensate the fuel burn on per trip basis.

So it depends on how you want to express the "efficiency".

I ran the estimates several times and always end up with fuel burn on per seat basis that is still within the uncertainty at this stage.

If you don't need the capacity, then obviously the A350-1000 matches better your need. If you need that capacity for long haul flights then 777-9 seems to be more interesting.

Of course it is not always about cost on per seat basis, you also need to bake in the revenue.

Cathay Pacific, Etihad Airways, Iran Air (probably moot) and Qatar Airways have performance guarantees for both airplanes that would answer the question posed by this thread. If only an employee from one of these airlines would leak a little comparison from these guarantees, we could get at least a preliminary answer.

Revelation · Fri Aug 24, 2018 8:03 pm

par13del wrote:
The 777X is not yet flying, the process mandates a design freeze, once that occurred, anything that the competitor does cannot be addressed until the frame is flying, in which case, we still have time to wait and see what the initial product can do in testing.

I'm not sure what you are getting at. Development continues between design freeze and first flight. Some of those development efforts can be responses to competitive issues.

VV · Fri Aug 24, 2018 8:38 pm

OldAeroGuy wrote:
VV wrote:
According to my estimates, that I already mentioned in my blog, the A350-1000 and 777-9 would be in the same ballpark if the fuel burn is expressed on per seat basis. This is obtained using the airframers' seat count.

The 777-9 is normally much heavier than the A350-1000. However, the difference of capacity compensate the fuel burn on per trip basis.

So it depends on how you want to express the "efficiency".

I ran the estimates several times and always end up with fuel burn on per seat basis that is still within the uncertainty at this stage.

If you don't need the capacity, then obviously the A350-1000 matches better your need. If you need that capacity for long haul flights then 777-9 seems to be more interesting.

Of course it is not always about cost on per seat basis, you also need to bake in the revenue.

Cathay Pacific, Etihad Airways, Iran Air (probably moot) and Qatar Airways have performance guarantees for both airplanes that would answer the question posed by this thread. If only an employee from one of these airlines would leak a little comparison from these guarantees, we could get at least a preliminary answer.

Guarantees can be missed or met or bettered.

Guarantees don't guarantee anything from technical perspective. I hope people understand what it means, don't expect me to explain further.

planecane · Fri Aug 24, 2018 8:46 pm

VV wrote:
According to my estimates, that I already mentioned in my blog, the A350-1000 and 777-9 would be in the same ballpark if the fuel burn is expressed on per seat basis. This is obtained using the airframers' seat count.

The 777-9 is normally much heavier than the A350-1000. However, the difference of capacity compensate the fuel burn on per trip basis.

So it depends on how you want to express the "efficiency".

I ran the estimates several times and always end up with fuel burn on per seat basis that is still within the uncertainty at this stage.

If you don't need the capacity, then obviously the A350-1000 matches better your need. If you need that capacity for long haul flights then 777-9 seems to be more interesting.

Of course it is not always about cost on per seat basis, you also need to bake in the revenue.

In addition to the seating capacity, can the 777-9 carry more revenue cargo the same distance as the A350-1000 (after filling all the seats)? If yes, then this could be another benefit to pay for the increased fuel burn.

Eyad89 · Fri Aug 24, 2018 8:59 pm

zeke wrote:
Eyad89 wrote:
We can’t conclude based on a single flight on a certain route. On the 16th of August, SQ’s A359 climbed straight away to 34,000 ft on the SIN-SFO route, and it spent roughly the last 40% cruising at 41,000 ft.

The 359 will go to FL350 departing at MTOW, I haven’t flown the 35K anywhere near max weights year, regionally it is performing line the 359. I suspect on long haul it will 200 ft below initially and joining the same profile as the 359 as fuel is burnt off.

The A350 does not like high ISA temperatures at cruise, eg ISA+15-20

You are right, SQ’s A359 climbed immediatley to 35,000 ft in today’s SIN-SFO, and that took 30 mins. It’s as if the pilot read this threat and he had something to prove lol.

flipdewaf · Fri Aug 24, 2018 9:14 pm

planecane wrote:
VV wrote:
According to my estimates, that I already mentioned in my blog, the A350-1000 and 777-9 would be in the same ballpark if the fuel burn is expressed on per seat basis. This is obtained using the airframers' seat count.

The 777-9 is normally much heavier than the A350-1000. However, the difference of capacity compensate the fuel burn on per trip basis.

So it depends on how you want to express the "efficiency".

I ran the estimates several times and always end up with fuel burn on per seat basis that is still within the uncertainty at this stage.

If you don't need the capacity, then obviously the A350-1000 matches better your need. If you need that capacity for long haul flights then 777-9 seems to be more interesting.

Of course it is not always about cost on per seat basis, you also need to bake in the revenue.

In addition to the seating capacity, can the 777-9 carry more revenue cargo the same distance as the A350-1000 (after filling all the seats)? If yes, then this could be another benefit to pay for the increased fuel burn.

When the 779x is full of pax it goes 7560nm whereas the A351 will go 8400nm. If the A 351 were to go 7560nm then it may have available MTOW reserves of some ~12t (1.5hrs fuel). Not sure if the max payload of both aircraft so there may be a cross over somewhere at lower ranges.

Fred

Sent from my iPhone using Tapatalk

OldAeroGuy · Fri Aug 24, 2018 9:39 pm

VV wrote:
OldAeroGuy wrote:
VV wrote:
According to my estimates, that I already mentioned in my blog, the A350-1000 and 777-9 would be in the same ballpark if the fuel burn is expressed on per seat basis. This is obtained using the airframers' seat count.

The 777-9 is normally much heavier than the A350-1000. However, the difference of capacity compensate the fuel burn on per trip basis.

So it depends on how you want to express the "efficiency".

I ran the estimates several times and always end up with fuel burn on per seat basis that is still within the uncertainty at this stage.

If you don't need the capacity, then obviously the A350-1000 matches better your need. If you need that capacity for long haul flights then 777-9 seems to be more interesting.

Of course it is not always about cost on per seat basis, you also need to bake in the revenue.

Cathay Pacific, Etihad Airways, Iran Air (probably moot) and Qatar Airways have performance guarantees for both airplanes that would answer the question posed by this thread. If only an employee from one of these airlines would leak a little comparison from these guarantees, we could get at least a preliminary answer.

Guarantees can be missed or met or bettered.

Guarantees don't guarantee anything from technical perspective. I hope people understand what it means, don't expect me to explain further.

All guarantees have some technical basis. If they don't, the OEM can be subject to substantial liquidated damages.

A comparison of guaranteed OEW, fuel burn and payload for specific routes would be more meaningful than much of the speculation in this thread.

zeke · Fri Aug 24, 2018 10:51 pm

planecane wrote:
In addition to the seating capacity, can the 777-9 carry more revenue cargo the same distance as the A350-1000 (after filling all the seats)? If yes, then this could be another benefit to pay for the increased fuel burn.

This is history repeating itself again. The A340-600 carried more payload over a given distance than the 77W but did so at a higher fuel burn. In reality airlines never fly around all the time 100% full, so as soon as you move away from full aircraft the most flexible aircraft wins. A good way to see how much weight you would be carrying at less than full loads is to look at the empty weight per seat, the 77W has lower empty weight per seat compared to the A340-600.

There is already an overcapacity of belly freight capacity in the market. It makes little sense to fly freight ULH unless it has very high value and I s time sensitive. A one or many stop connection for the same freight can be flown st much lower cost with not that much difference in time.

The strength of the 777-9 over the A350-1000 is the additional cabin area which airlines can configure with a higher premium cabin or with more seats. It will need to deployed on the routes which need that additional seating capacity.

OldAeroGuy wrote:
All guarantees have some technical basis. If they don't, the OEM can be subject to substantial liquidated damages.

A comparison of guaranteed OEW, fuel burn and payload for specific routes would be more meaningful than much of the speculation in this thread.

I agree that the contractural basis does have a technical basis. There is already more than enough on this thread to know where Boeing was pitching the 77X.

Earlier in this thread there was a graphic posted which suggested the projected OEW of the 777-9 would be between 184.6-188.2 tonnes, with 400 seats that puts the empty weight per seat around 450-460 kg/seat. Similar the 777-8 assuming 15 tonnes lighter based upon a 6.9 meter shorter fuselage with 350 seats would range between 480-490 kg/seat.

The A350-900 based on 300 seats with as built weights is around 450 kg/seat, and the A350-1000 with 350 seats around 420 kg/seat.

The biggest challenge for the 777-X seems to be weight.

zeke · Sat Aug 25, 2018 5:37 am

RJMAZ wrote:
If they are correct then Airbus must have sprinkled some magic fairy dust on the A350-1000.

from http://aviationweek.com/singapore-airsh ... re-airshow the empty weight after the flight testing was completed was found to be on specification at 129 tonnes.

"Revealing the outcome of recently completed flight tests, Airbus says the Rolls-Royce Trent XWB97-powered aircraft is meeting or beating performance targets. Empty weight is on specification at 129,000 kg (284,000 lb.), while noise is slightly better than expected with a 16.5 EPNdB (effective perceived noise in decibels) margin to ICAO Chapter 4 standards, allowing the aircraft to meet the stringent QC0.5/1 rules for nighttime operations at London Heathrow – a global yardstick for noise-sensitive arrivals and departures.

In recent testing the aircraft also showed better-than-expected airfield performance, with the ability to take off at more than 5.3 tonnes higher weights in hot weather conditions, 7.2 tonnes greater weights than forecast out of obstacle limited runways and 3.8 tonnes better out of high altitude airfields. Airbus has meanwhile delivered 142 of the smaller A350-900 sibling version and says dispatch reliability is currently at 99.3%."

jagraham · Sat Aug 25, 2018 6:47 am

flipdewaf wrote:
planecane wrote:
VV wrote:
According to my estimates, that I already mentioned in my blog, the A350-1000 and 777-9 would be in the same ballpark if the fuel burn is expressed on per seat basis. This is obtained using the airframers' seat count.

The 777-9 is normally much heavier than the A350-1000. However, the difference of capacity compensate the fuel burn on per trip basis.

So it depends on how you want to express the "efficiency".

I ran the estimates several times and always end up with fuel burn on per seat basis that is still within the uncertainty at this stage.

If you don't need the capacity, then obviously the A350-1000 matches better your need. If you need that capacity for long haul flights then 777-9 seems to be more interesting.

Of course it is not always about cost on per seat basis, you also need to bake in the revenue.

In addition to the seating capacity, can the 777-9 carry more revenue cargo the same distance as the A350-1000 (after filling all the seats)? If yes, then this could be another benefit to pay for the increased fuel burn.

When the 779x is full of pax it goes 7560nm whereas the A351 will go 8400nm. If the A 351 were to go 7560nm then it may have available MTOW reserves of some ~12t (1.5hrs fuel). Not sure if the max payload of both aircraft so there may be a cross over somewhere at lower ranges.

Fred

Sent from my iPhone using Tapatalk

VV · Sat Aug 25, 2018 8:28 am

OldAeroGuy wrote:

All guarantees have some technical basis. If they don't, the OEM can be subject to substantial liquidated damages.

A comparison of guaranteed OEW, fuel burn and payload for specific routes would be more meaningful than much of the speculation in this thread.

Indeed there is absolutely no guarantee the guaranteed numbers will be met.

It is not very useful to compare guarantees when you want to know the reality about fuel efficiency.

XAM2175 · Sat Aug 25, 2018 9:43 am

VV wrote:
OldAeroGuy wrote:
All guarantees have some technical basis. If they don't, the OEM can be subject to substantial liquidated damages.

Indeed there is absolutely no guarantee the guaranteed numbers will be met.

Excellent example here being the MD-11 - which was always going to have a difficult time selling given it was a warmed-over DC-10 going against the 767-300ER and the Airbus and Boeing proposals that would become the A330, A340, and 777 respectively - but that was almost completely abandoned by several key customers when it became apparent that the initial P&W-powered models had been advertised as having a 7000 nmi / 13000 km range with 61,000 lbs / 28,000 kg payload but could in fact only;

SQ cancelled their 20 orders and took the same number of A343s instead, while AA held out but sold their 19 to FX in 1995 when even after MDD and P&W delivered a PIP the aircraft still couldn't fly DFW-HKG.

Polot · Sat Aug 25, 2018 12:43 pm

VV wrote:
OldAeroGuy wrote:

All guarantees have some technical basis. If they don't, the OEM can be subject to substantial liquidated damages.

A comparison of guaranteed OEW, fuel burn and payload for specific routes would be more meaningful than much of the speculation in this thread.

Indeed there is absolutely no guarantee the guaranteed numbers will be met.

It is not very useful to compare guarantees when you want to know the reality about fuel efficiency.

It’s not very useful to talk about the reality about fuel efficiency when one of the planes has not even completed assembly yet let alone flown. The reality is we don’t know the 777X’s fuel efficiency so any discussion has to be on educated opinion or assumption. Until then we don’t know if the 777X will miss assumptions (a la the MD-11) or beat them (a la the 77W).

WIederling · Sat Aug 25, 2018 12:48 pm

educated opinion or assumption.

Always interesting how educated guessing converges on reality.
( OK, sometimes not. )
Sad if this is muddied by those going for winning an argument
in lieu of gaining knowledge.

Polot · Sat Aug 25, 2018 12:50 pm

WIederling wrote:
educated opinion or assumption.

Always interesting how educated guessing converges on reality.
( OK, sometimes not. )
Sad if this is muddied by those going for winning an argument
in lieu of gaining knowledge.

If you have the 777X’s numbers by all means share with the class. Until you do you are just making assumptions based on information that Boeing has given.

VV · Sat Aug 25, 2018 1:42 pm

XAM2175 wrote:
VV wrote:
OldAeroGuy wrote:
All guarantees have some technical basis. If they don't, the OEM can be subject to substantial liquidated damages.

Indeed there is absolutely no guarantee the guaranteed numbers will be met.

Excellent example here being the MD-11 - which was always going to have a difficult time selling given it was a warmed-over DC-10 going against the 767-300ER and the Airbus and Boeing proposals that would become the A330, A340, and 777 respectively - but that was almost completely abandoned by several key customers when it became apparent that the initial P&W-powered models had been advertised as having a 7000 nmi / 13000 km range with 61,000 lbs / 28,000 kg payload but could in fact only;
achieve that range by cutting payload to 48,500 lbs / 22,000 kg, or
achieve that payload by cutting range to 6493 nmi / 12,025 km

SQ cancelled their 20 orders and took the same number of A343s instead, while AA held out but sold their 19 to FX in 1995 when even after MDD and P&W delivered a PIP the aircraft still couldn't fly DFW-HKG.

It is very often forgotten that there have been 200 MD11 deliveries. Although it didn't meet the promised (or was it guaranteed?) performance, it fulfilled the needs of several airlines.

There are other aircraft programs with fewer than 200 deliveries.

There may have been other guarantee failure occurrences. I know nothing about it, but if MD11 is a known example, perhaps it was not the only and unique case.

As far as an outsider like us is concerned, the only way to evaluate and compare the efficiency of the A350-1000 and 777-9 is to use the different declaration of each airframes.

So far, my estimates put the two aircraft in the same ballpark if the efficiency is evaluated on per seat basis using the passenger count provided by the manufacturers and it is estimated within an acceptable uncertainty band.

As previously mentioned, the choice of aircraft between the A350-1000 and 777-9 will be based on other criteria than fuel cost on per seat basis. I do not know what those criteria are.

mk2 · Mon Aug 27, 2018 7:22 pm

In the following thread, we managed to have a good conversation on the A359 and 35K OEW.

viewtopic.php?f=5&t=1370539

A number of persons contributed OEW data from airline experience.

I extrapolated the OEW from the Airbus A350 ACAP:

A359 OEW is about 138 700 kg
A35K OEW is about 155 800 kg

For more details, please go through the thread.

smartplane · Mon Aug 27, 2018 8:59 pm

OldAeroGuy wrote:
Cathay Pacific, Etihad Airways, Iran Air (probably moot) and Qatar Airways have performance guarantees for both airplanes that would answer the question posed by this thread. If only an employee from one of these airlines would leak a little comparison from these guarantees, we could get at least a preliminary answer.

Think you might be referring to scaled performance guarantees, where Boeing previously offered a series of 'adjusted' purchase prices, linked to different performance, to entice 2-3 'easier to please' customers to go unconditional.

No customer has gone unconditional on the 777X. After attempts late last year / beginning of this year, Boeing seems to have put efforts on hold.

Reality check. New, large WB aircraft / new engine, not yet flying in production configuration + current industry engine issues = very hard to please financiers + demanding performance expectations supported by watertight, punitive guarantees.

Guarantees have always been subject to a documented arbitration process, with the guarantors credit assessed. Latest trend is to require guarantees are underwritten / guaranteed by a third party in addition to the OEM, also credit assessed.

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