Can anyone think of a reason why short runway performance of the A359 would be a lot worse than 77E, 787? For the Wellington (WLG) runway extension study Astral Consulting looked at takeoff and landing performance with both the current 2081m strip and a 355m extension. Here's the link: http://www.connectwellington.co.nz/static/documents/Technical%20Report%201.pdf. Strange thing is, the 359 looks to be the most capable type off an extended runway but has a unique problem with takeoff and landing in the wet on the current strip: "takeoff not practical on existing runway nil wind when wet" (pp37-38) and "landing not practical on existing runway nil wind when wet" (p51). The Boeings (77E, 788, 789) seem able to land with max pax or better in the wet on the current runway and A330 ceo and neo don't seem to have the same problem as the 359. Have Astral got it right? Is there maybe a minimum control speed issue unique to the 359?

I ran some numbers on the Airbus performance database, off the current 16 it will takeoff with 255.5 tonnes dry and 245.0 wet. Off a dry runway 16 it will do PEK with 315 pax and 9.1 tonnes of payload, flight time of 12.43 (assumed 6000 air nautical miles).

I ran the landing distance calculations, the A350-900 will be able to land on 16 at MLW in 5418 ft.

So I dont put too much value into the report.

All right,

Very interesting Zeke ! Thanks
I've seen this report, that might alse be wrong on the weights

Happy new year everybody !

zeke wrote:

I ran some numbers on the Airbus performance database, off the current 16 it will takeoff with 255.5 tonnes dry and 245.0 wet. Off a dry runway 16 it will do PEK with 315 pax and 9.1 tonnes of payload, flight time of 12.43 (assumed 6000 air nautical miles).

I ran the landing distance calculations, the A350-900 will be able to land on 16 at MLW in 5418 ft.

... so on the face of it we could see a commercially viable service to Singapore or Hong Kong using 359s off the current strip? Tantalizing prospect (though that doesn't square with the technical case being made for the 355m extension).

In the meantime SQ's new Canberra/Wellington service is a reminder that Wellington can handle routine wide-body operations (the 77E looked very comfortable coming in this afternoon), though the short hop back to Canberra doesn't tell us much about the current runway's ability to support 11-12 hour flights by new-generation wide-bodies.

What is the MTOL for the 359?

bjorn14 wrote:

What is the MTOL for the 359?

Assuming you meant MTOW, it is 280,000kg for the -900

It will not lift this off Wellingtons runway however.

77west....Thanks but I meant Minimum Take Off Length. I may have forgotten the abbreviation.

bjorn14 wrote:

77west....Thanks but I meant Minimum Take Off Length. I may have forgotten the abbreviation.

The minimum takeoff length required would depend on TOW, wind, flap setting and power used. I would assume out of NZWN, full power would be used, and whatever flap setting gives the shortest takeoff length (as obstacle clearance is not really an issue)

Performance should be better than the 777 or 787 as it has significantly lower wing loading than either of them.

77west wrote:

bjorn14 wrote:

What is the MTOL for the 359?

Assuming you meant MTOW, it is 280,000kg for the -900

Eventually.

That MTOW won't be available in service until 2018 (for the -900ULR) and 2020 for the standard -900.

LAX772LR wrote:

77west wrote:

bjorn14 wrote:

What is the MTOL for the 359?

Assuming you meant MTOW, it is 280,000kg for the -900

Eventually.

That MTOW won't be available in service until 2018 (for the -900ULR) and 2020 for the standard -900.

Hmm... was just going of Airbus website which states 280t. http://www.airbus.com/aircraftfamilies/ ... fications/

That said, they have a habit of exaggerating and at times lying (as does Boeing) so...

77west wrote:

LAX772LR wrote:

77west wrote:

Assuming you meant MTOW, it is 280,000kg for the -900

Eventually.

That MTOW won't be available in service until 2018 (for the -900ULR) and 2020 for the standard -900.

Hmm... was just going of Airbus website which states 280t. http://www.airbus.com/aircraftfamilies/ ... fications/
That said, they have a habit of exaggerating and at times lying (as does Boeing) so...

No one's exaggerating/lying about anything.
The 280T A359 is available for sale, now, thus Airbus has every reason to show it on their site as such.

It however will not be in operation until the aforementioned dates, so (in reference to a thread about runways) 280T isn't particularly applicable at this time. Heck, IINM, we don't even have 278T in the standard A359 until PR gets theirs.

LAX772LR wrote:

77west wrote:

LAX772LR wrote:

Eventually.

That MTOW won't be available in service until 2018 (for the -900ULR) and 2020 for the standard -900.

Hmm... was just going of Airbus website which states 280t. http://www.airbus.com/aircraftfamilies/ ... fications/
That said, they have a habit of exaggerating and at times lying (as does Boeing) so...

No one's exaggerating/lying about anything.
The 280T A359 is available for sale, now, thus Airbus has every reason to show it on their site as such.

It however will not be in operation until the aforementioned dates, so (in reference to a thread about runways) 280T isn't particularly applicable at this time. Heck, IINM, we don't even have 278T in the standard A359 until PR gets theirs.

You are right, that said, 260, 270, 275, 280 or 20000 the A359 is limited to 255.5 max out of NZWN.. as posted by Zeke

Got to say the very small differences in performance between a 275, 278 and 280t puts all three in a very similar bracket. We are not talking about a massive difference like the A330 going from 212t to 242t

Now, what would a 300t A359 be capable of... hmmm. Would need the A3510 gear probably.

77west wrote:

That said, they have a habit of exaggerating and at times lying (as does Boeing) so...

Keep things in order: B is Master and Airbus a far away second in the domain of "fantastic" statement.

Current A350XWB highest Weight Variant is 275t. ( from the ACAPS document )
If you buy one today it will be available with 280t. ( no slots earlier

77west wrote:

Now, what would a 300t A359 be capable of... hmmm. Would need the A3510 gear probably.

That was Airbus' original proposal:
Essentially an A359 frame with A35K wing/box/gear + similarly modified tanks, at an MTOW of up to 298T.

Thing is though, it probably would not have had more range, in fact, it might've had even less; as it would've offered the same fuel capacity as the A359ULR, but at a much heavier operating weight. Massive payload increase over that range though.

Moot however, as no airline bit. At least one airline wants the A359ULR... though I wouldn't be surprised to see it stay at one.
Good thing that it was likely a cheap derivative to make.

WIederling wrote:

Keep things in order: B is Master and Airbus a far away second in the domain of "fantastic" statement.

Dunno about that, they've both told some whoppers in their time; and Airbus is no laggard in that regard.

Especially the John Leahy of the early '00s.
The spin he'd have to use for promotion of the A340 was legendary... I'm talking "Comical Ali" legendary!

LAX772LR wrote:

WIederling wrote:

LAX772LR wrote:

At least one airline wants the A359ULR... though I wouldn't be surprised to see it stay at one.
Good thing that it was likely a cheap derivative to make.

It is a massive step towards a much more efficient airframe for the task.)

For SQ's (atypical) task, sure.

But every other airline is thus far finding it better to "abuse" a standard A359 (or 789), or to go for a 778's raw lifting power, rather than deal with the massive drop in payload that an A359ULR would require over range.

Which isn't altogether surprising as the ULR marke property, increased MTOW, is offered on the regular A359
for future deliveries. We'll see if Airbus will offer different fuel volumes too.

The 789 is a limited airframe up against a (hard MTOW limit) wall.

The 778 is a super heavy airframe that is imho limited to paper efficiency.
The 789 won't perform all that much better.

WIederling wrote:

We'll see if Airbus will offer different fuel volumes too.

Not sure what you mean. Different fuel volumes on what?

WIederling wrote:

The 778 is a super heavy airframe that is imho limited to paper efficiency.

The 778's efficiency isn't derived from being a polite fuel sipper, it's meant to be the bastard child of a sumo + Kenyan marathoner:
Something that can move massive amounts of weight over long distance.

And again, let's keep in mind that multiple airlines have found even that to be preferable, versus the A359ULR.

LAX772LR wrote:

WIederling wrote:

We'll see if Airbus will offer different fuel volumes too.

Not sure what you mean. Different fuel volumes on what?

currently the same wing and center wing box tankage could have 3 (now 4 ) different "soft" available tank volumes
138,000 l -800
140,795 l -900
165,000 l -900ULR
156,000 l -1000
( mostly configuration in software and some plumbing changes.)

WIederling wrote:

The 778 is a super heavy airframe that is imho limited to paper efficiency.

The 778's efficiency isn't derived from being a polite fuel sipper, it's meant to be the bastard child of a sumo + Kenyan marathoner:
Something that can move massive amounts of weight over long distance.

And again, let's keep in mind that multiple airlines have found even that to be preferable, versus the A359ULR.

Was any 778 ordered in recent times ( i.e. after the ULR was offered? )

to answer myself:
latest order for 778x : June 2014
offer of A350ULR ~Oct. 2015

WIederling wrote:

LAX772LR wrote:

WIederling wrote:

We'll see if Airbus will offer different fuel volumes too.

Not sure what you mean. Different fuel volumes on what?

currently the same wing and center wing box tankage could have 3 (now 4 ) different "soft" available tank volumes

I'm aware of all that, but what I don't understand is the nature of your question:
Are you wondering if they'll standardize around a singular volume (which wouldn't make sense on the various models), or are you suggesting that they'll offer even more options on volume than currently exist (and if so, on what)?

WIederling wrote:

Was any 778 ordered in recent times ( i.e. after the ULR was offered? )

I don't know.

First, that depends on what we'll define as "offered"
Airbus publicly began discussions with airlines about ULH specifications in summer of 2015, with a formal launch in October 2015 with an order by SQ.

Second, Boeing's website doesn't define the variant for 77X orders; two customers (QR and unidentified) ordered twenty 77X within the time frame above (June 2015+). If any of these were 778, then it could be claimed that they were offered during the time where an A359ULR could've been procured. If not, then no.

LAX772LR wrote:

the massive drop in payload that an A359ULR would require over range.

This is a workable tradeoff for some airlines and routes. For US non-stop Qantas for many years have been making a go of it with low-density layouts plus seat blocking westbound on their 744s. They're now going with an ultra-low density configuration on the 789 to allow routes like Perth-London. UA are blocking 30-plus seats westbound to Singapore on their already low-density layout 789s. In each case we're talking payloads far short of MZFW. The real point is that the 359 and to some extent the 789 can be viable on ULR routes in low-density configuration because fuel burn is so much lower than eg 772LR. And the problem the 789 has, as Wiederling pointed out up thread, is that it is a limited airframe with a hard MTOW limit (plus a hard fuel volume limit) that mean it can't match the 359 on true ULR routes.

tealnz wrote:

UA are blocking 30-plus seats westbound to Singapore on their already low-density layout 789s. In each case we're talking payloads far short of MZFW.

But there's a difference: in each case, you're also talking about aircraft that give you the OPTION to increase that layout should you 1) desire it and/or 2) rotate those ships into routings that don't require such a divestment.

The A359ULR, will be papered to a hugely restricted MZFW on any route (as opposed to airlines choosing to short seats or lower density on selected routes), and thus will not.

Unless I'm missing something MZFW will be hardly different from the 280t non-ULR version. There's minimal extra structural weight in the ULR, right?

I cannot believe SQ will only put 170 seats on the 900ULR for JFK-SIN. Surely that metal tube can do better? I was thinking 250ish.

LAX772LR wrote:

And again, let's keep in mind that multiple airlines have found even that to be preferable, versus the A359ULR.

To be fair, all 778 orders were placed before the A359ULR was offered. The former being on sale since 2013. We don't know how many sales the A359ULR will have in 3-4 years.

tealnz wrote:

Unless I'm missing something MZFW will be hardly different from the 280t non-ULR version.

To clarify, the structural MZFW won't be any different

The operational ZFW will be hugely limited on paper though, as the aircraft has to devote so much of its MTOW to the extra 24,000L of fuel that it can/will tank; over the (eventual) standard A359 at the same MTOW.

bjorn14 wrote:

I cannot believe SQ will only put 170 seats on the 900ULR for JFK-SIN. Surely that metal tube can do better?

That's 9 seats more than the A345 ever took, and 70 seats more than it was taking before SQ got rid of it.

bjorn14 wrote:

I was thinking 250ish.

Based on what?

KarelXWB wrote:

To be fair, all 778 orders were placed before the A359ULR was offered. The former being on sale since 2013.

Which doesn't mean much, as those orders can easily be cancelled/converted, with the carriers selecting the A359ULR instead. We're talking about 3 airlines who buy widebodies like candy.

Of course, they're not going to do that, as there's no way the A359ULR can do the mission profile that they want the 778 for, but still.

bjorn14 wrote:

I cannot believe SQ will only put 170 seats on the 900ULR for JFK-SIN.

253 on their current 359s doing SIN-SFO. But the 170 figure has been around since they announced the re-launch of New York and the ULR order. I guess they have a good feel for the level of premium demand from past experience.

LAX772LR wrote:

To clarify, the structural MZFW won't be any different
The operational ZFW will be hugely limited on paper though, as the aircraft has to devote so much of its MTOW to the extra 24,000L of fuel that it can/will tank; over the (eventual) standard A359 at the same MTOW.

Doesn't make sense. Sure, if you fill the tanks you're going to be severely limited in payload, either on the ULR or the 280t regular model. But there are routes where you can make that work because of the non-stop premium. SQ did the numbers before they ordered. QF are going to do the same with the 789 to Heathrow.

But you're telling me you won't be able to load a ULR to 195t MZFW and fly it 5500nm just like any other 359? Really???

LAX772LR wrote:

Which doesn't mean much

Actually it means a lot. It's pretty obvious that an aircraft that was launched years earlier could have more orders.

But let's be real here: there are just 3 777-8 customers, and 1 A359ULR customer. It's not like the market for such aircraft is that big.

as those orders can easily be cancelled/converted, with the carriers selecting the A359ULR instead.

I'm aware Emirates is an exception, but most airlines don't just cancel airplane orders for another type.

However, nobody needs to cancel 778 orders because:

Of course, they're not going to do that

Of course not, the A350ULR is a different aircraft. It's almost like saying someone should cancel his A330s on order in exchange for 777s. Ain't gonna happen.

The 777-8 is clearly targeted at 777-200LR customers, the A350ULR isn't.

tealnz wrote:

But you're telling me you won't be able to load a ULR to 195t MZFW and fly it 5500nm just like any other 359? Really???

Calm down dude, dang.

Anyway, Airbus has not publicly released the exact MZFW that the aircraft's software in -900ULR configuration will allow, but analysts have already predicted that they're going to artificially limit it, for the following reason:

By lowering the MZFW, Airbus can regulate the max wing bending moment of the -900ULR to be at the same level as the standard version despite having a higher MTOW.

https://leehamnews.com/2015/10/23/bjorns-corner-increasing-an-aircrafts-range-further-considerations/

That, of course, in addition to the simple operational math.
There was a member here who expanded even further on the concept in one the A350 threads, if you care to look for it.

KarelXWB wrote:

I'm aware Emirates is an exception, but most airlines don't just cancel airplane orders for another type.

It's not unprecedented at all... we saw quite a bit of that, with a varied range of carriers, with the 777 vs A340.

EK, AC, SQ (famously), CX, MU, etc.

LAX772LR wrote:

The operational ZFW will be hugely limited on paper though, as the aircraft has to devote so much of its MTOW to the extra 24,000L of fuel that it can/will tank; over the (eventual) standard A359 at the same MTOW.

That is entirely correct, more fuel = less payload.

That said, 24,000L is just a maximum number and not every ULR route would require fully filled fuel tanks. For all we know, maybe SQ only needs [random pick] 15,000L fuel on an average sector. And while that's still a significant drop in payload, the non-stop flight would charge a higher ticket price to offset the loss of potential payload.

I get it that you can't afford to break the wings... so if you're going to fill that big tank in the wing box you have to limit the bending force at the fuselage join .... ergo you have to limit weight in the fuselage (pax/catering etc). That's what MZFW is about, right? But we got into a debate here about whether the ULR takes a big hit on payload by comparison with standard 359s at lesser ranges. Technically I can't see why: it's the same structure apart from fuel probes. Or am I missing something: does the manufacturer specify a MZFW that always assumes max fuel? Can't see why they would do that: it should be a sloping line or curve that follows maximum acceptable wing/fuselage bending moment at various combinations of fuel and payload.

I thought the ULR was to have the -1000 gear as they were pushing maximum pavement limits if they were to increase mtow more.

zeke wrote:

I thought the ULR was to have the -1000 gear as they were pushing maximum pavement limits if they were to increase mtow more.

If they push it any more, they will have issues at some airports. Surely the A359 already has the largest weight for a 4 - 4 gear arrangement? On the 280t it will be 35t per wheel!!

I realise by spreading the wheels out a bit more they can reduce the load on a specific point of pavement, but surely they are at those limits now.

77west wrote:

Surely the A359 already has the largest weight for a 4 - 4 gear arrangement? On the 280t it will be 35t per wheel!!.

Let's not get facts in the way of a good story

zeke wrote:

I thought the ULR was to have the -1000 gear as they were pushing maximum pavement limits if they were to increase mtow more.

That was the original offering: A359 frame, A35K wing+box+gear, ~298T.

Launched offering: A359, 280T, strengthened gear/brakes, increased tank capacity over the A35K with 2 additional pumps + modified jettison and inerting systems.

zeke wrote:

77west wrote:

Surely the A359 already has the largest weight for a 4 - 4 gear arrangement? On the 280t it will be 35t per wheel!!.

Let's not get facts in the way of a good story

? I Am not doubting you but I simply divided the MTOW of 280t by 8, which gives 35000kg per wheel. I don't see any other airplane that comes close on a per-wheel basis. I realize full well that there is more to it than that, including the spread of the wheels, the load on the nose gear (minimal) and stated that the A359 has, most likely, the highest loading on a conventional 8-wheel main gear. No need to say sniping comments like "Lets not let facts get in the way of a good story" - Trust me, I am the first person to defend the industry due to overzealous media reporting, and am probably one of only a handful of people on here that actually like A and B equally. I have stated quite clearly in the past that the 77W used to (and still has) one of the worst "per-wheel" gear loading in the industry. The A359 gets around some of this by spreading the wheels out more, but this primarily affects the ACN and concrete PCN numbers per your graph. It does NOT change the fact that each tire is applying 35,000kg on the contact zone, which is what can cause runways to start to crack and break.

I have got to say a comment like that from a CX pilot... left me quite riled up! I generally have a great deal of respect for you guys. If I am wrong, by all means, tell me, with facts and in a congenial tone, but implying I am like one of Trumps media people is... well.., sad.

77west wrote:

I have got to say a comment like that from a CX pilot... left me quite riled up! I generally have a great deal of respect for you guys. If I am wrong, by all means, tell me, with facts and in a congenial tone, but implying I am like one of Trumps media people is... well.., sad.

It is unfortunately the case that one can always count on Zeke to present facts with the maximum amount of aggression and snark. One simply has to overlook the tone and critique his arguments on their merits, or lack thereof.

You certainly did say explicitly "weight per wheel"...although that is not quite the same as pavement loading (as you agree), and the latter is presumably the more relevant metric in anticipating potential real world issues.

77west wrote:

I Am not doubting you but I simply divided the MTOW of 280t by 8, which gives 35000kg per wheel

What is that validity of doing that ? It is not used in any operational aspect. Besides it has 10 tyres.

77west wrote:

I realize full well that there is more to it than that, including the spread of the wheels, the load on the nose gear (minimal) and stated that the A359 has, most likely, the highest loading on a conventional 8-wheel main gear. No need to say sniping comments like "Lets not let facts get in the way of a good story"

Sorry it is not sniping, you are just plain wrong. The A350 does not have high pavement loading compared to other similar types as the ACN/PCN chart clearly shows. The chart clearly shows the 787 to have higher pavement loading and it too has 4 main gear wheels.

77west wrote:

It does NOT change the fact that each tire is applying 35,000kg on the contact zone, which is what can cause runways to start to crack and break.

That is where you have it clearly wrong. Take the 77W compared to the A359, the main gear leg on the 77W at maximum mass has around 163 tonnes coming down, the tyres are spread over an area of 3.54 sq.m (2.93x1.40m), giving a pavement load of 46.05 tonnes per sq.m. The A359 has a mass of around 130 tonnes coming down over an area 4.10 sq.m giving a pavement load of 31.74 tonnes per sq.m. If you take the 787-9, another 4 main gear airliner similar to the 359, it has around 117 tonnes coming down over an area of 2.30 sq.m (1.51x1.52m) giving a pavement load of 51.29 tonnes per sq.m. How the ground handles this load depends if its characteristics are like a foam mattress or a tiled floor (flexible or rigid base).

The pavement loading (pressure) is all about force (mass x gravity) over the area it is spread (and the ground characteristics), the A359 is clearly lower than both the 77W and 787-9 which is what the ACN/PCN chart shows. That is what airports and airlines use for operational purposes.

If you have a two 1 sq meter boards, hammer 200 nails on one, and 400 nails in the other, turn them upside down and stand on each one in turn. Both exert the same pressure on the 1 sq.m of ground below them when you stand on them, despite one having double the number of nails as the other.

77west wrote:

If I am wrong, by all means, tell me, with facts and in a congenial tone, but implying I am like one of Trumps media people is... well.., sad.

All the facts you needed were in the chart posted, it showed the A359 pavement loading compared to the 787-8 and 787-9.

Zeke:
"Take the 77W compared to the A359, the main gear leg on the 77W at maximum mass has around 163 tonnes coming down, the tyres are spread over an area of 3.54 sq.m (2.93x1.40m), giving a pavement load of 46.05 tonnes per sq.m. "

In this context and looking at the provided graph: Why would the 77X have higher loading than the 77W.
IMU MTOW is the same and basic gear arrangement too.

787 is shown to be at a hard limit maxing out pavement loading.
One explanation why MTOW appears fixed.

Is there no room in the MLG well to widen and lengthen the footprint?

Pavement loading is the actual tyre contact area and don't forget the nosewheels also carry some load. Spreading the gears will only change the moment arm not the contact area which remains the same and the only way to decrease the loading is to add more wheels.

Secondly, it's the damage that can be caused to the runway or taxiways from too high a pavement loading and not so much whether the aircraft can handle it or not.

WIederling wrote:

In this context and looking at the provided graph: Why would the 77X have higher loading than the 77W.
IMU MTOW is the same and basic gear arrangement too.

787 is shown to be at a hard limit maxing out pavement loading.
One explanation why MTOW appears fixed.

Is there no room in the MLG well to widen and lengthen the footprint?

The 777X main gear is 6" or 20 cm narrower than the 77W, less area for the load. I don't know if the load per gear is the same, it is feasible that the nose gear load has reduced due to the additional span and moving the engines further from the fuselage (mass is moving rearwards).

I don't know about the room available in the 787 gear bay.

PITingres wrote:

77west wrote:

I have got to say a comment like that from a CX pilot... left me quite riled up! I generally have a great deal of respect for you guys. If I am wrong, by all means, tell me, with facts and in a congenial tone, but implying I am like one of Trumps media people is... well.., sad.

It is unfortunately the case that one can always count on Zeke to present facts with the maximum amount of aggression and snark. One simply has to overlook the tone and critique his arguments on their merits, or lack thereof.

You certainly did say explicitly "weight per wheel"...although that is not quite the same as pavement loading (as you agree), and the latter is presumably the more relevant metric in anticipating potential real world issues.

My point was, no matter how far the tires are spread apart, the asphalt or concrete will react to how much pressure on a given contact area, and I believe the 777, 787 and A350 all fall into a very similar area here. Good luck telling the ground, "oh you shouldn't have cracked because our graphs show that our contact pressure is more spread out than a 77W!" But I do realise that this is difficult to measure, and hence pavement loading is a good standard to go with. There are many airports out there where the supposed PCN numbers are not quite right. I Grew up in FACT and we regularly had 747s taking bits of the tarmac with them off 19. (This end was particularly bad)

As to peoples snark, well, I really don't have time for it, there are so many topics these days where I start typing out what I believe to be a measured and fact-backed response, and actually just end up closing the tab, afraid of getting into an argument..

zeke wrote:

The 777X main gear is 6" or 20 cm narrower than the 77W, less area for the load.

Hadn't noticed the difference. That explains it then. Thanks.

77west wrote:

My point was, no matter how far the tires are spread apart, the asphalt or concrete will react to how much pressure on a given contact area, and I believe the 777, 787 and A350 all fall into a very similar area here. .

Airports publish their PCNs, and manufacturers publish their ACNs. It is really not that hard. You have been caught out trying some B/S which has no operational relevance.

If there was some relevance the manufacturers would publish it in the airport planning documents, i.e. The ACAPS, it is not in there.

There are multiple flexible and rigid ACNs published for each type and this is matched against the airports published classifications.

77west wrote:

My point was, no matter how far the tires are spread apart, the asphalt or concrete will react to how much pressure on a given contact area, and I believe the 777, 787 and A350 all fall into a very similar area here.

From the physics side you have a staggered arrangement of limits.
A downward surface force devolves in a downward open cone.
I.e. going down the same force is transmitted over an ever growing area
continuously reducing material stress.
At any depth the load has to be lower than destructive stress.
If you have a single point force this limit comes into effect at the contact interface.
Now if you distribute your force over a number of load points
each point can take its full capacity. Now the next limit is where load cones
start to overlap.
The further apart your load points are the further down
this overlap and stress increase happens.
( in this process you have also keep in mind that load bearing capability
of the earth under the surface enforcements ( concrete or asphalt )
is a magnitude or two lower.

To conclude: Splayed out feet work rather well.
If you have the space in the gear well available this is a cost effective solution.

Different lengths of wheelbase can create different amounts of "scrub" (hence why the back wheels on triple bogies have some steering built in to them. There is a mistake often made when deciding on the type of road surface and construction that small roads need less good quality construction than the big ones but really people are driving slowly on the small ones and often making tight turns into driveways and at junctions which causes the road to break up.
I understand Zeke saying its not relevant to the planning docs but a derived number only gets you so far in understanding the problems associated with creating and using certain surfaces. Like a lot of things its gets hugely more complicated when you look beyond the initial number kind of like a headline pressure and flow value for a fan, tells you something but really you need to interrogate the fan curves to get the more useful information.

Fred

Fred you are absolutely correct, the amount of engineering that goes into pavement design at airports is not simplistic. Different areas are tailored to uses and aircraft types. An area that sees heavy braking or turning has different specifications to an aircraft stand.

Like most aspects of airport design, the pavement, electrical, and fuel reticulation are amazing engineering problems with many very novel solutions worldwide.

zeke wrote:

77west wrote:

I Am not doubting you but I simply divided the MTOW of 280t by 8, which gives 35000kg per wheel

What is that validity of doing that ? It is not used in any operational aspect. Besides it has 10 tyres.

77west wrote:

I realize full well that there is more to it than that, including the spread of the wheels, the load on the nose gear (minimal) and stated that the A359 has, most likely, the highest loading on a conventional 8-wheel main gear. No need to say sniping comments like "Lets not let facts get in the way of a good story"

Sorry it is not sniping, you are just plain wrong. The A350 does not have high pavement loading compared to other similar types as the ACN/PCN chart clearly shows. The chart clearly shows the 787 to have higher pavement loading and it too has 4 main gear wheels.

77west wrote:

It does NOT change the fact that each tire is applying 35,000kg on the contact zone, which is what can cause runways to start to crack and break.

That is where you have it clearly wrong. Take the 77W compared to the A359, the main gear leg on the 77W at maximum mass has around 163 tonnes coming down, the tyres are spread over an area of 3.54 sq.m (2.93x1.40m), giving a pavement load of 46.05 tonnes per sq.m. The A359 has a mass of around 130 tonnes coming down over an area 4.10 sq.m giving a pavement load of 31.74 tonnes per sq.m. If you take the 787-9, another 4 main gear airliner similar to the 359, it has around 117 tonnes coming down over an area of 2.30 sq.m (1.51x1.52m) giving a pavement load of 51.29 tonnes per sq.m. How the ground handles this load depends if its characteristics are like a foam mattress or a tiled floor (flexible or rigid base).

The pavement loading (pressure) is all about force (mass x gravity) over the area it is spread (and the ground characteristics), the A359 is clearly lower than both the 77W and 787-9 which is what the ACN/PCN chart shows. That is what airports and airlines use for operational purposes.

If you have a two 1 sq meter boards, hammer 200 nails on one, and 400 nails in the other, turn them upside down and stand on each one in turn. Both exert the same pressure on the 1 sq.m of ground below them when you stand on them, despite one having double the number of nails as the other.

77west wrote:

If I am wrong, by all means, tell me, with facts and in a congenial tone, but implying I am like one of Trumps media people is... well.., sad.

All the facts you needed were in the chart posted, it showed the A359 pavement loading compared to the 787-8 and 787-9.

So, I have to ask, with all due respect:

Zeke, if you know all of this and did the math, why did you even ask the question you did in reply 34?

zeke wrote:

77west wrote:

My point was, no matter how far the tires are spread apart, the asphalt or concrete will react to how much pressure on a given contact area, and I believe the 777, 787 and A350 all fall into a very similar area here. .

You have been caught out trying some B/S which has no operational relevance.

Aaaaand thats me out of this one. You are a rude person Zeke. I was not "trying" Anything.

Suppose I better go re do my engineering degree... oh well... there goes 4 years.

I wish to add to a previous post of mine, after talking to a maintenance friend. Loading per wheel is fully taken into account by them, it governs the tires, brakes, wheel assemblies, he actually laughed when I said a pilot said that wheel loading is irrelevant and pavement loading governs all. He stated wheel and axle loading is an operationally relevant factor that is specifically mentioned in their manuals, especially at airports that have a "published" number but a realistic actual number well below this. So perhaps an airline like CX would not consider it relevant, but our airlines do. (And I say this after defending CX in another thread - ironic much). The point I am trying to make is that irrespective of what the ACN / PCN numbers say, you cant argue with the fact that over 90-95% of the weight of an airliner is on the main gear, which could mean 30-35ton per wheel for an 8-wheel A350. (Zeke - triggered!!!)

Point is, no matter how you cut it, it is still 30-35t per wheel. "Oh but PCN / ACN / ABC / XYZ - yes but divide the weight by the main gear, sure give it a 10 or 20 percent credit for the nose gear...

The published pavement loading is crap and often catches airports out, and they rip up the surface. My point has always been, the loading per tire contact area is what matters in real ops.

I am happy to be corrected by Zeke, as a professional pilot and concrete, asphalt and general engineer.