Upper limit of jetliner size?

I do note the lack of structural/OEW estimates in the Stanford study. Maybe they did it, and then did not bother to give numbers. What they do seem to say is that wing weight is small enough that even if it does undergo square-cube increase, it still remains a minor factor.

For example, compare B-36 with B-29. The 70 m wingspan of B-36 is bigger than any jets till An-124. Yet B-36 has a huge useful load and long range. At which wingspan would the structural weight start to seriously limit useful load and range?

What about An-225 and Hughes Hercules wing structural weight?

I guess the study did well in not mentioning the OEW. Most predictions are based on past aircraft and work best if one does not exceed that limits. Manufacturers have problem to guess the weight of their aircraft within 5% (see Boeing 787).

When comparing size one should compare capability, too. The A380 for example is much faster than the An-225, giving more design challenges for the wing and structural margin versus flutter.

Well, the wing might reinforce the fuselage against sidewards bending. But this does nothing about the possibility of the whole wing, wingbox and fuselage bending vertically…

What utter tosh, I think you should go and check out section inertia theory before making such silly claims…. please look up the calculation of second moment of area (I) and you will find that the strength and stiffness increase exponentially in proportion to the area resisting bending at the extremity…. which in Concords case is the section of both the fuse & wing…..http://en.wikipedia.org/wiki/Second_moment_of_area.

If anything Concord had at least one amendment to normal cert conditions (i.e. Concord’s TSS’s and not JAR’s) due to the high vertical bending stiffness of its Fuselage.

What about An-225 and Hughes Hercules wing structural weight?

The latter could barely pull its weight out of the water, and the former – with only one built – proves the point about lousy economics, perhaps?

I wouldn’t read too much into the Stanford study. It is a trend recognition, but it fails to take into account the practicalities of building larger and larger aircraft. There is a finite amount of stress that current materials can take, which increases with size, and what the study fails to note is how the weight of the aircraft itself starts to rise rapidly as we apporach the finite limit.

I do note the lack of structural/OEW estimates in the Stanford study. Maybe they did it, and then did not bother to give numbers. What they do seem to say is that wing weight is small enough that even if it does undergo square-cube increase, it still remains a minor factor.

As I said earlier, we are about there in terms of limit, unless we get some major advances in material technology. Otherwise, as Schorsch noted, the aircraft will be carrying more and more of its own weight, with a lower and lower useful payload.

For example, compare B-36 with B-29. The 70 m wingspan of B-36 is bigger than any jets till An-124. Yet B-36 has a huge useful load and long range. At which wingspan would the structural weight start to seriously limit useful load and range?

What about An-225 and Hughes Hercules wing structural weight?

I wouldn’t read too much into the Stanford study. It is a trend recognition, but it fails to take into account the practicalities of building larger and larger aircraft. There is a finite amount of stress that current materials can take, which increases with size, and what the study fails to note is how the weight of the aircraft itself starts to rise rapidly as we apporach the finite limit.

As I said earlier, we are about there in terms of limit, unless we get some major advances in material technology. Otherwise, as Schorsch noted, the aircraft will be carrying more and more of its own weight, with a lower and lower useful payload.

Overflew the study. The numbers for the A380 (=A3XX) are 100tons low in weight

Agreed.

and the wing span way too high.

I get the opposite. They give “251 ft”, which is about 76,5 m, while the now A380 is 79,8 m. The plane must have grown some…

As for square-cube, see

http://aero.stanford.edu/bwbfiles/largeACopt.html

The limit does not seem to be nigh.

Overflew the study. The numbers for the A380 (=A3XX) are 100tons low in weight and the wing span way too high. If it was that easy Airbus wouldn’t employ hundreds of engineers in flight physics. In general an aircraft larger in size than the A380 wouldn’t not gain in structural efficiency.

I’d be careful about making predictions about air travel.

There is a story when the new all metal 20 passenger Boeing 247 was rolled out sombody was heard to say…
“They’ll never make them any bigger”.:D

Still at some point you’d think there would have to be either a technical or practical (passenger related or ground handling) limit.

Yet another thing is turn round time on the apron as the aircrafts size makes this increasingly tricky. Airbus went to a lot of trouble to get this down to the minimum, as the longer its on the stand the less money it earns. They issued a critical path analysis of the turnround times, and the biggest issue was not getting the passengers sorted as maybe you would think, but the fuel. With only one pump truck it can be done in just under a couple of hours for most journies, but the intention is that it should normally have two and hence take under an hour, but that is still the longest part of the turn round even then.

If I remember correctly there was also a scenario where if only single deck loading was available then this gave problems with the catering supply and an extended turnaround was needed, but they may have fixed that.

Anyway, I think typical turnround is about 130 minutes.

Incidentally I believe that the A380 needs an 88m wide by 81 long stand to give sufficient space for the dozen or so vehicles needed to service it, based on some notes I took about a year ago.

With limitations. The structural weight increases fast than weing area (so called square-cube law, structural weight increases as cubic function of size while wing area only as quadratic function).
The solution is either increase of the wing loading or reduction of the volume-specific structural weight, or of the loads acting on the aircraft.

The A380 is in the end of the useful region, anything bigger than the A380 will become less efficient and primarily lift its own weight.

As for square-cube, see

http://aero.stanford.edu/bwbfiles/largeACopt.html

The limit does not seem to be nigh.

Don’t know what the An-124/225 landing gear assembly weighs.
A380 landing gear weighs about 20 tonnes.

The A380 is in the end of the useful region

I think that’s probably correct. We’ll need to see some fairly large advances in materials technology before we get much larger. Whilst it is technically possible to build much larger aircraft now, the economics will go to hell in a handcart.

Another thought on a much earlier post – the AN225 doesn’t have to worry about the “box” – since it doesn’t tend to park at passenger terminals. Cargo aprons are typically much larger, since there is a lack there of limiting factors – eg, airbridges.

Some guy from Antonov said that you can basically design an aircraft any size. Only problem is that from some point on the landing gear becomes so heavy that the payload drops to zero.
Ha! – Flying boats then! Like the Beriev 2500 or Boeing Pelican WIGs.

With limitations. The structural weight increases fast than weing area (so called square-cube law, structural weight increases as cubic function of size while wing area only as quadratic function).
The solution is either increase of the wing loading or reduction of the volume-specific structural weight, or of the loads acting on the aircraft.

The A380 is in the end of the useful region, anything bigger than the A380 will become less efficient and primarily lift its own weight.

Concorde flew above turbulences.

Yes, but the impact of touchdown exerts vertical bending momentum. Exactly the direction not reinforced by the delta wing.

Some guy from Antonov said that you can basically design an aircraft any size. Only problem is that from some point on the landing gear becomes so heavy that the payload drops to zero.
Ha! – Flying boats then! Like the Beriev 2500 or Boeing Pelican WIGs.

Except that the Pelican is a pure landplane.

The Pelican main landing gear consists of 38 legs totalling 76 wheels – 2 wheels per leg. Thus resembling the An-124 and An-225 main landing gears – 10 and 14 legs respectively, 2 wheels each.

How heavy are An-124 and -225 landing gears? And what about the Pelican landing gear?

Well, the wing might reinforce the fuselage against sidewards bending. But this does nothing about the possibility of the whole wing, wingbox and fuselage bending vertically…

Concorde flew above turbulences.

Some guy from Antonov said that you can basically design an aircraft any size. Only problem is that from some point on the landing gear becomes so heavy that the payload drops to zero.
Ha! – Flying boats then! Like the Beriev 2500 or Boeing Pelican WIGs.

For a single deck airplane like Concorde, overwing exits is no problem, which is why Concorde has 29 m root chord

Eh? Concorde has a 29m chord since it was designed with a delta wing – I can’t imagine the issue of emergency exits was top of the agenda. In any case, putting doors either over a wing or away from a wing is not an issue. Compare an A320 with an A321 for a case in point.

As for the A380, I would be surprised if Airbus hadn’t considered a slide down onto the wing from the upper deck. I would be equally surprised if the legislation covered this point, since the A380 is the first full scale twin decker…

TA

Problem is that this fuselage needs to be lifted, and even on the A380 it gets increasingly problematic to accomodate for the wing root. The loads acting on the intersections of fuselage and wing are tremenduous and a reason why the A380 is quite a heavy beast (more OEW per pax than a B747).

One restriction for A380 is the 18,3 m limit between exits. It matters because A380 is a doubledecker.

For a single deck airplane like Concorde, overwing exits is no problem, which is why Concorde has 29 m root chord.

However, A380 is a doubledecker. There is a pair of overwing exits – on main deck. If you look at the upper deck, it has exits just ahead of wing leading edge and just behind the trailing edge – the slides have to go clear of the wing. The maximum 18,3 m distance between exits means that the wing could not be made any wider than it is.

(Could the matter be fixed by a middle staircase, or could it not be done?)

As for subsonics, A380-900 is intended to fill the box exactly – with length of 79,8 m to match the 79,8 m wingspan. But Gulf carriers and Udvar-Hazy are clamouring for even longer planes. How do you think will airport gates handle A380-1000?

If air travel growths enough and people get used to the idea of exceeding this completely random limits (it was part of Airbus attempt to appeal to the FAA, which did quite a lot to torpedo the A380), we might see Airbus giving its big baby a new wing. With an MTOW in excess of 650t this might make sense. The fuselage can extended beyond 80m I guess, at least its fuselage ratio wouldn’t be worse than that of an A340-600 or B757-300.

A380-1000 would make a nice name. Maybe with 90klbs GEnx engines, folding wings and extra body landing gear!!! 😀

It doesn’t make sense to lengthen the fuselage without making it thicker. If we apply the thickness ratio (length divided by fuseage diameter ) of a B757-300 to an A380, we arrive at something like a 100m fuselage. Problem is that this fuselage needs to be lifted, and even on the A380 it gets increasingly problematic to accomodate for the wing root. The loads acting on the intersections of fuselage and wing are tremenduous and a reason why the A380 is quite a heavy beast (more OEW per pax than a B747).

Making an aircraft even bigger will reduce the its overall efficiency. And just if anybody now thinks everything is gonna to be shiny with “advanced materials”: No, doesn’t change the game. The A380 uses quite a lot of that (for example a composite center wing box, the world’s first). The ability of Airbus to exceed its originally proposed OEW by less than 1.5% is remarkable, Boeing and its B787 is at ~5% currently, the B747-8 also has some weight issues.

Besides that, there is hardly a market for anything bigger than an A380-900ER.

You’d think it was because the Concorde has an enormous wing running almost the entire length of the fuselage. So, surely, wings like this and the wing boxes are incredibly strong, tough structures. You end up with a very rigid fuselage.

Well, the wing might reinforce the fuselage against sidewards bending. But this does nothing about the possibility of the whole wing, wingbox and fuselage bending vertically…