Size limit to heavier-than-air aircraft

[tartare]

All - is there any fundamental aerodynamic law or principle that limits the physical size and weight of a heavier than air aircraft - i.e. the square cube law?
MTOW for the AN-225 is shown as 640 tonnes.
Assuming there was no PCN restriction could an aircraft be built, flown with MTOW of 1000, 2000 tonnes?
If necessary thrust was available, would the strength of control surfaces and their ability to exert pitch, yaw, roll forces on a theoretical super-massive airframe pose a limit?
No, I'm not planning to build one...

[pattern_is_full]

Well, the Saturn V/Apollo vehicle was 2800 tonnes at liftoff, so it probably depends on how you define "heavier-than-air aircraft".

The SV didn't have wings - but then, it didn't need wings.

There are ways around the cube-square law, because that only really applies to solid objects - vehicles are mostly "hollow", which is why an iron ship can float, but a solid chunk of iron sinks.

Birds have hollow bones, but are still mostly "meat" by volume, thus a bird as big as an An-225 is impossible - but the An-225 itself flies just fine.

I'm sure that, given an infinite airspace (depth and breadth) there is probably some point where the aerodynamic equations may start to warp or break down. I'm also sure that such limits are comically large compared to a simple problem such as - what happens if your two wing tips are in different weather systems?

My bet is that there is no theoretical reason why a 10000-tonne aircraft could not fly. It would be an expensive and difficult engineering problem (but that is technology, not theory).

[Burnie5204]

As above, if there were runways long enough, wide enough and strong enough combined with a demand for an aircraft that size then yes, you could build aircraft much bigger than currently. However, they would have to have Harrier style outriggers and massive support structures to stop the wings breaking off or scraping the ground when on the ground or snapping off under lifting forces in flight.

I suspect that might be the biggest limiting factor as there will be a point at which the support structure required to hold the designed aircraft together becomes too heavy to lift.

But again, thats a materials engineering issue whereby as stronger, lighter materials are developed (e.g. carbon nanotubes) the biggest possible aircraft size increases, as opposed to a flight theory one.

[Pugilistic Animus]

I wonder what 4, 6, or 8 GE 115Bs could power

[tartare]

Pattern - I should have specified `winged' vehicles - but good point!
After asking - I did find this:
Size Effects on Aircraft Performance (http://aero.stanford.edu/bwbfiles/largeacopt.html)
and this:
Theoretical limits to wing and aircraft size? (http://forum.nasaspaceflight.com/index.php?topic=29699.0)
I was just wondering if there was a point at which compressibility issues or control surface/actuator strength might be a problem.
I imagine rate of roll, yaw, pitch would be an issue for something that large as well.

[SeenItAll]

I suppose you could mitigate some of these structure stress issues by building this big bird as a biplane.

[marianoberna]

The only limits are money and time. Given enough of both, anything is possible.

[Slatye]

In practical terms, there's no limit. Current aircraft already have to be designed with consideration for parts bending under load. Taking that to extremes and allowing really massive deformations under load, you could make a thousand-tonne plane by sitting ten B744s side-by-side and sticking the wingtips together with something so flexible that they might as well not be connected at all. Technically it's one plane, but it flies just like ten B744s in a very tight formation. Clearly such a thing is possible, although finding a suitable runway may not be.

Obviously if you set out to design a plane with a thousand-tonne payload, there'd probably be more efficient ways than sticking a bunch of existing planes together - but the thought experiment shows that there is at least one way to achieve this goal. Beriev proposed the Be-2500 (http://www.beriev.com/eng/Be-2500_e/Be-2500_e.html) ages ago, which would fit the bill and looks reasonably conventional. Boeing's Pelican is a similar concept. Both are designed to take advantage of the ground effect much of the time, while retaining the ability to fly at reasonable altitudes when necessary.

[tartare]

Tks Slayte - had seen the Caspian Sea Monster, but wasn't aware of this - interesting.

[awblain]

It might be an long-running April Fool, but these guys are planning to strap bits of two 747s together to turn Virgin Galactic's VIP lounge into a transport cafe.

S T R A T O L A U N C H - S Y S T E M S (http://www.stratolaunch.com)