scaling aircraft size

[Molotov]

Does there exist a limit to which a cargo carrying aircraft can be scaled up in size?

 

For example:

 

The Cessna 421 has a wingspan of 12m, a length of 10m, and a maximum take-off weight of 3103kg. This a common private plane.

 

The Mcdonnell Douglass DC-9 has a wingspan of 28m, a length of 40m, and a maximum take-off weight of 55,000kg. This is a standard US military transport aircraft.

 

The Antonov 225 has a wingspan of 89m, a length of 84m, and a maximum take-off weight of 600,000 kg. Only one exists. It was built by the soviets for thier space program that collapsed with the end of the cold war.

 

 

Anyone can see the scale moving up largely between these similarly engineered aircraft.

 

My question... is there anything keeping us from going larger? If we built an airstrip the size of a large city, how far would the laws of physics allow us to keep scaling up the size of our aircraft? Is it feesable with today's technology to build an aircraft say twice the size of the Antonov 225?

 

Could we someday be living on flying cities gracefully skimming through the stratosphere?

[insane_alien]

its possible. just damn expensive

[Mokele]

I would think, just guessing, that it would suffer the same problem as flying animals: If you double the length and keep the proportions, you have 4x as much wing area but 8x as much weight. So, proportionally, the wings need to increase in size a lot faster than the increase in size of what they're supporting. There's probably and upper limit, defined by materials strength and fuel needed.

 

Mokele

[calbiterol]

I spose it would help if we were actually 99.99% certain how airfoils work in the first place. There's quite the debate about whether the Bernouli Principle means anything due to some discrepancies and contradicions in the data, particularly with airfoil performance.

[insane_alien]

well if you use the entire aircraft as a wing...

[J.C.MacSwell]

I would think' date=' just guessing, that it would suffer the same problem as flying animals: If you double the length and keep the proportions, you have 4x as much wing area but 8x as much weight. So, proportionally, the wings need to increase in size a lot faster than the increase in size of what they're supporting. There's probably and upper limit, defined by materials strength and fuel needed.

 

Mokele[/quote']

 

But if you scaled the speed also you would have 16x the lift. ....

 

....But unfortunately that would take 32x the energy

[Douglas]

Does there exist a limit to which a cargo carrying aircraft can be scaled up in size?

It seems to me, that if you double the size of an aircraft, that you may have to double the takeoff speed required for liftoff..............No?

[J.C.MacSwell]

It seems to me, that if you double the size of an aircraft, that you may have to double the takeoff speed required for liftoff..............No?

 

If you scaled everything exactly you would need 41% more takeoff speed.

(square root of two times the takeoff speed)

[DV8 2XL]

The limiting factor in any heaver-than-air craft is the Power-to-Weight ratio.

It maxes out when you can no longer lift the motive power (and its fuel)

[marklar]

insane_alien: Indeed, I think the solution is to enclose the entire volume of the aircraft within an active aerofoil. Since the force on the aerofoil is proportional to the volume of air displaced, increasing the volume should increase lift.

 

While this is fine in theory, you can never make the entire aircraft generate lift and I'm sure there is a limit to undercarriage size.