Is it possible to have an aircraft carrier that travels on land instead of water? Assuming that the land aircraft carrier is the same size as a regular one the shape can be different but the overall size the same.
DISCLAIMER: I'm not an engineer so take everything I say on a conceptual base, because I can't back this up by facts to prove that it would work.
Water carriers are wide and flat only because it's convenient for them to be that way given the nature of water.
Attempting to adopt the same principles to land vehicles would probably be akin to an attempt to drive nails with a screwdriver (or vice-versa).
You have the objective - to drive the object into the wall (house and launch/land aircraft).
You have the condition - the nail (land).
You are looking at the screwdriver (the seagoing aircraft carrier) like it's almost a solution to your problem which just needs some adjustments.
Stop and think about it, sometimes you need to invent a hammer to do what a screwdriver shouldn't.
Due to the nature of land not being flat, making something that is stiff will not work when bending pressure will happen, so we have to make something that is able to bend. Good news, there's a good example already available to us. In the real world this is solved nicely in the concept of trains. Think of trains as people-carriers, they house people, they launch people and they land people. Fortunately, as people, we can operate on land ourselves so the launching and landing is not that big of a problem for us, we can just exit and enter the train from the side of it.
Although I'm going with the train model in this approach, any chained vehicular model should work.
Let's look at the objectives we have and see if we can fit them with the train model.
- House aircraft
- Launch aircraft
- Land aircraft
Objective 1: Housing aircraft.
Adjust the train dimensions so that a single plane can fit nicely on every car of the train.
Obligatory crude paint drawing:
Objective 2: Launching aircraft.
I believe we need to take a page from the soviet rocket launcher truck "Katyusha". And by that I mean we raise the the train car pad at an angle so the trajectory of the plane is to rise above the train, and then extend the platform to provide a long enough runway, which we then can secure to the ground by telescopic legs reaching down and adjusting height as necessary given any terrain. You can even temporarily detach it from the train if necessary. (Each car could have an ability to operate as an independent transporter for a limited time.)
Another crude drawing:
Objective 3: Landing an aircraft.
This might be the trickiest one to pull off since the landing space needs to be straight, flat and connected, all of which we abandoned with the chained cars approach. However if each car has a portion of the landing space which can connect with each other that the car can pull out looks promising. Add the ability to position and rotate it, throw in a couple of those telescopic legs in and you've got a pretty good landing strip, even if the train is currently bent.
More crude elaboration:
Terrain shown as green, landing strip parts shown in red and telescopic legs shown in blue.
Once the plane has landed it can roll back or forth on the strips segments to navigate to a segment which is linked to an empty car which does not currently house a plane. After which the strips disconnect and the plane gets spatula'd onto the car platform.
The reason carriers work in the water is because water is [usually] flat so you never have to lift the carrier. On land, you would have to lift yourself over bumpy terrain, whereas on water the only terrain you might have to climb are the waves which are picking you up by themselves.
There ARE vehicles which carry massive things like the vehicle which carried the space shuttle to the launch site. These beasts needed extraordinarily flat (and strong) ground to work and definitely wouldn't be able to ride up a hill. These are also smaller than an aircraft carrier.
The closest you could probably come would be a long train with cars full of planes and cranes (where the cranes are to lift the planes onto the plains so they can take off). Yes, I had fun with that sentence.
However, that's a far cry from an aircraft carrier.
I will not expend why a big flat vehicle is structurally challenging on land.
As @Ceiling Gecko said, you need to revisit your assumptions and design a solution from scratch.
What does an aircraft carrier need to do?
- House people, material, and planes
- Give a runway for planes to take-off and land
The first question we need to ask: what does being monolithic offers us?
On water, the reasons to be monolithic are easy to understand:
- taking-off or landing from open waters is challenging because of waves, so we need a flat platform
- transferring planes from one ship to another is impractical (even stationary, ships still pitch uncontrollably), so the same ship need to both house the planes and provide the runway
However on land neither reason hold:
- no need for a pre-built platform, we just need to flatten the land
- transferring is easy, just have a ramp (not even a crane) and a cable (see https://en.wikipedia.org/wiki/Tow_truck#/media/File:Flat_Bed_Tow_Truck.jpg)
So what's the solution?
I would recommend a modular fleet of vehicles, composed of:
- camping cars/trucks to house people and materials
- a couple "big" trucks for repairing planes on the move
- at least one flat-bed truck by plane to be transported
- a number of bulldozers and flattener trucks, which may be transported on faster moving vehicles
- add ground offensive/defensive capabilities as suited
Whenever you want to have a plane take-off or land, prepare a runway, then:
- for take-off: disembark the plane from the flat-bed and go
- for landing: embark the plane on the flat-bed and go
The only issue with this design is response time; depending on the surrounding terrain quality and the tolerance for rough terrain of the planes you have, it may require some time to prepare an acceptable fleet. Story-wise, it's good for the plot, as it means that leaving the plains for rougher terrain (maybe hilly) puts pressure on the crew.
A land based aircraft carrier has little practicality for a number of reasons.
The primary reason is that equipment of that size and weight would be so slow as to be essentially immoble on land, and make a hugely attractive target. Moving large equipment already takes a great deal of planning and time, and that's with a route that is prepared ahead of time.
Getting the carrier moving in the first place would require massive amounts of energy, and the mechanics of rolling on the ground would require continual energy output that far exceeds the amount of energy it takes to move a ship.
A ground vehicle with the mass of an aircraft carrier would be so heavy that it could only traverse certain terrain - it wouldn't be able to climb any sort of slope nor would it be able to cross wet ground without sinking in and getting stuck. For obvious reasons, once stuck it would be practically impossible to dislodge.
Finally, it would be a hugely vulnerable target. Countermeasures and mobility are the main defenses against modern bombs and missiles, but a land-based aircraft carrier would sorely lack that mobility. A real aircraft carrier can move over 30 knots, while the largest mobile equipment like the crawler-transporter moves a fraction of that speed - 1 mph. That's on a road prepared specifically for that vehicle to travel over.
Also, there are alternatives such as portable airfields, such as airfields made of pierced steel planking. A team of engineers can prepare and deploy an airfield in only a day or two using modern equipment that is portable with standard trucks or even aircraft. There is also little need for a portable aircraft carrier as modern aircraft generally have the ability to operate from airfields far from the front - for all intents and purposes, with in-flight refueling the only limit to their range is the endurance of their crews.
But, I suppose that if you ignore all of those downsides and insisted on a land-based aircraft carrier, you could possibly create a piece of (track-based) heavy equipment large enough to operate small aircraft - especially STOL / VTOL aircraft - off of. It would be slow and unwieldy, but it could be done.
The Mobile Launcher Platform has a mass of only 3730 metric tons - even a light aircraft carrier has a significantly larger mass (random example: HMS Hermes of 1924, ~11000 tons unloaded, ~13900 tons fully loaded).
However, a land-based carrier could probably made considerably smaller than their ocean-faring counterparts. For example, personnel quarters, workshops, radar systems, fuel/supplies, idle aircraft and so on could travel separately by truck.
Also note the strategical usefulness of a land-based aircraft carrier. Instead of bombarding an enemies base/city, simply send your aircraft carrier into it. ;-)
Large land vehicles of any kind are impractical in the real world, not because of slopes, which they could climb or drive around if you're willing to spend the money, but because of rivers.
By being forced to stay within fixed boundaries they are simply not cost effective, at least not compared to an army of smaller vehicles that can cross bridges.
Most of the answers here have been talking about airstrips. However, one big component of carriers is repair and support facilities. You need much more repair and ground crew than flight crew. You need ammunition, munitions, countless tons of jet fuel, expendables, parts, the list goes on.
In theory, you could eliminate the need for airstrips by limiting yourself to VTOL aircraft. Whether you do that or use one of the aforementioned portable airstrip solutions, the most straightforward way to deal with the rest of it is to have a fleet of trucks, busses and RVs holding crew and material. You may also need some way to put up some sort of temporary hanger so that your crew doesn't have to overhaul the engine in driving rain/snow/darkness.
This actually has a limited advantage over a carrier. If an attack is imminent, the entire operation can scatter, making it much harder to kill more than just a redundant portion of the operation.
There have been experiments with land-based aircraft carriers. They don't look much like sea-going ones, though: they more closely resemble a flatbed truck.
In a nuclear war, an airport is an immobile, indefensible sitting duck. Consequently, during the 1950s, a number of countries experimented with ways to make those airports mobile. The most common solution was a fighter or fighter/bomber that could be trucked around, and launched directly off the transport using extreme rocket-assisted takeoff. By the time guided missiles made them obsolete, these launches were fairly routine.
Landing is a different matter. The US Air Force attempted a carrier-style arrested landing on an inflatable mat with the ZELMAL project. This didn't work too well: the shock of landing tended to wreck airplanes and disable pilots, even when the airplane's tailhook didn't tear the inflatable mat open.
If I were designing a land-based "aircraft carrier", it would be a convoy of airplane launcher/transports plus assorted support vehicles. Landing would be accomplished with portable carrier-style arresting gear to let me turn any short, straight stretch of road into a temporary runway.
Before the aircraft carrier, the battleship was the queen of the battlefield. With impressive firepower and extremely thick armour, a battleship was the last word in firepower.
And well, people tried to build land based versions of it.
The planned nazi Ratte tank might be a good example. It was an attempt to build a superheavy tank - which by naval standards wouldn't have been very big, a mere 10,000 tons. It would have crushed bridges and not moved very fast or far.
A aircraft carrier would have had many of those problems writ large.
You can't really move it, can you.
That said, an aircraft carrier is really a big ship designed to move a landing strip and store planes. Its designed to project airpower where there's no other way to land a plane. or is there.
A landing strip is a nice large flat straight piece of tarmac. And well laying down roads temporarily is a solved problem. Have some way to level them, and your aircraft can land. While many aircraft have rough aircraft landing capability lets assume you want your fancy high performance birds landing. You want good, quality tarmac.
Just lay down prefab concrete slabs, and you have a landing strip.
Aircraft carriers also have catapults. Not really necessary, but you could probably build one into a large trailer, and design your prefab slab with launch rails.
Add some hardened prefab containers for maintainance and you're good.
If you want total mobility, you'd still need a caravan of vehicles but of a different sort.
What kind of vehicle would be suitable? I'd say a modified version of a bridge layer would work. Park the vehicles end to end, connect up deployed 'runway' sections, add emals (maybe powered by vehicles in each segment), and launch off it. Still sounds like a crazy idea when you can have some unskilled grunts and heavy machinary just throw together a temporary landing field...
Perhaps a traditional aircraft carrier wouldn't work. I don't really know the exact details of why we don't see massive vehicles, but I assume inefficiencies get too large to sustain.
However, perhaps a traditionally sized truck could hold a sort of temporary railway for the aircraft. The aircraft is transported in a truck facing backwards. When the aircraft needs to launch, the truck finds a clear length (long straight road or empty field), crew assembles a railway out the back of the truck (suspended above the ground). The aircraft then launches along the railway. Further supplies (such as fuel, ammo, and repair supplies) could be held in a second/third truck.
Landing could be more problematic. One option is that these trucks don't facilitate landing, and simply launch, then pack up and head home, where the aircraft land also. Another option is that the ground crew assemble a more stable landing structure for landing (using supplies from the secondary trucks).
Build multiple airstrips around the area you want to cover. Include basic structures and facilities at each. When you want to "move", load critical gear and personnel into air transports, fly all your planes to the new place, and have additional crew and gear loaded into trucks and buses and driven there.
It would cost a lot less, and be far more mobile.
(An aircraft carrier is a floating city, that houses and feeds around 6,000 people for MONTHS at a time. The personnel are as big (or more of) a problem than just making a moving surface for taking off and landing.)
A few decades ago, Germany tried another approach to have airstrips all across the country, at positions where no airstrip has gone before.
The center guardrail of freeways could be removed at short notice, turning the autobahn onto an airstrip. The autobahn section would need to unobstructed by bridges or traffic signs, of course.
There's a limited case in which it could be done: Sand.
You use much of the power of your reactor to blow air down into the sand. Do it right and you can fluidize it--and now your ship can move through it much like it would with water. (Albeit slower and I would hate to think of the erosion on your screws!)
I can't think of any situation where it would make sense to do in these days of guided weapons, though. In times past think of how potent a battleship would be in the Sahara, though.