There are 2 major problems that make mechs - variable or otherwise - extremely impractical - materials and power.

On fighter planes materials have to be strong and lightweight. On variable mechs the stresses imposed would be even greater and the load paths more complex meaning the materials it's made up of need to be either bigger or stronger. If they're bigger the mech is going to be chunkier which limits its range of motion an increases its weight. Current materials just aren't strong enough for a variable mech to have any sought of fatigue life. They may last a couple of years and then scrapped ( and given the cost of a mech no ones going to buy one that lasts only a couple of years)

As for power, while we have engines capable of lifting a mech vertically ( see the f119 and f135 engines ) they don't produce enough electrical power to power all the servos and motors a mech needs. That means a secondary power source is needed which is going to eat into your already precious internal space, most of which has already been lost in making a mech fit into the space of a plane. This leaves the problem of fuel. While modern engines are more efficient than ever they still require lots of fuel. A variable mech would probably have enough space of maybe 5 minutes of flight. This could be remedied but a new type of engine - I believe in Macross the used nuclear fusion engines - but currently none exists and there are none on the horizon.

Materials and power are the 2 main issues but there's hundred of others like fuel lines, powerful enough motors, wiring, weapons, emergency procedures, etc. That said I still want one and I can't watch that first transformation sequence from Macross Zero only once, so if you ever overcome the materials and power issues I'll be the first to sign up to help you build a variable mech.

Impossible with current or foreseeable future technology. We have enough trouble building capable fighters as it is and then the end result of this would be an object which is neither optimized for flight or the ground and would furthermore suck at both.

[edit on 18/8/2009 by C0bzz]

Hello there Deltaboy,

I love your threads because you think outside the box and post some interesting stuff.

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A jetfighter that can change into a mech? That is way, WAAAAAAAAY out of our scientific league yet. The materials required to withstand such an extreme forces do not exist yet. Maybe Grafeen but that substance is extreemly hard to produce and if you want to build a whole plane out of it, then the costs for a single mech-jet fighter would run into the hunderds of billions of dollars. The entire project would run in the trillions.

Asides from problems with materials and required funding, you also have maintainance problems because of the huuuge range of different parts required of doing 2 functions in 1 machine.

Other problems are that the RCS value of such a fighter would be incredibly large and you would appear on radars all over the world. Considering the ever increasing speed of missiles today, even the supposedly added maneuverabillity of the mech form, would be nullified since the missiles are going to be speeding at you at Mach 6 at the very least. (If it isnt too far in the future that is. If it is, prepare for Mach 15+ missiles.)

To be short: Not practical, economic armageddon for any country, easy target in the BVR range.

I don't really see a practical function for an aircraft that can shift into a 'mecha. Now - for an armored vehicle (tank) - that might be an interesting idea (Tank traps? pick them up and move them out of the way. Mountain? That is what feet are for).

The exception would be for extra-planetary activity - exploring other planets, for example. Something that could navigate within an atmosphere and also handle rugged terrain with no prefabricated structures/facilities. Of course, oxygen-rich atmospheres seem to be in rather short supply, so you'd be looking at a form of engine/propulsion that doesn't 'breathe' and can function in a vacuum, as well.

Not to mention structural challenges.

A lot of work, considering you could drop a powered-armor suit and retrieve via a VTOL drop-ship.