wrote:

I'm assuming there is no "weight" limit on the catapult. The immagine
the catapult would have a broad specification of
1 firstly the force it can generate at say zero speed.
2 secondly the maximum speed it can reach.
3 maximum power it can transfer.
4 the amount of energy it can transfer (I assume there is some kind of
steam reservoir or accumulator)

There might be a weight limit on the deck. I see no reason say a
160,000lb aircraft can't be launched so long as it can be accelerated
to above its stalling speed which of course needs to be lower the
larger the aircraft gets.

In the 1930s the Germans were catapulting the 38,500lb 4 engined Blohm
& Voss Ha 139 using a pneumatic catapult.


http://www.century-of-flight.net/Avi...s%20Ha.139.htm


The theoretical limit would be the total energy (E=mv**2) that can be
transferred in the distance allowed by the cat stroke. With a
constant-pressure system, the force applied is essentially constant, so
the acceleration would also be essentially constant. Theoretical max
force at the cat piston would be the max (nominal 1200 psi) steam
pressure of the ship's system times the surface area of the piston.
Acceleration would then be inversely proportional to the mass of the
airplane (F=ma), so end speed would be limited by total energy
available.

If you know the steam pressure, diameter of the cat piston, and the
length of the stroke, you could calculate a theoretical max force
applied, and then the max energy available. Of course, system friction
losses and component limits would reduce that somewhat. Mass of the
airplane would be limited by required end speed (stall + margin -
headwind).