Re: PLAN Aircraft Carrier programme..News & Views
Not so. What you described above is that a new ship is more efficient, which is a different concept to EMALS being more efficient. When people talk about efficiency, the are referring to the following cascades.
For steam catapult:
Energy storage -> work
For EMALS:
Energy storage -> work
In a steam catapult, majority of the energy is lost before becoming work. You can even see this lost in the form of steam leaking from the catapult during launch of an aircraft.
Well, saying that one layer of the cascade is more efficient than the other is moot. How is the energy storage created? - First law of thermal dynamics? lets take it from the thermal energy start; nuclear reaction or chemical combustion being the source energy.
For steam catapult:
1) Thermal energy is used to heat water to steam, and to desalinate makeup water (distilling)
2) Steam pressure is released in piston and convert pressure into work
For EMALS:
1) Thermal energy is used to generate steam to push a turbine
2) The turbine is used to drive a fly wheel
3) The fly wheel is used to drive an generator which generates electrical current
4) the electrical currents drives the magnetic rail to produce work.
So yes step 4 of EMAL may be more efficiency than step 2 for steam catapults; but what about the other steps?
If I have a bunker fuel turbine power source; thermal efficiency to steam is ~99.5%, max generator efficiency is ~50% on a really good turbine. (which is why modern destroyers uses turbine drive with electrical motors for propulsion; generating steam is efficient, but converting steam to shaft power - the whole process have an efficiency of ~30%). But the point being is, steam for steam cats are an efficient process. - but maybe if the study includes propulsion, then it could be different.
Then again all of this is relatively moot for a nuclear powered carrier. The reactor is what, 3-5% efficient? thats already sufficient energy to generate enough steam to do both.
Again, my point being that EMAL is not necessarily more efficient (and hence cheaper) than steam cat; vis-a-vis, it is most likely that steam cats are more efficient
In case of catapults, energy efficiency is not such a big concern, especially on nuclear powered ships. EMALs are revolutionary because (theoretically
) they have smaller size then steam cats, need less maintenance, have even acceleration and could launch heavier or lighter aircraft then steam cats .
I think, the pros and cons for EMALs are well discussed, electro-mechanical transmissions had been in discussion for a long time for exactly the same reasons; it is a concept that worked well in ship/subs propulsion and trains; but fails horribly in some land vehicle design (Porsche Tiger/Elephant, Soviet IS-6, and other tanks) which proved that maintenance is more than traditional mechanical drive systems.
The reason they work well in destroyers and trains, but not in tanks is more due to the power pack, large vehicles maintenance is performed by just hauling out the turbine unit and replacing it with one that had been maintained in a shipyard or train yard. Thats why maintenance for the crew is less and simiplier. But for tanks, like the Abrams, maintenance had to be done on the vehicle which then becomes very tough due to the space constraints.
So the fabled less maintenance... I will believe it when I see it, right now to me it is only a sales pitch.
The other stuff, steam cats can do as well, just need to update the design.
More even acceleration? -> Characteristic Control Valve design, and Hi-Lo pressure design
Heavier aircraft launch? -> max load is determined by EM rail capacity and steam pressure tube design.. so it is not something that EMAL have an advantage of, it is a question of design
Lighter aircraft launch? -> use less current, use less steam, both can be done; just need to update the steam cat design to allow it, with less steam loss.
