Catapult On A New Aircraft Carrier

How can such launching speeds are attained with themanual NAEC-MISC-06900 is also a good authority,
referenced system. Something along the lines of abut it only mentions "fluid" in the context
steam piston pumped up in pressure until a speciallyof the arresting gear. Ditto the LSO manual;
designed part breaks and the aircraft is flung into the"engine fluid" but never
air. There are two aspects left out that seem"water."
pertinent to me (as both an engineer and retiredVery little of the steam escapes the catapult- the
Navy engineer):vast majority of it is reclaimed and reheated. It's far
1. the launching valve is a very fast opening-closingeasier to turn 211 degree water into steam than to
valve.boil seawater from scratch!
2. Prior to the launching valve, steam isThe structure supporting the catapult is incredible, as
"stored" in a steam accumulator,is the water brake- ships are designed as a giant
essentially a large insulated tank.cantilever beam with most of the displacement in the
The combination of the accumulator and launchingcenter, and the bow and stern as cantelievers. And I
valve is what delivers a large amount of hightell you what- the entire bow of the ship shakes
temperature and high pressure steam to the pistonswhen the catapult slams into the water brake! All
in a very short time. There is definitely a quick actingthat massive steel and it still moves under the
launch valve, length of time the valve is open isstresses, it's incredible.
calculated based on take off velocity and weight ofPre-heating has other purposes as well. Like most
the aircraft. The "holdback device" is themetallic systems, catapults expand when heated.
part that breaks. The aircraft carrier carries a literalThey will expand significantly (I don't recall the
truckload of the holdback devices for the duration ofnumbers) from ambient to operating. If one were to
the voyage, since it's a one-time use device.try to operate the catapult without the system being
For ground-based operations, the aircraft can be heldheated and expanded, I suspect there will be
against the brakes until the engine is developing fullsignificant mechanical problems, including even the
thrust. To do that on a carrier, you'd need to findpossibility of the ram hanging up. "Very little
some way of coordinating brake release with steamsteam" escapes, this is relative. I believe as the
valve opening - and it's probably easier just to have aequivalent of over a hundred gallons of water is lost
weak link in the system instead.on each cat shot, assuming steam leaks are minimal.
I don't believe water is used as a hydrauli fluid in theFrom my experience, its not just the bow of the
arresting gear machinery. It is a Water-Brake, but thisship sthat "shakes" on launch, you can
is part of the catapult, not the arresting gear. On thefeel it everywhere on the ship! You can't really feel
catapult, the pistons that are pushed forward by thethe bow cats outside of the bow, or the waist cats
steam need to decellerate from ~160 mph to zero inmuch outside of the sponson. I mean, there's a little
a matter of feet. This is accomplished by using abit of noise but not really any noticeable vibration and
"water brake", and the water does getthere's so much noise from elsewhere it's drowned
very hot, and must be refilled periodically.out. If you're down 2nd deck and below aft of about
Don't take fresh water too casually. A lot of landframe 100 or so, you'd never even know they were
based arresting gear is water-filled - I'd be surprised iflaunching or recovering aircraft.
the shipborne stuff was significantly different.I think they use a lot of steam, but I can guarantee
According to the LSO manual, the launching valvesthey're not loosing a hundred gallons of water during
have adjustable orifices control the pressure of thelaunch, there just isn't that much steam coming
steam into the pistons. The holdback device is alsothrough the slit, a couple of gallons, maybe ten
called a tension bar and when that breaks, thegallons at the most. If you were losing that much
built-up steam then expands to push the piston andsteam over the length of the catapult, it would lose
aircraft forward. Note that the manual discusses thepressure and stop accelerating towards the end;
importance of pre-heating the entire assembly toinstead we just see a tiny bit of seepage. Perhaps,
ensure that the steam's energy is not wasted init's a difference in carriers.
heating up mechanical components. The carrier