What is so hard about a proper catapult on aircraft carrier?

Discussion in 'Boat Design' started by Squidly-Diddly, Apr 21, 2018.

  1. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I'm seeing these NEW British and Russian (top tier tech powers and ship builders...more or less) producing these BIG full size supersonic fighter jet carrying flatops with only ski-jump launch of fixed wing.

    What is so hard about a proper catapult? I could see if these were stop-gap hack-jobs, but for a purpose-built show-case mega-money ship??? IIRC the first modern cat system was that Nazi carrier that never quite got finished, and that was long time ago.

    Seriously, I bet any Junior College engineering student could design and spec-out off the shelf parts for a catapult able to reliably launch anything a carrier could carry, and for a lot less than cost of single aircraft. Mechanical Engineering of a straight line accelerator has been well sorted for 100+ years for a variety of power sources.

    Seems simple enough to me without even thinking too hard. Take a big electrical motor and a big cable and spool, attach one end of cable to a "shoe" that runs in a track and the shoe hooks onto the jet's front landing gear from the rear. They already got jets with cat-ready gear. I guess the USN used steam but I'm pretty sure a big (or bunch) of electric motors would do fine. Electric would seem the easy way to program in exact amount of force for each launch, all through the launch. Motors, cables and tracks are dirt cheap and easy to replace.

    Without a catapult everyone is launching low on fuel and/or weapons. Its like the Junior Varsity of carrier operations.
     
  2. Blueknarr
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    Blueknarr Senior Member

    Ski jumps have some advantages:
    Greater rate of climb immediately after launch
    Lower launch speed
    Lower acceleration forces
    Less wear to equipment
    Less wear to pilot
    Less deck space needed
    Smaller launch vessels
    Cheeper
    Safer

    Perhaps the junior varsity navies are thinking straight because they aren't roided up

    Ski jumps could be combined with catapults if unconscious pilots at 200 feet were desirable
     
  3. alan craig
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    alan craig Senior Member

  4. rwatson
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    rwatson Senior Member

    When the Australian Navy was accepting the Spanish designs with the Ramps, t hey looked at removing them for the straight deck.

    They found that there was so much equipment built inside the ramps that it wasn't economical to make the design changes.
     
  5. Squidly-Diddly
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    Squidly-Diddly Senior Member

  6. Squidly-Diddly
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    Squidly-Diddly Senior Member

    let me guess, new regulations requiring bathrooms for all 3 genders?

    Seems like the #1 task of a carrier would be to launch (not recover, we can worry about recover later) uncompromised aircraft in as capable a config as possible (full fuel for starters) and anything else is "who cares?"

    Given cost of related operations, I doubt I'd care if launching a jet required a big 1000lb disposable rack or jig of some sort flung into the sea and lost for each launch, or "high priority" launch.
     
  7. upchurchmr
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    upchurchmr Senior Member

    Squid,
    Catapults are not that simple, they require lots of maintenence, and they are really expensive.
    They work because a whole lot of engineering went into the development - Not Junior college level work.
    Did you see that the new ones on the latest carrier had to be redesigned and rebuilt? And that was on top of the mega dollar work done initially.

    Also, all the answers Blueknarr gave. Every single facility on a carrier fights for space when it is designed. How much space and equipment do you think is required to fling a 60t aircraft off a carrier at 200MPH?

    Not having a catapult CAN reduce the weight of the aircraft structure required.
     
  8. PAR
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    PAR Yacht Designer/Builder

    Ski jumps seem the easy way, but they're really not and this was proven out long ago in testing by the USN. After the Essex class served its role, the later class of aircraft would become much heavier, require much higher takeoff speeds, much longer takeoff runs, etc. It was determined that carrying the fuel you need to reach full up combat load takeoff speeds aboard the aircraft, wasn't very economical, so some sort of assisted launching device was envisioned. A great deal of experimenting was tried, but the Midway class easily proved the cat was the way to go. Subsequent super carriers Forrestal and Kitty Hawk, refinements and atomic power abilities yet to come, kept the catapult as the logical way to keep the flight deck relatively short, while still employing 4 elevators and 4 cats.
     
  9. Rurudyne
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    Rurudyne Senior Member

    Also catapults let you carry a heavier load. They're like honey badgers in that they don't give a darn what you hook up to them: it'll either fly or be likely far enough ahead of the ship that it'll sink before the ship gets there.

    Without catapults the USN might have had to built pykrete super ships to have enough deck to handled heavily loaded F4s to F14s, and maybe even F18s.

    And here we get to why ramps are finally becoming popular: the thrust to weight ratio with these new engines really has improved a lot.

    I suspect that non nuclear carriers don't have the super abundance of steam that the nuclear ships do.
     
  10. Squidly-Diddly
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    Squidly-Diddly Senior Member

    Mostly I'm just looking at the cost of new ramp carrier at several billion, and thinking that for ???? how much money could it be for a gang of big electric motors, cable, track and controller, given that the VALUE of going cat VS ramp must be in the high 100s of millions, given the cost/effectiveness of the feature.

    Wouldn't need to be even 1/3 as fast as USN fancy E-CAT or old steam to double and more the planes launched.

    What might a typical bid be for all the equipment, including capacitor banks if needed, before you tell them where its going to go and what its going to do, ballpark?

    What motor or group of motors could wind a cable or chain to send 80,000lb 0-200mph in 300ft?

    I'm thinking a drive chain running under the deck on front and rear sprockets on (geared?) motors. Says 140,000 max and 14,000lb working, but be OK if it wears out fast. At 23.5lbs/ft it would be OK to run more than one per plane. Item # MSR2856, 6.000" Pitch Chain, Straight Sidebars On Allied-Locke Industries http://chains.alliedlocke.com/item/msr-class-bushed-roller-steel-chains-2/msr-class-bushed-roller-steel-chains/msr2856-1
     
  11. PAR
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    PAR Yacht Designer/Builder

    Steam turbine propulsion supplied the juice for the cats, which were introduced with the Midway class. The Enterprise class was the first atomic powered carrier. The amount of steam needed to launch aircraft isn't all that much, easily handled by conventional turbine propulsion systems.
     
  12. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I guess tapping existing steam worked, but seems like it would take some real engineering and custom build money. I remember hearing how for each launch they'd need to SKILLFULLY play with all the steam settings for all the various factors. I'm thinking today all ships have huge generators, and electric motors, chain and sprockets would be off the shelf and plug&play and AUTOMATICALLY optimize for each launch. I remember seeing a motor about 4ft tall and it came with built in control module that plugged into a laptop.

    First thing to do would be a land-based prototype with whatever big motors could be borrowed or salvaged. Sounds a lot cheaper and surer than messing around with steam.

    Had a construction foreman who served as Chief Petty or something on cat-crew of 'Nam era carrier and said it was hell, partly due how "live steam would suck all the moisture out of the air"????
     
    Last edited: Apr 22, 2018
  13. alan craig
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    alan craig Senior Member

    Squiddly, did you read my link? It was only one page and half of that was pictures. Anyway, electric catapults have arrived, as shown here:

    It's not much of a video; same shot repeated many times but there are others on YT including testing on land.
     
  14. PAR
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    PAR Yacht Designer/Builder

    I wonder how much steam it takes, to drive the generators to make the juice to run the cat?
     

  15. alan craig
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    alan craig Senior Member

    This description gives more info than anyone needs:
    Carrier-Based Launch of Aircraft to Use Power Electronics Instead of Steam Catapult http://www.powerelectronics.com/power-management/carrier-based-launch-aircraft-use-power-electronics-instead-steam-catapult
    ....except that I wanted to know how much electrical power was applied to the linear motor during a launch. The article says that a typical launch takes 3 seconds and the max. available energy is 136kWh (about 1.5 fully charged Tesla S). So a max. power launch is a constant 163,200kW or about 217,000 h.p.
     
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