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Watch the US Navy Test Its Electromagnetic Jet Fighter Catapult
An anonymous reader sends word via Engadget that the U.S. Navy has tested its Electromagnetic Aircraft Launch System for the first time with a "dead-load" (a wheeled steel sled that weighs as much as a jet) aboard the Gerald R. Ford carrier. The article goes on to say: "Its advantages over traditional catapults that use steam instead of electromagnetic energy include smoother acceleration and its ability to place less stress on the aircraft — plus, it was designed to work even with more advanced carriers that the military will surely use in the future." You can watch a video of the "dead-load" testing here.
I'm not a practicing engineer, but am one by training. I would imagine that an EM system allows one to "ramp up the power" vs a steam head slamming into a piston and the resulting sudden strain on the plane.
My question is, could you not use something similar for civilian aircraft using a longer ramp up time to lower the amount of fuel on the plane a saving some cost?
http://en.wikipedia.org/wiki/E...
Advantages
Compared to steam catapults, EMALS weighs less, occupies less space, requires less maintenance and manpower, is more reliable, recharges more quickly, and uses less energy. Steam catapults, which use about 1350 pounds of steam per launch, have extensive mechanical, pneumatic, and hydraulic subsystems.[4] EMALS uses no steam, which makes it suitable for the Navy's planned all-electric ships.[14] The EMALS could be more easily incorporated into a ramp.[4]
Compared to steam catapults, EMALS can control the launch performance with greater precision, allowing it to launch more kinds of aircraft, from heavy fighter jets to light unmanned aircraft.[14] EMALS can also deliver 29 percent more energy than steam's approximately 95 megajoules, increasing the output to 122 megajoules.[4] The EMALS will also be more efficient than the 5-percent efficiency of steam catapults.[2]
Mit der Dummheit kämpfen Götter selbst vergebens
goombah99 mentions there's no shortage of steam, but newer carriers are moving away from needing steam to be generated, preferring to take power directly from their generators to the linear motors up top.
Aren't they going to have to generate steam at some point to make power with their nuclear reactors? This is an advance nonetheless because steam is a bitch in a way that electricity isn't. A pinhole in your insulation might cause a shock, but it won't cause people to be cut in half. Steam is awful.
"You're right," Fisheye says. "I should have set it on 'whip' or 'chop.'"
Catapult launches have specific power requirements to get a given mass to a specific acceleration. This has to be exact. To much or to little causes issues to the airframe in question.
Steam has minimum power/ pressure requirements just to get the system moving. That means there is a minimum load that can be launched. For fully fueled jets or cargo planes that isnt a big deal. For a UAV at half the size it means you have launch issues.
Emals always a much larger load range at launch. You can tailor the power requirements for the mass/ acceraltion ratio you want at launch. This means you can launch a quarter size drone and a full sized jet easily. Something steam struggles with.
Seriously this is Slashdot and basic physics.
i thought once I was found, but it was only a dream.
Steam seems like an ideal solution to me. Steam expands so well the dynamic range of it's force curve seems apropos to the task. How much of the EM energy goes into force? surge currents and magneto striction are usually things people find shorten the lifetime of electo devices yet here they are at the extreme in these. Presumably there's no shortage of steam available and it's a great way to store energy.
Really? My intuition is completely the opposite. Steam may expands well in the dynamic range but electricity will do anything it's controlled to. Want an exponential acceleration? Linear? Sinusoidal? You name it.
With sectorization and a few feedback control unit, it seem to me that you could precisely and instantly control the power transmitted into the catapult anywhere along the ramp. You could also drastically change the speed if needed, also something that doesn't seem as easy with steam. You since those carrier are nuclear-powered it take way less space than a whole steam system.
But, since my field is electrical engineering, I guess my opinion is a little biased.
Elok
That old news was overcome by events over half a year ago. Prince of Wales is not going to be mothballed at infancy after all. 2014 September 5: "The Royal Navy's second new aircraft carrier, the Prince of Wales, is to be brought into service rather than sold off or mothballed, Prime Minister David Cameron has announced. ... Both carriers will not be fully operational until 2023, the Ministry of Defence said."
Jeeze, struggling to no more than the third and fourth sentences of Wikipedia would have told you that.
The Queen Elizabeth class aircraft carrier program has been beset with enough heavy weather without having to cite obsolete information.
Former carrier pilot here, so I'm familiar with the output of the old steam systems (having used/lived-and-not-died by them).
You would think that steam is better, and in terms of simplicity of energy supply, it might be: Run a bunch of pipes maintaining the steam energy levels, and hit the button--boom! You're done.
However, reality is hella more complicated. Old catapults were one-shot; you loaded up the steam, and hoped to hell that the spike in acceleration didn't break your aircraft (thus leading to a lot of over engineering of the aircraft and very careful quadruple-checking that you have it set for the right weight/speed/etc.)
Newer catapults were progressive--you add steam along the travel of the ram, and the acceleration was smoother. However, that means that you have to have multiple valves that function exactly right--enough of them go wrong at once, and you're just going to launch a $30+ million aircraft and crew into a minor speedbump in front of the carrier.
The ram itself is very impressive. Carriers have a couple hanging on the walls of the hangar deck, and they are monstrous--I don't have any stats, but they are like 30+ foot long torpedoes that have to be accelerated with the aircraft, then stopped in a very short distance. When carriers launch, you feel the entire ship shake from this massive metal rod hitting the front end of its track.
Then there's maintenance. We're talking live steam here, not the piddling crap that comes from your tea kettle. It's "dry", as in superheated and has to be kept that way. But that means complicated insulation, piping, and constant checking that you're not eating away at your metals in this environment. Not only to you have to keep it at the correct condition before using it, but you have to do something with the used steam--which means an equally complicated recovery system.
All of this adds up to a massive effort to slingshot some dumbass (speaking as one) off the front end of a ship so he can use equally complicated gear to try to stop him after a cycle or two.
Steam works, but only because it was the only medium that could do the job at the time. I don't know the details of the EM rails, but I'm sure that the final design probably uses electric/electronic analogs to the system...but you can replace a bad circuit board or switch a helluva lot easier than you can a bad valve or piping. That, and more refined control of the overall launch makes this an obvious evolution.
Never confuse movement with action. --Hemingway
That's all well and good but surely the power you speak of is allocated for propulsion?
Some numbers: the Nimitz-class carrier generates at least 190MW, a steam catapult on that carrier requires up to 72MJ of energy per launch (at maximum). So a Nimitz-class carrier could launch one airplane per second without using a great deal of its power. In practice, it's rare for a steam catapult to launch more than one aircraft per minute, which means that even with 4 steam catapults going at their maximum rate and hauling a maximum load, the average energy use would be about 18MW, or less than one tenth of the steam power available.
Hint for you: not all of the steam power is allocated for propulsion; much is for "other uses". The Nimitz-class carriers can use only up to 140MW for propulsion.