Navy Uses Railgun To Launch Fighter Jet 314
Phoghat writes "In 2015 the aircraft carrier USS Gerald R. Ford will take to the seas and the plan is to use a railgun to launch planes, instead of steam powered catapults. From the article: 'The Navy developed its Electromagnetic Aircraft Launch System as a replacement for the steam catapults currently used on aircraft carriers. The EMALS is a linear induction motor that's capable of accelerating a 100,000 pound aircraft to 240 miles per hour in the space of 300 feet. Compared to a steam catapult, the railgun catapult is much smaller, more efficient, simpler to maintain, gentler on airframes, and can deliver up to 30% more power. It's also capable of being cranked down a whole bunch, meaning that it can also launch smaller (and more fragile) unmanned drones.'"
A linear induction motor is not a railgun. (Score:5, Informative)
n/t
Re:Rail Gun Weld (Score:5, Informative)
Isn't one of the problems with railguns that sometimes the projectile will weld itself to the rail? What happens if that occurs with a jet launcher on the rail, and a plane hooked to that?
As another poster pointed out [slashdot.org], this technically isn't a railgun. It's a linear motor. This is more like a mag-lev train. The other big advantage is that in a real railgun, the rails need frequent replacement.
If you were expecting technical accuracy from our esteemed professional Slashdot editors, that day has not yet arrived. They're still trying to figure out how to work a spell-checker and how to use basic English grammar. As long as the ad revenues and the paid account revenues keep on flowing, I suppose they don't feel much pressure to get these things right.
Re:A linear induction motor is not a railgun. (Score:3, Informative)
v = 400km/h = 111m/s
s = 100m
v^2 = 2as
a = v^2/2s
a = 12321/200
a = 61m/s^2
g = 9.8m/s^2
a = 6.3g
Re:Carrier stumbles over chair, 1000's Embarresed (Score:5, Informative)
USS Gerald R. Ford? You have to be kidding me. What's next. USS Chevy Chase?
Trust me, many Navy vets (including this one, who served on a carrier) are tired of the Navy naming our biggest capital ships after politicians. Layups like George Washington or Thomas Jefferson, no problem. But Gerald Ford? Really? There's a feeling in the Navy that we should stick to traditional names.... the Essex, the Hornet, the Lexington, etc, for our most prominent ships. But don't look for this practice to end, because appealing to political egos helps grease the Congressional appropriation machine.
Re:A linear induction motor is not a railgun. (Score:5, Informative)
Same accelerator concept though.
No, it is not. It is far more similar in concept to a mass driver.
A railgun consists of two parallel, electrically conductive rails, each connected to one terminal of a charge storage device (usually a capacitor, but if you've got something better, go with it). The charge storage device is charged to full power, and then a conductive projectile is placed across the rails, completing a circuit.
The completed circuit resembles a large inductor, in that it is a large conductive loop with current flowing through it, whose inductance is proportional to the area enclosed by the loop. The magnetic field generates a force upon all the components of the railgun, but since the projectile is the only part not rigidly fixed, it is moved by the force. The force acts to increase the size of the inductive loop, driving the projectile away.
The key component to note here is that the projectile needs to be conductive, not ferromagnetic, and the rails must be exposed in order to pass current. This limits military applications because the presence of dirt in the rails could break the circuit, causing an electric arc flash, causing the system to act more like an arc welder. Also, the rails wear out due to the heating caused by the lack of superconductivity.
Read the Wikipedia articles for Railgun and Mass Driver more details.
Re:A linear induction motor is not a railgun. (Score:4, Informative)
A lot fewer moving parts and better control over the stroke energy
Looks like they've done over 220 test fires of this already in 2010
http://www.navair.navy.mil/NewsReleases/index.cfm?fuseaction=home.view&id=4468 [navy.mil]
http://en.wikipedia.org/wiki/Electromagnetic_Aircraft_Launch_System#Advantages [wikipedia.org]
Re:Rail Gun Weld (Score:5, Informative)
Only at sufficient speeds/friction. There's no reason a railgun-based aircraft launcher would be more prone to this problem than a steam-based one.
As I understand the issue, it has nothing to do with friction. In fact it's probably more likely to get welded if it's going too slowly.
A rail gun is basically an arc welder in a way, you're passing massive amount of energy in the form of electricity through the interface between the rails and projectile. A high power rail gun has enough energy passing through to basically vaporize nontrivial amounts of metal off the rails every time it's fired. If you're unlucky on the other hand it'll simply weld the projectile to the rails.
Re:Carrier stumbles over chair, 1000's Embarresed (Score:5, Informative)
Carter was never a sub captan. He served on a submarine but was not a commander.
Actually the shouldn't have named the sub after Jimmy Carter or the Carrier after Bush. It is tradition that no Navy ship is named after a living person. It was broken by the Burke class. It was unintentional because it takes so long to design a new ship that the Navy was sure that Burke would have passed on by the time the Burke was launched. He lived to a very ripe old age and mess up tradition.
There is no reason to not name a ship after a President of the US and what most people don't know is that Gerald R. Ford was actually a very good president under considering what he had to work with. He as also a very good and honorable man as politicians go. I don't think you can find a single blemish on his record and historians today say his pardon of Nixon was the right thing to do.
Re:But why have a catapult at all? (Score:5, Informative)
Yes because cats are a better solution.
You can launch heavier aircraft with a cat than with a ski jump. The Russians and UK can not operate aircraft like the E-2. Also the UK is going to put cats on their latest carrier because the F-35b may fail.
Also a Ski jump can not launch while the carrier as at a stop which can be useful.
So yes the sky jump has one benefit but a lot of drawbacks. The Russians used them because it was a low risk for their first real carrier. The brits used them because they only had the Harrier. It did work very well for the Harrier but the Harrier was not as good of a fighter as the F-14 or F-18. It also was not as good of an attack aircraft as the F-18, A-6, or A-7. But it was better than nothing.
Re:But why have a catapult at all? (Score:5, Informative)
Where fighter and bombers get all the glory there are a few equally important heavy aircraft that need catapults to launch:
AEW:
Aircraft such as the the E-2 Hawkeye http://en.wikipedia.org/wiki/Northrop_Grumman_E-2_Hawkeye [wikipedia.org] are critical to hiding the location of the fleet. If the enemy sees a ship based radar they know where the ship and usually the fleet is. If they see an airborne radar the fleet could be very far away. Also airborne radar can see further.
COD;
Carier Onboad Delivery, Need those critical parts or personel delivered outside of helicopter range? Need to evacuate critically injured personnel? You need a long range aircraft to do it.
Tankers;
Need to extend range to a target? Need to loiter for long periods on CAP. Need a sip of fuel to get back to the carrier because you used to much afterburners in the fight? Tankers are your friend. This role is currently done in the US Navy by the F/A-18E/F http://en.wikipedia.org/wiki/F/A-18E/F_Super_Hornet#Tanker_role [wikipedia.org]
Without catapults none of these aircraft would get off the deck.
Re:A linear induction motor is not a railgun. (Score:5, Informative)
Perhaps. But depending on the capacity of the steam reservoir - which is presumably huge on a nuclear aircraft carrier - the pressure drop is almost certainly negligible.
It's not. I've manned the steam generator control station on an aircraft carrier, and the drop in water level and steam pressure is dramatic and it takes several minutes to recover. Of course, we had 16 steam generators on the USS Enterprise in the 80's. Perhaps the newer carriers with just 4 steam generators (2 per reactor) are more efficient. But I do recall flight ops were a very very busy time for the MMs in the hole.
This looks like a big improvement. Electricity generation is a much closer to a steady-state kind of operation for a naval nuclear power plant.
Re:A linear induction motor is not a railgun. (Score:5, Informative)
You know that the starting velocity is zeroish(maybe a little bit of taxiing; but negligible) and that the end velocity is 240mph; this makes calculating average acceleration over those 300 feet trivial;
Actually, it doesn't. Average acceleration is defined as the change in velocity divided by the time interval over which the velocity changes: a_avg = delta v / delta t. The problem here is that you aren't given delta t, but rather the distance through which the jet accelerates. Now, if you know the acceleration is constant, it is easy to calculate the acceleration by means of the formula v_f^2 = v_i^2 + 2a delta x, but for non-constant acceleration, delta t over a fixed distance will depend on the shape of the acceleration curve. Therefore the average acceleration will also depend on the shape of the curve.
Re:A linear induction motor is not a railgun. (Score:4, Informative)
Re:Carrier stumbles over chair, 1000's Embarresed (Score:4, Informative)
Really? Not even a simple google search?
Re:A linear induction motor is not a railgun. (Score:5, Informative)
Re:A linear induction motor is not a railgun. (Score:4, Informative)
To accelerate a 100000 pound object to 240 mph requires an energy of 260 MJ (sorry I converted all units to SI before I started calculating so you have to convert it back to BTU or kcal or whatever the right unit for energy you want to use yourself). Assuming a linear acceleration over 300 feet to 240 mph gives an acceleration time of 1.7 s. This results in an average power of 153 MW. AFAIK there is no electrical turbine that will supply an extra 153 MW at the flip of a switch. Electrical energy has to be stored somewhere to let the catapult work.
Nyh
It's more than just the weather (Score:5, Informative)
Steam systems are a nightmare to maintain in any weather conditions - switching from steam to electricity has been an ongoing process in the Navy for decades. The old Charles Adams class DDGs had all-steam propulsion plants - meaning that every oil pump, fuel pump, and every other system ran on some kind of steam. Those guys spent their lives maintaining steam turbines. As time has gone by, the Navy has gotten away from steam in a big way for exactly that reason - all that steam technology required a lot of sailors to keep running, and sailors are expensive. For what it's worth, I'm qualified as a Navy Engineering Officer of the Watch (EOOW) in 1200 lb steam, so I have some considerable personal experience with this.
I also think that you're likely to get performance improvements from EMALS. So I really doubt that this move has much to do with an anticipated Arctic war - there are big advantages to moving away from steam in any weather conditions.
Re:A linear induction motor is not a railgun. (Score:4, Informative)
Probably not, as the steam piston moves down the bore, it takes increasing volumes of steam to be delivered to maintain the constant presure and that is unlikely to be possible. The gas flowing through the pipes is going to encounter resistances which will cause presure and temperature flucuations, the nice dry superheated steam is going to have areas where condesation occures and saturated steam results causing even more flocuations. Most of these effects will be chaoic and erratic so they build some over-kill into the system to compensate. The video of the launch looked real nice and smooth, regualar steam catpults launches seem much more jerky.