Navy Uses Railgun To Launch Fighter Jet

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.'"

Comments

A linear induction motor is not a railgun.

[John Hasler]

n/t

Re:A linear induction motor is not a railgun.

[Anonymous Coward]

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.

[kindbud]

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.

[Anonymous Coward]

As being an MM many years ago, I can attest that steam is a real bitch to deal with. First there's a lot of maintenance involved to keep the cat risers in top order. And the steam to operate them places a lot of demand on the plants. If it's hard to "make water" for some reason, some birds may not be flying that day. (Running generators to charge capacitors means you could keep a lot more of that water in closed loop and a lot more held in reserve.) Not only that, but steam isn't exactly the most efficient working medium. Steam or at least the heat associated with it has a funny tendency to leak out in places and thermal insulation isn't perfect, so you have a lot of spaces on a carrier that can inadvertently become saunas. (And it's already too F'ing hot in places like the Persian Gulf. A/C can't always win when adjacent to some steam system.) A slow leak (as opposed to a much more noticeable one that's jetting out), is going to end up with a lot of water or condensation pooling around somewhere. (There's usually catch trays for that, but that means more plumbing. And those drains can and will plug up at times. Not to mention extra valves for DZ and all that.) Also with the rush of steam in pipes, there's a LOT of noise generated. Just the whoosh of the mass moving, or constant tic-tic-tic of thermal expansion and places where water hammer may be occurring in the lines. Then of course with the steam catapult systems, there's these huge pistons. So those things are massive in their own right in addition to the weight of the aircraft. And they're not exactly easy to work on and require a whole lot of grease. If there's a big enough problem with one of those, the carrier pretty much has to go back to the shipyard.

Now some old timers may look at it with disdain, as it makes A-Div less needed aboard ship. Not to mention there'd be less talk between M-div and topside. But from my perspective, anything that means less running outside of the plant for engineering means that the ship would be operating much more efficiently. Less shit to fix, and therefore less shit to go wrong. Then again life in E-Div on a carrier will probably get more interesting, as more and more systems go from steam to electric and require EMs where MMs used to be involved.

Re:A linear induction motor is not a railgun.

[arivanov]

Not necessarily. Multiple injection steam pusher is a concept old as the world. Most submarine launchers are like that - as the missile goes up more nozzles come into play on the sides giving it a good enough kick to clear the submarine and the water above it without breaking it in the process.

The article misses the biggest advantage of electric vs steam. Electric has a much lower chance of failures in sub-zero temperatures. Steam is a nasty business at -5 or less. It condenses and freezes at all the inevitable leaks along the catapult pusher path. A couple of launches and the pusher is bound to get stuck damaging the aircraft in the process.

IMHO, A ship with an electric catapult (or a ramp) has "Arctic/Antarctic war" stickered all over it. On the positive side this means that we are done with the Gulf and its surroundings. On the negative side this is one place which has seen very little war (except the North Atlantic portion of the Arctic in 1941-44).

Re:A linear induction motor is not a railgun.

[JustinRLynn]

MM = Machinist Mate, think Mechanical Engineer but for maintenance operations on mechanical equipment. EM = Electrician's Mate, think Electrical Engineer but for maintenance operations on electrical equipment. A-Div: various shops and other groups that maintain the mechanical systems such as Hydraulics, AC, Steam and Heat, the catapults, fire pumps and water distribution systems, among others. M-Div: Machinery division refers to the group of MMs. E-Div: same for EMs. Afraid I don't know what DZ means, though it's a METAR code for drizzle, so perhaps that's what's being referred to. No first hand knowledge here, just stuff gained from reading, so please if you've got first hand or links, please correct.

Re:A linear induction motor is not a railgun.

[Anonymous Coward]

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.

32. Eight reactors, 4 steam generators per reactor.

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.

...

Nope. Somebody was lying to you. We just needed to watch our water levels in the secondary. Which on the EnterPig you had to be on top of anyway - and that was 20+ years ago. I can't imagine how bad that ship is now.

Of course, some could fuck up even the watching of water levels. One PPWO "lost" 7,000 gallons of water - and it wasn't even during flight ops. Since the 4 steam plants on the Enterprise could be interconnected in some ways, he was calling around to the other EOS's trying to find his lost water. The joke in the wardroom later was, "How the hell can you lose 7,000 gallons of water? And not be able to find it? 7,000 gallons of water will find YOU!" Prior to this incident, this one officer's nickname was "Rock" - as in "dumb as a". After someone remarked "He's not a rock, he's a fucking boulder" because of the "lost" water, he was known as "Boulder".

The full nickname has been redacted to protect the not-so-innocent.

Re:Carrier stumbles over chair, 1000's Embarresed

[DesScorp]

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:Rail Gun Weld

[Rakishi]

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:But why have a catapult at all?

[LWATCDR]

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?

[jklovanc]

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 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

Without catapults none of these aircraft would get off the deck.