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.

[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: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.