Electromagnetic catapult

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Electromagnetic catapult

Abstract:

The electromagnetic aircraft launch system (EMALS) is a type of aircraft launching system currently under development by general atomics for the united states navy. The catapult, identical to those that launch airplanes abroad navy carriers. Electromagnetic catapult was developed for navy’s General R. Ford-class aircraft carrier. He was first to use electromagnetic catapult.

Due to flexible architecture, EMALS can launch a wide variety of aircraft weight and can be use on a variety of platforms with differing catapult configuration.

Need to use electromagnetic catapult:

The system launches carrier-based aircraft by means of a catapult employing a linear induction motor rather than the conventional steam piston. Basically, it is design to replace the steam catapult system. Steam-powered catapults, expensive and difficult to maintain, are operating near their limits and will not be able to accommodate heavier aircraft planned in future.

As the 21st century dawns, steam catapults are running out of steam. Massive system that requires significant manpower to operate and maintain, they are reaching the limits of their abilities, especially as aircraft continue to gain weight. Electromagnetic catapult will require significant manpower to operate and improve reliability; they should also lengthen aircraft service life by being gentler on airframes.

The amount of steam require to launch an airplane depends on the craft’s weight, and once a launch has begin, adjustments cannot be made, if too much steam is use, the aircraft. If too little steam is use, the aircraft won’t reach take off speed and will tumble into the water. The launch control system for electromagnetic catapult, on the other hand, will know what speed an aircraft should have at any point during the launch sequence, and can make adjustments during the process to ensure that an aircraft will be within 3 mph of the desire take off speed.

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weight capacity of catapult

Electromagnetic catapult:

As hydraulic catapults gave way to steam in the 1950s, so the early years of the new millennium have seen the development of an alternative technology for launching aircraft, the electro-magnetic (EM) catapult.  EM catapults are power not by a steam driven piston but by linear induction motors or LIMs.  Linear induction motors work on the same basic principle as all induction motors except that the motor is effectively unroll to provide a linear stator and rotor. The movement of the armature or rotor through stator’s electric field is thus linear rather than angular or rotational.

The principle was first demonstrate in the military field in 1944 when the Luftwaffe test a LIM- power anti-aircraft gun.  LIMs have since been use to power monorails at Euro Disney in Paris and on Vancouver’s rapid-transit system. They have also been use to drive roller coasters into the 160,000 kph. range and an experimental LIM- powered train has achieved 400 kph. The USN is currently developing the Electro Magnetic Aircraft Launch System (EMALS) for installation in the USS Gerald R Ford (CVN-78), the first of its new generation of super carriers. This is a particularly interesting development as the USS Ford will be nuclear powered and thus has abundant steam available for conventional steam catapults.  Despite this, the USN has chosen to develop EM technology.

An EM launch system offers the requisite higher launch energy as well as substantial improvements in areas other than performance. These include reduced weight, volume and maintenance, and increased controllability, availability, reliability and efficiency. The ability of an EM system to vary speed and thrust to meet the needs of the vehicle being launch makes a single catapult suitable for a wide range of airframes, both manned and uninhabited.

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first electromagnetic catapult

How does it work:

The scale model in the Lakehurst lab is a linear induction motor. An efficient way to generate thrust with a minimum of moving parts. Shipboard electromagnetic catapults will be base on larger linear induction motor. Made up of three main parts: two 300-foot-long stationary beams, or stators, spaced a couple of inches apart, and a 20-foot-lonf carriage, or shuttle. Which  is sandwich between the two beams and can slide back and forth along their lengths.

Each beam is made up of dozens of segments. Running down the spaces alongside the two beams, in sealed housings, is the wiring need to energize them and turn them into an electromagnetic force to propel the carriage. Selectively turning on and off each beam’s segments generates an attractive magnetic force at the carriage’s leading edge and a repulsive magnetic force at its rear. At no point are all the beam’s segments near the moving carriage are energized, creating this effect of a magnetic waves.

The interface between carriage and airplane runs through the aircraft’s nose wheel landing gear, using the same hardware employed by the current steam catapult system. After hooking up to the carriage, aircraft are electro-magnetically push and pull down the catapult until airborne. After releasing an aircraft at speeds approaching 200 mph, the carriage will come to a stop in only 20 feet, its forward movement countered by reversing the push-pull electromagnetic forces of the two beams. The same energy is then use to return the carriage to its starting position.

speed of working:

An electromagnetic catapult can launch every 45 seconds. Each three-second launch can consume as much as 100 million watts of electricity, about as much as a small town uses in the same amount of time. In shipboard generators develop power is store kinetically in rotors spinning at 6400 rpm. When launch order is given, power is pull from the generators in a two-to-three-second pulse, like a burst of air being let out of a balloon. As power is drawn off, the generators slow down and the amount of electricity they produce steadily drops. But in the remaining 42 second between launches, the rotors spin back up to capacity burst of energy.

Working of electromagnetic catapult based on circuit diagram:

For the design that is being use for this project contains a rectifying circuit for charging of the capacitors. The capacitors that are being use in this application are two 250V 12,000µF which are not capable of being fully charge by a regular power supply. In order to fully charge the capacitors, the charging circuit will contain several voltage doublers to give enough voltage to charge the capacitors. Once the capacitors are charge they amount of charge will be monitor in Lab-View by using a voltage divider and scaling the low voltage in Lab-View appropriately to give an accurate reading.

The amount of charge stored in the caps will vary depending on the amount of weight that is trying to be launch. Attach in between the capacitors and coil is a 4 layered PNPN SCR (Silicon Controlled Rectifier) which is trigger by a lower voltage of 1.7V. When the lower voltage is apply at the gate of the SCR the current from the capacitors passes through the PNPN junction and flows through the coil.  When current is flowing through the coil it generates a magnetic field around the piston that has an opposing magnetic charge of the coil repelling it through the channel at very high speeds.

Several switches are use in the circuit for safety including a charging switch and firing switch. The control system for this project will all be finish through Lab-View which will apply the 1.7V to gate of the SCR to trigger the device.  In addition to triggering the SCR, Lab-View will also be responsible for determining how much charge the capacitors will hold depending on how much weight is being launch by thresholds set in the program.

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circuit diagram

Present electromagnetic catapult:

The present EMALS design centre around a linear synchronous motor, supplied power from pulsed disk alternators through a cyclo-converter. Average power, obtain from an independent source on the host platform, is store kinetically in the rotors of the disk alternators. It is then release in a 2-3 second pulse during a launch. This high frequency power is fed to the cyclo-converter which acts as a rising voltage, rising frequency source to the launch motor. The linear synchronous motor takes the power from the cyclo-converter and accelerates the aircraft down the launch stroke, all the while providing “real time” closed loop control.

Advantages of electromagnetic catapult:

The main advantage is that it accelerates aircraft more smoothly, putting less stress on their airframes. Compared to steam catapult, EMALS are less expensive and require less maintenance and can control the launch performance with greater precision. It also reduces the carrier’s requirement of fresh water, thus reducing the demand for energy-intensive desalination.

Benefits of electromagnetic catapult:

1.EMALS provides significant benefits over current launch system, including:

2.Reduces manning and lifecycle cost.

3.Reduced thermal signature.

4.Increased launch operational ability for manned and unmanned aircraft.

5.Reduced topside weight.

6.Reduced installation volume

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