Can I postulate from this post that the US EMALS catapult suffers from fundamental design problems and any solutions would be a patch job? They would have to abandon this catapult and start all over?I was watching this.
At 4:07 it is said that US EMALS LIM (linear Induction Motor) has open magnetic circuit. So I re-read "Electromagnetic Aircraft Launch System - EMALS by Michael R. Doyle et al." And also found a research papers from China published in IEEE.
Here is the difference between the US EMALS and China's.
US.
China.
The difference is apparent that US EMALS has its magnetic field going outwards through the air to create a loop. China's magnetic field is almost closed except the gap where the carriage is inserted.
Here comes the interesting and important part, the EM interference of LIM to aircraft's and missiles' electronics. So I found another Chinese research paper on the subject from IEEE.
It means, from the gap within 2m working equipment need to be shielded. Within 5 meters equipment not shielded at all will be interfered. I think this means civilian grade equipment, not military grade which should always have some kind of shielding.
I remember an old topic about the EM interference of US EMALS which is troubling Ford class. The design difference above could be the fundamental cause. The Chinese approach has that small gap being the source of the EM leak. In the gap most magnetic flux reaches the other ends, only small portion leaks. Most of that gap is filled by the carriage blocking the leak. While in the American approach the saddle carriage only cover the top and side but leaving the bottom opened. The opening is much much larger than the gap. Also the carriage (as the LIM rotor) is always shorter than the excited stator coil winding. The exposed stator coils are totally free to emit EM field to the surrounding area. Even in the Chinese design, interference within 2m is unbearable that need shielding. One can imagine the much stronger interference in the US design and how difficult to deal with.
This again proves why Admiral Ma said that China is leading in the field. It also dismissed the notion "US can't so China must not".
Some other difference interesting but not necessarily related to the above.
US: 149 stator segments each 0.64m long. 8 poles per segment. Using Hall effect sensor to control the speed.
China: 24 stator segments each 4.07m long. 28 poles per segment. DSP analyzing the interference of stator current by the carriage to control the speed. Sensorless.
PLAN Catapult Development Thread, News, etc.
- Thread starter antiterror13
- Start date
Thanks. But I remain in doubt.
I've been researching this and Western media gives EMALS an efficiency of 90%, clearly versus 5% for the steam catapult system. If there are 4 rotors for each catapult, that means that 484 MJ are generated for each, if we multiply by 3, it gives a total of 1,452. If a catapult can effectively launch an aircraft with 121 MJ, the efficiency of the US EMALS is not 90%. It would be 25% efficiency, but I've never read about 25% efficiency, only 90% and also 4 rotors for each catapult. If you can solve my doubts, please.
asif iqbal
Lieutenant General
no all wrong
you missed the fact that steam is very wasteful due to the second law of thermodynamics
Before beginning to calculate, you need to know or tell from what end to what end is that 90%. If the media did not say then they don't know what they are talking about.
The EMALS energy storage system (ESS) which is shared between the four catapults provides up to 60 MJ each, the USS Gerald Ford holds 12 ESS for each carrier, which totals 720 MJ. That is, from the ESS that uses the input of electrical energy that is stored in the form of kinetic energy, the kinetic energy can be described as "motion energy", in this case the movement of a rotating mass, called a rotor, the rotor provides up to 484 MJ for shared use between the four catapults, that is, if we are going to use as a base the 720 MJ that is stored through the ESS for the rotor, the estimated loss is 236 MJ, in a percentage above 32%.
The American EMALS produces 29% more energy during launch than a steam catapult (121 MJ versus 95 MJ), and can consume something like 100 MW (voltage ~13,000 V, current ~8,000 A) in 2-3 seconds of acceleration and requiring cooling for 10 MW of dissipated heat. From what I've studied of the American EMALS, it's not 125 MJ of one EMALS only, this energy is only one rotor, the EMALS system uses four rotors which gives a total of 484 MJ, basically 4 rotors that release 121 MJ each. The 90% efficiency from what I learned is based on losses in MJ, ie the estimated losses for MJ would be 10%, which totals 435 MJ for the four catapults of the USS Gerald Ford. The fourth catapult cannot be used at its maximum power like the remaining three, which leaves only 72 MJ for the fourth catapult, removing the estimated 10% loss.
It would be the efficiency of the rotors estimated at 90%.
Steam really is inefficient. But it only served as a basis for comparison with EMALS which they say is much more efficient in terms of generating and accumulating energy, as I am reporting, they say it is 90% efficient.
that sounds right, but than it is unfair to compare this 90% with the steam. The 5% of steam is measured from the reactor's steam outlet (thermal energy) to the shuttle on the launch track. A fair comparison should measure EMLS from the same point, that is certainly not 90%. I don't know if that would be 25% as you calculated, but you are probably close to the truth.
I think you misunderstood it.
The launch energy for one track is maximum 121MJ. This is provided by the four rotors together. Each rotor (flywheel/disc alternator) can store up to 121MJ at 6000RPM. However, due to the fact that flywheel's power density is lower than requirement, the 121MJ can not be released during the 2-3 seconds launch time frame. So four such rotors are put together to provide that 121MJ. At the end of a launch, each rotor will have 75% energy left unused.