PLAN Catapult Development Thread, News, etc.


taxiya

Brigadier
Registered Member
I read Ma Weiming's paper again. "电磁发射系统中电力电子技术的应用与发展" / "Applications and Development of Power Electronics in Electromagnetic Launch System".

Found something that I did not pay enough attention before.
1654195909902.png
In China's EM launcher, the energy stored in the flywheel is converted from AC to DC first. Then the required AC power is generated by DC/AC conversion. This is essentially a localized DC based IEPS. In this case, the flywheel is the primary mover as GT or Steam turbine in IEPS, the DC grid is the MVDC power bus in IEPS, the linear motor is the local load in IEPS. Because EM launcher is very violent in changing load , frequency, current and voltage, successfully operating EM launcher would be a great affirmative validation for MVDC IEPS introduction.

The idea of this design is based on the same consideration of MVDC IEPS, to decouple the primary mover's frequency and voltage/current from the demand of the load. It also simplify the controller design of the launcher because the linear motor's input is constant.

Therefor, I am thinking that land based EM launching test may be sufficient to prove IEPS's reliability before putting it in a ship, at least on a small ship that operates on low constant power level. The peak power of EM launcher is more than 100MW close to the total power of 055, much larger than 054's 27MW.

For reference, EMALS (US) design uses cycloconverter between flywheel and linear motor. It is an AC-AC conversion.
 
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taxiya

Brigadier
Registered Member
I got a feeling that the arresting gear shown in CCTV program long time ago was not Chinese one but AAG from USN. CCTV just used some footage from US.

Here is from CCTV
电磁拦阻系统2.jpg
compares with AAG

AAG-system 3.jpg

The mounting rack is exactly identical, even to number of bolts and locations. The ridges of the motor (or water twister) also matches.

I got this suspicion after coming across this picture from 2017. Here the cone shaped cable hoist is replaced by "加塞带卷扬盘" (belt insertion hoist). It does the same thing as the cone shaped hoist that is to convert the speed of releasing cable and rotation of the gear. Instead of changing diameter of the cone, the hoist insert a non-compressible belt between cables to achieve the desired diameter of each revulsion. It is claimed to be one third in size of cone shaped hoist in axial direction, weighted one third.

电磁阻拦.jpg
The advantage is smaller, lighter system and better regulation of torque. The force to arrest the aircraft is created by 1 electrical motor, 2 momentum of the water twister, 3 the momentum of the hoist, 4 momentum of everything else. To accurately adjust the force, the motor changes its current(force). However all other parts act as a spring due to their momentum, this leads a delay of the desired force change, the higher the collective momentum the worse. By reducing the overall mass/momentum, the arrest gear would be more accurately controlled.

The ideal system would to replace the water twister with electrical brake which replaces the force from momentum with EM resistance. To this end there is a patent from Harbin Polytechnic University.

I can not be sure if China's EM arrest gear used water twister or the EM brake, but I think the cable hoist is likely different from US counterpart because this is a mature mechanical tech.
 

davidau

Senior Member
Registered Member
I got a feeling that the arresting gear shown in CCTV program long time ago was not Chinese one but AAG from USN. CCTV just used some footage from US.

Here is from CCTV
View attachment 91781
compares with AAG

View attachment 91782

The mounting rack is exactly identical, even to number of bolts and locations. The ridges of the motor (or water twister) also matches.

I got this suspicion after coming across this picture from 2017. Here the cone shaped cable hoist is replaced by "加塞带卷扬盘" (belt insertion hoist). It does the same thing as the cone shaped hoist that is to convert the speed of releasing cable and rotation of the gear. Instead of changing diameter of the cone, the hoist insert a non-compressible belt between cables to achieve the desired diameter of each revulsion. It is claimed to be one third in size of cone shaped hoist in axial direction, weighted one third.

View attachment 91783
The advantage is smaller, lighter system and better regulation of torque. The force to arrest the aircraft is created by 1 electrical motor, 2 momentum of the water twister, 3 the momentum of the hoist, 4 momentum of everything else. To accurately adjust the force, the motor changes its current(force). However all other parts act as a spring due to their momentum, this leads a delay of the desired force change, the higher the collective momentum the worse. By reducing the overall mass/momentum, the arrest gear would be more accurately controlled.

The ideal system would to replace the water twister with electrical brake which replaces the force from momentum with EM resistance. To this end there is a patent from Harbin Polytechnic University.

I can not be sure if China's EM arrest gear used water twister or the EM brake, but I think the cable hoist is likely different from US counterpart because this is a mature mechanical tech.
Excellent job. And to China's researchers, scientists and engeers, we salute your innovations and achievements.
 

Interstellar

Junior Member
Registered Member
I got a feeling that the arresting gear shown in CCTV program long time ago was not Chinese one but AAG from USN. CCTV just used some footage from US.

Here is from CCTV
View attachment 91781
compares with AAG

View attachment 91782

The mounting rack is exactly identical, even to number of bolts and locations. The ridges of the motor (or water twister) also matches.

I got this suspicion after coming across this picture from 2017. Here the cone shaped cable hoist is replaced by "加塞带卷扬盘" (belt insertion hoist). It does the same thing as the cone shaped hoist that is to convert the speed of releasing cable and rotation of the gear. Instead of changing diameter of the cone, the hoist insert a non-compressible belt between cables to achieve the desired diameter of each revulsion. It is claimed to be one third in size of cone shaped hoist in axial direction, weighted one third.

View attachment 91783
The advantage is smaller, lighter system and better regulation of torque. The force to arrest the aircraft is created by 1 electrical motor, 2 momentum of the water twister, 3 the momentum of the hoist, 4 momentum of everything else. To accurately adjust the force, the motor changes its current(force). However all other parts act as a spring due to their momentum, this leads a delay of the desired force change, the higher the collective momentum the worse. By reducing the overall mass/momentum, the arrest gear would be more accurately controlled.

The ideal system would to replace the water twister with electrical brake which replaces the force from momentum with EM resistance. To this end there is a patent from Harbin Polytechnic University.

I can not be sure if China's EM arrest gear used water twister or the EM brake, but I think the cable hoist is likely different from US counterpart because this is a mature mechanical tech.

That doesn't seem like English to me.
 

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OppositeDay

Junior Member
Registered Member
A Chinese article I was reading around the time of Fujian's launch had a one-line speculation on the potential application of electromagnetic catapult to land-based airstrips. Are energy storage/release systems still needed if the catapult can draw from a nearby city-sized power grid?
 

dingyibvs

Junior Member
A Chinese article I was reading around the time of Fujian's launch had a one-line speculation on the potential application of electromagnetic catapult to land-based airstrips. Are energy storage/release systems still needed if the catapult can draw from a nearby city-sized power grid?
I'd think so. Grids need to load match, and very high power intermittent systems like EMALS would probably present an issue. Also, I'd imagine that the use case would be more for remote areas that require longer runways than can be practically built, e.g. in mountainous terrains or very high altitude locations. In other places you can just build longer runways.
 

taxiya

Brigadier
Registered Member
I got a feeling that the arresting gear shown in CCTV program long time ago was not Chinese one but AAG from USN. CCTV just used some footage from US.

Here is from CCTV
View attachment 91781
compares with AAG

View attachment 91782

The mounting rack is exactly identical, even to number of bolts and locations. The ridges of the motor (or water twister) also matches.

I got this suspicion after coming across this picture from 2017. Here the cone shaped cable hoist is replaced by "加塞带卷扬盘" (belt insertion hoist). It does the same thing as the cone shaped hoist that is to convert the speed of releasing cable and rotation of the gear. Instead of changing diameter of the cone, the hoist insert a non-compressible belt between cables to achieve the desired diameter of each revulsion. It is claimed to be one third in size of cone shaped hoist in axial direction, weighted one third.

View attachment 91783
The advantage is smaller, lighter system and better regulation of torque. The force to arrest the aircraft is created by 1 electrical motor, 2 momentum of the water twister, 3 the momentum of the hoist, 4 momentum of everything else. To accurately adjust the force, the motor changes its current(force). However all other parts act as a spring due to their momentum, this leads a delay of the desired force change, the higher the collective momentum the worse. By reducing the overall mass/momentum, the arrest gear would be more accurately controlled.

The ideal system would to replace the water twister with electrical brake which replaces the force from momentum with EM resistance. To this end there is a patent from Harbin Polytechnic University.

I can not be sure if China's EM arrest gear used water twister or the EM brake, but I think the cable hoist is likely different from US counterpart because this is a mature mechanical tech.
I've read GA's patent for AAG again. Here
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In it there is this paragraph
  • [0026]
    For the arresting gear 10, the use of a passive, energy-dissipating fluid turbine 34 in combination with the low inertia electric motor 40 allows for controlled arrestments over a relatively large operating envelope (i.e. large range of aircraft weights and landing speeds) without the bulk and weight of the power trains required if an electric motor was used alone. It is anticipated for the arresting gear 10 that in a maximum-energy arrestment, approximately 65% of the aircraft energy is absorbed by the energy-dissipating fluid turbine 34, approximately 25% by the dump resistors 52, and approximately 10% is recycled.
From the GA patent, it can be seen that GA has considered the feasibility of EM brake (a motor) but rejected it because of size and weight consideration.

In the CCTV photo, it can be seen that the "Water twister" in Chinese Arresting Gear (CAG) is much larger in size than AAG's water twister (fluid turbine 34). It is also much heavier necessitating its own stand which is very solid construction. On the contrary in AAG, the water twister is mounted on the same stand of cable drum as an appendix.

GA's notion of EM brake being bulky and heavy matches the CAG's photo. This makes me think again. I now believe that the CCTV photo is CAG. The CAG is using EM brake rather than water twister. EM brake is used in this patent from Harbin Institute of Technology
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. Note Harbin Institute of Technology is one of the top Chinese military technology institutes, they have been involved in CV tech such as landing and launching management, catapult force dynamic studies.

I speculate that China's choice of EM brake is due to experience from HSR which uses EM braking as the primary method. This choice is also reflected by Ma Weiming's saying "EM arresting (in CAG) is the reversed process of EM launching", and we know that is not the case in AAG (65% energy absorption is mechanical).
 
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taxiya

Brigadier
Registered Member
A further look of the CCTV footage gives me some more thought
1666111113943.jpeg
See the markings.
电磁拦阻系统2 marked.jpg

As can be seen, the two stands on both sides of cable the drum are identical. This indicates that both are electrical motors. My previous post said that instead of water twister, CAG uses kind of EM brake (in place of water twister) which could be either eddy current brake that convert kinetic energy to heat or electrical motor/generator. Now after re-examine the footage, it is more likely that it is an electrical motor.

In AAG, 65% energy is absorbed by water twister, 25% by electric motor to resister bank to heat, 10% by capacitor. The 10% is recoverable energy that can be fed to the grid.

In CAG, if my observation is right, 100% energy can potentially be recovered by the two motors. The output electricity can be fed back to the grid through flywheels as buffers if the grid has the matching load demand, if not the excessive energy can be dumped as heat through resisters. This is better than using eddy current brake which will always dump the energy as heat just like the water twister. Also note that the flywheels in the CAG are likely the same pool of flywheels in the catapult.

It once again is reflected by Ma Weiming's notion that CAG is just reverse of catapult. CAG's rotary motors/generators are equivalent to the linear motor of the catapult. The generators charge the flywheels in reverse of flywheels discharge to power the linear motor in launching mode. The flywheels act as buffer to smooth the high power variable frequency/voltage current before entering the grid. It is exactly a reversed process.

Ma Weiming also said "it is just a reverse, once the catapult is done there is nothing difficult in arresting gear, we used half??? time of catapult to finish the arresting gear." It is indeed as he have said, there CAG is piece of cake after the catapult is done.

Back to AAG, in my previous post I quoted US article saying the reason of not using motor alone was due to the bulk and mass of electrical motors. I speculated that the real reason was the lack of expertise in EM braking. I must add one more reason here which is the architecture. Remember that China's catapult is a AC-DC-AC mini grid while EMALS is a AC-AC grid? In CAG the electricity restored in the Flywheels can be either used by the catapult or fed to the grid through the DC bus. AAG can not do it without big headaches because it does not have the DC grid. The current AAG solution is the least troublesome (best) solution for the existing architecture.
 

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