PLAN Catapult Development Thread, News, etc.


Matheus S

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I think a good way to compare efficiency would be to find out the amount of steam needed to launch an aircraft via EMALS, since we know the amount needed to do it via the steam catapults.
Each steam catapult uses 615 kg of steam (at 237°C, 2.8 MJ/kg) for each launch. Well, the internal energy of these 615 kg of steam adds up to 1730 MJ and delivers up to 95-100 MJ to the aircraft, which gives 5.5-5.8% system efficiency (within the expected range of 4-6% efficiency ).

How will we make this conversion?
 

nlalyst

Junior Member
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Each steam catapult uses 615 kg of steam (at 237°C, 2.8 MJ/kg) for each launch. Well, the internal energy of these 615 kg of steam adds up to 1730 MJ and delivers up to 95-100 MJ to the aircraft, which gives 5.5-5.8% system efficiency (within the expected range of 4-6% efficiency ).

How will we make this conversion?
We can't without a quoted steam figure for EMALS.

All we can do is to estimate the losses along the energy chain:

Steam -> steam turbine generator -> (1) AC power -> rectifier -> (2) DC power -> motor -> (3) kinetic energy -> generator -> (4) AC power -> LIM -> (5) shuttle/aircraft kinetic energy

Please feel free to correct these figures.
1) 0.33
2) 0.97
3) 0.85
4) 0.95
5) 0.765 = (0.9 LIM efficiency * 0.85 friction/drag losses on aircraft)

Total efficiency = 1) * ... * 5) = 0.19
 
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Matheus S

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I think the overall efficiency of EMALS is on the order of 60.5%.

The ESS (energy storage system) you posted is the first of the EMALS subsystems. EMALS uses 12 ESS energy storage subsystems that you posted, and each ESS of that accumulates 60 MJ, that's a total of 720 MJ.

What we do know is that this system is shared-mode between the 4 catapults, so most EMALS components are all shared-mode, and may include the rotors. Actually, I've read that the Ford has some design flaws that need to be addressed with the catapult. If one fails, the entire system is compromised. With the steam system, if one catapult falls, the other three can still function normally due to the level of independence of the catapult system, but in EMALS this is not possible due to the design requirement. With EMALS, if one catapult fails, it is impossible to repair it while the other catapults are in use. They cannot be isolated from each other, unlike the steam system. This is explained by the sharing of the various EMALS components for the 4 catapults.

The complete EMALS system from what I've read has only 4 rotors, each providing 121 MJ for the 4 catapults, it doesn't have 4 rotors for each catapult, as then it would have a 2000 MJ accumulation - totaling 16 rotors, this is totally unnecessary for EMALS, as there would be a lot of energy left, is too high a converted energy for the efficiency that the system imposes.

Based on what I've found available from the general EMALS system it uses four rotors which gives a total of 484 MJ, basically 4 rotors which release 121 MJ each. Well, knowing this information, there is a loss of 236 MJ of the 720 MJ accumulated in the ESS, which means an overall efficiency of 67.2% of the EMALS.

Taking as an example the USS Gerald Ford that uses 4 catapults, the fourth catapult does not operate at its maximum efficiency, that is, 3 catapults can use 121 MJ, but the last one cannot operate launching an aircraft with 121 MJ. Knowing that efficiency is 90% as various media reports, this means that of the 484 MJ of the rotors, removing a loss in efficiency of 10%, there is 435 MJ left for the 4 catapults. If each of the three catapults operate at their maximum capacity, it gives a total of 363 MJ used, leaving 72 MJ for the fourth catapult.

If we take as an example the 720 MJ accumulated from the ESS up to the launch of the aircraft with 435 MJ from the four catapults, this gives an overall EMALS efficiency of 60.5%.

Remembering, that was my conclusion so far of the overall effectiveness of EMALS. I didn't find other more realistic hypotheses for the efficiency of EMALS.
 

nlalyst

Junior Member
Registered Member
The complete EMALS system from what I've read has only 4 rotors, each providing 121 MJ for the 4 catapults, it doesn't have 4 rotors for each catapult, as then it would have a 2000 MJ accumulation - totaling 16 rotors, this is totally unnecessary for EMALS, as there would be a lot of energy left, is too high a converted energy for the efficiency that the system imposes.
There are 12 motor-generators flywheel sets. That's 12 rotors.
Based on what I've found available from the general EMALS system it uses four rotors which gives a total of 484 MJ, basically 4 rotors which release 121 MJ each. Well, knowing this information, there is a loss of 236 MJ of the 720 MJ accumulated in the ESS, which means an overall efficiency of 67.2% of the EMALS.
You should think this through again. That's not how you calculate efficiency. Efficiency = output_power/input_power. No source that I've found claimed that more than 121 MJ are delivered to the aircraft.

Take a look at the estimate I made in a previous post. I got 19% efficiency.

Here's an example of how much energy would need to be delivered for a fully loaded F-35:
Runway = 91m
Weight: 31,800kg
Launch speed: 78 m/s
Kinetic energy: 0.5 * 31,800 kg * (78 m/s)^2 = 98.73 MJ
The F-35 can provide about 190kN thrust with its engine. Over 91m of runway that amounts to 17.2 MJ. Let's assume that the friction/drag losses on the aircraft are 15%. Therefore, we have 98.73 MJ / 0.85 = 116.15 MJ than need to be delivered to the aircraft. Accounting for the F-35's engine contribution, 116.15 MJ - 17.2 MJ = 98.95 MJ would have to be delivered by the catapult. That's well within the 121 MJ EMALS budget.
 
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gelgoog

Captain
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I have never heard efficiency being claimed as an advantage of EMALS vs steam on any literature. The typically stated advantages are more continuous acceleration, leading to reduced airframe fatigue, and easier to adjust to use with smaller/weaker airframes like drones.
 

KevinG

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I have never heard efficiency being claimed as an advantage of EMALS vs steam on any literature. The typically stated advantages are more continuous acceleration, leading to reduced airframe fatigue, and easier to adjust to use with smaller/weaker airframes like drones.
No need of fresh water is definitely another advantage. I watched a documentary film about the Ford class. It says that for the Nimitz Class, if it launches too many aircrafts in a single day, there will be a shortage of fresh water and thus a shower ban on crews. Even for a nuclear powered carrier, fresh water is not unlimited, let alone a convectional carrier
 

taxiya

Brigadier
Registered Member
The steam catapult has a reservoir called "steam accumulator". It stores steam for the launch. It is equivalent to the flywheel storage of EM launchers.
Illustrated in
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1625857723366.png
and
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1625857786630.png

This reservoir is fed by the steam plant (boiler). If we calculate the EM launcher's efficiency at the boiler outlet, the steam accumultor should be included when calculating the steam cat's efficiency.

A fair comparison with EM launcher would need to take into consideration of the loss (efficiency) of energy of this device over the period of operation (many hours in a real life battle).

We know that flywheel can keep 90% energy for many hours, while how much energy is left in the steam accumulator after many hours? In other words the steam accumulator could be a very low efficient storage system.

The efficiency I am talking about is the overall system wise operation efficiency, not a single launch efficiency that excludes the leak.
 

Matheus S

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The steam catapult has a reservoir called "steam accumulator". It stores steam for the launch. It is equivalent to the flywheel storage of EM launchers.
Illustrated in
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View attachment 74508
and
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View attachment 74510

This reservoir is fed by the steam plant (boiler). If we calculate the EM launcher's efficiency at the boiler outlet, the steam accumultor should be included when calculating the steam cat's efficiency.

A fair comparison with EM launcher would need to take into consideration of the loss (efficiency) of energy of this device over the period of operation (many hours in a real life battle).

We know that flywheel can keep 90% energy for many hours, while how much energy is left in the steam accumulator after many hours? In other words the steam accumulator could be a very low efficient storage system.

The efficiency I am talking about is the overall system wise operation efficiency, not a single launch efficiency that excludes the leak.
I found a source that says the overall efficiency of EMALS is 15%, pretty much what nlalyst reported.

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Says the following: "
1.2 Features of electromagnetic ejection system
...
   Compared with the steam catapult, the electromagnetic catapult is more efficient, more flexible, more stable, and more practical. Specifically: First, high efficiency. The efficiency of the American steam catapult is 4%-6%, and a single ejection consumes 614 kg of steam. The total efficiency of the electromagnetic catapult is 15%, which is about 3 times that of the former. The equivalent of a single ejection consumes about 200 kg of steam. In the fully closed state, it takes less than 15 minutes for the electromagnetic catapult to reach the ready-to-eject state from activation, while it takes several hours for the steam catapult to reach the ready-ejected state from the start. The second is that the weight and volume are small, and the volume and weight of electromagnetic ejection are about half of that of steam ejection. The third is more stable performance and easy maintenance. The steam catapult "average non-critical failure usage times" is 405 times, and the electromagnetic catapult is expected to target 1,300 times. At the same time, because the steam catapult does not have a closed-loop control system, the average peak-to-average ratio of the thrust of the carrier aircraft during ejection is 1.25, and the maximum can reach 2.0. The electromagnetic catapult can continuously correct the thrust deviation during the ejection process, and the peak-to-average ratio The ratio is controlled within 1.05. The fourth is a wider range of catapult models. The maximum ejection energy of the steam catapult is about 102MJ, and the electromagnetic ejection system can reach 122MJ, which enables the aircraft carrier to carry more and heavier models while ejecting small and light drones. The fifth is to comply with the trend of full electrification of ships. Electromagnetic catapults use electricity, which is more suitable for the full electrification of aircraft carriers in the future."
 

Philister

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I have never heard efficiency being claimed as an advantage of EMALS vs steam on any literature. The typically stated advantages are more continuous acceleration, leading to reduced airframe fatigue, and easier to adjust to use with smaller/weaker airframes like drones.
Cuz on USS Ford, efficiency isn’t that big of a problem, it’s a nuclear powered beast ,however on 003 it would be critical since PLAN is still using old fashioned steam turbines and diesel generators ,as a matter of fact, before converting into EMALS,003 had 2 steam catapult ,efficiency has always been a major advantage of EMALS.
 

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Matheus S

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Cuz on USS Ford, efficiency isn’t that big of a problem, it’s a nuclear powered beast ,however on 003 it would be critical since PLAN is still using old fashioned steam turbines and diesel generators ,as a matter of fact, before converting into EMALS,003 had 2 steam catapult ,efficiency has always been a major advantage of EMALS.
Does 003 use steam or gas turbines? Is the steam turbine confirmed?
 

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