Aircraft Carriers II (Closed to posting)

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Jeff Head

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Here's some nice pictures of the Brazilian Carrier, Sao Paulo, A12. These are after the more recent refit.
As you can see, there are no weapons systems for self defense.


a12-00b.jpg

a12-00c.jpg

a12-00d.jpg

a12-00a.jpg

From everything I have seen, the 100mm guns and the Simbad & Crotale missile launchers were all taken off long ago when the carrier was delivered.

The only weapons I have been able to see in Brazilian service have been several 12.7mm machine guns mounted around the carrier to combat small craft and boarders.

In French service as the Foch, the other weapons were plain to see. Here you see, from the stern port quarter, one of the Crotale missile launchers aft, and two of the 100mm guns forward.


Foch.jpg
 

bd popeye

The Last Jedi
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thunderchief

Senior Member
Gentlemen, read the article, the EMALS is "over-stressing" the aircraft equipped with external fuel slung on pylons. The fuel on the end of the Pylon needs to be accelerated at a much lower rate, in order not to overstress the wing. As the aircraft is accelerated at a very high rate, the heavy fuel resists that acceleration, that force tends to rotate around the aft attach point of the pylon to the wing, overstressing the front mount with a down-ward/rear-ward stress caused by that very heavy fuel tank acting at the end of that long moment arm.

This downward/rearward force moment exerts extreme stress on the front of the pylon at the wing and fuel tank attach points, and exerts a downward twisting moment on the wing and the spar trying to pull the wing leading edge down and back, resulting in a twisting moment that the wing does NOT like, even losing that front fuel tank mount will result in a catastrophic failure right at rotation.
The solution is real simple and the EMALS forte, you dial the acceleration back, as the EMALS has more than ample force to launch the fighter aircraft, as well as the heavy CODS. Once you have that fuel moving and accelerating then you can sling that puppy off the deck without undo stress. The EMALS will be much easier on all aircraft due to that very nature having excess force that you can tune to your application!

and YES, IT IS ROCKET SCIENCE! really it is, very snarky kool, but its a whole new field to understand, develop, and employ in the field? The main reason I think it would border on foolish for the Chinese to try to jump into this on their first indigenous carriers, but hey, who asked me?

Let's simplify things a bit ;)

- Super Hornet with fuel tanks has certain weight .
- In order to fly, at the exit of the ramp , it needs to have certain minimum speed ( that speed depends on weight)
- Steam cats were able to accelerate Super Hornets on elder carriers to that speed without much problem .
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So far so good . But ....

Physics says that dV = a * dt . When integrated that becomes V = U + Integral ( a * dt ) from 0 to t .

U is initial speed , in case of aircraft carrier is 0 . Therefore you have V = Integral ( a * dt ) from 0 to t .
-----

In case of steam catapults, acceleration varies . On average it is somewhere between 2.5 to 3.5 g. But steam cats do not deliver uniform acceleration . Therefore peak acceleration could go up to 4g or even higher according to some sources . And the acting on aircraft goes up with acceleration, according to well known equation F= m* a

Biggest advantage of EMALS is that , unlike steam cats, it delivers more gradual and even acceleration . So, instead of going from 1g to 4g , it could go steady with 3 g all the way . Therefore , peak force acting on aircraft and its parts would be actually smaller then on carriers using steam cats .

-----

So what is the problem ?

All the things I wrote would hold , if one requirement is fulfilled : length of the steam catapult run and EMALS run is the same . But unfortunately, it is not . According to official data :

The complete EMALS system will use a 300-ft long LIM to accelerate a 100,000-lb (45,000-kg)
aircraft to more than 130 knots (67m/sec) and lighter aircraft to 200 knots (100m/sec).
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300 ft is barely 91.44 m , it is shorter then aircraft run on Vikramidtya . And that lighter aircraft requiring 200 knots is our Super Hornet with external tanks (minimum speed with stores and ordnance )

In our best case scenario, with constant acceleration , we have S= a * t *t /2 and V = a*t , with known S (91.44 m ) and V (100 m/s ) . Therefore getting a to be 5.57g . And 5.5 g is something your aircraft with fuel tanks could not endure . ;)
 

strehl

Junior Member
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In our best case scenario, with constant acceleration , we have S= a * t *t /2 and V = a*t , with known S (91.44 m ) and V (100 m/s ) . Therefore getting a to be 5.57g . And 5.5 g is something your aircraft with fuel tanks could not endure . ;)[/QUOTE]

If you refer to Jeff's catapult specification table (https://www.sinodefenceforum.com/modern-aircraft-carrier-catapult-systems-including-emals.t7115/), the longest steam catapult is only 307 feet long (actual shuttle track length). If there are g limit problems with EMALS, they would be present for existing catapults as well. Also, top end speeds are listed at only 140Kts so your 200Kt Hornet will be in trouble even allowing for another 30Kts of carrier/wind speed.

In any event, the specification table indicates EMALS matches the steam catapults in top end speed and track length. From the CGI renderings of Ford, it doesn't look like the catapults are any shorter than existing systems so it is unlikely that the EMALS designers screwed up and forgot about g limits. This whole story seems to be another concoction of the professional naysayer crowd.
 
Thud I'm not getting this
... S= a * t *t /2 and V = a*t , with known S (91.44 m ) and V (100 m/s ) . Therefore getting a to be 5.57g . ...
are you assuming 45 tons being accelerated?? I'm inferring it from the quote in your post (but I didn't check if then it made sense) ... in high-school physics you'd be asked to specify the mass ... as g is Newton per kilogram as well as meters per second squared ... written off top of my head while drinking afternoon coffee, so ... am I publicly embarrassing myself? :)

or am I the only one who believes the Engineers working for the US Navy calculated the length of the deck correctly? LOL
 

strehl

Junior Member
Registered Member
Thud I'm not getting this

are you assuming 45 tons being accelerated?? I'm inferring it from the quote in your post (but I didn't check if then it made sense) ... in high-school physics you'd be asked to specify the mass ... as g is Newton per kilogram as well as meters per second squared ... written off top of my head while drinking afternoon coffee, so ... am I publicly embarrassing myself? :)

or am I the only one who believes the Engineers working for the US Navy calculated the length of the deck correctly? LOL

He is assuming 9.8 meters/second squared as "g". It is independent of mass.
His numbers hold up if you assume you need 200Kts exit speed.
 
He is assuming 9.8 meters/second squared as "g". It is independent of mass.
His numbers hold up if you assume you need 200Kts exit speed.

I'm going to believe it since I found this :) very recent
Navy Fixes Carrier Catapult to Launch Jets with External Fuel Tanks
The Navy plans to fix the software on its new carrier-based electromagnetic catapult system so that it can launching F/A-18s and Growlers carrying additional external fuel tanks under the wings, service officials said.

The changes will be finished on the Navy’s Electro Magnetic Aircraft Launch System, or EMALS, in time for operational testing aboard the Navy’s first Ford-class carrier — the USS Gerald R. Ford — in 2017, said Navy Cmdr. Thurraya Kent.

In April 2014, the Navy discovered an issue during testing at its facility in Lakehurst, N.J., that prevents the system from launching F/A-18 Super Hornets and EA-18 Growlers that are configured with external wing tanks, service officials said.

“The Navy understands the issue and will address it with a software modification well before any planned operational launch and recovery of aircraft. The fix will only involve a software change and will be completed well before any planned operational launch and recovery of aircraft,” she said.

The external fuel tanks, positioned beneath the wings on the E/A-18G Growler electronic jamming aircraft and F/A-18s, add additional stress to the aircraft when launched by EMALS, an issue which could wind up shortening the operational life of the aircraft.

The software updates are anticipated to begin by March of next year.

“No additional hardware or hardware changes to equipment already installed onboard CVN 78 are required, and there are no modifications required for any of the aircraft affected,” Kent explained.

EMALS is a next-generation carrier-deck launch systems engineered to replace existing steam catapults and go on the services’ new Ford-class carriers.

The first EMALS system has been under construction for several years aboard the USS Gerald R. Ford, or CVN 78, the first in class of the new carriers expected to deliver to the Navy next year.

The USS Ford has been heavily criticized by lawmakers and government watchdog groups for cost overruns and delays with the new technologies. The ship is on track to come in under its congressionally-mandated cost cap of $12.9 billion.

“Two of the four catapults are completely built. The other two are almost built,” said Rear Adm. Thomas Moore, Program Executive Officer, Carriers.

The system is part of a new series of carrier-based technologies designed to significantly increase the sortie rate and engineer a tailorable catapult that can achieve the desired amount of power for a an aircraft’s dimensions and weight – all while reducing wear and tear on airframes.

“EMALS gives the Navy the flexibility to make adjustments based on aircraft weight and configuration to accommodate a wider range of aircraft, including lightweight unmanned aerial vehicles that cannot be launched with a steam catapult,” Kent said. “EMALS can be adjusted more optimally and rapidly than a steam catapult could accommodate, providing the Navy with the ability to increase sortie generation rate for our entire inventory of combat aircraft.”

Additional laboratory testing of the software glitches will be performed this year before control algorithms and fine-tuning can take place, Kent added.

“This will be followed by dead load launches, comparative steam catapult launches and aircraft launches at Lakehurst next fiscal year,” she said.

The fixes are designed to build upon how EMALS is engineered to adjust power and thrust depending upon the weight of the aircraft. As a result, Navy officials say the system can be adjusted to accommodate the aircraft loaded with extra fuel tanks under the wings.

“EMALS will allow us to do the fine-tuning as necessary,” Kent said. “The resolution of this issue is straight-forward because the Navy will leverage this inherent capability of the system to tune the catapult forces for these wing tank configurations. There is no impact to ongoing shipboard installation or shipboard testing and this will not delay any CVN 78 milestones,” Kent said.

On the USS Ford, the below-deck EMALS equipment has been installed. This consists of a series of transformers and rectifiers designed to convert and store electrical power through a series of motor generators before brining power to the launch motors on the catapults, Moore explained.

“By having this electrical pulse come down, you are pulling the aircraft down to the catapult to launch it. You can dial in the precise weight of the aircraft. As you accelerate the aircraft down the catapult, you can accelerate it to the precise speed it needs to launch,” Moore said.

Unlike steam catapults which use pressurized steam, a launch valve and a piston to catapult aircraft, EMALS uses a precisely determined amount of electrical energy. As a result, EMALS is designed to more smoothly launch aircraft while reducing stress and wear and tear on the airframes themselves, he added.

“By the time the aircraft gets to the catapult it is at the right speed. Minimizing stress on the airframe, over time, reduces maintenance,” Moore added.

On the ship, EMALS will be engineered such that any of the ship’s four catapults will be able to draw power from any one of three energy storage groups on the ship, he said.
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