Aircraft Carriers II (Closed to posting)

Thanks for posting Franklin.. looks like the building of this CV is stagnate. But like Jeff states, much more is going on inside that hull.

There are of course merit of using CAT and Ski together

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No there's not. Because if this were true the USN ,the greatest perpetrator of the steam catapult, would have installed a ski-ramp catapult by now.

Lezt said:

With all due respect, I would disagree in principle. The stress on the undercarriage of an carrier launch aircraft is always immense regardless of if you use a CAT or a ski.

Lets run some simple numbers, lets say a 44 ton (lets say 4000 kg), F14 is propelled down the enterprise with a .. actually i can't find the launch force, but lets use your numbers; 300 feet = 100 meters, 130 knots = 67 m/s. Work = force X displacement, assuming work = K energy retained, so F X D = 1/2 X m X V^2

F = 0.5*4000*67^2/100 = 89.8 kN; around 20,000 lbf? does this sound right?

Assuming the nose gear is 1.5 meter high, that is 135 kNm or ~100,00 lbft of moment,

Assuming the nose gear is 4 inch diameter steel rod or 100 mm with a 10 mm wall, the shear stress is XX kPa; where the modulus of rigidity for steel is ~70 GPa

These are large numbers -> if I did not do something wrong, well I am a Mech, not a Material engineer; so I have no perception of how reasonable they are.

assuming a 12 deg ski vs a flat top,..... Actually, i don't want to go into a inertia calculation as all the simplifications will make it pretty moot.

What I am willing to say is that the rate of descend with the slamming of the front wheel onto the deck when the plane traps, will most likely result in a large compressive force on the front carriage assembly than a CAT can exert on a ski jump.

There are of course merit of using CAT and Ski together, you can use a smaller carrier to launch fully loaded planes that world normally require a fairly large flat top to launch. You also have the ability to launch CAP from battle damaged carrier that have so unluckily lost it's steam plant.

And frankly, the pulley system exist already, in the form of launched roller coasters. The Formula Rossa launches its cars at 150 mph in 4.9 seconds, while the Hypersonic XLC launches at 109 mph at 1.8 seconds. these roller coasters have a 90 deg vertical ramp. Of course a roller coaster is very different than an aircraft.

Note also, most of the lift an aircraft experiences is from the angle of attack, not from the lifting profile of the wing. Infact at low speeds angle of attack generate 80% of the lift while the profile itself only 20%? And the max profile lift is when the angle of attack is around 15 deg?

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It still comes back to the same basic question, you have 300ft of deck for launch, a 12 degree ramp at the end, and you only have to reach 80 knots off the end of the ramp. If your aircraft cannot manage that under it's own power then no pilot in his right mind is going to fly such an underpowered coffin into combat. If you can afford the cost and complexity of a catapult, then you don't need the ramp; your aircraft will be leaving the deck at full flying speed anyway. The purpose of the ramp is to get you into the air before you have reached flying speed, but it buys you time to continue your takeoff roll after you have become airborne. The 80 knot speed limit for undercarriage is not my figure, it is from the people who did this for real for several decades: the Fleet Air Arm. Ask people like John Farley, one of those who worked on the Harrier family and the ski jump since the sixties, he drops in on other forums (PPRuNe) regularly to offer advice.

Aircraft undercarriage are usually not made of steel, try magnesium. Like most airframe components, they are weight critical. And yes rollercoasters do accelerate their cars using chain driven conveyers up a ramp, but the cars are unpowered, analagous to gliders. Are you intending to launch gliders off a carrier? Or jet fighters with a high thrust to weight ratio?

I'll say it again, if you can get you aircraft to 130+ knots before the end of the deck, there is absolutely no need for a ramp, the wings of the plane will get it into the air. THERE WILL NEVER BE A COMBINED CATAPULT/SKI JUMP ON ANY CARRIER BECAUSE THERE IS NO JUSTIFICATION FOR DOING SO, NO BENEFIT TO BE DERIVED.

Jeff Head said:

Exterior on the structure, not much work will occur while she is sitting there in that position. However, I have been told that significant work continues internal to the carrier.

We saw a similar circumstance for years with the Liaoning while she sat at her berth. Ultimately, the big cranes were used and the exterior work necessary was accomplished, particularly to the island when it was modified.

But the IAC is new construction so the bow, stern and elevators, along with the island all still need to be added externally and that will not happen until she is back next to the cranes.

In the mean time, I would imagine outfitting (piping, HVAC, internal compartments, etc.) are moving forward. as they can.

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What you said may well be true, but to me it doesn't make sense. The more work they do on the interior the heavier the ship hull becomes. Wouldn't that make it more difficult to put her back into the dry dock again and not to mention it would become even more difficult to relaunch her with all those extra weight. It would be more logical to put her back into the dry dock first finish the exterior structures relaunch her and then fit her out with all the necessary sensors and interior works. The fact that they didn't do that to me means that the project is facing some kind of difficulty.

Obi Wan Russell said:

It still comes back to the same basic question, you have 300ft of deck for launch, a 12 degree ramp at the end, and you only have to reach 80 knots off the end of the ramp. If your aircraft cannot manage that under it's own power then no pilot in his right mind is going to fly such an underpowered coffin into combat. If you can afford the cost and complexity of a catapult, then you don't need the ramp; your aircraft will be leaving the deck at full flying speed anyway. The purpose of the ramp is to get you into the air before you have reached flying speed, but it buys you time to continue your takeoff roll after you have become airborne. The 80 knot speed limit for undercarriage is not my figure, it is from the people who did this for real for several decades: the Fleet Air Arm. Ask people like John Farley, one of those who worked on the Harrier family and the ski jump since the sixties, he drops in on other forums (PPRuNe) regularly to offer advice.

Aircraft undercarriage are usually not made of steel, try magnesium. Like most airframe components, they are weight critical. And yes rollercoasters do accelerate their cars using chain driven conveyers up a ramp, but the cars are unpowered, analagous to gliders. Are you intending to launch gliders off a carrier? Or jet fighters with a high thrust to weight ratio?

I'll say it again, if you can get you aircraft to 130+ knots before the end of the deck, there is absolutely no need for a ramp, the wings of the plane will get it into the air. THERE WILL NEVER BE A COMBINED CATAPULT/SKI JUMP ON ANY CARRIER BECAUSE THERE IS NO JUSTIFICATION FOR DOING SO, NO BENEFIT TO BE DERIVED.

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Very well stated OBI WAN, there is no reason to engage in that kind of engineering circus for no actual benefit, I had not heard the 80 knot rule on ski ramp launch, but I have no reason to doubt you. For those of you who like these little engineering excercises and what, thats "KOOL", but in the real world you have a choice the Cat or the Ramp, both have limitations, the Cat has far fewer operationally, and yes I have flown my aeroplane off a hump below flying speed, and I can tell you it takes a little balancing act of milking off that high AOA and flap a little at a time to fly away normally. You have to resist the temptation to increase pitch when she starts to sink, if you lower the nose to early you will not fly away, it is a balerina act, standing on your aerodynamic tippy toes. AFB

Re: PLAN Carrier Operations..News, Videos & Photos II

bd popeye said:

Ahem.. On the America CV-66 while at anchor in St Thomas US Virgin Island in February 1981 VS-33 launched one S-3A from a waist cat (don't know which one) while at anchor. I know because I saw it with my own eyes. I was assigned to VS-33. And S-3A had a lot of wing span with a lot of lift.

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Would have loved to have witnessed that! Must have been a site to behold.

Jeff Head said:

Would have loved to have witnessed that! Must have been a site to behold.

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She went off the angle deck. It was aircraft 700..the bird was stripped down. No avionics except NAV & COMM..so she did not weigh that much. Her mission was to fly to Rosey Roads PR pick up some mail and cargo that needed to go to the the FID i.e Forrestal and Then fly back to the America. Just as we got underway the America was overflown by two F-4 Phantoms from the mighty FID!!! See we were having the old war games against the FID.. So they got the jump on us. Buzzing Miss "A" like that..they should have been ashamed of themselves...Showing off with those old smokey Phantoms.. why we had Tomcats....VF-114 & VF-213.

Fear not.... While aircraft 700 was aboard the FID her aircrew stole something from VS-30 ready room that was beneficial to the up coming war games. Special radio frequencys & other info for use during the wargames. Guess what? VS-33 was able to score hits on the "Orange" forces with that info.. However the America was "sunk" during the wargames by a Canuck missile hit or torpedo..imangine that?!..

Franklin said:

...The fact that they didn't do that to me means that the project is facing some kind of difficulty.

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They were having difficultes and they explained it when they floated her. Apparently while in transit to the yards some of her machinery was involved in an accident and had to be refabricated, so they freed up the dry dock for another project and kept doing what work they could do in the interior while waiting. And HVAC, berthing and other compartmental work like that (if that is what they are doing), would not add appreicably to the displacement and would not detract at all from the dry dock time.

I know sometimes there is not only a desire, but an actual expectation that somehow almost anything the Indians do is somehow messed up...but that is not the case. They do have a mix-match of equipment that has to play havoc with their logisitics IMHO, but they are not to be underestimated either.

Anyhow, I expect they will have the Virkam in service in late 2013, and that this vessel will actually launch for sea trials either in late 2013 or sometime in the first half of 2014.

At that point they will have a capable STOBAR rebuild flying Mig-29Ks and a new indegenous STOBAR carrier going through trials and flying the same...which at some point will be augmented by their LCA Tejas aircraft.

Obi Wan Russell said:

It still comes back to the same basic question, you have 300ft of deck for launch, a 12 degree ramp at the end, and you only have to reach 80 knots off the end of the ramp. If your aircraft cannot manage that under it's own power then no pilot in his right mind is going to fly such an underpowered coffin into combat. If you can afford the cost and complexity of a catapult, then you don't need the ramp; your aircraft will be leaving the deck at full flying speed anyway. The purpose of the ramp is to get you into the air before you have reached flying speed, but it buys you time to continue your takeoff roll after you have become airborne. The 80 knot speed limit for undercarriage is not my figure, it is from the people who did this for real for several decades: the Fleet Air Arm. Ask people like John Farley, one of those who worked on the Harrier family and the ski jump since the sixties, he drops in on other forums (PPRuNe) regularly to offer advice.

Aircraft undercarriage are usually not made of steel, try magnesium. Like most airframe components, they are weight critical. And yes rollercoasters do accelerate their cars using chain driven conveyers up a ramp, but the cars are unpowered, analagous to gliders. Are you intending to launch gliders off a carrier? Or jet fighters with a high thrust to weight ratio?

I'll say it again, if you can get you aircraft to 130+ knots before the end of the deck, there is absolutely no need for a ramp, the wings of the plane will get it into the air. THERE WILL NEVER BE A COMBINED CATAPULT/SKI JUMP ON ANY CARRIER BECAUSE THERE IS NO JUSTIFICATION FOR DOING SO, NO BENEFIT TO BE DERIVED.

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Magnesium is as strong as and lighter than steel; for all intent and purpose, the material is not the limit, make it out of titanium if you must.

You also have not read about the roller coaster; the two I have suggested are either pneumatic powered with nitrogen gas in a piston, or hydraulic powered with dissolved air in the hydraulic fluid.

Your statement is about powered combat plane and unpowered glider is also irrelevent to physics. Let me rephrase it for you, do you need more power to push an object along which have trust pushing it as well by itself; or the same mass object that does not produce trust to the same speed? simple force reaction will tell you that the object with out trust will require more power. As a mini cooper is around 1000 kg; or around the weight of a single car of a roller coaster. Do you think that a fully laden combat aircraft is heavier than a 16 car roller coaster powered by a pneumatic or hydraulic pulley system? I assure you a system capable of hurling a 16 tonne mass to 100 mph in 2 seconds will not have issues hurling a 4 tonnes mass in the same time frame.

I think you are set in your mind what is considered good. The ski is intended to increase the lift capacity at take off by the angle of attack; in the way so that you can reduce take off speed - your number of 130 knot to 80 knot (67 m/s and 42 m/s). Can a fully laden high power combat aircraft reach 80 knots off a ski by itself - NO. Can a fully laden high power aircraft reach 80 knots with assist? -YES. Does propelling an aircraft to 80 Knots use less energy than 130 Knots? -YES. Does machinery developing less power require less maintenance? - YES; you are looking at 2/3rd the operating pressure. Can you use use lighter, less complex machinery to develop less power? - YES. So do you see from an engineering stand point, ski jump and cat does have a merit?

Here is the quick math for you, Kinetic energy = 1/2 X m X V^2; mass of 4000 kg, for 80 knots, you need ~9 MJ of energy, for a 80 Knot launch, you need, 3.3 MJ of energy. Lets say the plane can supply 2 MJ; Can you see that a system developing 1.3 MJ is much smaller than one developing 7 MJ; or 600% greater?

Using kienamatics; Vf^2 = V0^2 +2XAXD; D lets take 300 ft or 100 m, for Vf(80knots); A(80) = 8.4 m/s2. for Vf(130); A(130) = 22.45 m/s2. Using conservation of energy, F = m X A; Lanuch force of F(80) = 33 Kn; F(130) = 90 Kn; Can you see that 90 Kn is 1/3 the force required. This is also relevant to the fluid pressure, we know that the force = pressure X piston face area. your hydralic/punematic for a ski-cat require only 30% of the design pressure of a pure cat system.

Does it take an engineer to understand that a system producing only 1/3rd of the stress (pressure) and 1/6th of the power is a much less maintenance intensive system; a much cheaper system and a much more simpler system? So do you dare say that there is no merit?

Granted I am no expert on carrier ops; But I can pretty much darn tell you that inherent design wise, a ski-cat system will be much more reliable, smaller and cheaper to build and to operate due to the lower forces required.

Tactically, do a carrier which cannot launch any aircraft if the cat system (flat top) fails is more resilient or a carrier which can still launch CAP (with 2 AAM) w/ ski if the cat fails? is there no merit in that?

Huh??? ^^^

Tactically, do a carrier which cannot launch any aircraft if the cat system (flat top) fails is more resilient or a carrier which can still launch CAP (with 2 AAM) w/ ski if the cat fails? is there no merit in that?

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I made 7 major deployments on 5 US navy aircraft carriers. Kennedy, Midway, Hancock, America & Nimitz. I've seen thousands of cat shots and arrested landings. I've never see a "Cold Cat" ..never...ever. It happens . But not very frequently. So more than likely your question is not viable.

But I can pretty much darn tell you that inherent design wise, a ski-cat system will be much more reliable, smaller and cheaper to build and to operate due to the lower forces required.

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On paper what you post may be correct.

I posted this on the other page;

No there's not. Because if this were true the USN ,the greatest perpetrator of the steam catapult, would have installed a ski-ramp catapult by now.

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And how can it be more reliable? The present system employed by the USN works nearly flawlessly.

You know what? The USN at one time (1952-1991) hurled these 70,000 behemoths in the air..behold the A-3 Skywarrior. Launched with smaller cats as installed on Essex class carriers.





Some of you fellows with your brainiac selves need to get a clue. "Cause I've been there and done that"..been on the flight deck that is. Fact.

bd popeye said:

Some of you fellows with your brainiac selves need to get a clue. "Cause I've been there and done that"..been on the flight deck that is. Fact.

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Calm down big guy! May be you're a lucky charm! Saying "you've been there are done that" is like saying all swans are white because you've never seen a black one! Mechanical devices do break! Sorry Brainiac Skepticism at work!

Maybe things have gotten out of hand on this point but if it's always going to be down to your personal experiences you might as well just start threads write down the correct answers lock it we can all read them and be on our way!