PLAN Aircraft Carrier programme...(Closed)

Engineer said:

Seems like your Mr. Common Sense is an imposter then.

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The left bow take-off-line is used as parking lot. And the beginning of the take-off-line is still kept clear.

Engineer said:

Might as well push the aircraft overboard. That would give you 100% vertical velocity, straight into the sea.

Aircraft need horizontal speed to take off. That's why runways exist. Please review how air foil works before coming up with any more crappy suggestions.

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No, Engineer. The purpose of the ski ramp is to be able to take off safely at a lower speed and have the time to accelerate in the air to the speed needed to fly horizontally while taking account of the case with engine failure. Vids of J-15 launches show no semi-parabolic flight path because there is no engine failure.
It's already an old concept. I learned it at the University about forty years ago when it was pointed out that using thrust deflection as used on the British mini-carriers was not necessary.
You can modulate the force of an EM cat to achieve the same velocity at the end of the track with and without engine failure.

delft said:

No, Engineer. The purpose of the ski ramp is to be able to take off safely at a lower speed and have the time to accelerate in the air to the speed needed to fly horizontally while taking account of the case with engine failure. Vids of J-15 launches show no semi-parabolic flight path because there is no engine failure.
It's already an old concept. I learned it at the University about forty years ago when it was pointed out that using thrust deflection as used on the British mini-carriers was not necessary.
You can modulate the force of an EM cat to achieve the same velocity at the end of the track with and without engine failure.

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No delft. From your postings, I can say you swapped the cause and effects.

You are thinking ski ramp got invented, then take off at lower speed became possible. What actually happened was that aircraft couldn't get the speed they needed to take off, so ski ramp was invented. To put it differently, you think ski ramp brought a new feature to the table, yet ski ramp is merely a patch in response to an existing issue. There is a subtle difference.

Ski ramp doesn't even remove that existing issue. Catapult does. When the original constraint is removed, the problem ski ramp was designed to address is no longer there, so ski ramp isn't needed any more. Proposing adding a ski ramp to a catapult is just adding a ski ramp for the sake of having one.

No, Engineer. We were looking at the picture of Liaoning and saw the jet blast deflector in the way of the landing area. I reminded you of the fact that take off with a ski ramp reduces the velocity with which an aircraft has to depart the deck. Assuming the same acceleration, after all people are all very similar, a cat can be shorter if it is built into the ski ramp so enabling a smaller carrier, of the size of Liaoning, to use both bow cats while still receiving aircraft. After all it is as easy to build a bend EM cat as a straight one. China will want to build up a fleet of several aircraft carriers as soon as possible just to gather the experience of operation them and this would let it do so at a lower cost.

delft said:

No, Engineer. We were looking at the picture of Liaoning and saw the jet blast deflector in the way of the landing area. I reminded you of the fact that take off with a ski ramp reduces the velocity with which an aircraft has to depart the deck.

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No delft. An aircraft accelerated solely under its own power will have a low exit velocity, regardless of the existence of a ski ramp.

A ceiling needs support columns because of gravity. It will be extremely silly if someone were to say that those support columns created gravity, would you agree? Well, saying "ski ramp reduces exit velocity" is similar to saying "support columns created gravity."

delft said:

Assuming the same acceleration, after all people are all very similar, a cat can be shorter if it is built into the ski ramp so enabling a smaller carrier, of the size of Liaoning, to use both bow cats while still receiving aircraft. After all it is as easy to build a bend EM cat as a straight one. China will want to build up a fleet of several aircraft carriers as soon as possible just to gather the experience of operation them and this would let it do so at a lower cost.

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First, the assumption of same acceleration is invalid to begin with, because the approaches do not have the same acceleration. Catapult provides higher acceleration, which is why aircraft can have higher exit velocity over the same distance, and why catapult is a better approach.

Second, even when using your own assumption, catapult-in-ramp approach has no benefits over ramp-only or catapult-only designs, because acceleration is the same, thus all three perform as the same. Not only have you invalidated the catapult-in-ramp approach, such approach is actually worse because it is an overly complicated solution compared to the other two.

Third, a catapult can be made short, by design, without any assistance from a ski ramp. A catapult can be shorten to one meter if needed, while the ramp will ceased to be a ramp shortening that much. Quit trying to add a ramp where one doesn't belong.

Also, catapults can be tuned for different aircraft types and take-off velocity needs, and theoretically an aircraft can use catapult assist to reach required velocity that it otherwise couldn't reach on it's own, or even with the added vertical buffer from a ski ramp.

A ski ramp,
1. Makes the aircraft leave the ship at a slight positive angle of attack to the airflow, so reducing the horizontal speed requirement for generating the same lift compared to traveling horizontal. (The ramp I think are designed from 9 to 15 degrees but seldom greater, and this seems to be the range for airfoil before going into the turbulent air flow region?)

2. Provides a vertical initial speed component, which means that if an aircraft does not have enough speed to generated the required lift (maybe it was carrying heavier load), it can have leeway in time to accelerate before the aircraft loses the vertical 'bonus'.

So with cats it's either success or fail, and the plane have to leave with the required velocity.
With ramp, the plane can leave with enough lift generated already due to higher angle of attack into wind flow even at slightly lower speed, or if you want to carry more and push the boundary, leave the ramp with not quite the needed lift but make up for it with continued acceleration from it's engines while it is still ascending from leftover vertical momentum from the ramp (and maybe the engine contributing some since it is pushing at an angle).

Intrepid said:

If Liaoning had two cats on the bow, you couldn't use the lefthand cat when landing operation is in progress.

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That's right in a general sense of the launching area extends far enough back into the landing zone. But in a pinch, on the Liaoning, I bet they could do it.

I would not recommend it for any type of high volume operations,.

Just the same, I was speaking of two cats on the bow and Liaoning doesn't have any.

It clearly cannot apply to any carriers (cats or not) who launching area on the port side of the bow extends far enough back into the landing area.

That would be self evident.

Just the same, for those that can do so, having two cats forward, where there is room, does allow for simultaneous launch and recovery. That is my only point.

Engineer said:

Seems like your Mr. Common Sense is an imposter then.

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Common sense is not an imposter...it just does not necessarily apply in this example.

Clearly, the Chinese have shown that they can do both form the Liaoning as your picture attests.

Why?

Because the launch area forward on the port side does not extend far enough back into the landing area to prevent it.

Just the same, I would not recommend it for any high volume air ops requiring simultaneous launch from the two positions forward (particularly the port side) and recovery

Kwaig, you have been in flight ops on US carriers...what do you think of that photo?

Popeye?

Engineer said:

Said who?

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Are you suggesting the yellow protoype J-15 in this case is in the port takeoff position?

Because I don't think that is the case; rather it is merely being parked close to the port jet blast deflector but still beyond the boundary of the landing strip.

Clearly on Liaoning (and Admiral K) it would not be wise to launch a plane from the bow port position if one also wanted to conduct a landing within the same short timeframe, given the port JBD intrudes well into the landing strip boundary.
That said I think the ability to simultaneously launch and arrest a landing plane is overrated; one can easily stagger a scheduled launch and landing by a few seconds for either one or the other to occur first.

That said, if the Liaoning hull's dimensions were used for a CATOBAR design I imagine the bow flight deck width would be expanded rather than tapering off so much for the STOBAR arrangement, and depending on the length of the catapult there could be enough space for the two catapults and their associated JBDs to be arranged in a way that will allow for the port JBD to not intrude on the landing strip and to allow for simultaneous or near simultaneous launch from both bow positions.

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edit: are nimitz class carriers able to launch two jets from their bow catapults simultaneously, or is it common practise? A quick google search with relevant key words don't give me any pictures. I'm aware that simultaneous launch from a waist and bow catauplt are common, but more often than not it seems either one bow cat is either used for parking, or if both cats are used for launching, the launches seem to be staggered.

This is the closest picture I've found; a staggered launch. I imagine of both bow cats launched at the same time simultaneously, the two jets would crash into each other shortly after launch, or at the very least they would be unacceptably close to each other and be very dangerous. And of course this doesn't include the launch of an E-2 with a jet in close proximity given the greater wingspan of an E-2.

Engineer said:

No delft. An aircraft accelerated solely under its own power will have a low exit velocity, regardless of the existence of a ski ramp.

A ceiling needs support columns because of gravity. It will be extremely silly if someone were to say that those support columns created gravity, would you agree? Well, saying "ski ramp reduces exit velocity" is similar to saying "support columns created gravity."


First, the assumption of same acceleration is invalid to begin with, because the approaches do not have the same acceleration. Catapult provides higher acceleration, which is why aircraft can have higher exit velocity over the same distance, and why catapult is a better approach.

Second, even when using your own assumption, catapult-in-ramp approach has no benefits over ramp-only or catapult-only designs, because acceleration is the same, thus all three perform as the same. Not only have you invalidated the catapult-in-ramp approach, such approach is actually worse because it is an overly complicated solution compared to the other two.

Third, a catapult can be made short, by design, without any assistance from a ski ramp. A catapult can be shorten to one meter if needed, while the ramp will ceased to be a ramp shortening that much. Quit trying to add a ramp where one doesn't belong.

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What are you talking about? Acceleration is limited by the ability of the pilot to withstand it.
The aircraft is accelerated by its engines, or one engine after an engine failure, and the cat. It will be delivered to the end of the ski ramp at a speed that will allow it to fly away even after an engine failure, with or without dropping external ordnance as decided by the specification. That speed is less than that necessary to fly away from a classical cat so the cat length can be reduced compared to that needed for a classical cat and ramp take off without using a cat.
Btw the angle of attack leaving the deck is governed by the undercarriage geometry not by the ramp.