PLAN Aircraft Carrier programme...(Closed)

delft said:

What are you talking about? Acceleration is limited by the ability of the pilot to withstand it.

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For catapult launch, yes. For short take-off, no. Hence another reason why you can't just assume acceleration is the same for all methods of launch.

delft said:

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.

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No. The speed that is necessary for flight is the same regardless of whether the aircraft is leaving from a ramp, from a catapult, or self powered. Lift is determined by the aircraft's aerodynamics, not anything else.

Bltizo said:

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

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It is not I who suggested it. The picture was posted back in 2013 by a person who was on board that saw it happening, to settle the very same debate we are having now.

no_name said:

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?)

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Actually after further thought this point is not entirely correct. The plane will leave at an angle relative to the ship's deck but the angle of attack it makes with the airflow would still be zero since the speed difference and heading respective to still air is provided by the aircraft itself. This is assuming that the carrier is stationary. If the carrier is traveling through the water horizontally and assuming there is no net wind, then the extra difference translates to airflow that makes an angle of attack to the plane's wing surface at the angle the wings leave the ramp.

So I think Eng is correct for the case when the carrier is still, the total speed (hor+vert components) required for the same plane leaving a ramp and a cat would be the same. In fact a curved cat on a ramp would have to do more work because it will have to launch the plane against gravity. However this is assuming that the plane is leaving the ramp with already with the required speed for flight, but there is always a altitude leeway available for it to further accelerate a bit.

Then all this is complicated by the fact that if you compared the plane leaving the ramp and the cat at the same speed, the lift generated by their wings would be the same but pointing at different direction (since it is always normal to the wing and the wing of the two plane is at different angle of attack) and only the portion of lift that raises the plane's altitude is useful.

In short, I wont bother join in the argument

Engineer said:

It is not I who suggested it. The picture was posted back in 2013 by a person who was on board that saw it happening, to settle the very same debate we are having now.

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I see. But I hope you can understand the skepticism of the claim, given we have ample photos of the location, positioning of the port JBD and launch position as well as all the

Perhaps there was some misunderstanding originally, maybe the original poster was in denial, or maybe they actually did do a landing with the J-15 very close to the port launch position but without the JBD erected (as that photo does at least show).
If such a maneuvre of simultaneous recovery and launch from the port position was attempted then I would be horrified and I imagine it would have very quickly been discontinued.

However the key point still remains, that with the evidence which we have and our pretty familiar understanding of Liaoning's flight deck geometry, a simultaneous port launch and recovery is not practical/outright dangerous.

Engineer said:

For catapult launch, yes. For short take-off, no. Hence another reason why you can't just assume acceleration is the same for all methods of launch.


No. The speed that is necessary for flight is the same regardless of whether the aircraft is leaving from a ramp, from a catapult, or self powered. Lift is determined by the aircraft's aerodynamics, not anything else.

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I'm talking about cat launch at an angle to the horizontal. Assuming engine failure, after leaving the ramp the lift derives from the aerodynamic lift and the vertical component of the thrust of the surviving engine. By flying at an angle of attack insufficient to maintain flight you will follow a semi-parabolic trajectory at a reduced drag. This improves acceleration and allows you to safely get away at a lower speed than necessary when leaving a flat deck. There is the advantage of integrating an EM cat into the ski ramp.

delft said:

I'm talking about cat launch at an angle to the horizontal. Assuming engine failure, after leaving the ramp the lift derives from the aerodynamic lift and the vertical component of the thrust of the surviving engine. By flying at an angle of attack insufficient to maintain flight you will follow a semi-parabolic trajectory at a reduced drag. This improves acceleration and allows you to safely get away at a lower speed than necessary when leaving a flat deck. There is the advantage of integrating an EM cat into the ski ramp.

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First, with catapult launch, there is enough acceleration to get the aircraft up to the required speed for flight in the first place, even taking in account of engine failure. With enough speed, there is no need to get a special angle-of-attack, as the aircraft already has enough lift to begin with. With no need for special angle-of-attack, there is no need for a ramp. There is no advantage in an integrating a curved catapult into a ramp.

Second, assuming horizontal acceleration remains and then assume vertical acceleration comes as a bonus is flawed, as such assumption violates the Laws of Conservation of Energy. More vertical acceleration means less horizontal acceleration. Less horizontal acceleration means lower exit velocity where the aircraft starts out with less lift. To use what little engine thrust left for vertical acceleration means even less horizontal acceleration. That is no different than pouring oil in attempt to put out a fire.

Engineer said:

First, with catapult launch, there is enough acceleration to get the aircraft up to the required speed for flight in the first place, even taking in account of engine failure. With enough speed, there is no need to get a special angle-of-attack, as the aircraft already has enough lift to begin with. With no need for special angle-of-attack, there is no need for a ramp. There is no advantage in an integrating a curved catapult into a ramp.

Second, assuming horizontal acceleration remains and then assume vertical acceleration comes as a bonus is flawed, as such assumption violates the Laws of Conservation of Energy. More vertical acceleration means less horizontal acceleration. Less horizontal acceleration means lower exit velocity where the aircraft starts out with less lift. To use what little engine thrust left for vertical acceleration means even less horizontal acceleration. That is no different than pouring oil in attempt to put out a fire.

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Your are right if your flattop is large enough. That's why USN super carriers are 102k tons. For a ship of the size of Liaoning the cats would be too large to allow launching from two cats and receiving an aircraft at the same time. By decreasing the length of the cats and using a ski ramp to make launches as "safe" as with a flat cat you win valuable deck real estate.
As for your energy tale remember that a semi-parabolic trajectory beginning at the lip of the ski ramp takes much more time to near the water surface than one beginning at the end of a flat deck, time available for acceleration. Just make a number of simulations of such launches in your computer to see what I mean.

delft said:

Your are right if your flattop is large enough. That's why USN super carriers are 102k tons.

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Don't build small carriers. Simple solution.

delft said:

For a ship of the size of Liaoning the cats would be too large to allow launching from two cats and receiving an aircraft at the same time. By decreasing the length of the cats and using a ski ramp to make launches as "safe" as with a flat cat you win valuable deck real estate.

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Shorter catapults can compensate for loss of length with additional acceleration. No ramp is needed. In the case of Liaoning, the issue isn't about length, but the need to accommodate the third launch position. Such accomodation wouldn't be needed if catapults were used in the first place.

delft said:

As for your energy tale remember that a semi-parabolic trajectory beginning at the lip of the ski ramp takes much more time to near the water surface than one beginning at the end of a flat deck, time available for acceleration. Just make a number of simulations of such launches in your computer to see what I mean.

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That isn't a bonus. That is sacrificing some horizontal acceleration for vertical acceleration, to trade more time for more horizontal acceleration so as to finally get enough horizontal speed. It is a work around, a patch to an ongoing problem, not a benefit. A catapult can provide that horizontal speed by the time the aircraft reaches the edge of the deck. The problem is eliminated by the addition of catapults, so there is no problem left that requires a ramp.

delft said:

I'm talking about cat launch at an angle to the horizontal. Assuming engine failure, after leaving the ramp the lift derives from the aerodynamic lift and the vertical component of the thrust of the surviving engine. By flying at an angle of attack insufficient to maintain flight you will follow a semi-parabolic trajectory at a reduced drag. This improves acceleration and allows you to safely get away at a lower speed than necessary when leaving a flat deck. There is the advantage of integrating an EM cat into the ski ramp.

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Oh boy, another round of "extrapolating", and arguing for the validity of your "extrapolations".

I have however "proven your theory" by flying a low powered aircraft off of a hill/rise on a grass airstrip on a farm. As the aircraft leaves the hill without sufficient energy to fly away, you must increase the angle of attack in order to prevent an accident, as you apply aft stick?? you increase drag as you increase your angle of attack and the aircraft will most likely settle back onto the runway, having much less energy than it did when it departed the rise???, this will lengthen the take off run?

If on the other hand, your are already 50ft in the air as you depart the ramp, in an aircraft with sufficient thrust, you are able to "slightly reduce" that angle of attack to decrease that drag and allow the aircraft to accelerate to "flying speed", whereby you then "fly-away"?

operating safely off the ramp is enabled by the "Flankers" sufficient lift and excess thrust, you most likely will have to lower the weight of the aircraft, and leave below max gross in order to "fly away" with a sufficient margin to allow for losing an engine on the ramp?

as weight goes up, your "margin" goes away??

Wouldn't Chine be better served by more smaller ships that were just as efficient as the USN behemoths?
You make the cats as short as possible, and don't sacrifice deck real estate unnecessary, by going to the highest acceleration the pilots can routinely accept and you don't go to an even higher acceleration.
When using cats with the ski ramp there won't be a third launch position.
The bonus of the use of a ski ramp is that you use less deck real estate, the energy storage for the cats can be smaller, just as the cats themselves and you get a ship that is as efficient as a super carrier but at two third of the size and so at two third of the efficacy. The price might also be at two third of that of a super carrier. The main advantage would be that China gets more aircraft carriers in the same time frame and for roughly the save price to learn to use them.