J-15 carrier fighter thread

[Engineer]

No, no , no ! Lift is not a part of my calculations(I didn't even get to that ) .

Hence why your analysis is flawed.

I will try to explain in simple terms :

Imagine ball rolling down the deck and going to the ramp . Although it has no wings (no lift) it will go up when it leaves the ramp for some time until gravity takes over . Height gained by the ball is a potential energy that would later turn into kinetic energy (speed) when the ball starts descending .

Same principle applies to aircraft . Instead of going slightly down (as on carriers without ramp) it will go upwards and gain some height and time . That height is a potential energy and that time will be used by engines to accelerate aircraft . That is why I said ramp serves as extension of the deck

You completely forgot that the potential energy you spoke of came from the aircraft's kinetic energy in the first place! The ramp itself is completely passive and does not add any energy to the aircraft.

A lot of people think that the ramp shortens the take off length, but the ramp doesn't shorten anything. The take off length is still the same, just that a portion of that length is in the air.

As for lift - velocity vector point slightly upwards when aircraft leaves ramp , but later it would be more parallel to horizon . With extra time given , engines would accelerate aircraft and enough of the lift will be generated to sustain flight .

P.S.

Watch J-15 with payload from 0:49 . It goes up (vertical component of speed exists) and then continues almost parallel to horizon (vertical component disappears) . But those 2 extra seconds give engines more time to work :

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If you actually read my previous post, you would have noticed I addressed this very point already.

 

[delft]

A lot of people think that the ramp shortens the take off length, but the ramp doesn't shorten anything. The take off length is still the same, just that a portion of that length is in the air.

A crude picture and not relevant. We are interested in the length of deck necessary to get aircraft safely into the air, including of course the case with engine failure, because you have to pay for the ship, not for the virtual extension of the take off in front of her. We are also not interested in the take off length to 35 feet above the runway, as you calculate and test for with civilian aircraft, because no trees grow in front of the ship.

 

[Air Force Brat]

Hence why your analysis is flawed.


You completely forgot that the potential energy you spoke of came from the aircraft's kinetic energy in the first place! The ramp itself is completely passive and does not add any energy to the aircraft.

Actually Eng, the ship does provide the first 20 to 30 knots airspeed to the aircrafts kinetic energy in relation to the relative wind, as well as the upward momentum, in addition to the 40 to 60 ft altitude, all with-out the induced drag of the control deflections needed to pitch the aircraft into a positive alpha configuration at a very low airspeed.

There is indeed some induced drag from the additional friction on the tires, and the compression of the main and nose gear struts as the aircraft attempts to accelerate "through" the ramp. So although the ramp is not "free", it is a very good bang for the buck... brat

 

[Jeff Head]

A couple of posts of J-15 eye candy for everyone:

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[Jeff Head]

2nd post of J-15 eye candy:

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...and here's a couple of CG what we are going to see some day soon:

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...and here's one for equation, extolling the virtues of model building.

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[SteelBird]

A couple of posts of J-15 eye candy for everyone:

Hope we'll see this on the Liaoning soon.

 

[Jeff Head]

Hope we'll see this on the Liaoning soon.

Because of the engines?

It is interesting to note, that aircraft number 554 has appeared to have different engines on occasion, and has flown from the Liaoning:

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[Equation]

"At EASE...Ladies"!

 

[SteelBird]

Because of the engines?

It is interesting to note, that aircraft number 554 has appeared to have different engines on occasion, and has flown from the Liaoning:

I believe the 554 that took off from Liaoning was wearing AL-31s. What I want to see is WS-10s on aircraft carrier.

 

[thunderchief]

You completely forgot that the potential energy you spoke of came from the aircraft's kinetic energy in the first place! The ramp itself is completely passive and does not add any energy to the aircraft.

It doesn't add energy , it adds time . Ramp serves to convert kinetic to potential energy . Again , imagine ball . It doesn't generate lift but still goes up . Now imagine that same ball having engines . By the time gravity slows it down , engines would work and add more energy to the system (from chemical energy of the fuel)

A lot of people think that the ramp shortens the take off length, but the ramp doesn't shorten anything. The take off length is still the same, just that a portion of that length is in the air.

It shortens the ship damm it . That is whole purpose of the ramp , to be able to takeoff from relatively small carrier . Example from Wiki :

For example, an AV-8B Harrier with a gross weight of 29,000 lb (13,000 kg) on a 59 °F (15 °C) day and a 35 kn (40 mph; 65 km/h) wind over the deck would require 400 ft (120 m) to takeoff using a 12° ski jump ramp designed as on the Principe de Asturias, but 750 ft (230 m) without the ski jump ramp.[22]

For a MiG-29 launching over the ski jump ramp on the Tbilisi, takeoff speed is reduced from about 140 kn (160 mph; 260 km/h) to about 70 kn (81 mph; 130 km/h) (depending on many factors such a gross weight).[23]

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