J-15 carrier fighter thread

[Air Force Brat]

The conclusion drawn from that calculation is flawed. Any increase in upward velocity is taken from forward velocity, which is not a performance gain. You need to look at this in terms of kinetic energy, rather than simple trigonometry.

That's correct, and in simple English, as a figure of speech, it is important to note that not only is airspeed off the ramp important, a more important factor is rate of acceleration and thrust. Were it not for the J-15s tremendous thrust to weight ratio, this aircraft, at this weight would NOT be operating of the Liaoning or any other Stobar carrier. This aircraft will "always" depart or recover from this aircraft carrier while the ship is steaming at 20+ knots into the prevailing wind. On a combat air patrol, you will launch and climb to altitude initially and once there pull the throttles back to a very efficient power setting to "loiter" on the threat vector, factor in sufficient fuel for a 10 to 20 minute engagement, and return from altitude, to the ship with a "reserve" in case of a bolter or weather.

This discussion isn't nearly as nebulous as some would make it out, the J-15 will have very similar numbers to our own F-15 or even more accurately the Su-27 and her variants, because that gentlemen is what she is, a very lovely, sweet little Flanker, she is not large, she is lovely and very well proportioned, and 90% of the time, there is no need to launch her at MTOW, NADA/NONE!

 

[hlcc]

They are new design , with some improvements in technology . Compare ranges of Mig-29K and Su-33 .

J-15 similarly have access to newer designed engines. In addition to WS-10 variants, Saylut apparently already have contract to supply Al-31 FN Series 3 (137kN compared to 125kN engine used in Su-33) to China.

 

[Engineer]

That is why you have cos(angle) part . Basically , we are calculating distance plane would go before it starts descending . Best results are for 45 degrees , but this is a very rough first order calculation . For a better results you would need integral calculus , incorporating increase of speed . And then you would need to incorporate all forces acting on the plane , height of the ramp etc ...

For a 14 degrees you would get 73.9m "deck extension" and 232.5 km/h speed

And I am telling you it doesn't work that way. Increasing the ramp angle for more upward velocity means reduction in forward velocity. Since lift is a function of airspeed, reduction in forward velocity means a reduction in lift generated, canceling the additional upward velocity. You cannot get extra benefit out of nothing.

 

[Jeff Head]

And I am telling you it doesn't work that way. Increasing the ramp angle for more upward velocity means reduction in forward velocity. Since lift is a function of airspeed, reduction in forward velocity means a reduction in lift generated, canceling the additional upward velocity. You cannot get extra benefit out of nothing.

But what you do get is time. Time for the engines to power the aircraft to enough air speed to generate the lift necessary to sustain flight before gravity overcomes the additional "upward" velocity imparted by the ramp. Then the wings take over.

 

[chuck731]

But what you do get is time. Time for the engines to power the aircraft to enough air speed to generate the lift necessary to sustain flight before gravity overcomes the additional "upward" velocity imparted by the ramp. Then the wings take over.

What you get with a ramp is reduction in induced drag as the plane runs down and leave the deck, and thus giving the plane faster horizontal acceleration, and better margin of speed and safety.

When a plane runs down a flat deck it needs vertical velocity. To gain this it must rotate to increase the angle of attack of the wings. This increases lift from the wings and gives the plane the extra lift needed to gain vertical velocity. But increased angle of attack increases lift induced drag on the wings. As a result, it reduces the plane's forward acceleration.

When a plane runs off the end of the ramp the ramp imparts a vertical velocity. Even though the aircraft appears to be pitched up its relative angle of attack to ambient airstream remains low. As a result, the plane runs down the deck, up the ramp and then off the ramp in an attitude with low induced drag, and this increases its ability to sustain forward acceleration.

 

[Jeff Head]

When a plane runs off the end of the ramp the ramp imparts a vertical velocity.

Uh...which is exactly what I said.

...the additional "upward" velocity imparted by the ramp.

 

[chuck731]

Uh...which is exactly what I said.

Yes, but the key reason why using ramp to gain vertical velocity is good is because it reduces the induced drag the plane experiences while gaining the vertical velocity.

If there is no reduction in induced drag, then it would make no difference whether the plane gains the vertical velocity by using a ramp, or by pitching up to increase the lift of its own wings, and the ramp would just be dead weight for the ship.

 

[thunderchief]

And I am telling you it doesn't work that way. Increasing the ramp angle for more upward velocity means reduction in forward velocity. Since lift is a function of airspeed, reduction in forward velocity means a reduction in lift generated, canceling the additional upward velocity. You cannot get extra benefit out of nothing.

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

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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[Deino]

Also posted in the regular Flanker-tread ... does anyone know for what missile this new huge pylon under both the inner wing-pylons as well as the ones under the intake trunks are for ???

They are very much different to the PL-12-pylons !

Deino

 

[bd popeye]

The former would allow for some 6,5-7 tons of fuel and enough armament. That in itself is still quite a bit, enough for 900-ish km combat radius high flying missions. If that's the worst case scenario like it seems it could be, that's still pretty good.

For comparisons sake here's a Super Hornet's stats;

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