J-15 Carrier Multirole Fighter thread

Max Demian

Junior Member
Registered Member
How do you actually calibrate the end speed by just watching a video? Can you please walk me through your calculations.
...
Is your position mathematically supportable or is it merely an assumption based on unknowns?
I would also like to know this.

In the video 0:58, the J15 took off from extended position of 190m in 7 seconds, achieving approximate acceleration of 8m/s² and velocity of 200 kmph off the jump.
(Su33 stall speed is about 250kmph). Since the ski jump is angled at about 14°, Horizontal V is 190kmph and Vertical V is 50kmph. Vertical V is used as a safety against sink rate until target lift is achieved.
I think he assumed constant acceleration, whereby an acceleration of 7.75m/s can be derived from the other two variables (time, distance). In absence of air resistance and friction, you would need 225kN of thrust to accelerate a 29t object at that rate.

What I am skeptical is how the horizontal V was derived at the end of the ski-jump: I think the trajectory acceleration drops over the ski-jump section (due to impact and having to fight gravity).
 

Bhurki

Junior Member
Registered Member
How do you actually calibrate the end speed by just watching a video? Can you please walk me through your calculations.
Middle school physics.
Dist = 1/2 x Acc x (time)²
Dist was known 185m, time was observed 7 sec
(Important Note: Time observation may be fallible with negative degree. Any correction towards higher time decreases acceleration which indicates even lower T/W. If thrust is known, that would mean higher Takeoff weight which is trivial since we are trying to establish a bound safe high limit.)
Acc= 7.5m/s²
Velocity =acc x time
Velocity at end of deck about 200kmph
The deck is angled at 15°,
Vertical component of velocity is sin(15°) = 50 kmph(15m/s)
Horizontal " " " " cos(15°) = 190 kmph(55m/s)
Same with the thrust - Vertical thrust is 25% and Horizontal thrust is 96% of total thurst(26 mgf).

After take off before achieving flight sustaining lift, the jet would rely on its high AoA control characteristics which are unknown, so lets give it a disadvantage of being considered a nominal shape.
It hence follows a ballistic trajectory countered by vertical thrust.
Gravity pulls down with 10m/s², vertical thrust pushes up by about 2m/s² (this holds up until T/W of 0.8) creating a resultant of 8m/s². Trading 100% vertical velocity(15m/s) gives it 2 seconds to increase its horiz velocity over stall speed. The altitude provides extra safety against negative vertical velocity which can be cut by pitching up and increasing vertical thrust.
The horizontal thrust gives it extra 50-60 kmph within those 2 seconds to start sustaining required lift.
(In reality, aero lift will aid the jet within those last 2 seconds as well)

A lot of these numbers can be moved around but only in the same direction(aero lift,over deck wind considered 0, but will certainly be higher), which gives it even more safety. One might note that no aero lift equation is used, this is because the characteritics of the body are considered consistent upto sustained flight and target v has been set to 250 kmph.
 

Brumby

Major
Middle school physics.
Dist = 1/2 x Acc x (time)²
Dist was known 185m, time was observed 7 sec
(Important Note: Time observation may be fallible with negative degree. Any correction towards higher time decreases acceleration which indicates even lower T/W. If thrust is known, that would mean higher Takeoff weight which is trivial since we are trying to establish a bound safe high limit.)
Acc= 7.5m/s²
Velocity =acc x time
Velocity at end of deck about 200kmph
The deck is angled at 15°,
Vertical component of velocity is sin(15°) = 50 kmph(15m/s)
Horizontal " " " " cos(15°) = 190 kmph(55m/s)
Same with the thrust - Vertical thrust is 25% and Horizontal thrust is 96% of total thurst(26 mgf).

After take off before achieving flight sustaining lift, the jet would rely on its high AoA control characteristics which are unknown, so lets give it a disadvantage of being considered a nominal shape.
It hence follows a ballistic trajectory countered by vertical thrust.
Gravity pulls down with 10m/s², vertical thrust pushes up by about 2m/s² (this holds up until T/W of 0.8) creating a resultant of 8m/s². Trading 100% vertical velocity(15m/s) gives it 2 seconds to increase its horiz velocity over stall speed. The altitude provides extra safety against negative vertical velocity which can be cut by pitching up and increasing vertical thrust.
The horizontal thrust gives it extra 50-60 kmph within those 2 seconds to start sustaining required lift.
(In reality, aero lift will aid the jet within those last 2 seconds as well)

A lot of these numbers can be moved around but only in the same direction(aero lift,over deck wind considered 0, but will certainly be higher), which gives it even more safety. One might note that no aero lift equation is used, this is because the characteritics of the body are considered consistent upto sustained flight and target v has been set to 250 kmph.
Thanks for that.

Just a recap on what we are dealing with. Previous calculations of a fore launch conclusively ruled out a full fuel load.

An aft launch @ 29 tons suggest an end speed of 200 kmh plus probable add on of 50-60 kmh during its vertical lift albeit with sink-off. This effectively gets it to stall speed. Favorable wind conditions might get it above the finishing line but with no safety margin.

This means, a J-15 with full fuel load and 2 tons of weapons load out can only be launched via aft under favorable conditions but with no safety margin.
 

Bhurki

Junior Member
Registered Member
This means, a J-15 with full fuel load and 2 tons of weapons load out can only be launched via aft under favorable conditions but with no safety margin.
Final safety limit will be close to 30 tons for aft position and 25 tons for fore positions.
 

Intrepid

Senior Member
A regular safety margin is stallspeed * 1,3 (some bush pilots may use stallspeed * 1,05, but they do not live long)

An other rule is reference speed (stallspeed * 1,3) plus half of wind plus gusts.

There should be a maximum speed for the ramp due to stress on the airframe and landing gear.
 

Tam

Captain
Registered Member
With your "RWR", the main receiving antenna --- as with ESM --- would be the tube. ESM antennas tend to have a cylindrical form. The angled tips are for both reception and emission and each end would contain a small phase array. That means they are intended to emit something both towards the front and the back of the plane. I already mentioned to you this is done for cross eye jamming. One pod would sample, lets say Pod A, but the distorted copy intended for spoofing, would be emitted on the other pod, which would be Pod B, and likewise the sample on Pod B would have the spoofing signal emitted on Pod A. They would do this alternatively.

The second pod you call SPJ, which has phase array antennas on the end pointed downwards, is clearly aimed at projecting beams to ground targets. Sampling for the ground targets would have to be taken with the previously mentioned pod.

As these comes from a magazine, the author is doing his own conjecturing.

This plane these pods go with, is likely to be armed with a YJ-91 or some other ARM missile. Sampling from the wingtip pods would provide the ARM missiles their targets.

For all intents and purposes, it appears to be a SEAD suite to me.
 
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Scchwerter_

New Member
Registered Member
I am interested in these. Looks to me it is RWR and SPJ Can someone please translate.

View attachment 56326
Upper picture
Red words: tactical jamming receiver
Black words: Can perform real-time signal aqquisition, parameters measurement, dynamic information update and accurate direction measurement (persumably of radar signal source)

Lower picture:
Red words: electronic jamming pod
Black words: Can provide high-frequency barrage jamming on a large area (also mentioned something along the lines of "blanket jamming"), or perform spoofing on enemy aircrafts

To sum up I think this is more like the AN/ALQ-218 electronic warfare system that EA-18G has (which makes sense because the J-15D's role is very similar, if not identical, to that of the EA-18G)
 
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