JF-17 Thunder Multirole Fighter [Thread 5]

[Tempest II]

Fatigue Analysis Software – Reducing Costs in the Sky - Aerospace Technology

"Traditionally, fatigue failures have been fixed by overdesign. But increasingly, engineers are under pressure to 'design down' to save weight and material costs. Overdesign is no longer a viable option and the need for sophisticated fatigue analysis tools has become increasingly apparent, .... .... BAE Systems, Rolls-Royce, Thales UK and Meggitt hope the latest developments in aerospace fatigue analysis will be found at Cranfield University, where the integrated vehicle health management (IVHM) centre was launched in November. .... ... "We did an experiment once where we asked 12 organisations to use their fatigue analysis software to calculate the fatigue life of a sample component on a helicopter. We then did an experimental measurement to find the correct answer, which was 400 flight hours. Whilst some of the companies were within a few hours, some suggested the fatigue life should be 250 hours and one said it was 12,000."

Again, I am just suggeting that the 200% load tests see to say Chengdu were cautious and are doing more work to open up the performance of the FC-1. It is not unheard of neither is it unique to the FC-1.

 

[VCheng]

Fatigue Analysis Software – Reducing Costs in the Sky - Aerospace Technology


Again, I am just suggeting that the 200% load tests see to say Chengdu were cautious and are doing more work to open up the performance of the FC-1. It is not unheard of neither is it unique to the FC-1.

I will quote a previous post here for its relevance:

I think you both are confusing Carrying heavy weapons on hardpoints vis a vis an increased load capacity. The engine is same. The fuel carrying capacity is same, there is no chance of increased load capability.

What " load tests " or " increased load carrying " means is JF-17 hardpoints and wings were tested up to it's limit by carrying heavy payload to see designed hardpoint could carry the load up to it's limit for which it is designed.

For last past 3-4 years, we only seen PL-5 hanging on wingtips or drop tanks. With these tests it can carry more heavy weapons reaching it's limit to 4600 KG payload

 

[Tempest II]

... .... , though I would consider it remote, that the JF-17 is over-designed to that extent. .... .....

What do you think of the structure passing 200% design load testing?

 

[VCheng]

What do you think of the structure passing 200% design load testing?

That is routine. It is done even on passenger jets:

 

[Tempest II]

I will quote a previous post here for its relevance:

Bratva is saying what he “thinks”.
He even says “up to it's limit by carrying heavy payload to see designed hardpoint could carry the load up to it's limit for which it is designed” … … This is contrary to the report which says “200% of design load”.

 

[VCheng]

Bratva is saying what he “thinks”.
He even says “up to it's limit by carrying heavy payload to see designed hardpoint could carry the load up to it's limit for which it is designed” … … This is contrary to the report which says “200% of design load”.

So what happens next? You cannot overload all hard points and then use the same engine and reduced fuel to load to get the plane up in the air, or can you?

 

[Tempest II]

So what happens next? You cannot overload all hard points and then use the same engine and reduced fuel to load to get the plane up in the air, or can you?

Yes, you can load (I would not recommend "overload") the hardpoints and take off with less fuel and use IFR to get more fuel.

The thrust and the empty weight of the FC-1 and Gripen are comparable. The maximum payload is where the FC-1 is in an inferior catergory. ... ... The 200% load tests say there is unexploited potential in the structure. ... ... No change in structure necessary, no new engine, just some experimentation and validation of a higher load regime.

 

[VCheng]

Yes, you can load (I would not recommend "overload") the hardpoints and take off with less fuel and use IFR to get more fuel.

Yes, but then what good are the 200% overload tests? The things to keep in mind are that rated loads for each hardpoint, and the designed limits for total take off weight are there for very good reasons, and unlikely to change much over the life of the airframe.

 

[Irfan Baloch]

The construction techniques used for the JF-17 are a generation or two older than the ones used for the Gripen, resulting in a heavier unloaded airframe that can carry only so much, given its engine.

looking at its avionics, armaments and variety of missions available ..I say its not bad for a 2nd or 3rd generation fighter. only need to sort out this combat range and flight time.

 

[VCheng]

looking at its avionics, armaments and variety of missions available ..I say its not bad for a 2nd or 3rd generation fighter. only need to sort out this combat range and flight time.

Of course. The JF-17 is a great match for the PAF, and it will play an important role in the air defense needs for a long time to come. I am sure it will serve very ably, for what it offers is what PAF can afford. With IFR, the limited internal fuel capacity is not as much of a deal as its engine limitation.

 

[VCheng]

The thrust and the empty weight of the FC-1 and Gripen are comparable. The maximum payload is where the FC-1 is in an inferior catergory. ... ... The 200% load tests say there is unexploited potential in the structure. ... ... No change in structure necessary, no new engine, just some experimentation and validation of a higher load regime.

If there is any unexploited potential, it will not be more than a few per cent more. The JF-17 will never approach the Gripen's payload, given its basic limitations. The NG version is even more impressive.

 

[Tempest II]

A limiting factor I see is the (JF-17 vs Gripen) is that the Gripen has nearly 25% more wing area if canards are included. That, while I am not sure to what extent, would put the Gripen in a payload category above the FC-1.

 

[VCheng]

A limiting factor I see is the (JF-17 vs Gripen) is that the Gripen has nearly 25% more wing area if canards are included. That, while I am not sure to what extent, would put the Gripen in a payload category above the FC-1.

Wing loading can be higher for one design vs another for payload considerations. Wing surface area is only one consideration.


Edit: Please compare the F-20 Tigershark as an example of higher payload despite a smaller wing area. The JF-17 is a modern day version of that jet quite similarly.

 

[Chak Bamu]

1. Wing loading is a very important factor. No need to split hair about whether wing surface area is 'only' one consideration. This just shows ignorance of engineering principles.

2. Engineering Factor is a routine methodology. Things are 'over-designed' for a purpose. For example for elevators the engineering factor is 10; meaning that an elevator cleared to carry 1000 Kg weight is designed to carry 10,000 kg. Similarly though JF-17 structure is designed to match its performance, the design limit would be significantly higher than the allowable max weight. 200% wing loading test just shows that the engineering factor is at least 2 in case of JF-17 wings. We can be confident that a higher thrust engine could certainly help carry higher weight.

3. If anyone recalls Dubai airshow demo of JF-17, towards the end the high angle of attack slow pass followed by a turn and steep climb shows that the aircraft is not under-powered as such. With a single RD-93 powering the aircraft, one can indirectly tell that the 'over-design' does not impact its performance in any apparent negative way.

4. As I observed earlier, if PAF thought that the aircraft had lesser range or too little loiter time, the last redesign could have lengthened the fuselage a little to improve fuel capacity. That did not happen and it clearly shows that there are no serious issues as such. JF-17 has had at least 2 redesigns (maybe 3) if I am not wrong. I do not think that the air-frame has any glaring deficiencies.

5. @VCheng , the day you can prove that the JF-17 airframe is 2nd generation will be the day I will take you seriously. You are wasting people's time by engaging in senseless discussions for the sole purpose of deflecting criticism of your statements. A couple of pages back I asked you to provide reference for your assertions ( JF-17 Thunder Multirole Fighter [Thread 5] | Page 272 ) just because you seemed to be pulling stuff from thin air. Your very inadequate reply only confirmed my suspicion. I decided not to embarrass you (whether you could possibly feel embarrassed is a valid question) and did not press the issue ( JF-17 Thunder Multirole Fighter [Thread 5] | Page 272 ). I would now very much like you to provide valid references for your questionable claims, which are:

a) "The initial planes had 4,000 lbs of internal fuel and the newer ones are closer to 5,000 lbs." Post #4065 made by you. My question about planes 'initial' and which planes 'newer' remains unanswered.

b) You seem to be implying that RD-93 is quite like old RD-33, ignoring obvious differences such as control over smokey trails, indicating better fuel usage and probably better fuel efficiency. (My post #4063 vs your post #4065)

c) Your assertion that "The construction techniques used for the JF-17 are a generation or two older than the ones used for the Gripen" (post #4101). It is well known that Gripen is fourth generation, by Western classification. So you are saying that JF-17 airframe is possibly 2nd generation. Saying such a thing takes some guts. You make it sound so casual. Let us see you just as casually substantiate your claim.

 

[VCheng]

5. @VCheng , the day you can prove that the JF-17 airframe is 2nd generation will be the day I will take you seriously. You are wasting people's time by engaging in senseless discussions for the sole purpose of deflecting criticism of your statements. A couple of pages back I asked you to provide reference for your assertions ( JF-17 Thunder Multirole Fighter [Thread 5] | Page 272 ) just because you seemed to be pulling stuff from thin air. Your very inadequate reply only confirmed my suspicion. I decided not to embarrass you (whether you could possibly feel embarrassed is a valid question) and did not press the issue ( JF-17 Thunder Multirole Fighter [Thread 5] | Page 272 ). I would now very much like you to provide valid references for your questionable claims, which are:
a) "The initial planes had 4,000 lbs of internal fuel and the newer ones are closer to 5,000 lbs." Post #4065 made by you. My question about planes 'initial' and which planes 'newer' remains unanswered.
b) You seem to be implying that RD-93 is quite like old RD-33, ignoring obvious differences such as control over smokey trails, indicating better fuel usage and probably better fuel efficiency. (My post #4063 vs your post #4065)
c) Your assertion that "The construction techniques used for the JF-17 are a generation or two older than the ones used for the Gripen" It is well known that Gripen is fourth generation, by Western classification. So you are saying that JF-17 airframe is possibly 2nd generation. Saying such a thing takes some guts. You make it sound so casual. Let us see you just as casually substantiate your claim.

The proof is in the performance figures, which can be seen to be clearly inferior to other aircraft of its size, particularly the Gripen. The JF-17 is a modern day F-20, arriving a quarter century too late. The RD-93 is the same basic engine as the RD-33 with some re-positioning of components. Sprinkling holy water on it does not reduce its fuel consumption. The JF-17 airframe was designed in the 70s using the technology of its day, and remains the same basic design, with modern avionics.

Before you get all bent out of shape, would you like to compare the three planes: F-20, JF-17 and Gripen, to see what the figures actually show? Telling things like they actually are takes only a bit of moral courage, that is all.

Or, since you are a Mod and I am only a (the most?) hated member, may be I should just concede?

Yeah, that is better: I accept that the JF-17 is a 4/4.5/5th generation jet fighter that is so over-engineered that it will be developed to carry far more payload.

There, I said it. Ramadan is coming up and I do NOT wish to fight with you or anyone.

Peace!