JF-17 Thunder Multirole Fighter [Thread 7]

[araz]

No, it does not.

Let us take the F-16, a jet that the PAF flies, for example...

The JDAM is certified only on stations 3 and 7 as shown above. The smallest JDAM is the is the GBU-38 at 500 lbs, so we can use that for our example.

On the F-16, each wing's internal fuel load is about 500 lbs.

Let us say that an F-16 reported a hung JDAM, or failed to release.

Let us say that the F-16 can transfer fuel anywhere.

Are you telling everyone that in the event of a hung 500 lbs JDAM, the F-16 is going to engage in a captive fuel situation, as in keeping fuel in place in the opposite wing, to maintain balanced flight?

Never mind the laws of physics that says aerodynamics forces using trimming can be greater than 500 lbs in the opposite direction to maintain equilibrium. You would rather use captive fuel thereby reducing range? That is assuming you have enough fuel in the first place. What if you have no external and internal fuel wings to use? Are you going to say use trimming? Then why not use trimming in the first place and use the fuel to get home?

Like Mr. Shabi, you are willing to make this leap of faith, not because you put any real effort into research, but because you NEED to satisfy your own feelings that the JF-17 is better than the American product -- at any cost.

What if the hung ordnance is the larger JDAM of 1,000 lbs? The opposite wing can only hold 500 lbs. Where is the counter-balance now? Let me guess -- trimming? Then why not use trimming in the first place?

How much internal wing fuel on the JF-17?

Let me put this scenario to you...

A JF-17 pilot radioed an inflight emergency (IFE) of a hung ordnance situation. He engaged captive fuel to balance out the jet. But in doing so, he now lacks to fuel range to make home. Can he get an air refueling assist?

So now the PAF is going to launch an air refueling rescue when there have ALWAYS been a better alternative to counter-balance a hung ordnance -- trimming.

Do you see how absurd is this mental experiment? It defies logic and common sense. If you answer use trimming and captive fuel, then why not use trimming in the first place and save everyone the headache?


Nowhere have I declared that wing-to-wing fuel transfer on a jet fighter is technically impossible. But it does defies logic and common sense when there is a better alternative -- trim the jet.

I know...I know...We Americans are stupid...

A great debate and a learning opportunity. Gambit it is always a pleasure and a learning opportunity to read your posts. People need to realize that posters like you and a few others are an assett for the forum. You can be harsh and a bit abrupt but the quality of your posts cannot be faulted. So kudols to you sir.
Regards
A

 

[MastanKhan]

Hi,

What people are not understanding is that 'trimmings' has its limitations.

Larger the vehicle---larger the wings---for same amount of weight in question---trimming would be easier---.

As compared to a smaller vehicle with a smaller wing with a similar weight as above---trimming would be difficult---.

As per the laws of physics---there would come a weight limit---that once you exceed that threshold---trimming is not possible---once the weight is discharged from the main body.

Trimming is not the magic bullet under all conditions---.

 

[ghazi768]

trimming has limits... what bull crap is being spewed here.

Of course everything has limits, if trimming is useless than that means a full stick at one side is useless. you are most probably flying with less than half a wing on one side.

 

[gambit]

Hi,

What people are not understanding is that 'trimmings' has its limitations.

Larger the vehicle---larger the wings---for same amount of weight in question---trimming would be easier---.

As compared to a smaller vehicle with a smaller wing with a similar weight as above---trimming would be difficult---.

As per the laws of physics---there would come a weight limit---that once you exceed that threshold---trimming is not possible---once the weight is discharged from the main body.

Trimming is not the magic bullet under all conditions---.

Yes, there are limits.

As stated earlier, there are two types of asymmetric loading:

- Drag
- Weight

A 'hung ordnance' is the worst because it combines both. Fuel is contained, so trapped/captive fuel in one wing or in a fuselage tank create only the asymmetric weight condition. On the other hand, a 'hung bomb' is a mass that is also exposed to aerodynamic forces, so the aircraft would have both types of asymmetric loading at the same time.

When you trim an aircraft, you uses some of the movement range of the flight control element. It is a quasi permanent state in that as long as the asymmetric loading condition exist, you have to keep constant that trim. If the fuel pump started working again, or the hung bomb somehow dropped off, you can restore the flight control element to its neutral position.

If the asymmetric loading condition is severe enough, as in battle damage, your trimming may take most or even all of the range of movement of that flight control element. WW II pilots, especially the bomber types, knew this well. Fuselages and wings with holes creating asymmetric drag, forcing the both pilots to manhandled the yokes in the opposite direction to maintain controlled flight. And they had to hold that until they land. Flying back then was hard work. Pilots back in those days may not have been elite athletes but they were certainly above average when it comes to being physical.

For the Grumman Avenger above, he lost approximately half of his port wing. This would be an asymmetric loading of both drag and weight. Not only that, lift is severely compromised on the damaged wing. The aircraft would have a tendency to roll port. Note his starboard aileron: displaced up.

That is trimming and the starboard aileron also lost some of its range of movement if there is a need for it to displace any more edge up.

In this debate, the difference between an airliner and a combat jet fighter is like man and woman. People unfamiliar with aviation assumes that the two classes of aircraft shares all attributes and behaviors. That is like saying if a woman can give birth, so can a man.

 

[Armchair]

trimming has limits... what bull crap is being spewed here.

Of course everything has limits, if trimming is useless than that means a full stick at one side is useless. you are most probably flying with less than half a wing on one side.

People asked for photographic evidence of asymmetric loadout, you gave them.

They required an explanation, he gave that too.

They asked for credentials, which was uncalled for, that was available too.

basically what happened is that the american poster rightly pointed out that technically, the F-16 isn't able to move fuel to balance loadout between wings, only front to rear or vice versa. He then assumed that the JF-17 can't either. All the babus got behind this and can't see past this mistake.

 

[gambit]

basically what happened is that the american poster rightly pointed out that technically, the F-16 isn't able to move fuel to balance loadout between wings, only front to rear or vice versa. He then assumed that the JF-17 can't either. All the babus got behind this and can't see past this mistake.

Wrong. I asked for proof. And what I asked for is reasonable based upon my experience. There was no 'mistake'.

If anyone made any mistake, it was on Mr. Shabi's part when he ASSUMED that the JF-17 is able to transfer fuel between wings to maintain controlled flight in the event of an asymmetric load condition.

Asking for proof is far from making assumptions.

 

[Armchair]

As I have said for the nth time, he provided photographic proof with an asymmetric loadout. That's proof. What else would you demand? A confirmation from ISPR?

 

[MastanKhan]

As I have said for the nth time, he provided photographic proof with an asymmetric loadout. That's proof. What else would you demand? A confirmation from ISPR?

hi,

And I tell you---he has proved nothing----. You have an elctronics engr on one side and someone associated with F16 and F111 on the other side---.

Your man Shabi has no experience in the field---and very poor analysis ability---.

 

[ghazi768]

People asked for photographic evidence of asymmetric loadout, you gave them.

They required an explanation, he gave that too.

They asked for credentials, which was uncalled for, that was available too.

basically what happened is that the american poster rightly pointed out that technically, the F-16 isn't able to move fuel to balance loadout between wings, only front to rear or vice versa. He then assumed that the JF-17 can't either. All the babus got behind this and can't see past this mistake.

I have not read that part of the thread to know why posters started discussing using fuel to balance JF-17, it is not needed.. What gambit is mentioning is, in my opinion, correct.

Why I jumped into this discussion was because some one was using this to doubt JF-17's ability to use asymmetric payloads. This is also because I had this discussion with a specific poster before but he keeps bringing this thing again and again, I do not for what reason. I have given a pointer that you can drop everything on one wing and still Jf-17 will fly fine. But it is of no avail (like bhens ke age been bejana)

 

[gambit]

As I have said for the nth time, he provided photographic proof with an asymmetric loadout. That's proof. What else would you demand? A confirmation from ISPR?

That was not proof.

You need something like this...

https://theaviationist.com/2014/09/15/f-15-lands-with-one-wing/

There must have been fuel transfer between the wings, no? After all, we have photographic 'proof' right here.

He realized that the F-15 was badly damaged when the aircraft fell in a very tight spiral after a huge fuel leak from its right wing.

After regaining the control of the aircraft Nedivi was ordered to eject but decided not to bail out since he was confident he could land the plane at the nearest airfield, 10 miles away, even thought the F-15 was flying on vapors: he began to reduce speed but the missing right wing (that the Israeli pilot was still unaware of) caused a new spin.

The asymmetric load created a tendency towards a spin. If counterbalancing with fuel was one of the tricks Nedivi used to save the jet and himself, that would have been included. If that trick did not worked, that info would have been included as well.

How about another source...

http://www.uss-bennington.org/phz-nowing-f15.html

The wing is a fuel tank, and the fuel indicator showed 0.000 so I assumed that the jet stream sucked all the fuel out of the other tanks. However, I remembered that the valves operate only in one direction, so that I might have enough fuel to get to the nearest airfield and land. I worked like a machine, wasn't scared and didn't worry. All I knew was as long as the sucker flies, I'm gonna stay inside. I started to decrease the airspeed, but at that point one wing was not enough. So I went into a spin down and to the right. A second before I decided to eject, I pushed the throttle and lit the afterburner. I gained speed and thus got control of the aircraft again.

Note the highlighted: '...the valves operate only in one direction...'

McDonnell Douglas attributes the saving of this aircraft to the amount of lift generated by the engine intake/body and "a hell of a good pilot".

But nothing about fuel transfer between the wings as even an attempt to balance the jet. MD and Nedivi would have mention it as inside each mishap event, as much as possible is recorded for everyone to see. A flying technique or a cockpit trick could save someone else's life.

So how does this square with an F-15E source...??? I understand that this event involved an F-15D, but internally, the D and E shares the same base structure.

http://www.f-15e.info/joomla/technology/fuel-system/90-internal-fuel-system

The task of the fuel transfer system is to transfer fuel to and from internal and external tanks to prevent imbalances caused by different fuel quantities in different tanks. The system should keep fuel imbalances between left and right sides below 200 pounds in case of internal wing tanks and below 1000 pounds in case of CFT's. If the aircrew experiences any imbalance greater than these and lasting for more than 5 minutes, then it's a malfunction and should be reported.

The highlighted SEEMS to indicate that fuel transfer BETWEEN the wings are possible. It SEEMS that way until a deeper understanding of how internal fuel management is reached.

So let us take each part of that paragraph carefully...

"...to prevent imbalances caused by different fuel quantities in different tanks."

How is this possible? A major reason why on jet fighters there are fuel tank quantity imbalances is because of the design of the fuel tank system itself. There are many individual tanks with different shapes in different locations that behaviors are different under maneuvers. Commercial airliners do not have this issue. It is a design 'issue', not a 'problem'. You have to be careful with language so as not to mislead the readers.

"The system should keep fuel imbalances between left and right sides below 200 pounds in case of internal wing tanks and below 1000 pounds in case of CFT's."

We can disregard the CFTs for now.

What is the best way to maintain that 200 lbs margin? Do you transfer between tanks, or do you simply feed more from one tank than other until that tolerance is reached? From an engineering perspective, it is easier for the latter.

The internal feed tanks does exactly what it says: feed the engines.

Other tanks supplies the engine feed tanks.

At the top paragraph of the F-15E source...

"Tank 1 and the wing tanks (1,4) are transfer tanks, which means that they are used to transfer fuel to and from other tanks through them to compensate from any aircraft imbalances originating from consuming fuel during flight."

Note the highlighted. It means the internal wing tanks are used as transfer stations for other tanks -- through them. Not between themselves.

The cockpit fuel management panel do not have switches that says you can transfer fuel between internal wings.

I am NOT using the F-15E source to prove or disprove the JF-17's internal fuel management or to disprove Mr. Shabi's claim. I am using the F-15E source to show how much work is involved to support one's claim and his arguments are seriously lacking. A photo and assumption do not -- as we Americans say -- cut it.

The fact that the fuel tank arrangement differences between an airliner and a jet fighter should have been clue enough to do further research to see if the differences affects other items like management and performance. In this case -- there are. If the F-15's fuel system is this much different from the F-16 that warrants this level of research depth, then how can you make assumptions about the JF-17 based upon an airliner?

 

[Shabi1]

You guys just can't let it go. I don't have the time to keep talking on this topic.

Since credentials keep popping up I'm sharing something from commercial airliners and I've worked on these systems so if anyone wants to disagree please don't use the credentials card for those parts.

Primary function of the fuel system is to empty tanks in a preset order. But in case of an emergency you can control the fuel pumps and move fuel as needed through redundant paths.

It's pretty established trim is used for managing a dis-balance, no arguments here. I have never said trim method can be completely replaced by fuel CG method. Disadvantage of trim is it adds unwanted drag and affects range. In newer commercial airliners as long as there is enough fuel in the tank available if there is a dis balance a system which uses fuel to alter CG is can be used instead of trim. Once not enough fuel to do this then there is more reliance on trim. Its a complex system upto the pilot to let the FCS manage or do it manually. This way you can avoid unwanted drag for as long as possible. For some aircrafts like Airbus310 there is a unusable fuel amount in the tank for this task.

Now the argument the fighter aircraft are too small for such system.

F-16 and F-15 were designed in 70s (you can correct the era to be precise) and the F-15 despite it's updates only got FBW in the latest F-15SE variant. Some of their control systems/cockpit controls remain the same, they are not any less capable because their FCS techniques havn't been changed, it's just that when you upgrade them you don't mess with somethings that are working well.

Does this mean their flight control systems are similar to all aircraft designed afterwards. No, aircraft are unique, techniques are evolving and all very different. Which is why what Mr Gambit is saying from his experience is right but cannot be inferred for all aircraft.

If you read this through you can see the JAS-39 has a fuel management system for CG control via fuel
https://saabaircraftindustry.com/en...ls/designing-the-world-s-best-control-system/
SAABs official website has link for a system as well

Similarly the link to the book I sent says Eurofighter and JSF use fuel to to control CG. If you look at the diagram there are multiple paths for fuel including directly between wings and this adds redundancy in case of any fuel pump failure as well.

The use of fuel to alter CG is more useful in fighters since modern jets are designed unstable and instead of FBW correcting it via control surfaces its better to avoid the added drag from the surfaces when you want to fly straight and supersonic.

Aircraft Systems: Mechanical, Electrical, and Avionics Subsystems Integration
https://books.google.com.pk/books?id=Hcgh8SturJQC&pg=PT157&lpg=PT157&dq=eurofighter+fuel+crossfeed&source=bl&ots=x3vXr8p_fg&sig=7tjigkW8GuInxEndCiAN7bOeb1I&hl=en&sa=X&ved=0ahUKEwiLlqy4_draAhULso8KHSSAD54Q6AEISDAF#v=onepage&q=eurofighter fuel crossfeed&f=false

Because of PAFs strict rules regarding in service personal sharing information online I'm pretty sure any active personal working on the JF-17 cannot comment on the subject right now and I agree with this rule. I have friends in PAF very careful about this and know even a selfie on Facebook can lead to a court martial. So you don't have to agree with me if you don't want for the next part. It's an analysis. Analysts job's are to infer information from sources and correlations when first hand not available and it's a pretty decent field in private sector as well as defense.

Now to JF-17, non of us are the authority on it, and no one has worked on it to confirm but one can use a intelligent deduction that it's FCS is similar to the other aircraft that were designed in eras after the F-15 & F-16 just like Gripen, Eurofighter & F-35. And the technology is not an issue since same tech is now available commercially, it's not sensitive tech. Two reasons to support this claim.

1.
For this configuration to work where there is a single tank on one wing and no tank on other the wing fuel pumps on both wings must have individual control feature so that the one uneven fuel load tank on the wing works. And it's a unnecessary burden on the pilot so should be managed by FCS.
Another reason for needing a control mechanism is that you can't have a single ON/OFF for both wing tank pumps, they need to be controlled separately if there is no fuel on one side ext tank. Reason being it's common knowledge that running a fuel pump dry will damage it as fuel passing through it is also it's coolant. And if wing fuel can be controlled independently then what reason is there not to use it for CG change as well.

2.
Fuel control panel system F-16. When it goes supersonic the aircraft CG is adjusted to remove it's instability.
http://www.f-16.net/forum/viewtopic.php?t=3870

Fuel control panel F-15. Manual Controls

Fuel Control panel Airbus A320. Note the crossfeed valves between paths. Managed by computer.

Fuel control panel B777. Managed by FCS

Fuel control panel/MFD Eurofighter. Managed by FCS

Fuel control panel/MFD F-35. Managed by FCS, no control buttons

Fuel control panel/MFD JF-17. Managed by FCS, doesnt take an expert to decide which generation of jets its similar too.

The whole reason why I brought up fuel management to control CG was to counter a argument with a technical and alternate method on how it can be avoided when Mr Mastan quoted AVM that the JF-17 will tip over after firing if it carried the Raad on its wings. I assumed you all would understand it was to work in tandem with trim hence didnt mention trim in my initial posts.
It turned out to be a mis interpretation by Mr Mastan. AVM actually meant something else and it was posted 1-2 pages back.

I hope we can now settle this as everyone is correct in their own way and let it be. Too much time spent on this topic.

 

[CrusherChamp]

Hi,

The problem over here is that the neighbor has changed the rules of combat---ie the rules of engagement and disengagement---.

A superior aircraft would launch all its BVR missiles from a distance and scoot away----no merge---.

See---the JF17 or the BLK52 can only launch 1 BVR missile at one enemy aircraft at one time---otoh---the SU30 can launch a volley of 4 BVR missiles at the same target in one go---.

So---a JF17 would have to fight off 4 BVR missiles at one go---.

This is what I have stated for many a years---and I have yet to come across a pakistani who has the ability to understand the intensity of the issue at hand---.

At least no one has replied back to me acknowledging the fact---.

The SU30 can carry upto 12 BVR missiles---let us say 8 BVR missiles for convenience---.

2 SU30's flying in---face 4 JF17's---they launch a volley of 4 missiles each at the JF17's and then turn and run---.

The JF17's are forced into taking evading turns---.

While that is happening---another SU30 pops up---the 4 JF17's are trying to save their lives---this SU30 gets in closer to an 80% kill range---it has 8 BVR missiles---.

Now it launches a volley of 2 BVR missiles at each target---the targets are in desperate move to save their lives from the original 4 BVR's on each target---.

I would like to hear from a Paf pilot---how they would counter it---.

With all due respect do u realy think thak jft is build to fight su35.
Lests suppose our enemy have 800 jetts.
All of them r su35 is it realy possible. I dont thik so. Jft is built to fight below su35 level like miraj2000. Tajas. Migs etc.
Now lets suppos 4 jft facing 2 su35 as u say.
First of all 4 jft dident fire 1 bvr why.
Second option 2 fjt r foward position and 2 r at back when su35 fired their bvr 2jft turned back a d trying to save them selves or trying to deceive rockets with thear flair other 2 come forwad and target 2 su35 turning back.
Third option 2 jft r facing head to head 2 su35 other 2 jft r attacking same 2 su35 from left and right side. Su35 fired bvr on first 2 jft and after that they r turni g back or turni g towards other 2 jft. What do u thing will happen.. bro what do u think paf pilots trainers land crew radar operators do all day sit back and enjoy. They dont kmow how to.plan and engage incomming birds. Come on yar har cheaz equipment he nai hotti planing executing the plan skills or patta nai kaya kuch matter karta ha. Ham to bara aram sa kah data ha ya jazba kuch nai hotta hath main 1 ak47 ho to.khali jazba sa tank k muqabala nai ho sakta. Chotti se bat btow ap agar koi b game khailta ho chaha wo cricket ho badminton ho ya koi b or jab ap ko lagta ha na k agla banda ap sa acha khalari ha to ghabrahat sa ap ke parformence p faraq parta ha. Issi tarha ap socho jang main ap mar sakta ho to ap ke performence main kitna faraq para ga. Assa moqa p.jazba kam atta ha
Han ap is had tak sahi ho.k.Pakistan jft ke improvement ma tazi lanni ho ge.
According to me it is better that 4 jft r facing 2 su35 than 4 f7pg facing 2 su35. First of all u have to replace f7 then miraj and after that u will tink about replacig f16s

 

[MastanKhan]

With all due respect do u realy think thak jft is build to fight su35.
Lests suppose our enemy have 800 jetts.
All of them r su35 is it realy possible. I dont thik so. Jft is built to fight below su35 level like miraj2000. Tajas. Migs etc.
Now lets suppos 4 jft facing 2 su35 as u say.
First of all 4 jft dident fire 1 bvr why.
Second option 2 fjt r foward position and 2 r at back when su35 fired their bvr 2jft turned back a d trying to save them selves or trying to deceive rockets with thear flair other 2 come forwad and target 2 su35 turning back.
Third option 2 jft r facing head to head 2 su35 other 2 jft r attacking same 2 su35 from left and right side. Su35 fired bvr on first 2 jft and after that they r turni g back or turni g towards other 2 jft. What do u thing will happen.. bro what do u think paf pilots trainers land crew radar operators do all day sit back and enjoy. They dont kmow how to.plan and engage incomming birds. Come on yar har cheaz equipment he nai hotti planing executing the plan skills or patta nai kaya kuch matter karta ha. Ham to bara aram sa kah data ha ya jazba kuch nai hotta hath main 1 ak47 ho to.khali jazba sa tank k muqabala nai ho sakta. Chotti se bat btow ap agar koi b game khailta ho chaha wo cricket ho badminton ho ya koi b or jab ap ko lagta ha na k agla banda ap sa acha khalari ha to ghabrahat sa ap ke parformence p faraq parta ha. Issi tarha ap socho jang main ap mar sakta ho to ap ke performence main kitna faraq para ga. Assa moqa p.jazba kam atta ha
Han ap is had tak sahi ho.k.Pakistan jft ke improvement ma tazi lanni ho ge.
According to me it is better that 4 jft r facing 2 su35 than 4 f7pg facing 2 su35. First of all u have to replace f7 then miraj and after that u will tink about replacig f16s

Hi,

Welcome to the forum---. Respect the decorum of the forum---the language spoken here is english---. Thank you.

The basic rule of combat is---whatever you have to fight with---that is what you have to fight with---.

At the time of combat---there would be no referee to ask you if both of you opponents are on equal footings---.

So---yes---if the JF17 is the primo fighter that Pakistan has---then it would be pitched against whatever the enemy pitches in the battle---.

Your battle scenario is wrong---. The SU can fire a volley of upto 6 BVR missiles at one target---let us say---even if it is 4 BVR's per target---.

 

[aftab_s81]

Although many people talk about JF-17 as primary fighter of PAF, I don't believe in that theory. The project SabreII was primary meant to replace aging F-7 (and it's variants), A-5s and Mirages. It wasn't meant to replace F-16s. I don't think PAF, in 90s, envisaged such thing like they are sanctioned and denied now.
So I think there is a need for an MRCA. Although project Azm has been started but it will take at least 15-20 years for us to see something happening. The only viable solution to me is 2-3 squadrons of J-10s. They can also replace Mirages and play same role. Remember PAF spends quite some time, money and energy to learn the maritime skills they currently have with Mirages and even though they are old, PAF still keeps them as an important asset. My two cents.
@MastanKhan

 

[aftab_s81]

I think JF-17 can not be pitched against every AC in IAF inventory, especially Su-30 and Rafale. So an MRCA like J-10 is cry of the day.