KAI KF-21 Boramae (KFX Korean Indigenous Fighter program)

Personally, I would say that published technical information is more important than classification into a specific block. The definition of specific blocks (3 and beyond) is still an ongoing process; however, the article reveals some very interesting points.

The so-called 'KF-21EX', which is likely just a working name used by KAI, will apparently differ visually from the current aircraft.

The IBWs will be much deeper than what we might have assumed based on the image of the 'provided space' in the fuselage structure of the prototype under construction.

This will require significant structural modifications and new development of certain sections. The 'reprofiled canopy' is most likely also related to compensating for the loss of fuselage fuel space, which will be created behind the aircraft’s cockpit.
 
Koreans have likely chosen the smartest approach among all the new players in the field of supersonic aircraft development. It may be a case of a "fortunate accident" (or more likely the result of political compromises), but the evolutionary strategy is working brilliantly.

- At the outset, a pragmatic yet highly promising design with baseline LO built into its design and construction—based on realistic requirements and an acknowledgment of technological dependence on foreign partners.

- Rapid development and an unprecedentedly short timeline between the prototype's maiden flight and the planned IOC.

- In the meantime, the definition of future requirements (these remains extremely dynamic—not only in light of technological progress but also due to shifts in global politics and the specifics of ROK domestic politics).

- Parallel to this, gradual development of key indigenous technologies, with costs efficiently spread out over time.

- Simultaneously, expansion into new export markets and consolidation of existing ones.

- As a result, by the second half of the 2030s—possibly earlier than some traditional players—South Korea could field a system that fully meets generational transition standards; powerful, independent from dominant suppliers, cost-effective and highly exportable.

We're talking about a VLO platform with 110 kN-class engines, supercruise capability, advanced sensors and avionics, internal carriage of ALCMs, a suite of cutting-edge domestic weaponry, and MUM-T & CCA technologies.)

Wow.
 
snne said:
You essentially have to pay the same price as the F-35 but for less capability.
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While arguably true, the F-35 has a whole load of strings attached to it due to US foreign policy. Which makes it not viable for many countries, even countries not indirectly aligned with China or Russia.

And for India, especially given recent rhetoric from POTUS and his Indian counterpart, that may be enough to drop every bit of interest in it. While KF-21 uses US engines, it's arguably easier to source different engines down the line than source everything else to replace in an F-35. I think the fears of repeating the Iranian F-14 experience is real in many countries. And Europe doesn't have a comparable aircraft on offer right now, otherwise the Indians would have probably gone for that, given their historical affinity to French aircraft.

A Su-57 purchase would also be politically unviable for them as it would tie them firmly to Russia on an international stage. And after the two parties leaving the previous FGFA agreement on bad terms, with the Russians not having the desire to develop basically a whole new plane and do tech transfer for peanuts, it's unlikely terms of a Su-57E purchase would be too favorable (Su-57M/ME is basically off the table).

The KF-21 is a politically safe option that still offers a large degree of independence and the possibility of transfer of technology and perhaps even assembly. If these rumors are true, and we should treat them as rumors for now, they would be reasonable though. I don't see a better offer for the Indians right now tbh.
 
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Geo said:
As a result, by the second half of the 2030s—possibly earlier than some traditional players—South Korea could field a system that fully meets generational transition standards; powerful, independent from dominant suppliers, cost-effective and highly exportable.
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KF-21 is not independent. It is subject to ITAR and US export restrictions for several critical systems including engines (GE F414), and electric power generation and environmental control systems (Collins Aerospace).

Basically without US approval, KF-21 is just a lump of metal that can't fly. There are also several systems subject to European export restrictions (including Meteor AAMs), which may seem more benign but could be an issue if KF-21 is competing head-to-head against a European fighter design.
 
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NMaude said:
I assume that the South Koreans are working on indigenous replacements for those US systems including the F414?
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The issue being that makeing ingenious jet engines is very hard, china has only recently managed it, japan is far farther along with more resources and its still very unlikely it will be read for there 6th gen fighter, just because south korea has a program dosnt mean the kf-21 is ever going to get those engines, if korea muddles through then those engines are more likely for there next gen aircraft.
 
Cjc said:
The issue being that makeing ingenious jet engines is very hard, china has only recently managed it, japan is far farther along with more resources and its still very unlikely it will be read for there 6th gen fighter, just because south korea has a program dosnt mean the kf-21 is ever going to get those engines, if korea muddles through then those engines are more likely for there next gen aircraft.
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Projected performance ceilings also play a role, China managed to produce lower power engines much earlier than their top of the line WS-15. The Koreans also have access to various US engines, I bet they are having a good look at them whenever possible and try to learn important lessons.
 
EmoBirb said:
I don't think Rafale and KF-21 directly compete, in a sense they complement each other and share missiles actually. The engine will be an issue though, KF-21 with an indigenous or European engine would be much more attractive on the export market imo.
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But they do - absolutely same niche, mostly similar capabilities. Rafale advantage is maturity, KF-21 - 25 years of progress.
Moreover, KF-21 will kill AMCA for good; it's more or less same aircraft, just a decade earlier.
 
CV12Hornet said:
Correct - in the case of the F414 they're working on an indigenous engine.
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I think it’s more accurate to say that Hanwha has done some conceptual design work on a « F414 like » engine. But it’s unclear if they have met the technological pre-requisites to actually build such an engine, as in fact they have been reaching out to more established engine makers like Safran in order to secure outside help.

If they do proceed with a domestic engine they have stated that it will take over 10 years and over $1B. Have those funds been committed by the South Korean gov?
 
CV12Hornet said:
As far as engines, India is allegedly starting to get the Kaveri working, and are planning to use a dry variant to power some new combat drones. But it's not in the same class as the F414.
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That's the so-called KDE, also called dry Kaveri. And their mil-thrust rating is still not quite at the ballpark they want ot to be, althought it is indeed the closest it has ever been. More importantly, they still haven't been able to sort the reheat thrust issues, which hass been one of the main issues they've had with the Kaveri programme.

They are still stuck with K9+.

snne said:
You essentially have to pay the same price as the F-35
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Not quite. Block 1 production contract is much cheaper than F-35 lot 15-17 flyaway.

Scott Kenny said:
I thought that Block II was getting an AAM bay?
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I don't know how many times this has been iterated on this thread, but block II differs purely by software and operational flight clearance with different ordnances when compared to block 1. Almost no hardware change. It will be ready within just 2 years, by 2028.
 
H_K said:
KF-21 is not independent. It is subject to ITAR and US export restrictions for several critical systems including engines (GE F414), and electric power generation and environmental control systems (Collins Aerospace).

Basically without US approval, KF-21 is just a lump of metal that can't fly. There are also several systems subject to European export restrictions (including Meteor AAMs), which may seem more benign but could be an issue if KF-21 is competing head-to-head against a European fighter design.
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Re-read the comment you are replying to. He is saying second half of 2030s. That is when the advanced variant of KF-21 is supposed to enter production and replace KF-16, alongside Korean SRAAM and BVRAAM. Research for domestic replacement of those possibly export-restricted systems and components are in the pipeline. The situation is much different compared to current baseline KF-21.

Besides, there has rarely been Korean arms export interest that goes against US foreign policy. One of those rare cases being the export of EW pod to Pakistan for example, which has been denied by the US quite obviously. This was in mid 2010s. Apart from that, there aren't any particular occasions that comes into my mind where a major Korean arms export campaign has been denied by the US.

H_K said:
I think it’s more accurate to say that Hanwha has done some conceptual design work on a « F414 like » engine. But it’s unclear if they have met the technological pre-requisites to actually build such an engine, as in fact they have been reaching out to more established engine makers like Safran in order to secure outside help.
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That's because you only consider Hanwha. Doosan is arguably much more experienced when it comes to designing proprietary gas turbines in Korea and they've entered aviation gas turbine business around 7 years ago. They are developing 10,000 lbf medium bypass turbofan right now for use in UAVs. As for the ongoing discussions with foreign manufacturers, they are looking for joint development and sales partners with international market in mind. They are not looking for a TAC. You seem to forget that it is undecided if this project will be joint development programme or not in the first place. They're just evaluating options and more importantly, the project lead is not decided either between Hanwha and Doosan.
 
At the 170th Defense Acquisition Program Promotion Committee meeting held at the Ministry of National Defense on Friday, August 8, 2025 (Korean time), the addition of air-to-ground capabilities to the KF-21 was brought forward. Originally planned to be implemented in late 2028, this capability will now be phased in, beginning in the first half of 2027.
 
Maro.Kyo said:
They're just evaluating options and more importantly, the project lead is not decided either between Hanwha and Doosan
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So we both agree that no work has started on a Korean engine for KF-21. Because there were several posters here saying that “they are working on” an indigenous F414 alternative.

Probably more accurate to say that right now this is just an aspirational idea that will take 10-15 years, *if* they get the greenlight and the budget and *if* all goes well.
 
briantk said:
CG concept from different angle.
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The weapons in the bays look like GBU-31 JDAMs with BLU-109 warheads i.e. 2000 lbs class.
Length also checks out, around 4 m, compared to the KF-21's 16.9 m.

I remember back in the day it was said the bays could carry 1000 lbs class weapons. The CGI sure looks very optimistic regarding the depth of the weapon bays and where the engine bays are located...
 
eagle said:
I remember back in the day it was said the bays could carry 1000 lbs class weapons. The CGI sure looks very optimistic regarding the depth of the weapon bays and where the engine bays are located...
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Assuming that the limit on the bay capacity is depth, the difference between a 1000lb and 2000lb weapon is about 4".
 
eagle said:
The CGI sure looks very optimistic regarding the depth of the weapon bays and where the engine bays are located...
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Agreed. Scaling off the images the front of the F414 engine is level with end of the weapon bays. Passing the air intake over the deep weapons bays will be difficult without the aircraft becoming fatter. That's a complete redesign.

Pushing for two 2000lb class weapons in my opinion will kill the performance of the design. It will become too fat, too much drag, empty weight will exceed 14 ton. Korea won't produce an indigenous engine that can reliably produce thrust over 100kn. Thrust to weight, fuel fraction will be noticably worse than today's F-35A.

If a 2000lb bomb is critical the obvious packaging solution is a single deeper 2000lb class station in the middle as it is a twin engine design. The bay can be shallower under the intakes for AMRAAM and Stormbreaker sized weapons.
 
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Scott Kenny said:
Assuming that the limit on the bay capacity is depth, the difference between a 1000lb and 2000lb weapon is about 4".
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That doesn't sound like much, but it quickly can become an issue as you move the rear of the weapon bay closer to the engine face.
And the difference in length between 1000 and 2000 lbs class weapons is substantial. About 3 vs. 3.85 meters.
 
insidersource said:
Pushing for two 2000lb class weapons in my opinion will kill the performance of the design. It will become too fat, too much drag, empty weight will exceed 14 ton. Korea won't produce an indigenous engine that can reliably produce thrust over 100kn. Thrust to weight, fuel fraction will be noticably worse than today's F-35A.
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I was thinking raising the top of the bay ~2" and dropping the belly 2" if necessary.

Yes, it's a modification to the OML.



insidersource said:
If a 2000lb bomb is critical the obvious packaging solution is a single deeper 2000lb class station in the middle as it is a twin engine design. The bay can be shallower under the intakes for AMRAAM and Stormbreaker sized weapons.
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Yes, that's a valid answer if a single 2000lb weapon is acceptable.



eagle said:
That doesn't sound like much, but it quickly can become an issue as you move the rear of the weapon bay closer to the engine face.
And the difference in length between 1000 and 2000 lbs class weapons is substantial. About 3 vs. 3.85 meters.
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Granted. I wasn't sure which dimension was the limiting factor. I know that the F-22's bay is too shallow for 2000lb weapons but IIRC is long enough.

I know I would have designed the KF-21 with a 14ft length volume, to allow for longer AAMs and/or tandem SDBs if nothing else.
 
H_K said:
So we both agree that no work has started on a Korean engine for KF-21. Because there were several posters here saying that “they are working on” an indigenous F414 alternative.

Probably more accurate to say that right now this is just an aspirational idea that will take 10-15 years, *if* they get the greenlight and the budget and *if* all goes well.
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It is already a DAPA sanctioned programme. Hanwha is working on preliminary designs in the hopes of winning the bid to become design lead. Moreover, I don't know why you seem to be so hell bent on a comment which noted that it "could" become something, not "will". No one disagrees with you that things are not a given.

eagle said:
The CGI sure looks very optimistic regarding the depth of the weapon bays and where the engine bays are located...
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It's a model based on the internal CAD data of KAI so I'm pretty sure that they know better than any of us here.

insidersource said:
Passing the air intake over the deep weapons bays will be difficult without the aircraft becoming fatter. That's a complete redesign.

Pushing for two 2000lb class weapons in my opinion will kill the performance of the design. It will become too fat, too much drag, empty weight will exceed 14 ton.
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Hence the reason they are trying to develop a turbofan engine that has same dimensions to the F414 with higher thrust. It's to offset additional drag created by airframe changes. There's no such engine in the market apart from upgrade proposals that never materialised.

insidersource said:
Korea won't produce an indigenous engine that can reliably produce thrust over 100kn. Thrust to weight, fuel fraction will be noticably worse than today's F-35A.
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Sorry but that's just bullshit.
 
Maro.Kyo said:
Hence the reason they are trying to develop a turbofan engine that has same dimensions to the F414 with higher thrust. It's to offset additional drag created by airframe changes.
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The F414 has one of the highest thrust to weight ratios in the world. The only engines that beat it have a fraction of the time between overhauls. India has spent a decade trying to make an engine in the F414 size range and they can't even reach the thrust levels of the F414.

Maro.Kyo said:
Sorry but that's just bullshit.
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Korea will be no better than the Chinese and the Russians when it comes to making their own engines. Neither can reach 100kn of thrust with their latest RD-33 and WS-13 that are the same size of the F414. India has spent decades and can't even reliably hit 80% of the thrust of the F414.

I take it you are Korean and you think you can skip multiple decades of research and development?
 
insidersource said:
The F414 has one of the highest thrust to weight ratios in the world. The only engines that beat it have a fraction of the time between overhauls. India has spent a decade trying to make an engine in the F414 size range and they can't even reach the thrust levels of the F414.
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My friendos please don't even compare India, who is buying K9s, to the frigging maker. As of now KC-X is in momentum and it would not suprise me that from the tidal waves comes a new host of aspiring SK turbojet engineers.

Mad projection.
 
EmoBirb said:
I think KF-21 with tech transfer and local assembly would offer a lot of know how that will bring their AMCA project along.

I agree on all you said on the KF-21 though, it's a good deal. I used to view it very critically when it was announced, thinking there wouldn't be much of a market. But by now I think the exact opposite, I think in Asia (SEA, South Asia and West Asia) there's plenty of export potential. And the Koreans are just generally very open for good deals, local assembly, transfer of IP etc.
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Korea should be reaching out to partner with Mexico. Mexico has a rapidly growing Aerospace industry and a cheaper Mk1 would likely be a good seller in the Americas, especially if they can go with a non-US engine.
 
Desertfox said:
Korea should be reaching out to partner with Mexico. Mexico has a rapidly growing Aerospace industry and a cheaper Mk1 would likely be a good seller in the Americas, especially if they can go with a non-US engine.
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Larin and South America aren't exactly big spenders for military hardware, the KF-21 is very much overkill for most nations. A far better option for Mexico and the region would be FA-50s.

A non US engine is a pipe dream for now. The Koreans aren't paying the integration cost except for their domestic option maybe 10 years from now and can't see a customer paying for the M88 or other option to get on to the KF-21.
 
insidersource said:
The F414 has one of the highest thrust to weight ratios in the world. The only engines that beat it have a fraction of the time between overhauls. India has spent a decade trying to make an engine in the F414 size range and they can't even reach the thrust levels of the F414.


Korea will be no better than the Chinese and the Russians when it comes to making their own engines. Neither can reach 100kn of thrust with their latest RD-33 and WS-13 that are the same size of the F414. India has spent decades and can't even reliably hit 80% of the thrust of the F414.

I take it you are Korean and you think you can skip multiple decades of research and development?
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WS-19 is meant to be in the 120kN class similar to the EJ-270/F-414 EPE proposals and still fit into the same footprint as WS-13/RD-33 series. It's definitely doable since WS-19 had its maiden flight in 2023.
 
Tomboy said:
WS-19 is meant to be in the 120kN class similar to the EJ-270/F-414 EPE proposals and still fit into the same footprint as WS-13/RD-33 series. It's definitely doable since WS-19 had its maiden flight in 2023.
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It will reach that thrust and then blow up 30 seconds later. It is well known that engines can trade significant durability for a small thrust increase.

The F135 for instance produced 51,000lb in testing more than a decade ago. Today it is still rated at 43,000lb maximum as it lasts an extremely long time at that thrust limit.

The AL-31 in the Suhkoi Su-30 was always thought to have compatible thrust-to-weight to their western counterparts. Then India operated the Su-30 and the engines were failing every second flight. Russia traded significant durability to match the US engine performance. If the US was happy to accept that level of poor durability I'm sure the F414, F110 and F135 engines could have their thrust ratings increased by 20+%.

Korea might be perfectly happy with a Korean built engine that can match the thrust-to-weight ratio of the F414 but only lasts a fraction of the time between overhauls. That will be hard to sell to an export customer as it puts up the maintenance cost. If the engine is derated to give lower maintenance cost then the performance will drop well below the F-35.
 
insidersource said:
It will reach that thrust and then blow up 30 seconds later. It is well known that engines can trade significant durability for a small thrust increase.
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WS-19 is meant to be highly reliable while outputting wet thrust in that class. F414 is a product of the 90s, you have far underestimated turbofan development in the 30 odd years since then.
 
DAPA stated that it is open to collaboration with foreign companies and that negotiations are progressing slowly. Recent news from RR expressing interest in participating in joint development through the RSP program echoes this sentiment. In any case, South Korea is seeking to develop the 16,000Ibf engine, but nothing has been finalized yet.

The 5,500bf UAV engine will be exhibited at ADEX 2025 on October 17th and will undergo flight test evaluation starting in November. The 10,000lbf engine, for which Doosan is participating, is currently undergoing turbine aerodynamic and cooling design technology evaluation and is scheduled for completion by 2030. In the long term, Korea will continue to pursue higher thrust and fuel efficiency through continuous research and development, including these two engines. However, I personally believe this is a challenging goal.

It aims for the same size as the 414 but with higher thrust and a specific fuel consumption of 0.8 lb/hr/lbf.
 
synetic said:
[...] In the long term, Korea will continue to pursue higher thrust and fuel efficiency through continuous research and development, including these two engines. However, I personally believe this is a challenging goal.

It aims for the same size as the 414 but with higher thrust and a specific fuel consumption of 0.8 lb/hr/lbf.
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I don't think it's that challenging. The F414 burns 0.84lb/hr/lbf, so you're only talking ~5% fuel burn improvement. There's been quite an improvement in turbine engines since the F414 was designed. For example, the CFM56-2 (737 classic) burns 0.386-0.396lb/hr/lbf while the -7B (737NG burns 0.356-0.386lb/hr/lbf at takeoff. That's a ~10% improvement at the low range.
 

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