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

Ainen said:
More Sheldon graphics, this time with some additional details
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They say increased internal fuel on the EX. I wonder how they'll achieve that while also fitting the internal weapons bay? Could conformal tanks be fitted to the sides (like the F-15), or the upper fuselage (like the F/A-18 & Rafale)? Enlarged spine (Mig-29SMT)? Fuselage stretch?
 
H_K said:
They say increased internal fuel on the EX. I wonder how they'll achieve that while also fitting the internal weapons bay? Could conformal tanks be fitted to the sides (like the F-15), or the upper fuselage (like the F/A-18 & Rafale)? Enlarged spine (Mig-29SMT)? Fuselage stretch?
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The official ROKAF project designation reads "Korean Low-Observable Fighter" programme, and it is focused on upgrading the pre-existing block 2 airframes, which ROKAF will be operating 120 of.

So a fundamental alteration of the airframe structure such as stretching the fuselage is not in the book. What is being explored is replacing the flat ventral surface, where the recessed MEL is located, with a bulging bay door, akin to that of F-35. Increase in drag caused by the new bay doors (frankly, I think the operational loadout of the EX-T will yield lower drag than block 2, but anyways) and gross weight will be offset by the new engine with higher thrust. As for how they'll achieve higher fuel load is unknown and I can't think of any proper solution right now.
 
I was talking about the indigenous turbofan development effort. The design of the new engine is such that structurally, it could adopted as a drop-in replacement of the F414 without any major revamp of the host airframe. Although the increase in thrust could require structural reinforcement, I don't know the stress margins of the KF-21 airframe structure and if the extra 4000 lb/f could become a problem.
 
@helmutkohl @Maro.Kyo
A stupid question perhaps, but was it ever specifically mentioned that EXT goes for 2000lb?
I saw many assumptions, but eye-gauging gives substantially longer and potentially wider bay than one which is fully occupied by GBU-31 (388 cm long).
It's almost as if it's GBU-72 sized to be honest.
 
H_K said:
Thanks. Interestingly the graphic doesn’t say anything about the engine. Did the conference provide an update about the domestic engine?

Also are there any Korean source materials about the KF-21’s development cost or how much has been spent until now?
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From what I know, the new F414 equivalent turbofan and Doosan/Hanwha Aerospace was not part of the discussion. Though, recently there has been a mandatory (since they are a publicly traded company, and the contract value exceeded their annual revenue-based threshold) single sales/supply agreements disclosure by Hanwha Aerospace concerning the engine development contract So things are proceeding behind the scenes.

As for the budget of KF-X programme, the full development cost comprises of preliminary research expenditure and systems development cost.

Preliminary development cost has been sanctioned between 2011 and 2012, and was ₩55 billion in total, split between Korea and Indonesia 4:1.

Systems development including EMD prototyping, block 1 IOC and block 2 was expected to approximately cost ₩8 trillion 842.1 billion based on KIDA's estimates. By 2025 this cost actually reduced to ₩8 trillion 814.2 billion. Considering the COVID hardships and rapid inflation post 2022, as well as severe depreciation of KRW in recent years, I think it's a pretty serious feat.

Sources are included as an attachment. One of them is a 2015 National Assembly Research Service report, and the other is a 170th Defense Acquisition Program Promotion Committee disclosure from 2025.

The NARS report also includes other interesting tid bits from the time, so it's quite worth a read.
 

Attachments

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snne said:
Looks like there are 12 KF-21s on the assembly line... :D
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View: https://www.youtube.com/watch?v=rmeXUIkwDWM


This video features the KF-21 test pilot himself explaining the behind-the-scenes story of the aircraft's development.

What I’ve recently learned are the subtle differences between the KF-21 prototype and the production models.

This is the tail boom of the first production model.

According to the test pilot's explanation, the production model features a thicker tailboom design to reduce airframe vibration.

In response to feedback that the aircraft was somewhat sensitive along the roll axis during flight, the control stick design was modified and the OFP was improved.

According to rumors circulating online, the first production model will be delivered to the Air Force on the 17th of next month.

The first Meteor launch from the KF-21 Block II prototype is scheduled for this month, August. The Block II prototype is equipped with not only the EO TGP but also a 480-gallon external fuel tank as standard. This test is intended to verify whether the Meteor can be launched safely with this configuration.
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(Via: urban mine/DefenceHub)
 
https://defencesecurityasia.com/en/philippines-40-kf-21-fighters-indo-pacific-airpower/

Philippines Eyes 40 KF-21 Fighters—A Major Indo-Pacific Airpower Shift​

The Philippines is reportedly leaning toward a single fleet of 40 KF-21 Boramae fighters, potentially strengthening Manila’s combat-aircraft mass and expanding South Korea’s strategic influence across the Indo-Pacific.​

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to be fair, this article also highlights limitations such as the financial aspects and immaturity of the KF-21
 
TomcatViP said:
So, what was the total design time (from early mandated study, paid by Korea, to this first delivery) ?
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depends what you want to count as the start..
Government interest in a new fighter jet = 1999
Start of KFX studies = 2001
Selection of design that would lead to the KF-21 = around 2014 (before that, they were looking at different forms, such as canard deltas, single engine, twin engined, etc)
 
It is a very nice looking bird and they developed it fairly quickly out of necessity and good for them. Based on the features, I think the US assisted based upon requested input but it's their design all the way.
 
Hydroman said:
It is a very nice looking bird and they developed it fairly quickly out of necessity and good for them. Based on the features, I think the US assisted based upon requested input but it's their design all the way.
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IIRC LockMart had an assist contract, but couldn't share anything specific. So if you look at the KF-21, it doesn't have any skin-integrated arrays, they're all either inset or scabbed on top. I believe those LockMart engineers said "It took us a really long time to figure out how to do that, we recommend continuing to develop the ability in-house but do not recommend planning on having them on the early KF-21s."
 
helmutkohl said:
depends what you want to count as the start..
Government interest in a new fighter jet = 1999
Start of KFX studies = 2001
Selection of design that would lead to the KF-21 = around 2014 (before that, they were looking at different forms, such as canard deltas, single engine, twin engined, etc)
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2016-18 might be the better starting point for the KF-21 design in its current form, as that's when their preliminary design started wind tunnel testing and evolved from C105 to C107 and the final C109.

Prior to that they were doing concept studies. From Wikipedia:
Following approximately two years of wind tunnel experiments and continued domestic technology development, the C109, jointly proposed by ADD and KAI, was selected in 2018 as the prototype design for the KF-X. The preliminary design was finalised in June 2018, and a critical design review in September 2019, examining 390 technical data sets, confirmed that the KF-X met ROKAF's requirements.
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I wonder if the USAF could end up buying some KF-21s once they're in production?
 

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