Design Challenge: Lightweight Multirole Fighter (LMF)

[4decaa]

This thread is quite interesting, and I just wanted to openly appreciate it
I would absolutely enjoy reading (and maybe participating in) any future "design challenges"... Amazing work!

 

[VTOLicious]

This thread is quite interesting, and I just wanted to openly appreciate it
I would absolutely enjoy reading (and maybe participating in) any future "design challenges"... Amazing work!

Thank you 4decaa, you are welcome to join Btw, the B-21 3D model you've created looks awesome!

 

[VTOLicious]

Maybe you are right, since that model was exhibited by the Chengdu firm itself and presented as a model, I only speculated a little about what its interior would be like. Greetings

Do you have any pictures of the model exhibited?

 

[Cjc]

So after reading the arguments about the dorsal intakes on the last few pages, it dose make me wonder, how much more ordinance would you be able to fit inside this plane if dorsal intakes could be made to work. A second boeing weponds bay behind the current one ? Or gust 2 more amrams were the intakes are now?

Also would you be able to keep the add on weponds bays on top of the aircraft with dorsal intakes, seems like that would cause engine ingestion issues.

 

[RJMAZ]

I just signed up to this forum due to the impressive work done by VTOLicious. I have been a proponent to a mini-F-35 for quite some years on another forum.

Where to fit short range air to air weapons?
Traditional we have medium range missiles, short range missiles and a cannon. With AMRAAM missiles being able to hit targets at 5 miles away I think a single weapon can replace the role of both the Sidewinder and cannon. A single IRIS-T or Sidewinder is a bad choice as it only gives one shot and then you have no cannon. My solution would be four 19kg mistral tube launched missiles. Two per side on the upper surfaces above the air intake. They are already designed for air to air launch and are the largest tube launched missiles. Mounted on the upper side of the aircraft is a big advantage when dog fighting as it allows the seeker a better view of the target. Alternatively 3 smaller Stinger missiles per side would also work. The cannon could now be removed due to having multiple short range missiles.

FAR-21 Vs F-35A
FAR-21 is approximate 60% of the weight, 55% of the thrust and 40% of the fuel capacity of the F-35A. The range will be much shorter than the F-35A which is to be expected. I could see this smaller aircraft being 75% of the cost of the F-35A but offer only 50% of the capability. Four FAR-21 are needed to perform the same mission of two F-35A. Any country that was allowed to purchase a USA built FAR-21 design would also be allowed to buy the F-35A as they both have all the same sensitive technology. A country would then be better off buying fewer F-35A for more capability for less money.

Production volume versus unit cost
As production volume increases the cost per unit reduces. This is the main advantage to the F-35 and allows the aircraft to be relatively cheap for the size and capability. I think an aircraft would have to be much smaller and simpler to reach half the price of the F-35. Lower price will exponentially increase sales of a loyal wingman version. I think the 2,000lb weapon requirement will make it difficult for the FAR-21 design from hitting the small size and low price point required. I also doubt that the market requires a 2,000lb class weapon.

Engine selection
The F414 is a very low bypass engine that has all the attributes to create a supercruising fighter. The problem is it has poor dry fuel consumption and will be a bad match for a low end fighter or drone derivatives that will spend a large portion of the time subsonic. This depends on the mission profile. If this aircraft was to be a short ranged interceptor then the engine is a good choice. The old RB199 which has a bypass ratio of 1:1 would be a better selection and give a 20% range increase with subsonic cruise. This small design would now have enough range to match the F-35A in the loyal wingman role.

French FAR-21
France historically has sold aircraft to countries that were not allowed to buy US made F-16's. I think a French built FAR-21 using an M88 would probably have the greatest chance of this design being a sales success on the foreign market. France would sell to customers that could not buy the F-35. The smaller FAR-21 could probably beat a Rafale in most missions simply due to the much lower radar cross section. As the M88 is a little smaller than the F414 France could make a slightly larger front fan version of the M88. This would improve the bypass ratio and fuel efficiency compared to the F414 at the same size and engine weight.

Is Supersonic performance needed to be a low end compliment to the F-35?
An aircraft with similar layout and size to the FAR-21 but limited to subsonic speeds would be lower cost and have a get significant range improvement. It would no longer be a lightweight fighter like a stealthy F-20 or Gripen. It would be more like a stealthy A-7 with BVR air to air capability. I think a low cost subsonic stealth fighter would be a slam dunk. For decades supersonic fighters have been flying 99% of missions entirely subsonic. Reduce the leading edge sweep angle by 10 degrees and increase the wing span by 1-2 metres improves the lift to drag and cruising fuel efficiency. Add one of the many higher bypass private jet engines. It would be like a slightly larger MQ-28. I would even add a two seat version and build it to have fewer sensitive technologies.

Packaging of FAR-21.
As an aerospace engineer that has worked on fast jets I think your packaging is a little tight. I would need to see some closeups to confirm. The bulkheads might require a bit of extra thickness say 6inchs of added clearance between the weapons bays, intake ducts, landing gear bays and around the engine. The MQ-28 landing gear retracts rearwards beside the engine which could be used in this design. The landing gear pivot point is already very close to the aft end of the main weapon bay. If the landing gear was moved rearwards by a foot and also retracts rearward then the weapon bay could be four AMRAAM wide and now much more shallow. The air intake ducts then do not have to travel up as high. The fuselage will now be a slab design underneath like the F-22. I understand that you want to keep the Boeing weapons pod layout. If the 2,000lb weapon is no longer required it will be slightly better to go four AMRAAM wide with a shorter and shallower bay.

 

[kqcke for you]

I just signed up to this forum due to the impressive work done by VTOLicious. I have been a proponent to a mini-F-35 for quite some years on another forum.

Where to fit short range air to air weapons?
Traditional we have medium range missiles, short range missiles and a cannon. With AMRAAM missiles being able to hit targets at 5 miles away I think a single weapon can replace the role of both the Sidewinder and cannon. A single IRIS-T or Sidewinder is a bad choice as it only gives one shot and then you have no cannon. My solution would be four 19kg mistral tube launched missiles. Two per side on the upper surfaces above the air intake. They are already designed for air to air launch and are the largest tube launched missiles. Mounted on the upper side of the aircraft is a big advantage when dog fighting as it allows the seeker a better view of the target. Alternatively 3 smaller Stinger missiles per side would also work. The cannon could now be removed due to having multiple short range missiles.

I could see some problems arising with the use of cold launched missiles in the aircraft.

Production volume versus unit cost
As production volume increases the cost per unit reduces. This is the main advantage to the F-35 and allows the aircraft to be relatively cheap for the size and capability. I think an aircraft would have to be much smaller and simpler to reach half the price of the F-35. Lower price will exponentially increase sales of a loyal wingman version. I think the 2,000lb weapon requirement will make it difficult for the FAR-21 design from hitting the small size and low price point required. I also doubt that the market requires a 2,000lb class weapon.

Hard to say as i would assume that 2000Ib bombs are probaly the most powerful weapons many smaller countries can actualy use.

Engine selection
The F414 is a very low bypass engine that has all the attributes to create a supercruising fighter. The problem is it has poor dry fuel consumption and will be a bad match for a low end fighter or drone derivatives that will spend a large portion of the time subsonic. This depends on the mission profile. If this aircraft was to be a short ranged interceptor then the engine is a good choice. The old RB199 which has a bypass ratio of 1:1 would be a better selection and give a 20% range increase with subsonic cruise. This small design would now have enough range to match the F-35A in the loyal wingman role.

But using RB199 in the existing configuration would mean reduced kinematics which still are important.

French FAR-21
France historically has sold aircraft to countries that were not allowed to buy US made F-16's. I think a French built FAR-21 using an M88 would probably have the greatest chance of this design being a sales success on the foreign market. France would sell to customers that could not buy the F-35. The smaller FAR-21 could probably beat a Rafale in most missions simply due to the much lower radar cross section. As the M88 is a little smaller than the F414 France could make a slightly larger front fan version of the M88. This would improve the bypass ratio and fuel efficiency compared to the F414 at the same size and engine weight.

Could also use an EJ200 and do the same / Just bringing them to the modern standard (in case of EJ200). The enhance performance even more would be to cut off the afterburner.

 

[FlyGuy369]

I've drafted wingtip-pods which can accommodate short range AAM's.
Those pods are in addition to the main bay ( 4x AIM-120) and are intended to be detachable/ interchangeable. The missile would be deployed with a "trapeze launcher", similar to the on used in the F-22's side bays.
Furthermore, those wingtip-pods could also be utilized to house EW- or ISR-equipment, or may be used as additional fuel tanks.

What do you guys think?

Depicted: AIM-132 ASRAAM
Length: 2,9 m
Diameter: 0,166 m
Wingspan: 0,45 m

View attachment 673229View attachment 673230View attachment 673231View attachment 673232

What did you use to model this?

 

[RJMAZ]

I could see some problems arising with the use of cold launched missiles in the aircraft.

Hard to say as i would assume that 2000Ib bombs are probaly the most powerful weapons many smaller countries can actualy use.

But using RB199 in the existing configuration would mean reduced kinematics which still are important.

Could also use an EJ200 and do the same / Just bringing them to the modern standard (in case of EJ200). The enhance performance even more would be to cut off the afterburner.

I would expect no issues with the tube launched missiles.

2,000lb bombs are rarely carried as weapons are getting increasingly accurate. Carrying a single 2,000lb bomb and then preventing no other internal weapons would be a deal breaker for most missions. A shallower bay like the F-22 to fit four AMRAAM would be far more flexible. It could theoretically allow one 1,000lb bomb, four 250lb glide bombs and a single AMRAAM at the same time.

The RB199 is just used as an example due to its unique attributes. Fuel burn during cruise is 20% better than the F414. The RB199 would give a decent range boost for every mission with very little negatives. I think the F414 is a poor choice for FAR-21. The only reason the thrust to weight ratio is so high is because GE sacrificed bypass ratio to fit as much power in the same dimensions as the F404. As a result fuel burn is not much better than a 1960's turbojet. I think the F414 was only selected due to thrust to weight ratio without thinking of the fuel burn.

Your suggestion of cutting off the afterburner does reduce the engine weight and length by 25-30% based on a few examples I've seen. I would actually take the General Electric F118 over the F414 for the mission profile that I expect from this aircraft. The engine is only 750lb heavier but it is 4 feet shorter and 1 foot wider. It would probably package better in such a small aircraft with a central weapon bay. The F118 has nearly 50% more dry thrust than F414 but it has no afterburner so slightly less maximum thrust. The 0.81:1 bypass ratio gives the F118 a nice 10ish % fuel burn improvement which easily makes up for the extra 750lb of engine weight. When it comes to low speed acceleration during dogfighting the 19,000lb of dry thrust from the F118 would actually beat the 22,000lb of afterburning thrust from the F414 due to higher mass air flow. Think of it like the initial takeoff acceleration of a turboprop versus a turbofan. The turboprop has a large mass airflow so the slow speed acceleration is very good.

The ideal engine for this FAR-21 design doesn't exist. A scaled down F101 engine would be perfect. Two Ivchenko-Progress AI-222-25 afterburning turbofans like on the Hongdu JL-10 would actually be the best off the shelf solution. If only they were western made. Two AI-222-25 engines are the exact weight of a single F414. They have 20% less thrust but 20% better fuel burn. Two engines for redundancy. Two engines results in the less length in the engine area and more width which actually suits the FAR-21 design perfectly

 

[kqcke for you]

I would expect no issues with the tube launched missiles.

Well there cold launched so there ejected out with a velocity of 40m/s before the actual engine starts and also drop there ejector.

2,000lb bombs are rarely carried as weapons are getting increasingly accurate. Carrying a single 2,000lb bomb and then preventing no other internal weapons would be a deal breaker for most missions. A shallower bay like the F-22 to fit four AMRAAM would be far more flexible. It could theoretically allow one 1,000lb bomb, four 250lb glide bombs and a single AMRAAM at the same time.

2000Ibs place means that a lot of small cruise missiles fit. One can still make it 3-4 AMRAAMs wide but the option is still important for the design goal of the aircraft.

The RB199 is just used as an example due to its unique attributes. Fuel burn during cruise is 20% better than the F414. The RB199 would give a decent range boost for every mission with very little negatives. I think the F414 is a poor choice for FAR-21. The only reason the thrust to weight ratio is so high is because GE sacrificed bypass ratio to fit as much power in the same dimensions as the F404. As a result fuel burn is not much better than a 1960's turbojet. I think the F414 was only selected due to thrust to weight ratio without thinking of the fuel burn.

The reason for the F414 is because its based on the Saab gripen (and F-18 EWP Pod). Tought like he said before a good alternative like EJ-200 could also have been used.

Your suggestion of cutting off the afterburner does reduce the engine weight and length by 25-30% based on a few examples I've seen. I would actually take the General Electric F118 over the F414 for the mission profile that I expect from this aircraft. The engine is only 750lb heavier but it is 4 feet shorter and 1 foot wider. It would probably package better in such a small aircraft with a central weapon bay. The F118 has nearly 50% more dry thrust than F414 but it has no afterburner so slightly less maximum thrust. The 0.81:1 bypass ratio gives the F118 a nice 10ish % fuel burn improvement which easily makes up for the extra 750lb of engine weight. When it comes to low speed acceleration during dogfighting the 19,000lb of dry thrust from the F118 would actually beat the 22,000lb of afterburning thrust from the F414 due to higher mass air flow. Think of it like the initial takeoff acceleration of a turboprop versus a turbofan. The turboprop has a large mass airflow so the slow speed acceleration is very good.

The ideal engine for this FAR-21 design doesn't exist. A scaled down F101 engine would be perfect. Two Ivchenko-Progress AI-222-25 afterburning turbofans like on the Hongdu JL-10 would actually be the best off the shelf solution. If only they were western made. Two AI-222-25 engines are the exact weight of a single F414. They have 20% less thrust but 20% better fuel burn. Two engines for redundancy. Two engines results in the less length in the engine area and more width which actually suits the FAR-21 design perfectly

Alternatives for the AI-222 could also be the AI-322, HTFE-25, TEI-TF6000 or maybe even an modernised no afterburner RB199.

Edit: but all dual engine layout would increase SPFC other the single F414 for no trust increase, a little lower weight and a lot of extra complexcity.

 

[VTOLicious]

First and foremost I choose the F414 to make this concept design directly comparable to JAS 39 E/F. And secondly to KF-21, as it may feature the same level of LO-technology.
Anyways, it's a well performing and reliable engine. Further improvements, like increased thrust, decreased fuel consumption can be reasonably assumed (e.g. EDE/EPE).

 

[kqcke for you]

First and foremost I choose the F414 to make this concept design directly comparable to JAS 39 E/F. And secondly to KF-21, as it may feature the same level of LO-technology.
Anyways, it's a well performing and reliable engine. Further improvements, like increased thrust, decreased fuel consumption can be reasonably assumed (e.g. EDE/EPE).

They have given some Numbers for EDE and EPE but i don't think that an combined number was released (or proposed). Tought based on the given scource the SPFC should decrease by 3-6%. Thrust would be 69kN dry and 117kN wet which is very good tought i still think afterburnerless may be a good idea.

Edit: Same goes for EJ-200 or RB199.

 

[VTOLicious]

... Thrust would be 69kN dry and 117kN wet which is very good tought i still think afterburnerless may be a good idea.

Edit: Same goes for EJ-200 or RB199.

For aircraft intended mainly for attack / strike strike missions maybe, but I find it hard to imagine that a lack of instantaneous thrust-increase of typically 70% is acceptable for a full-fledged fighter design.

 

[kqcke for you]

For aircraft intended mainly for attack / strike strike missions maybe, but I find it hard to imagine that a lack of instantaneous thrust-increase of typically 70% is acceptable for a full-fledged fighter design.

Yeah for the LMF goal it would need a lot of trust to be able to ignore the lost of the afterburner (my guess ~95kN's dry).

Edit: yes only half of the benefits from the afterburner but we still have some other edges.

 

[RJMAZ]

The market analysis is just as important as the actual design in my opinion. Which is why I discussed which country would make this FAR-21 design and highlighted France as having the most success with this design using the M88.

The projected weight, fuel capacity and engine performance points towards a stealthy short ranged aircraft with a decent thrust to weight ratio. A 5% fuel burn improvement on such a fuel guzzling engine will make little difference. This would make a great homeland defense interceptor like a stealthy F104.

The range would be too low to perform interdiction which is the primary reason to need a 2,000lb bomb. An unmanned version would not have sufficient range to penetrate beyond the manned fighters and drop that 2,000lb bomb. If you fit external fuel tanks it becomes difficult to penetrate with the inferior radar cross section.

The F-35 can carry two 2,000lb bombs and two AMRAAM internally. You would need three FAR-21 aircraft to carry this weapon load internally. The F-35 would easily have 50% greater range and endurance. To cover the same area you might need 4 FAR-21 aircraft to match a single F-35. For an unmanned strike aircraft a smaller subsonic MQ-28 would have greater range than FAR-21 due to the appropriate engine selection.

The FAR-21 is like the F-20 and the F-35 is like the F-16. No one wanted the short ranged F-20 if they could purchase the larger F-16. There was only a couple countries that weren't allowed to buy the F-16 yet considered trustworthy enough to buy the F-20. The same problem would apply to this FAR-21 aircraft. Any country not allowed to buy the F-35 would most likely not be allowed to buy the FAR-21. This is why the FAR-21 design would not be successful if US built.

The US would want this design to compliment the F-35 and future 6th gen manned aircraft. A penetrating strike drone to drop that single 2,000lb bomb would want a combat radius longer than the F-35. A loyal wingman drone to sit in front of the manned F-35 would need similar range to the F-35. The low fuel capacity and fuel guzzling F414 engine will not give the required range.

The FAR-21 design would need a massive internal fuel increase if you insist on keeping the F414. Think of your current design like the F-35A, it needs to turn into the F-35C. Bigger wing with more internal fuel. There will be an empty weight increase and the thrust to weight and speed will become worse.

There is no modern equivalent to the RB199 with its bypass ratio above 1:1 and excellent fuel burn. While the most powerful RB199 has less thrust than the F414 on paper you must think that the design would need less internal fuel to reach the same design range. The empty weight could then be lighter with the RB199 engine. For example to hit a 700nm combat radius the F414 powered version might have a 9,000kg empty weight and 5,000kg of internal fuel. The RB199 version might have a 8,500kg empty weight and 4,000kg of internal fuel. The F414 engine has 25% more thrust but it needs an aircraft fully fueled that weighs 14% more. The thrust to weight ratio of the F414 aircraft isn't much higher than an old RB199 if you design for a set range.

A custom engine will be difficult but is what this aircraft ideally would need. Sweden fitted an afterburner onto a civilian turbofan to create an afterburning engine that at the time had the highest bypass ratio. The Volvo RM8B. Unfortunately the modern private jet engines have seen their bypass ratios massively increase making it impossible to fit an afterburner for this unique application. We have seen a massive gap created where we have high bypass ratio civil engines to provide long range and very low bypass afterburning turbofans for high speed manned fighters. There is nothing in between for a small fighter aircraft to get decent range while maintaining supersonic ability. Turkey has the TEI-TF10000 which will be a 10,000lb afterburning turbofan with a bypass ratio of 1:1. Two of these would suit this sized design. Turkey would be one of the countries that has the ability to sell a small stealthy manned fighter to countries that cannot buy the F-35. The Bayraktar Kızılelma drone will be able to fit two of these new 10,000lb engines. Simply put a manned cockpit in the nose and you have something very unique on the export market.

Eliminating the supersonic requirement will give a huge range boost at the same aircraft size. Instantly it compliments the manned F-35 and becomes an aircraft that the US would buy. Higher bypass ratio private jet engines then become an available in every thrust increment. If dogfighting is a potential requirement then it easy to oversize the engine to still achieve a good thrust to weight ratio without needing an afterburner. This is why I mentioned the F118 engine versus the F414 as an example.

 

[Scott Kenny]

What I just read is that we use the old RB199s and call it done. Plus this makes the plane ITAR-free...

 

[RJMAZ]

ITAR free is a bonus. Hundreds of RB199 engines are in service and being maintained. I'm not sure if brand new engines are in production.

It is also worth noting the RB199 weight includes thrust reversers. We can probably remove 200lb if this is removed. It is a slightly smaller engine than the F414 and is closer to the M88 in size.

RB199 versus the F414.
84% of the weight.
78% of the afterburning thrust.
75% of the dry thrust.
20% better fuel burn during subsonic cruise.

Optimising the FAR-21 design around the smaller and shorter RB199 would allow tighter packaging of the airframe. This could give either save a few hundred kilos of empty weight or allow a bit of extra volume for increased fuel capacity.

It is worth noting the F414 actually has slightly worse fuel efficiency than the F404. The bypass ratio was reduced to get more power in the same package. Just because the Gripen E and Super Hornet uses the engine does not mean it is the perfect engine for their mission profiles. The F414 was selected because it fit the engine bay from the older Hornet/Gripen and had extra thrust for the additional weight of the Gripen E and Super Hornet. The Super Hornet is a relatively slow fighter yet it has a very low bypass engine that does not suit it at all.

The KF-21 is the perfect match to the F414 by comparison. The KF-21 is big enough to have good range with a very low bypass ratio engine. The two F414 engines combined has a dry thrust of 26,000lb of thrust which is the same as the empty weight of the aircraft. This high thrust to weight ratio, plus the higher exhaust velocity of a very low bypass engine plus the sleekness of the design allows good supercruise. All three boxes must be ticked to supercruise. The FAR-21 would struggle to supercruise as its thrust to weight would be lower with one F414. Supercruising between mach 1.1 and 1.25 has lots of transonic drag so it is best to avoid sitting at this speed for extended periods. I doubt the FAR-21 with the F414 could supercruise above mach 1.3 so it is best to give up and just settle for mach 0.85 cruise with a very efficient RB199.

There is a clear lack of suitable engines. The Tornado was the last supersonic dedicated ground attack aircraft which is why it used a higher bypass ratio. Since then we have had air to air fighters take over the strike role with their lower bypass ratio engines. So all the latest engines have a low bypass ratio.

Turkey with their jet powered drones are developing engines with higher bypass ratio and afterburner. The TEI-TF10000 won't need any fancy technology inside the core or turbines to comfortably have better fuel burn the F414. The bypass ratio is the biggest contributor to fuel burn. A pair of TE-TF10000 would actually be my choice for FAR-21. I'm sure two of these engines will be cheaper than one F414. No ITAR restrictions. The two smaller engines actually integrate better with that centeal Boeing weapon pod. The air intake for the F414 engine no longer have to go up above the pod. With two engines the intakes would go around the sides of the pod. The two smaller engines are nearly a metre shorter which definitely helps with that long weapon pod. The fuselage would then be a bit wider and flatter which is great for body lift. It would be great if VTOLicious could produce a version of his model with two TE-TF10000 engines.

https://www.tei.com.tr/en/products/tei-tf10000-turbofan-engine

 

[kqcke for you]

The market analysis is just as important as the actual design in my opinion. Which is why I discussed which country would make this FAR-21 design and highlighted France as having the most success with this design using the M88.

The projected weight, fuel capacity and engine performance points towards a stealthy short ranged aircraft with a decent thrust to weight ratio. A 5% fuel burn improvement on such a fuel guzzling engine will make little difference. This would make a great homeland defense interceptor like a stealthy F104.

~5% less while making 20% more thrust.

The range would be too low to perform interdiction which is the primary reason to need a 2,000lb bomb. An unmanned version would not have sufficient range to penetrate beyond the manned fighters and drop that 2,000lb bomb. If you fit external fuel tanks it becomes difficult to penetrate with the inferior radar cross section.

The F-35 can carry two 2,000lb bombs and two AMRAAM internally. You would need three FAR-21 aircraft to carry this weapon load internally. The F-35 would easily have 50% greater range and endurance. To cover the same area you might need 4 FAR-21 aircraft to match a single F-35. For an unmanned strike aircraft a smaller subsonic MQ-28 would have greater range than FAR-21 due to the appropriate engine selection.

The FAR-21 is like the F-20 and the F-35 is like the F-16. No one wanted the short ranged F-20 if they could purchase the larger F-16. There was only a couple countries that weren't allowed to buy the F-16 yet considered trustworthy enough to buy the F-20. The same problem would apply to this FAR-21 aircraft. Any country not allowed to buy the F-35 would most likely not be allowed to buy the FAR-21. This is why the FAR-21 design would not be successful if US built.

The US would want this design to compliment the F-35 and future 6th gen manned aircraft. A penetrating strike drone to drop that single 2,000lb bomb would want a combat radius longer than the F-35. A loyal wingman drone to sit in front of the manned F-35 would need similar range to the F-35. The low fuel capacity and fuel guzzling F414 engine will not give the required range.

The FAR-21 design would need a massive internal fuel increase if you insist on keeping the F414. Think of your current design like the F-35A, it needs to turn into the F-35C. Bigger wing with more internal fuel. There will be an empty weight increase and the thrust to weight and speed will become worse.

There is no modern equivalent to the RB199 with its bypass ratio above 1:1 and excellent fuel burn. While the most powerful RB199 has less thrust than the F414 on paper you must think that the design would need less internal fuel to reach the same design range. The empty weight could then be lighter with the RB199 engine. For example to hit a 700nm combat radius the F414 powered version might have a 9,000kg empty weight and 5,000kg of internal fuel. The RB199 version might have a 8,500kg empty weight and 4,000kg of internal fuel. The F414 engine has 25% more thrust but it needs an aircraft fully fueled that weighs 14% more. The thrust to weight ratio of the F414 aircraft isn't much higher than an old RB199 if you design for a set range.

F414 EPE/EDE has 69kN of thrust so around ~62% more dry and and ~57% more wet. So while rb199 is more efficient we do put out alot more than it. So the RB199 only has ~13% better SPFC but produces ~62% less dry thrust.

A custom engine will be difficult but is what this aircraft ideally would need. Sweden fitted an afterburner onto a civilian turbofan to create an afterburning engine that at the time had the highest bypass ratio. The Volvo RM8B. Unfortunately the modern private jet engines have seen their bypass ratios massively increase making it impossible to fit an afterburner for this unique application. We have seen a massive gap created where we have high bypass ratio civil engines to provide long range and very low bypass afterburning turbofans for high speed manned fighters. There is nothing in between for a small fighter aircraft to get decent range while maintaining supersonic ability. Turkey has the TEI-TF10000 which will be a 10,000lb afterburning turbofan with a bypass ratio of 1:1. Two of these would suit this sized design.

You know that the TF10000 replace the F110s in Kaan ? You wont even get close 2 using two of them in LMF.

Eliminating the supersonic requirement will give a huge range boost at the same aircraft size. Instantly it compliments the manned F-35 and becomes an aircraft that the US would buy. Higher bypass ratio private jet engines then become an available in every thrust increment. If dogfighting is a potential requirement then it easy to oversize the engine to still achieve a good thrust to weight ratio without needing an afterburner. This is why I mentioned the F118 engine versus the F414 as an example.

Tought the focus isn't being a compliment to the F-35.

 

[kqcke for you]

ITAR free is a bonus. Hundreds of RB199 engines are in service and being maintained. I'm not sure if brand new engines are in production.

It is also worth noting the RB199 weight includes thrust reversers. We can probably remove 200lb if this is removed. It is a slightly smaller engine than the F414 and is closer to the M88 in size.

RB199 versus the F414.
84% of the weight.
78% of the afterburning thrust.
75% of the dry thrust.
20% better fuel burn during subsonic cruise.

But you're forgetting thats F414 EPE/EDE
So its:
~84% of weight
~63% of the wet thrust
~61% of the dry thrust
~13% better SPFC

Optimising the FAR-21 design around the smaller and shorter RB199 would allow tighter packaging of the airframe. This could give either save a few hundred kilos of empty weight or allow a bit of extra volume for increased fuel capacity.

Only an modern version with modern tech of an rb199 could be an alternative in my eyes.

It is worth noting the F414 actually has slightly worse fuel efficiency than the F404. The bypass ratio was reduced to get more power in the same package. Just because the Gripen E and Super Hornet uses the engine does not mean it is the perfect engine for their mission profiles. The F414 was selected because it fit the engine bay from the older Hornet/Gripen and had extra thrust for the additional weight of the Gripen E and Super Hornet. The Super Hornet is a relatively slow fighter yet it has a very low bypass engine that does not suit it at all.

The difference between F414 and F404 is close to nonexisting.

The KF-21 is the perfect match to the F414 by comparison. The KF-21 is big enough to have good range with a very low bypass ratio engine. The two F414 engines combined has a dry thrust of 26,000lb of thrust which is the same as the empty weight of the aircraft. This high thrust to weight ratio, plus the higher exhaust velocity of a very low bypass engine plus the sleekness of the design allows good supercruise. All three boxes must be ticked to supercruise. The FAR-21 would struggle to supercruise as its thrust to weight would be lower with one F414. Supercruising between mach 1.1 and 1.25 has lots of transonic drag so it is best to avoid sitting at this speed for extended periods. I doubt the FAR-21 with the F414 could supercruise above mach 1.3 so it is best to give up and just settle for mach 0.85 cruise with a very efficient RB199.

FAR-21 will probaly BE able to go mach 1.3 with AtA loadout. Weight is similiar tought no external drag trought missiles and increased thrust.

There is a clear lack of suitable engines. The Tornado was the last supersonic dedicated ground attack aircraft which is why it used a higher bypass ratio. Since then we have had air to air fighters take over the strike role with their lower bypass ratio engines. So all the latest engines have a low bypass ratio.

And were still getting close to having the needed performance. Right now its an 80/20 solution. You get around 80% of the capabilitys with 20% of the cost.

Turkey with their jet powered drones are developing engines with higher bypass ratio and afterburner. The TEI-TF10000 won't need any fancy technology inside the core or turbines to comfortably have better fuel burn the F414. The bypass ratio is the biggest contributor to fuel burn. A pair of TE-TF10000 would actually be my choice for FAR-21. I'm sure two of these engines will be cheaper than one F414. No ITAR restrictions. The two smaller engines actually integrate better with that centeal Boeing weapon pod. The air intake for the F414 engine no longer have to go up above the pod. With two engines the intakes would go around the sides of the pod. The two smaller engines are nearly a metre shorter which definitely helps with that long weapon pod. The fuselage would then be a bit wider and flatter which is great for body lift. It would be great if VTOLicious could produce a version of his model with two TE-TF10000 engines.

https://www.tei.com.tr/en/products/tei-tf10000-turbofan-engine

TF10000 is mutch bigger diameter than F414 and less trust. Having to engines will also Not only not increase SPFC but we also have a mutch heavier and bigger jet.

 

[Foo Fighter]

I thought this was supposed to be a lightweight fighter? Why comparisons with primarily an interdiction aircraft?

Suggesting lightweight and fighter suggests no interdiction or strike role which simplifies things somewhat.

The multirole aspect suggests lightweight has a limit it would be difficult to go beyond, like the F-35 size/class.

 

[H_K]

Production volume versus unit cost
I think an aircraft would have to be much smaller and simpler to reach half the price of the F-35. Lower price will exponentially increase sales of a loyal wingman version. I think the 2,000lb weapon requirement will make it difficult for the FAR-21 design from hitting the small size and low price point required. I also doubt that the market requires a 2,000lb class weapon.

French FAR-21
I think a French built FAR-21 using an M88 would probably have the greatest chance of this design being a sales success on the foreign market.

Is Supersonic performance needed to be a low end compliment to the F-35?
An aircraft with similar layout and size to the FAR-21 but limited to subsonic speeds would be lower cost and have a get significant range improvement. It would no longer be a lightweight fighter like a stealthy F-20 or Gripen. It would be more like a stealthy A-7 with BVR air to air capability. I think a low cost subsonic stealth fighter would be a slam dunk.

Packaging of FAR-21.
the weapon bay could be four AMRAAM wide and now much more shallow. The air intake ducts then do not have to travel up as high. The fuselage will now be a slab design underneath like the F-22. I understand that you want to keep the Boeing weapons pod layout. If the 2,000lb weapon is no longer required it will be slightly better to go four AMRAAM wide with a shorter and shallower bay.

@RJMAZ I actually had started sketching out a smaller fighter/trainer & loyal wingman with some (but not all) of the same ideas in mind. See this thread: https://www.secretprojects.co.uk/th...advanced-trainer-light-combat-aircraft.44269/

Step 1 was to design a smaller, wide & shallow weapons bay (~1,250L volume) to facilitate aircraft integration, air intake routing etc. This can still fit 2-3 AAMs or 500lb A/G weapons, or up to 6 small 250lb weapons. This fits with the expected mission set flying alongside manned aircraft (loyal wingman fighter, air interdiction, SEAD/DEAD), rather than acting as a "penetration bomber" carrying 1,000lb or 2,000lb weapons.



Step 2 was to aim for a transonic low-drag, non-afterburning design with a short M88 engine to make packaging easier. Also with provisions for a two-seater advanced trainer (without internal weapons bay, as this volume is needed for fuel & avionics) to increase production volume and lower costs.


Step 3 was to go with a triple delta wing with levcons as this helps with packaging fuel & landing gear inside the wing without a "fat" fuselage, and helps with transonic performance. My hope would be some supercruise capability (Mach 1.2, 1.3?) might even be possible.

I wasn't able to finish but the ultimate goal would be to aim for something much smaller than current fighters, and even smaller than some advanced trainers such as the M346.


Although this may feel impossibly small, it would actually be a return to some of the small 1950s fighters such as the Mirage I, Etendard VI etc, but with optimized internal packaging (lifting body and triple delta wing for more volume, no gun, smaller engine etc).

 

[RJMAZ]

You know that the TF10000 replace the F110s in Kaan ? You wont even get close 2 using two of them in LMF.

Tought the focus isn't being a compliment to the F-35.

The TF10000 is not going into KAAN. Turkey is developing an engine double the size named TF35000.

The TF6000 and TF10000 are designed as a direct replacement for the AI-222-25 engine in both non afterburning and afterburning variants.

The focus should be on designing an aircraft that isnt just cool but something that would sell in large numbers if it existed. This is why I have focused on who would be building this aircraft and the potential customers and competitors.

TF10000 is mutch bigger diameter than F414 and less trust. Having to engines will also Not only not increase SPFC but we also have a mutch heavier and bigger jet.

The TF10000 is much smaller and lighter than the F414 with a smaller fan diameter. Turkey has included all of accesories on the engines with their dimensions.

The TF10000 is an afterburning version of the existing TF6000 and that weighs only 400kilograms. If we look at the F110 and F118 we can see that adding an afterburner increases the weight and length by around 30%. Two TF10000 engines would weigh around 2,500lb.

The two TF10000 engines would definitely take up more total volume inside the airframe due to the much higher bypass ratio. This will always be the case if you want better subsonic fuel burn. Total packaging wouldn't be any worse as the engines are shorter and the air intakes of the two engines are now in a much better position relative to the central weapons bay. With the current FAR-21 design the engine needs to be mounted a metre aft of the weapons bay to allow the intake duct to come down. The twin engine layout wouldn't need this extra spacing. The TF10000 engine itself is also a metre shorter than the F414. The FAR-21 design with the pair of TF10000 could be easily be 1.5 metres shorter in length. There could then be a large central fuel tank above the weapons bay where the current intake duct is. The extra fuselage width has many benefits for body lift.

 

[RJMAZ]

I thought this was supposed to be a lightweight fighter? Why comparisons with primarily an interdiction aircraft?

Suggesting lightweight and fighter suggests no interdiction or strike role which simplifies things somewhat.

The multirole aspect suggests lightweight has a limit it would be difficult to go beyond, like the F-35 size/class.

The title says "Multirole Fighter" and it has been designed around being able to carry a 2,000lb bomb. This sounds like interdiction and very similar to the F-35 design requirement.

I am pointing out the conflicting design attributes. Low fuel fraction, small wing, an inefficient engine all point to a short range interceptor. No need to add a 2,000lb bomb requirement as it doesn't have the range to perform interdiction. This is why I would either remove the 2,000lb bomb ability and optimise it as a fighter or keep the 2,000lb bomb capacity and optimise it for longer range.

 

[kqcke for you]

The TF10000 is not going into KAAN. Turkey is developing an engine double the size named TF35000.

Ah yeah you're right just looked it Up that was my mistake.

The focus should be on designing an aircraft that isnt just cool but something that would sell in large numbers if it existed. This is why I have focused on who would be building this aircraft and the potential customers and competitors.

The whole goal of the thread was based on this: XY: "A stealth fighter in the size of a Saab Gripen is impossible without compromising its performance to a point where it becomes useless".
Me: "Hold my beer..."

Its about an theoretical stealth design that is around the same size as an gripen. Now that was designed in a way for the most customers tought there allways trade offs.

The TF10000 is much smaller and lighter than the F414 with a smaller fan diameter. Turkey has included all of accesories on the engines with their dimensions.

Same for the F414.

The TF10000 is an afterburning version of the existing TF6000 and that weighs only 400kilograms.

Well it is larger in diameter and total height while having a slightly smaller By-pass Ratio so it has a little more changes.

If we look at the F110 and F118 we can see that adding an afterburner increases the weight and length by around 30%. Two TF10000 engines would weigh around 2,500lb.

The two TF10000 engines would definitely take up more total volume inside the airframe due to the much higher bypass ratio. This will always be the case if you want better subsonic fuel burn.

Would it even be better? I mean even if both engines burn only 0.6 lb/(lbf⋅h) the combined consumption would be greater than the one of the F-414 EPE/EDE while also not having more thrust or lower weight.

Edit: to be fair under optimal condition (we take the best numbers now) the F-414 EPE/EDE has an SPFC of ~0,7614 lb/HR/lb of thrust so to beat that with 2 engines each needs to be around ~ 0,3807 lb/HR/lb.

Total packaging wouldn't be any worse as the engines are shorter and the air intakes of the two engines are now in a much better position relative to the central weapons bay.

Yeah that would be better/ make it simpler tought i would still stand with the F414

With the current FAR-21 design the engine needs to be mounted a metre aft of the weapons bay to allow the intake duct to come down. The twin engine layout wouldn't need this extra spacing. The TF10000 engine itself is also a metre shorter than the F414.

No only 0.76m.

The FAR-21 design with the pair of TF10000 could be easily be 1.5 metres shorter in length. There could then be a large central fuel tank above the weapons bay where the current intake duct is. The extra fuselage width has many benefits for body lift.

Yeah as allways ITS a trade of game but i think that the current configuration is quite good. But your earlier points to the landing gear are some things i think one could consider. Either for a larger main bay or for a smaller one if the volume is there