Design Challenge: Lightweight Multirole Fighter (LMF)

[VTOLicious]

She's alone and that's why she's sad. Besides, she can hardly see the target

Lock-on after launch (LOAL)

 

[Foo Fighter]

Not being an expert, I can only say it looks great and you have obviously put a lot into it. It shows.

 

[Goha]

Either... or...

...Being whimsical, could you fit something within the "area rule bump"?

Haha, I'm already exploring the option to fit a single IRIS-T in the bump above the engine. The last resort so to say, just for self defence.

It basically fits, I just need to expand the bump a little bit more. However, the biggest concern is access to the bay for loading it.
I thought to make use of a "trapeze launcher" that pivots towards the rear, so that the missile can be slid onto the launch rail from the rear end. But I need to figure that out in detail.

I'll post some pics soon

Edit: F-22's "trapeze launcher" added:
View attachment 673517

I finally found some time to explore the option of fitting a single IRIS-T into the "area rule bump". I´m quite happy with the result...

The main thing: You cut the power structure in half with a compartment with a rocket.

 

[VTOLicious]

Power structure? I guess you are concerned about the structural integrity of the airframe. Obviously it would be better to avoid every "cutout". But in reality aircraft need cabin doors, landing gear compartments, etc. Internal weapon bays are no different in this regard.

 

[djfawcett]

Either... or...

...Being whimsical, could you fit something within the "area rule bump"?

Haha, I'm already exploring the option to fit a single IRIS-T in the bump above the engine. The last resort so to say, just for self defence.

It basically fits, I just need to expand the bump a little bit more. However, the biggest concern is access to the bay for loading it.
I thought to make use of a "trapeze launcher" that pivots towards the rear, so that the missile can be slid onto the launch rail from the rear end. But I need to figure that out in detail.

I'll post some pics soon

Edit: F-22's "trapeze launcher" added:
View attachment 673517

I finally found some time to explore the option of fitting a single IRIS-T into the "area rule bump". I´m quite happy with the result...

I really like the creativity, but I suspect the IRIS-T is an accident waiting to happen. Sooner or later, the missile is going to attempt a "hard landing" in the back of the pilots helmet much like the D-21 attempted to drive thru Bill Park & company's head. Fortunately Bill survived the breaking of the SR's back. Unfortunately, the same can not be said for his back seater. Moreover, I bet the bird will want to pitch up in a big way when the missile and launch system are deployed in the free stream. Just an opinion, but founded in a bit of history.

 

[helmutkohl]

on the subject of missiles, any reason why the IRIS-T is chosen over say, the ASRAAM?
I would imagine the ASRAAM would fit into a narrow bay better due to its lack of control surfaces

 

[VTOLicious]

on the subject of missiles, any reason why the IRIS-T is chosen over say, the ASRAAM?
I would imagine the ASRAAM would fit into a narrow bay better due to its lack of control surfaces

IRIS-T is the most capable SRAAM as far as I know.
It features thrust vectoring and can engage targets behind the launching aircraft, offering a 360° close-in defence capability. Also, it has the unique ability to target and shoot down other air-to-air and surface-to-air missiles.

 

[VTOLicious]

Either... or...

...Being whimsical, could you fit something within the "area rule bump"?

Haha, I'm already exploring the option to fit a single IRIS-T in the bump above the engine. The last resort so to say, just for self defence.

It basically fits, I just need to expand the bump a little bit more. However, the biggest concern is access to the bay for loading it.
I thought to make use of a "trapeze launcher" that pivots towards the rear, so that the missile can be slid onto the launch rail from the rear end. But I need to figure that out in detail.

I'll post some pics soon

Edit: F-22's "trapeze launcher" added:
View attachment 673517

I finally found some time to explore the option of fitting a single IRIS-T into the "area rule bump". I´m quite happy with the result...

I really like the creativity, but I suspect the IRIS-T is an accident waiting to happen. Sooner or later, the missile is going to attempt a "hard landing" in the back of the pilots helmet much like the D-21 attempted to drive thru Bill Park & company's head. Fortunately Bill survived the breaking of the SR's back. Unfortunately, the same can not be said for his back seater. Moreover, I bet the bird will want to pitch up in a big way when the missile and launch system are deployed in the free stream. Just an opinion, but founded in a bit of history.

That's a legitimate concern and a thorough analysis would be necessary to determine the potential risk.
Anyways, I think avionics systems of modern combat aircraft would only permit missle launch in a predefined / safe envelope (dependent on actual aircraft speed, altitude, AoA, AoS, etc.). Therefore, I think this risk is manageable.

 

[Scott Kenny]

To minimize the mass of the fighter, I propose to make two weapons bay for medium-range missiles / bombs, and hang short-range missiles conformally.
2 * 1.06 m3 = 2.12 m3
2.12 m3 : 0.9 or 0.13 = 16.3 m3 - 23.6 m3
In this case, the maximum take-off weight of the fighter without taking into account the conformal suspension is 8000 - 11800 kg.

If you do that, you limit how big a bomb you can stuff in the bay to whatever is the diameter of your chosen AAM's wingspan.

I like the way this thread is getting into detailed design of intakes and cockpits.
I agree with VTOLicious that a 2-seater version is superfluous. Consider the examples of F-22 and F-35 that lack 2-seater variants and depend instead on ground-based simulators for pilot proficiency. Any Third-World air force is going to struggle to pay for flight time and will cheerfully rent simulator time to keep their pilots current.

I'm not sure that a single seat aircraft will be capable of wrangling drones in a fight. I'd want a backseater to work the extra drones while the pilot flies his plane.

Another option for the internal carriage of SRAAM's would be conformal pods above the air inlets. Similar to the bump on the F-35A, which houses the gatling gun.
View attachment 673301
Such a conformal pod may provide a solution for an optional gun as well, but I would need to free up some internal space for the ammunition.

If there's space under the belly, I'd just go with a belly pod instead of a scabbed-on gun. F-35C style. The -C actually has almost 33% more ammunition than the F-35A does, 220 rounds versus 180.

IMOHO, a joint effort will get a better result but they have to agree a mission first to fit the majority of roles. Do-able but tough. Easier after current events I think.

Could probably make the argument that a 5gen Gripen is for air policing and interception first, secondary light strike if stealth is still required. I would want internal capacity for 6+ BVRAAMs, or 2x BVRAAMs and 2x 2000lb bombs. Yes, I know that's the F-35's payload. With a bay deep enough to hold GBU-31s, you can fit more AAMs in if you need the capacity, I think I've seen a proposal for 8-10x AMRAAMs in the F-35's bays before, stuffing 3 or 4 into the space of the 2000lber.

However.

Air policing means cruising around and eating up your range flying in circles. But let's go with F/A-18C/D range/loiter time for a realistic "small fighter" range: 400 miles for the air to air mission, which is about 45min flight time. (Is the legacy hornet really only capable of flying 400 miles? or is Wiki confusing combat range and combat radius again?) I'm going to assume that Wiki is being stupid and that's actually a radius number. Hour and a half or so loiter time for the Air Policing/airborne intercept role.

 

[Foo Fighter]

A2A refueling can give more loiter time, as it has for a good long while but, is a CAP really where we are now?

Also factoring in the ability of the 'wingman' to be the missile storage platform and you again reduce the payload requirement.

 

[Scott Kenny]

A2A refueling can give more loiter time, as it has for a good long while but, is a CAP really where we are now?

Air policing is one of the primary jobs of the Gripen.

Also factoring in the ability of the 'wingman' to be the missile storage platform and you again reduce the payload requirement.

Assumes that your wingman drone is cheap enough to buy en masse. I'm not sure that a wingman is going to be cheap enough to do that, due to all the systems needed for the jobs desired.

 

[paralay]

If you do that, you limit how big a bomb you can stuff in the bay to whatever is the diameter of your chosen AAM's wingspan.

The dimensions of the weapons bay determine the size of the aircraft and with it the mass. The relative size of weapons bay, at the moment, reaches 8 - 13.5% of the airframe volume

 

[Scott Kenny]

The dimensions of the weapons bay determine the size of the aircraft and with it the mass. The relative size of weapons bay, at the moment, reaches 8 - 13.5% of the airframe volume

Yes.

Are you willing to give up the ability to carry a 2000lb class weapon internally? I am not.

 

[paralay]

You'll have to pay for it. Now you don't have a "light fighter", but a "medium" one. With the appropriate price tag and current expenses

 

[riggerrob]

A2A refueling can give more loiter time, as it has for a good long while but, is a CAP really where we are now?

Also factoring in the ability of the 'wingman' to be the missile storage platform and you again reduce the payload requirement.

I question if air-to-air refuelling is affordable for the smaller second and third world nations that would struggle to afford a dozen or two dozen light fighters. Most of those nations already struggle to afford one or two KC-130 Hercules or a jet airliner to transport the despot on his begging missions … er … deliver-in-style the “elected” president to diplomatic conferences.
Har!
Har!

 

[Scott Kenny]

You'll have to pay for it. Now you don't have a "light fighter", but a "medium" one. With the appropriate price tag and current expenses

Given that even the armed LIFTs can carry a pair of 2000lb bombs, I think that the Stealth-Gripen class fighter is going to need roughly that capacity internally.

Will it be used for bombs? Almost never. But it does mean that you could stuff 3x or 4x AMRAAM sized missiles into that part of the bay and that would be your standard flying load. 6x AMRAAMs and 2x ASRAAMs. Isn't that what the Turks and Koreans are designing?

 

[Scott Kenny]

I question if air-to-air refuelling is affordable for the smaller second and third world nations that would struggle to afford a dozen or two dozen light fighters. Most of those nations already struggle to afford one or two KC-130 Hercules or a jet airliner to transport the despot on his begging missions … er … deliver-in-style the “elected” president to diplomatic conferences.
Har!
Har!

Probably only a couple of tankers for the larger countries. Chile and Argentina are kinda on the edge, Brazil and India definitely (and I'm pretty sure India already has air tankers).

 

[Scott Kenny]

Oh, I have solid numbers for my desired bomb bay size. 25"x50"x165" (May need to grow a little for clearances, but not beyond 30"x55")

That is large enough for a pair of 2000lb bombs (~4500lbs), a single 2000lber and a pair of AMRAAMs (~2800lbs), or a max air to air load of 4-6 AMRAAMs and a pair of AIM-9s (~2500lbs).

I think that's about the right total load for the internal capacity of a "stealthy Gripen"

 

[paralay]

0.635 m * 1.27 m * 4.191 m = 3.38 m3
3.38 m3 : 8% = 42,25 m3
3.38 m3 : 13.5% = 25 m3

The volume of the airframe is in the range of 25 - 42 m3.The maximum take-off weight is 12.5 - 21 tons. Realistically, you can count on 17 - 21 tons

 

[stealthflanker]

Will it be used for bombs? Almost never. But it does mean that you could stuff 3x or 4x AMRAAM sized missiles into that part of the bay and that would be your standard flying load. 6x AMRAAMs and 2x ASRAAMs. Isn't that what the Turks and Koreans are designing?

Or the weapon have to be smaller and achieve same effects.
Unfortunately one can't just "future proof" internal bay, especially if it's already small from the beginning.

Korean KFX and Turkish Kaan is not really Gripen sized.

 

[VTOLicious]

I would recommend everyone to read this thread from the beginning. Topics like weapon bay volume, fuel fraction, etc was already discussed earlier on.

This thread is about the design of a 5th generation LIGHT fighter powered by a single F414 thrust class engine!

 

[VTOLicious]

Oh, I have solid numbers for my desired bomb bay size. 25"x50"x165" (May need to grow a little for clearances, but not beyond 30"x55")

That is large enough for a pair of 2000lb bombs (~4500lbs), a single 2000lber and a pair of AMRAAMs (~2800lbs), or a max air to air load of 4-6 AMRAAMs and a pair of AIM-9s (~2500lbs).

I think that's about the right total load for the internal capacity of a "stealthy Gripen"

https://www.secretprojects.co.uk/th...eight-multirole-fighter-lmf.38539/post-506704
That's the max internal volume a light fighter can afford for weapons...

 

[Scott Kenny]

I would recommend everyone to read this thread from the beginning. Topics like weapon bay volume, fuel fraction, etc was already discussed earlier on.

This thread is about the design of a 5th generation LIGHT fighter powered by a single F414 thrust class engine!

And I think you can fly a bay the size I mentioned on a single F414, especially an F414EPR.

The problem with the bay size you have chosen is that it leaves zero room for air to air weapons if the mission requires dropping a BLU-109 bunker buster on someone. No way to fight your way into or back out of the defended zone.

 

[red admiral]

And I think you can fly a bay the size I mentioned on a single F414, especially an F414EPR.

So i'd think you could "fly" it, but you'd be massively down on peroformqnce compared to F-35 which uses a c. 75% more powerful engine with that size of weapon bay (and very tight packaging). So you're unlikely to be supersonic with the F414.

 

[Scott Kenny]

So i'd think you could "fly" it, but you'd be massively down on peroformqnce compared to F-35 which uses a c. 75% more powerful engine with that size of weapon bay (and very tight packaging). So you're unlikely to be supersonic with the F414.

Does a fighter have to be supersonic, or just have good excess power (as per Energy-Maneuverability Theory)?

I will note that all the current-generation LIFTs, the aircraft we are designing a replacement for, are only transonic. Nothing faster than Mach 1.2 that I have seen. The T-7 Redtail only gets to Mach 1.05!

I'm assuming an airframe that is almost 100% composite, and one much less dense than the F-35 since we don't need to deal with carrier compatibility and all that reinforcement. My goal is an airframe gross weight of no more than 26,400lbs/12,000kg (~4000lbs lighter than a Gripen). I can accept going a bit heavier due to fuel, but I would want the 50% fuel weight, the "combat weight", to be under 25,000lbs with 2x AMRAAMs and a BLU-109 internally (~3000lb payload) in that case, for a power to weight ratio of 1.056:1.

A Gripen carries ~2400kg/5200lbs of fuel, so that's another datum I want to equal.

So let's backtrack a bit.
5200lbs of fuel
3000lbs payload in the bay
2500lbs engine dry weight
Gun... Are we including a gun? They make a great way to give an idiot one last warning before you blow his tail off with a Sidewinder...
Assume 1000lbs for gun and max ammo (probably high, but do have to include the ammo drum in that)
Total: 11,700lbs already, which leaves 14,700 for airframe, landing gear, actuators, computers, and cockpit

14,700lbs/~6700kg... Gonna be very tight indeed.

Again, the problem with using the Super Hornet stealthy weapons pod as the bay size is that it doesn't give you any space for defensive weapons for the mission where you need to drop a BLU-109 on some command bunker. Make the bay just a little wider so that it can hold a pair of AAMs in addition to that BLU-109, that's what I'm asking.

 

[Scott Kenny]

Korean KFX and Turkish Kaan is not really Gripen sized.

Correct, the Boramae is 56000lbs gross with 2x F414s, and the Kaan is 60000lbs gross with 2x F110s.(Didn't realize Kaan was planned to be that big!)

The more I look at the other aircraft in the rough design space, the less I think a single F414 "stealthy Gripen" is going to be viable: All the systems needed to packed inside are the expensive part, so going to 2x F414s like the Boramae adds a lot of capability without adding too much cost...

 

[zen]

Late 1950s
Vickers Supermarine Type 571 single engine to GOR.339.
Twin seats.
A single Medway of 14,000lb dry and 23,000lb reheated thrust.
Supersonic at low level, mach 2+ at altitude.
Met 600nm ROA with single Red Beard store of 2,000lb in an internal bay.
1,000nm with external drop tanks.
Small wing of high loading.

Yet now.....with all the benefits of technology.
With avionics allowing a single seat.
With turbofans being higher performance for less fuel burned.
When you don't need to flow low level.
People are saying it cannot be done?

 

[paralay]

on the same scale

 

[kqcke for you]

Are there not any other engine that are possible to use? I think EJ200 (like EJ230 which i think had the same size) is better
EJ200 alone has a smaller diameter but is a little longer. A little higher trust and a some 200kg lighter. Well atleast if compared to F414 G400

 

[Scott Kenny]

Are there not any other engine that are possible to use? I think EJ200 (like EJ230 which i think had the same size) is better
EJ200 alone has a smaller diameter but is a little longer. A little higher trust and a some 200kg lighter. Well atleast if compared to F414 G400

Probably, but the idea is "stealthy Gripen", which currently uses an F404.

 

[kqcke for you]

And F414 where the EJ200 could have been instead but yeah i forgot that. But one could call it a what if maybe better Option. If i ever find the time and hardware i may could make something like that.

 

[Scott Kenny]

And F414 where the EJ200 could have been instead but yeah i forgot that. But one could call it a what if maybe better Option. If i ever find the time and hardware i may could make something like that.

I should note that I actually agree with you on the EJ200, because that would allow whoever is making this small LO fighter to sell it without ITAR issues from the US.

 

[kqcke for you]

Yeah. We also know that they atleast tought that around 72-78kn trust was possible dry. Way more powerful, lighter and itar free? You bought me but f414 is it for now. Will it be an f414 with epe ?

 

[Scott Kenny]

Yeah. We also know that they atleast tought that around 72-78kn trust was possible dry. Way more powerful, lighter and itar free? You bought me but f414 is it for now. Will it be an f414 with epe ?

This thread is mostly about @VTOLicious design, but I think so. I know I'm assuming the F414EPE, with 26,000lbs thrust.

 

[VTOLicious]

The problem with the bay size you have chosen is that it leaves zero room for air to air weapons if the mission requires dropping a BLU-109 bunker buster on someone. No way to fight your way into or back out of the defended zone.

I don't see a problem...
Bunker buster could be delivered by an uncrewed version derived from FAR-21 (CCA-21?). A mix of FAR /CCA can be configured AA or AG as required.
Anyhow, independent of what is loaded in the main bay FAR/CCA-21 always carries a single IRIS-T in the dorsal bay
And there is the option of "beast mode" as well.

 

[Scott Kenny]

I don't see a problem...
Bunker buster could be delivered by an uncrewed version derived from FAR-21 (CCA-21?). A mix of FAR /CCA can be configured AA or AG as required.
Anyhow, independent of what is loaded in the main bay FAR/CCA-21 always carries a single IRIS-T in the dorsal bay
And there is the option of "beast mode" as well.

Ah, right, you did add that dorsal bay. Forgot about that, sorry.

 

[kqcke for you]

Anyhow, independent of what is loaded in the main bay FAR/CCA-21 always carries a single IRIS-T in the dorsal bay

I think the dorsal Bay makes more sense for more flares and decoys then an Iris-t which one could put there like this
which could make even more sense with an dorsal air intake.

 

[VTOLicious]

I think the dorsal Bay makes more sense for more flares and decoys then an Iris-t which one could put there like this View attachment 705750
which could make even more sense with an dorsal air intake.

I abandoned the depicted proposal because it would add too much weight and drag.

 

[kqcke for you]

I guess having them there we're the air intake's are right now won't help mutch either and you would need to put the air intake somewhere else. But that are the limitation set by the requirements

 

[VTOLicious]

I guess having them there we're the air intake's are right now won't help mutch either and you would need to put the air intake somewhere else. But that are the limitation set by the requirements

As discussed earlier, a dorsal air intake would be optimal to free up internal volume for weapons and/or fuel. Although dorsal intakes have found application in stealth aircraft (e.g. B-2, various UCAV,...) there is no practical example that would confirm suitability for stealth fighters.