Design Challenge: Lightweight Multirole Fighter (LMF)

[paralay]

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[paralay]

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[Kryptid]

Wow, so much effort has been put into this. I'd like to see paralay design an entire air force (and navy) of new planes (including transports, tankers and bombers). I know that would take quite a long time, unfortunately.

 

[paralay]

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[VTOLicious]

Size comparison... It illustrates pretty good what "lightweight fighter" really means.

I would consider KF-21 as a medium- to heavyweight fighter. Although its published maximum takeoff weight (25600 kg) is significantly less than F-35A (31750 kg) the combined thrust of two GE F414 engines is equal to a single PW F135 engine and KF-21 is the larger aircraft as well.

In contrast, FAR-21 is estimated to have a maximum takeoff weight in the region of JAS39 Gripen E (16500kg), which is powered by a GE F414 as well.

 

[helmutkohl]

awesome render!
a related question.

So FAR-21 is a nice example of a light Gripen sized fighter stealth aircraft with internal bays, angled body, etc
however my question is.. is there a market for these kinds of light weight stealth aircraft?

 

[UpForce]

awesome render!
a related question.

So FAR-21 is a nice example of a light Gripen sized fighter stealth aircraft with internal bays, angled body, etc
however my question is.. is there a market for these kinds of light weight stealth aircraft?

If a "hot take" is allowed, smaller nations that only need to gain temporary superiority (or practice policing) mainly in their own airspaces; it's not for nothing that the proportioning here largely follows that of Gripen.

Admittedly a simplistic and theoretical starting point as more, let's say, "empireycally" (see what I did there) positioned larger powers tend to get rather liberal in terms of where their A2/AD capabilities (at least theoretically) extend so the airspace could be contested even in the best of times. Simplistic as well to consider this jet in isolation from other supportive systems, I guess. "Other systems" in mind, this design could lend itself well for autonomous variants, it has that "big brawny brother of" Loyal Wingman feel to it.

Another option that comes to mind is - somewhat counterintuitively to what I just wrote - a carrier version; Tejas has at least tentatively been considered for such a role.

 

[VTOLicious]

awesome render!
a related question.

So FAR-21 is a nice example of a light Gripen sized fighter stealth aircraft with internal bays, angled body, etc
however my question is.. is there a market for these kinds of light weight stealth aircraft?

One could assume Saab would be in a much better position against LM (and other competitors) with a NATO compliant 5th generation fighter in the likes of FAR-21. I think of the Finnish HX fighter contest, recently won by LM.
As mentioned before, a "loyal wingman" option could make it even more attractive.

 

[Pioneer]

You might have already addressed this question VTOLicious and if so I apologise, but does your design facilitate addition external hardpoints for overload configuration - i.e. after air-superiority is achieved and stealth isn't so much of a factor, additional air-to-ground weapons can be hung from these external hardpoint....?

Regards
Pioneer

 

[VTOLicious]

You might have already addressed this question VTOLicious and if so I apologise, but does your design facilitate addition external hardpoints for overload configuration - i.e. after air-superiority is achieved and stealth isn't so much of a factor, additional air-to-ground weapons can be hung from these external hardpoint....?

Regards
Pioneer

Sure, external hardpoints are considered as an option.

 

[UpForce]

Jim Smith writes about Bud Nelson's light fighter concepts on Hush-Kit. While the overall tone of the article is somewhat dismissive (about the suitability of such jets at the time they were considered, i.e. 1970 - 1982), there's also this:

As technology is continuing to evolve, lighter-weight fighters are making a come-back, as aircraft like the Gripen and Tejas are demonstrating that highly integrated systems with long-range missiles and highly effective sensors can now be packaged into a single-engined and single-seat airframe.

Something which seems to go into the potential markets question "helmutkohl" was pondering. All of the concepts featured in the article are also to be found here in different discussions, I think (didn't bother to check one by one) and interesting in their own right.

Unbelievably Sleek Fighter Cold War Combat Aircraft: Bud Nelson’s Light Fighter Concepts

A series of sleek exotic fighter aircraft concepts were explored between 1970 and 1982 in the US. With the fabulous good looks of a fictional spaceship, these Cold War studies were extremely lightw…

hushkit.net

 

[UpForce]

Did it ever become clear whether the Swedish prime minister meant a wholly indigenous fighter project to replace Gripen in his speech (quote below) on the 15th of June, 2020 or did he just refer to their participation in the Tempest program in a roundabout way? (Found in the discussion "Sweden to Propose Development of a New Fighter Aircraft".)

When it comes to the Air Force the current fighter JAS 39 C/D will be maintained, as the new fighter JAS 39 E is integrated into the squadrons and becomes operational. This allows the Air Force to keep six fighter squadrons. The development of the next generation fighter aircraft will also commence.

Försvarsminister Peter Hultqvists anförande på UK NATO Heads of Mission’s Forum

Digitalt anförande via videolänk från Försvarsdepartementet. Stockholm, 15 juni 2020. Det talade ordet gäller.

www.regeringen.se

 

[Foo Fighter]

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.

 

[MadRat]

Superb work. A true son of the mighty F-20 Tigershark.

If you want it to more closely follow the area rule, you'll certainly have to replace the aft positioned ruddervator with a vertical (think M2K) or fill the gap b/w the wing trailing edge with a section increase of some sort.

Thank you. I like the F-20 analogy.

In regards of area rule: Have a close look. It actually has a "hump" to fill the gap between wing an V-tail.
View attachment 672398

I'd suggest two smaller, low tech F125-class engines for this theoretical design. Less height needed. Spread them out to disperse IR emissions. Flat nozzles with simple single-action paddles to provide instant positive pitch control. Shorter, less height for the tailerons and make them all-moving with sawtooth fit like on F-117A. Chisel-point, rather than pointed nose, and integrate the targeting sensors and laser designators into the shape. Leading outer tip of the intakes needs to move forward to improve intake geometry. You need a pronounced leading edge extension coming out of your main wing that blends into the top edge of the intake to improve angle of attack for literally no extra cost. Drop the seat by deepening the cockpit in relationship to the chine. Remove the single-piece windscreen and move towards high quality pin-hole cameras for general sight augmented with an AI-directed electro-optical bubble on each side of the fuselage to get zoom views. Bubble canopies were great for Mark 1 eyeballs before electronics surpassed the human eyeballs. Less glass overall, the better it will be to streamline the shape. Keep it a sliding canopy that seals up to the fuselage, but lifts up and slides back to open. Focus on flat, wider shaping for the fuselage. You need a proportionately large horizontal area in relationship to the vertical height for RAM to maximize the absorption of wave-form energy. You also want wingtips as far apart as practical to optimize the coordination of radar detectors to get passive, directional information.

 

[VTOLicious]

Superb work. A true son of the mighty F-20 Tigershark.

If you want it to more closely follow the area rule, you'll certainly have to replace the aft positioned ruddervator with a vertical (think M2K) or fill the gap b/w the wing trailing edge with a section increase of some sort.

Thank you. I like the F-20 analogy.

In regards of area rule: Have a close look. It actually has a "hump" to fill the gap between wing an V-tail.
View attachment 672398

I'd suggest two smaller, low tech F125-class engines for this theoretical design. Less height needed. Spread them out to disperse IR emissions. Flat nozzles with simple single-action paddles to provide instant positive pitch control. Shorter, less height for the tailerons and make them all-moving with sawtooth fit like on F-117A. Chisel-point, rather than pointed nose, and integrate the targeting sensors and laser designators into the shape. Leading outer tip of the intakes needs to move forward to improve intake geometry. You need a pronounced leading edge extension coming out of your main wing that blends into the top edge of the intake to improve angle of attack for literally no extra cost. Drop the seat by deepening the cockpit in relationship to the chine. Remove the single-piece windscreen and move towards high quality pin-hole cameras for general sight augmented with an AI-directed electro-optical bubble on each side of the fuselage to get zoom views. Bubble canopies were great for Mark 1 eyeballs before electronics surpassed the human eyeballs. Less glass overall, the better it will be to streamline the shape. Keep it a sliding canopy that seals up to the fuselage, but lifts up and slides back to open. Focus on flat, wider shaping for the fuselage. You need a proportionately large horizontal area in relationship to the vertical height for RAM to maximize the absorption of wave-form energy. You also want wingtips as far apart as practical to optimize the coordination of radar detectors to get passive, directional information.

 

[MadRat]

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.

I believe this design is relegated to a very light fighter role, play only supporting roles, and would require targets of opportunity versus any mainline roles. YourTWR is impossible to challenge much heavier fighters, so aim for low cost motors with adequate thrust to perform supporting roles. No need to put a giant matchstick that would be impossible to conceal IR emissions. At the same time, you don't need fancy thrust vectoring to steer you into supermanueverability, but flat paddles help reduce emissions and reinforce pitch command without moving control surfaces. Using two separate paddles in only one axis does allow some roll control, too, along the same reasons. You want to also have the smallest control surfaces, too, for keeping radar reflections lower. They would be much too small for adequate RAM on them to hide them from most reflections, so keep the size down as much as possible. Where you do have them, use zigzag surface boundaries where you cannot blend them, and use bending hinges like F-35 where you can to allow continuous RAM connections until they reach extreme movements. Everything is about the stealth.

Emphasizing stealth limits your missions. But as a support fighter there is no reason it has no reason to exist. It can be a mule, to augment mainline fighters. You could offload standoff targeting information from external sources for them to release missiles and bombs. Preferably your aircraft has internal room for at least one 1,000-kg class weapon AND two 200-kg class weapons such as AIM-120. Anything external would mostly negate any stealth going for it. When not needing stealth you'd want one 1,000-kg class weapon and one 200-kg class load underneath each wing and the ability to carry extra fuel internally. Everything needs to be jettisoned by gas, no fancy trapezes.

Whatever choice you make, you probably want to limit the budget to <$40 million a plane. Having an AI pilot would be bonus, since no oxygen-generating equipment would limit you.

 

[riggerrob]

Emphasizing stealth limits your missions. But as a support fighter there is no reason it has no reason to exist. It can be a mule, to augment mainline fighters. You could offload standoff targeting information from external sources for them to release missiles and bombs. Preferably your aircraft has internal room for at least one 1,000-kg class weapon AND two 200-kg class weapons such as AIM-120. Anything external would mostly negate any stealth going for it. When not needing stealth you'd want one 1,000-kg class weapon and one 200-kg class load underneath each wing and the ability to carry extra fuel internally. Everything needs to be jettisoned by gas, no fancy trapezes.

Whatever choice you make, you probably want to limit the budget to <$40 million a plane. Having an AI pilot would be bonus, since no oxygen-generating equipment would limit you.

Please keep in mind that most client air forces (e.g. Canada or Australia) will struggle to finance one type of fighter airplane, ergo high-low strike packages are far too expensive.

Yes, networked sensors are nice, but we wonder if the manufacturing nation will be willing to export recent versions of the software.

This raises similar questions about AI pilots. Is the exporting nation willing to sell recent versions of the software? How quickly can they shut down said software when the client air force gets uppity?
What about all those princes and sons of powerful families that want to aggrandize their egos while flying supersonic fighters?

 

[Fighterreaper97]

Superb work. A true son of the mighty F-20 Tigershark.

If you want it to more closely follow the area rule, you'll certainly have to replace the aft positioned ruddervator with a vertical (think M2K) or fill the gap b/w the wing trailing edge with a section increase of some sort.

Thank you. I like the F-20 analogy.

In regards of area rule: Have a close look. It actually has a "hump" to fill the gap between wing an V-tail.
View attachment 672398

I'd suggest two smaller, low tech F125-class engines for this theoretical design. Less height needed. Spread them out to disperse IR emissions. Flat nozzles with simple single-action paddles to provide instant positive pitch control. Shorter, less height for the tailerons and make them all-moving with sawtooth fit like on F-117A. Chisel-point, rather than pointed nose, and integrate the targeting sensors and laser designators into the shape. Leading outer tip of the intakes needs to move forward to improve intake geometry. You need a pronounced leading edge extension coming out of your main wing that blends into the top edge of the intake to improve angle of attack for literally no extra cost. Drop the seat by deepening the cockpit in relationship to the chine. Remove the single-piece windscreen and move towards high quality pin-hole cameras for general sight augmented with an AI-directed electro-optical bubble on each side of the fuselage to get zoom views. Bubble canopies were great for Mark 1 eyeballs before electronics surpassed the human eyeballs. Less glass overall, the better it will be to streamline the shape. Keep it a sliding canopy that seals up to the fuselage, but lifts up and slides back to open. Focus on flat, wider shaping for the fuselage. You need a proportionately large horizontal area in relationship to the vertical height for RAM to maximize the absorption of wave-form energy. You also want wingtips as far apart as practical to optimize the coordination of radar detectors to get passive, directional information.

Excellent idea 2lb 22 inch compact low cost modular 3d printed honeycomb sandwich armoured structure/plating spread out equally over all vital areas plus 2 Giat 30 30mm cannons canard foreplanes to assist with shortening take off & landing distances and a rugged a-4 style undercarriage to operate from ice snow sand water areas mountains grass fields rocky cliffs rainforests roads highways volcanoes lava etc

 

[GTX]

undercarriage to operate from ice snow sand water areas mountains grass fields rocky cliffs rainforests roads highways volcanoes lava etc

What sort of gibberish is this?

 

[overscan (PaulMM)]

@Fighterreaper97 you are sailing close to being banned from posting. I suggest you read more and post less for a while rather than spamming multiple topics with semi-coherent posts on what is clearly a specific 'hobbyhorse' of yours.

 

[Fighterreaper97]

@Fighterreaper97 you are sailing close to being banned from posting. I suggest you read more and post less for a while rather than spamming multiple topics with semi-coherent posts on what is clearly a specific 'hobbyhorse' of yours.

My most sincere apologies I’m just trying to keep any topics from year ago alive & not forgotten. My reasons are
1 I’m a curious person with a high functioning autism spectrum for which I personally apologize for that.
2 I have my believes that ruggedly simple high reliability low cost low maintenance aircraft (basically low tech aircraft designed to survive in high tech environments).
I’m inspired via Pierre Sprey & Blacktail Defense with stamping the hypocritical bureaucracy that is the believe that bombing houses bridges roads railways factories ports & people would win wars when those people explain the truth that it was Russia that caused hitler to lose the war & not allied bombing like so many people believe & also it was Russias on Japan that caused japan to surrender & not little boy & fat man being dropped on Hiroshima & Nagasaki in ww2
3 I’m inspired by the Douglas A-4 Skyhawk the Northrop F-5 family & Fairchild Republic A-10 thunderbolt II & finally
4 I’m against far left and far right wing politics being shoved down people’s throats which is NOT okay at all. I understand the need for human rights and freedom of speech however I don’t approve of politics being used to belittle attack & humiliate others! It’s making people of different genders races orientations religions etc look bad. Anyway, I’m sorry for the excessive amounts of topic updating. I’m just trying to keep the older topics up to date & prevent them from being forgotten.

 

[GTX]

Further to what Paul said, I would recommend you read a bit more and especially further afield. Certainly don't be fooled into believing that low-cost/simple is always best. A rock is certainly low cost and simple but it isn't going to cut it against a tank. Often the additional complexity that comes with modern systems (especially when used/supported by trained professionals) far outweighs any perceived deficiencies when compared to something much simpler.

In the same vein remember that the world has moved on from the 1950s/60s70s (when most of your offered platforms originate). In the intervening 50+yrs a lot has changed.

These are things the likes of Pierre Sprey and others didn't/don't seem to recognise or comprehend.

 

[overscan (PaulMM)]

Simpler isn't necessarily better. Pulse radars are simpler than pulse-doppler, but nobody is going to suggest building a fighter with a pulse radar today. Leading edge technology often has a steep learning curve and cost, but may turn into cheap and reliable technology in time.

There are always tradeoffs between simplicity, reliability, capability, and cost. No one factor is uniquely "good", you try to get the best balance between them. The F-16 was in some respects more high tech than the F-15.

 

[Fighterreaper97]

While the F-16 fighting falcon is a capable multi role fighter originally designed as a compact air superiority fighter aircraft it can’t operate from rough forward air strips which the F-5 family of fighters can operate on like the Migs

 

[overscan (PaulMM)]

The F-5 participated in rough field trials after modifications to its tires (http://ghostmodeler.blogspot.com/2014/03/green-dreams-us-army-evaluates-n-156f_15.html). I don't see any inherent advantage to the F-5 in this area over any other plane?

It had a short takeoff by 1961 standards, but I'm not sure it would beat a lightly loaded F-16A.

 

[icyplanetnhc (Steve)]

I’m inspired via Pierre Sprey & Blacktail Defense with stamping the hypocritical bureaucracy that is the believe that bombing houses bridges roads railways factories ports & people would win wars when those people explain the truth that it was Russia that caused hitler to lose the war & not allied bombing like so many people believe & also it was Russias on Japan that caused japan to surrender & not little boy & fat man being dropped on Hiroshima & Nagasaki in ww2

I strongly suggest that you look elsewhere for inspiration and take cues from more reputable and accredited sources on warfare and history.

Warfare has shifted considerably since Pierre Sprey was last engaged in the defense industry.

 

[riggerrob]

what if rather one large bay for a light fighter

what about two smaller ones like on UCAVs?

what if rather one large bay for a light fighter

what about two smaller ones like on UCAVs?

Structurally, that looks much simpler and lighter than the - failed - Grumman A-12 Avenger II. The nose-wheel bay is far enough forward and the main-wheel bays plus bomb-bays are far enough aft that you can route a forward spar straight across to transfer loads between the wing leading edges. Straight load paths equal simpler and lighter structures.

 

[VTOLicious]

Earlier on in this thread a discussion about the implementation of dorsal inlets on supersonic fighters started, which provide some obvious advantages, especially when low RCS and fuselage volume for IWBs is required. https://www.secretprojects.co.uk/th...eight-multirole-fighter-lmf.38539/post-508005

However, the main concern is the air distorted by the fuselage, wings, lerx, especially at higher AoA.

I had a second look on that matter and thought about an inlet similar to the one on Su-75, but upside down:

I think this far forward position, with the intake side walls going all the way down to the leading edge, would be beneficial for intake performance. The sketch isn't to scale btw. It should just illustrate the concept.

 

[Foo Fighter]

I did suggest such a thing but was ignored which, my not being a designer, is a fair point.

 

[VTOLicious]

I did suggest such a thing but was ignored which, my not being a designer, is a fair point.

You have not been ignored. You actually started the discussion I'm referring to in my post above

 

[Foo Fighter]

I was talking about the inlet being further forwards than my original suggestion, which was more likely missed, I chose the word ignored. Silly thing to do but I was doing several things at once and over two computers. Sorry folks.

 

[TMA1]

Lovely drafts, VTOLicious! Usually I get irritated when I see inlets on top of an aircraft but I think in the future we will start seeing more specialized drones and fighters that wont have the same requirements for extreme manoeuvring. Inlets on the back of an aircraft might indeed have advantages. Particularly with bombers (tu-22, b-2), attack drones (neuron, s-70) and interceptors (product 701).

 

[red admiral]

I think with that concept then you'll suffer at moderate alpha from vortex generation off the bottom lip/corner, and there is significant blockage and vortex shedding from the canopy under beta. Not that its necessarily impossible.

I think the likes of a separate intake from the forebody is a better way to go, as this also shortens the duct. Think HP.115 with strong stable vortices either side of the intake able to maintain good performance at high alpha.

 

[VTOLicious]

In regards of vortex generation off the bottom lip: I would think this applies to every intake with a bottom lip, be it chin, side intakes, or anything else. Therefore I would assume this isn't an issue.
In regards of vortex shedding from the canopy: I think one should not underestimate the strong suction of the engine. Of course the shape of the canopy and the interaction with the inlet is an important consideration to make. But this is no different to the careful shaping required for a DSI bump.
However, speaking of DSI: The illustrated inlet would most probably need boundary layer suction.

 

[red admiral]

When you look at Model 401 it has a significant splitter, or on X-47A then they seem to add internal fences as they must have had issues.

Not impossible, just more complex to integrate than having an intake further back that is more isolated from the forebody

 

[VTOLicious]

When you look at Model 401 it has a significant splitter, or on X-47A then they seem to add internal fences as they must have had issues.

Not impossible, just more complex to integrate than having an intake further back that is more isolated from the forebody

Indeed, I almost forgot about 401. Thx for the hint!

 

[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...

 

[paralay]

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

 

[lantinian]

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

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...

That is very creative indeed. Have you also thought about how it will be mounted by the ground crew?
It seams to you you will need to design a special equipment just for that 1 job

 

[VTOLicious]

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

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...

That is very creative indeed. Have you also thought about how it will be mounted by the ground crew?
It seams to you you will need to design a special equipment just for that 1 job

Mounting is indeed a concern. I think it could be slided on the rail from the rear. But special equipment is required for sure.