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Can a stealthy 5th/6th generation fighter jet Gripen sized?

helmutkohl

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It was a topic that I saw on the now dying Keypublishing forum, but saw again mentioned on the KAI KFX thread.

most stealth fighter designs right now are generally considered heavy such as the J-20, Pak-fa, F-22, YF-23, etc

or, medium. such as the F-35 which might look short but is quite beefy.. and probably the J-31 too, which I'll say are mid-weight.

Can there be a stealth jet that is more of a lighter fighter like the Gripen or FC-1 class?

The closest I've found is the Mitsubishi X-2 which is closer in size and weight to the Gripen but it carries no internal armaments.

I suppose that because of this internal compartment requirement, it might not be possible to have it at this size class?
 

Dragon029

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I don't see why not, but any such aircraft would have to accept either a reduced internal payload, internal fuel capacity, or engine thrust (or some combination of those). A light stealth fighter might only carry 2x or 4x AMRAAM equivalents internally, have a single F414 equivalent and perhaps carry a maximum of 5,000-7,500lb of fuel internally.

Empty spaces in aircraft (serpentine intake ducts, weapon bays, etc) are ironically heavy due to the less mass-efficient structures you need to wrap around them, so you'd also likely opt for something akin to a slightly smaller X-32 in design (so you can run wing spars right across the fuselage and hang the engine off it), but with simplified weapon bays (perhaps located as bumps under the wing root), no thrust vectoring, a regular 4-poster tail, etc. Even then I'm sure it'd still come out as one of the heavier light fighters on the market, at something like 20,000lb.
 

sferrin

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Or start with something like the Taiwanese F-CK-1, use dorsal inlets (to free space below for small weapons bays).
 
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stealthflanker

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The bigger question would be "Why it has to be in Gripen weight-size class ?"
 

red admiral

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If you mean "mass" by "size" then yes but you're having to reduce payload-range or air vehicle performance.

If you mean "geometry" by "size" then probably not unless you use much smaller and/or fewer weapons. E.g. like on the various microfighter designs Boeing/Northrop which used small tube launched weapons.
 

VTOLicious

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Something like Northrop MRF comes to my mind
 

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totoro

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Theoretically it can be done, but it's performance parameters would suffer heavily.
Here's one rough idea how it could be done. Just for fun, mostly.
stealthy 6700kg.jpg

I'm talking about a plane in the JF-17/Gripen A/C class, as per the opening post. That's between 6600 and 6800 kg. So 6700 kg limit it is.

The issues with the above sketch are numerous. Since i tried hard to stay within the 6700 kg empty figure, I had to make the plane shorter than Gripen, with shorter intakes. Shaving off structure wherever possible. Because the weapon bays and landing gear took up valuable room and made the plane chunkier than Gripen is.

Even so, anything more than weapon bay for 2 amraams seems impossible. (amraams here aren't the best drawn, if they were rotated correctly two of them should fit)

But the biggest issue is fuel. F-16 for example has some 1070 gallons of internal fuel. (gripen has 750 gallons internally) This plane is likely not going to fit more than 500, 600 gallons at most. That's going to translate into quite poor range. Not helped by the fact the plane would be chunky.

Short simple intakes and drag are probably going to make it quite slow. At best as fast as F-35.

Shaving off more weight, I went with a butterfly tail. Which while good for stealth is not so good for maneuverability. Perhaps all moving tails might help there a bit, though in the end it might be that 3d vectoring engine is going to be needed to rectify the lack of pitch authority.

Is 2 amraam class missiles going to be enough? Probably not in today's world. And lack of range would simply stop this kind of design from being made. Gripan can do 3000 km ferry range with internal and external fuel of 1650 gallons. This plane would have a little more than a third of that range. (Perhaps 1200-ish km?) So range would be abysmal, comparable with MiG-21 on internal fuel only. Now, since the whole point of the project is to have a very stealthy plane, then external tanks are probably off limits for combat missions. Same thing can be said for adding weapons externally.

It just shows how clogged the design is, when trying to fit everything into such a small package.

What would probably happen then is what always happens when requirements are trying to be met. Plane would get bigger, longer, heavier etc. So to get any sort of usable ferry range (2500 km?) with, say, 3 AAMs we'd probably be looking at something closer to F-35 in weight class than to Gripen.

I guess plane could be made a bit lighter (or made a bit bigger for the same weight) if airframe was made to last only a short time. Or if wings weren't designed to carry any heavy loads. But would that be worth it? Having a still expensive stealthy plane that can do only 3000 flight hours and can never carry external ordnance heavier than 500 kg under wings? All for a few hundred kg lighter airframe?

So it's obvious why we're unlikely to see stealthy planes in tiny, gripen-sized packages.
 

DWG

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Let's not forget that the value of 5th/6th gen fighters isn't simply stealth, it's also software and sensor fusion. If you want the same sort of fusion capabilities as F-35, it's going to cost the same as F-35, it's not scalable in the same way as agility or signature, where you can go smaller and retain the same capabilities.

We've seen a continuous increase in the size of fighter aircraft since the earliest days. A Camel was smaller than a Gladiator was smaller than a Spitfire was smaller than a Tempest was smaller than a Hunter was smaller than a Typhoon. It's not unreasonable to expect a similar evolution in the size of the smallest viable fighter.
 

Desertfox

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Gripen size might be hard, but F-16 XL size should be doable. For weapons you could go with conformal weapon bays and the new Raytheon Peregrine AAMs. If you forgo all-aspect stealth and focus on front aspect only, you can get away with recessed AAMs like the Korean KFX. A full size X-36 powered by a F414 with 4xPeregrine AAMs? Probably not worth it in these days of multi-role missions, but I'd say doable for single-purpose missions.
 

Colonial-Marine

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Boeing seemed to have studied a lightweight stealth fighter on at least one occasion. There was also a tailless design that seems to be related. On either I'd expect some weight growth from the paper version to an operational aircraft. However both only seem to have AIM-9X for self-defense (no AIM-120) so that seems like a bit of a limitation. To perform the air-to-air mission these days you need medium-range missile capability.

Boeing-Model-24F.jpg Boeing-Model-MRF-24X.jpg

Northrop also had a handsome design that resembled a smaller single-engine YF-23 I've seen in a few topics on these boards.
 
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quellish

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Sure! As you point out the sizing for internally carried weapons is a major factor. If you have small weapons you can have a small airplane - like a UCAV carrying SDBs, etc.
 

LMFS

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Boeing seemed to have studied a lightweight stealth fighter on at least one occasion. There was also a tailless design that seems to be related. On either I'd expect some weight growth from the paper version to an operational aircraft. However both only seem to have AIM-9X for self-defense (no AIM-120) so that seems like a bit of a limitation. To perform the air-to-air mission these days you need medium-range missile capability.

Northrop also had a handsome design that resembled a smaller single-engine YF-23 I've seen in a few topics on these boards.

Good find, thanks for posting!

I didn't knew those, but a small "mental exercise" from mine resulted in something relatively similar to the first example, at least in regards of the internal layout. My idea was a bit bigger than a Gripen, rather inspired by the F-16 since I think internal bays with a modicum of A2G ordnance capacity and a strict light fighter design are not really compatible. 9-10 tons empty weight look the minimum, considering the sizes of today's weapons at least. Not a real problem IMO, since they could be served with one heavy-fighter sized engine.

LMFS_151.png
 

helmutkohl

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The bigger question would be "Why it has to be in Gripen weight-size class ?"

because there already is a mid-weight class 5th gen aircraft. the F-35 and the J-31.. possibly the Tempest, FCAS, TFX.. and not sure but perhaps the KAI KFX?

but there's a potential market for a lighter (less mass) one as mass tends to be synonymous with operating costs and some air forces may not need something mid weight range. (so its not so much length, as the F-35 is shorter than some so called light aircraft.. but weight.. as the F-35 is quite heavy for its size)

something around 8,000kg empty weight and under
(F-16 is around 8500, Gripen around 6500. The Mitsubishi X-2 despite being about the same length as the Gripen is 9500)

however like some others said, this is a question if stealth fighters can even be scaled down to a Gripen/FC-1/Tejas/F-20 weight category, or is the F-35 and friends, the smallest one can go as a stealth fighter due to its unique requirements of needing an internal bay, in addition to gas, sensors, other avionics, etc
 
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rooster

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Something like Northrop MRF comes to my mind
There is a pic of this model in a Northrop pic of numerous scale models from a few years ago. I can't locate it but maybe someone else remembers this somewhat famous pic?
 

TomS

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It's conceivable that the current generation of downsized munitions (SDB, Cuda, and even smaller weapons) might make a small aircraft with internal carriage more effective.

But I'm not sure a smaller stealth aircraft would be dramatically cheaper. There's a lot of fixed overhead for stealth aircraft design and manufacturing that will remain high even for a smaller airframe. Then amortize those costs across a smaller production run. Boom, it's cheaper to just buy F-35s.
 

stealthflanker

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Yeah, being stealth alone incurs cost which may make the airplane more expensive than comparable aircraft in her weight-size class.
 

TomS

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helmutkohl

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Something like Northrop MRF comes to my mind
There is a pic of this model in a Northrop pic of numerous scale models from a few years ago. I can't locate it but maybe someone else remembers this somewhat famous pic?
This one?

wow some awesome pics! lookalike the MDD JAST had one normal sized bay and 2 AAM sized ones

--
some approximate numbers being thrown out for empty weight of 5th gen aircraft with a 4th gen for comparison
in KG

Model 24: 9,400
X-2: 9,700

X-35: 10,000
X-32: 10,000
FCAS: 11,000?
KFX: 12,000
F-35A: 13,000
TFX: 14,000?
Tempest: 14,000?
J-31: 15,000

Su-57: 18,500
J-20: 19,000
F-22: 19,700

--- 4th gen---

F-15: 20,000
Su-35: 17,500
F-16: 9,000
Gripen C: 6,800
Ching-kuo: 6,500
Tejas: 6,500

seems like going for 6000-7000kg might not be possible, but perhaps a 9,000-ish is realistic? the Model 24 is close in weight to the Mitsubishi X-2.
but looking at its belly doesn't seem like its possible to make space for any bay
8dc62ff3922fd0d0903d99743905a090--stealth-aircraft-april-.jpg
 

totoro

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These are very nice finds!

And they're quite fascinating, even hard to believe. The above design is basically just a bit bigger than F-16 block 50, weight wise. (8600 kg vs 9000 kg)
But Boeing managed, at least on paper, to cram in two side weapon bays for sidewinders and a central weapon bay measuring 447 by 89 cm. Even assuming some of that bay length is tapered, shallow ends, it's still enough for at least two amraams. Or two 2000 lb class bombs. So basically, they've got close to F-35 requirement, with two large bombs. Only changing the 2 additional amraam requirement into 2 sidewinders requirement. And probably the central bay can't feature more than 3 amraams (3 would have to be staggered as in F-22) whereas F-35 can possibly cram in a total of 6. So that's 6 versus 3+2 short ranged missiles.

But still quite respectable, considering the weight is just 9000 kg! Compare that to F-35A's 13300 kg.
Then there's internal fuel. F-35A carries 8300 kg of fuel, while this design proposal cites only 3945 kg. Granted, F-35 is almost 50% heavier so that amount of fuel would likely be enough for 70% or so of F-35's range. (hard to tell how draggy this design is, and range is also function of payload) Which... is actually still poor. 2000+ km ferry range is nowadays not nearly enough.

Anyway, tradeoffs are quite evident, so the whole design is still somewhat understandable.

But the lower design is just wow. That's a 12.9 m long plane with 8.3 m wingspan. And empty weight of just 5700 kg! That's a whole ton less than a Gripen. Basically the lightest, smallest combat plane the West made since F-5 or something like that. And yet... And yet it carries 2933 kg of fuel internally. Ferry range it should be even better than the above plane, being that light. It might even be closer to F-35 ferry range. Of course, when carrying bombs, combat radii will probably start degrading heavily compared to larger designs like F-35.

Still... Boeing managed to cram in a bomb bay measuring some 3-ish m by 1 meter and two side weapon bays for 1 sidewinder each. It's unclear to me if the main bomb bay can actually go to 3.7 meters required for amraam, but i'd say it can't, looking at the room needed for the intake.

So the whole plane is more of a bomb truck. Which the document actually says, mentioning "sized for interdiction mission". That could explain why no tail surfaces either. The design is more of a striker than a fighter, not requiring serious maneuverability. But still... 5700 kg empty weight for all that range and decently sized weapon bays???

I'd say those designs are actually rather far from what could be achieved. Because if they were possible, then Boeing could have scaled those up to X-32 weight class and could have blown the X-35 out of the water. Which it did not.

Curiously enough, the overall layout of these two designs is still quite similar to what Boeing proposed with their X-32. Intake is a bit different, the wing is a bit different and the end of the plane is unique to each variant. but the same philosophy can be observed. And even the tail differences aren't that drastic. Boeing was unsure what to go with, depending on requirements, when it comes to tail for X-32. More of a fighter required a full tail. Semi striker-fighter was possible with a butterfly tail. And evidently they thought they could get away without a tail for a pure strike plane.

Also - what's up with those short engines? Above design has a 3 m long engine drawn in, and the below design features an engine just 2.6 m long. Apparently lacking afterburner, which is curious since top speed of both is above mach 2. And it looks to me that the afterburner could not even fit in the design below as it is drawn.
 

Desertfox

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Well I think the first step is to define the mission, is this a light fighter like the original F-16? A strike fighter closer to the Jaguar or F-117? Or are we trying to go the Gripen route and do all of the above? By 5th gen are we talking all-aspect stealth? Or datalinks/sensor fusion? Single-mission should be doable, but if we are talking Gripen, then stealth will likely have to be sacrificed.

Stealth is not necessarily costly, you can get 80% of the way there with shaping alone. And if you need ferry range, you can always slap on some external tanks.
 

paralay

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According to statistics, volume bays weapons of a modern fighter is in the range of 8.5-13.5 %. Volume JAS-39 33.3 m3. Volume of bays: 33.3 m3 * 10% = 3.3 m3
If this volume will fit 2 medium-range missiles and 2 short-range missiles, the is stealth fighter
 

LMFS

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About the F-35 and why it may not be a 100% applicable example when estimating the chances of creating a stealth light fighter, I think the STOVL requirement is the key aspect to consider: it forced the engine forward, then the bays had to be moved at the sides of the engine. (BTW, the lift fan is also incompatible with ventral, central bays). This alone increases the cross sectional area, which increases weight and drag and forces to scale up the engine again and so on. The good part of it is the big internal fuel that all that cross-sectional area enables, but apart from it is mainly downsides. A light or light to medium fighter designed from the onset with a more conventional approach could have the engine placed as backwards as possible and the weapon bay in front of the engine, resulting in much better aerodynamics, weight, engine commonality etc. Just to give some rough numbers, the F-16 has IIRC a bit more than 4 sqm frontal section, the F-35, more than 8. My rudimentary model above is slightly above 5 sqm. The need of space for the bay forces a fuselage mid section to be a bit longer than the F-16 and the intake a bit forward, but the sizes remain similar to a great extent.
 

helmutkohl

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I think for a light fighter, a single bay with 2 small ones like Parlay suggests looks feasible. the Saab concept goes that route.

I am also thinking, due to space constraints, as well as the trend in seeing more pure deltas in 6th gen design perhaps a smaller version of this would be good. but single engined and with a different tail. but same wing for more fuel and better supersonic performance?

 

Hood

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Would not a Gripen-sized sixth-gen fighter be a loyal wingman?
 

rooster

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What's the point of a small lightweight stealth fighter these days? Might make sense for small European countries for air defense, launch aircraft, deploy missiles and cruise back to base, but if its expected to patrol long distances, unless there are stealth drop tanks, I don't see the usefulness. Sounds like Sprey's kind of small light aircraft but with LO.
 

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If you put a fuel tank inside the wb, it might have a significant range for certain types of mission. You can even immerge missiles into the fuel (giving that the wb is sealed closed) and instant dry it under its trapeze before firing. I am sure this would be feasible today.

Also as was written numerous time here and elsewhere, small is less smaller today. As part count drops, thanks to better analytical design and composites, a plane can be bigger and keep the same overall cost (buy and sustainement).

There is a market for a smaller 5th Gen that could still fill most of the mission profile bigger 4th Gen do today (16, 18, Su30, M2K, Gripen...).
Up to the Franco Germans, the Swedes or anyone to take it.
 
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kaiserd

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If you put a fuel tank inside the wb, it might have a significant range for certain types of mission. You can even immerge missiles into the fuel (giving that the wb is sealed closed) and instant dry it under its trapeze before firing. I am sure this would be feasible today.

Also as was written numerous time here and elsewhere, small is less smaller today. As part count drops, thanks to better analytical design and composites, a plane can be bigger and keep the same overall cost (buy and sustainement).

There is a market for a smaller 5th Gen that could still fill most of the mission profile bigger 4th Gen do today (16, 18, Su30, M2K, Gripen...).
Up to the Franco Germans, the Swedes or anyone to take it.

"Wet" weapon bays sound like a profoundly bad idea.
And once you get into having a internal weapons bay or bays carrying anything like a meaningful load (we are probably talking 4 medium range missiles at a very base minimum - for many it will be the F-35 sized internal weapon load) then its a case of "larger" aircraft making more sense.
Just as the F-16 effectively "killed" the F-5 sized market (made it into a small niche where that the likes of the Gripen A-D and Korean T-50/FA-50 survived but only sold to limited extents, and which the Gripen E/F grew in size and weight out of) then the F-35 (and to a lesser extent the Typhoon & Rafale) and what comes after will also re-shape (and "re-size") the fighter market.
The domination of the Russian and Chinese (and their clients) fighter markets by Flanker variants (and the development of approx. Flanker sized successors) and the near total eclipsing of Fulcrum variants speaks to how even customers culturally and historically predisposed to light fighters can make a cost/ benefit analysis and move beyond what they used to favor to something different (in this case something larger).
 
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