How small can low observable (stealth) combat aircraft designs get?

[red admiral]

Sure, but I suspect that the minimum acceptable internal weapons load is still going to be 2x 2000lb bombs and 2x BVRAAMs.

At which point you end up with an F-35 sized aircraft.

KF-21's 4 x AMRAAM or 4 x SDB + 2 x AMRAAM is probably more what I'd consider minimum for multi-role.

Or go back to the 60s and just have 2 x AMRAAMs?

 

[Prophet141]

There were accuracy issues with the Vigilante system. Bombs tended to get carried along in the wake and bounce around.

I read in another thread here that the accuracy issues with the tube-magazine weren't necessarily related to any aerodynamic effects, but rather the ballistic computer not being programmed with the tube in mind, leading to inaccurate drops (much less of an issue with a nuclear weapon, of course). And that's assuming that you're using an iron bomb at all (Which is of course preferable on cost grounds) and not a guided weapon.

The tubes extending to the back of the aircraft take up a lot of volume unless you design new weapons with folding fins etc. With multiple tubes then you'll also end up with a lot of rear fuselage volume which is bad for drag.

I think the volume is the key thing; for a small supersonic aircraft with internal weapon bays then you really need to minimise the numbers of weapons carried as this drives max cross sectional area, then length, mass etc.

That's true, this could only work half decently with a two engine design, and at that point you're immediately straying out of the "light" fighter category.

 

[Scott Kenny]

At which point you end up with an F-35 sized aircraft.

That was kinda my point. Most people are going to want large bays which means an F-35 sized aircraft.

KF-21's 4 x AMRAAM or 4 x SDB + 2 x AMRAAM is probably more what I'd consider minimum for multi-role.

I thought the KF21 was packing 6x AMRAAM/Meteor?

But in any case 4x-6x SDB and 2x AMRAAM is definitely the minimum anyone would expect. But I still think anyone wanting a 5th gen fighter would specify bays deep enough to hold 2000lb bombs, for those rare targets that need a Surprise Bunkerbuster.

 

[F-2]

What about something like Lampyidae? Or mako. In this loyal wingman era do you even need a weapons bay?

 

[Scott Kenny]

What about something like Lampyidae? Or mako. In this loyal wingman era do you even need a weapons bay?

Do you want to fly an unarmed aircraft into a shooting match? At the very least I'd require some defensive AAMs to be carried.

Any nuclear state will insist that their nukes be delivered by a manned plane for a long time. That means your minimum bay size is however big the national nuclear weapon is, IIRC the US/NATO B61 is roughly the length of a 2000lb bomb but is only about as wide as a 1000lb bomb.

While it's technically possible to make a nuclear warhead that would fit into the SDB form factor, it'd be limited to about 1kt based on reported yields of 155mm and 203mm cannon warheads. A warhead that shape, like a rugby ball, has two problems: one is that it'd be very inefficient and so need a lot more fissionables to go boom at all, and the second is that you wouldn't be able to pack nukes as tightly as the SDBs get carried. Packing warheads inches apart would cause a nasty neutron flux that would be unhealthy for pilots and ground crew, not to mention causing radiation effects in the electronics of the plane.

B-52 bomb "clips" and rotary racks show roughly how far apart you can safely stow nukes, and it looks to be a good 30" apart. So one bomb per bay regardless of yield, might as well use one that fills more of the bay and has greater flexibility.

And while I'd ordinarily say that any nation that would be interested in the "smallest" possible stealth fighter wouldn't be one of the nuclear states, sadly, the events of 2022 have proven that any given nation really needs nukes if they don't want one of their unfriendly neighbors to try something.

 

[paralay]

Make inconspicuous missiles/bombs and weapon bay will not be needed.
In addition to the weapon bay, the take-off weight is also affected by the mass of electronic equipment. The modern fighter has 4.5 - 5% of the maximum take-off weight.

 

[Shoes31]

Make inconspicuous missiles/bombs and weapon bay will not be needed.

Wouldn't the external ordinance make it hard to keep the jet stealthy, even if those missiles/bombs were shaped with LO qualities? I keep hearing that even if you make the airframe LO, and the missiles LO, and the pylons LO, there are a number of weird reflections and interactions that make it difficult to shape the items so everything is LO when together.

 

[F-2]

Wouldn't the external ordinance make it hard to keep the jet stealthy, even if those missiles/bombs were shaped with LO qualities? I keep hearing that even if you make the airframe LO, and the missiles LO, and the pylons LO, there are a number of weird reflections and interactions that make it difficult to shape the items so everything is LO when together.

Store them conformally and shape the not pylons be shaped. Not too impossible for two self defense missiles.

 

[Kat Tsun]

Wouldn't the external ordinance make it hard to keep the jet stealthy, even if those missiles/bombs were shaped with LO qualities?

HAVE DASH II addressed this in the 1980's: https://www.secretprojects.co.uk/threads/loral-ford-aeronutronics-have-dash-ii.14091/

Might be mass producible these days but cylinders are still cheap.

I keep hearing that even if you make the airframe LO, and the missiles LO, and the pylons LO, there are a number of weird reflections and interactions that make it difficult to shape the items so everything is LO when together.

It would require the external whatever to be designed to fit a particular airframe. This isn't a big deal if you use pods or something.

 

[stealthflanker]

Problem with conformal is it takes away range of weapons that can be mounted there. Also necessitating some large procurements of the weapons and platform. Otherwise one may have a Zummwalt.

 

[quellish]

Wouldn't the external ordinance make it hard to keep the jet stealthy, even if those missiles/bombs were shaped with LO qualities? I keep hearing that even if you make the airframe LO, and the missiles LO, and the pylons LO, there are a number of weird reflections and interactions that make it difficult to shape the items so everything is LO when together.

Yes. This is also why summing the RCS of aircraft components does not work. Also why “Low RCS tanker” doesn’t make sense

 

[stealthflanker]

Wouldn't the external ordinance make it hard to keep the jet stealthy, even if those missiles/bombs were shaped with LO qualities? I keep hearing that even if you make the airframe LO, and the missiles LO, and the pylons LO, there are a number of weird reflections and interactions that make it difficult to shape the items so everything is LO when together.

Yeah. as therre are multiple reflection phenomenon here, where EM Wave bounce from say a missile to other missile. It creates constructive interference where the reflection strengthen eachother thus you ended up with strong and large reflection. External load is just better be avoided whenever possible.

For example this is my estimates on F-16 with Have Glass-like treatment and how external load affect the RCS

https://twitter.com/x/status/1751611023214473318

View: https://x.com/Flankerchan/status/1751611023214473318




One interesting thing however is about "stealthy external weapon bay" Unfortunately currently i only make single concept for my Su-35 model. This is the external bay, the Su-35 with extenal bay have clean wing also with wingtip ECM's.





Then we compare that one with full counter air suite here. This Su-35 model has 4x R-37, 2 R-77-1 and 2 R-73 also a jammer pod. also with an armed F-16, with 4x Amraam and 2x Sidewinders

Su-35 Counter Air	F-16 Counter Air

The result is as follows. SImulated using Ansys HFSS and data processed in MS Excel.



One may notice the apparent benefit of external weapon bay. Still however it would need some optimizations. I havent test the case for wing mounted bay.

 

[F-2]

Yeah. as therre are multiple reflection phenomenon here, where EM Wave bounce from say a missile to other missile. It creates constructive interference where the reflection strengthen eachother thus you ended up with strong and large reflection. External load is just better be avoided whenever possible.

For example this is my estimates on F-16 with Have Glass-like treatment and how external load affect the RCS

https://twitter.com/x/status/1751611023214473318

View: https://x.com/Flankerchan/status/1751611023214473318




One interesting thing however is about "stealthy external weapon bay" Unfortunately currently i only make single concept for my Su-35 model. This is the external bay, the Su-35 with extenal bay have clean wing also with wingtip ECM's.



View attachment 731212

Then we compare that one with full counter air suite here. This Su-35 model has 4x R-37, 2 R-77-1 and 2 R-73 also a jammer pod. also with an armed F-16, with 4x Amraam and 2x Sidewinders

Su-35 Counter Air	F-16 Counter Air
View attachment 731211	View attachment 731216

The result is as follows. SImulated using Ansys HFSS and data processed in MS Excel.

View attachment 731217

One may notice the apparent benefit of external weapon bay. Still however it would need some optimizations. I havent test the case for wing mounted bay.

What do you think a DSI might do to help?

Here is a paper on the J-10B/C DSI.

 

[stealthflanker]

What do you think a DSI might do to help?

Here is a paper on the J-10B/C DSI.

It's more like into the shape which to break down the radar reflection into smaller less harmful lobes, while at the same time expanded the velocity range where the inlet can be efficient. The bump can also serve as additional volume where something can be placed there e.g Fuel.

The signature benefit however is remains to be seen. Might be easier to apply thick absorber composite due to nonmoving parts.

 

[Scott Kenny]

It's more like into the shape which to break down the radar reflection into smaller less harmful lobes, while at the same time expanded the velocity range where the inlet can be efficient. The bump can also serve as additional volume where something can be placed there e.g Fuel.

The signature benefit however is remains to be seen. Might be easier to apply thick absorber composite due to nonmoving parts.

Also has no discontinuities that like to massively increase signature.

 

[stealthflanker]

Also has no discontinuities that like to massively increase signature.

The bump can be considered discontinuities tho, that's why it needs to be treated with absorbers, and maybe that careful shaping to make use of the discontinuities to break down the lobes into less harmful thing.

 

[Scott Kenny]

The bump can be considered discontinuities tho, that's why it needs to be treated with absorbers, and maybe that careful shaping to make use of the discontinuities to break down the lobes into less harmful thing.

Even an untreated bump is better than the discontinuities in an F-15 inlet.

 

[Training_Dummy]

Put an IRST into the DSI!

 

[Manuducati]

Put an IRST into the DSI!

That solution was studied by Northrop with at least one of the ATF early configuration studies (Critical Technology Demonstrator) of 1983.
See Paul Metz "Northrop YF-23 ATF" book p19.

 

[Scott Kenny]

Put an IRST into the DSI!

Yes, if you need the bump there for aerodynamics, find something else that needs a bump for visibility.

IIRC, the Vought engineers used the bottom of the F8, F8U3, and A7 radomes as part of the inlet surface for the same reason.

 

[Justo Miranda]

Hi

Germany had laughably bad stealth aircraft in World War I

During World War I, Germany set out to make the first stealth aircraft and successfully did so, creating multiple invisible planes in 1912 that later saw

www.wearethemighty.com

 

[helmutkohl]

Dunno if anyone here is following the Northrop Grumman Vanguard but you have a flying stealthy looking plane
internal bay for 2 AIM-120s
max take off wait of 10,000 lbs or 5 tons
41 feet long or 12.5 meters
max altitude of 25,000 feet
expected to have a range of 3000 miles
no idea on the speed

so NG was able to build something with the same IWB capacity as some of the estimates here
but in a much lighter package

 

[RJMAZ]

I think it's possible to have a smaller but still useful manned aircraft if you drop the supersonic and turning performance requirements while keeping range and payload relevant. Think more of a stealth A-4 or A-7 than F-16. Such a hypothetical aircraft would obviously require a large development program without bringing anything to the table that a slightly larger but more versatile stealth fighter can't, which kind of explains why we haven't seen a plane in this category since the F-117.

However, like others here have said, the obvious answer to your question is drones.

This post I definitely agree with.

The Model 437 Vanguard is the perfect example of this. It is said to be able to carry two AMRAAM internally and it has a range similar to the F-35. It weighs less than half of a Gripen.

Removing the supersonic requirement easily doubles the range of an aircraft with the similar empty weight. The design can have a longer wing with less wing sweep to dramatically improve lift to drag ratio. The engine can be a high bypass ratio from a private jet.

Removing the turning performance requirement allows a dorsal intake to be used that makes it much easier to fit a big weapons bay in a small design.

The MQ-20 Avenger uses a similar engine to the Model 437 but has much greater wingspan. That translates into a higher MTOW and even greater range. Top speed has now come down to turboprop levels which demonstrates the trade off between speed and range.

The MQ-28 Ghost bat shows a layout that would have higher speed and agility. The intakes are on the sides and the wingspan is less for better transonic drag. A small afterburning engine could allow the MQ-28 to have moderate supersonic performance. The MQ-28 design scaled up ever so slightly to allow a single afterburning Honeywell F124 gives a 6,100lb dry and 9,500lb wet thrust. A manned cockpit with a small AESA radar like the Raytheon PhantomStrike would be good. Three AMRAAM sized weapons in a central bay would be sufficient for air to air. This allows 6 SBD and 2 AMRAAM for strike missions.

It is worth noting that a MK84 2,000lb bomb body without the tail cone is shorter than an AMRAAM and has diameter of the bomb body is the same as the AMRAAM wingspan. It would be possible to developing a bunker buster bomb that fits in the footprint of the AMRAAM. If you look at the GBU-28 4,000lb bunker buster it is very heavy for its size due to the thick steel casing for penetrating bunkers. A 2,000lb bunker buster with a similar heavy steel casing could fit in dimensions of a AMRAAM providing it had pop out fins on the rear and the GPS section is very compact. It is worth making compact weapons for stealth fighters when internal weapons bay volume is so hard to build into the design. Designing a light fighter to have a 5m long weapon bay to fit a 50cm 2,000lb bomb makes no sense. It would be better to simply design a new 2,000lb bomb.

Also tube launched short range missiles would reduce the need for 4+ AMRAAM. Tube launch missiles are very volume efficient that would help in small stealth fighters and small loyal wingman drones. The modifications to the missile wouldn't be that hard. The soft launch feature would be removed so they would fire like an APKWS. If they are mounted on a weapon bay door the rocket exhaust is then outside of the aircraft. Or if the tubes are fixed inside the aircraft then an exhaust duct from the back of the tubes can vent outside of the aircraft. The French Mistral is the most capable tube launched missile weighing just short of 20kg. Being fired at high subsonic speeds would allow it to hit targets 10kms away. Definitely enough to replace the Sidewinder. Stealth versus Stealth engagements might see detection at fairly short range so 10km short range missiles might be very useful.

 

[publiusr]

Once Starshield and other constellations come on line--would stealth drones even need much in the way of avionics, radars, etc? You want combat craft not much more expensive than small private planes. That should shave off some weight.

 

[Joint Soviet Fighter]

Dunno if anyone here is following the Northrop Grumman Vanguard but you have a flying stealthy looking plane
internal bay for 2 AIM-120s
max take off wait of 10,000 lbs or 5 tons
41 feet long or 12.5 meters
max altitude of 25,000 feet
expected to have a range of 3000 miles
no idea on the speed

so NG was able to build something with the same IWB capacity as some of the estimates here
but in a much lighter package

As is the case with China's J-36, how is the pilot supposed to be able to see anything behind them?

Either way, it looks like Heinkel's Volksjager is making a comeback, LOL.

 

[Byeman]

Once Starshield and other constellations come on line--would stealth drones even need much in the way of avionics, radars, etc? You want combat craft not much more expensive than small private planes. That should shave off some weight.

Satellite comm and sensors has no bearing on the matter

 

[Scott Kenny]

Once Starshield and other constellations come on line--would stealth drones even need much in the way of avionics, radars, etc? You want combat craft not much more expensive than small private planes. That should shave off some weight.

You do realize that most "small private jets" are actually more expensive than the CCAs and are on par with F-16s, right?

 

[publiusr]

When I said small private planes I was thinking Pipers.

 

[Ainen]

You do realize that most "small private jets" are actually more expensive than the CCAs and are on par with F-16s, right?

Come to think of it, design challenge to design an off the shelf jet fighter/drone controller as large (and expensive) as WW2 light fighter could be fun.

 

[martinbayer]

Boeing Bird of Prey comes to mind.

 

[Scott Kenny]

Boeing Bird of Prey comes to mind.

Not a combat aircraft. Or did you mean as the drone controller?

 

[martinbayer]

Not a combat aircraft. Or did you mean as the drone controller?

No, I meant as a basic platform that could be weaponized in any way, shape, or form, mindful that its signature would most likely increase.

 

[Scott Kenny]

No, I meant as a basic platform that could be weaponized in any way, shape, or form, mindful that its signature would most likely increase.

It's the size of the car you drive.

 

[martinbayer]

It's the size of the car you drive.

2006ish Corolla.