Design Challenge: Lightweight Multirole Fighter (LMF)

[H_K]

@VTOLicious Have you looked at Boeing’s Model 24F and MRF-24X designs? They seem like a decent starting point, though the first is a little big (9t empty weight) and the second almost too small (5.5t empty weight), so some scaling may be required.

Discussed in the thread you mentioned in the OP and also here:

'Boeing Fighter Studies, 1970s to ATF'
https://www.secretprojects.co.uk/threads/boeing-fighter-studies-1970s-to-atf.398/post-166555

'Boeing MRF-24X Tailless Fighter'
https://www.secretprojects.co.uk/threads/boeing-mrf-24x-tailless-fighter.528/

 

[VTOLicious]

Thanks for writing this thread, and capturing your ideas.

Have you thought about how the weapon bay will be loaded for this configuration? I would think it difficult to not clash with the main gear because the doors on this style of bay sweep through a large angle. Your main gear basically has to swing out sideways before rotating downwards which is challenging for both the mechanism and clearances to other items e.g. the wing. Undercarriage is annoying.

I think you're overconstraining yourself in your problem. I'd focus on mass as the target rather than physical size. Empty mass is most closely related to cost. Any physical size constraints are driven by infrastructure e.g. hangars but most of these are really quite big nowadays

The clearance of main gear legs and bay doors are indeed an area of concern. But I think it's not a showstopper... For instance, Gripen's landing gear is hinged in a way that the wheel rotates to the desired position in the compartment. See the attached video...

I focus on physical size because I cannot design mass in CAD. Once I've established a CAD model I hope to be able to estimate mass.

View: https://youtu.be/zvuzkEfky-g

I think the problem its not how the landing gear goes down or up. But looking at your sketch when the plane on the ground, the landing gear is in bay door's way. So the bay door cannot fully open(?) and make payload installation become harder to do.

No worries, sketches are not up to scale. I'll account for that.

 

[VTOLicious]

@VTOLicious Have you looked at Boeing’s Model 24F and MRF-24X designs? They seem like a decent starting point, though the first is a little big (9t empty weight) and the second almost too small (5.5t empty weight), so some scaling may be required.

Discussed in the thread you mentioned in the OP and also here:

'Boeing Fighter Studies, 1970s to ATF'
https://www.secretprojects.co.uk/threads/boeing-fighter-studies-1970s-to-atf.398/post-166555

'Boeing MRF-24X Tailless Fighter'
https://www.secretprojects.co.uk/threads/boeing-mrf-24x-tailless-fighter.528/

Those two are interesting indeed. Especially the latter. I've never seen a good enough copy to read the numbers... 5700 kg empty, that's 1000 kg less than the legacy Gripen! And it was supposed to have more internal fuel as well (2900 kg)!
Any idea what's that PW-1442 engine?
And what is the length / wingspan of the 24X?

From the front it looks quite fat btw.

 

[Sundog]

For weapons bays, you may consider what Sukhoi used for the short range AAM on the Su-57. It's basically using conformal carriage with a cover fairing. What I don't know is if the inside of the door is the launcher, which would make sense, or if there is an ejector rail. So think conformal carriage with a cover. This doesn't add much drag and doesn't add too many cutouts to the fuselage to minimize structural weight. I would have one in each lower fuselage side, sized for the largest ASM weapon you expect to carry while being stealthy and one under the wing, near the root, but outside where ever the MLG is located for an Medium Range AAM. Outside of that I would have one for a Short Range AAM, most likely an ASRAAM, due to it's small frame and fin span.

 

[VTOLicious]

For weapons bays, you may consider what Sukhoi used for the short range AAM on the Su-57. It's basically using conformal carriage with a cover fairing. What I don't know is if the inside of the door is the launcher, which would make sense, or if there is an ejector rail. So think conformal carriage with a cover. This doesn't add much drag and doesn't add too many cutouts to the fuselage to minimize structural weight. I would have one in each lower fuselage side, sized for the largest ASM weapon you expect to carry while being stealthy and one under the wing, near the root, but outside where ever the MLG is located for an Medium Range AAM. Outside of that I would have one for a Short Range AAM, most likely an ASRAAM, due to it's small frame and fin span.

I though about something like that, but only for short range AAM's in addition to the main bay. I also considered if pods for single AAM's at the wing tips would be a viable option.
...I think S-57 uses kind of a ejector rail like the F-22.

 

[VTOLicious]

After some further research I stumbled across EADS Mako. Intended as a trainer and little bit too small, but otherwise an almost perfect example of a lightweight fighter with stealth features and powered by an F404 engine!

 

[BLACK_MAMBA]

After some further research I stumbled across EADS Mako. Intended as a trainer and little bit too small, but otherwise an almost perfect example of a lightweight fighter with stealth features and powered by an F404 engine!

View attachment 670617

What is the wing configuration you are going for? When pondering a aircraft to meet these same type of requirements I've always been drawn to a pure delta design to maximise the wing fuel tank volume while keeping the fuselage relatively small. Only problem with a delta is the edge alignment criteria. The proposed Lockheed X-44 Manta with a Raptor as base is a good starting point - only with twin canted verticals to suit the requirements of the concept persued in this thread.

 

[zen]

Everyone forgets the landing gear in a first draft

Just like the heads in ship design...

And as for the plumbing.......ugh!

 

[zen]

So, where to start?

Ok so this is the key question and your answer should be "what do I need this airplane to do?"

Define what the solution needs to be, not what is 'cool' or what fits.

What radius of action with what weapon?
What level of agility with what weapon?
What performance of sensors?
What level of LO needed and when?

What are the requirements?
What performance criteria?
What is the enemy capable of?

 

[VTOLicious]

@VTOLicious Have you looked at Boeing’s Model 24F and MRF-24X designs? They seem like a decent starting point, though the first is a little big (9t empty weight) and the second almost too small (5.5t empty weight), so some scaling may be required.

Discussed in the thread you mentioned in the OP and also here:

'Boeing Fighter Studies, 1970s to ATF'
https://www.secretprojects.co.uk/threads/boeing-fighter-studies-1970s-to-atf.398/post-166555

'Boeing MRF-24X Tailless Fighter'
https://www.secretprojects.co.uk/threads/boeing-mrf-24x-tailless-fighter.528/

Those two are interesting indeed. Especially the latter. I've never seen a good enough copy to read the numbers... 5700 kg empty, that's 1000 kg less than the legacy Gripen! And it was supposed to have more internal fuel as well (2900 kg)!
Any idea what's that PW-1442 engine?
And what is the length / wingspan of the 24X?

From the front it looks quite fat btw.

Meanwhile...
Based on the size of the guy in the side view and the wing reference area given in the specs (301 ft² = 28 m²) I played around a with the scale of the drawing and was able to determine the dimensions of the tailless version (X). It is indeed a very compact design:

Length: 12,5 m (!)
Wingspan: 8m

Based on the contour of the engine visible in the side view I was able to judge the diameter of the engine to approximately 0,8 m. This is equivalent to the diameter of an F404 / F414. The distance from the rear end of the aircraft to the engine face is 4,4 m.

I've measured the length of the weapons bay doors with 3 m. As suggested by the specs, it is not intended to carry medium / long range AAM's.

 

[VTOLicious]

So, where to start?

Ok so this is the key question and your answer should be "what do I need this airplane to do?"

Define what the solution needs to be, not what is 'cool' or what fits.

What radius of action with what weapon?
What level of agility with what weapon?
What performance of sensors?
What level of LO needed and when?

What are the requirements?
What performance criteria?
What is the enemy capable of?

JAS 39 Gripen is the reference. Whereas the legacy Gripen is the baseline and the new generation is the threshold. That's it, that's all.
Feel free to translate that into specific requirements / specifications.

 

[H_K]

Ok so this is the key question and your answer should be "what do I need this airplane to do?"

1) Air defense (CAP or intercept).
A typical scenario might involve 2 defenders facing 4-6 attacking aircraft, so carriage for 6 AAMs per fighter probably necessary. I would put the emphasis on long range shots and BVR more than 9g maneuverability.

2) Air interdiction / SEAD
A typical scenario with 6 attackers and 20+ aim points means at least 4 bombs per aircraft (e.g. SDBs). Plus 2 AAMs each for self defence.

3) Strike
One aim point per attack aircraft means 1 large bomb/glider weapon in the 2,000lb class. Not sure if this should be internally carried or instead rely on carrying cruise missiles externally?

Range:
I wouldn’t make this a priority and instead would rely on traditional solutions for long range missions (drop tanks + buddy refueling).

 

[VTOLicious]

After some further research I stumbled across EADS Mako. Intended as a trainer and little bit too small, but otherwise an almost perfect example of a lightweight fighter with stealth features and powered by an F404 engine!

View attachment 670617

What is the wing configuration you are going for? When pondering a aircraft to meet these same type of requirements I've always been drawn to a pure delta design to maximise the wing fuel tank volume while keeping the fuselage relatively small. Only problem with a delta is the edge alignment criteria. The proposed Lockheed X-44 Manta with a Raptor as base is a good starting point - only with twin canted verticals to suit the requirements of the concept persued in this thread.

I think the MRF-24X posted above perfectly fits your description

 

[zen]

Ok so this is the key question and your answer should be "what do I need this airplane to do?"

1) Air defense (CAP or intercept).
A typical scenario might involve 2 defenders facing 4-6 attacking aircraft, so carriage for 6 AAMs per fighter probably necessary. I would put the emphasis on long range shots and BVR more than 9g maneuverability.

2) Air interdiction / SEAD
A typical scenario with 6 attackers and 20+ aim points means at least 4 bombs per aircraft (e.g. SDBs). Plus 2 AAMs each for self defence.

3) Strike
One aim point per attack aircraft means 1 large bomb/glider weapon in the 2,000lb class. Not sure if this should be internally carried or instead rely on carrying cruise missiles externally?

Range:
I wouldn’t make this a priority and instead would rely on traditional solutions for long range missions (drop tanks + buddy refueling).

Let's refine that.
1. Air Defence Missions
1a. QRA Inspection/Interception
1b. CAP endurance at what distance?
1c. Air Superiority (strictly this tips over to Air Offensive Missions)

2 Interdiction
2a. SEAD/DEAD
2b. Interdiction of mobile ground assets.

3. Strike
3a fixed infrastructure strikes
3b Anti-ship strike

Radius of Action (RoA) on internal
Dictated by 1a, and 2b, where rapid reaction and turnaround are key. 2a dictates high LO requirements where drop tanks and external stores are prohibited.
Assume a 400nm radius of action hi-lo-hi with ARM/PGM for SEAD/DEAD.
Extended SEAD accompanying Strike is more reliant on EW as well. Two seater may be needed here.
Assume 100nm for LO optimised 2b mission. As mobile assets may be attended by SPAAMS and SPAAGs.

Permissive environmental missions permit external stores.

RoA Strike would be with drop tanks and stand off cruise missile type weapons. Accompanied by Top Cover and SEAD. Depending.

 

[H_K]

Based on the size of the guy in the side view and the wing reference area given in the specs (301 ft² = 28 m²) I played around a with the scale of the drawing and was able to determine the dimensions of the tailless version (X). It is indeed a very compact design:

Length: 12,5 m (!)
Wingspan: 8m

I tried scaling based on the length of the AIM-9X (3.02m) and GBU-32 (3.04m)... got slightly larger results for the MRF-24X:
Length: 13.2m
Wingspan: 8.4m

 

[Dynoman]

You may want to consider moving the inlet above the airframe, or a dorsal mounted inlet, with the appropriate engine match. There are a number of benefits for the design. The internal weapons bay volume could increase; its RCS stealth performance could improve from ground-based aspect angles; and the reduction of FOD issues could be reduced. I've read that the leading edge extension vortices created in conjunction with the dorsal inlet can help energize the flow into the inlet at high angles of attack, reducing turbulent flow into the duct.

 

[Dynoman]

The only concerns from what I understand with a dorsal mounted inlet is in the realm of supersonic maneuvering. However, most engagements occur at high subsonic or transonic speeds. If necessary, a dorsal mounted inlet design could have dual-mode intake louvers (similar to the MiG-29, which was used primarily for soft-field operations), but on the ventral side of the aircraft, opening in high-alpha states. The geometry of the louvered inlet could be smaller and placed where the current MRF-24X inlet is located. The geometry of this dual-mode inlet could follow a similar, but 'more angled' path to the primary inlet duct. It may even be bifurcated around the cockpit or located in the LERX.

 

[Sundog]

The only concerns from what I understand with a dorsal mounted inlet is in the realm of supersonic maneuvering. However, most engagements occur at high subsonic or transonic speeds. If necessary, a dorsal mounted inlet design could have dual-mode intake louvers (similar to the MiG-29, which was used primarily for soft-field operations), but on the ventral side of the aircraft, opening in high-alpha states. The geometry of the louvered inlet could be smaller and placed where the current MRF-24X inlet is located. The geometry of this dual-mode inlet could follow a similar, but 'more angled' path to the primary inlet duct. It may even be bifurcated around the cockpit or located in the LERX.

Actually, one of the biggest problems with dorsal inlets was low speed and high alpha with yaw. The inlet could ingest the vortex causing massive flow distortion at the inlet leading to a possible compressor stall. It looks like designers are getting around it now by placing the dorsal inlets far enough forward that even with yaw the vortex will only hit the outside side of the inlet.

 

[Sundog]

Some more references for you;

https://www.secretprojects.co.uk/threads/northrop-pre-atf-and-atf-studies.185/page-3#post-457426

https://www.secretprojects.co.uk/threads/northrop-post-atf-concepts.1748/#post-14714

The wing shown on the STOVL variant was also on a version of their MRF (See Tony Chong's Flying Wings and Radical Things book). It generates a lot of pitch authority.

 

[VTOLicious]

Based on the size of the guy in the side view and the wing reference area given in the specs (301 ft² = 28 m²) I played around a with the scale of the drawing and was able to determine the dimensions of the tailless version (X). It is indeed a very compact design:

Length: 12,5 m (!)
Wingspan: 8m

I tried scaling based on the length of the AIM-9X (3.02m) and GBU-32 (3.04m)... got slightly larger results for the MRF-24X:
Length: 13.2m
Wingspan: 8.4m

Hmm, I assumed if the wing reference area is accurate the rest should be as well.

 

[riggerrob]

Thanks for writing this thread, and capturing your ideas.

Have you thought about how the weapon bay will be loaded for this configuration? I would think it difficult to not clash with the main gear because the doors on this style of bay sweep through a large angle. Your main gear basically has to swing out sideways before rotating downwards which is challenging for both the mechanism and clearances to other items e.g. the wing. Undercarriage is annoying.

I think you're overconstraining yourself in your problem. I'd focus on mass as the target rather than physical size. Empty mass is most closely related to cost. Any physical size constraints are driven by infrastructure e.g. hangars but most of these are really quite big nowadays

The clearance of main gear legs and bay doors are indeed an area of concern. But I think it's not a showstopper... For instance, Gripen's landing gear is hinged in a way that the wheel rotates to the desired position in the compartment. See the attached video...

I focus on physical size because I cannot design mass in CAD. Once I've established a CAD model I hope to be able to estimate mass.

View: https://youtu.be/zvuzkEfky-g

I think the problem its not how the landing gear goes down or up. But looking at your sketch when the plane on the ground, the landing gear is in bay door's way. So the bay door cannot fully open(?) and make payload installation become harder to do.

Yes, it is common for wheels to both fold and twist (translate) during retraction. See CF-104 and CF-18A.

Is it practical to mount AIM-9 Sidewinders on the inside of main wheel doors?
How long do you need to delay rocket motor ignition to avoid setting the rubber tire on fire?

 

[helmutkohl]

After some further research I stumbled across EADS Mako. Intended as a trainer and little bit too small, but otherwise an almost perfect example of a lightweight fighter with stealth features and powered by an F404 engine!

View attachment 670617

what do you think of the X-2 as a base?

its actually built and flew

at 14.2m long, 9.1m wingspan, 4.5m height
and 9700kg empty and two 49kn engines

heavier (but shorter) than the Gripen, with slightly more engine thrust but probably worse thrust to weight ratio
certainly larger than the Mako

it doesnt look like there's enough space for a bay, but what if the engine intakes, which currently droop upwards, was lowered to give more space on the bottom fuselage? perhaps a bay could then be fitted?

 

[VTOLicious]

After some further research I stumbled across EADS Mako. Intended as a trainer and little bit too small, but otherwise an almost perfect example of a lightweight fighter with stealth features and powered by an F404 engine!

View attachment 670617

what do you think of the X-2 as a base?

its actually built and flew

at 14.2m long, 9.1m wingspan, 4.5m height
and 9700kg empty and two 49kn engines

heavier (but shorter) than the Gripen, with slightly more engine thrust but probably worse thrust to weight ratio
certainly larger than the Mako

it doesnt look like there's enough space for a bay, but what if the engine intakes, which currently droop upwards, was lowered to give more space on the bottom fuselage? perhaps a bay could then be fitted?

X-2 would be a good starting point as well. But I think Mako is the better fit.
First of all it is single engine (F404) and the fuselage layout favours the weapons bay layout I already chose. I wanna keep the fuselage compact to enable a small cross sectional area. The X-2, viewed from the front, looks rather chunky.

 

[VTOLicious]

The air intake design of X-2 may be worth to consider. As pointed out by @Trident a diverterless supersonic intake (DSI) most likely favours a trapezoid shaped intake (approximating an arc). I'm also a little worried that the design of a DSI is beyond my CAD skills

 

[paralay]

The relative volume of the weapons bay of a modern fighter is 9-13% of the volume of the aircraft. Thus, the dimensions of the missiles / bay determine the volume of the aircraft and its mass. How many and which missiles do you want to place in the weapons bay?

 

[VTOLicious]

The relative volume of the weapons bay of a modern fighter is 9-13% of the volume of the aircraft. Thus, the dimensions of the missiles / bay determine the volume of the aircraft and its mass. How many and which missiles do you want to place in the weapons bay?

Interstingly the layout in your sketch is almost exactly what I propose! Nice sketch btw! Kind of a "stealthified" Saab Draken
In regards of weapons bay size refer to my earlier posts, e.g.:
https://www.secretprojects.co.uk/th...eight-multirole-fighter-lmf.38539/post-506704
https://www.secretprojects.co.uk/th...eight-multirole-fighter-lmf.38539/post-506739
https://www.secretprojects.co.uk/th...eight-multirole-fighter-lmf.38539/post-506796

Please note: The attached sketch is a schematic drawing and not up to scale.

 

[helmutkohl]

what if rather one large bay for a light fighter

what about two smaller ones like on UCAVs?

 

[paralay]

Interstingly the layout in your sketch is almost exactly what I propose! Nice sketch btw! Kind of a "stealthified" Saab Draken

Our models match because they are based on the same prototype JAS-39

 

[paralay]

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.

 

[VTOLicious]

Ok so this is the key question and your answer should be "what do I need this airplane to do?"

1) Air defense (CAP or intercept).
A typical scenario might involve 2 defenders facing 4-6 attacking aircraft, so carriage for 6 AAMs per fighter probably necessary. I would put the emphasis on long range shots and BVR more than 9g maneuverability.

2) Air interdiction / SEAD
A typical scenario with 6 attackers and 20+ aim points means at least 4 bombs per aircraft (e.g. SDBs). Plus 2 AAMs each for self defence.

3) Strike
One aim point per attack aircraft means 1 large bomb/glider weapon in the 2,000lb class. Not sure if this should be internally carried or instead rely on carrying cruise missiles externally?

Range:
I wouldn’t make this a priority and instead would rely on traditional solutions for long range missions (drop tanks + buddy refueling).

Let's refine that.
1. Air Defence Missions
1a. QRA Inspection/Interception
1b. CAP endurance at what distance?
1c. Air Superiority (strictly this tips over to Air Offensive Missions)

2 Interdiction
2a. SEAD/DEAD
2b. Interdiction of mobile ground assets.

3. Strike
3a fixed infrastructure strikes
3b Anti-ship strike

Radius of Action (RoA) on internal
Dictated by 1a, and 2b, where rapid reaction and turnaround are key. 2a dictates high LO requirements where drop tanks and external stores are prohibited.
Assume a 400nm radius of action hi-lo-hi with ARM/PGM for SEAD/DEAD.
Extended SEAD accompanying Strike is more reliant on EW as well. Two seater may be needed here.
Assume 100nm for LO optimised 2b mission. As mobile assets may be attended by SPAAMS and SPAAGs.

Permissive environmental missions permit external stores.

RoA Strike would be with drop tanks and stand off cruise missile type weapons. Accompanied by Top Cover and SEAD. Depending.

@zen / @H_K :

What about adding "loyal wingman" to the ConOps? E.g. one manned LMF, accompanied by two unmanned LMF's. One acting as a ordnance carrier / attack platform and the other one as a tanker (weapons bay contains a fuel tank and refuelling equipment). And all three acting together as a combat system? (EW, ISR, etc...)

 

[riggerrob]

Ok so this is the key question and your answer should be "what do I need this airplane to do?"

1) Air defense (CAP or intercept).
A typical scenario might involve 2 defenders facing 4-6 attacking aircraft, so carriage for 6 AAMs per fighter probably necessary. I would put the emphasis on long range shots and BVR more than 9g maneuverability.

2) Air interdiction / SEAD
A typical scenario with 6 attackers and 20+ aim points means at least 4 bombs per aircraft (e.g. SDBs). Plus 2 AAMs each for self defence.

3) Strike
One aim point per attack aircraft means 1 large bomb/glider weapon in the 2,000lb class. Not sure if this should be internally carried or instead rely on carrying cruise missiles externally?

Range:
I wouldn’t make this a priority and instead would rely on traditional solutions for long range missions (drop tanks + buddy refueling).

Let's refine that.
1. Air Defence Missions
1a. QRA Inspection/Interception
1b. CAP endurance at what distance?
1c. Air Superiority (strictly this tips over to Air Offensive Missions)

2 Interdiction
2a. SEAD/DEAD
2b. Interdiction of mobile ground assets.

3. Strike
3a fixed infrastructure strikes
3b Anti-ship strike

Radius of Action (RoA) on internal
Dictated by 1a, and 2b, where rapid reaction and turnaround are key. 2a dictates high LO requirements where drop tanks and external stores are prohibited.
Assume a 400nm radius of action hi-lo-hi with ARM/PGM for SEAD/DEAD.
Extended SEAD accompanying Strike is more reliant on EW as well. Two seater may be needed here.
Assume 100nm for LO optimised 2b mission. As mobile assets may be attended by SPAAMS and SPAAGs.

Permissive environmental missions permit external stores.

RoA Strike would be with drop tanks and stand off cruise missile type weapons. Accompanied by Top Cover and SEAD. Depending.

@zen / @H_K :

What about adding "loyal wingman" to the ConOps? E.g. one manned LMF, accompanied by two unmanned LMF's. One acting as a ordnance carrier / attack platform and the other one as a tanker (weapons bay contains a fuel tank and refuelling equipment). And all three acting together as a combat system? (EW, ISR, etc...)

Smaller air forces would probably use the same basic airframe for all three roles. The only question is whether or not the manufacturing nation is willing to sell them the software and software updates.

For comparison, rumor has it that the Russian Air Force only wants to buy Sukhoi LTS Checkmate un-manned versions, while they will sell simplified, manned versions to Third World nations.

 

[VTOLicious]

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.

I'll stick to the single bay (with four AIM-120, or the other ordnance-options, as advertised by Boeing).

However, I consider detachable/ interchangeable wingtip pods in addition to the main bay.
Such a pod may contain a short range AAM, a towed decoy, EW or ISR-equipment, or may be used as additional fuel tank. This would provide maximum versatility.

I don't know to which extent those pods would compromise stealth characteristics and aerodynamic performance. One way or the other aircraft design always involves compromises*.

*we have already seen the F-35 fitted with a pod for a drag chute.

 

[VTOLicious]

Btw, wingtip weapons pods are shown in "Flying Wings and Radical Things" page 256

 

[paralay]

I'll stick to the single bay (with four AIM-120, or the other ordnance-options, as advertised by Boeing)

Okay, your compartment: 0.6 m2 * 4.27 m = 2.56 m3 : 0.13 ~ 0.09 = 19700 ~ 28500 kg (the maximum take-off weight)
A light fighter with such a compartment will not work, it is an "Average" fighter. Or a bomber without the possibility of active maneuvering

 

[VTOLicious]

I'll stick to the single bay (with four AIM-120, or the other ordnance-options, as advertised by Boeing)

Okay, your compartment: 0.6 m2 * 4.27 m = 2.56 m3 : 0.9 or 0.13 = 19700 - 28500 kg (the maximum take-off weight)
A light fighter with such a compartment will not work, it is an "Average" fighter. Or a bomber without the possibility of active maneuvering

Ok, that's an interesting subject!
It is actually my goal to create a 3D model in order to get the real volume of the aircraft.

If I understand you correctly the rule of thumb to estimate maximum take-off weight is multiplying total aircraft volume by 1000 (1000 kg/m³).

Can you provide the reference volume of representative combat aircraft? And the source of those numbers would be of importance as well.

 

[red admiral]

If I understand you correctly the rule of thumb to estimate maximum take-off weight is multiplying total aircraft volume by 1000 (1000 kg/m³).

I don't think anyone else agrees with that method. The large majority of the volume is air not heavy stuff.

If you're using a fixed engine then just take the typical MTOM thrust/weight figures. For a single F414 you're looking at 15-16,000kg i guess from your other thoughts.

Once you've drawn out to scale you could use some of the parametric mass estimation methods e.g. Raymer to estimate empty mass. Mostly characteristics like length and cross sectional area in these equations.

 

[paralay]

To evaluate the characteristics of aircraft, I use not a "real" volume, but a certain approximate value. It is derived from three projections. This is not entirely accurate, but it allows you to do without building a 3-D model.
Spreadsheet here: http://www.paralay.ru/paralay_tab.xls
in the upper left corner (A2), you can switch to English
the formula in line 25

 

[VTOLicious]

To evaluate the characteristics of aircraft, I use not a "real" volume, but a certain approximate value. It is derived from three projections. This is not entirely accurate, but it allows you to do without building a 3-D model.
Spreadsheet here: http://www.paralay.ru/paralay_tab.xls
in the upper left corner (A2), you can switch to English
the formula in line 25

Thanks for providing the spreadsheet. I didn't had time to look at it yet.

Why 1000 kg / m³?

 

[paralay]

statistics is an exact science

 

[red admiral]

Correlation is not causation