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Ok, so this is a slightly complex question, that I think will get a complex answer - but here goes.

The Repulsor Execution has two main guns - each off set of the centreline of the turret, quite unlike modern tanks. Now, I know why this has been done - two guns is rule of cool, and GW have no idea about vehicle design really. Fair enough. They are just a mini company. However, all MBT's that I can call to mind have their main armament mounted centreline. This is usually so that the breech can depress through the turret ring and provide greater elevation. However, if we assume the Repulsor had some incredibly strong and high torque motors to counteract weight, and mounted the main armament by the breech (Thus not needing to depress through the turret ring), we get to the crux of my question:

How would being mounted offset affect the ability to track and engage targets?

There are several multigun designs that utilise harmonisation to hit a single point with all guns, but this creates dead spots and misses at ranges above and below the intended range (Think WW2 Fighter aircraft). But with only a single gun, so long as the targeting equipment is on the bore axis, would it be as accurate and simple to operate as a centreline mounted gun?

I'm trying to bend my mind around the concept, so any thoughts would be appreciated.

Lots of real tanks have had offset weapons. The Grant/Lee and all those wacky british tanks detroyer/assault guns come to mind. Although I guess those are all hull mounts. World of tanks has various examples but I'm not sure how many were actually produced I guess.

It's only a problem if you try and hit the same target with all the weapons firing at the same time. Although the game mechanics has all the weapons firing at the same time, it represents the tank firing over a period of time, so one weapon could fire a burst the n the turret turns slightly to bring the other weapons to bear in turn.

Some old soviet light tanks were even built with the turret being off-center (I think it was because the engine took a lot of room on one side of the hull). And even if modern tanks have their main gun centered in the turret, the coaxial machine gun is usually a bit to the side.

Normally, you wouldn't fire both guns at the same time and at the same target anyway: the main gun is for vehicles/fortifications, the machine gun is for infantry.

 Warpig1815 wrote:
How would being mounted offset affect the ability to track and engage targets?

It wouldn't.

Its what sophisticated cogitators, aka tracking computers, are for and current modern systems are pretty good at tracking moving targets, you just have to account for gun position and trajectory in the calculations.

Even if it represented a problem with 21st century technology, you should expect some advancements over a few millenia.

And if that doesn't suit, remember, its not real!

Flinty wrote:Lots of real tanks have had offset weapons. The Grant/Lee and all those wacky british tanks detroyer/assault guns come to mind. Although I guess those are all hull mounts. World of tanks has various examples but I'm not sure how many were actually produced I guess.

It's only a problem if you try and hit the same target with all the weapons firing at the same time. Although the game mechanics has all the weapons firing at the same time, it represents the tank firing over a period of time, so one weapon could fire a burst the n the turret turns slightly to bring the other weapons to bear in turn.

Aye. As you say, the mid/early War designs had offset weapons, but those weapons were mounted centre-line in their respective turrets. The issue that is confounding me is if you had a gun mounted off the centre line, then it rotates not around a single point, but around the circumference of a circle. And I don't know whether that makes it more difficult to target with. I suspect not, but I thought I'd ask to see if anyone knew of any difficulties.

Tiennos wrote:Some old soviet light tanks were even built with the turret being off-center (I think it was because the engine took a lot of room on one side of the hull). And even if modern tanks have their main gun centered in the turret, the coaxial machine gun is usually a bit to the side.

Normally, you wouldn't fire both guns at the same time and at the same target anyway: the main gun is for vehicles/fortifications, the machine gun is for infantry.

Aye, and obviously, coaxial's work. But they're often mounted far closer to the main gun, and nearly centreline.

Fictional wrote:

 Warpig1815 wrote:
How would being mounted offset affect the ability to track and engage targets?

It wouldn't.

Its what sophisticated cogitators, aka tracking computers, are for and current modern systems are pretty good at tracking moving targets, you just have to account for gun position and trajectory in the calculations.

Even if it represented a problem with 21st century technology, you should expect some advancements over a few millenia.

And if that doesn't suit, remember, its not real!

Sure, targeting computers could probably assist, and have done for MBTs, but I'm more concerned with any physical limitations. Just saying 'It wouldn't because computers' kind of glosses over the limitations of geometry, physics and programming. They are not a wonder cure for everything, great as they are. Trajectory isn't an issue, because the vertical isn't affected - it's the gun position, and it's axis of rotation that I'm confused over.

Also, I shouldn't really need to say this, but I will - I know it's not real. I'm just one of those people who like 'SCIENCE Fiction', not 'Science FICTION'. Much as I love all the shenanigans and I appreciate 40k has less science and more fiction, (Being a queer blend of fantasy in there too), my enjoyment of Sci-Fi is when you have technologies or vehicles that almost might be in our grasp now. Because I find technology fascinating. In the case of the Repulsor, I accept grav-plates as being beyond our grasp just now, but I'd like all my other bits of tech (In this case gun placement) to be in the realms of reality. It's just personal preference friend. Just because it isn't real, doesn't mean it can't conform to what bits we know are real.

Also - I'm an avid converter of models. So this is all in aid of a conversion. That said, I am acutely aware that I may be vastly overthinking this, all in the name of a conversion. I didn't want to reposition the gun if I could help it, so maybe it's better to apply handwavium.

The panzer 1 and 2s had pretty offset weapons in their turrets. They seemed tondonok, butvtheyvwere more armed with mgs and auto cannon rather than big main guns. According to.world.of.tanks the ELC EVEN 90 had a very offset gun but that was never mass produced for adopted.

Good news is lasers don't have recoil and gatling guns have very minimal recoil compared to an artillery cannon.

Flinty wrote:The panzer 1 and 2s had pretty offset weapons in their turrets. They seemed tondonok, butvtheyvwere more armed with mgs and auto cannon rather than big main guns. According to.world.of.tanks the ELC EVEN 90 had a very offset gun but that was never mass produced for adopted.

Ahhhhh. I forgot the Pz. 2. I looked at the 1 last night, but dismissed it because the guns were harmonised to fire at a set range together. But the 2 had separate ordnance. Hmmm - that kind of set's my mind at ease a little, because the Pz 2 had no significant targeting problems. Which saves me converting the Repulsor unnecessarily. Thanks for that Flinty. It just takes someone else to look at things in a different light

Xenomancers wrote:Good news is lasers don't have recoil and gatling guns have very minimal recoil compared to an artillery cannon.

Aye, but recoil was not the issue here, rather my overthinking in how the rotation of an off centre gun would affect targeting. But as Flinty points out, it has been done, and successfully enough. Thanks for the input though

Yeah - the gyro on turrets are so strong now that weight bearing is not an issue at all. Plus it could just be counter balanced by an opposing weight source to the diagonal anyways.

Teehee... but offset solid round cannon on a grav platform... I hope the crew likes.spinning around In circles

 Warpig1815 wrote:
Aye, but recoil was not the issue here, rather my overthinking in how the rotation of an off centre gun would affect targeting. But as Flinty points out, it has been done, and successfully enough. Thanks for the input though

But that's the thing, MBT weapons are mostly mounted centreline because they need to cope with massive recoil. With main armament of primaris tanks being lasers/plasma that's a complete non-issue and they can be mounted whatever way you want.

As for tracking, just look at this:


This vehicle requires some of the most precise, accurate targeting on modern battlefield yet you can't offset the guns more even if you tried...

Irbis wrote:

 Warpig1815 wrote:
Aye, but recoil was not the issue here, rather my overthinking in how the rotation of an off centre gun would affect targeting. But as Flinty points out, it has been done, and successfully enough. Thanks for the input though

But that's the thing, MBT weapons are mostly mounted centreline because they need to cope with massive recoil. With main armament of primaris tanks being lasers/plasma that's a complete non-issue and they can be mounted whatever way you want.

As for tracking, just look at this:

Spoiler:

This vehicle requires some of the most precise, accurate targeting on modern battlefield yet you can't offset the guns more even if you tried...

Hmm. Recoil is an issue - but not the full story. The main reasons are 3 fold:

1. Elevation. Guns are BIG. The barrel is almost matched in length by the breech block. When elevating the gun, the breech must depress through the turret ring in order to get a higher elevation. If you mount offset, you aren't at the maximum diameter of the turret ring, so your breech ends up being stopped by the edge of the ring.

2. Attempting to circumvent the above problem by mounting gun's pivot point on the extremity of the breech hits another problem - the weight. Main armaments weigh at least a ton and a half. To have all that pivoting on the extreme of the breech would be simply to stressful by modern technology standards. So, the breech is mounted further back to provide a counterbalance to the weight of the barrel.

3. Even if you could find a super strong motor to survive the stress of the above solution - it's not a great idea to have your breech, and it's fairly sensitive firing mechanisms, outside your turret. If it was hit by a round, you risk either a premature detonation of the round in the breech, or damage to the firing mechanism. In which case you become a glorified taxi. Armouring the breech with a mantlet isn't a practical solution, as it just adds more weight, requiring a bigger engine, which needs more armour to cover it, which adds more weight, and on and on and on we go down the rabbit hole of tank design.

As for that design - the concept isn't the same. It's a self propelled AA unit, and each gun is harmonised so that the rounds converge at a set range. Now whilst that range can be increased or decreased be a computer, you will get to a point where they cannot be harmonised close enough in range. And at that point you end up with a dead zone, where neither weapon can engage without turret traverse. Which, in an MBT, is less than ideal if it's engaged in an urban area (Although, doctrine would suggest not sending an MBT into a built up area. But it happens).

 Flinty wrote:
Teehee... but offset solid round cannon on a grav platform... I hope the crew likes.spinning around In circles

It depends how the hover tanks anti grav works. If it is exerting some kind of force it could probably be modified to counter the recoil of a large weapon. Good point about the turret spinning not to mention sheering forces for an off center large cannon. A good solution would be 2 large cannons on each side!

 Warpig1815 wrote:
1. Elevation. Guns are BIG. The barrel is almost matched in length by the breech block. When elevating the gun, the breech must depress through the turret ring in order to get a higher elevation. If you mount offset, you aren't at the maximum diameter of the turret ring, so your breech ends up being stopped by the edge of the ring.

Was there ever a tank in which that was an issue though? If your gun reaches deep enough into the turret to hit the other side of the turret ring, you don't have any room for recoil anyway. I don't recall even a single tank where elevation was the problem, in fact, much bigger problem is depression of the gun as then you hit the roof of the turret.

Funnily enough the French tried to avoid both point 1 and 2 by simply welding the gun into the turret and moving the turret instead (see AMX-13). And it even worked!

3. Even if you could find a super strong motor to survive the stress of the above solution - it's not a great idea to have your breech, and it's fairly sensitive firing mechanisms, outside your turret. If it was hit by a round, you risk either a premature detonation of the round in the breech, or damage to the firing mechanism. In which case you become a glorified taxi. Armouring the breech with a mantlet isn't a practical solution, as it just adds more weight, requiring a bigger engine, which needs more armour to cover it, which adds more weight, and on and on and on we go down the rabbit hole of tank design.

Technically, T-14 Armata, newest Russian tank, has in fact just armoured breech (most of the turret is cosmetic, thinly armoured, and only serves as mounting point for all the gear and targeting mechanisms that need to be outside). Granted, they had to put the crew under the turret but it can be done.

As for that design - the concept isn't the same. It's a self propelled AA unit, and each gun is harmonised so that the rounds converge at a set range. Now whilst that range can be increased or decreased be a computer, you will get to a point where they cannot be harmonised close enough in range. And at that point you end up with a dead zone, where neither weapon can engage without turret traverse. Which, in an MBT, is less than ideal if it's engaged in an urban area (Although, doctrine would suggest not sending an MBT into a built up area. But it happens).

Ok, another example then. BMP-3 is a vehicle very similar to primaris tanks, it has both transport capacity and two guns mounted side by side (rapid fire 30 mm autocannon and 100 mm main gun) in almost identical way as Cawl's boxes. Urban fighting is pretty standard mission for it, too. So, yeah, it's not that outlandish even for vehicle with pretty big recoil.

1. Yeah - the 17pdr. Mounting the 17pdr proved to be an incredible pain for the British in the Second World War. It was needed, because it was the best gun for countering German armour, but most tanks available to the British simply couldn't mount it properly. The Sherman required a novel solution of removing the radio equipment to a bustle, and mounting it on it's side so that it could elevate and depress properly and still had sufficient recoil clearance. On the A34 Black Prince, which was based on the Churchill tank, the hull had to be widened to accomodate a wider turret ring, which in turn was to accommodate the 17pdr. The only adequate solution was a complete redesign of the 17pdr, by shortening it and providing higher pressure ammunition to compensate, which resulted in the 77mm HV gun, mounted on the Comet tank.

As for the AMX-13 - it worked! No. Not really. It worked as a light tank based on the French doctrine of the time, but it was flawed for several reasons. The design of the turret, termed an oscilating turret, is designs precisely so that larger armaments can be carried on smaller hulls . It was also an impractical design because not only do oscillating turrets have a shot trap/NBC breach by design (underneath the main gun in the hinge area), the AMX-13 could only hold 12 main armament rounds in a revolver magazine, which required loading by external means.

Regarding the problem of elevation/depression - take a look at Wikipedia's article on oscillating turrets, explains the problems of conventional turrets, how oscillating turrets were designed to be a solution, but ultimately proved to be more problematic than the original.

2. Yeah. Fine. But the T-14 is, as you say, not in the same category. The mere presence of a turret hatch on the Repulsor indicates an occupant. Hence all the attendant problems of manned turrets. I think my point still stands?

3. I'm not sure what you mean here... The BMP-3 has a coaxial 30mm. Being coaxial, it's mounted mere centimetres away from the main gun. Hence the dead zone is negligible. With the Repulsor, there is a considerable gap between. Roughly analogous to the VT tank (Which independently targeted guns).

Anyway. I think the conclusion is that I am definitely overthinking this in terms of modelling. But I'm willing to continue the tank discussion if you'd like

the repulsor itself is honestly fine, heck the off center posioning of the gun makes a degree of sense when you step back and look at the whole package, the main gun will, when firing forward, line up perfectly with the hull mounted bolter or double las canon.

Regarding the rotation of the thing: it's not really a problem where on the turret the gun is attached, it'll still rotate like the turret does. If you turn 15° on one side, the gun will turn 15° to that side too. In other terms, if there was a third, centered gun in the usual placement, the two others would remain parallel to it at all times. So there shouldn't be any trouble with aiming, unless maybe you're at point blank range.
Either each gun is supposed to be aimed and shoot separately and the optics can be used to aim either or they are set to focus at a certain distance, in which case it shouldn't be a problem to have some machine spirit taking care of angling the guns to adjust that focal point as needed. Since the guns are an anti tank weapon and an anti infantry one, I doubt they're expected to shoot at a single target though.

 Warpig1815 wrote:
Sure, targeting computers could probably assist, and have done for MBTs, but I'm more concerned with any physical limitations. Just saying 'It wouldn't because computers' kind of glosses over the limitations of geometry, physics and programming. They are not a wonder cure for everything, great as they are. Trajectory isn't an issue, because the vertical isn't affected - it's the gun position, and it's axis of rotation that I'm confused over.

As we arent dealing with manually fired rifles or cannons, having an offset gun does not require visually direct line of sight to the target relatvive to the tank or crew.

You point the barrel at the target and fire, I'm not sure why this causes so much confusion.

Try it with your arm, it is offset from your nose.

Look at something a few metres away, something lets say 10cm wide.

Your nose, centre mounted gun, is pointing directly at it.

Now hold out your arm out in front of you. It, by default, is not pointing at the object.

Now, rotating only your hips, point your arm directly at the object.

That's how a turret works and why the gun being offset doesn't matter, except where you calculate a firing solution.

Fictional wrote:You point the barrel at the target and fire, I'm not sure why this causes so much confusion.

@Fictional - Sorry, I was labouring under the illusion that I could ask questions about things I was unsure about. My apologies, I'll try not to upset your day by asking anything else The answer is - because it did. Sometimes people just get hang ups about things. Not that I should have to explain my motivations, but I was just interested in the dynamics of tangental rotation, instead of rotation around an point, and whether it would make targeting more difficult. Evidently it doesn't, case closed. Funnily enough, despite the snide-ness, your explanation helped. So thanks, I guess.

Watching an M1 Abrams move at combat speed all while the barrel stays perfectly on target is a sight to behold.

Now add in anti-gravitic plates and POTMS and bam you've got yourself a repulsor chassis.

but as stated above, no issue at all.

And I'm pretty confident that anyone can ask questions & anyone can answer them. just WTF, you dont need to be a dic if you think the question shouldnt be answered.

At least the reason he gave for asking was tangential.....

@Racerguy180 - I wasn't trying to be a . I just didn't think my asking was such a problem. Yeah, I was confused. Yeah, my head made an issue out of nothing. If I didn't want an answer, I wouldn't have asked the question in the first place. But I didn't think it warranted a snide answer, as if to suggest I was a dullard for being a little confused...

 Warpig1815 wrote:
@Racerguy180 - I wasn't trying to be a . I just didn't think my asking was such a problem. Yeah, I was confused. Yeah, my head made an issue out of nothing. If I didn't want an answer, I wouldn't have asked the question in the first place. But I didn't think it warranted a snide answer, as if to suggest I was a dullard for being a little confused...

I think you misunderstood my post, I wasnt talking about you, it was in response to @fictional's tone towards you. Sorry for any confusion.

@Raceguy180 - My mistake, I just assumed it was directed at me. No need to apologise

And yes, there are few things that are quite as awesome as watching an MBT at full pace, but still managing to put rounds down with pinpoint accuracy (As much as a 120mm L30 can manage to be 'pinpoint' ). Fantastic technology!

 Warpig1815 wrote:

Fictional wrote:You point the barrel at the target and fire, I'm not sure why this causes so much confusion.

@Fictional - Sorry, I was labouring under the illusion that I could ask questions about things I was unsure about. My apologies, I'll try not to upset your day by asking anything else The answer is - because it did. Sometimes people just get hang ups about things. Not that I should have to explain my motivations, but I was just interested in the dynamics of tangental rotation, instead of rotation around an point, and whether it would make targeting more difficult. Evidently it doesn't, case closed. Funnily enough, despite the snide-ness, your explanation helped. So thanks, I guess.

Oh, my apologies, I wasnt trying to be snide, or in any way offensive, about it.

Its just that its a simple concept, things shoot where you point them and it just strikes me that its easily overthought. Perhaps I am just too logical.

However, yes, actual targetting is probably slightly more complex, but in the end, its just trigonometry and the shell still flies towards the target in the direction the barrel is pointing.

@Fictional - It's no problem. Your comment did seem a bit disdainful, but there again, this is the internet - easy to read something entirely different than the intention.

You are right though, it is easy to overthink it. Which I have. I was labouring under the assumption that rotation around a circumference, rather than an axis, would produce a different effect, because of the offset. It doesn't, and should have been obvious to me, but it wasn't.

But you see, it isn't as simple as 'point and shoot'. Because even though the barrel is pointed on target, as per my original question, targeting itself is more difficult, if only by virtue of needing more components in the actual computation. Having a centreline gun just eliminates another neccessity. So in that respect, my confusion was from thinking too much about the necessities of targeting than is justified for making a model.

But hey, the question was asked, and answered, so that's all that needs to be said. Thanks all

Well, aiming is always a bit more complicated than "point and shoot" anyway, even without considering ballistics, because the optics you're using to aim are always a little bit away from the barrel. Ideally, you'd want the optics to be inside the barrel so they could be perfectly aligned with it, but that's obviously not feasible, or at least not without ridiculously complex equipment.
Picture a rifle with a scope attached on top. If you were shooting point blank, looking through the scope, you wouldn't hit where you're aiming. The scope is only accurate for a given distance, otherwise it's too high or too low. If you place it to the side, then you're either aiming too much left or right. To give a non-weapon example, it's why photographers came up with the single-lens reflex camera: it lets you actually see through the lens so you know the picture you're taking is the one you're seeing. Otherwise, you're always a bit off, no matter what.

Correcting that alignment error is not very difficult, though. As long as you know the distance between you and your target (and there are plenty of ways to measure that), it's simple trigonometry to calculate the proper angle you need to rotate, something a computer could do almost instantly.