Tank Layout

[Jeeps_Guns_Tanks]

Beer coolers were a popular item on M48s in Vietnam, and it was considered bad form to shoot up another tanks cooler, if you had to machine gun some VC that had climbed on the tank, when your crunchies ran off, or got distracted.  

[EnsignExpendable]

I wonder if the Viet Cong ever discussed the American worship of their god "Budweiser" and their reluctance to fire at his idols.

[Xoon]

So while I was tinkering with the engine compartment layout I came up with these three layouts inspired by Soviet design:

 

Layout 1:

 

This layout has the advantage of being the shortest of the three. This is because the rounds lie along the length of the engine on each side.  The total ammunition count here was about 36 rounds when using the 120x570mm NATO shell, with the entire engine compartment being 1,8m wide and about 1m tall. One potential I see with this design is that it could possibly be retrofitted on a Leopard 2. By shrinking the fuel tanks on each side of the engine, and isolating the ammunition and modifying the engine deck, this should be possible.  This layout also works with the 130mm without being any longer, at the cost of even smaller fuel tanks in the engine compartment. 

 

 

 

Layout 2 and 3:

 

 

Layout 1 here is just for almost for the fun of it. Put simply, it is longer than layout 1, but gives you a ludicrous ammunition capacity. You can fit about 72 shells of 120x570mm NATO ammunition in there! Any tanker that thinks that a tank with over 72 rounds of ammunition has to little ammunition deserves a slap.

 

Layout 2 here is a bit more realistic, sacrificing ammunition capacity for space for fuel and/or a APU or whatever you want to fit there. With identical length to layout 1 by the way. However, this layout still sports a pretty solid amount of ammunition, around 54 rounds in fact!

 

 

Of course, all of these layouts use isolated ammunition with blowout panels and a blast door, so in case of a penetration the crew will survive. Also, if I am not mistaken, tanks with all of their ammunition in the hull experienced less cook offs after penetration. And of course, this design allows for smaller turret, with either a 16 rounds ready rack bustle, a Leclerc style autoloader with 16 rounds, or the glories Soviet carousel autoloader. 

 

 

Any questions?

[Collimatrix]

OK, after taking a closer look at this, I do have some questions.

 

1)  What is the powerplant intended for layout 1?  The pictures I've seen of the Leo 2 seem to show that the powerpack is big enough that it takes up most of the rear hull.  Have engines gotten small enough that you could do this layout in an existing Leo 2 hull?

 

2)  How does the radiator work in layout 1 exactly?  Is it sitting on top of the transmission?

 

3)  Can NATO 120mm ammunition fit into a carousel-style autoloader?  M829 is just under a meter in total length, and the turret ring of an Abrams is a little over two meters in diameter.  So just from those figures we can see that it's a tight squeeze.  But actually it's worse than that; the quoted turret ring diameter is the diameter of the ring cut on the top of the hull, and it spills over into the sponsons as this guy's models show:

 

 

As you can see, the distance across the inside of the hull is smaller than that.

[SH_MM]

1)  What is the powerplant intended for layout 1?  The pictures I've seen of the Leo 2 seem to show that the powerpack is big enough that it takes up most of the rear hull.  Have engines gotten small enough that you could do this layout in an existing Leo 2 hull?

 

 

MTU/Renk EuroPowerPack proposal for the Leopard 2. The next-generation MTU engine of the MT890 series (i.e. the twelve cylinder version should be labeled MT893 to stay with the previous naming scheme) is 50% smaller (in terms of volume) and 10% more fuel efficient.

[Xoon]

OK, after taking a closer look at this, I do have some questions.

 

1)  What is the powerplant intended for layout 1?  The pictures I've seen of the Leo 2 seem to show that the powerpack is big enough that it takes up most of the rear hull.  Have engines gotten small enough that you could do this layout in an existing Leo 2 hull?

 

2)  How does the radiator work in layout 1 exactly?  Is it sitting on top of the transmission?

 

3)  Can NATO 120mm ammunition fit into a carousel-style autoloader?  M829 is just under a meter in total length, and the turret ring of an Abrams is a little over two meters in diameter.  So just from those figures we can see that it's a tight squeeze.  But actually it's worse than that; the quoted turret ring diameter is the diameter of the ring cut on the top of the hull, and it spills over into the sponsons as this guy's models show:

 

 

As you can see, the distance across the inside of the hull is smaller than that.

 

1. The powerplant intended here would be the MTU MB 883 V12 or 890 V12. The MB 830 dimensions are about 1488x972x742mm (LxWxH). For a transmission the standard RENK would do. The with of the inside of the hull is usually around 1,8-2m wide on the inside, which leaves 820-1020mm of space left, 410-510mm on each side. Two rounds wide, and 3 high, which gives 12 rounds actually, ops, a miss calculation earlier.  But for a 1892mm wide inside of the hull, it would still be 36 rounds

 

Here you can see the old engine, MB 873 was it? As you can see, at each side of the engine you have fuel tanks, by removing these you should be able to fit some rounds in there. 

I don't remember the dimensions of the older engine, but it was a bit bigger.  Obviously, if you are already going to upgrade the Leopard 2, then you might as well change the powerpack while you are at it. 

 

2. Yes, the radiators would be on top of the transmission since it is a bit shorter than the engine, and because of the extra space the raised engine deck gives.  Here is a example:

 

3. There is NO WAY you can fit the 120x570mm NATO into a carousel autoloader without using two piece. Well you can, if all the rounds are standing, with a unmanned turret. So it's a no go for a manned turret. I have literally messes around for hours to see if I could make a 120x570mm carousel autoloader, but it didn't worked out without making mayor comprises.

Sorry about that one, I should have been more specific, if 125mm shells were used, then it would be possible. 

 

 

And for those that wonder where the fuel went, it would probably be moved to the sponsons, or you could remove the front rack on the Leopard 2 and install a fuel tank there. Do you think it is possible to fit a APU there too?

[Collimatrix]

Wow, I knew the new powerplants were supposed to have somewhat better power density, but I didn't realize that the improvements were that dramatic.

[Xoon]

 

MTU/Renk EuroPowerPack proposal for the Leopard 2. The next-generation MTU engine of the MT890 series (i.e. the twelve cylinder version should be labeled MT893 to stay with the previous naming scheme) is 50% smaller (in terms of volume) and 10% more fuel efficient.

Weird choice of imagery there when talking about the MTU MT890, considering that is a MB883 engine.  

 

But they are very close in size, but I do believe the 890 was 668mm high, and 700mm wide. The length I was unable to find.

 

This is a clean MTU MT890 V10 engine:

 

[Collimatrix]

What about the following variation on your layout 3 Xoon:

 

The turret ring is round, but the ammo stowage is in a straight line.  The ammo racks nearest the center of the hull will be easier to access, because there will be less of a gap between them and the turret ring.

 

So instead of reserving space on one side for fuel/APU, reserve space on both sides, and have the ammo rack only in the center.  Have the fuel tanks extend into the little triangular gap between the round turret basket and the square hull, and use those fancy fuel tanks that double as armor, so that the ammo (and engine) has a little more protection from oblique side penetrations.

[SH_MM]

Weird choice of imagery there when talking about the MTU MT890, considering that is a MB883 engine.  

 

But they are very close in size, but I do believe the 890 was 668mm high, and 700mm wide. The length I was unable to find.

 

The image shows the EuroPowerPack (MT883 + Renk HSWL 295TM), which is what I wrote. This already is enough for placing NATO ammunition in front of the engine. I just was too lazy to search for a rendering of the MT890 V12 engine in the Leopard 2, because there is (afaik) only one file containing such.

 

[Xoon]

What about the following variation on your layout 3 Xoon:

 

The turret ring is round, but the ammo stowage is in a straight line.  The ammo racks nearest the center of the hull will be easier to access, because there will be less of a gap between them and the turret ring.

 

So instead of reserving space on one side for fuel/APU, reserve space on both sides, and have the ammo rack only in the center.  Have the fuel tanks extend into the little triangular gap between the round turret basket and the square hull, and use those fancy fuel tanks that double as armor, so that the ammo (and engine) has a little more protection from oblique side penetrations.

 

 

Here you have your suggested layout, in a high and low capacity variant. 

 

 

I find the high capacity variant the most logical, considering the fact that you have enormous space for fuel. Maybe even a ultra high capacity variant would make more sense, which would come out with something like 66 rounds. However, the ultra high capacity and maybe the high capacity version depending on hull width would need a frontal layout like the M1 series or fuel in the sponsons.

 

 

But since you are talking about using fuel as armor here is the estimated protection the fuel tanks would provide in a hull which is 1,8m wide on  the inside:

For the high capacity version: 32mm of RHAe at 0 degrees, 64mm at 60 degrees. 

For the high capacity version: 75mm of RHAe at 0 degrees, 150mm at 60 degrees. 

 

This is estimated with the claim that a fuel tank is 1/7 as effective as RHS, which supposedly comes from the designer of the Merkava series. Feel free to correct me if I am wrong. 

 

 

If we take the Leopard 2A4 are a basis here,  the estimated protection on each side of the ammunition rack would be:

 

For the high capacity version:

At 0 degrees: 13+40+32= 85mm of RHAe.

At 60 degrees: 23+80+64= 167mm of RHAe.

 

For the low capacity version:

At 0 degrees: 13+40+75= 128mm of RHAe.

At 60 degrees: 23+80+150= 253mm of RHAe.

 

This does not however take into consideration the spacing or the armor the roadwheels would provide. Or a steeper angle for that matter.

 

 

And with this layout, would it be possible to quickly reload the ammo rack by lower the rack though the roof with a crane? Like a quick reload method. 

[Walter_Sobchak]

Wow, I knew the new powerplants were supposed to have somewhat better power density, but I didn't realize that the improvements were that dramatic.

 

I have that image of the space savings of the MT-883 inside a Leo 2 in a brochure.  One thing that always bugged me about it, they don't say what they did with the fuel tanks.  As shown in one of the pictures earlier in this thread, the MB873 of the regular Leopard 2 has fuel tanks along the side of the engine.  This is pretty common for engines mounted lengthwise.  The image of the MT883 in the Leo 2 shows a transverse mounting, so I assume there is no space for fuel tanks on the side.  So while there is significant space savings with the MT883, that image might be cheating a little if you want to keep the same fuel capacity in the vehicle.

 

As to the size difference between the two engines, they are quite different in age.  The MB 873 was developed as the German engine for their version of the MBT-70, so that means it was designed in the 1960's (as was the AGT-1500 in the abrams).  The MT-883 is an eighties era design, so it has the advantage of twenty years of technological advancement.  MB 873 is a big engine, displacement is 39.6 L (2416 cubic inches).  While the Germans were developing the MB 873, the US Army said to Continental Motors, :"Hey guys, we really like that 1100 cubic inch 500HP aircooled engine you made, can you get 1500 hp out of it?"  And the guys at Continental were either brave enough or dumb enough to try it.  By putting variable compression ratio pistons into that engine, and increasing the displacement up to 1360 cubic inches, they were able to squeeze 1500 HP out of it.  In terms of cylinder displacement, the MB-873 is almost twice as big as the Continental AVRC-1360.  Of course, the actual size of the engine is not as pronounced between the two as the disparity in cylinder displacement would suggest.  Anyhow, I guess my point in all this rambling is that the German Army probably took the better approach, making a bigger, more conventional engine while the US Army asked for something a bit crazy and got a crazy design in return.  Anyway, the US Army went with the turbine over the Continental Diesel and the US has not designed a production worthy MBT diesel engine since.  

[Xoon]

I have that image of the space savings of the MT-883 inside a Leo 2 in a brochure.  One thing that always bugged me about it, they don't say what they did with the fuel tanks.  As shown in one of the pictures earlier in this thread, the MB873 of the regular Leopard 2 has fuel tanks along the side of the engine.  This is pretty common for engines mounted lengthwise.  The image of the MT883 in the Leo 2 shows a transverse mounting, so I assume there is no space for fuel tanks on the side.  So while there is significant space savings with the MT883, that image might be cheating a little if you want to keep the same fuel capacity in the vehicle.

 

As to the size difference between the two engines, they are quite different in age.  The MB 873 was developed as the German engine for their version of the MBT-70, so that means it was designed in the 1960's (as was the AGT-1500 in the abrams).  The MT-883 is an eighties era design, so it has the advantage of twenty years of technological advancement.  MB 873 is a big engine, displacement is 39.6 L (2416 cubic inches).  While the Germans were developing the MB 873, the US Army said to Continental Motors, :"Hey guys, we really like that 1100 cubic inch 500HP aircooled engine you made, can you get 1500 hp out of it?"  And the guys at Continental were either brave enough or dumb enough to try it.  By putting variable compression ratio pistons into that engine, and increasing the displacement up to 1360 cubic inches, they were able to squeeze 1500 HP out of it.  In terms of cylinder displacement, the MB-873 is almost twice as big as the Continental AVRC-1360.  Of course, the actual size of the engine is not as pronounced between the two as the disparity in cylinder displacement would suggest.  Anyhow, I guess my point in all this rambling is that the German Army probably took the better approach, making a bigger, more conventional engine while the US Army asked for something a bit crazy and got a crazy design in return.  Anyway, the US Army went with the turbine over the Continental Diesel and the US has not designed a production worthy MBT diesel engine since.  

They did indeed cheat on the numbers. You should never fully trust a advertisement.

 

With fuel, it is closer to 400mm of saved space, if the hull inside is 2m and the required fuel capacity is 1200L.

You could cut it down the amount of fuel because of the engines higher fuel efficiency, and then you would save 460mm.

 

 

Does anyone know what the sponsons of the Leopard 2 are used for?

[SH_MM]

The majority of the fuel is stored in the Leopard 2's sponsons.

But since you are talking about using fuel as armor here is the estimated protection the fuel tanks would provide in a hull which is 1,8m wide on  the inside:

For the high capacity version: 32mm of RHAe at 0 degrees, 64mm at 60 degrees. 

For the high capacity version: 75mm of RHAe at 0 degrees, 150mm at 60 degrees. 

 

This is estimated with the claim that a fuel tank is 1/7 as effective as RHS, which supposedly comes from the designer of the Merkava series. Feel free to correct me if I am wrong. 

 

 

If we take the Leopard 2A4 are a basis here,  the estimated protection on each side of the ammunition rack would be:

 

For the high capacity version:

At 0 degrees: 13+40+32= 85mm of RHAe.

At 60 degrees: 23+80+64= 167mm of RHAe.

 

For the low capacity version:

At 0 degrees: 13+40+75= 128mm of RHAe.

At 60 degrees: 23+80+150= 253mm of RHAe.

 

This does not however take into consideration the spacing or the armor the roadwheels would provide. Or a steeper angle for that matter.

...and this is why the layout as used on the Leopard 2 and Leclerc tanks is more practical. You get much better protection for the ammunition and the crew at the same time.

[Xoon]

The majority of the fuel is stored in the Leopard 2's sponsons.

...and this is why the layout as used on the Leopard 2 and Leclerc tanks is more practical. You get much better protection for the ammunition and the crew at the same time.

Are you referring to the ammo rack up in the front, or that the engine has fuel on each side of it?

[LoooSeR]

I guess i forgot to post this here.

 

Leclerc layout proposals:

 

AS31, crew of 3 in frontal part of hull, unmanned turret. T-14 have same layout.

 

 

 

 

AS22 - low profile turret for 2 members of the crew, driver in the front, frontal engine and ammunition rack in the back. Gun is loaded from hull ammorack by autoloader.

 

AS12 - closer to "classis" layout - low-profile turret for 2, driver in the front, engine in the back.

 

Object 490A from USSR and AS12 have same general layout

 

One more:

Gunner and driver in the hull, commander in the turret. This arrangement provided best visibility for commander.

[Xoon]

So first of I got a question about hydropeumatic suspension.  When used as a active suspension you have to have a pump, valve and reservoir to increase and decrease the pressure in the cylinders right? 

If this is the case, it would take up extra volume and require two pipes going to each suspension arm. 

 

Considering this, would be electromagnetic suspension be more space efficient?  I assume it would use electricity to regulate it's height. If this is the case, then much thinner cables could be used instead of pipes. Also the system would be powered most likely by a APU, which seems like it is becoming a standard in most tanks. 

 

 

Next question is whether or not front mounted engines make more sense now then ever. Considering how much the powerpacks have shrunk, would be front mounted setup be more compact than a crew capsule?   When I took some measures of myself I found out I could comfortably fit with a height of 900mm, 80-100mm extra for seats and helmets, and 170mm extra for head space against IED explosions, if we are to thrust the Swedes.  When it came to width I ended up with something like 600mm, but I do know 500mm is considered roomy, so for the benefit of the crew capsule, we will use that. And by multiplying this by 3, we get a total width of 1500mm.  And for length, I ended up with 1350mm, when sitting straight. The length may be longer if you want a lower capsule or more leg room. 

 

This would be us the dimensions: 1350x1500x1150mm for the crew capsule.

 

 

The powerpack is more rough measurements, but from what I understand, the MTU 890 V12 is 700mm wide, 550mm tall, and while the length is not given, it could be the same as the 883, which is 1480mm wide. The newer RENK transmissions seems to be about 500mm long, about 1500mm wide, and 500-600mm tall. So by placing the MTU 890 in a tranverse mount, the combined length would be about 1200mm, with a width of around 1600 when including the mechanical linkages between the engine and the transmission, and 550mm tall.

 

The dimensions of the powerpack would thus be: 1200x1600x550mm. This does not include the cooling, or piping or smaller systems that might add more volume, so adding 1-200mm here and there should be expected.  The overall height would not really be much more when the cooling is installed, since it can be placed on top of the engine, so unless you want a 45 degree slope, there should be enough space.

 

Next we about the pros and cons of this setup:

 

Front Mounted Crew Capsule:
Pro:

-The main armor protection is placed around the crew.
-The Periscopes are positioned in such a way that the driver can drive even when all cameras and electronics fail. 
-Smaller frontal heat signature. 
-Less likely to suffer a mission kill.
-Smaller front sprocket

-Less Likely to throw a track. 

 

Cons:
-When the armor is penetrated from the front, the crew is highly likely to be injured, since nothing can stop the shrapnel of projectiles. 
-The crew hatches forces the roof to extend forward to avoid shells hitting the hatches, which cause the frontal area needed to be protected to be larger, this also may cause a reduction in gun depression, or a higher turret. Also the hatches may be blocked by special armor or the gun barrel. Lastly, if the hatch is angled, it will have a notch weak spot if the front is up armored.
-Crew has to be evacuated through their hatches, which is not the easiest thing is the world.

-Crew is exposed to enemy fire while evacuating from the tank.
-Crew is more likely to be wounded or killed by a mine or IED.

 

Front mounted powerpack:
Pros:

-Potentially smaller frontal area needing protection.
-A door, or ramp, which would make crew evacuation easy, and wounded crew member could simply be dragged straight on to a stretcher from their seats.
-Crew is protected by the tank when evacuating.

-The powerpack and potentially the internals of the tank would protect the crew from shrapnel and the projectile during a penetration. 
-Crew is less likely to be wounded or killed by a mine or IED.
 

Cons:

-More likely to suffer a mobility kill.
-More likely to throw a track.

-Larger thermal signature.

-Less ideal crew protection.

-No back up in case of failure.

 

So with the introduction of unmanned turret, and smaller powerpacks. I see frontally mounted powerpacks. 
Or maybe sponsons mounted engines, which would make the tank shorter.

[Collimatrix]

IIRC, front-mounted drive sprockets aren't categorically more likely to throw track, they're more likely under certain circumstances while rear-mounted ones are more prone to it under a different set of circumstances.  ToT covers it, but I don't have that to hand at the moment.

 

Edit:  Maybe it's not in ToT, I'll see if I can find it.

[SH_MM]

So with the introduction of unmanned turret, and smaller powerpacks. I see frontally mounted powerpacks. 

Or maybe sponsons mounted engines, which would make the tank shorter.

 

I disagree. A modern powerpack such as the MT890V12 will still be larger than a small two or three men crew capsule. Germany has tested two-men-crews and Israel is currently thinking about having only a two-men-crew for the Carmel.

 

Just look at the Puma's powerpack including the MT892 Ka-501 engine:

(ignore the red arrow)

 

On a tank one most likely wants a V12 engine with at least 1.500 horsepowers - if you take a look at German projects (like the canceled NGP modular combat vehicle and the Leopard 2A7V upgrade), it seem that one wants even more power than just 1,500 hp. Yes, one could use an uprated version of the MT890V12, but this still should require larger cooling units, better brakes and better fuel systems than used on the Puma - so even more spaced is occupied by the powerpack. On future combat vehicles, the demand for larger APUs will also be important. The Leopard 2A7V will already feature an upgraded APU compared to the Leopard 2A7, but this is just the start. On future combat vehicles, there should be more electronics and other power-consuming features (such as an active protection system).

 

One can place the APU in another part of the tank, but in general it seems desirable to place the engine and APU within the same part of the tank - it makes the fuel systems less complex, allows the fire extinguishers to work for engine and APU at the same time, while cooling and exhaust systems can be shared between APU and engine.

 

The main problem with your suggestion of future MBTs moving towards front-mounted engines is that there are no real benefits of this. Your list includes five pros for front-mounted engines, but only one is valid. The option to have a rear door or ramp is the main benefit of front-mounted engines and the only reason why some APCs, most IFVs and the Merkava tanks have their engines located at the front. The other advantages are half truths or not true at all. You have also overlooked a few major drawbacks of front-mounted engines here.

 

For example you said that having the engine located at the front is an advantage in terms of protection against mines and IEDs. In theory mine/IED will detonate below the engine, the crew is not directly affected by the blast, only by the shock? But this doesn't work. There are mines and IEDs that are triggered by thermal signatures, some of which have been used in Iraq against the Stryker and Bradley. Soldiers from the US Army even demanded a rear-mounted engine in the Mobile Protected Firepower vehicle just to be better protected against such IEDs/mines. Pressure sensitive mines might have been a common threat in the Cold War, but technology evolves and the battlefield changes. In many cases IEDs are fuzed by mobile phones or other methods requiring user input: then a front-mounted engine does offer no benefits in terms of protection.

 

You wrote that a front-mounted engine could potentionally reduce the frontal area needing protection. How? Unless you want to claim that the engine acts as enough armor to stop anything by itself, this won't happen IMO. Tanks and other combat vehicles (such as wheeled and tracked infantry fighting vehicles) with front-mounted engines are always taller at the front than current combat vehicles with rear-mounted engines. Even if it was possible to create an engine, that delivers enough power while being small enough to not affect the height/width of the vehicle, the frontal area requiring protection should remain the same size as with a rear-mounted engine in best case. Why? Because the crew has to sit in front of the turret (or directly below the turret), if one wants to have optical sights (vision blocks) as back-up solution for electronic systems. If you want a rear door or ramp to evacuate the crew, the height of the hull might even be increased compared to currently existing tanks.

 

Another issue with front-mounted engines is armor integration. In Germany the VTF (Versuchsträger Frontantrieb) was tested in 1984, after Germany considered the concept of a MBT with front-mounted engines. An major issue seen with the VTF was the weight distribution: Having thick frontal armor and the powerpack at the vehicle front caused a massive weight disbalance, which affects the mobility. Unless the turret is mounted in the rear of the vehicle - which would eliminate the option of having a rear ramp - the tank cannot have the same armor thickness at the hull as with a conventional layout.

 

The cooling and exhaust of front-mounted engines are an issue. If the engine is front-mounted, you cannot move the exhaust and air vents to the rear of the vehicle, unless giving up any gained spaced (which is required for a rear door). This means there are ballistic holes, i.e. the engine vents won't be protected close to the same level as the rest of the hull. Any hit here by an ATGM or an APFSDS could lead to a penetration. This is sub-optimal, because it would be located in the frontal 60° arc. In general the tank needs to have more side skirts for protecting the frontal 60° arc, when the crew is moved further away from the front.

 

Three further problems of tanks with front-mounted engines according to the German military are lowered visibility for the driver (the engine creates a huge dead zone for his optics), reduced gun depression (only 7° on the Merkava) and reduced mobility when driving at maximum speed through very uneven engine (otherwise the drive sprocket located at the front of the tank can hit the terrain and be damaged, leaving the tank immobilized).

 

So I don't see any reason why future tanks should move to front-mounted engines. Just the demand of better protection per weight should already favour rear-mounted engine concepts.

[Xoon]

I disagree.

You are fully allowed to do so, this is a discussion after all.

 

 

A modern powerpack such as the MT890V12 will still be larger than a small two or three men crew capsule. Germany has tested two-men-crews and Israel is currently thinking about having only a two-men-crew for the Carmel.

 

Just look at the Puma's powerpack including the MT892 Ka-501 engine:

(ignore the red arrow)

 

The powerpack is more rough measurements, but from what I understand, the MTU 890 V12 is 700mm wide, 550mm tall, and while the length is not given, it could be the same as the 883, which is 1480mm wide. The newer RENK transmissions seems to be about 500mm long, about 1500mm wide, and 500-600mm tall. So by placing the MTU 890 in a tranverse mount, the combined length would be about 1200mm, with a width of around 1600 when including the mechanical linkages between the engine and the transmission, and 550mm tall.

 

The dimensions of the powerpack would thus be: 1200x1600x550mm. This does not include the cooling, or piping or smaller systems that might add more volume, so adding 1-200mm here and there should be expected.  The overall height would not really be much more when the cooling is installed, since it can be placed on top of the engine, so unless you want a 45 degree slope, there should be enough space.

 

I was talking about a tranverse mounted engine, not a conventionally mounted engine as seen in the picture.  Imagine the picture, but now remove the drivers compartment, and rotate that engine 90 degrees, 

do you see all that extra space that is freed up?

 

 

On a tank one most likely wants a V12 engine with at least 1.500 horsepowers - if you take a look at German projects (like the canceled NGP modular combat vehicle and the Leopard 2A7V upgrade), it seem that one wants even more power than just 1,500 hp. Yes, one could use an uprated version of the MT890V12, but this still should require larger cooling units, better brakes and better fuel systems than used on the Puma - so even more spaced is occupied by the powerpack. On future combat vehicles, the demand for larger APUs will also be important. The Leopard 2A7V will already feature an upgraded APU compared to the Leopard 2A7, but this is just the start. On future combat vehicles, there should be more electronics and other power-consuming features (such as an active protection system).

First, I was talking about 1500HP engines only. I should have specified this and it is entirely my fault.  For a bigger engine, a front mounted setup would most likely not work out.  

 

Second, APUs are compact, and they already produce a large amount of power, the Abrams is going to get a upgraded APU too:

http://www.scout.com/military/warrior/story/1728632-army-builds-new-abrams-tank-variant-for-2020s

(Shown by Damian in his thread on AW)

 

The APU shown here has a claimed max output of 1KA. That is A LOT of power, and should be more than sufficient to power a APS, cameras, turret traverse, FCS, computers and sub systems.

 

 

One can place the APU in another part of the tank, but in general it seems desirable to place the engine and APU within the same part of the tank - it makes the fuel systems less complex, allows the fire extinguishers to work for engine and APU at the same time, while cooling and exhaust systems can be shared between APU and engine.

At least in the case of the Leopard 2, the APU is separate from the engine compartment right?  The main reason I see for placing the APU in the back of the sponsons is because it does not take up any space inside the hull, and because it is the tallest part of the sponsons, also it helps that it can have it's exhaust going out the back.  When it comes to complexity, yes , it would be more complex, but not by much, a longer power cable, and since the MBT would most likely have fuel mounted in it's sponsons, the a longer fuel line would not be needed. 

 

 

The main problem with your suggestion of future MBTs moving towards front-mounted engines is that there are no real benefits of this. Your list includes five pros for front-mounted engines, but only one is valid. The option to have a rear door or ramp is the main benefit of front-mounted engines and the only reason why some APCs, most IFVs and the Merkava tanks have their engines located at the front. The other advantages are half truths or not true at all. You have also overlooked a few major drawbacks of front-mounted engines here.

 

Next question is whether or not front mounted engines make more sense now then ever. Considering how much the powerpacks have shrunk, would be front mounted setup be more compact than a crew capsule?

This would be us the dimensions: 1350x1500x1150mm for the crew capsule.

 

I was saying that front mounted engines made more sense now, not that all MBT designs are going to use them.  If you are refering to my last bit of line, that was spelling error, I meant "I could see front mounted powerpacks in the future". As in, they might have some potential.

 

My list was more food for thought honestly. And I was simply listing everything I could think of. So of course I overlooked some mayor drawbacks, this is why I post here, to get other peoples opinion. How true they are is up to you to decide, they are just theories. 

 

 

For example you said that having the engine located at the front is an advantage in terms of protection against mines and IEDs. In theory mine/IED will detonate below the engine, the crew is not directly affected by the blast, only by the shock? But this doesn't work. There are mines and IEDs that are triggered by thermal signatures, some of which have been used in Iraq against the Stryker and Bradley. Soldiers from the US Army even demanded a rear-mounted engine in the Mobile Protected Firepower vehicle just to be better protected against such IEDs/mines. Pressure sensitive mines might have been a common threat in the Cold War, but technology evolves and the battlefield changes. In many cases IEDs are fuzed by mobile phones or other methods requiring user input: then a front-mounted engine does offer no benefits in terms of protection.

The idea was that electromagnetic sensitive, pressure sensitive, laser, thermal mines and IEDs are most likely to explode under the front of the vehicle, and with the crew in the back they would physical be as fast away as possible, for example the explosion would not be as strong as at the epicenter, and it cause of hull breach, the crew would be further away. Drivers are the most likely crew member to die of mines or IEDs after all.

If the IED or mine is timed, programmed or remote operated this would make little of a difference, that is true. But those are more expensive, newer or more risky. And of course it would be easily countered, it is not a mayor advantage, more a minor one. 

 

 

You wrote that a front-mounted engine could potentionally reduce the frontal area needing protection. How? Unless you want to claim that the engine acts as enough armor to stop anything by itself, this won't happen IMO. Tanks and other combat vehicles (such as wheeled and tracked infantry fighting vehicles) with front-mounted engines are always taller at the front than current combat vehicles with rear-mounted engines. Even if it was possible to create an engine, that delivers enough power while being small enough to not affect the height/width of the vehicle, the frontal area requiring protection should remain the same size as with a rear-mounted engine in best case. Why? Because the crew has to sit in front of the turret (or directly below the turret), if one wants to have optical sights (vision blocks) as back-up solution for electronic systems. If you want a rear door or ramp to evacuate the crew, the height of the hull might even be increased compared to currently existing tanks.

A common trick in tank design to reduce the frontal area that needs protection is to slope the roof at a high angle, about 82-83 degrees.  In the case of a crew capsule, the crew needs hatches, which usually needs the plain, flat surface. This minimizes the potential to slope the roof, which increases the frontal area needing protection. You can slope the hatches too, but most designers have moved away from this practice. Also, turret armor and the gun barrel blocks these hatches, this can be seen on the Leo 2A5, or any T-series. Without the hatches the designers can freely create a overhand without worrying about trapping the crew. I already explained how we could accomplish the same height as a crew capsule, and if you wondering about the cooling system, just create it is the same way the Puma did, by letting it fill the space between the slope and the engine. 

 

Example one:

'

 

 

Example 2:

 

As you can see (with writing that could kill) in this example, the front mounted powerpack has a frontal height 50mm smaller than the crew capsule.

And if you are wondering what the length of that flat is, it is 450mm.

 

 

Regarding optical vision, I think I stated that in the pros and cons. As you have to entirely rely on cameras. 

And, how does a rear door in itself increase the height of the vehicle?

 

 

Another issue with front-mounted engines is armor integration. In Germany the VTF (Versuchsträger Frontantrieb) was tested in 1984, after Germany considered the concept of a MBT with front-mounted engines. An major issue seen with the VTF was the weight distribution: Having thick frontal armor and the powerpack at the vehicle front caused a massive weight disbalance, which affects the mobility. Unless the turret is mounted in the rear of the vehicle - which would eliminate the option of having a rear ramp - the tank cannot have the same armor thickness at the hull as with a conventional layout.

This is true, but it can have the same thickness. But not without a few drawbacks. 

 

 

The cooling and exhaust of front-mounted engines are an issue. If the engine is front-mounted, you cannot move the exhaust and air vents to the rear of the vehicle, unless giving up any gained spaced (which is required for a rear door). This means there are ballistic holes, i.e. the engine vents won't be protected close to the same level as the rest of the hull. Any hit here by an ATGM or an APFSDS could lead to a penetration. This is sub-optimal, because it would be located in the frontal 60° arc. In general the tank needs to have more side skirts for protecting the frontal 60° arc, when the crew is moved further away from the front.

See CV90. Front mounted engine, rear mounted exhaust. And a rear door/ramp. 

 

And about the sideskirts, depends on the country. Swedish requirements were 65 degrees coverage of the front, not the crew. 

 

 

Three further problems of tanks with front-mounted engines according to the German military are lowered visibility for the driver (the engine creates a huge dead zone for his optics), reduced gun depression (only 7° on the Merkava) and reduced mobility when driving at maximum speed through very uneven engine (otherwise the drive sprocket located at the front of the tank can hit the terrain and be damaged, leaving the tank immobilized).

1. This is not a issue as stated earlier, cameras, which are becoming widespread. 

 

2. With my proposed layout, you might even gain gun depression. It is unfair to compare it to the Merkava, which has a huge conventionally mounted engine. 

 

3. Could you rephrase this one, I did not quite get this one.  "Though very uneven engine"?

 

 

So I don't see any reason why future tanks should move to front-mounted engines. Just the demand of better protection per weight should already favour rear-mounted engine concepts.

You are correct that a two-man crew capsule can provide better protection per weight than a front mounted engine pack, simply because you have more room to play with. But in my opinion vs a 3-man crew capsule, I think it would actually tip in my proposals favor. 

 

 

Anyways, thanks for commenting, and I am very tankful that you provided so much great information.

 

 

 

 

IIRC, front-mounted drive sprockets aren't categorically more likely to throw track, they're more likely under certain circumstances while rear-mounted ones are more prone to it under a different set of circumstances.  ToT covers it, but I don't have that to hand at the moment.

 

Edit:  Maybe it's not in ToT, I'll see if I can find it.

 

Huh, thanks for letting me know that!

 

 

 

IIRC, front-mounted drive sprockets aren't categorically more likely to throw track, they're more likely under certain circumstances while rear-mounted ones are more prone to it under a different set of circumstances.  ToT covers it, but I don't have that to hand at the moment.

 

Edit:  Maybe it's not in ToT, I'll see if I can find it.

huh, thanks for the information!

 

 

 

 

Another thing brought to my attention from tank-net is hybrid electric drivetrains. 

It seems to be two viable solutions:

 

1. Soft hybrid parallel.:

The soft hybrid parallel would be the same system as already used in tanks, but with a small electric motor added to the axle between the engine and the gearbox, as well as a electric motor coupled to the turbochargers axle. And a battery of course. How the system would work is that the electric motor coupled to the turbocharger would spool it up when starting, effectively eliminating turbolag and the need for a second turbo. This same engine would be used as a generator to harvest excess energy from the turbocharger too. The small electric motor between the engine and the gearbox would work as a regenerative break when the tank is breaking, reclaiming some energy, and optionally adding power when driving and using excess energy stored in the batteries is available. This could increase acceleration and fuel economy and performance in general. Of course, this system would be take more space then a conventional drive train, and also be a bit heavier.

 

2. Full serial hybrid:

Here the engine would get the same aid as said earlier, but instead of sending it's power to the gearbox, it sends it to a generator. This would allow the engine to run at optimal RPM. This generator would then feed into a rectifier, and then into the main battery, which would feed into two Speed controllers that would control two electric motors. These electric motors would also work as regenerative breaks. To avoid de-synchronization, you simply make the engines communicate and adjust to each other. This system allows the engine(s) to be moved away from the "transmission" and placed anywhere, like the sponsons, or even the turret. The battery would have a capacity to allow the tank to run in silent mode, and to recapture as much energy as possible while breaking. This way the tank could also do a cold start and heat up the engine while it moves away.

 

Alternatively, you could go turbine electric. Maybe you could attach a electric motor to the main shaft to spool up the turbine faster? Anyhow, if I am not mistaken, turbines run quite efficiently when they are at their optimal RPM, which should help greatly on fuel usage. The tank would also be able to start immediately, and spooling up the engine while running on battery power. This would remove the 30 second spool up time of the turbine. Also hilariously, the tank could still technically be charged from a house socket, if it carried a charger with it, or be charged by the APU, in case of engine failure. 

 

Batteries would have to be stored in the sponsons with blow out panels most likely, since lithium batteries have a tendency to explode when hit.

 

[Mighty_Zuk]

I disagree. A modern powerpack such as the MT890V12 will still be larger than a small two or three men crew capsule. Germany has tested two-men-crews and Israel is currently thinking about having only a two-men-crew for the Carmel.

 

And yet, the Carmel demonstrator is more than likely to retain a frontally placed engine despite being a clean sheet design.

 

 

On a tank one most likely wants a V12 engine with at least 1.500 horsepowers - if you take a look at German projects (like the canceled NGP modular combat vehicle and the Leopard 2A7V upgrade), it seem that one wants even more power than just 1,500 hp. Yes, one could use an uprated version of the MT890V12, but this still should require larger cooling units, better brakes and better fuel systems than used on the Puma - so even more spaced is occupied by the powerpack. On future combat vehicles, the demand for larger APUs will also be important. The Leopard 2A7V will already feature an upgraded APU compared to the Leopard 2A7, but this is just the start. On future combat vehicles, there should be more electronics and other power-consuming features (such as an active protection system).

 

I have to disagree.  As the weight goes down, the need for higher power engines reduces.  If you can make the heavy weight class future MBTs weigh ~55 tons (7-13 tons less than modern tanks), there is no reason to keep the 1,500hp engines, as they will needlessly consume more fuel which reduces autonomy and increases operation costs - unwanted.  I don't know why the T-14 has a 1,500hp engine. Seems excessive to me.

You could argue though, that to better handle autonomy and fuel consumption issues, future tanks will utilize hybrid engines, or less likely, electric. And they're usually larger, though provide higher torque.

I'd like to continue this discussion. 

 

 

The main problem with your suggestion of future MBTs moving towards front-mounted engines is that there are no real benefits of this. Your list includes five pros for front-mounted engines, but only one is valid. The option to have a rear door or ramp is the main benefit of front-mounted engines and the only reason why some APCs, most IFVs and the Merkava tanks have their engines located at the front. The other advantages are half truths or not true at all. You have also overlooked a few major drawbacks of front-mounted engines here.

 

Having a rear door/ramp is not the only advantage. Aside from having a further layer of protection behind the main armor, Tal would often refer to the frontally mounted engine as a way to secure a safe position for the ammo, to which he attributed at least as much importance as safety of the crew compartment. So for those less familiar with his philosophy, basically ammo protection = crew protection. 

There is a multitude of advantages; Carrying injured infantry in the back. Safe exit for the crew. Easy and quick resupplies. Reducing potential firing angles fatal for the crew. 

What is the disadvantage? Bad weight distribution. But that was fixed with a center-rear mounted turret and unevenly spread wheels. 

 

You wrote that a front-mounted engine could potentionally reduce the frontal area needing protection. How? Unless you want to claim that the engine acts as enough armor to stop anything by itself, this won't happen IMO. Tanks and other combat vehicles (such as wheeled and tracked infantry fighting vehicles) with front-mounted engines are always taller at the front than current combat vehicles with rear-mounted engines. Even if it was possible to create an engine, that delivers enough power while being small enough to not affect the height/width of the vehicle, the frontal area requiring protection should remain the same size as with a rear-mounted engine in best case. Why? Because the crew has to sit in front of the turret (or directly below the turret), if one wants to have optical sights (vision blocks) as back-up solution for electronic systems. If you want a rear door or ramp to evacuate the crew, the height of the hull might even be increased compared to currently existing tanks.

 

This is a misconception you often repeat without trying to understand actually, how one needs to armor a frontal-engine design. The hull becomes taller indeed, but it doesn't mean the entirety of the hull frontal profile needs to have thick armor. The Merkava series of tanks, especially the earliest, show that armor directly above the engine is rather thin, as the angle becomes far too high (akin to Abrams' concept of UFP armor).  There is only a certain portion on the UFP that needs armor, and that is the nose and the engine cover-plate. The main armor though, would come in the form of near vertical plates located behind the fuel tanks, as suggested by Rolf Hilmes and Ogorkiewicz. 

Also supported by various accounts of Merkava tanks fending off ATGMs and ATRs that would leave a few fuel leaks (would switch to other fuel tanks on the sides and rear) but with non-perforated main armor and undamaged engines.

Again, looking at any other tank, you see that not 100% of the height is protected with thick armor.

 

Another issue with front-mounted engines is armor integration. In Germany the VTF (Versuchsträger Frontantrieb) was tested in 1984, after Germany considered the concept of a MBT with front-mounted engines. An major issue seen with the VTF was the weight distribution: Having thick frontal armor and the powerpack at the vehicle front caused a massive weight disbalance, which affects the mobility. Unless the turret is mounted in the rear of the vehicle - which would eliminate the option of having a rear ramp - the tank cannot have the same armor thickness at the hull as with a conventional layout.

 

There are ways to fix the weight distribution issue, you know. Rear placed ammo and center-rear placement of turret are a good way to counterbalance. 

 

The cooling and exhaust of front-mounted engines are an issue. If the engine is front-mounted, you cannot move the exhaust and air vents to the rear of the vehicle, unless giving up any gained spaced (which is required for a rear door). This means there are ballistic holes, i.e. the engine vents won't be protected close to the same level as the rest of the hull. Any hit here by an ATGM or an APFSDS could lead to a penetration. This is sub-optimal, because it would be located in the frontal 60° arc. In general the tank needs to have more side skirts for protecting the frontal 60° arc, when the crew is moved further away from the front.

 

It's possible to place heavy side skirts exclusively behind the vents and in front of the crew compartment and provide the same level of protection. The only exception I see is the Mark 4 and prototypes of Mark 3 utilizing thick side armor throughout the whole length, but that was when the Kassag mods were added, including the better armor distribution, which also included turret armor on the sides.

 

Three further problems of tanks with front-mounted engines according to the German military are lowered visibility for the driver (the engine creates a huge dead zone for his optics), reduced gun depression (only 7° on the Merkava) and reduced mobility when driving at maximum speed through very uneven engine (otherwise the drive sprocket located at the front of the tank can hit the terrain and be damaged, leaving the tank immobilized).

 

And how experienced is the German military with frontal engine tanks? Surely such design is no good for a country with rough, rocky, uneven terrain, which is why no such country has adopted one. 

Sarcasm off, the only problem with mobility on the Merkavas at least, was the engines. 

First the AVDS-1790-6 had issues when going up slopes, and now the MTU 883 is problematic enough to opt for a less powerful 1,200hp engine instead.

 

Oh and the gun depression of 7° on the Merkavas is only relevant to the Mark 3/4. On 105mm armed variants, it was 8.5°. 

 

So I don't see any reason why future tanks should move to front-mounted engines. Just the demand of better protection per weight should already favour rear-mounted engine concepts.

 

One of the main conclusions of the post-battle analysis in 1973 of thousands of destroyed tanks belonging to Israel, Syria, and Egypt alike, that people often ignore, is that the rate of mission kills was exactly the same for penetrations to the engine compartment, and penetrations to crew compartment - 100%. These would always bring a tank to a halt. 

But what is the tactical advantage of a frontal mounted engine? Prevent the first and keep the latter at minimum. 

The end result is an unchanged rate of knocked out tanks and required replacements, but a much higher survivability of the crew, which is highly important to anyone who wishes to maintain a well trained army for prolonged conflicts or attrition warfare.

 

The Merkava tank, while slightly taller than average, is shorter by quite a margin, which helps to keep its weight down.

[Walter_Sobchak]

First the AVDS-1790-6 had issues when going up slopes, and now the MTU 883 is problematic enough to opt for a less powerful 1,200hp engine instead.

 

I would be interested in hearing what you know about issues the IDF has had with the MTU 883.  

[Mighty_Zuk]

Frankly, I dont know any more than the average concerned citizen following the news.

A little over 10 years ago, Israel ordered a batch of 100 engines. IIRC 4 were unusable from the beginning, and a few more broke shortly after. It didnt help that they were significantly more expensive than the AVDS alternative.

The IDF thankfully does have a long experience in engine designing and making, so the problem was fixed with General Dynamics approval fairly quickly.

However they still broke down more frequently than the IDF would consider normal.

According to IDF Spokesperson unit, the fixes were tested and proven in numerous conflicts, however by the year 2012 a reserve brigade using the Mark 4 was for the most part shut down, as most of its tanks were inoperable and awaiting engines.

The Namer, for these reasons, had initially been fitted with the AVDS-1790-9AR used on the Merkava 3, and was said to later receive the MTU883. However it kept the AVDS to this day and there are no discussions about changing it.

It's worth mentioning the AVDS-1790-9AR costs about a third of an MTU883.

[Walter_Sobchak]

Frankly, I dont know any more than the average concerned citizen following the news.

A little over 10 years ago, Israel ordered a batch of 100 engines. IIRC 4 were unusable from the beginning, and a few more broke shortly after. It didnt help that they were significantly more expensive than the AVDS alternative.

The IDF thankfully does have a long experience in engine designing and making, so the problem was fixed with General Dynamics approval fairly quickly.

However they still broke down more frequently than the IDF would consider normal.

According to IDF Spokesperson unit, the fixes were tested and proven in numerous conflicts, however by the year 2012 a reserve brigade using the Mark 4 was for the most part shut down, as most of its tanks were inoperable and awaiting engines.

The Namer, for these reasons, had initially been fitted with the AVDS-1790-9AR used on the Merkava 3, and was said to later receive the MTU883. However it kept the AVDS to this day and there are no discussions about changing it.

It's worth mentioning the AVDS-1790-9AR costs about a third of an MTU883.

 

God Bless the AVDS-1790.  It's what kept food on the family table when I was a child and it's what pays for my fathers pension these days.  I've had a lot of conversations with my pop over the past decade about the tank engine business.  He has some pretty strong opinions, but I will refrain from posting details here.  I'll just say that he was not a fan of MTU.  

[Collimatrix]

 

You wrote that a front-mounted engine could potentionally reduce the frontal area needing protection. How? Unless you want to claim that the engine acts as enough armor to stop anything by itself, this won't happen IMO. Tanks and other combat vehicles (such as wheeled and tracked infantry fighting vehicles) with front-mounted engines are always taller at the front than current combat vehicles with rear-mounted engines. Even if it was possible to create an engine, that delivers enough power while being small enough to not affect the height/width of the vehicle, the frontal area requiring protection should remain the same size as with a rear-mounted engine in best case. Why? Because the crew has to sit in front of the turret (or directly below the turret), if one wants to have optical sights (vision blocks) as back-up solution for electronic systems. If you want a rear door or ramp to evacuate the crew, the height of the hull might even be increased compared to currently existing tanks.

 

 

Look at object 416:

 

 

It had a shorter hull than a T-54, and it had a front-mounted engine.

 

It's definitely possible to make an engine that fits in the hull of a tank without pushing the hull very tall.  The engine just has to be something other than a conventional diesel V.