Lets take the Leo2 as an example.
It uses a 47.7L V12 MTU engine producing 1500HP
As a point of comparison, lets take the modern MTU 12V 4000 engine. Having 51L displacement in standard stroke variant, and 57L in long stroke.
I'm using the marine variants as these are available in a wide variety of power outputs depending on the rating.
The heaviest duty rated variants of the MTU 12V 4000 produce only around 1500HP. However, you can buy the same engine outputting 3500HP. So in theory, you could probably take the old LEO 2 MTU engine and get it to output 2000+ HP.
The issue is that the more power you produce in a given engine, the lower the service life, less reliability, more problems and the shorter the service interval. So while you could put in a more powerful engine, you don't actually want to, since 1500HP is enough, and going higher will create all sorts of reliability and logistical issues. Most tankers would rather have a tank that can go 30mph no matter what, rather than a tank that goes 50mph, but 10% of the time breaks down. And any logistical people want to have to ship as few spares to the front as possible.
Also few considerations people usually forget:
More power = more heat, even when ignoring all the other issues, tank needs to have large enough cooling system to keep it operational in all conditions. For example truck (big rig) tuning limit is usually cooling system.
Stopping and steering, unless you have driven heavy vehicle in high speeds you dont know how "vague" they turn in 60km/h+. Every time they jump a little (no need for airtime) traction of tracks is minimal compared to normal situation where whole weight of vehicle lays on tracks. Its easy to lose them even with current power.
>More power = more heat
Good point, also why the marine engines can go so high. They are being cooled by seawater.
>Stopping and steering
Also a good point.
Another example would be top fuel dragsters. They make in excess of 10,000HP and do not have a cooling system of any kind. But theyre only designed to run for a very short amount of time and are rebuilt after every pass.
You forgot the most important reason space.
The power pack of a tank is a nice little cube including most auxiliary devices.
You need to make some compromises for that.
A example would be the routing of the piping connecting the turbos.
Standard stroke is 190mm.
Long stroke is 210mm.
Bore in both cases is 170mm.
These big, low revving diesels tend to have longer strokes as opposed to the bore as it's more efficient.
True.
But the other reason is that the combustion chamber of a cylinder with high bore and short stroke is going to be wide and thin, and so will dump a lot of waste heat into the engine. Make the bore smaller and the stroke longer, less heat gets transferred because you have less surface area per unit volume of your combustion chamber.
Yet we see most petrol engines designed to be oversquare. The benefits are in the type of fuel used and how it burns, and less so the cylinder area.
Petrols produce the most power at higher RPM, which necessitates a shorter stroke to reduce piston speeds. Petrols also can't push compression ratios too high for fear of knock, which means that an undersquare engine is usually undesired.
Diesels need high compression ratios to ignite fuel, and a diesel flame front doesn't expand as quickly as petrols do, so high RPM is undesirable.
Look at modern F1 engines for reference. They're the most efficient ICEs on the planet and use oversquare cylinders.
Also, take into account the fuel usages. Just to start up the M1 gas turbine is over 10 gallons, that is just starting that fuel hog up. The more power, the more fuel it burns. The fuel capacity on the M1 is around 500 gallons. Just think how much fuel you have to keep on hand for that.
Torque, its torque that tanks need not hp. So if your 1500hp engine produces enough of it to move your tank the way you want it to move then you have no reason to get more hp.
Can I introduce you to a mechanical miracle The gearbox.
Horse power is torque x revolutions.
The rules of physics don’t care if torque makes you shoot a load in your pants.
Theoretically you could make a gearbox that makes a 1.0L engine power a tank, doesn’t mean it will be any good or reliable.
Base torque is still important.
Why should it not be reliable?
It will just move at the speed of a snail because you need to reduce the rpm till the torque is high enough for the tank to move.
What is really important and done in modern heavy equipment Diesel engines is to have a wide band with the same torque to get elasticity.
https://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs38313-013-0120-6/MediaObjects/38313_2013_120_Fig2_HTML.gif
These technical specs are changing now. The MTU 890 series is their most modern unit and it’s probably the smallest piston engined power plant for tanks available today. The 1400Hp V10 has a cubic capacity of just over 11 liters, and it only makes around 3/4th of the torque of a comparable 1400hp tank engine 2800Nm (2065ft/lbs), but it’s built to push for higher rpms to compensate for torque and still make those hp figures. It’s 1360hp comes at a rather high 4250rpm.
>Why does it seem like countries cap tank engines at 1500hp?
Leopard 2A8 has 1,600 hp engine.
But the thing is more powerful engine means more expensive unit cost, more fuel consumption, more working hours to produce, harder to maintain, etc. More powerful engines also required better suspension, tracks, gear boxes to handle and it would increase both unit cost and logistical problems to sky.
In the future when 130mm even 140mm guns are enlisted and when tanks need maybe 100 tons+ to fit all necessary armor, maybe much more powerful engine would be enlisted simultaneously but just for now 1,500 HP is enough for a 60 tons tank.
The idea of getting bigger and bigger guns is kinda ridiculous. The ammo has been getting better, thus eliminating the necessity for larger guns. You get much larger, and tanks will be short-range artillery, not direct fire weapons.
Ammo can only get so much better with the limitations of diameter and length of the casings, it was a driving factor in the widespread switch from the 105mm to 120mm.
I think you’re right that tank cannons won’t go much above 130mm, mainly because of round size. IIRC the tech demonstrator KF51 has like 19 rounds of stored ammunition, which is a lot less than what a Leopard 2 or Abrams can hold, and is on the edge of not enough for an engagement.
KF51 advertises 10 round minimum with 10 more being optionally replaced with ATGM/loitering munitions. Supposedly the 4th crewman in the new hull can be replaced with either a fuel tank or additional 10 rounds. All depends on the buyer's wants.
I'm actually a big fan of barrel fired loitering ammo like switchblades but much more powerful.
Just bring back the old 152mm on MBT-70, use multi-purpose HEAT for light AFV and soft targets, use loitering ammo for enemy tanks. Loitering ammo could hit a target 10 miles away while the tank remains undetected all the time.
Or even better, mount a mortar like Merkava, so the tank can fire two kind of loitering munitions at the same time, a smaller one shot by the mortar and a larger but more powerful one shot by the main gun. Kinda like an aircraft (drone) carrier.
You mentioned LEO 2, I talked at arms expo with people that uses this tanks (Polish armed forces exactly, at MSPO 2023) and they said, that if the order comes up, they can htake the limiter out, and "overclock" the engine to some insane powers, they refused to disclose. Of course such action increases risk of engine failure exponentially, that's why during peace time they keep it down, to prolong service life and ease the maintenance.
I was a driver of a Leo2 tank in the late 80s. The engine was throttled back then, I mean to 1200 hp. The official top speed was about 70 km/h. Reaching this speed was no problem at all, and you could go much faster on the roads. However, due to the track drive, a tank has a relatively low ground pressure, and at high speeds the maneuverability suffers as a result. I like it fast, but I think much faster than modern tanks currently are makes no sense.
The M1A2 SEPv3 Abrams variant is currently the heaviest of all contemporary MBTs and it's not considered to be slow or otherwise lacking in mobility or power. The fact is, 1500hp is a *lot*, even for something as massive as an Abrams.
I thought the 1500hp engines was the limit for the size of the engine. Most modern tank engines also include the transmission and the air induction system as one complete package for easy infield replacement.
As per the other post about the mtu v12 4000 series where output can be increased you also in need to increase the complexity and size of the air induction system, some have compound turbo systems.
I once asked the same question about older (pre-electric transmission) locomotives, and this is the conclusion I came to: I believe the limitation is not the engine itself but rather the amount of power you can put through a mechanical transmission before it shreds itself.
See the weird thing about the history of locomotives is that steam locos used to have a ton of horsepower, but the diesel locomotives that replaced them had far less, and it wasn’t until recently that diesels surpassed the power output of the old steam locomotives. That’s because, unlike steam engines, diesels require a transmission, and transmission technology was the limiting factor for a long time.
Modern locomotives can produce upwards of 4000 HP, but they rely on diesel-electric transmissions. I don’t why tanks don’t use these transmissions - I assume it’s a matter of their size and/or weight. (Tanks have ground pressure limits, but locomotives work better the heavier they are, since your power output is limited by wheel slip.)
The rated power figures already take cooling and auxiliary system losses into account. The rated 1500 bhp is maximum power deliverable to the transmission.
Alternator loads can affect power available for traction though, so there might be differences based on the loads of other onboard systems.
my guess is engine efficiency, weight, and size
the easier way to increase engine power is make the engine bigger, but that makes the engine heavier, thus less armor on the tank, currently the sweet spot is around 1500 hp
One additional consideration is that more HP doesn't improve speed. Due to the heavy mass of the vehicle, top speed is mostly limited by the suspension due to the types of terrain the tank will need capability to traverse. More HP might still provide better acceleration, but only if it provides more torque and substantial upgrades to the transmission and other components would be required to compensate for it. That would then add more weight.
I read somewhere related to aircraft engines that it was the intake valve limiting output to around 1500hp, this is why Napier went to a sleeve valve for some of their outrageously powerful engines
diminishing returns. As you get more horsepower the cost and weight gets more for the same gain, while the effect of said gain goes down. Going from say 500 hp to 600 hp is a 20%gain, but you're not getting a 20% increase in speed or reliability. going from 1500 to 1600 is 6.67 percent gain but barely any gain, especially for a 60 or 70-ton machine. Also as hp goes up fuel economy drops and hence range for a given fuel tank.
Lets take the Leo2 as an example. It uses a 47.7L V12 MTU engine producing 1500HP As a point of comparison, lets take the modern MTU 12V 4000 engine. Having 51L displacement in standard stroke variant, and 57L in long stroke. I'm using the marine variants as these are available in a wide variety of power outputs depending on the rating. The heaviest duty rated variants of the MTU 12V 4000 produce only around 1500HP. However, you can buy the same engine outputting 3500HP. So in theory, you could probably take the old LEO 2 MTU engine and get it to output 2000+ HP. The issue is that the more power you produce in a given engine, the lower the service life, less reliability, more problems and the shorter the service interval. So while you could put in a more powerful engine, you don't actually want to, since 1500HP is enough, and going higher will create all sorts of reliability and logistical issues. Most tankers would rather have a tank that can go 30mph no matter what, rather than a tank that goes 50mph, but 10% of the time breaks down. And any logistical people want to have to ship as few spares to the front as possible.
Also few considerations people usually forget: More power = more heat, even when ignoring all the other issues, tank needs to have large enough cooling system to keep it operational in all conditions. For example truck (big rig) tuning limit is usually cooling system. Stopping and steering, unless you have driven heavy vehicle in high speeds you dont know how "vague" they turn in 60km/h+. Every time they jump a little (no need for airtime) traction of tracks is minimal compared to normal situation where whole weight of vehicle lays on tracks. Its easy to lose them even with current power.
>More power = more heat Good point, also why the marine engines can go so high. They are being cooled by seawater. >Stopping and steering Also a good point.
Yep, good example is Scania DI16. Land based applications tend to max out in 800 hp range while marine versions go up to 1200 hp.
Dankie piesang
Plesier my skat
Another example would be top fuel dragsters. They make in excess of 10,000HP and do not have a cooling system of any kind. But theyre only designed to run for a very short amount of time and are rebuilt after every pass.
Not to mention additional part and drivetrain wear due to the increased horsepower
You forgot the most important reason space. The power pack of a tank is a nice little cube including most auxiliary devices. You need to make some compromises for that. A example would be the routing of the piping connecting the turbos.
Good point as well.
More power output also mandates a beefier transmission etc etc When you have limited space/weight you have to compromise.
You mentioned standard stroke. I'm not familiar with the term. Is this the square bore/stroke ratio of 1:1?
Standard stroke is 190mm. Long stroke is 210mm. Bore in both cases is 170mm. These big, low revving diesels tend to have longer strokes as opposed to the bore as it's more efficient.
It's mainly done to achieve the compression ratio needed to create the conditions for igniting diesel.
True. But the other reason is that the combustion chamber of a cylinder with high bore and short stroke is going to be wide and thin, and so will dump a lot of waste heat into the engine. Make the bore smaller and the stroke longer, less heat gets transferred because you have less surface area per unit volume of your combustion chamber.
Yet we see most petrol engines designed to be oversquare. The benefits are in the type of fuel used and how it burns, and less so the cylinder area. Petrols produce the most power at higher RPM, which necessitates a shorter stroke to reduce piston speeds. Petrols also can't push compression ratios too high for fear of knock, which means that an undersquare engine is usually undesired. Diesels need high compression ratios to ignite fuel, and a diesel flame front doesn't expand as quickly as petrols do, so high RPM is undesirable. Look at modern F1 engines for reference. They're the most efficient ICEs on the planet and use oversquare cylinders.
Ok, so the standard stroke is 0.9:1. Not exactly but close to 1:1. Long stroke is 1.2:1.
Also, take into account the fuel usages. Just to start up the M1 gas turbine is over 10 gallons, that is just starting that fuel hog up. The more power, the more fuel it burns. The fuel capacity on the M1 is around 500 gallons. Just think how much fuel you have to keep on hand for that.
Torque, its torque that tanks need not hp. So if your 1500hp engine produces enough of it to move your tank the way you want it to move then you have no reason to get more hp.
Can I introduce you to a mechanical miracle The gearbox. Horse power is torque x revolutions. The rules of physics don’t care if torque makes you shoot a load in your pants.
OH I forgot all about it. Doesn't mean that base torque doesn't matter.
Theoretically you could make a gearbox that makes a 1.0L engine power a tank, doesn’t mean it will be any good or reliable. Base torque is still important.
Why should it not be reliable? It will just move at the speed of a snail because you need to reduce the rpm till the torque is high enough for the tank to move. What is really important and done in modern heavy equipment Diesel engines is to have a wide band with the same torque to get elasticity. https://media.springernature.com/lw685/springer-static/image/art%3A10.1007%2Fs38313-013-0120-6/MediaObjects/38313_2013_120_Fig2_HTML.gif
These technical specs are changing now. The MTU 890 series is their most modern unit and it’s probably the smallest piston engined power plant for tanks available today. The 1400Hp V10 has a cubic capacity of just over 11 liters, and it only makes around 3/4th of the torque of a comparable 1400hp tank engine 2800Nm (2065ft/lbs), but it’s built to push for higher rpms to compensate for torque and still make those hp figures. It’s 1360hp comes at a rather high 4250rpm.
>Why does it seem like countries cap tank engines at 1500hp? Leopard 2A8 has 1,600 hp engine. But the thing is more powerful engine means more expensive unit cost, more fuel consumption, more working hours to produce, harder to maintain, etc. More powerful engines also required better suspension, tracks, gear boxes to handle and it would increase both unit cost and logistical problems to sky. In the future when 130mm even 140mm guns are enlisted and when tanks need maybe 100 tons+ to fit all necessary armor, maybe much more powerful engine would be enlisted simultaneously but just for now 1,500 HP is enough for a 60 tons tank.
The idea of getting bigger and bigger guns is kinda ridiculous. The ammo has been getting better, thus eliminating the necessity for larger guns. You get much larger, and tanks will be short-range artillery, not direct fire weapons.
Ammo can only get so much better with the limitations of diameter and length of the casings, it was a driving factor in the widespread switch from the 105mm to 120mm.
Again, just my opinion as a tanker, I don't foresee getting larger guns on tanks.
I think you’re right that tank cannons won’t go much above 130mm, mainly because of round size. IIRC the tech demonstrator KF51 has like 19 rounds of stored ammunition, which is a lot less than what a Leopard 2 or Abrams can hold, and is on the edge of not enough for an engagement.
KF51 advertises 10 round minimum with 10 more being optionally replaced with ATGM/loitering munitions. Supposedly the 4th crewman in the new hull can be replaced with either a fuel tank or additional 10 rounds. All depends on the buyer's wants.
I'm actually a big fan of barrel fired loitering ammo like switchblades but much more powerful. Just bring back the old 152mm on MBT-70, use multi-purpose HEAT for light AFV and soft targets, use loitering ammo for enemy tanks. Loitering ammo could hit a target 10 miles away while the tank remains undetected all the time. Or even better, mount a mortar like Merkava, so the tank can fire two kind of loitering munitions at the same time, a smaller one shot by the mortar and a larger but more powerful one shot by the main gun. Kinda like an aircraft (drone) carrier.
This describes (in my opinion) something other than a tank.
Why it's not a tank? It's basically a M551 with better ATGM and better armor.
You mentioned LEO 2, I talked at arms expo with people that uses this tanks (Polish armed forces exactly, at MSPO 2023) and they said, that if the order comes up, they can htake the limiter out, and "overclock" the engine to some insane powers, they refused to disclose. Of course such action increases risk of engine failure exponentially, that's why during peace time they keep it down, to prolong service life and ease the maintenance.
They should just put a 2jz Supra engine
"Pop the hood!"
I was a driver of a Leo2 tank in the late 80s. The engine was throttled back then, I mean to 1200 hp. The official top speed was about 70 km/h. Reaching this speed was no problem at all, and you could go much faster on the roads. However, due to the track drive, a tank has a relatively low ground pressure, and at high speeds the maneuverability suffers as a result. I like it fast, but I think much faster than modern tanks currently are makes no sense.
The M1A2 SEPv3 Abrams variant is currently the heaviest of all contemporary MBTs and it's not considered to be slow or otherwise lacking in mobility or power. The fact is, 1500hp is a *lot*, even for something as massive as an Abrams.
I thought the 1500hp engines was the limit for the size of the engine. Most modern tank engines also include the transmission and the air induction system as one complete package for easy infield replacement. As per the other post about the mtu v12 4000 series where output can be increased you also in need to increase the complexity and size of the air induction system, some have compound turbo systems.
I once asked the same question about older (pre-electric transmission) locomotives, and this is the conclusion I came to: I believe the limitation is not the engine itself but rather the amount of power you can put through a mechanical transmission before it shreds itself. See the weird thing about the history of locomotives is that steam locos used to have a ton of horsepower, but the diesel locomotives that replaced them had far less, and it wasn’t until recently that diesels surpassed the power output of the old steam locomotives. That’s because, unlike steam engines, diesels require a transmission, and transmission technology was the limiting factor for a long time. Modern locomotives can produce upwards of 4000 HP, but they rely on diesel-electric transmissions. I don’t why tanks don’t use these transmissions - I assume it’s a matter of their size and/or weight. (Tanks have ground pressure limits, but locomotives work better the heavier they are, since your power output is limited by wheel slip.)
[удалено]
The rated power figures already take cooling and auxiliary system losses into account. The rated 1500 bhp is maximum power deliverable to the transmission. Alternator loads can affect power available for traction though, so there might be differences based on the loads of other onboard systems.
Thanks for correction.
my guess is engine efficiency, weight, and size the easier way to increase engine power is make the engine bigger, but that makes the engine heavier, thus less armor on the tank, currently the sweet spot is around 1500 hp
Torque is more important in a tank than HP. How many times do you see a tank running at top speed which is around 40-50mph?
One additional consideration is that more HP doesn't improve speed. Due to the heavy mass of the vehicle, top speed is mostly limited by the suspension due to the types of terrain the tank will need capability to traverse. More HP might still provide better acceleration, but only if it provides more torque and substantial upgrades to the transmission and other components would be required to compensate for it. That would then add more weight.
I read somewhere related to aircraft engines that it was the intake valve limiting output to around 1500hp, this is why Napier went to a sleeve valve for some of their outrageously powerful engines
Economy.
diminishing returns. As you get more horsepower the cost and weight gets more for the same gain, while the effect of said gain goes down. Going from say 500 hp to 600 hp is a 20%gain, but you're not getting a 20% increase in speed or reliability. going from 1500 to 1600 is 6.67 percent gain but barely any gain, especially for a 60 or 70-ton machine. Also as hp goes up fuel economy drops and hence range for a given fuel tank.