Saturday, May 30, 2020

Electric Armoured Fighting Vehicles?

 By Jastej Singh Matharu

Let us examine the possibility of having an electric Armoured Fighting Vehicle (AFV).

Electric components have always been a challenge in the design of AFVs. For example In the case of tanks a large number of services which are utilised need electrical power. A tank uses electricity for radio and intercommunication, for the wipers, for the various types of night vision devices, for the computer systems, for the automotive auxiliaries like the various types of pumps, the gauges, the navigation equipment, lighting systems, ventilation systems, gun control system and the fire control system.

To cater for these electrical loads, like any other vehicle the tank also has batteries that are charged by using the power from the main engine. Some tanks have an auxiliary engine for charging the batteries thus conserving the life of the main engine. Also the auxiliary engine operates at a much lower level of noise than the main engine.

In a tactical situation a tank often needs to function in silent watch mode. During this time the tank uses the power stored in its batteries. It follows that we need to have batteries with sufficient capacity to allow functioning of the tank in such a mode.

The heaviest drain on the batteries is during starting. To get around this problem certain tanks have an air starting system, in which air bottles are charged by a compressor getting drive from the main engine and this pressurised air is used for starting the engine.

So in a tank, say which is in the 40 tons to 50 tons range, you will have a 1000 bhp plus engine, which will be the largest component of the vehicle and occupy considerable space in the engine compartment.

If we were to replace the engine with an electric motor, we would need a very large battery to power this motor.
This will be a major problem because the envelope of the tank has to be kept very tight. An increase in the volume of a tank makes it heavier as additional armour protection becomes necessary. The weight penalty would become unacceptably high. An electric powered tank will have to wait, therefore, for the design of very high energy density batteries, much more powerful than the present day lithium ion batteries.

However, as lithium ion batteries have higher energy density than lead acid batteries, we could replace the existing lead acid batteries of tanks with lithium ion batteries. This will increase the time for which the tank can operate in silent watch with its main engine turned off and thus operate with no noise and a much smaller heat signature. This can be of advantage in a tactical situation. To that extent there is a case for increasing the battery capacity of tanks by replacing the present day lead acid batteries with lithium ion batteries.
It follows that being able to design high energy density lithium ion batteries will help in designing a better tank.

Moving away from tanks let’s go on to a lighter AFV, say we look at the Armoured Personnel Carrier (APC) or the Infantry Combat Vehicle (ICV). An ICV often needs to be amphibious and may have a tracked or wheeled configuration. In this case, because the vehicle is lighter than a tank, therefore it becomes more conducive to the possibility of being powered electrically.

A purely electric vehicle would need a fairly large battery, and there is another aspect which will come in, and that is that normally when we are operating in a battle area, the availability of electricity is unlikely. Therefore, while you may be able to have a fully electric ICV in a peacekeeping role or a policing role, it may not be a viable option in the case of a battle area even though it may be feasible to design such a vehicle.

However, a hybrid ICV may become a possibility. In such a vehicle the balance between the capacities of the internal combustion engine and the electric motor will have to be decided with a lot of care.

In a purely electric vehicle the logistics of transporting fuel to it will disappear. In a hybrid vehicle the fuel consumption will reduce and refueling logistics will ease out somewhat.
Where the electric vehicle has a clear advantage over the internal combustion vehicle is that the torque curve of the electric vehicle is the best possible torque curve. It provides very high torque at slow speeds thus making the electric ICV very agile from rest and at slow speed. This is an advantage in a tactical situation. The electric ICV will not need gears and the driver could make it accelerate quickly just by pressing the accelerator pedal.

Another advantage which an electric ICV will have over the internal combustion engine ICV is the ability to move silently. This will be a big advantage in a tactical situation. Therefore the hybrid ICV again seems to suggest itself as a possible option.

In a tracked ICV an internal combustion engine drives the tracks through a driveline and sprockets. However, in a wheeled ICV each wheel has to be given drive. This means that you have the engine at one end of the vehicle, usually the front end, and you have to transmit this drive mechanically to all the wheels through a system of drive shafts and differentials and you need to provide for differential locks and inter axle locks so that the vehicle is able to pull itself out of a difficult position. This adds a large amount of weight to the overall weight of the vehicle.

On the other hand, in the case of an electrical vehicle while the battery will be large and will have considerable weight but the drive to the wheels will be much lighter as compared to the mechanical drive needed in an internal combustion engine, as each wheel will have its own electric motor.

These motors can be very easily utilized through a computer which can be designed to control the motion of these motors. 

This will allow the driver to engage different drive configurations. Let us take a six wheeled vehicle and say that two wheels are slipping due to inadequate surface grip, you just cut the drive to the motors driving these wheels and extricate the stuck vehicle by giving drive to the remaining four wheels which are not slipping. This will be a very powerful advantage of having an electrical vehicle.

The next thing which comes is that ICVs need to be amphibious, over here we need to ensure that the electric motors are totally sealed and kept free from any possible water ingress.

Also an amphibious vehicle has to propel itself in water. This may be done by the wheels, or propellers or water jets. Traditionally such drives have been difficult to achieve, as these were mechanical drives. On the other hand it will be easy to give an electric drive to a propeller through an appropriately placed drive motor. 

The designer of an electrical vehicle will have much more flexibility as compared to the designer of an internal combustion engine vehicle. An electrical ICV will be equally agile on land and on water.

In any AFV whether a tank or an ICV there is a need for having a minimum speed which is needed to operate in a tactical environment. Also there will be a need to have adequate top speed on both roads and cross country. Here also the electric powered vehicle will be better as the electric motor gives excellent torque at slower speeds without any need of changing gears.

For vehicles which are even lighter than ICVs like armoured reconnaissance vehicles the hybrid vehicle may become a viable option.

Storing liquid fuels in AFVs has always been a challenge as this gives rise to a fire hazard problem. Any reduction in fuel storage requirements will reduce this hazard. Thus there is an advantage of having electric or hybrid vehicles.
Maintenance requirements of electric vehicles are typically less than internal combustion engines.

Internal combustion engines are vulnerable to quick wear and tear in deserts as dust may be ingested. To prevent this air cleaning systems have to be designed and maintained with perfection. Electrical vehicles will have no such problem.
Broadly speaking as far as design is concerned; in a tank you would have a more powerful electrical system with lithium ion batteries, which will give a tank a greater ability to operate silently. In ICVs you may have hybrid vehicles which will be very agile both on water and land, and in the case of the lighter reconnaissance armoured vehicles you may be able to have vehicles which may be fully electric or hybrid vehicles. Hybrid vehicles have higher ranges of operation with the same amount of fuel thus easing the logistical load of supplying fuel.

Storing and transporting fuel is a major challenge in any operation and any easing of this load will free resources for other logistic tasks. Though conversely spare battery packs will have to be provisioned for the electric and hybrid vehicles. However, if we were to use a standardised battery pack in all vehicles it would also lead to helping out with other battery powered equipment which we already have in a battle area.

Finally it appears that with the technology available in the civilian electric vehicle industry, such as better batteries and motors, it looks that the day is not far when we will see vehicles which have large capacity batteries or full fledged electric or hybrid armoured fighting vehicles in the battlefield milieu.

My Thoughts on Main Battle Tank Design

 By Jastej Singh Matharu

[I have recorded my thoughts and transcribed them. So the text may come across like a conversation. I have been associated with Armoured Fighting Vehicles since 1984 mainly as a maintenance engineer and also for a few years I worked on design related to an engine retro-fitment project. I also taught tank technology for a couple of years.]
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Essentially if you look at a tank it has everything that a vehicle has got and then a lot more. I will talk about the battle tank; ground upwards, something like if you were to talk about a car tyres upwards.

First and foremost what is in touch with the ground is what we call the running gear which is consisting of the tracks and the bogie wheels which ensure that the tank is able to move. The running gear is getting its drive from a sprocket which is connected from the engine compartment and in order for the tracks to go around smoothly on the other end we have an idler which allows the tracks to go around and lay itself below the road wheels which are also called bogie wheels.
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In order to hold the tracks on the bogie wheels we have something called a horn which is there on every track link and the bogie wheels are in pairs; the horns are going through the bogie wheels between the bogie wheels and that’s why when the tank is turning the tracks do not come off or in the language of armoured fighting vehicle the tracks do not shed.

The bogie wheels are in turn connected to the hull of the tank through the suspension system. Typically the suspension system has got axle arms with some sort of a suspension mechanism which absorbs the shocks from the ground. So as the tank moves there is a combination of a spring and a damper in every suspension. The purpose of the spring is to absorb the shock and every time the tank hits a bump the spring compresses to absorb the shock and does not transmit directly to the hull; in addition to this, so that the tank does not keep bobbing up and down we have the shock absorber or what we call the damper which dampens the up and down bobbing of the spring. With this system we get connected to the hull and there are a variety of suspension systems. They can be coil spring pneumatic spring or other designs.

Now we move on the hull. Typically the hull of a tank is divided into three parts. In front is the driver’s compartment, there are tanks which have got the engine right in front, but usually the driver’s compartment comes in front.

Then we have the fighting compartment and in the rear of the tank we have the engine compartment from which the drive goes out the sprocket which I had mentioned earlier.

The driver’s compartment since it is only having the need of holding a driver it normally has space on either side of the driver so this space can be used for storing ammunition or fuel or batteries, things like that.

Behind the driver’s compartment is the fighting compartment. The main element which is there in the fighting compartment is the turret in this compartment you would have three people the commander the loader and the gunner. Certain tanks have got an automatic loading system, in that case in the fighting compartment the loader is replaced by the automatic loading mechanism. In this case the fighting compartment has only the commander and gunner. New tanks are coming up which will have no one in the fighting compartment. It will be all automated.

Behind the fighting compartment we have the engine compartment. While between the driver’s compartment and the fighting compartment there is really no separation and there is no bulkhead. The driver can exit out of the fighting compartment and the commander and loader can exit out of the driver’s compartment. But in the case of the connection between the fighting compartment and the engine compartment there is a bulkhead. The purpose of the bulkhead is to totally isolate the engine compartment, for obvious reasons, because the engine will have gasses and fuel and fumes which are not good for the crew so the engine and the crew are kept separate.

This bulkhead has various features, for example it will have inspection plates from where we can peer into the engine compartment, specially during maintenance and it will have a number of wires and looms ad pipes going from the fighting compartment to the engine compartment. For electrical connections normally sockets are used.

The engine compartment has the engine, the transmission and the final drives which in turn connect to the sprockets. The sprockets get the drive from the final drive and then run the running gear.

The engine compartment will have the various systems, the engine itself, the lubrication system, the cooling system, the fuel system, the electrical system, the air intake system, the fire fighting system and such like systems.

The engine compartment as I said will be enclosed and the cooling will be achieved through the means of a cooling fan. The cooling fan can achieve cooling in various ways. One way is where it throws out air from the engine compartment creating a low pressure and this results in air being sucked into the engine compartment through the radiators. Normally there will be a number of radiators, water, oil, hydraulic and such like.

The engine compartment will also have an inlet for the air to the air cleaner which will supply air to the engine inlet.

There will also be a passage for the exit of the exhaust from the engine compartment.

Usually tanks have diesel engines but one has a gas turbine engine. Some time tanks have a main engine and an auxiliary engine.

A word over here about the auxiliary engine and the starting system. Normally the starting of a big engine takes a lot of current and drains the battery. So we could have an auxiliary engine which will recharge the battery. This is needed if the electrical starting is the main starting of the tank. However in certain tanks the starting is through air starting in which case the auxiliary engine is dispensed with. And then you have the air starting in which case the main engine keeps the air bottle charged and the stored air pressure is used for starting the main engine thus conserving the electric charge of the battery.

The purpose of the battery here is to give enough power for the tank to be able to operate it’s electrical systems with the main engine being switched off. If you had the auxiliary engine that could keep running as being smaller it produces very little noise and heat. Starting the main engine would be a give away of your location. So having an auxiliary engine or not is a result of a balance which has to be made.

Tank design is all about balancing one type of requirement with another.

Coming back to the fighting compartment. The main thing which is there is the turret. The turret is mounted on turret ring in the hull. The turret is able to rotate 360 degrees. The electrical connection of the turret to the hull is through some sort of a device like a rotary base junction which is placed at the bottom of the turret from where the turret rotates. In this manner we achieve the supply to the many electrical systems in the turret.

The main thing which the turret houses is the main gun of the tank. The main gun is a huge gun. Main guns of tanks fire very high velocity projectiles. So an important part of the design here is how to contain the recoil of the gun within the space of the turret.

In the turret there are two more important systems. These are the gun control system and fire control system. The purpose of the gun control system is to allow the commander or the gunner to rotate the turret at will and to acquire targets. The purpose is to quickly swivel the turret around and bring the gun onto the target.

The fire control system decides the manner in which the gun will be fired. Nowadays tanks have the stabilising system which means irrespective of how the hull is moving the gun remains locked onto the target. This is what makes the tank a very lethal weapon. A tank can move very fast and at the same time remain locked onto the target and fire accurately. This is the final aim of the designer of the tank.

The gun itself can be rifled or smooth bore. The main purpose of the gun is to be able to fire a projectile which will defeat the adversary tank’s armour. So high velocity rounds are needed and a variety of ammunition has been invented for this.

Coming back to the hull. It is very important for the designer to make a hull which is able to protect the tank from the adversary’s projectiles. Here again the issue of balance comes. Normally the frontal part of the tank, which is known as the frontal arc is heavily protected and the sides, rear and bottom less so. It is impossible to protect a tank heavily from all sides.

A variety of armours have been developed. There used to be the monolithic armour which was a chunk of steel, now new armours have come up which are designed to defeat projectiles without too much of a weight penalty.

The classic balance a tank designer has to achieve is between the firepower and the mobility and the protection. The running gear, the engine the sprocket these all provide the mobility aspect. The firepower is by the gun, it’s calibre’ the speed of the projectile’ accuracy of the projectile and the ability to be able to move and fire.

Protection is through the armour.

It is obvious that if you want a bigger gun it means it will be heavier and the tank’s weight will go up.

Similarly if you want to increase the protection the tank’s weight goes up.

If you want now to put in a bigger more powerful engine you need more space in the engine compartment this will make the tank’s hull bigger which in turn will again require protection.

So in tank design one thing leads to another and you have to strike an optimum balance based on your requirement.

Various armies according to their requirements based on their own situations have designed different tanks. A lot of technology goes in to ensure that you are able to get the optimum firepower, mobility and protection as per your own requirements.

It is expensive technology. Developed after tremendous research and development. 

In spite of the variety of other weapons, both on the ground and in the air, the main battle tank remains the most lethal weapon on the battlefield even today