Gulf War and the M1 A1 Abrams Main Battle Tank (Part 7)

In the previous part of our article series, we discussed the mobility, engine selection, power pack and ease of maintenance of the M1A1 Abrams tank. We focused on the operational capabilities and tactical advantages that these features bring to the M1A1 Abrams main battle tank. In this section, we will continue to focus on the engine and power pack.

The relevant section can be accessed from the link below.

Gulf War and the M1 A1 Abrams Main Battle Tank (Part 6)

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What were the major problems encountered during the development of the AGT 1500 engine?

The cover image shows the M1A2 Abrams tank and the AGT 1500 engine removed from the tank.

High fuel consumption; Initially, the M1 Abrams tank was known for its very high fuel consumption. The tank was considered one of the least fuel efficient tanks on the battlefield, travelling less than one mile per gallon. This resulted in the tank requiring constant refuelling, limiting its operational capability.

Lack of an auxiliary power unit (APU); Early models did not have an auxiliary power unit (APU). Therefore, the engine had to be continuously idled to provide power to the tank's main systems (fire control, night vision and fire suppression systems) in the standby position. This led to unnecessary fuel wastage and increased the thermal visibility of the tank, making it more easily detectable. A temporary solution was found by utilising battery power. However, as this solution quickly depleted the batteries, the tank engine had to be switched on to raise the diminishing battery level. The APU unit could be installed on M1A2 tanks in 2017.

Air filtration problems; The engine had to draw large amounts of air through the air intakes, and the first air filters were not sophisticated enough to block fine dust and debris such as sand. This resulted in the first XM-1 tanks not working well in dry and sandy environments. This problem was addressed by building better air filters.

Congressional pressure and the desire to develop a diesel engine; As the Army continually found problems with the gas turbine engine, Congress recommended that the diesel engine design be developed simultaneously. Congress wanted the diesel engine to be an alternative in case the gas turbine engine proved problematic.

Despite these problems, General Dynamics and Textron continued to develop the Lycoming AGT 1500 engine and made various improvements to improve fuel efficiency. The high-pressure turbine rotor was made more efficient, a new coating was applied to the turbine cylinder, the materials of the recovery unit were changed, and the power turbines were resized. These improvements improved fuel efficiency by about 10 per cent. In addition, technologies such as the Turbine Engine Diagnostics (TED) system, following the experience gained after the Gulf War, have facilitated the fault detection and repair of the engine and accelerated maintenance processes.

The engine of the M1 Abrams tank is a turbine engine. Reasons for choosing this engine?

Lightness and Power: The turbine engine is much lighter than an equivalent diesel engine (weighing only 1.1 tonnes) and produces 1500 horsepower. This allows the tank to have a high power-to-weight ratio. As a comparison, the Challenger 2's V12 diesel engine weighs 2 tonnes and produces 1200 horsepower. The German MTU MT883 Ka-500/501 27.4 litre (27,361 cc) 90° V-block 12-cylinder liquid-cooled diesel engine used in the Leopard 2 A4 main battle tank weighs 1.8 tonnes and produces 1500 horsepower at 2,600 rpm (1104 kW). In 2002 an improved version was tested using the MT883 Ka-501 providing 1630 horsepower.

High Power to Weight Ratio: Thanks to the light weight and high power of the turbine engine, the M1 Abrams does not compromise acceleration and top speed despite the addition of armour layers. The M1 can accelerate from 0-32 kilometres in 7 seconds and has a top speed of 72 kilometres per hour. The gas turbine takes a short time from idling to running at full power. As long as the fuel provides stable combustion, the components can reach the operating temperature and full power can be generated in a short time, which can improve the acceleration of the tank. The gas turbine takes only 2.5 seconds to go from idle to full output power, while the diesel engine needs 2 to 3 times.

The image above shows the M1A1 Abrams main battle tank on a dirt road among palm trees.

Fuel Flexibility: The AGT1500 is a truly flexible engine with multi-fuel capability. It can use a variety of liquid fuel types, including jet fuel, diesel, petrol and marine fuel, with high efficiency without requiring any changes to engine or fuel system settings. This versatile fuel compatibility offers operators significant operational adaptability.

In addition to diesel fuel, the turbine engine can also run on different fuel types such as marine diesel, petrol or gas oil. This is a great advantage in military logistics and simplifies the supply of fuel. It also helps the tank to operate in different weather conditions; for example, crystallisation of diesel fuel can be prevented by using kerosene in cold weather. The use of diesel fuel as armour offers high effectiveness in absorbing energy from blast and kinetic energy weapons. This feature creates an advantageous situation in which the fuel can both ensure the functioning of the engine and protect the tank. The non-flammable nature of diesel fuel makes it a relatively safe option for armour function.

Suitability for Cold and Hot Weather Conditions: Turbine engines perform better in cold weather compared to diesel engines. Since diesel fuel can crystallise at low temperatures, the turbine engine overcomes this problem by running on alternative fuels such as kerosene. The gas turbine has fewer friction parts and a smaller starting torque, so a starter motor with a lower ratio can be used. The gas turbine can be started without preheating at a low temperature of -31°C; the Leopard 2 tank MB873 diesel engine requires preheating at -18°C to start.

High Torque: The turbine engine produces higher torque, especially at low shaft speeds. This allows the tank to perform better in difficult terrain.

Ease of Maintenance: Because the combustion chamber is mounted perpendicular to the engine and protrudes outwards, maintenance access to the combustion chamber is simplified. This allows maintenance to be carried out more quickly with the simple removal of a bolted cover. Oil consumption is only 1/10th of that of a diesel engine, and you do not need to change the oil and oil filter regularly.

Efficiency with Recuperator: The recuperator in the turbine engine of the M1 improves fuel efficiency by recovering the heat from the hot exhaust of the engine. It also reduces the thermal visibility of the tank by lowering the heat signature of the exhaust.

The turbine engine of the M1 Abrams tank offers many advantages such as light weight, high power, fuel flexibility, ease of maintenance and high torque. These characteristics significantly increase the combat effectiveness and operational capability of the tank.

However, the biggest disadvantage of turbine engines is that they consume more fuel compared to diesel engines. The M1A1 consumes approximately 4.6 litres of fuel per kilometre when travelling at 40 km/h, while the Leopard 2 consumes 2.2 litres per kilometre when travelling at 40 km/h. However, the US military found the advantages of the turbine engine worth the cost of fuel consumption.

In the following years, research on diesel engine alternatives for the M1 Abrams main battle tank had the objectives of reducing fuel consumption and increasing fuel efficiency. These alternatives aim to offer lower fuel consumption and higher fuel efficiency. In 1997, General Dynamics Land Systems (GDLS) began researching a diesel engine configuration known as EuroPowerPack.

This project was created by integrating the 1500 horsepower V12 MT-883 diesel engine produced by the German company MTU with the HSWL 295TM transmission developed by RENK, also a German company. This integration was intended to provide an alternative power system for the M1 Abrams tank. In this context, studies conducted on the Heavy Combat Vehicle Test Bed (HCVTB) show that the MT-883 diesel engine produces the same power as the gas turbine engine, while offering up to 50 per cent more cruising range thanks to its fuel efficiency. The MT-883 diesel engine was first tested in 1997 under the EuroPowerPack regulation and the results of these tests were made public in 2000. Later, it was also used in HCVTB and GD-883 projects.

The AGT-1500 gas turbine engine is a high performance propulsion system inspired by aviation technologies. The turbine engine burns low cetane (octane) diesel fuel mixed with compressed and heated air. Air entering the engine air intake passes through two compressors. The compressed air is heated by exhaust gases in a recuperator to aid combustion. The heated and compressed air is directed into the combustion chamber where it mixes with fuel vapour. When combustion is initiated by an ignition spark, continuous combustion occurs. The ignition spark is switched off at the completion of the start-up cycle.

The combustion gases rotate two turbines that drive two compressors. The gases then drive the free power turbine, which drives the gearbox via a reduction gearbox. The exhaust gases from the power turbine are passed through the recuperator to heat the incoming air and then sent to the exhaust. The AGT-1500 engine is connected to the Allison X 100-3B transmission through a two-stage power turbine and an epicyclic reduction gear. The power turbine ensures that the transmission's torque converter remains locked over a wide speed range, minimising parasitic power losses and improving fuel efficiency.

The compact design of the engine is made possible by integrating the exhaust heat recovery system around the power turbine, epicyclic reduction gear and connecting shaft. This saves space and improves the overall efficiency of the engine. The power output of the engine is 1120 kW. At maximum power output, the speed of the power turbine is 3000 rpm, the speed of the low-pressure compressor is 33500 rpm and the speed of the high-pressure compressor is 43500 rpm.

The turbine engine of the M1 Abrams tank has a distinctive sound signature. When the engine is started, there is a short period of silence. Then, as the engine speed increases, the sound gets louder. This sound can be described as a characteristic buzz caused by the rotating turbine blades inside. This sound characteristic of the turbine engine distinguishes it from other types of engines.

The turbine engine of the M1 Abrams tank has a twin drive shaft system. This system allows the power generated by the engine to be used for different functions.

The primary drive shaft transmits the main output power of the engine to the wheels, allowing the tank to move. This shaft controls the acceleration, deceleration and change of direction of the tank.

The secondary drive shaft uses the engine's power to drive the tank's auxiliary systems. These systems include compressors, electronic equipment and hydraulic systems. Compressors help the engine to run efficiently by providing air flow to the combustion chamber of the engine.

Electronic equipment supports the tank's communication, navigation and fire control systems. Hydraulic systems are used to rotate the turret, guide the gun and perform other mechanical functions.

The twin drive shaft system allows the engine of the M1 Abrams tank to operate in a versatile and efficient manner. In this way, the tank allows all the necessary systems to function properly while maintaining its mobility. The transmission controls three tank functions: driving, steering and braking. The power from the reduction gearbox of the turbine to the gearbox is transferred through the outputs of the gearbox to move the gears. Steering of the tank is done inside the gearbox. Steering commands from the driver's steering-throttle control cause a hydraulic pump/motor to accelerate one transmission output shaft and decelerate the other.

Braking of the tank is done at each transmission output. A cable from the service brake pedal is connected to pulleys in the transmission. Pressure applied to the pedal rotates the pulleys to engage both brake packs by hydraulic action. Pressure applied to the parking brake pedal is increased through a hydraulic cylinder to mechanically engage both brake packs. Gear Control.

The transmission has four forward speeds and two reverse speeds, a neutral and a pivot state. A remote control lever on the steering-throttle control electrically controls the transmission setting. The remote control can set the transmission to D (normal forward range), L (low forward range), R (reverse), N (neutral), or PVT (pivot). If the transmission control electrical power is interrupted, the transmission will continue to operate in the selected setting until the engine is switched off. When the engine is switched off, the control remains selected, but the transmission automatically shifts to neutral.

Modular Design and Advantages of AGT1500 Engine

The modular design of the AGT1500 engine offers several advantages, significantly improving both logistics and maintenance processes. Here are the main advantages of this design.

Increased Flexibility: The modular construction allows different parts of the motor to be handled separately. This means greater flexibility in logistics and maintenance processes. For example, a failure in one module can be solved by replacing only that module instead of replacing the entire engine.

Reduced Spare Motor Requirement: Thanks to the modularity of the engine, instead of having a complete engine in reserve, it may be sufficient to have only certain modules in reserve. This both saves storage space and reduces costs.

Low Life Cycle Cost: Modular design reduces the lifecycle cost of the engine by simplifying maintenance and repair processes. The ability to easily replace a failed module means less downtime and lower labour costs Efforts to reduce the cost of the Textron Lycoming AGT1500 engine have focused on reducing operating and support costs, particularly for the M1 Abrams tank. Here are some highlights on this topic:

High Costs: Initially, the sustainment cost of the M1 Abrams tank power pack (engine and transmission) was estimated at 21 per cent of the total M1 sustainment cost, with the engine alone accounting for 14 per cent of this cost. Although this cost was less than the initial estimate of 30 per cent, it was still considered a significant expense.

Targeted Savings: The US Army had targeted a 50 per cent reduction in sustainment costs. Textron Lycoming implemented an aggressive reliability improvement programme to achieve this goal. By 1988, the power pack sustainment cost had been reduced to 10 per cent of the total M1 sustainment cost.

Improving the Field Maintenance Concept: A 1989 study showed that additional and significant operating and support cost reductions could be achieved by improving the engine's field maintenance concept and execution.

Integrated Logistics Support Plan (ILS): Developing an effective and economical logistics support capability is one of the most complex tasks in the acquisition of a modern weapon system. The ILS plan includes maintenance, personnel, supply support, training and test equipment. At the beginning of the M1 Programme, insufficient attention was paid to integrated logistic support planning and life cycle cost issues. This had the potential to adversely affect operational and support costs in the long term.

Modular Engine Design: The AGT1500 engine was designed with reliability, easy maintenance and serviceability in mind. The engine consists of four fully interchangeable basic modules. This modular design means flexibility in logistics and maintenance, less spare motor requirements and lower life cycle costs.

On-Condition Maintenance: Unlike other turbine engines, the AGT1500 engine does not have a specific overhaul period. Maintenance operations are symptom-oriented, which minimises maintenance requirements and costs.

Maintenance Levels: The Army requires maintenance to be carried out at the lowest possible level (advanced repair concept). The M1 tank is supported by a three-level maintenance system:

Organisational (Troop) Maintenance: Performed by troop mechanics or tank crews, includes simple adjustments and replacement of easily replaceable failed components (LRU).

Direct Support (DS) / General Support (GS): Performed by mechanics in the Forward Support / Main Support Battalion and includes repair of some components.

Depot Maintenance: Includes overhauls of end products and components, equipment modernisations and all maintenance that exceeds the maintenance capacity of other levels.

High Rate of Depot Returns: Initially, about 60 per cent of engine failures resulted in the return of complete engine units to the depot. By 1988, this rate had fallen to 40 per cent, but was still high. This resulted in high depot repair costs. It was also found that 39 per cent of modules returned to the depot were actually field serviceable.

Direct Support Plus (DS Plus) Programme: This programme aimed to engage field-level engine specialists to help identify faulty modules and prevent unnecessary return of complete engines to the depot. The DS Plus programme implemented in South Korea has led to a significant reduction in costs. For example, the cost per failure dropped from 60 per cent to 26 per cent, with a total saving of $1.2 million.

Use of Expert Systems: The Army has begun using expert systems to manage maintenance schedules and improve diagnostic accuracy. These systems aim to assist mechanics by bringing the knowledge of design engineers and system experts to the field. Expert systems, such as Turbine Engine Diagnostics (TED), are also used at the direct support level.

Cost Saving Potential: According to the calculations, there is a potential savings of $17.8 million for the AGT1500 engine, including $11 million by reducing the NEOF modules and $6.8 million by repairing the modules.

These studies show that significant steps have been taken to reduce the operating and support costs of the AGT1500 engine. In particular, better implementation of the modular maintenance concept, raising the level of field maintenance and the use of specialised systems will continue to be an important focus for future cost reduction efforts.

Easy Maintenance and Serviceability: The modular construction of the AGT1500 engine simplifies maintenance and serviceability. The engine's main accessories (such as electromechanical fuel control, oil pump, hydraulic pump, starter motor) are accessible even when the power pack is installed in the vehicle. In addition, 70% of engine accessories can be replaced without removing the power pack from the vehicle, reducing maintenance times and labour costs.

Fast Fault Detection and Repair: The modular structure makes it easier to detect faults. Since the fault is concentrated in a specific module, maintenance personnel can find the source of the problem more quickly. In addition, replacing the faulty module reduces the time it takes to bring the motor back into service.

The modular design of the AGT1500 motor offers significant advantages by simplifying maintenance and repair processes, providing flexibility in logistics, creating less need for spare motors and reducing life cycle cost. Thanks to this design, the operational efficiency of the engine is increased and maintenance costs are reduced.

Professional Maintenance and Overhaul of Gas Turbine Engines

Gas turbine engines are widely used in critical applications requiring high performance and reliability. Regular maintenance and overhaul of these engines is of great importance for their long life and efficient operation.

Need for Overhaul; Gas turbine engines are subject to wear and tear over time. This may adversely affect the performance of the engine and increase the risk of failure. For this reason, the engine should be overhauled at certain intervals or when a decrease in performance is observed. The overhaul process involves a detailed inspection of the engine, cleaning, repairing or replacing parts. Specialised personnel and special equipment are required in this process.

Part Wear and Reuse; In engine overhauls, reuse of partially worn parts can reduce costs. However, this may raise questions about the long-term performance and reliability of the engine. The use of worn parts can shorten the life of the engine and lead to unexpected failures. Therefore, care should be taken when replacing parts and the criteria set by the manufacturer should be followed.

High Speed and Temperature Effect; Gas turbine engines operate at high speeds (for example, power turbine 3000 rpm, compressors 33500 and 43500 rpm) and temperatures. These operating conditions can accelerate the wear of engine components and require more frequent maintenance. High temperature and speed place stress on parts such as turbine blades and combustion chambers in particular. It is therefore important that these parts are regularly checked and replaced when necessary.

Sensitivity and Contamination Risk; Gas turbine engines are susceptible to contamination due to their sensitive nature. Factors such as metal contamination may require the engine to be overhauled. This situation indicates that care must be taken in the maintenance processes of the engine. To prevent contamination, a clean working environment must be provided, appropriate filters must be used and care must be taken with the lubrication system.

Metal contamination refers to the presence of metal particles in the lubricating oil of AGT1500 gas turbines. This can occur as a result of wear or damage to parts inside the turbine and is an important criterion for engine overhaul.

Importance of Metal Contamination:

Requires Inspection: Detection of metal contamination in the oil indicates that the turbine should be further inspected and, if necessary, disassembled and overhauled. This indicates potential problems that could adversely affect the reliability and performance of the engine.

Symptom of Malfunction: The presence of metal particles in the oil is caused by friction or wear of parts inside the engine. This indicates a malfunction or wear in the internal mechanisms of the turbine.

Overhaul Criteria: Metal contamination is a priority inspection criterion in overhaul procedures for AGT1500 turbines. When metal is detected in the oil, the turbine is automatically dismantled and subjected to a detailed inspection.

Professional maintenance and overhaul of gas turbine engines is critical to ensure long life, reliable and efficient operation of the engine. Overhaul processes require the use of specialised personnel and equipment, careful parts replacement, consideration of high speed and temperature effects, and minimising the risk of contamination. In this way, the performance of gas turbine engines can be maximised and operating costs reduced.

Iraqi Army T-72MI 6th Nebuchadnezzar Motorised Infantry Division, Northwest Kuwait, Gulf War, 1991

T-72MI Technical Specifications

Crew: 3 Combat weight: 41.5 tonnes

Power-to-weight ratio: 19.8 hp/t (14 kW/T)

Body length 6,86 m

Total length: 9.53 m

Width 4.75 m (with side skirts) 3.59 m (with side skirts removed)

Height to turret roof: 2,19 m

Engine: V-46-6 12-cylinder, four-stroke, multi-fuel diesel, 780 hp (575 kW) 2000 rpm

Transmission: Mechanical, synchromesh, 7 forward, 1 reverse

Fuel capacity: 1000 litres internal, +400 litres external

Max. speed (road): 37.3 mph

Maximum speed (off-road): 28 mph

Best cruising speed: 25 mph Max. range: 300 miles on internal fuel

Fuel consumption: 1 gallon/mile

Transition depth: Unprepared 1.2 m/prepared 5.0 m Slope: 30% slope, 25 side slope Obstacle: 0.85 m vertical, 2.9 m trench

Main gun: 2A46M (D-BITM) 125 mm smoothbore

Muzzle velocity: 5900 ft/s (3UM7 APFSDS), 2790 ft/s (30F19 HE-Frag)

Max. effective range: 2000 m

Stored main gun shells: 44

Weapon stabilisation: 2E28M electro-hydraulic, two axis Weapon lowering/raising: -6 to +14

Secondary armament: coaxial PKT 7.62 mm machine gun

Smoke exhausters: Type 902A: 12 units cover 300 m2 for 2 minutes

Crew self-defence: AK-745 assault rifle, 10 F-1 grenades

Since I have given many technical specifications about the M1A1 Abrams in the previous parts of the article series, it is only now time for the technical specifications of the T-72MI, the most powerful tank in the hands of the Iraqi Army during the Gulf War.

Comparative Analysis of Propulsion Systems of M1A1 Abrams and T-72MI Main Battle Tanks in the Gulf War

The M1A1 Abrams and T-72MI main battle tanks are equipped with different propulsion systems. These differences have significant effects on the performance and logistic requirements of the tanks.

Engine Type

The M1A1 Abrams was powered by a 1500 horsepower AGT1500 gas turbine engine, while the T-72M1 used a 780 horsepower V-46-6 12-cylinder diesel engine. Gas turbines offer higher power output despite being lighter than diesel engines of the same period. This gave the M1A1 Abrams superior mobility. However, the fuel consumption of gas turbines is higher than diesel engines. While the fuel consumption of the T-72MI tank is 1 gallon/mile, the fuel consumption of the M1A1 HA Abrams tank is 1.83 gallons/mile. This means that the Abrams tank consumes approximately 83% more fuel than the T-72. In order to keep the operational range of the M1 Abrams tank at a sufficient level, high-capacity fuel tanks have been integrated by the manufacturer General Dynamics. The latest M1 variant has a fuel capacity of 1,850 litres (490 gallons) and can travel approximately 426 kilometres (265 miles) with a single refuelling.

The images below show sections of the T-72MI tank. The first image shows the T-72M1's 125 mm gun, tank commander, gunner stations. In the second image, the CAD drawing shows the driver's station, the storage area where the ammunition is stored, the internal fuel tanks where the diesel fuel is stored in dark red in the front of the tank and the area where the V-46 diesel engine is located in the tank, the transmission, and the 2 barrels in green in the back show the external fuel tank. The third image shows the ammunition storage area, the engine compartment of the V-46 diesel engine and the gearbox compartment with the hatches closed. The fourth image shows the V-46 diesel engine and gearbox. Image source Amusing Hobby model kit.

The image above shows the 3D drawing of the 12-cylinder V-46 engine used by the T-72 main battle tanks. Image source Renderdock.

Fuel Compatibility

The turbine engine of the M1A1 Abrams has the ability to run on multiple fuel types, including petrol, diesel and jet fuel JP8. This feature increases the logistical flexibility of the tank, allowing it to be used in different operational environments. The T-72MI, on the other hand, can only operate with diesel fuel types due to its diesel engine.

The gas turbine engine of the M1A1 Abrams provides the tank with superior mobility and the flexibility to use multiple fuel types. However, this resulted in higher fuel consumption and logistical requirements. The T-72MI's diesel engine offered lower fuel consumption, but less mobility and fuel flexibility. Both engine types have their own advantages and disadvantages.

The power system of the M1A1 battle tank has a gas turbine engine designed for continuous high speed operation. This engine produces high power continuously, as in helicopters, and continues to consume fuel to keep its main systems active even when the tank is not in motion. In contrast, diesel engines can be adjusted according to the amount of power required, making them a more fuel-efficient option.

The gas turbine engine of the M1A1 battle tank has a higher airflow requirement compared to diesel engines. This can lead to operational difficulties, especially in dusty and sandy environments such as deserts. This is because the intake of excessive dust and particles can damage the internal components of the engine and adversely affect its performance. Therefore, vehicles with gas turbine engines should be subjected to more frequent and detailed maintenance and cleaning in such harsh conditions.

The cooling system of the gas turbine engine of the M1A1 battle tank consumes less energy compared to diesel engines. The M1A1's gas turbine engine consumes approximately 30 horsepower for the cooling system, while this figure can reach up to 160 horsepower in diesel engines. This shows that gas turbine engines have a more efficient cooling system.

The M1A1 Abrams can reach a maximum speed of 72 km/h (45 mph), while the T-72MI has a top speed of around 60 km/h (37 mph). These data show that the M1A1 has higher mobility.

Although the M1A1 Abrams has superior speed and manoeuvrability, it has some difficulties in adapting to high fuel consumption and desert conditions. Therefore, when fuel logistics are interrupted by the enemy or stopped for some reason, the tank's survival probability and efficiency decrease rapidly. Although the T-72MI has lower speed and power, it stands out with its fuel efficiency and better adaptability to different terrain conditions.

This concludes the 7th part of our article series. See you in the 8th part. Bibliography will be included in the last part of the series.