Flywheels Guide – Explanation, Design, Uses and Types

Flywheels are very important parts of engineering systems. We use them in different kinds of practical applications. Their structure may seem very basic but their job is not basic. You can see them as big round parts that are placed near the engines or machines. When these engines work, they rotate. Here we explain the flywheels on a very detailed basis. You can find this information here;

  • What is a flywheel?
  • What are the types of flywheels?
  • How to design them?
  • What are their main uses of them?
  • Advantages and disadvantages
  • FAQs

What is Flywheel?

A very big flywheel application(Image Source:

We use flywheels in the rotational energy storage units in rotating machinery. If we think about rotating machinery such as an internal combustion engine. These systems are working with the combustion of fuel inside the engine. When this fuel burns, the pistons are moving to the downside of the engine blocks. And they come back with the rotation of the crankshaft.

To obtain a complete cycle of rotation from internal combustion engines, the pistons must have 4 strokes of movement. In each stroke, their moving acceleration and dynamic effects on the system are not the same. For example in the combustion phase, the moving speed of the pistons is higher. And in the exhaust phase, it is slower. So, this uneven accelerations and motions will give very harsh oscillations to the system. And the efficient working and smooth working of the system become impossible.

Flywheels come into duty in this phase. They are heavy disks that rotate with the rotating machinery. And also they are directly attached to the rotating machinery. With its heavy weight, flywheels give smooth and oscillation damping working to this uneven working system. Because its angular moment dampens these uneven effects.

As you see above, a flywheel is very important in a rotating system to obtain smooth working.

Also, with rotation, they can store energy. They are heavy and if they rotate, this rotation stores a very good amount of energy. And flywheels can release this energy whenever we want. This is another important fact about them.

Design of Flywheel Systems

As we stated above, flywheel systems are very important systems in engineering applications. They rotate to store energy and they provide smoother applications. So, we need very strict engineering calculations.

If you need a procedure to design these systems, you can use the general procedure. So, it will be very easy for you to design these systems.

Selecting a Material

Selecting proper materials for flywheel applications is very important stuff. Because there are different kinds of materials that they use in these systems. For example, if you have little space for the attachment of flywheels, you can consider heavy materials such as steel or cast iron.

Define the Coefficient of Fluctuation

As you read above, this is a very important parameter in the design of flywheel systems. We have a table that shows the general coefficients of fluctuation values for flywheel systems. You can select one of these values to use in the calculations.

Also, you can easily calculate by using the formula above. But, you need to know the general working characteristics of your system.

Torque and Position Curve

Determining the torque and position curve is one of the hardest ones for a system. You need to know which torque is applied in which rotational position of the shaft. You need to use some sensors and analyzers to obtain the graphical data of it. It is very important to determine the kinetic energy.

Average Load

From this curve, you can find the average load or average torque that you have from the system. This is also a very important calculation for kinetic energy.

Locations of Maximum and Minimum Velocities

Also, it is very hard to define. You need to use the curve again. You need to calculate the maximum velocity and minimum velocity positions of the shaft of your system. These parameters are also very important in the calculation of kinetic energies.

Calculation of Kinetic Energy with Integral

You need to use this integral equation to calculate the required stored kinetic energy of a flywheel;

Flywheel kkinetic energy calculation.

In this equation,

  • The boundaries of the integral calculation are the locations of maximum and minimum angular velocities in the system where we design flywheels. The unit is the angle.
  • Taverage is the average torque that we calculated in the average load calculations. The unit of the torque is N.m or lbf.ft.
  • Tload is the load torque of the flywheel application.

So, this will give the required value of kinetic energy in flywheel application.

Average Angular Velocity

After that, you need to determine the average angular velocity that we need.

Calculate the Mass Moment of Inertia

After calculating all these factors, you need to calculate the mass moment of inertia of the flywheel shape. You can use the formula that we give above. And also, you can use the calculator.

Determine the Shape of the Flywheel

Once you calculated the required mass moment of inertia, you can easily obtain the general shape. You can use the mass moment of inertia equations of common shapes that are available on this website.

In terms of the material costs and mass moment inertia calculations, you can obtain the required system by placing most of the weight at the outside perimeter of the flywheel. So, you can obtain the mass moment of inertia that you need with a lower weight.

Calculation of Stored Kinetic Energy on Flywheels

Flywheels are rotating parts and store energy with rotation. So, the stored energy in flywheel systems is the kinetic energy of rotation. We calculate this kinetic energy with this equation;

Kinetic energy.

As you see above, the mass moment of inertia Im is a very important factor in the energy storage in flywheels. Also, the angular velocity is a very important value. With the increasing angular velocity, the kinetic energy increases with square.

Because of this, they produce flywheels very heavy and big to obtain the very big mass moment of inertia value.

But this equation is for the known sizes, dimensions, and systems. You need to use the integral above to calculate the general requirements.

Kinetic Energy Calculator to Design Flywheel Systems

In the light of the information above, you can use the calculator below to easily calculate the important parameters of flywheels. If you are designing a flywheel system, you are probably dealing with lots of kinds of parameters and calculations. If you have a useful calculator below your hand, you do not give lots of effort to making hand calculations. Check this calculator below;

Flywheel Kinetic Energy Calculator

The use of the calculator is very simple. Firstly you need to enter these values inside the brackets of this calculator;

  • The kinetic energy that you need in the units of Joule or BTU in English units. 
  • The maximum angular velocity that your system has. The unit is radian per second.
  • And the minimum angular velocity that your system has.
  • Average angular velocity.

And then, click on the ‘Calculate!’ button to see these results;

  • The total mass moment of inertia is in the units of kg.m2 or lb.ft2.
  • The coefficient of fluctuation.

You can compare the coefficient of fluctuation value with the values that we give for different machinery.

After calculating the required mass moment of inertia, you can easily calculate the required mass and shapes. You can make the sizing adjustments in CAD programs. CAD programs have very good tools to calculate the mass moment of inertial volume and mass calculations of 3D objects. So, you can easily optimize the best shape of them.

Sizing of Flywheels

This is the most important part of the design of flywheel systems. Because the sizes of a flywheel system directly define the working efficiency. The size of these systems is directly dependent on the mass moment of inertia of the system. So, special to these systems, we calculate the general mass moment of inertia with this equation;

Mass moment of inertia of flywheels.

In this equation, we need to know how much energy we want to store in a flywheel. You can find how to calculate the needed kinetic energy storage in the design procedures of flywheels below.

And you need to enter the coefficient of fluctuation “C”. We stated that we use flywheel systems in machinery to compensate for the unintended fluctuations. So, we need to thoroughly define the coefficient of fluctuation for a system.

We can easily calculate it with the maximum and minimum shaft speed in a system;

Coefficient of fluctuation.

Here, you need to enter to find the maximum, minimum, and average shaft speeds of a system. So, the coefficient of fluctuation is directly related to the difference between the rotational speeds of shafts.

With the decreasing coefficient of fluctuation, the sizes, and diameters of flywheels increase. So, this is an extra cost for a system.

Coefficient of Fluctuations in Different Machines

These are some average coefficient of fluctuation values for different machines;

  • Crushing machines: 0.200
  • Electric engines: 0.003
  • Shearing machines of the sheet metal: 0.030-0.050
  • Spinning systems machines: 0.010-0.020
  • Textile systems machines: 0.025
  • Machine tools in machining: 0.030
  • Paper-making tools: 0.025
  • Pumping machines: 0.030-0.050
  • Internal combustion engines with belt transmissions: 0.030
  • Milling machines: 0.020
  • Power transmissions: 0.020
  • Hammering tools: 0.200

For example, crushing machines are very dynamic systems that have very huge fluctuations. This is because their duty is very hard. In crushing applications of different objects and materials, they have very big energy and motion fluctuations. So, you can see the biggest flywheel applications on them.

Also in textile machinery, the need for big flywheel systems is very important. Because their fluctuations are also very big. There is a lot of uneven moving equipment in these systems.

These are the general procedures to follow to design flywheel systems.

Types of Flywheels Throughout the History

Flywheels are very important parts of different kinds of machinery. They are storing rotational energy and minimize the damaging physical vibrations of systems. Also, the use of flywheel systems are very common throughout history. You can check the general instructions below. So, it is not easy to classify the flywheels according to their types. But we can make this classification for use purposes of them.

Flywheels from Historical Times

Big application of flywheel.
Another big flywheel(Image Source:

People use this physical principle since ancient times. They generally apply in different kinds of systems such as pottery shaping and water wheels.

In pottery shaping machines, there is a wheel that we turn with our power. This wheel is heavy and we need to apply extra power to rotate it. Once the rotation of the pottery wheel starts, there is rotational kinetic energy storage on that wheel. And this wheel smoothly rotates and we shape our clay on that rotating machine.

Also in mill grinders, we have rotating wheels to grind the wheat to flour. The kinetic energy of the wind is very fluctuating and is not steady. It rotates the windmill. And there is mechanical power transmission of this rotation to the rotating heavy weights. Once the heavyweights start to rotate, they store rotating energy. And each time that they get rotation energy, they store it and give it more smoothly and regularly.

People also use the mechanical energy of flowing water. Some mills rotate with the flowing water. And this mill transfers this rotation to heavy and rotating mills.

Classic Applications of Flywheels

Flywheels are also very common parts of machinery in the industrial revolution eras. So, we use them in same advantage in internal combustion engines such as diesel engines. And also, old engines provide much more unsteady oscillating motion to the systems. So, they have very big flywheels near them if you look at the old photos.

Different Applications of Flywheels

You can see the different applications that we use the flywheel systems. There is a wide variety of practical and engineering applications of them. You will see that they are very important engineering parts in different power consumption systems of machinery.

Crushing Machines and Mills

If we take a look at the general working principles of these machines, they are very similar to grinding mills. So, very smooth torque and rotational motion that we need in this system. And also, if we are using power sources as internal combustion engines, we need flywheel systems in them.

Flywheels are transforms the uneven forces and loads into a more smooth way. And this smooth power is transmitted to the grinding machinery that makes the duty. This is a very important use of these systems.

Electrical Engines

Also, electrical engines and electrical systems require flywheel systems. Because start-ups and slowdowns of electrical engines are very instant. So, we need to smooth the effects of flywheels in these systems.

We use electrical engines in lots of kinds of systems. And according to the type of the system and requirement of smooth power, we use different sizes of flywheels.

Sheet Metal Punching and Shearing Machines

In the sheet metal industry, different kinds of machinery make stamping, shearing, and cutting operations. Also, there are reciprocating systems in sheet metal punching machines. And the power systems are generally electric motors.

So, if we directly use the moment and the power of the electrical motor in these reciprocating machines, the movement of the stamping, punching, and shearing machines will be very oscillating. So, the effectiveness of machines will decrease and we can not obtain the required tolerances from the products.

And if we use flywheels between the electric motor and the shearing, punching, and stamping tools, their reciprocating motions of them will be more smooth. And the quality of the sheet metal products will be very high.

Spinning Systems

We use the spinner machines for different purposes. We use these systems in a different filtering and centrifuge applications in industry and medicine. In spinning machines, there are rotating discs that spin the materials inside them. So, we have smoothly spinning applications.

Like the examples above, the general motion of engines will be very oscillating for this smooth spinning. So, the use of flywheels is very common in these systems.

Textile Systems

There are different kinds of machinery motions in textile systems. These motions are very important to obtain the stitches and sewings of fabrics. And the power systems are generally electrical motors of these systems. And we require the use of the flywheels between the tools and the power generation systems. We need to have a smooth motion for the work of the tools.

Machine Tools in Machining Operations

There are different kinds of machining operations in the manufacturing industry. Around these machining operations, turning, drilling, milling, machining centers, broaching, and so on. So, there are different movements and types in these machines.

To obtain these complex movements, it is very important to have a smooth power supply to the toolings of machining centers. Also, there are different motions in machining operations such as feed motion and primary motions. So without a flywheel, these machines will not work.

Paper Making Automations

Papermaking is also a very important business. There is also very complex machinery that has electrical engine power sources. With the increasing complexities of machines, the requirement for the smoothness of the power source increases. So, we need the use effective flywheel systems in these paper-making machines also.

Pumping Systems

We use the pumping systems commonly in different kinds of machinery. Pumps are very important to increase the mechanical energy of fluids by increasing their pressures. They are working with electrical engines.

The pump vanes are rotating elements that are generally directly connected to electrical engines. But also in bigger pumping systems, the use of the flywheel systems is very common.

Internal Combustion Engines

Steam engine flywheel.
Steam engine flywheel.

Internal combustion engines are very common systems as you know from automobiles. Because they are the general system for power generation from fossil fuels. But also, the movements of the pistons in internal combustion engines are very oscillating. And this motion is not useful for most systems.

So, we generally use flywheel systems on petrol engines. The reciprocating movement of the piston is directly transferred to the crankshaft. And the rotation of the crankshaft will not be smooth. So, this crankshaft is directly connected to a flywheel. And this flywheel provides a smooth motion to the whole system.

At the wheels of the car, we obtain a very smooth rotation to cruise.

Power Transmission Systems

In general, all the flywheels are part of power transmission. The main objective of the power transmission is, they take the power from the power source and leave that power to the end tools of the machine. Such as the end effectors or end tools are the rotating wheels of a car.

So in these systems, the use of flywheels is very common. Because the power transmission systems must transmit the power smoothly to obtain efficient work.

Hammering Machines

Hammering machines are the type of machinery where the shaping of materials takes place. There is a hammer that makes reciprocating motions. And this hammer comes into contact with the material at very high speeds and intensities. So, we need very complex machinery systems and power transmission that converts the unsteady motion of the engine to the steady reciprocating motion of hammers.

So, flywheel applications are very common in hammering machines to obtain a smooth power source for the hammers.

Modern Applications of Flywheels

Here, you can find information about some of the modern applications of flywheels. You will see that the use of these systems is not only smoothing the jerky movements of machinery. We use it for different kinds of purposes. So, this information will enhance your general viewpoint of you these systems.

Regenerative Brakes in Trucks and Buses

There are renowned bus and truck manufacturers such as MAN and Mercedes-Benz that use regenerative brake systems in their products. These systems depend on the general working principles of flywheels.

In these systems, if the bus or truck slows down, the regenerative flywheels take the kinetic energy that gives an extra slow-down effect on the truck. And if they accelerate, the stored kşnetic energy is transferred again to the powertrain system. So, this is a very useful system in stop-and-go situations of these heavy systems. In these systems, the general rotation speed of flywheels is around 10.000 RPMs.

KERS Systems of Formula 1 Cars

KERS system of flywheel.
KERS system(Image Source:

These systems are also very common in Formula 1 cars. KERS is the acronym for the “Kinetic Energy Reduction System” which uses the general working principle of the flywheels. There is a very compact flywheel system in KERS systems that absorbs the energy of braking. Without the KERS system, this kinetic energy will be transferred to heat. But it is stored in a compact flywheel that rotates up to 70.000 RPMs. So, pilots can use this kinetic energy to boost the acceleration of F1 cars to give extra speed to them.

Flywheel Use in Power Plants

In some modern power plants, there are flywheel applications to store extra energy. We use this extra energy where the higher demands of electricity consumption take place several times. You know that the power plants use rotating machinery to produce electricity with generators. Also, they store kinetic energy on huge flywheels for extra energy. We can use this extra electrical energy that comes from flywheels easily.

As you see above both in historical and modern days, the use of flywheels is very common. The working principles of flywheels can be easy but their use is very common in engineering.

Advantages and Disadvantages of Flywheels

Like the other machinery parts, these systems has also advantages and disadvantages. A designer or an engineer always considers the advantages and disadvantages before applying them to the systems.


  • Among the biggest advantages of them, they provide extra energy storage to use them more smoothly. So, the smooth working of most of the machinery depends on a flywheel. Also, there are lots of machines that can not work without any flywheel.
  • The general shapes of these parts are generally very basic. They have a round shape in general. So, this round shape will give them very easy manufacturing. They are the very systems that we can manufacture easily and very useful systems.
  • In modern systems, flywheels save very much energy from braking and speeding up the systems. So, this energy saving adds extra efficiency to the general system.


  • The most important disadvantage of the flywheel systems, they are very heavy and they add extra heaviness to the systems. For example, if we think about the KERS systems of F1, flywheels add lots of weight to these cars which decreases the acceleration or motor efficiency.
  • Flywheels are exposed to very big stresses because of very high-speed rotations. So, it is a very big problem that they can shatter or fail. We need a very strict design procedure for flywheels to prevent these failures.
  • Also, they add extra cost to a system. Because we need extra fittings and machine elements to mount them in the systems. And also, they have additional costs because they manufacture them. They are heavy and big parts if we compare them with other parts of engines and machinery. So, the manufacturing of these systems can be heavy.

Conclusion on Flywheels

So as you see above, the design procedures of flywheels need extra attention. The working principle of the flywheels may seem very basic. But, we need very strict calculations to properly design one of them for the systems. Around the calculations, kinetic energy storage calculations and mass moment of inertia calculations are the most important ones. From the mass moment of inertia calculations, we can calculate the shape and weight of the systems.

The use and applications of these systems are very common in engineering. Nearly in most of the machinery where the power source rotation is converted into different machinery motions, we use flywheel systems to obtain smooth motions.

Also in history, different types of these systems are very common. And in modern applications, we use flywheels in energy store units to save energy mechanically. In KERS and regenerative braking systems of trucks and buses, you can see these modern applications.

And we need to consider the general advantages and disadvantages of flywheel systems. Because there are very important aspects to consider before applying to our engineering system.

Finally, do not forget to leave your comments and questions below about the flywheel systems.

Your precious feedbacks are very important to us!

FAQs About Flywheels

What are flywheels used for?

There are different purposes that we use these systems in engineering applications. But the general purpose is to store kinetic energy with rotation. We use this kinetic energy for different purposes such as providing more smooth movements and energy saving in braking and acceleration systems of automotive systems.

What is a flywheel in simple terms?

A flywheel is a rotating heavy disc that has a stored rotational kinetic energy in itself. This rotation is directly taken from a power source which produces a motion in a very oscillating and jerky way. So, instead of using this oscillating motion of the power source directly, we can use this power from flywheels which provides more smooth power.

How does a flywheel work?

The working principle of these systems, there is a heavy rotating disc that stores kinetic energy in them. So, we can use this kinetic energy for different kinds of purposes. The storage of this kinetic energy takes place, rotating at very high RPMs of a high mass moment of inertia. With the increase of these two factors, the total kinetic energy increases.

Are flywheels used in cars?

Yes, the use of these systems is very common in car engines. Car engines produce very oscillatory motion which is generally very jerky to use. So, with the flywheel systems, this jerky movement is converted into a more smooth motion.

Why is it called flywheel?

Because it rotates and stores kinetic energy. Maybe people visualize this rotation as flying of these systems. Because of this analogy, people call these parts flywheels.


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