# Flywheel | Definition, Function, Working, Types, Application

By Mohit Uniyal|Updated : May 26th, 2022

In the list of engineering mechanical devices, the Flywheel is one of the most important devices, it was invented 1000 years ago (between the years 1038 – 1075) by Neolithic spindles and potter’s the wheel. So, what is a flywheel? What is the purpose of inventing the flywheel? Let us discuss this in this article.

It is a very simple device that we can see in many machines. This article gives a basic idea about the flywheel, requirements, and functions of the flywheel, the working principle of a flywheel, the force acting on the flywheel, type, and the application of the flywheel.

## What is a Flywheel?

Generally, a flywheel is the perfectly rigid circular element that is mounted on the crankshaft of the engine, or a rotating shaft subjected to transfer the power. The flywheel function is to control the fluctuation in the rotating element. The flywheel has a high mass moment of inertia, due to this, it has the ability to absorb and release a high amount of energy whenever required.

Many machines have load patterns that cause the torque time function to vary over the cycle. So, to overcome this type of condition the flywheel is the best solution. As Cast iron is cheap, mostly cast iron is used for the manufacturing of the flywheel. For longer life steel can also be used, as it has properties of high strength and anticorrosion, making it durable

## The Function of the Flywheel

In general, flywheel functions are to provide smooth power output in case of the fluctuating mode of an energy resource (for example IC engine, Steam engine) or to provide a sufficiently large amount of energy in a short period of time. Based on this the main functions of the flywheel are as follows:

1. To minimize the jerk in the machine element
2. To store the excessive amount of rotational kinetic energy when the machine is in idling or no-load condition
3. To supply a large amount of energy in the minimum time.
4. Balancing the rotating element mounted on the same haft but in a different plane

## Working Principle of Flywheel

The main working principle of the flywheel is based on the Rotational mass moment of inertia, Where the rotational kinetic energy is stored and released in the wheel, when the wheel store kinetic energy the rotational speed of the wheel gets increases. When the demand for high energy is required, the Wheel releases its kinetic energy and the wheel's speed gets slower.

The Kinetic energy stored on the flywheel depends on the mass moment of inertia and the speed of the flywheel. The energy stored in the flywheel is given by the equation

Kinetic Energy= (1/2) I ω2

• Where, I – Mass moment of inertia
ω– Mean angular speed of the wheel

As speed changes kinetic energy associated with the flywheel also changes, the change in the kinetic energy of the flywheel is given

Change in Kinetic Energy= Kinetic energy at initial−Kinetic energy at final

Change in Kinetic Energy= (1/2) I ωi-  (1/2) I ωf2

Δ K.E.= (1/2) I ω2 [(𝜔i− 𝜔f)/𝜔]

Where

• 𝜔i- The initial angular speed of the wheel,
• 𝜔f- Final angular speed of the wheel

## Type of Flywheel

As per our requirement, availability of space and design point of view flywheel can be classified into the following type:

• Rim type flywheel – Used for low Speed
Moment of inertial for Rim type flywheel is given by: I= (MR2)/2
• Rim and Spook type flywheel – For medium speed
• Disc type flywheel – For high speed
Moment of inertial for Rim type flywheel is given by: I = MR2

## Application flywheel

The main uses of the flywheel are as follows:

1. IC Engine, Steam engine – In this case flywheel stores a fluctuating form of energy and supply smooth and less fluctuating power in the output
2. Diesel generator
3. Punching and blanking operation – In this case, a smooth input energy source is there, but with the help of a flywheel, we generate a high amount of energy in less time.
4. Gyroscope – Applying a flywheel in a gyroscope is to maintain stability and control the direction, where friction is not dominant. For example – satellite direction is controlled by using the flywheel in the gyroscope

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## FAQs on Flywheel

•  A mechanical device used in machines serves as a reservoir, which stores energy during the period when the supply of energy is more than the requirement and releases energy when the demand is more than the supply.

•  The flywheel controls and minimizes the fluctuation of speed within the cycle, Flywheel can’t control the speed in inter-cycle fluctuation i.e changes in the speed due to change in loading over the engine.

• The flywheel controls and minimizes the fluctuation of speed within the cycle, Flywheel can’t control the speed in inter-cycle fluctuation i.e changes in the speed due to change in loading over the engine.

• No, as the working principle of the flywheel is the base of the mass moment of inertia, which is only directly related to the mass and rotational speed of the wheel.

This is one of the best advantages that it can work in the absence of gravity. The direction of satellites is controlled by the flywheel.

• No, in practice, we can’t store energy in the flywheel for a long period of time.

We can use it to store energy, but only for a very short period. The function of flywheel is to absorb and release it over one complete cycle. In the case of IC engine, it stores energy during the power stroke and release it during suction, compression and exhaust stroke, the time require to complete all this fore cycle is very less that’s why flywheel is used to store energy in this type of cases.

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