# Flywheel Size for Small vs Large Engines - Which is Best?

• loocary
In summary, the need for a flywheel in an engine is determined by the variable geometry of the slider-crank mechanism. The kinetic energy of the assembly must be sufficient to reach TDC and run at low speeds, and a flywheel may be necessary to store additional energy. The torque pulses from the cylinder firing and variable geometry can also affect the need for a flywheel. The amount of flywheel needed varies depending on the engine, and it must be designed along with the rest of the engine for the system to function properly.
loocary
do we need a massive flywheel for a small engine or a large engine?
i blive that the lager engine will require a smaller flywheel.
and for a high speed engine i think we are going to need a larger flywheel to minimize its speed, otherwise wouldn't the care be out of control.

The whole matter of the flywheel is tied to the slider-crank mechanism that is used in the internal combustion (IC) engine. Because of the variable geometry of the slider-crank mechanism, the effective mass moment of inertia of that portion of the engine oscillates roughly (only roughly) sinusoidally about a positive mean value.

When the piston approches TDC (top dead center) on the compression stroke, gas is being compressed on top of the piston, and the crank speed is being reduced as a result. It is absolutely essential that the kinetic energy of the assembly be sufficient to get it to the TDC where the spark will fire, adding heat energy to the system and the kinetic energy will increase. If the kinetic energy of the slider-crank mechanism alone is too small, then a flywheel must be added to store additional energy to enable the engine to run at low speeds. This is the reason that some lawnmower engines will not run if the blade is removed; the blade is the essential flywheel element.

Every time the cylinder fires, there will be a gas pressure torque pulse transmitted to the crankshaft. This will cause the crank to accelerate. If there is only a single power cylinder this is more pronounced than will be the case with multiple power cylinders. The variable geometry also cause a torque pulse, a negative torque pulse, that tends to retard the crank speed, so that the total torque over a cycle consists of both positive and negative components.

Some engines have been built (mostly very old designs) where the speed change between firing pulses might be as much as 30 rpm. If this were powering a generator, it could play havoc with generator frequency for an AC machine, or generator voltage for a DC machine.

There is no cut and dried rule as to how much flywheel is needed on any particular engine. The flywheel must be designed along with the rest of the engine in order for the whole system to function.

Please remember that this is a schoolwork-type question, guys. Make the OP do some of the reading and research to answer his questions...

loocary said:
do we need a massive flywheel for a small engine or a large engine?
Is this a homework question? If so, were any additional details mentioned other than "massive flywheel" and small or large engine?

I would approach this question by considering the fundamental principles of physics and mechanics. The purpose of a flywheel in an engine is to store rotational energy and provide a smooth and consistent output of power. Therefore, the size of the flywheel should be determined by the specific requirements of the engine, rather than the size of the engine itself.

In general, a larger flywheel will have a greater moment of inertia, meaning it can store more energy and provide a smoother output. This is beneficial for larger engines that require a higher output of power and torque. On the other hand, a smaller flywheel may be sufficient for smaller engines with lower power requirements.

However, it is important to also consider the speed of the engine. As the commenter pointed out, a high-speed engine may require a larger flywheel to minimize its speed and prevent the vehicle from becoming out of control. In this case, the size of the flywheel would need to be carefully selected to balance the need for a smooth output of power with the need to control the speed of the engine.

Ultimately, the best flywheel size for an engine will depend on a variety of factors, including the size and power requirements of the engine, as well as the intended use and speed of the engine. It is important to carefully consider all of these factors in order to determine the most suitable flywheel size for a specific engine.

## 1. What is the purpose of a flywheel in an engine?

A flywheel is a mechanical device that is used to store rotational energy in an engine. It helps to maintain the engine's rotational speed and provides smooth and consistent power delivery.

## 2. How does the size of a flywheel affect engine performance?

The size of a flywheel affects the inertia and torque of an engine. A larger flywheel will have a higher inertia, which means it can store more energy and provide smoother power delivery. It also helps to reduce engine vibrations and maintain a consistent speed.

## 3. Is a larger flywheel better for small engines?

In most cases, a larger flywheel is better for small engines. This is because small engines have a lower inertia and can benefit from the added stability and smoothness provided by a larger flywheel. However, the size of the flywheel should be carefully selected to match the engine's power and performance needs.

## 4. Are there any benefits to using a smaller flywheel in a large engine?

In some cases, a smaller flywheel may be beneficial for a large engine. It can help to reduce the overall weight and size of the engine, which can be beneficial for certain applications. However, a smaller flywheel may result in a decrease in engine stability and may not be suitable for high-performance engines.

## 5. How do I determine the appropriate flywheel size for my engine?

The appropriate flywheel size for an engine depends on several factors, including the engine's power and performance needs, the type of vehicle or equipment it is used in, and the desired level of smoothness and stability. It is best to consult with a professional or refer to the engine manufacturer's specifications to determine the appropriate flywheel size for your specific engine.

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