flywheel

Spoked flywheel
Flywheel from stationary engine. Note the castellated rim which was used to rotate the engine to the correct starting position by means of a lever.
A Landini tractor with massive flywheel

A flywheel is a rotating disk used as a storage device for kinetic energy. Flywheels resist changes in their rotational speed, which helps steady the rotation of the shaft when a fluctuating torque is exerted on it by its power source such as a piston-based (reciprocating) engine, or when the load placed on it is intermittent (such as a piston pump). Flywheels can be used to produce very high power pulses as needed for some experiments, where drawing the power from the public network would produce unacceptable spikes. A small motor can accelerate the flywheel between the pulses. Recently, flywheels have become the subject of extensive research as power storage devices for uses in vehicles; see flywheel energy storage. Flywheel drive is common in low-cost toys.

A momentum wheel is a type of flywheel useful in satellite pointing operations, in which the flywheels are used to point the satellite's instruments in the correct directions without the use of thrusters.

Physics

Energy is stored in the rotor as kinetic energy, or more specifically, rotational energy:

where
is the angular velocity, and
is the moment of inertia of the mass about the center of rotation.
• The moment of inertia for a solid-cylinder is ,
• for a thin-walled cylinder is ,
• and for a thick-walled cylinder is .
where m denotes mass, and r denotes a radius. More information can be found at list of moments of inertia

The amount of energy that can safely be stored in the rotor depends on the point at which the rotor will warp or shatter. The hoop stress on the rotor is a major consideration in the design of a flywheel energy storage system.

where
is the tensile stress on the rim of the cylinder
is the density of the cylinder
is the radius of the cylinder, and
is the angular velocity of the cylinder.

Applications

In application of flywheels in vehicles, the phenomenon of precession has to be considered. A rotating flywheel responds to any momentum that tends to change the direction of its axis of rotation by a resulting precession rotation. A vehicle with a vertical-axis flywheel would experience a lateral momentum when passing the top of a hill or the bottom of a valley (roll momentum in response to a pitch change). Two counter-rotating flywheels may be needed to eliminate this effect.

The flywheel has been used since ancient times, the most common traditional example being the potter's wheel. In the Industrial Revolution, James Watt contributed to the development of the flywheel in the steam engine, and his contemporary James Pickard used a flywheel combined with a crank to transform reciprocating into rotary motion.

History

Simple flywheel in motion. Constructed based on drawings by Leonardo da Vinci

The principle of the flywheel is already found in the Neolithic spindle and the potter's wheel.[1]

The flywheel as a general mechanical device for equalizing the speed of rotation is first decribed in the Kitab al-Filaha of the Andalusian engineer Ibn Bassal (fl. 1038-1075), who applies the device in a chain pump (saqiya) and noria.[2]

According to the American medievalist Lynn Townsend White, Jr., such a flywheel is also recorded in the De diversibus artibus (On various arts) of the German artisan Theophilus Presbyter (ca. 1070-1125), who records applying the device in several of his machines.[1][3]

References

1. ^ Lynn White, Jr., “Theophilus Redivivus”, Technology and Culture, Vol. 5, No. 2. (Spring, 1964), Review, pp. 224-233 (233)
2. ^ Ahmad Y Hassan, Flywheel Effect for a Saqiya.
3. ^ Lynn White, Jr., “Medieval Engineering and the Sociology of Knowledge”, The Pacific Historical Review, Vol. 44, No. 1. (Feb., 1975), pp. 1-21 (6)

• Flywheel highlight: Hypervideo showing construction and operation of four cylinder internal combustion engine (courtesy of Ford Motor Company)
Video of a simple flywheel in motion

Constructed based on drawings by Leonardo da Vinci

In case of problems, see Wikipedia:Media help.

kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity.
Rotational speed (sometimes called speed of revolution) indicates, for example, how fast a motor is running. Rotational speed is equivalent to angular speed, but with different units. Rotational speed tells how many complete rotations (i.e.
torque (or often called a moment) can informally be thought of as "rotational force" or "angular force" which causes a change in rotational motion. This force is defined by linear force multiplied by a radius.

The SI unit for torque is the newton meter (N m). In U.S.
piston is a rigid, lubricated sliding shaft that fits tightly inside the opening of a cylinder. Its purpose is to change the volume enclosed by the cylinder, to exert a force on a fluid inside the cylinder, to cover and uncover ports, or some combination of these.
A reciprocating engine, also often known as a piston engine, is a heat engine that uses one or more pistons to convert pressure into a rotating motion. This article describes the common features of all types.
An engine is something that produces an output effect from a given input. The origin of engineering however, came from the design, building and working of (military "engines") because before such devices came to be employed in battles there were very few mechanical devices used.
pump is a device used to move liquids or slurries. A pump moves liquids from lower pressure to higher pressure, and overcomes this difference in pressure by adding energy to the system (such as a water system).
Flywheel Energy Storage (FES) works by accelerating a rotor (flywheel) to a very high speed and maintaining the energy in the system as rotational energy. The energy is converted back by slowing down the flywheel.
Momentum wheels are a type of flywheel, mainly used for gyroscopic stabilization of spacecraft: momentum wheels have high rotation speeds (around 5000 rpms) and mass.
kinetic energy of an object is the extra energy which it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its current velocity.
rotational energy or angular kinetic energy is the kinetic energy due to the rotation of an object and is part of its total kinetic energy. Looking at rotational energy separately in an object's centre of mass frame, one gets the following dependence on the object's moment
angular velocity is a vector quantity (more precisely, a pseudovector) which specifies the angular speed at which an object is rotating along with the direction in which it is rotating.

Moment of inertia, also called mass moment of inertia and, sometimes, the
Mass is a fundamental concept in physics, roughly corresponding to the intuitive idea of "how much matter there is in an object". Mass is a central concept of classical mechanics and related subjects, and there are several definitions of mass within the framework of relativistic
The following is a list of moments of inertia. Mass moments of inertia have units of dimension mass × length2. It is the rotational analogue to mass. It should not be confused with the second moment of area (area moment of inertia), which is used in bending calculations.
Hoop stress is mechanical stress defined for rotationally-symmetric objects being the result of forces acting circumferentially (perpendicular both to the axis and to the radius of the object).
angular velocity is a vector quantity (more precisely, a pseudovector) which specifies the angular speed at which an object is rotating along with the direction in which it is rotating.
Precession refers to a change in the direction of the axis of a rotating object. In physics, there are two types of precession, torque-free and torque-induced, the latter being discussed here in more detail.
The word roll has these meanings:
• A thin flexible solid wound around a centre
• Something wrapped around a tube, e.g. toilet roll.
• Paper strips wrapped around a thin quilling tool, e.g.

potter's wheel is a machine used in the shaping of round ceramic wares. The wheel may also be used during the process of trimming excess body from dried wares and for applying incised decoration or rings of colour.
Industrial Revolution was a period in the late 18th and early 19th centuries when major changes in agriculture, manufacturing, and transportation had a profound effect on socioeconomic and cultural conditions in Britain and subsequently spread throughout the world, a process that
James Watt (19 January 1736 – 19 August 1819) was a Scottish inventor and engineer whose improvements to the steam engine were fundamental to the changes wrought by the Industrial Revolution. His influential teacher was Joseph Black.
steam engine is an external combustion heat engine that makes use of the heat energy that exists in steam, converting it to mechanical work.

Steam engines were used as the prime mover in pumping stations, locomotives, steam ships, traction engines, steam lorries and other
James Pickard was an English inventor. He modified the Newcomen engine in a manner that it could deliver a rotary motion. His solution, which he patented in 1780, involved the combined use of a crank and a flywheel.
A crank is a bent portion of an axle, or shaft, or an arm keyed at right angles to the end of a shaft, by which motion is imparted to or received from it; also used to change circular into reciprocating motion, or reciprocating into circular motion.