Composite Flywheel: A Mechanical Alternative

The conventional flywheel characterized by low speed and high density demanded a call for carrying out research to find viable alternative. Composite flywheel can be a promising modification for these flywheels. In this context, flywheels made from composite materials like epoxy, glass fiber reinforced plastic, carbon fiber reinforced plastics is proved to be successful.

Composite flywheels have gained much interest recently as an alternative to fuel cells or Acid batteries. The construction employs basic metallurgy to ceramic, polymer/co-polymer, and carbon fiber techniques. The advanced flywheel made of high strength composite filaments is able to operate at a safe speed range of 42,000 rpm to 65,200 rpm releasing large amounts of power i.e... 750 kW for about 20 seconds or even about 100 kW for up to one hour. It requires Magnetic bearings as speeds increase, to reduce friction found in conventional mechanical bearings.

This paper presents a theoretical approach to optimal design of flywheels to optimize the Specific Energy Density (SED) of flywheels. The work presented also considers the

application of composite flywheels as a source of energy accumulation and less density to strength. An overture has been made to calculate the various stresses in the design of composite flywheel and those obtained are compared with the conventional flywheel. It can be inferred that by using composite materials, a conventional flywheel with a weight reduction of 22.35 % to 33.18% may be fabricated.

A Microsoft Visual basic program is developed to design the composite flywheel in shortest period of time with more accuracy. The viability of Flywheel energy storage in aerospace applications is also examined.
A future attempt may be made to analyze the stresses in the composite flywheel by varying the thickness of laminates, with the aid of Analysis System Software (ANSYS).

What is a flywheel?

Archeologists describe the flywheel as an early example of industrial automation; it was used in the potter’s wheel to enable the production of pottery at a rate faster than hand molding. Later, several forms of engine technology required flywheel for damping the effect of shaft speed fluctuations. They are universally appreciated as a kinetic store of energy.

A flywheel is traditionally composed of metals like cast iron, steel which are characterized by low speed and high density but a composite flywheel is considered to have more kinetic storage per weight

Up until recently most satellites used batteries to store energy for those times when the solar cells couldn't produce enough electricity for the satellite. But Batteries in space have the same problem as batteries on earth. They wear out after about 1000 heavy charge/discharge cycles, and while they are wearing out their capacity is continually reduced. To the rescue comes the high speed composite flywheel that runs at 100,000 RPM and are made mostly of plastic and carbon fiber. They use magnetic bearings which have no contacting parts unlike ordinary bearings which wear out too fast.

What are composite materials?

Composite materials are a new class of materials that combine two or more separate components into a form suitable for structural applications. While each component retains its identity, the new composite material displays macroscopic properties superior to its parent constituents, particularly in terms of mechanical properties and economic value. Resin Composites, Metal Composites, Carbon-Carbon Composites, Hybrid Metal Carbon-Carbon Composites and Hybrid Resin Carbon-Carbon Composites are a few prominent examples of composite materials.

Why make composite flywheels?

The faster we can spin a flywheel and the more massive we can make it, the flywheel, and the more kinetic energy we can store in it. However, at extreme speeds, even metal flywheels can literally tear themselves apart from the shear forces which are generated. Further, the energy storage characteristics of the flywheel are influenced more strongly by its maximal rotational velocity than by its mass.

Manufacturing of composite flywheel:

The flywheel rim and arbors are constructed using a combination of Toray M30S intermediate modulus graphite, Toray T700 standard modulus graphite, and
Owens-Corning S2 fiberglass (Table) the resin is a Fiberite 977-2 thermosetting epoxy resin system toughened with thermoplastic additives.

Merits of composite flywheel

• Compact
• Energy storage system more efficient
• Less weight
• Long life
• High efficiency
• Low maintenance
• No aerodynamic noise

De merits
• Safety concerns
• High material costs
• Expensive magnetic bearing

Composite Flywheels are not only used for Electric Vehicles and Hybrid Electric but it also finds space applications.


In the design of composite flywheel, the following is usually considered
1. power developed or energy stored
2. speed of the drive or flywheel
3. material used
The following requirements must be met for the design of fly wheel
(a)The flywheel should have sufficient strength so that it will not fail under any working conditions with in the desired limit
(b)The cost of the flywheel should not be so much that it will not fail under operating condition.
(c)With the mountings of flywheel, the vibration set up in the engine parts and the base should be minimum. This is the most desirable, feature of the flywheel mounting.
(d)The alignment of the flywheel and other parts such as shafts, keys should be considered because they effect on the performance of the flywheel and also total engine
(e)The lubrication of the engine fly wheel should be satisfied wherever required

Energy stored in flywheel:
When flywheel absorbs energy as in the case of internal combustion engines, velocity increases and the stored energy is given out, the velocity or speed diminishes.

Fluctuation of energy
If the velocity of flywheel changes, energy it will absorb or gives up is proportional to the difference between the initial and final speeds, and is equal to the difference between the initial and final speeds, and is equal to the difference between energies which could give out, if brought to a full stop position that which is still stored in it at the reduced velocity.