EngineerHub.orgHow to use this calculator
Follow the three steps below. Start with the example values, replace them with your own data, and read the result together with the assumptions and limitations.
Inputs
Results
Background
Engineering basis, equations, assumptions, interpretation and practical limitations for this calculator.
E = ½Iω²
Solid disk: I = ½mr². Thin rim: I = mr². Thick ring: I = ½m(rₒ²+rᵢ²).
Usable energy is less than total stored energy because the flywheel normally operates between maximum and minimum speed and has conversion losses.
Frequently Asked Questions
Practical questions about assumptions, inputs, interpretation and limitations.
Flywheel kinetic energy is E = ½Iω², so stored energy is proportional to the square of angular speed. Doubling rotational speed produces four times the stored energy if moment of inertia is unchanged.
Shape changes the moment of inertia. Moving more mass toward the outer radius increases inertia and therefore stored energy at the same mass and rotational speed. A thin rim has higher inertia than a solid disk of equal mass and outer radius.
No. Rim speed is useful context but is not by itself a safe-speed criterion. Stress depends on geometry, material properties, defects, fatigue, joints and manufacturing quality, and high-speed systems require suitable containment and overspeed protection.
No. The displayed runtime is an ideal energy divided by constant output power calculation. Bearing drag, windage, motor-generator efficiency, converter losses and the unusable energy remaining at minimum operating speed all reduce real runtime.
No. It is suitable for education and preliminary energy estimates only. High-speed flywheel design requires stress analysis, fatigue assessment, rotor dynamics, bearing design, containment and validated material data.