# Would this high speed flywheel concept work?

1. Apr 10, 2014

### Webbd050

Im working on designing a high speed flywheel as part of a project. The main issue is the centrifugal forces acting on the flywheel to tear it apart. If i was to construct a flywheel using interference fit tubing which is put together using thermal expansion of the outer tubes so that they are effectively crushing the flywheel when they cool, would these crushing forces oppose the centrifugal forces thereby allowing the flywheel to spin faster without breaking? Or would the outer tubes be under tension and experince a force from the inner core outwards which would assist the centrifugal forces making the flywheel weaker near the surface where there is the greatest inertia? If any of that made any sense to you do you think it would work? Would it need a stronger material to provide the crushing force? Such as a titanium tube around a steel core? I know they use carbon fibre wraps around flywheels in Kers systems is that the same principle? Thanks.

2. Apr 10, 2014

### Staff: Mentor

3. Apr 12, 2014

### AlephZero

You need to do a proper stress analysis on the design. To store kinetic energy, you want most of the the mass at a large radius. On the other hand for maximum strength, most of the material is at a smaller radius to resist the force from the outer rim. For example look at the different shapes of rotating disks in a jet engine (find cross-section images on Google), depending on the RPM, radius, and the amount of radial load on the rim from the different sizes of the blades.

If you produce a radial compressive stress in part of the structure, you will probably also create a circumferential tensile stress somewhere else. The question is whether the tradeoff between the two is beneficial or not.

4. Apr 13, 2014

### Staff: Mentor

Some of the students at my uni (many years ago) were working on a flywheel-driven light vehicle design. The project was abandoned when they realized it was in danger of flipping over sideways if it tried to go up a steep incline.

Could two opposing flywheels overcome gyroscopic problems?

5. Apr 14, 2014

### AlephZero

Sure. But the equal and opposite forces are still acting on the bearings of the two flywheels, so the bearing supports need to be designed to withstand with that.