Flywheel calc to simulate a vehicale mass

Dear sir,

A veichle, no matter how big is, if conceptually imagined, does not require power to keep running after reaching its travel speed. As a lab schematic to reproduce what you want would depend on the vehicle dimensions, atrict with the pavement, atrict with air, climbs/downhills simulation, etc, I'd suggest a controllable dynamometer to do the job. To help in the simulation, a flywheel could be used together with the dynamometer. This is a standard arrangement for engine tests.

But, if you want to simulate the vehicle acceleration in a simplified way, you can use a flywheel only. But be aware that it will not work well in constant speed, once if you continue to apply a high torque from the engine in the flywheel, it would continue accelerating until something breakes.

To simulate the vehicle inertia is a kind simple. 16 tons x 110 km/h has accumulated 7.47E6 J. (E=1/2 x m x v^2).

Use the flywheel speed and calculate the required polar inertia by the formula: E = 1/2 x I x a_speed^2.

Ultimately, if you know what is the relationship in the real vehicle between its linear speed and the drive output angular speed, the above equations would allow you to find a relationship between the vehivle mass and the required I to simulate the mass.

Just remember to use consistent units. I recommend SI: E[J], m[kg], v[m/s], I[kg.m^2], a_speed[rad/s].

Then, with the I you need, design the flywheel, trying to obtain the maximum I with minimum mass. This is specially required to avoid the flywheel shaft to have problems with vibration amplification by natural frequency of the shaft.

After designing the flywheel and the shaft general geometry, then go to find some bearings and accessories like couplings and so to fit your application. With accessories defined, make the final drawing.

Sorry if it sounds a little vague, but it's not possible to say too much without going into the numbers themselves.

Dear Sir, thank you for the reply. I just want to confirm that I am on the right track. What type of safty would you suggest for the design to compensate for the vibration, possibly a SF of 3?

Regards

Ok. Of course, if your application would be mounted in a vehicle, with weight considerations and large scale economic considerations, I'd suggest using some more specific calculations to make your parts work in a more tight spec.

But, as I understand, it is a one time design for static construction. So, use the civil engineers approach.

Preview impact load... SF=2

Preview for fatigue infinite life (in case of steel)... SF=3

Final SF=6.

You'll see that when you find your bearings, the diameter required for the shaft will give you this SF with lots of margin. They're made to do so.

I am sorry to say that if you have to develop such a test bench and you put the questions you asked it would be better to give the concept to a consultant since there are a lot of problems related to vibrations, resonance and so on. It is not a trivial problem especially if you deal with combustion engines. Of course you can go on but it is dangerous since the cost you will invest could be much bigger due to successive failures than the fees of a consultant. With respect to the tests the other comments are ok.

To B Dixon

The device you have as a suggestion has been successfully developed by a Professional Drag racer in the United States. I have utilized the dynomometer for test on 2000 HP. internal combustion engines which would be utilized to propel a 1800 lb. dragster. The flywheel was setup to replicate the mass of the dragster. The test of the internal combustion engine was at a maximum of 7200 rpm. If you need to develope a test bed for this application, look into contacting Fred Mandolini in Villa Park, Illinois, U.S.A. he has this unit within his facility the last time I utilized it for my engine development testing

Sounds like a good concept, I admire your desire (or need) to do it yourself although contracting out is, unfortunatly, usually more economical. However, best of luck building your testbed. If you use a large inertial load to simulate accels (+ and -) then you could get by with a much smaller dissapative load to simulate air drag and other losses. One word of caution I didn't see here yet. Fly wheels can be very dangorous if overspun. They will "explode" if the inners cannot hold the outers together. I think you will want to do a stress anaylsis on this as well.