2020 Trade Shows are cancelled so let DYNOmite bring them to you...

Trade Show Update

10/26/2020

Trade Shows have been cancelled for 2020 and we are disappointed as you are. But in anticipation of this reality, we have been working hard to create a new-to-the-world virtual booth for our devoted Customers. You will hear more about this in the next weeks, but look for:

  1. Live streaming content with industry experts
  2. Demonstrations with service techs of our equipment
  3. Live chat with Sales and Service staff to discuss industry needs and innovations
  4. Watch as some of the most popular SuperFlow and DYNOMite products are being built
  5. the coolest opportunity the industry has ever experienced – YOUR chance to interact with our Innovation team to finalize versions of software and controls

DYNOmite views this year as an opportunity to engage with you in ways we haven't been able to in the past. Please visit our show page to register for additional information as it becomes available.

Inertia Flywheels


Calculate the required polar-moment-of-inertia to simulate a vehicle's weight with a flywheel.

Intermediate | 07.20.20

What flywheel inertia is needed to simulate a vehicle’s weight on an engine dyno?

First, determine the “Vehicle Speed Factor” to scale DYNO-MAX’s “Speedometer” formula readings to duplicate your vehicle’s real world engine tach to speedometer relationship. Then, use that same factor in the equations below to calculate the required simulation flywheel polar moment of inertia.

Required_Polar_Moment_of_Inertia = Simulated_Vehicle’s_Weight / Vehicle_Speed_Factor^2 * 6.1

Tip: Weight must be in pounds to return the polar moment of inertia as ft-lb-sec^2

Example:

Say we want to add a flywheel to our engine dynamometer’s driveline which will simulate a 2,000 pound car’s mass during acceleration testing. We’ll assume we already determined that a Vehicle Speed Factor of 28.01 does a good job of matching our car’s 4th gear highway tachometer/speedometer relationship to that on the engine dyno. We can use the above formula to come up with it’s required polar moment of inertia. Here’s how:

2000 / 28.01^2 * 6.1 = Required_Polar_Moment_of_Inertia

squaring our 28.01 Vehicle Speed Factor yields:

2000 / 784.5601 * 6.1 = Required_Polar_Moment_of_Inertia

finishing the math:

2000 / 784.5601 * 6.1 = 15.55 ft-lb-sec^2

With the above inertia value, it is easy to use DYNO-MAX’s Inertia Calculator to figure a good diameter, length, and material combination to deliver that inertia. For instance, a 16″ diameter steel flywheel that is 39-1/2″ long is a good match.

WARNING: BEFORE ACTUALLY CONSTRUCTING ANY FLYWHEEL, VERIFY THAT YOUR PLANNED OPERATING RPM, FLYWHEEL DIMENSIONS, AND CONSTRUCTION MATERIALS KEEP EVERYTHING SAFELY BELOW THE CALCULATED BURST SPEEDS, ETC.

The same DYNO-MAX Inertia Calculator also makes it easy to determine the equivalent inertia required should you choose to gear the flywheel up or down from the shaft where the Vehicle Speed Factor was referenced. remember that there is a exponential (square) relationship between shaft speed changes and the effective vehicle inertia simulation weight.

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