I-Rotary Flywheels for Mazda Competition Rotary Engines
In 2001, Iannetti Designs was contacted by Steve Sanders, Manager of Mazda Motorsports, Research & Development (currently known as Mazda Motorsports) to develop a new flywheel for the Mazda competition rotary engine. The aftermarket flywheel that Mazda Motorsports was providing their customers at the time was randomly breaking during race events, a situation which was unacceptable to Mazda.
The Design of the I-Rotary FlywheelThe design requirements established for the I-Rotary Flywheel were the following:
- The flywheel had to be structurally reliable and perform without any issues when used in an endurance type racing application;
- The weight of the flywheel had to be made lower than the available models so as to increase the performance of the engine by lowering its moment of inertia. This lighter flywheel model had to be realized using the same large outer diameter of the production cast iron flywheel or at ~12 in. (30.5 cm) diameter, so that the stock starter engagement position of the production engines could be retained.
- The wear surface in contact with the clutch plate had to be made as a replaceable component.
- The flywheel design concept had to accommodate two different clutch diameters, a 4.5 in. diameter clutch and a 5.5 in. diameter clutch.
- The two different versions of the flywheel had to be able to be manufactured by two different suppliers.
After several studies, a flywheel design concept emerged which embraced the best compromise between structural integrity and weight. This 12 in. diameter flywheel achieved a low weight of 4.0 lbs (1.8 Kg) while using a thick and relatively heavy, 1/4 in. steel insert as the replaceable clutch wear surface.
Flywheel Design Studies
Finished 5.5 inch Flywheel with Steel Clutch Insert
It should be noted that the I-Rotary flywheel design could have been made even lighter in weight at the time. However, this lighter design alternative was not pursued since it was felt that its durability would have been questionable under the aggressive environment of a season which included several lengthy endurance races such as the 24 hours of Daytona, the 12 hours of Sebring and possibly the 24 hours of Le Mans.
Evaluation of the Structural Integrity of the I-Rotary Flywheel
A new I-Rotary designed flywheel for a 5.5 in. diameter clutch (Mazda P/N: 0000-02-9207) was tested in 2005 by a laboratory which specializes in the structural testing of flywheels for the automotive and performance industries. The test results showed that the catastrophic failure of this flywheel occurred at just below 33,000 RPM.
Flywheel Testing Summary
Flywheel after 32,880 RPM Burst Test
According to the flywheel testing laboratory, this was the first time that they had tested a flywheel of this diameter which achieved such a high level of rotation before its catastrophic failure. They had originally predicted that the flywheel would fail at around 16,000 RPM, and as such, the test was expected to only take 8 hours. This prediction was based on their experience with previously tested aluminum flywheels made for the aftermarket or racing industries of similar diameter as the I-Rotary flywheel. Instead, this test took over 2 days longer to perform than they had originally estimated.
Remarkably, the failure occurred, not from a structural failure of the flywheel aluminum body but from the failure of the replaceable steel clutch wear surface around one of the bolt holes. This failure allowed the bolt attaching this plate to the aluminum body to loosen which caused the flywheel to become out of balance. This unbalanced condition resulted in the catastrophic failure of this unit at just below 33,000 RPM.
Since 2003, there are several hundred of these flywheels in use around the world. They are being operated on regular basis at speeds greater than 8,500+ RPM. Some of the major applications of the I-Rotary flywheel have included all of the Grand AM GT series Mazda RX-8 race cars using the 20B, 3-rotor engine prepared by SpeedSource between 2005 and 2012. Thousands of hours of use were accumulated during this period by these RX-8 Grand Am race cars. As of 2019, there has never been a failure reported from any of the I-Rotary flywheels.
Today, I-Rotary is confident that this flywheel design could be further optimized to achieve a substantially lower weight than the already low weight of 4 lbs. with similar or better performance.
We want to give a special thanks to Ron Cochrane and the CADWORKS Company, Inc. in Franklinton, North Carolina for their assistance with this project. We also want to thank Rick Engman of Mazmart, Daryl Drummond of Daryl Drummond Enterprises, Inc. and Fidanza Flywheels for their help with this program.
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