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Date: Wed, 01 Nov 2006 00:47:26 -0500
From: cbeazley <cbeazley@innovista.net>
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Subject: Re: Flywheel machining and minimum inertia
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I have lightened many flywheels for race cars and never had a problem. 
It never occurred to me to try it on a rotary. The rotary has no 
reversals like a 4 cylinder piston engines, but has two powerful 
accelerations per revolution. There is no aircraft application for the 
stock flywheel lightened or otherwise. First of course is the 
unbelievable weight of the stock unit.
 
The counterweight is cast into it and it would take a month of machine 
time to reduce it nearly any amount. In racing there is no need at all 
for a flywheel. Just a low ground clearance Chevy button flywheel and a 
5 1/2" Tilton 2 disc clutch. Under 5 pounds for everything. Many flyers 
have notice that awful rattling sound when the idle is reduced too far.
 
Those are the sounds of the gear box loaded in acceleration then when 
the crank slows as the next rotor goes into compression, the crank slows 
and the gear lash stacks up in opposition. Makes you jump the first 
(every) time you hear it. The race car does it to the big strong road 
racing transmission. There are many gears involved, and it is loud. The 
driver always thought it was some terminal sound, and the weekend was 
over. Just bump the idle speed up a bit and it is gone. You might get a 
taste on shutdown.
 
The amount of energy you can store in a flywheel is a function of its 
mass among other things. Once at Indianapolis Racway park a bunch of 
RX-3s were coming onto the long straight when a big chunk of car went 
straight up in the air. The cowl, windshield, part of the rugs and floor 
board, and the transmission. All on the track. Half of the flywheel was 
stuck into the track. Trans oil everywhere. So there was a long cleanup. 
The car was toast. Lots of damage. Too many revs before a shift.
 
Then there were few aftermarket flywheels available, and some people 
actually lightened the stock wheel. The drivers feet are behind the 
bellhousing so rotaries need not run a scatter-shield. I don't have one 
on the new car. But the flywheel and clutch are so small in diameter and 
lack the mass to store much energy. Plus, the rev limiter stops it at 
9,600 RPM.
 
A rotary with no load can attain astounding RPM in the flick of a 
throttle cable. Never stand in the plane of the flywheel. A automatic 
counterweight and a flex plate are just fine.
 
A single rotor is a different deal. The more mass the better.
 
Lynn E. Hanover


Thanks Lynn.
Interesting stories as always.
Do you know any sources for 7.25'' (or 5.5") ring gears and lightweight 
starters that will mesh?

Cheers
Cary