Date: Thu, 12 Dec 1996 17:09:09 -0800 (PST) From: Mike West Subject: Flywheels 'n numbers Flyweel - Clutch , Now there's a couple misnomers. Flywheel don't fly any more and the clutches doesn't clutch any more. Those are both carry-overs from the "old days" when "flywheel" meant something. Same with the clutch, used to have a lever and you swing it over closing down a set of shoes that really "clutched" something else. You can still see a decent flywheel on those old 13 horse John Deeres or on a punch press, 3-4 foot in diameter. Some of them 20 foot or more. Those are flywheels! Clutches as described have about gone the way of the Wooly Mammoth. Just to get the clutch out of the way it's a sacrificial semi-slippery brake on end of a shaft, used to match the different rpm's and forces of shafts having different speeds and outputs. Instead of "clutching" it just pushes up against the puny flywheel. Flywheels, even our little jobby, are used to store mechanical energy. On a car, it does that but in a limited way for a totally differnt purpose. It's primary purpose is to smooth out the speed fluctuations caused by non-uniform flow of power from the pistons and imbalances of the engine. Sorry, it just slipped out! :-) It takes the power as it comes and averages it out so to speak. "Cushions" is another way to put it. Think of a steel pillow. :-) It's second function is easier to describe than lay a name on. Without the flywheel there would be such an instantaneous response from the end of the engine shaft that you'd wear out a clutch in a matter of hours. Probably wear yourself and the engine out in days. You may try this if you like but heres what's happening: You step on the gas and the energy is immediately headed for the output end but, you have to overcome the mass of the flywheel first. All energy has to go thru the flywheel. The flywheel has mass. Newtons first law says it hates to be pushed around. This flywheel is keeping you from over-revving faster than you can respond to let up on the gas. Without it, you'd have six grand before you could do anything about it. So I guess it's a governor but no max speed, just a lag of time. Those are the primary and secondary functions or call them two primaries if you like since they are of equal importance. The next function of the flywheel is to do the same "averaging" of "negative" forces that come from the road and thru the transmission. You ever push your car? Second favorite sport of VW owners, only superceded by kneeling behind one looking at the engine. Or laying underneath one. When you push the car, do you notice how every little pebble impedes your efforts? Yet you don't even know they're there when you drive. Because the same flywheel is absorbing and averaging them out. It's kind of neat the way that works, even if it is puny. That's why the flywheel is there. I said flywheels accumulated energy. To such a degree that if you want more horsepower, you put on a bigger flywheel. Lets see what it's doing from the inside view. :-) Some of those numbers: :-) E= [W(v)(v)]/2G Writing formulas on a standard typewriter is the pits. What the formula says is that E, energy in ft-lbs is equal to W, the weight of the rim times v, velocity of the rim in ft per second, squared and that is divided by 2 times gravity which is 32.2ft/sec/sec. That cleared it right up, hey?!! :-) The second part of the equation is another story: A counter-weighted crank weighs 5 pounds more than a stock crank. Both have a diameter of 5" roughly. The stock flywheel weighs 17-1/2 lb and has a diameter of 10-1/2" The lightened flywheel weighs 12-1/2 lb and has a diamater of 9-1/2" So when you ordered your crank the guy says you better get the lightened flywheel to compensate for the weight difference. Hey, I was there! It even sounds good! We'll use 4000 rpm as a constant. I was gone a while here while I numerated, - - and ciphered. The 5 pound flywheel gives us 6.77 ft-lb energy. The 12-1/2 pound flywheel gives us 32.18 ft-lb energy The 17-1/2 pound flywheel gives us 49.8 ft-lb of energy The five lb flywheel is just the diff. between the stock and the CW crank, and if we add that to the lightened flywheel we have a total of 39 ft-lb energy or torque. As you can see using the lightened flywheel you lose 10.8 ft-lb of energy or torque and running that thru the hp formula, 8.3 horsepower. Now that's with the stock crank and flywheel. If I add the cw crank and the stock flywheel, I get that 6-1/2 lbs added on which is even better. I don't know who started this but I think Berg did. He uses them on his racers. Works real well for him. Berg, never said the lightened flywheel was to compensate for the crank as far as I know. He just did it to get faster times out of the gate. What will happen with the stock flywheel is you'll get away slower but you'll have that energy to burn on the way up the hill. You won't have to shift down as soon, or as often. It ain't a lot but I think I'll use the stock in my rig. These numbers are always theoretical. Don't bet your pink-slip. Still they represent a damn sight more data than what that clerk has. And then, his job is to sell parts, right? :-) west