Toymods Car Club Inc: Tech & Conversions => 3TGTEU flywheel weight

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TA23-MBZQ-NNR
Occasional Poster

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canberra
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August 2002

flywheel weight	Mon, 11 November 2002 03:21

How about some of the basic science? Of the power that is left after burning your fuel (and throwing the majority (60-70%) out the exhaust) you may lose 20% due to things like friction, windage, pumping, and VIBRATION. Of this amount, I can use it to : 1/ accelerate 2/ store as rotational inertia (in the flywheel - BTW the weight of the flywheel is not as important as where the weight is, varies as the cube of the distance to the crank) The more I store in the fly, the less is available to accelerate! So, why have a fly at all? 1/ You're not always at F/T (although we might like to be) 2/ Smoothing of VIBRATION (increase in efficiency and longevity) 3/ Maintenance of rotational inertia 1 -> At partial throttle settings, you are at lower efficiency with less available power, so the losses tend to be more signficant. The fly tends to smooth the delivery to the 2,3 or 4 small explosions which occur every time the crank rotates. 2 -> With no fly, almost no engine would idle at a reasonable speed (or run well at low RPM), due to the slowing of the crank during compression, exhaust and intake strokes. This is more apparent when you have less power to play with (check out the size of the fly on a mower / chainsaw compared to the size of the pot). Having a rotating mass, means that power is stored and delivered to the other necessary strokes in the cycle. The smoothing of this and other vibrations increases available power (vibration wastes energy). Consider a crank rotating. If large amounts of power are applied at low RPM (crank having slowed to a minimum speed in the cycle), the crank will bend more than if the power was applied at a higher RPM (an averaged speed due to the fly). The bending of components means that there is higher losses due to friction, plus the elastic bending generates extra heat. Added to this is the consideration that vibrating parts will fail in fatigue sooner than well balanced components (try bending metal back and forth until it breaks). 3 -> It is desirable to have an engine not react significantly to small changes in external conditions (such as going over a small rise). An engine without energy stored will slow quicker than one which can draw from this source. So although you may have slightly more power available w/ a lightened flywheel, if the terrain, RPM and gearing requires more power than the engine can develop, then it will slow at a quicker rate. The choice is yours as to whether you wish to have an engine which accelerates hard (will be more prone to vibration and fatigue type failures) or one that is for cruising (but will not spin as freely). Hope this helps [Report message to a moderator]

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