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- Thread starter jaguar57
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BvU

Science Advisor

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I'm pretty sure the ##\omega## is the angular speed of the crankshaft and ##\theta## is its angle. If you could provide some more context, maybe we can settle this with more certainty.

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By "angular speed" do you mean the rotational speed of the crank where the connecting rod connects to it?

And the angle is from the vertical axis?

- #4

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The w is the lower case Greek omega: ##\omega##. It is usually used for angular frequency which in SI units is measured in radians/secondI need to know what the w is in this formula.

Also I am not 100% sure which angle it is using.

This is for figuring the inertia of the piston assembly in a 2 stroke engine.

thanksView attachment 226566

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Do I need to have all weights in kg and all lengths in meters? (I prefer the metric system)

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PISTON INERTIA = (piston assembly kg + .66 x con rod kg) x (piston stroke meters/2) x (radians(crankshaft angle change)/second)^2 x COS(crank angle) + ((piston stroke meters/2)/(connecting rod meters)) x COS(2 x crank angle) - ((.5 x piston stroke meters)^3 / (4 x (connecting rod meters)^3) x COS(4 x crank angle))

- #7

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PISTON INERTIA = (piston assembly kg + .66 x con rod kg) x (piston stroke meters/2) x ((radians(crankshaft angle change per second)^2 x COS(crank angle) + ((piston stroke meters/2)/(connecting rod meters)) x COS(2 x crank angle) - ((.5 x piston stroke meters)^3 / (4 x (connecting rod meters)^3) x COS(4 x crank angle)))

And it did work using the conventional angling of the crank with 0 degrees being with the piston at the top of its stroke.

TDC inertia for my engine is 287 (after converting N/m2 to lbf) and -186 at BDC. But that doesn't agree with the Wallace Racing piston inertia calculator at http://www.wallaceracing.com/Calculate-Inertia-Force-of-Piston.php

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