F1, trickle-down, etc.

[Andrew R. Ghali]

>
On Sat, 29 Sep 2001 18:16:20 +0000 (GMT+00:00), Wild Thing <thing at iobox.fi>
>
>I would argue that a 5cc model airplane engine doesn't run anything close
>to the piston speed of a 100cc kart engine. rpm and piston speed are
>different things. The kart engine with 5cm stroke revving 24000rpm would
>be about equal to a 2cm(?) stroke of the 5cc engine running at 60000rpm. I
>would think that they rev substantially less than that though.
>
>Talking about piston speeds is pretty irrelevant though, what is more
>important is the centrifugal force generated at the base of the con rod.
>Rpm increases this force exponentially while stroke increases it linearly.

It is a centripetal acceleration and it scales quadratically (i.e. to the
square) of RPM.  Force is mass times accelleration, so the "inertial load"
(as Corky Bell calls it) is directly proportional to piston mass.  However,
mass generally scales directly with volume, since displacement is volume,
piston mass should scale roughly with displacement.  So my guess is that
the loads on a 100c kart engine would be 50 times that of the 5cc motor at
the same RPM.  Or they are the same if the 5cc motor is running 7x the RPM.

I hope this helps.

Andrew
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