Scott, you're right about the speed being highest when the crankpin is at 90
and 270 degrees. Piston speed is momentarily zero at top and BDC. It's one
of those things that's kind of fun to graph out. Or you can just dig out a
copy of Ricardo and find it all there, figured out in detail at the turn of
the century. Connecting rod length is one of the big factors in determining
the max and min values of acceleration. A short rod is most like being
connected right to the crank. I seem to remember that speed is a sine curve
and acceleration is a cosine, but I really don't remember this stuff, but
I'll pull out my ancient copy of Ricardo tonight and refresh my memory.
-----Original Message-----
From: owner-fot@autox.team.net [mailto:owner-fot@autox.team.net] On Behalf
Of Fubog1@aol.com
Sent: Wednesday, May 19, 2004 3:21 PM
To: tstrange@sbcglobal.net; sbarr@mccarty-law.com; jerrybarr@charter.net
Cc: fot@autox.team.net
Subject: Re: FW: Crankshafts
In a message dated 5/19/2004 12:25:47 PM Pacific Daylight Time,
tstrange@sbcglobal.net writes:
> "Barr, Scott" <sbarr@mccarty-law.com> wrote:
> << You can tell that by actually measuring piston travel vs crank
rotation.
> It's pretty lazy up to about 90 degrees up the bore, then really speeds
up. >>
>
> Isn't this the opposite of what you'd expect? I would think that the
up/down
> piston travel would actually DECREASE in speed at the top and bottom of
the
> stroke as the rotation of the crank is more sideways (in cross-section)
than
> up and down. I would assume that the highest piston speed would occur
where
> the crank throw is at 90 degrees and 270 degrees from TDC. Am I wrong
about
> that?
>
>
If you look at the distance that the piston travels in the top half of the
stroke, compared to the bottom half, it is much greater on the top. It has
to
accelerate/decelerate the reciprocating mass more distance for a given
amount of
crank rotation. This translates into more inertia load.
Glen
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