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Hi Tim,
Good explanation. And 100% right on the effects of the flywheel weight. =
Not to discount the pulley at the front of the crank and its effect =
also.
=20
What you are feeling at around the 5200 mark is the 2nd harmonic of the =
crankshafts natural frequency. The 2nd harmonic is usually the most =
destructive harmonic and this is the crankshaft bending the most during =
rotation. Usually, but not always around the mid distance crank. But can =
be around the 2nd crank journal in the 4 Cyl engine. You will see that a =
lot of people will fit billet, machined, large main bearing cap around =
mid-crank length as they have had issues with either bearing =
=E2=80=98wipe=E2=80=99 of broken cap bolts. They are trying to =
counteract the 2nd harmonic by making the bearing journal stiffer.=20
=20
You don=E2=80=99t need to complete a complex calculation to understand =
what RPM=E2=80=99s you should minimise holding your duration at. The =
crank is suspended and =E2=80=98struck=E2=80=99 and the natural =
frequency that the crank vibrates/resonates at will give you =
it=E2=80=99s harmonic characteristics. Just like a tuning fork. This is =
the basis for setting your RPM=E2=80=99s and multiples of that RPM to =
stay away from. OR you need to reduce the effect at those RPM=E2=80=99s. =
Say, using a harmonic balancer design to reduce the harmonic effect at =
certain RPM=E2=80=99s.
=20
Just as Joe Alexander describes, the first harmonic is in the 2800 RPM =
range, but it is the least destructive so you almost miss feeling it.
=20
Hope that helps?
Have a great day
=20
=20
"You can Make a Small Fortune From Motor Racing. As long as You Started =
With A Lage Fortune!"
Kind Regards
Peter Vucinic
TR4 - TR7 V8 - Spitfire MkII
_______________________________________________
=20
<http://www.fot-racing.com/> http://www.fot-racing.com
=20
Archive: <http://www.team.net/archive> http://www.team.net/archive
Forums: <http://www.team.net/forums> http://www.team.net/forums
=20
=20
=20
=20
From: Fot [mailto:fot-bounces@autox.team.net] On Behalf Of timmmurphh--- =
via Fot
Sent: Friday, 22 May 2020 9:08 AM
To: fot@autox.team.net
Subject: [Fot] FW: Flywheel wt & crank harmonics -TR3/4
=20
=20
=20
From: timmmurphh@gmail.com <timmmurphh@gmail.com>=20
Sent: Thursday, May 21, 2020 6:06 PM
To: 'TeriAnn J. Wakeman' <tjwakeman@gmail.com>
Subject: RE: [Fot] Flywheel wt & crank harmonics -TR3/4
=20
The weight of the flywheel will definitely affect the harmonic =
frequency. The heavier the flywheel, the lower the harmonic frequency =
will be. The flywheel contributes a significant amount to the total =
rotating inertia due to its weight and that the weight is at greater =
radius than the other rotating masses. Inertia increases as the square =
of the radius. It is not a linear function of the radius.
=20
An RPM of 5200 was mentioned as the harmonic resonance. I had always =
heard that it was more like 6300 RPM. I have never seen a calculation =
for it. It would be complex. Note that lighter pistons and connecting =
rods would tend to lower the harmonic frequency as they would reduce the =
inertia in the engine.
=20
Tim Murphy
=20
From: Fot <fot-bounces@autox.team.net> On Behalf Of TeriAnn J. Wakeman =
via Fot
Sent: Thursday, May 21, 2020 2:44 PM
To: FOT <fot@autox.team.net>
Subject: [Fot] Flywheel wt & crank harmonics -TR3/4
=20
Something I have wondered about for years.
Does the weight of the flywheel affect the RPM and intensity of =
harmonics inherent in a TR3/4 stock crank? I've never found an answer to =
that question.
TeriAnn
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<o:idmap v:ext=3D"edit" data=3D"1" />
</o:shapelayout></xml><![endif]--></head><body lang=3DEN-AU =
link=3D"#0563C1" vlink=3D"#954F72"><div class=3DWordSection1><p =
class=3DMsoNormal><span style=3D'font-size:14.0pt;color:#1F497D'>Hi =
Tim,<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:14.0pt;color:#1F497D'>Good explanation. And 100% =
right on the effects of the flywheel weight. Not to discount the pulley =
at the front of the crank and its effect also.<o:p></o:p></span></p><p =
class=3DMsoNormal><span =
style=3D'font-size:14.0pt;color:#1F497D'><o:p> </o:p></span></p><p =
class=3DMsoNormal><span style=3D'font-size:14.0pt;color:#1F497D'>What =
you are feeling at around the 5200 mark is the 2<sup>nd</sup> harmonic =
of the crankshafts natural frequency. The 2<sup>nd</sup> harmonic is =
usually the most destructive harmonic and this is the crankshaft bending =
the most during rotation. Usually, but not always around the mid =
distance crank. But can be around the 2<sup>nd</sup> crank journal in =
the 4 Cyl engine. You will see that a lot of people will fit billet, =
machined, large main bearing cap around mid-crank length as they have =
had issues with either bearing =E2=80=98wipe=E2=80=99 of broken cap =
bolts. They are trying to counteract the 2<sup>nd</sup> harmonic by =
making the bearing journal stiffer. <o:p></o:p></span></p><p =
class=3DMsoNormal><span =
style=3D'font-size:14.0pt;color:#1F497D'><o:p> </o:p></span></p><p =
class=3DMsoNormal><span style=3D'font-size:14.0pt;color:#1F497D'>You =
don=E2=80=99t need to complete a complex calculation to understand what =
RPM=E2=80=99s you should minimise holding your duration at. The crank is =
suspended and =E2=80=98struck=E2=80=99 and the natural frequency that =
the crank vibrates/resonates at will give you it=E2=80=99s harmonic =
characteristics. Just like a tuning fork. This is the basis for setting =
your RPM=E2=80=99s and multiples of that RPM to stay away from. OR you =
need to reduce the effect at those RPM=E2=80=99s. Say, using a harmonic =
balancer design to reduce the harmonic effect at certain =
RPM=E2=80=99s.<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:14.0pt;color:#1F497D'><o:p> </o:p></span></p><p =
class=3DMsoNormal><span style=3D'font-size:14.0pt;color:#1F497D'>Just as =
Joe Alexander describes, the first harmonic is in the 2800 RPM range, =
but it is the least destructive so you almost miss feeling =
it.<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:14.0pt;color:#1F497D'><o:p> </o:p></span></p><p =
class=3DMsoNormal><span style=3D'font-size:14.0pt;color:#1F497D'>Hope =
that helps?<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:14.0pt;color:#1F497D'>Have a great =
day<o:p></o:p></span></p><p class=3DMsoNormal><span =
style=3D'font-size:14.0pt;color:#1F497D'><o:p> </o:p></span></p><p =
class=3DMsoNormal><span =
style=3D'font-size:14.0pt;color:#1F497D'><o:p> </o:p></span></p><p =
class=3DMsoNormal><b><span lang=3DEN-US =
style=3D'color:#7030A0'>"You can Make a Small Fortune From Motor =
Racing. As long as You Started With A Lage =
Fortune!"<o:p></o:p></span></b></p><p class=3DMsoNormal><span =
lang=3DEN-US style=3D'color:#1F497D'>Kind =
Regards<o:p></o:p></span></p><p class=3DMsoNormal><span lang=3DEN-US =
style=3D'color:#1F497D'>Peter Vucinic<o:p></o:p></span></p><p =
class=3DMsoNormal><span lang=3DEN-US style=3D'color:#1F497D'>TR4 - TR7 =
V8 - Spitfire MkII<o:p></o:p></span></p><p class=3DMsoNormal><span =
lang=3DEN-US =
style=3D'color:#1F497D'>_______________________________________________<o=
:p></o:p></span></p><p class=3DMsoNormal><span lang=3DEN-US =
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href=3D"mailto:fot@autox.team.net";><span =
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pan></p><p class=3DMsoNormal><span lang=3DEN-US =
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an></p><p class=3DMsoNormal><span =
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class=3DMsoNormal><span style=3D'font-size:14.0pt;color:#1F497D'> =
<o:p></o:p></span></p><p class=3DMsoNormal><span =
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0cm 0cm 0cm'><p class=3DMsoNormal style=3D'margin-left:36.0pt'><b><span =
lang=3DEN-US =
style=3D'font-size:10.0pt;font-family:"Tahoma","sans-serif"'>From:</span>=
</b><span lang=3DEN-US =
style=3D'font-size:10.0pt;font-family:"Tahoma","sans-serif"'> Fot =
[mailto:fot-bounces@autox.team.net] <b>On Behalf Of </b>timmmurphh--- =
via Fot<br><b>Sent:</b> Friday, 22 May 2020 9:08 AM<br><b>To:</b> =
fot@autox.team.net<br><b>Subject:</b> [Fot] FW: Flywheel wt & crank =
harmonics -TR3/4<o:p></o:p></span></p></div></div><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><o:p> </o:p></p><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><span =
lang=3DEN-US><o:p> </o:p></span></p><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><span =
lang=3DEN-US><o:p> </o:p></span></p><div><div =
style=3D'border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm =
0cm 0cm'><p class=3DMsoNormal style=3D'margin-left:36.0pt'><b><span =
lang=3DEN-US>From:</span></b><span lang=3DEN-US> timmmurphh@gmail.com =
<timmmurphh@gmail.com> <br><b>Sent:</b> Thursday, May 21, 2020 =
6:06 PM<br><b>To:</b> 'TeriAnn J. Wakeman' =
<tjwakeman@gmail.com><br><b>Subject:</b> RE: [Fot] Flywheel wt =
& crank harmonics -TR3/4<o:p></o:p></span></p></div></div><p =
class=3DMsoNormal style=3D'margin-left:36.0pt'><span =
lang=3DEN-US><o:p> </o:p></span></p><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><span lang=3DEN-US>The weight of the =
flywheel will definitely affect the harmonic frequency. The =
heavier the flywheel, the lower the harmonic frequency will be. =
The flywheel contributes a significant amount to the total rotating =
inertia due to its weight and that the weight is at greater radius than =
the other rotating masses. Inertia increases as the square of the =
radius. It is not a linear function of the =
radius.<o:p></o:p></span></p><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><span =
lang=3DEN-US><o:p> </o:p></span></p><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><span lang=3DEN-US>An RPM of 5200 was =
mentioned as the harmonic resonance. I had always heard that it =
was more like 6300 RPM. I have never seen a calculation for =
it. It would be complex. Note that lighter pistons and =
connecting rods would tend to lower the harmonic frequency as they would =
reduce the inertia in the engine.<o:p></o:p></span></p><p =
class=3DMsoNormal style=3D'margin-left:36.0pt'><span =
lang=3DEN-US><o:p> </o:p></span></p><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><span lang=3DEN-US>Tim =
Murphy<o:p></o:p></span></p><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><span =
lang=3DEN-US><o:p> </o:p></span></p><div><div =
style=3D'border:none;border-top:solid #E1E1E1 1.0pt;padding:3.0pt 0cm =
0cm 0cm'><p class=3DMsoNormal style=3D'margin-left:36.0pt'><b><span =
lang=3DEN-US>From:</span></b><span lang=3DEN-US> Fot <<a =
href=3D"mailto:fot-bounces@autox.team.net";>fot-bounces@autox.team.net</a>=
> <b>On Behalf Of </b>TeriAnn J. Wakeman via Fot<br><b>Sent:</b> =
Thursday, May 21, 2020 2:44 PM<br><b>To:</b> FOT <<a =
href=3D"mailto:fot@autox.team.net";>fot@autox.team.net</a>><br><b>Subje=
ct:</b> [Fot] Flywheel wt & crank harmonics =
-TR3/4<o:p></o:p></span></p></div></div><p class=3DMsoNormal =
style=3D'margin-left:36.0pt'><span =
lang=3DEN-US><o:p> </o:p></span></p><p =
style=3D'margin-left:36.0pt'><span lang=3DEN-US =
style=3D'font-size:13.5pt;font-family:"Adobe =
Garamond","serif"'>Something I have wondered about for =
years.</span><span lang=3DEN-US><o:p></o:p></span></p><p =
style=3D'margin-left:36.0pt'><span lang=3DEN-US =
style=3D'font-size:13.5pt;font-family:"Adobe Garamond","serif"'>Does the =
weight of the flywheel affect the RPM and intensity of harmonics =
inherent in a TR3/4 stock crank? I've never found an answer to that =
question.</span><span lang=3DEN-US><o:p></o:p></span></p><p =
style=3D'margin-left:36.0pt'><span lang=3DEN-US =
style=3D'font-size:13.5pt;font-family:"Adobe =
Garamond","serif"'>TeriAnn</span><span =
lang=3DEN-US><o:p></o:p></span></p></div></body></html>
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