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From: "Wolfgang" <Wolfgang@MiCom.net>
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Subject: Re: [LML] Re: Small tail, MK II tail, CG range
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CG location and stability is what it's all about. The CG is a physical =
space within which the designer wants you to stay. But little if =
anything is divulged about where that space's definition came from.
Saying the CG is 15% to 30% of the MAC is interesting but not conclusive =
without some assumptions of what the C in MAC stands for.
If a reference is given to a percent of MAC where C =3D Chord, then all =
is well and easily determined. However if C is intended to be Center =
then all bets are off without being given the location of that point by =
the aircraft designer.
The Mean Aerodynamic Chord is a geometric calculation and is not =
influenced by flight forces.
The Mean Aerodynamic Center of a wing is a point on the wing chord which =
results in a constant moment when the wing angle of attack is changed. =
If the cg is at the ac, the forces on the tail will be minimized.
Now keep in mind that MAC (chord) will give, well gee, the chord of the =
wing and then saying the CG is a % of MAC actually means something but =
using MAC (center) fails to give a usable reference for the purposes of =
CG determination.
So . . . I think we have to assume we're talking about MAC where C =3D =
chord
Wolfgang
-------------------------------------------------------------------------=
-------
From: Chris Zavatson <chris_zavatson@yahoo.com>=20
Sender: <marv@lancaironline.net>=20
Subject: Re: [LML] Re: Small tail, MK II tail, CG =
range=20
Date: Fri, 16 Jul 2010 05:57:11 -0400=20
To: lml@lancaironline.net=20
=20
=20
There appear to be different definitions for MAC out there. I am =
more familiar with MAC being used for "mean aerodynamic center". I =
suppose MAC could also refer to "mean aerodynamic chord", as you point =
out. My text on stability and control (Etkin) uses =AFc (with the bar =
over the c) for "mean aerodynamic chord". It is easy to tell which =
definition is meant in diagrams or equations. It is definitely not as =
clear in textual form. I suppose it is best to spell out the intended =
definition.
Chris Zavatson
N91CZ
360std
www.N91CZ.com=20
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<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DArial size=3D3>CG location and stability is what it's =
all about.=20
The CG is a physical space within which the designer wants you to stay. =
But=20
little if anything is divulged about where that space's definition came=20
from.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial>Saying the CG is 15% to 30% of the MAC is =
interesting but=20
not conclusive without some assumptions of what the C in MAC stands=20
for.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D3>If a reference is given to a percent of =
MAC where C=20
=3D Chord, then all is well and easily determined. However if C is =
intended to be=20
Center then all bets are off without being given the location of that =
point by=20
the aircraft designer.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial size=3D3>The Mean Aerodynamic =
<STRONG>Chord</STRONG> is a=20
geometric calculation and is not influenced by flight forces.<BR><BR>The =
Mean=20
Aerodynamic <STRONG>Center</STRONG> of a wing is a point on the =
wing chord=20
which results in a constant moment when the wing angle of attack is =
changed. If=20
the cg is at the ac, the forces on the tail will be =
minimized.<BR><BR>Now keep=20
in mind that MAC (chord) will give, well gee, the chord of the wing and =
then=20
saying the CG is a % of MAC actually means something but using MAC =
(center)=20
fails to give a usable reference for the purposes of CG=20
determination.</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial>So . . . I think we have to assume we're talking =
about MAC=20
where C =3D chord</FONT></DIV>
<DIV> </DIV>
<DIV><FONT face=3DArial>Wolfgang</FONT></DIV>
<DIV>
<HR>
<DIV>
<TABLE class=3DmessageData cellSpacing=3D0 cellPadding=3D0 =
width=3D"100%" border=3D0>
<TBODY>
<TR>
<TD>
<TABLE class=3Drfcheader cellSpacing=3D0 width=3D"100%">
<TBODY>
<TR vAlign=3Dtop>
<TD width=3D"100%">
<TABLE class=3Drfcheaderfields>
<TBODY>
<TR>
<TD class=3Drfcfieldname>From:</TD>
<TD class=3Drfcfieldvalue>Chris Zavatson=20
<chris_zavatson@yahoo.com></TD></TR>
<TR>
<TD class=3Drfcfieldname>Sender:</TD>
<TD =
class=3Drfcfieldvalue><marv@lancaironline.net></TD></TR>
<TR>
<TD class=3Drfcfieldname>Subject:</TD>
<TD class=3Drfcfieldvalue>Re: [LML] Re: Small tail, MK =
II tail,=20
CG range</TD></TR>
<TR>
<TD class=3Drfcfieldname>Date:</TD>
<TD class=3Drfcfieldvalue>Fri, 16 Jul 2010 05:57:11 =
-0400</TD></TR>
<TR>
<TD class=3Drfcfieldname>To:</TD>
<TD=20
=
class=3Drfcfieldvalue>lml@lancaironline.net</TD></TR></TBODY></TABLE></TD=
></TR></TBODY></TABLE></TD></TR>
<TR>
<TD>
<DIV>
<DIV><FONT size=3D3><FONT size=3D2>There appear to be different =
definitions=20
for MAC out there. I am more familiar with MAC being used=20
for "mean aerodynamic center". I suppose MAC could=20
also refer to "mean aerodynamic chord", as you point =
out. =20
My text on stability and control (Etkin) uses</FONT> <SPAN>=AFc =
(with the=20
bar over the c) for "mean aerodynamic chord". It is easy to =
tell=20
which definition is meant in diagrams or equations. It =
is=20
definitely not as clear in textual form. I suppose it is =
best to=20
spell out the intended definition.</SPAN></FONT></DIV>
<DIV><FONT size=3D3><SPAN></SPAN></FONT> </DIV>
<DIV><FONT size=3D3><SPAN>Chris Zavatson</SPAN></FONT></DIV>
<DIV><FONT size=3D3><SPAN>N91CZ</SPAN></FONT></DIV>
<DIV><FONT size=3D3><SPAN>360std</SPAN></FONT></DIV>
<DIV><FONT size=3D3><SPAN><A href=3D"http://www.n91cz.com/"=20
=
target=3D_blank>www.N91CZ.com</A></SPAN></FONT></DIV></DIV></TD></TR></TB=
ODY></TABLE></DIV></DIV></BODY></HTML>
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