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<DIV dir=ltr align=left><SPAN class=984464518-30092007><FONT face=Arial
color=#0000ff>What Ed said, but even more so.... ;-) It's not
even _that_ simple.</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=984464518-30092007><FONT face=Arial
color=#0000ff></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=984464518-30092007><FONT face=Arial
color=#0000ff>For optimum cruise, other factors enter in. Best range
is not necessarily at max L/D, but usually close.</FONT></SPAN><SPAN
class=984464518-30092007><FONT face=Arial color=#0000ff>
</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=984464518-30092007><FONT face=Arial
color=#0000ff></FONT></SPAN><SPAN class=984464518-30092007><FONT face=Arial
color=#0000ff></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=984464518-30092007><FONT face=Arial
color=#0000ff>Well done, Ed, for a structures guy.
;-)</FONT></SPAN></DIV>
<DIV dir=ltr align=left><SPAN class=984464518-30092007><FONT face=Arial
color=#0000ff></FONT></SPAN> </DIV>
<DIV dir=ltr align=left><SPAN class=984464518-30092007><FONT face=Arial
color=#0000ff>Jim</FONT></SPAN></DIV><BR>
<DIV class=OutlookMessageHeader lang=en-us dir=ltr align=left>
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<FONT face=Tahoma size=2><B>From:</B> nsrca-discussion-bounces@lists.nsrca.org
[mailto:nsrca-discussion-bounces@lists.nsrca.org] <B>On Behalf Of </B>Ed
White<BR><B>Sent:</B> Sunday, September 30, 2007 12:33 PM<BR><B>To:</B> NSRCA
Mailing List<BR><B>Subject:</B> Re: [NSRCA-discussion] Airplane angle of
attack<BR></FONT><BR></DIV>
<DIV></DIV>I work for Boeing, although in structures technology, not
aerodynamics. But I work with the aero folks enough to know the answer
they will give. Which will be, "Its not that simple." I know this
because that's the answer I get to every such question I ask.<BR><BR>There are a
lot of factors that will come into play in setting wing incidence. Where
is the cg? What pitch moment effect does the fuselage lift have?
Both these affect how much tail down force is needed to maintain trim conditions
(which affects longitudinal stability but also generates drag). Then there
is the wing-body interface. A knowledgeable aero person once described the
flow at the wing-body interface as "problematic" (code for we don't know for
sure until we try it). Then the fuselage is not a pure cylinder, the nose
is not axi-symmetric (because apparently pilots want windows to see out
of). The area at the wing-body interface has bump outs for wing carry
through structure and other things, and the tail is usually not placed on the
centerline of the fuselage and the tail cone is also not axi-symmetric to avoid
tail strike on take-off.<BR><BR>All of this and a whole lot of other factors go
into fuselage lift and drag.<BR><BR>The simple design objective is to maximize
the lift to drag ratio for the entire aircraft at cruise conditions. The
angle of attack of the fuselage will be designed to meet that goal as best as
possible and may not be 0, and is likely different for different
airplanes.<BR><BR>So now you are all aerodynamics experts. All you need to
know is the easy to learn phrase, "Its not that simple." Of course I can
find you folks at Boeing who will claim that when I am asked questions about my
real expertise, structural dynamics, I tend to use the same phrase. But
don't believe them.<BR><BR>Ed<BR><BR><B><I>Jeff Hill
<jh102649@speakeasy.net></I></B> wrote:
<BLOCKQUOTE class=replbq
style="PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: rgb(16,16,255) 2px solid">This
is a question about full size airplanes that has some <BR>applicability to
model design. We're talking about airliners that <BR>have an essentially
cylindrical fuse.<BR><BR>I'm having a debate with a friend at work about
whether or not full <BR>scale airliners fly slightly nose up. I claim they do
he claims they <BR>don't.<BR><BR>I claim they do because the airflow would be
more stable about a <BR>cylindrical body that was at a slight angle of attack,
and that if <BR>you make it nose up you also gain a little lift.<BR><BR>He
claims that airliners fly with no AOA in the fuse because the last <BR>thing a
designer wants is lift from the fuse because lift generates <BR>drag, the fuse
is not a good shape for generating lift, and <BR>consequently it isn't worth
paying the drag penalty.<BR><BR>What do you all think?<BR><BR>Jeff
Hill<BR>_______________________________________________<BR>NSRCA-discussion
mailing
list<BR>NSRCA-discussion@lists.nsrca.org<BR>http://lists.nsrca.org/mailman/listinfo/nsrca-discussion<BR></BLOCKQUOTE><BR></BODY></HTML>