Re: Wing section and angle of incidence

From:         Al Gerharter <agerhart@teleport.com>
Organization: Teleport - Portland's Public Access (503) 220-1016
Date:         Sat, 4 Apr 1998 05:28:44 GMT
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Followups:    1 2
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dennis.jensen@dwt.csiro.au wrote:

> In having a discussion with someone, there are a few points I would like to
> clear up.
>
> First, with commercial airliners, does anyone know which airliners have
> symmetrical airfoils, what NACA sections are used, and where these NACA
> sections can be found.
>
> Second, the wing is set at some angle of incidence to the fuse. Does anyone
> know what angles are generally used. Furthermore, does anyone know whether the
> AoA sensor measures the AoA of the airfoil, or of the fuse?
>
> I have been having an email disagreement, where this person claims that he has
> extensive aviation experience, and that he has seen a 747-400 fly for hours at
> zero AoA!!! Furthermore, he claims that the airfoil sections for all airliners
> are assymmetric. Please help.
>
> Dennis
>
> -----== Posted via Deja News, The Leader in Internet Discussion ==-----
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first: A symetrical airfoil, i.e. one of identical upper and lower surfaces, is
seldom
found on airliners. Often used on aerobatic aircraft, these airfoils generate the
almost
the same lift inverted. Large a/c airfoils may look near symetrical, and have
sections
(for fuel storage and high speed drag reduction) that approach symetrical, but
overall
they have large differences in the area of upper and lower surfaces.
    No, I don't know of any commercial airliners using symetrical airfoils. Yes,
the naca sections are undoubtedly available, but I can't help you there. The
manufacturer may
have specif data available.

second:
    This is the part I wanted to answer. Yes the wing is set at an angle of
incidence
to the fuselage. The root of the wing has a much greater angle of incidence than
does the tip. Called washout, it is the change in angle of incidence(or in flight,
AoA)
between the root and the tip. This loads most of the lift next to the root where
it
can be supported, and where the rest of the wing acts as a "fence" or winglet to
minimize the vortices produced by producing lift. The angle of attack shown in
the cockpit, excuse me, 'Flight Deck', are an indication of the 'mean' AoA. At
high speed cruise, with most of the lift generated by the inboard sections, and
the
outer most sections flying at near zero, or perhaps even a slightly Negative AoA,
you might might see a near zero indication on the AoA, but I doubt it.
    In smaller a/c, say a Lear 25, The AoA is always positive, assuming we are
prducing lift. At the high altitudes required for high speed flight, the air is so
thin
that the AoA, particularly during a turn, approaches the stalling AoA.
                                        Al