AOPA Pilot Magazine - November 2019 - 85

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AS THE ANGLE OF ATTACK of the wing increases, the point at which the flow separates from

Figure 4. As the angle of attack of the wing increases, the point at which the flow

the
airfoil surface
moves
the
leading
edge.the
When
the separation
bubble,
or the region
separates
from the
airfoiltoward
surface
moves
toward
leading
edge. When
the separation
of
reversed
flow
that
occupies
theof
region
between
thethe
airfoil
andbetween
the
flow,the
envelopes
most
Figure
4.
As
the
angle
of
attack
thethat
wing
increases,
the
point
at which
which
the
flow and
bubble,
or As
the
region
of of
reversed
flow
occupies
region
airfoil
the
Figure
4.
the
angle
attack
of
the
wing
increases,
the
point
at
the
flow
of
theenvelopes
airfoil,
the the
wing
stalls.
Interestingly,
even
at low
angles of
attack,
there
isangles
aseparation
smallof
bit of
separates
from
airfoil
surface
moves
toward
theInterestingly,
leading
edge.
When
the
flow,
most
of the
airfoil,moves
the wing
stalls.
even
at low
separates
from
the
airfoil
surface
toward
the
leading
edge.
When
the
separation
separated
near
the
trailing
edge
the
airfoil.
It isthe
minimized
with-and
the
reason
bubble,
or
the
of
reversed
flow
region
between
airfoil
and
the
attack,
a small
of separated
flowoccupies
near the
trailing
edge
of the the
airfoil.
It is
bubble,there
orflow
theisregion
region
ofbit
reversed
flowofthat
that
occupies
the
region
between
the
airfoil
andthat
the
wings
have-a
trailing
edge.
flow,
most
of
the
wing
stalls.
Interestingly,
minimized
withpointed
and
the
reason
thatthe
wings
a pointed
trailingeven
edge.at
flow, envelopes
envelopes
most
of
the airfoil,
airfoil,
the
winghave
stalls.
Interestingly,
even
at low
low angles
angles of
of

attack,
attack, there
there is
is a
a small
small bit
bit of
of separated
separated flow
flow near
near the
the trailing
trailing edge
edge of
of the
the airfoil.
airfoil. It
It is
is

minimized
with
and
that
wings
have
a
trailing
as
well. The
timelines
prove that
flow
minimized
with
and the
the reason
reason
that the
wings
have narrow
a pointed
pointedstreamlines
trailing edge.
edge.correspond to faster
across the top of the wing is much greater flow which, in turn, results in lower presthan the flow along the bottom. Those sure. With low pressure above the wing
two air particles of the equal transit the- and high pressure below it, lift is the net
ory will never meet again! Note also that force in the upward direction. That's it!
faster flow corresponds to streamlines that
All this represents just a few minare more closely spaced. Finally, Lippisch utes of The Secret of Flight video series.
uses a gas manometer to show the pressure Other highlights include the nature of a
is lowest along those regions of the airfoil wing stall (above) and a visualization of
at which the velocity is highest. Therefore, induced drag via wingtip vortices (p. 86).
aopa.org/pilot AOPA PILOT | 85

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AOPA Pilot Magazine - November 2019

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