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• August 30, 2016 Create Date
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National Advisory Committee for Aeronautics, Report - Wind Tunnel Investigation of NACA 23012, 23021, and 23030 Airfoils Equipped with 40% Chord Double Slotted Flaps

An inrestigation was conducted in the NAC’A ’7- by
10-foot wind tunnel to determine the fleet of the deflection-
of main and auxiliary slotted flaps on the aerodynamic
section characteristics of large-chord NAOA 23012, 23021,
and 28030 airfoils equipped with 40-percent—chord double
slotted flaps. The complete aerodynamic section charac—
teristics and envelope polar curses are gioenfor each airfoil-
r‘lap combination. The eject of airfoil-thickness isshown,
and comparisons are made of single slotted flaps with
double slotted flaps on each of the airfails.

The maxi-mum section lift coefiicient of an airfoil with
a 40-percent—chord double slotted flap was found to increase
slowly with increasing thickness, reaching a value of 3.7
for the 30-percent-thicl: airfoil. For any airfoil thickness,
the double slotted flap gate a higher value of section. maxi—
mum lift coefl'icient than either the 40-percent-chord or the
25.66-percent-chord single slotted flaps. The large lift
coefilcients jor the double slotted flaps were accompanied
by large pitching-moment coqflieients. The section profile-
drag ooeficient of an airfoil with a, double slotted flap in-
creased with an“ increase in thickness at all except rery
high lift coeflicients. For a given airfoil thickness, the
double and the single slotted flaps gave about the same sec-
tion profile-drag coefioients for section lift coefllcients less
than 2.0; abore this value the double slottedflap gate the
lower section profile-drag coeficients.

The National Advisory Committee for Aeronautics
has undertaken an extensive investigation of various
airfoil-flap combinations to furnish information applic-
able to the aerodynamic design of high-lift devices for
improving the safety and the. performance of airplanes.
A high-lift device capable of producing high lift wit-h
variable drag for landing and high lift with low drag
for take-off and initial climb is believed to be desirable.
Other desirable aerodynamic features are: no increase
in drug with the flap neutral; small change in pitching
moment with flap deflection; low forces required to
operate the flap ; and freedom from possible hazard due
to icing.