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National Advisory Committee for Aeronautics, Technical Notes - Wind Tunnel Investigation of an NACA 23012 Airfoil with Several Arrangements of Slotted Flaps with Extended Lips

An investigation was made in the NAGA 7- by 10-foot
wind tunnel to determine the effect of slot-lip location
on the aerodynamic section characteristics of an NADA
23012 airfoil with a 30-percent-chord slotted flap.
Tests were made with slot lips located at 90 and 100 per-
cent of the airfoil chord and with .two different flap
shapes. .

The results are compared with a slotted flap previ-
ously developed by the National Advisory Committee for
Aeronautics with a slot lip located at 83 percent of the
airfoil chord. The extension of the slot lip to the rear
increased the section lif.t and pitching-moment coefficients.‘

Comparisons made on a basis of pitching moment for
a given tail length show that the Fowler type flap, lip
extended to trailing edge of the airfoil. has the greatest
section lift coefficient. For moderate tail lengths, 2
to 3 chord lengths, there was only a slight difference
between the previously developed slotted flap and the slot-
ted flap with slot lip extended to 90 percent of the air-
foil chord. Of the three flaps tested, the Fowler flap
had the lowest drag coefficient at high lift coefficients.
The extension of the lower surface at the leading edge of
the slot had a negligible effect on 'the profile drag of
the airfoil-flap arrangement with the- flap deflected when
the lip terminated at 90 percent of- the airfoil chord.‘

The National Advisory -Committee- for- Aeronautics he}
undertaken an extensive investigation of high—lift devices
to furnish information applicable to the design of more
efficient and safer airplanes. Some of the desirable aero-

dynamic features of high-lift devices are: high lift ‘;
with variable drag for landing, high lift with low drag
for take—off and initial climb, no increase in drag with
the device-neutral, and smalchhange in pitching_moment
with the device in Operation. One of the most promising
devices developed up to the present time is an airfoil

in combination with a slotted.f1ap. Aerodynamic and load
data are available on'lzipercent-thick airfoil—flap com—
binations in references 1 to 6; references 1 and 2 give
aerodynamic data for slotted flaps with a short lip exten—
sion developed by the HACA;'and_references 3 and 4 give
aerodynamic data for Fowler flaps on which the slot lip
extends to the trailing edge of the airfoil. Load data
are given in reference 5 for one of the slotted flaps and
in reference 6 for the Fowler flap.