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National Advisory Committee for Aeronautics, Technical Notes - Wind Tunnel Tests on Model Wing with Fowler Flap and Specially Developed Leading Edge Slot

An investigation Was made in the N.A.C.A. 7 by 10
foot wind tunnel to find the increase in maximum lift co-
efficient whioh could be obtained by providing a model
wing with both a Fowler trailing—edge extension flap and
a Handley Page type leading—edge slot. A conventional
Handley Page slot proportioned to operate on the plain
Wing without a flap gave but a slight increase with the
flap; so a special form of slot was developed to work more
effectively with the flap. With the best combined arrange—
ment the maximum lift coefficient based on the original
area was increased from 3.17, for the Fowler wing, to 5.62.
The minimum drag coefficient with both devices retracted
was increased in approximately the same proportion. Tests
were also made with the special-type slot on the plain
wing without the flap. The special slot, used either with
or without the Fowler flap, gave definitely higher values
of the maximum lift coefficient than the slots of conven-
tional form, with an increase of the same order in the
minimum drag coefficient.
The purpose of the present investigation was to de-
termine-the maximum lift coefficient obtainable by com—
bining the best retractable trailing—edge and leading—
edge devices found to date in the general wind—tunnel in-
vestigation of high-lift devices'now being carried on by
the National Advisory Committee for Aeronautics. The re—
tractable devices that have given the largest increases
in lift are the FoWler slotted extension flap (reference
1) and the Handley Page leading—edge slot (reference 2).
The first step of the present investigation was to
test an airfoil based on the Clark Y section, incorporat—
ing the Fowler flap and Handlev Page slot, in the optimum
arrangement separately determined for each (references 1
and 2). The maximum lift coefficient obtained with this
combinati-on was only slightly higher than that for the
Fowler wing alone, which was ascribed to the unsatisfac~
tory location and action of the leading-edge slot on the
wing with the Fowler flap. A modified form cf slot was
therefore developed and tested with the slat in a number
of dii‘ferent positions, with the Fowler flap both extend—
ed and retracted.