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National Advisory Committee for Aeronautics, Technical Notes - Pressure Distribution on a Slotted R.A.F. 31 Airfoil in the Variable Density Wind Tunnel

Measurements were made in the variable density wind tun—
nel of the National Advisory Committee for Aeronautics to de-
termine the pressure distribution over one section;of a R.A.F.
31 airfoil with a leading edge slot fully open. WTo provide
data for the study of scale effect on this type of airfoil, the
tests were conducted with air densities of approximately one
and twenty atmOspheres.

Diagrams representing the pressure distribution over the
surfaces at several angles of attack, as obtained from the
tests at both the high and the low scale, are given together
so that the scale effect on pressure distribution may be stud—
ied. Curves representing the normal force coefficient and the
center of pressure at both the high and the low scale are plot—
ted against angle of attack. Vectors representing the air
forces on the auxiliary airfoil in the open position were de—
duced from the high scale tests and plotted in order to provide
data for designing a mechanism for controlling the slot. A
rule for estimating the air load on the auxiliary airfoil for
stress calculations is also deduced.

The slotted wing is not a new development and extensive
model tests have been carried out in England on this form of
airfoil. However, the full scale investigation of slotted air-
foils has been limited to a few flight tests. In view of the
small size of the slot and auxiliary airfoil used in tests of
slotted wing models and in view of the obvious importance of
viscosity effects withinithe slots, it has been generally con—
ceded that a large scale effect on such wings might be expected.
A n investigation of scale effect on.slotted airfoils can be
carried out to adVantage in the variable density wind tunnel
because tests at both a low and a high scale can be made under
similar conditions and the results of the two compared directly.
An extensive program of force tests on slotted wings in the
variable density wind tunnel has been formulated, but cannot be
carried out for some time. In the meantime, the deVelopment
of the automatic leading edge slot for lateral control has in-
creased the general interest in slotted airfoils and the need
for full scale test results