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National Advisory Committee for Aeronautics, Technical Notes - Effects of Compressibility on Normal Force, Pressure, and Load Characteristics of a Tapered Wing of NACA 66-Series Airfoil Sections with Split Flaps

A high—speed wind—tunnel investigation of a tapered wing of
NACA 66—series airfoil sections equipped with split flaps has been
conducted at'Mach numbers up to 0.585 to determine the effects of
compressibility on the normal—force, pressure, and load characteristics.
Both 55—percent—span and 98—percent—span flaps deflected 60° and having
chords of 20 percent of the wing chord were tested. The range of angle
of attack investigated was from approximately 4° up through the stall.

The maximum normal—force curves for the wing with flaps were some—
what similar in shape to the maximum lift curve for the wing without
flaps, although Mach number effects became apparent at lower speeds
and were larger for the wing with flaps. The maximum normal—force
coefficient for the wing with partial—span split flaps reached a minimum
value of 1.53 at a Mach number of 0.295 and a maximum value of 1.79 at
a Mach number of 0.585. The maximum normal—force coefficient for the
wing with full-span split flaps reached a minimum value of 1.87 at a
Ivhch number of 0.300 and a maximum value of 2.22 at a Mach number
of 0.550. There is further evidence that. the rapid rise in maximum lift
coefficient at higher Mach numbers is due to the sharp leading edge of the
wing as camber, camber location, and trailing—edge angle appear to have
little or no effect on the rise. '

Mach number has a very slight effect on the shift of-lateral center
of normal force for angles of attack below the stall.

Until recently only scattered results have been obtained from wind—
tunnel tests (references 1 and 2) and from flight tests (references 3
and 1L) on the effects of both Reynolds and Lhch numbers on the maximum—
lift characteristics of airfoils. These tests indicated the importance
of a more extensive knowledge of these effects on the maxim lift
coefficient both in the estimation of the maneuvering performance and
loads of high—speed aircraft and in the interpretation of wind—tunnel
maximum—lift data as applied to the prediction of airplane characteristics
at low speeds. Hence, an investigation of a series of typical fighter—
type wings has been undertaken in the Iangley 16—foot high—speed tunnel
and in the Langley 19—foot pressure tunnel. The primary purpose of the
investigation in the Langley 16—foot high—speed tunnel has been to study
the effect of Mch number on maximal—lift characteristics up to a Mach
number of approximately 0.60, and in the Langley 19—foot pressure tunnel,
the primary purpose has been to study the interrelated effects of Mach
number and Reynolds number on mximnn lift characteristics up to a Mach
number of approximately 0.35.