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National Advisory Committee for Aeronautics, Technical Notes - Effectiveness of Boundary Later Control, Obtained by Blowing Over a Plain Rear Flap in Combination with a Forward Slotted Flap, in Deflecting a Slipstream Downward for Vertical Takeoff

An investigation of the effectiveness of boundary-layer control,
obtained by blowing a Jet sheet of air over a plain rear flap in com-
bination with a forward slotted flap, in deflecting a propeller slip-
stream downward for vertical take-off has been conducted in a static—
thrust facility at the Iangley Aeronautical Laboratory. The investigation
indicated that the plain rear flap alone with a low momentum coefficient
for boundary-layer control provided larger turning angles than the com»
bined slotted and plain flaps without boundary-layer control. Within
the region of ground effects the configuration of this investigation mani-
fested reductions in turning angle and ratio of resultant force to thrust
that were similar to those shown for numerous configurations of previous
investigations with or without boundary-layer control.

The slotted and plain flap of this investigation (with boundary-
layer control over the rear flap) provided larger turning angles and
ratios of resultant force to thrust than the double plain flap config-
uration of a previous investigation (with boundary-layer control over
the forward flap).

An investigation of various wing-flap configurations has been con—
ducted at the Langley Laboratory in an effort to develop simple arrange-
ments capable of deflecting the propeller slipstream downward for vertical
take-off. The capabilities of some of these configurations are reported
in references 1 to 6. The effect of blowing boundary-layer control on the
ability of a wing to deflect the slipstream.was investigated in refer-
ences 5 and 6. In these studies boundary-layer control was applied at
the knee of the first flap. Experience has shown, however, that flow
separation is most likely to occur on the second flap. Therefore, an
exploratory investigation was undertaken to determine the slipstream
deflection characteristics of a wing with blowing boundary-layer control
applied only to the second flap. The investigation was conducted in a
static-thrust facility and employed a model wing equipped with a
67-percent-chord slotted forward flap and a 55-percent-chord plain rear
flap. A full-span blowing nozzle was located at the trailing edge of
the forward flap for applying boundary-layer control to the rear flap.