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National Advisory Committee for Aeronautics, Technical Notes - National Advisory Committee for Aeronautics, Technical Notes - Effect of Ground Interference on the Aerodynamic Characteristics of a 42° Sweptback Wing

The effects of ground interference on the aerodynamic characteristics
of a 1L2° swept'back wing have been investigated at distances 0.68 and 0.92
of the mean aerodynamic chord above the ground. The wing was tested with-—
out flaps'and with inboard trailing—edge split flaps and outboard leading-—
edge flaps deflected.

The nature and magnitudes of the ground interference effects on.the
aerodynamic characteristics of the sweptback wing are, in general, com-
parable to those obtained on unswept wings. The sweptback wing in the
presence of the ground sustained an increase in lift-curve slope and a
decrease in drag. The value of maximum lift for the sweptback wing
increased for the flaps—retracted configuration and decreased for the flaps-
deflected configurations as the distance from the ground became smaller.

The longitudinal stability at the stall for the sweptback wing with
and without flaps deflected was not materially affected by the presence
of the ground. There was, however, at the smallest distance from the
ground a destabilizing change in pitching—moment slope at an angle of
attack several degrees lower than the stalling angle of attack for the
flaps—deflected configuration. Because of the complexity of the phenomenon
at the stall, the possibility exists that the data for the BWeptback wing
tested are not indicative of the type of stability to be obtained at
distances from the ground greater than the mean aerodynamic chord of the
wing.

Certain aspects of the effects of the ground interference on the
aerodynamic characteristics of unswept wings have been thoroughly investi—
gated both theoretically and emerimentally (references 1 to 6). The
experimental results of these investigations have shown that, in the high—_
lift range, theoretical calculations by existing methods do not provide
either an estimate of the magnitude of the ground effects or an explana—
tion of the phenomena involved at the stall.