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National Advisory Committee for Aeronautics, Technical Notes - Theoretical Investigation of the Effects Upon Lift of a Gap Between Wing and Body of a Slender Wing Body Combination

Slender-body theory has been applied to the study of the effects
upon lift produced by the presence of a gap between wing and cylindrical
body of a slender wing-body combination. Two conditions were studied,
one in which both wing and body had the same angle of attack, and the
other in which only the deflected wing had an angle of incidence to the
free stream. The lift for the case of combined angle of attack and wing
deflection can be found by superposition.

The theory predicts large losses in lift even for minute gap widths;
it is anticipated, however, that the effects of viscosity and possibly
of compressibility not considered in the theory will serve to reduce such
losses in practice in the case of very small gap widths. The loss in
lift effectiveness due to gap effects is more severe when both wing and
body are at an angle of attack than when only the wing has incidence
relative to the free stream. For the wing—body combination exclusive
of the nose and afterbody, the gap effects, expressed in terms of per-
cent loss in lift, are more pronounced for larger ratios of body radius
to wing semispan; and the ratio of the lift obtained from wing deflection
to that due to angle of attack increases with increasing gap width.

The effect of the lift of the nose is to reduce the percent loss in lift due
to gap in the angle-of-attack case from that predicted for the portion
of the configuration considered above. As a consequence, the effective-
ness of the wing as a control surface may increase or decrease with
increasing gap width accordingly as the ratio of body radius to wing
semispan is small or large.

In connection with the uSe of all-movable lifting surfaces in
missile design, there arises the practical problem of the effects upon
the aerodynamic characteristics of the missile caused by the presence of
a gap between the wing panels and the fuselage. When the fuselage is
cylindrical, the gap is unavoidable for two reasons: In the first place,
a clearance between the movable wing panels and the body is required
from mechanical considerations, and secondly, a space between the wing
panels and the curved surface of the fuselage is created by the deflec-
tion of the wing with respect to the body.