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National Advisory Committee for Aeronautics, Technical Notes - Some Studies on the Aerodynamic Effect of the Gap Between Airplane Wings and Fuselages

The general result indicated by this study is that if de—
sirable from any viewpoint the gap between wing and fuselage
may be closed without detrimental aerodynamic effects, and with
a given monoplane there is less drag if the wing is directly
on top of the fuselage than if it is parasol.

The question often arises in planning a cabin airplane
whether the wing, if a high~wing monoplane, should be directly
on the fuselage or above it, as in the parasol type, or if a
biplane, whether the fuselage should extend to the upper wing or
leave a gap open. This question will be decided usually from
consideration of the structure, vision, or general arrangement,
but the effect on the aerodynamic characteristics of the air—
plane must also be considered.

This note gives the results of a few experiments to study
the changes in the aerodynamic characteristics. The experimental
work was done as theses by two students* in aeronautical engi—
neering at the Massachusetts Institute of Technology. The re—
sults must be considered largely qualitative due to the small
scale of the models, and the complete omission of propulsive
effects.

Models of three airplanes were used: (A) a small parasol
two—seater (Fig. l); (B) a familiar biplane type of training
airplane (Fig. 2);' (O) -a special high—wing cantilever cabin,
monoplane (Fig. 3). Three different arrangements of'each model
were tested which are indicated.on the sketches. Arrangement_

1 indicates in each case the unmodified design. Change in model
A consisted of two separate methods of totally closing the gaps
between parasol wing and fuselage; in model B two enclosed
cabins, one extending wholly to the upper wing, the other leer;
ing a very small gap; in model C the wing was first raised
above the fuselage, then the gap so formed filled, making again
a high—wing monoplane, but with someWhat deeper fuselage.