Tests on certain aircraft having disclosed discrepancies between the characteristics estimated from the figures for the individual components and those observed for the complete model, the present investigation was undertaken to determine the nature and magnitude of the effects of interference between the body and wings of aircraft and to ascertain the factors influencing the interference.

The models were made up of standard 3in. x 18in. duralumin aerofoils and fuselages of wood.

The aerofoils employed in the investigation were:–

1. (a) R.A.F.-15–a thin section.

2. (b) U.S.A.-27–a section of medium thickness.

3. (c) Gottingen-387–a thick section.

The fuselages used were:–

1. a. Fuselage A–of streamline form.

2. b. Fuselage B–of cabin form.

3. c. Fuselage C–of usual open cockpit form.

A number of typical monoplane and biplane combinations Of wings and fuselages were tested, and in some cases the effect of fairing between wings and fuselage was studied.

The results of the investigation indicate that the interference effects are dependent on the shape of the fuselage, the aerofoil section and the relative position of the fuselage and aerofoil. The better the aerodynamic form of the fuselage, and the thicker the aerofoil section, the greater are the interference effects and the more marked the influence of the relative vertical position of the wings and body on the interference.

Interference between wings and body tends, in general, to lower the critical angle and increase the drag of the combination as compared with the individual components. It may increase or decrease the lift.

From an aerodynamic standpoint, the best position for the wing is at the top of the fuselage, and the worst that at the bottom.

Fillets and fairing may improve a combination having poor characteristics, but have little effect if the arrangement already possesses good characteristics.

An explanation of the cause of the observed interference effects is advanced.