Interference effects at the root junction cause additional drag and the fuselage itself can cause a reduction in wing lift. Design of the wing-fuselage junction to avoid these adverse effects is extremely challenging.
Johan Bosman, JS Chief Aerodynamicist, explains: However before the wing-fuselage junction itself was designed, the optimum wing angle was established by assuming standard up wash and downwash angles from the airfoil and aligning these with the fuselage streamlines. For high and low speeds the optimal angle is different. The wing setting angle is nearer the high speed optimum as it is not such a big influence at low speeds.
Not much information was available on wing-fuselage junction design for sailplanes at the time when the JS1 Revelation was developed. Therefore a new approach to wing-fuselage design was taken in conjunction with Professor Krzysztof Kubrynski from Warsaw (who developed the panel method software KKAERO).
The aim was to minimise lift loss due to the fuselage and to maximise laminar flow area without flow separation problems at the operational angles of attack. This was achieved by applying a positive twist to the root section around the flap hinge point, thus compensating for the lift loss by increasing the local angle of attack. With KKAERO and self written software to ensure that airfoil geometries are not corrupted by twisting, the optimum wing-fuselage junction for the JS1 revelation has been obtained. Several iterations on the root airfoil were done to ensure a separation-free root junction.
For maximising laminar flow on the root area, the blending into laminar flow airfoils is made over a short distance and adequate fillets ensured no excess turbulent flow on the wings.