Abstract: Method for optimising the design of sealing rings of internal manhole covers which close the manhole openings over the inner surface of the skin of an aircraft structure, the surface that is in contact with the inner surface of the skin being the optimized surface of said sealing rings, the method including dividing the outer contour and the inner contour of the optimised surface into n points; grouping into families Fi the sealing rings of each manhole opening; generating the curves that are best adapted to the set of points taken for the outer contour and for the inner contour of each sealing ring for each one of the families Fi; generating a ruled surface among the curves generated for each one of the families Fi.