AIRCRAFT REINFORCING STRUCTURE

An object of the present invention is to prevent accumulation of moisture which has entered inside a honeycomb sandwich panel used for a stressed-skin structure of an aircraft. A reinforcing structure includes an outer panel constituting an outer shell of a tailplane and a honeycomb sandwich panel reinforcing the outer panel. The honeycomb sandwich panel includes a honeycomb core having a plurality of cells, an outer skin joined on the front side of the honeycomb core and disposed on the side of the outer panel, and an inner skin joined on the back side of the honeycomb core and disposed on the inner side of the tailplane. The inner skin has drainage channels formed therein through which each of the plurality of cells communicates with the outside of the honeycomb sandwich panel.