The WWII-era P-51 Mustang is a marvel of design. The plane’s efficient wing allowed it to fly great distances. One addition to the wing design, not seen in the earliest models, is a set of diaphragms adjoining the fighter’s dynamically and statically balanced ailerons. These lengths of fabric and aluminum are affixed to the rear spar at their leading edge, hugging each side of the aileron (which removed in this photo). They fill in the cavity between the wing and the control surface. This simple addition allows airflow over the wing to remain undisturbed and maintains the constant air pressures over the surface, no matter how the control surface is positioned.