the difference between the angles of incidence of the upper and lower wings of a biplane: A biplane has positive decalage if the angle of incidence of the upper wing is greater than that of the lower wing and negative decalage when the lower wing has the greater angle.
Origin of decalage
< Frenchdécalage ‘a shift, gap, displacement’ < décaler ‘to offset, shift’ (< dé-de- + caler ‘to fill up, wedge’ < cale ‘a wedge’) + -age-age
