A projectile, an airborne body or a missile, such as an article of ammunition, having extendable wings, whereby a wing covering is provided to extend between a front spar which is extendable through the action of a power element, and a rear spar which is retractable with its outer end against the front spar, as well as providing for a specially adapted power element for this purpose. The power element has one end thereof engaging at the front spar and has its opposite end engaging against a slider which is latched to the projectile so as to be supported thereon for displacement along the longitudinal direction, and wherein the rear spar has its inner end pivotable in front of the slider in the direction of displacement thereof, and upon the slider being unlatched, is pivotable further by the slider under the action of the power element for effectuating the tensioning of the wing covering.