Abstract: A damper, especially for a structural element of an aircraft and especially a propeller driven aircraft in which the propeller generates vibration in the structural element with a fundamental frequency and a frequency which is a harmonic of the fundamental frequency. The damper has a cantilever bar which can be flexed and a cup-shaped pendulum element affixed to the bar and tunable so that the mass of the pendulum defines a first eigenfrequency of vibration of the damper corresponding to the fundamental and the moment of inertia about an axis perpendicular to the axis of the bar is tuned to a second eigenfrequency corresponding to the fundamental.