The purpose of this paper is to pass on to airplane designers the things that have been learned in the past year about flutter and vibration of structures to which control surfaces are attached in order that, benefiting by all experience available, this great source of danger in new designs may be controlled. A review of structural failures in the air reveals that a resonant vibration was in nearly all cases responsible. The main factors which determine the potentiality of a resonant flutter are as follows: (a) The character of the air flow around the airplane as affected by drag distribution, speed, power, and air bumps. (b) The rigidity of the structures, rigging, controls, and fittings. (c) The design of control surfaces as affected by shape, aerodynamical balance, and mass distribution.