Some rockets or missiles have experienced body flutter. This phenomenon can be treated as a critical motion of the bending vibration combined with the pitching and bouncing of the vehicle. However. the bouncing can be considered to have little effect on the critical speed. The author pro poses here an idealized flutter model to obtain a rough estimation of the effect of the design factors on the critical speed. The model has two massless rigid bars which are connected with a elastic spring at their ends each other and each bar is attached by a concentrated mass at appropriate position. The spring, the masses and their positions are so adjusted that the model and the prototype have equal natural bending frequency, equal total weight and equal moment of inertia. In this report, the center of gravity of the model before the bending deformation is assumed to be fixed on the flight path even during the oscillation to neglect the effect of the bouncing. By such a assumption, the author presents here a simple formuato estimate the critical flutter speed. (See Eq. (17)). The design parameters, which give effect on the flutter, are discussed.

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