The author, in this paper, analytically investigates the torsional vibration of a propeller blade of varying cross-section, is analytically investigate. For the form of the blade, instead of the usual aerofoil section, an ellipse is used, whose geometrical moment of inertia and the modulus of torsion of the section are assumed to vary along its length x according to the expornential law e^αx and e^βx respectively.
In the analysis, α is conveniently taken equal to mβ. The solution is obtained in the form of Bessel function, by means of which the vibration frequencies are calculated for any value of m againest α; these are shown in the annexed figure.

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This report describes an air tunnel that was constructed at the Aircraft Division of the Watanabe Iron Works, at Fukuoka. The tunnel, horizontally placed, is of the single return Gottingen type, having a circular open jct 2·5m. in diameter at the experimental section. The fan, a six bladed wooden propeller, is driven by a 400_?? D.C. motor. The air speed at the experimental section can be accurately and smoothly contralled maximum speed reaching to 72m/s. The power ratio of the tunnel is about 0·39. The Reynolds' number, for which the coefficient of resistance of a 10cm. sphere has the value of 0·30 is 5·34×10⁵ and the turbulence factor is 1·15.
The condition of the air flow at the experimental section is satisfactory. The measuring apparatus is a six component balance that one enables to measure the 3 components of force and the 3 components of the moment acting on airplane model, giving any yaw angle that would rotates the balance and model together.

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