26.下列有關可控螺距螺槳使用上的缺點敘述，何者錯誤？ (A)構造複雜，葉片運動部分水密不易 (B)製造成本較定距螺槳高 (C)倒俥操控方式較定距螺槳差 (D)轂部大，推進效率較定距螺槳低

10.Longitudinal vibration of propulsion shafting systems is often excited by the variable thrust developed by the propeller due to the non-uniform wake pattern in which it operates. The predominant periodic component of the thrust developed by a propeller occurs at blade-rate frequency, i.e., the number of propeller blades times the rotational frequency of the shaft. For a four-blade propeller running at 60 rev/min, what is the predominant periodic frequency that excites the longitudinal vibration of the propulsion shafting systems? (A)1 Hz (B)2 Hz (C)3 Hz (D)4 Hz

26.下列有關可控螺距螺槳使用上的缺點敘述，何者錯誤？
(A)構造複雜，葉片運動部分水密不易
(B)製造成本較定距螺槳高
(C)倒俥操控方式較定距螺槳差
(D)轂部大，推進效率較定距螺槳低

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