Tuned RAT driveshaft

A ram air turbine comprising:

• a turbine assembly mechanically connected to a power conversion device through a driveshaft, the driveshaft comprising:
• a cylindrical body having an outer surface, an inner surface, a longitudinal axis, a first end section, a second end section opposite the first end section, and an elongated intermediate section connecting the first end section and the second end section,
• wherein the outer surface of the elongated intermediate section includes at least three separate grooves initiating at a location proximate to the first end section and extending parallel to the longitudinal axis across the outer surface to a location proximate to the second end section, the grooves being separated equidistantly around a circumference of the outer surface,
• wherein the grooves provide a high lateral bending stiffness and low torsional stiffness such that a drivetrain natural frequency occurs at a frequency below an operating range frequency and a critical speed for the driveshaft above an operating speed, and
• wherein the outer surface of the elongated intermediate section is tapered towards the second end section.