Beam theory for flexible rotor blades is developed

Description

This theory was a critical step in developing adequate structural models for the prediction of loads and stability. The initial paper on this subject is provided below,

Houbolt, J. C., and Brooks, G. W.: Differential Equations of Motion for Combined Flapwise Bending, Chordwise Bending, and Torsion of Twisted Nonuniform Rotor Blades. NACA Report 1346, 1958 

Source: "Milestones in Rotorcraft Aeromechanics", Johnson W., NASA/TP-2011-25971, May 2011, Page 33

(Note: Only the year for this milestone is valid)