What's the frequency of the letter "d" in:
Safe-life and damage-tolerant design approaches for helicopter structuresThe safe-life and damage-tolerant design approaches discussed apply to both metallic and fibrous composite helicopter structures. The application of these design approaches to fibrous composite structures is emphasized. Safe-life and damage-tolerant criteria are applied to all helicopter flight critical components, which are generally categorized as: dynamic components with a main and tail rotor system, which includes blades, hub and rotating controls, and drive train which includes transmission, and main and interconnecting rotor shafts; and the airframe, composed of the fuselage, aerodynamic surfaces, and landing gear.
Publication: NASA. Langley Research Center Failure Anal. and Mech. of Failure of Fibrous Composite Struct.
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In the text, there are thirty-one "d"s.
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