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For military helicopters such as the Sikorsky UH-60 Black Hawk:

What is the typical fatigue life of these helicopter main rotor dynamic components in cycles and hours?

a) Main rotor pitch links (aka main rotor push rod)

b) Main rotor pitch change horn

c) Main rotor blades

Helicopter or Rotary Wing Terminology

Main Rotor System of a Helcopter

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  • $\begingroup$ you can edit your previous question instead of making a new one. $\endgroup$ – ratchet freak Jul 18 '15 at 13:59
  • $\begingroup$ @ratchetfreak it has been Jay Carr to suggest him to split the question. $\endgroup$ – Federico Jul 18 '15 at 18:44
  • $\begingroup$ @Federico I see the other question has been edited enough, voting to reopen now $\endgroup$ – ratchet freak Jul 18 '15 at 19:24
  • $\begingroup$ Hi Everyone, firstly thanks for you suggestions as I'm a new. Both the questions I asked are specific and focus on two different aspects of helicopter design. This question focuses on the fatigue life of dynamic components while the other question focuses on the fatigue life of airframe for military helicopters such as the Black Hawk. I was suggested to split the question which I did so. Therefore, I will appreciate your help on both these questions. Thank you. $\endgroup$ – Raptor Jul 19 '15 at 4:34
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The fatigue life of helicopter dynamic components is determined by the manufacturer based on the number of hours flown and as such, varies from helicopter to helicopter.

In general, life of the dynamic components are less than that of the helicopter structure. The life of the dynamic components depend on the fatigue loads (the magnitude and load spectrum) and the materials used.

So, the same helicopter involved in more demanding operations (civil vs. military) will have less life. Actually, during development, the fatigue life is determined in number of cycles, which is then converted to flying hours based on the expected flying pattern. Also, the materials used make a difference, with composite materials having better fatigue resistance compared to metallic blades.

The life of the UH1 MRB (Main rotor Blade), for example is around 2500 hours. For UH60 MRBs, similar values have been quoted for metallic blades. However, Studies by MBB (Now part of Eurocopter) indicate that the composite blades under normal loading have a fatigue life of around 4000 hrs (AGARD conference Proceedings No. 297, Helicopter Fatigue Life Assessment).

The life of other dynamic components, e.g. pitch horn, pitch link etc. are usually around 1000 hours. However, with little data available in public domain for helicopters under service, it is hard to say with any certainty.

It should be kept in mind, however that these values are only indicative as all dynamic components are periodically checked using NDT methods and decision on their continued service is solely based on the results of these tests. For example, any damage to the bearing in the pitch links will result in their replacement. Also, the development of Health Usage Monitoring Systems (HUMS) means that most of the H/c manufacturers are moving away from a life based approach to a health based approach, resulting in variation in life of individual components.

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