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Aerospace Autorotation in helicopters

  1. Jan 19, 2009 #1

    Ivan Seeking

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    Are dead-stick landings ever practiced, or are they only used during a legitimate power-plant failure?

    Someone once told me that some breed of helicopter pilots have to perform a dead-stick landing before getting certified. Is that true?
  2. jcsd
  3. Jan 20, 2009 #2


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    Yes. Absolutely.

    We used to do autorotations for every maintaiance test flight as well as other things. The Army did institute a policy at one time that autorotations were not take to the ground but started at around 10,000 MSL down to some altitude which was treated as the ground. I don't know if they still do that or not.

    Despite the connotation, the act of an autorotation is not a violent or drastic event. Granted, the sound of engines going off-line is very un nerving the first few times you hear it. If you were to watch an autorotation being practiced, and it were done properly, an untrained eye might not even be able to tell it was happening.
  4. Jan 20, 2009 #3
    I saw on discovery(or mega structures on NGC), that in case of engine failures, pilots are trained to get the heli down by letting the blades wind mill(& hence create drag & slow the thing down)
  5. Jan 20, 2009 #4


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    Hint: That's called autorotation, what this thread is about...
  6. Jan 22, 2009 #5

    How come I didnt notice that while posting:grumpy:

  7. Jan 22, 2009 #6
    Also, the blades don't "create drag" on autorotation. That would inevitably slow the blades down, cause them to stall, and crash the helicopter.

    In autorotation, the blades simply balance kinetic energy and potential energy. Too much kinetic energy and the blades depart the rotor hub. To little kinetic energy and the blades stall and stop spinning (unrecoverable situation). The right balance is a range of RPM which the rotor blades must be maintained (usually the fixed RPM the blades spin in regular flight). The reaction time of an engine failure for a pilot is on the order of 1-2 seconds that he/she has to lower the collective before blade stall occurs. Its a very unforgiving situation.
  8. Jan 25, 2009 #7


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    One of the fellows that I know is a pro chopper pilot (and I'm going to take an indroductory flight lesson just so I can have that experience under my belt). He definitely had to practice engine-failure landings before being licensed. That's here in Canukville, though—I don't know the laws elsewhere.
  9. Feb 6, 2009 #8
    Another way to understand it is that during autorotation the blades have negative pitch near the hub and causing windmill effect as the a/c drops, transfering aerodynamic loads into rotational momentum in the rotor head. To land, the pilot pulls collective putting positive pitch on the blade tips, transfering rotational momentum to thrust.
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