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Helicopter questions

  1. Dec 6, 2006 #1
    I know this is not as serious of a topic as you are all used to, but hopefully someone could help me out anyways?


    - Imagine a helicopter hovering inside a cargo jet, (the jet is flying at cruising speed). What would happen to the helicopter if it was pushed outside the jet, with no changes being made to the controls. So if the main rotor keeps spinning at a constant speed... when the helicopter leaves the plane does it keep or lose altitude?


    - Imagine a helicopter hovering in a elevator. If the controls in the helicopter are not touched, what happens when the elevator moves?


    - If a helicopter is flying just feet off the ground, and the ground suddenly drops off (like a cliff), does the helicopter require more thrust to keep the same altitude?



    any input would be appreciated!
     
  2. jcsd
  3. Dec 6, 2006 #2

    FredGarvin

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    Science Advisor

    If we're assuming that no damage was done to the aircraft, I'd say it would gain altitude due to the fact that there would be a large inrush of air. It would effectively be going from a standstill to whatever speed the jet was going very quickly which would cause it to gain altitude. Then again, if something breaks, it will lose altitude.


    Think of it this way, the helicopter is hovering relative to the air in the elevator. If the elevator moves, so does the air in the elevator. I would think that the initial transient would cause the helicopter to drop a bit, but as soon as the acceleration dropped off, the helicopter would recover.


    It requires more power to maintain it's current altitude. It's called "flying in ground effect". It is a result of the increased circulation through the rotor disk due to the interaction with the ground. Usually ground effect is noticeable to about one rotor disk diameter above the ground.
     
  4. Dec 6, 2006 #3
    This is the best discription of Wing Lift I have found so far. Helicopter blades use the same lift principle as an airplanes wing does, the volume of downwashed air is displacing the aircrafts load.

    After a large cargo plane has moved through a volume of air there is a large downwash area left behind which will cause problems for any other aircraft in its wake, so to say. And there is also a condition called ground effect that would effect the helicopter after leaving the cargo bay. So I would think the helicopter would fall after being pushed out and this would increase its load and cause it to crash. The increased velocity from falling would need to be overcome by more thrust since the helicopter would experience more 'g' force or an increased load.

    In a moving elevator I would guess the helicopter would experience inertia and react to the change in motion of the elevator. And as for the ground falling consider ground effect and atmospheric pressure changes.
     
    Last edited: Dec 6, 2006
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