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In the animation movie "Planes 2" we see the helicopter (Blade character) performing first a 180° roll (getting inverted chassis up and rotor down) and then the U-shaped half loop down into the normal orientation. From Wikipedia it looks like the Split-S.

Are helicopters actually capable of doing this? The concerns are

  • An inverted wing still may provide a lift upwards, but the inverted rotor will pull downward. Hence the inverted orientation seems risky.
  • Wings provide air support while making the sharp U-turn. Can the helicopter rotor do the same?

If a helicopter would manage this figure, would it trade altitude to speed as the fixed wing planes do?

If the model is important, the helicopter looks somewhat like Augusta Westland.

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Yes, but you need a rigid head.

A rigid head does not have any hinges, instead, the blades flex up and down.

Wings don't know or care if they are upside down or right way up, indeed, most helicopter blades are symmetrical. It only cares how much airflow there is and at what angle it hits it.

Here's an EC-120 performing a split S and a Lynx showing what's possible.

Perhaps the best around is Chuck Aaron, displaying for Red Bull.

Here, Dennis Kenyon shows about as good as it can get with a semi-rigid head. He gets close to inverted but never actually flips over.

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  • $\begingroup$ "Wings don't know or care if they are upside down or right way up" although this is true, helicopters cannot maintain inverted flight because the rotary wing can't have negative pitch, where as even an airplane with an asymmetrical wing can fly inverted because it can have negative pitch. $\endgroup$
    – rbp
    Mar 17, 2016 at 15:03
  • $\begingroup$ @rbp: Right, but you don't need to be able to maintain inverted flight to do a split S, since you're only inverted momentarily. You can even do a split S while pulling positive Gs throughout, if you do the initial inversion with a half barrel roll rather than the traditional half aileron roll. $\endgroup$
    – Vikki
    Jul 10, 2021 at 16:40

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