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The answer may be a combination of the two.

Does a helicopter fly because air is caught by the rotor and thrown downwards, which causes an equal reaction in the opposite direction and 'throws' the helicopter upwards by conservation of momentum, or does each rotor use the Bernoulli principle like a fixed wing to generate lift on each individual surface which causes the helicopter to rise?

I know that the collective changes the angle of attack of each blade, but am unsure if this is to catch more air for momentum purposes or Bernoulli principle purposes. I'm also aware of ground effect but the above question should apply to helicopters in flight at altitudes where the ground effect is not a factor.

user356816
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It is the first: the helicopter blade hits the air that it comes on contact with. The inertia of the air mass acts in opposition to being accelerated (downwards) by the helicopter blade. That opposition to acceleration acts upon the helicopter blade in the direction opposite to where the air accelerated to.


Bernoulli's principle is relevant in the following way only: A well designed air foil is optimized for good lift-to-drag ratio.

In order to create lift: while a good lift-to-drag ratio is very much welcome, it isn't a necessity.

There are cases where the priority is elsewhere. Example: the wings of an aircraft designed for aerobatics

The wings of an aerobatics aircraft are pretty much just flat boards, in such a way that when the aircraft is flying upside down the amount of lift that is generated is about the same as when flying the right side up.

These aerobatics aircraft wings require a larger angle of attack than airfoil wing aircrafts (for the same amount of lift), so they produce more drag.


The incentive for designing the wings for good lift-to-drag ratio is: the better the lift-to-drag ratio the better the fuel economy.

Summerizing:
For understandinging lift in and of itself Bernoulli's principle is not necessary. Application of Bernoulli's principle is essential for being competative when it comes to the fuel econonomy of the aircraft.

Cleonis
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