In the case of the helicopter, it is pretty clear (well, for me) that it gets lift by pushing air downwards. And as a consequence, there is more pressure below its blades than above.
But on the other hand, when talking about plane wings, it seems that lift is caused by a lower pressure above the wing pulling it up, while the downwash is just the consequence.
If you consider the flap configuration for landing (to get more lift with less aircraft speed) it seems to me that flaps position is for "sending air downwards".
So what is here the cause and what is the consequence? Are they different for planes and for helicopters?
Edit (to justify the question).
The most voted answer to What really allows airplanes to fly? it is
Basically planes fly because they push enough air downwards and receive an upwards lift thanks to Newton's third law.
But the most voted answer to How much effect does the Bernoulli effect have on lift? says
All of the lift depends on the Bernoulli principle, because speed and pressure are in trade-off, but the physics need to be correctly understood.
Therefore, the answer is not the same for everybody. I could see 4 options:
- Lift is due to downwash. Pressure differences is a consequence.
- Lift is due to pressure differences. Downwash is a consequence.
- Lift is due to downwash plus pressure differences (Then: how much do they contribute?)
- It is the same phenomena. You may look at it either way.
To add confusion, it looks like Bernoulli equation is fair to calculate lift. (But I think this does prove nothing at all: only that you can make a calculation of a force by using a consequence of that force, not by measuring the force itself).
Another misunderstanding (well, I think) is that higher air speed on top of a wing it's what causes a low pressure zone, and this low pressure zone pulls the wing up. But IMHO this is wrong: air moves faster due to the low pressure: a plane can fly on "stoped" air, therefore it is the wing what disturbs the air (maybe sucking it back?).
Therefore, the helicopter image (to me, at least) makes it clear that air is being pushed down, increasing pressure under its blades. If this is true: downwash (alone) wins for the helicopter.
And if a heli blade is really a wing in disguise, then: downwash (alone) also wins for planes.