Why is it that the blade on a helicopter that is travelling opposite to the direction of flight still has lift

Question

It seems like the blade going into the wind would have more lift than the one going downwind.

Answer 1

there is indeed a difference in lift

or rather, there would be

but the rotor has a sophisticated mechanism which changes the angle of incidence of the blades, less for the blade travelling in the direction of flight (which is seeing faster air), and more for the one travelling in the opposite direction.

but ultimately, it is such an effect that limits the speed of the helicopter.

If the rotor is not that fast, then if you went beyond a certain speed, even adjusting the incidence angle, you'd lose all lift on the blade travelling back, and have an accident.

But if you make the rotor go fast, then while you won't lose lift on that backwards travelling blade, what will ultimately happen is that the forwards travelling blade would hit the sound barrier - which it can't or it'll blow up or at least lose lift.

hope this helps

Answer 2

Because it is travelling much faster than the flight speed of the helicopter. I would suppose that the blade going into the wind would have more lift, unless the alpha of the retreating blade is somehow changed.

Answer 3

You are correct, the blade going into the wind has more lift. But what else are you going to do with the other blades while they are awaiting their turn to go into the wind again? One possibility is to increase their pitch so that more of the engine power is used for forward thrust than for upward lift.

Answer 4

That is to keep the helicopter from slowly rotating in the direction of the main blade.

Answer 5

There is a linkage system at the propeller hub that adjusts the angle of attack of each blade as it is advancing and receding.