...about aerodynamics.  Today I was pondering about them again, something I often find myself doing.   And I got myself all confused about helicopters.

Okay, so I know that bernoullis principle basically states that the low pressure created over a wing pulls up the wing, which is lift.  But I am also aware that the pitch of a wing affects lift because as air flows under and over the wing it is directed in a downwards direction if th wing is pitched up and in an upwards direction if it is pitched down.

So I was thinking about helicopters, and I just cant figure it out.  As we know, a helicopter blade is basically a spinning wing.  The blades are shaped like an airfoil and as the spin air flows over the blades and that generates lift.  But a helicopter controls its vertical speed by changing the pitch of the blades, which suggests that the blades generate lift by forcing air down, explaining the rotorwash.

And now im getting MORE confused.  Does a prop force air in an aft direction pusing the plane, or dies it generate bernoulli lift pulling the plane.

I AM SO CONFUSED!

Oh Boy..  I wonder how many debates THIS thread will generate  

An airplane propellor "propels" an airplane, much like a boat propellor gets a boat to move through the water. It's all about AoA (pitch) and there's the same compromise between speed and power (high gear / low gear in a car) when it comes to how much pitch.

A helicopter blade's airfoil does provide some lift, but it's more about aerodynamics and stability, than it is about getting the helicopter to climb or hover. You're right that the blades are like wings and it is AoA that determines the lifting force. The drag and loss of airspeed that comes with increased AoA isn't the same type of problem for a helicopter blade as it is an airplane wing. It's more like the compromise that a constant-speed prop has to deal with. Same goes for a helicopter blade stalling... but this gets into VERY complex aerodynamics. Think about the helicopter cruising in level flight at 100kias. As the blades move through their cycle; at some point, they'll be moving through the air at their own rotational speed PLUS 100knots and 180 degrees later, their rotaitonal speed MINUS 100knots. Dramatic increases in thier AoA (pitch (collective)) can cause the reatreating blade to stall. Now.. throw in the cyclic pitch control and the aerodynamic puzzle becomes almost more than a computer can model  

hope I didn't confuse you more  lol

(because I'm confused now)

Throttle forward, stick back.  If you fly, it's aerodynamics, if you don't, it's gravity.


That's all you need to know.

it's both

Prop blades and wings aren't quite the same thing... when it comes to pressure differential.

Given enough airspeed.. a wing with zero AoA can keep a plane aloft. A prop uses AoA (pitch) to create thrust.

Constant-speed props capable absolute zero pitch (I think it's called beta)(90 gegrees from fully feathered) create almost no thrust. What little they do create is more than cancelled by the drag that a full "flattened" blade causes.

the prop on an air plane (and jets on jet planes), pull (or push, whatever u prefer) the plane through the air. this causes air to flow over the airfoil and creating lift, yada yada yada.... The props only purpose is to move air over the wing.... THE PROPS CREATE NO LIFT

Mobius wrote on Feb 15^th, 2007 at 1:53pm:



I wonder if a moving prop could split a hair...   

But it is worth noting, yes... a propellor blade bears an uncanny resemblance to a small wing... because it is an airfoil, and produces thrust by much the same means as a wing produces lift.