Why does do some aircraft have wings bent downwards?

Question

The harrier for example, its bent wings look very unstable and probably would be hard to recover from a sudden spin or stall...just from my point of view.

Answer 1

I cant really say exactly why they are bent down, but controlability and stability in an aircraft are inversely proportionate.   The less stable an aircraft is, the more controllable it is.  IE, faster to do rolls, turns, banks... etc.   The bent down wings certainly do take away from stability, and my guess it is to help increase controllability.  

My 2 Cents

Answer 2

For the harrier it creates a stronger down thrust for take off and landings, on others it makes the plane more manuverable.

Answer 3

Dihedral - Wings angle up

Anhedral - Wings angle down

It has to do with stability and control, airplane with dihedral are inherently more stable than aircraft with anhedral.  This is why mostly fighters and aerobatic aircraft have anhedral... lack of stability means higher maneuverability.

I can't really say why the C-17 has it.

Answer 4

Actually its because the wings attach to the top of the fuselage.  You see this in the C-17 as well.

The design has some advantages but isn't commonly used on commercial aircraft because the engines will occasionally spit flame and that has a tendency to scare the Christ out of people who generally think planes are on the brink of falling out of the sky anyways.

I believe its best attribute however is lateral stability which makes it a bit easier to fly slowly in a straight line without wind causing a lot of problems.  Thats why it is used on short take off craft like C-17's and the short to no take off Harrier.

The correct term is High-Wing.

Think of it like this:  An air hockey puck moves on a cushion of air.  When the wing is under the plane then the center of gravity for the weight of the plane is above the lifting surface just like the air hockey puck's.  The wings below the plane bend upwards which allows for the air under the wings to rush out to the edges just like a puck.  So the plane is basically floating on a surface that takes very little effort to push to one side or another.  If you hang the fuselage from the wing you get a more stable flight pattern because the lifting air cant be blown out from under the wing.  It's called horizontal slip.  The other advantage comes from having the wing box suspended higher in the fuselage for lower clearance of vehicles and other equipment inside the aircraft.  You don't want to drive up a ramp that 15 feet tall if you can drive up one that is 5 feet tall right?  I believe this was also part of the harriers design as the upward thrust could be better distributed by the airframe if its strongest components were above the engine instead of below.  I guess its also a matter of balance, is it easier to hang something from a string or balance it on a needle?

Answer 5

Mike is right with dihedral/anhedral; but they both contribute to stability.

Next time you can look at the the North American B-25 Mitchell of Doolittle Raid fame -- outer wing panels have anhedral.