dihedral = lift

[omega blood]

how or why does dihedral add lift?

[davidfee]

Who told you that it does?

[omega blood]

I rember seeing somewhere I don't rember where though. And I have seen it or at least I think I have. I had a stick fd stock with dihedral and had a good climb rate. I put an identical wing with ailerons and no dihedral and it had a very hard time climbing. Unless it is a false hood since you're asking me who told me that.

[davidfee]

I suspect there was something else going on with your stick fd. Possibly related to the incidence angle of the wing, or the airfoil. Dihedral gives a model some roll stability and will cause the plane to roll slightly with rudder input, but this isn't because of increased lift. The roll component basically comes from differential lift when the wing is yawed... but you weren't asking about that. ;)

Dihedral by itself does not increase lift, compared to a flat wing... assuming all else is held equal.

[Dick Huang]

omega blood,
davidfee is correct. In fact dihedral reduces total lift when projected flat wing area is used. Look at it this way, if your wing had 90 degree dihedral the lift would be zero!
Dick Huang:D

[omega blood]

Originally posted by Dick Huang
omega blood,
davidfee is correct. In fact dihedral reduces total lift when projected flat wing area is used. Look at it this way, if your wing had 90 degree dihedral the lift would be zero!
Dick Huang:D

Ok I guess you won't belive this then. On that same plane I looped is so much an so over weight that the wing folded in the middle into some where around 90 degrees. I flew it to a safe landing. But then again it was an 8 oz plane. If it were realy heavy it probably drop like a rock.

[Stregone]

You'd need 180 degree dihedral fo zero lift :)

[omega blood]

Originally posted by Stregone
You'd need 180 degree dihedral fo zero lift :)

LOL, I like that one!

[Dick Huang]

omega blood,
The dihedral angle is measured using the wing semi-span or 1/2 the span.
Dick Huang:D

[omega blood]

Originally posted by Dick Huang
omega blood,
The dihedral angle is measured using the wing semi-span or 1/2 the span.
Dick Huang:D

OK I see what you mean. I guess I miss understood. Thanks.

[Robbie d]

what happens with no dihedral is each wing produces the same lift straight up. unstable flight characteristics but high maneuverability. when you add dihedral, instead of the lift being straight up, it is slightly angled toward the centre of the wings. this reduces lift slightly but increases stability.

[wildpalms]

I wouldn't say that a wing with no dihedral is 'unstable'; certainly not as stable as one with dihedral but not unstable, in fact I would go as far to say it is neutral.

The dihedral gives you stablity (self righting) in this manner; Let's say you bank to the left. The left wing will become flatter and the right wing steeper, the left wing will generate more lift than the right and so will try and roll to the right, when the plane is level the lift is balanced.

--
Dave

[Robbie d]

yes, you're right. flat wing is neutral stability, on the other hand, anhedral is unstable.

[DeaninMilwaukee]

I built a plane with inadvertant anhedral, and it seemed about the same stability wise as my straight wing planes.

Still very easy to fly.

Anhedral was around 3 or 4 degrees, and interestingly, this plane would fly on forever in ground effect. Never did figure that one out. :confused:


Dean in Milwaukee

[Ollie]

Ten degrees of dihedral per side only reduces the vertical component of lift by about 1.52%. This is more a theoretical than practical consideration as far as dihedral's effect on lift is concerned. In other words, dihedral reduces lift but, not enough to matter.

[Slime-Lover]

Originally posted by DeaninMilwaukee
I built a plane with inadvertant anhedral, and it seemed about the same stability wise as my straight wing planes.

Still very easy to fly.

Anhedral was around 3 or 4 degrees, and interestingly, this plane would fly on forever in ground effect. Never did figure that one out. :confused:


Dean in Milwaukee

No need to be confused anymore, my friend (hopefully). Here is my best "armchair aerodynamicist" theories on the subject.

Check out Wing In Ground effect designs (WIGs), they are all built with anhedral or have downward pointing tip plates that have the same effect as anhedral. For that matter, hovercraft and air-hockey pucks also have downturned tips/perimeters to trap high pressure pockets of air underneath them. A wing with anhedral is, in effect, a hovercraft with its fore and aft "downturned tips/perimeters" removed. In as much as a hovercraft or WIG would be less effective in trapping pockets of air without downturned tips, a wing with dihedral, in effect, dumps high pressure air from beneath it instead of trapping it.

[wildpalms]

You can also use anhedral to reduce the stability you may have gained elsewhere.

The Harrier is a high wing design with so much mass below the wing you get a sort of stabilising pendulum effect. It has anhedral to reduce the inherant stability in the design. Not so much a case of anhedral being unstable as reducing excess stability.

When I was younger we played with a high wing trainer with an anhedral aileron wing; flew quite nicely if I remember but looked wrong.

--
Dave

[vintage1]

A swept back wing also has dihedral like characteristics.. Lots of plane s with sweepback use anhedral to reduce this effect.

Something to do with the fact that the sept back wing gains lift if its yawed to less sweepback or something.

[Ollie]

The purpose on dihedral is to increase stability in roll but when inverted it has the opposite effect. Another way to increase stability is to have the CG much lower than the center of lift (pendulum stability) as in a para glider. The third way is to use sweepback. Sweep back is most effective at high angles of attack, both upright and inverted but, less effective at low angles of attack. Both dihedral and sweepback work their "magic" through a yaw to roll coupling effect.

As stated in my earlier post, dihedral has little effect on lift unless the dihedral angle is extreme.

[Dick Huang]

Hi All,
So far the stability discussions are about the roll-axis. For a rudder/elevator model the amount of dihedral is very important as to whether the model will turn. With the correct amount of dihedrel, when the rudder is deflected (yawed or side-sliped) a rolling moment is developed causing the model to go into a banked turn in the commanded direction. Also, the amount of dihedral determines the spiral stability of a model. This term is called rolling moment due to side slip or Clbeta.
Dick Huang:D

[PTLdom]

I understand the original question. For instance, while turning with a high wing trainer with dihedral, you feel that you need less elevator to keep the turn at the same level, than you do with a non dihedraled high wing trainer. It may be due to the down wing being less banked. But so far I didn't read any theoretical explanation that supports it, maby because it doesn't hold true.:(

[Ollie]

Replacing a flat wing with an "identical" wing with dihedral is very hard to do without changing airfoil or incidence or something else a bit too. However, if you were able to do so, several things would happen. The dihedral would increase spiral stability or decrease spiral instability depending on how much dihedral was added. It would also increase pendulum stability by raising the average position of the wing relative to the CG. It would increase yaw to roll coupling. It would raise the drag vector which would cause a nose up trim change. How noticable these effects might be depends on how much dihedral was added and how far the original wing was positioned above or below the CG. When the average position of the wing is raised relative to the thrust line, down thrust must be added to compensate otherwise a nose up moment will be created that gets stronger with throttle advance.

Most likely what you saw was the nose up trim change due to raising the wing relative to the CG and the additional nose up tendency with throttle advance, also due to raising the average position of the wing.

[PTLdom]

... so in the end, with the nose up tendency, the wing will work at bit higher Cl and hence working with a higher lift (vector) force ... makes sense ...

[Ollie]

"... so in the end, with the nose up tendency, the wing will work at bit higher Cl and hence working with a higher lift (vector) force ... makes sense ..."

I don't think the lift force will increase.

When the nose up attitude increases the wing's angle of attack, the wing's Cl will increase. If the thrust remains the same and the incuced drag increases as the square of the Cl the plane will slow some until thrust once again equals drag and lift equals weight. If the plane is stable it will settle down to some non accelerated flight condition where the moments and forces are in balance.

[PTLdom]

You're right :) but the feeling may be " for the same speed as before I'm climbing whereas before the plane flew level ..."