Help on dihedral effect on low wing aircraft
Help on dihedral effect on low wing aircraft
(OP)
I know dihedral is added for stability and control but I'm having difficulty visualizing (and therefore explaining) the effect of a DIFFERENCE in dihedral on one side or the other. For instance; hypothetically speaking if the dihedral on a model is 10 degrees on the left side and 0 degrees on the right, which wing is producing more lift and therefore; which way would the aircraft roll???
Thanks for any help on this!
Thanks for any help on this!





RE: Help on dihedral effect on low wing aircraft
RE: Help on dihedral effect on low wing aircraft
RE: Help on dihedral effect on low wing aircraft
Does that help??
The reason mfg's put in dihedral is to make the plane self-stabilizing. Left wing drops - right wing loses some lift - plane rights itself - vice versa.
If you are a visual rules pilot and get caught in a cloud -most mfg's say "take hand off of controls - chop power a bit and trim for say a 500 fpm descent." Plane will fly itself out of the clouds perfectly level. I had to do it ONCE!!
Actaully - most piston planes have more right dihedral or less left dihedral to help counter the engine torque.
RE: Help on dihedral effect on low wing aircraft
RE: Help on dihedral effect on low wing aircraft
as to the question, maybe this helps ... for the inclined wing, you project it down onto the horizontal plane to determine it's effective lift
RE: Help on dihedral effect on low wing aircraft
Now if you draw a vector diagram, you will see that the vector on the left wing has 2 components: upwards and inwards; whereas the right wing only has an upwards component.
Evaluate the equilibrium of the system, and you will likely see that the roll moment is unbalanced, as is the lateral force. The airplane will then roll to re-establish equilibrium.
jetmaker
RE: Help on dihedral effect on low wing aircraft
Dan
RE: Help on dihedral effect on low wing aircraft
RE: Help on dihedral effect on low wing aircraft
RE: Help on dihedral effect on low wing aircraft
After a little thought, I imaged real world objects that I understood better and where the dihedral is more extreme: a shuttlecock for playin badminton, and a typical old style parachute.
If it is the dihedral effect that is stabilizing the shuttlecock, then why doesn't something like a parachute come down upside down?
I decided that basically the pendulum idea above does provide an intuitive explanation. For example aircraft with negative dihedral usually appear to be suspended underneath the wings, whereas aircraft with normal dihedral can have the body appear to sit on the wings, more like the shuttlecock arrangement.
From that,we can see that if both positve and neatve dihedral can work, then no dihedral is required, and some older planes just have horizontal wings. That isn't really a problem.
I think it just boils down to having the centre of mass below the centre of lift. It is the reason people hang underneath hanggliders and paragliders. Trying to ride on top of a hangglider would not be a good idea.
=
So one wing at 10 degrees and the other straight?
As somebody said, that amounts to having the body on the plane at an angle of 5 degrees. So you'd be sitting in a sloping cabin.
But then the tailplane would be on crooked too. In conventional planes (which are a stupid design) the tailplane pulls down and the main wing has to overcome the weight of the plane plus the downward drag of the rear wing. If that were on crooked, it would be pulling sideways too.
So I think your plane would be flying round in circles.
Eg if the tailplane were pulling down and 5 degrees right after the front wings had more or less levelled, then I think you'd be going round and round in left hand circles.
Since you'd have lost a little of the downward lift from the tailplane, I think the nose would be pitched downard too. You'd have to fly faster to achieve level flight.
RE: Help on dihedral effect on low wing aircraft
RE: Help on dihedral effect on low wing aircraft
Here's how to see the light and how dihedral works: Take a rectangular piece of paper and make a dihedral break in the middle to form a crude "wing". Now look at it from in front to see the leading edge. If you turn the wing as if the rudder was making it turn what will you see? The wing closer to you will show its lower side and the wing away from you will show its upper side.
Now think of your eyes as the airstream flowing over the wing. The wing near you will have increased angle of attack compared to the one away from you. This is by the way how single-channel RC models steer and roll.
If you put the wing on top of the cabin, the fuselage will add dihedral effect as will the fin. Some high-wing a/c have negative dihedral on the ground so that when the wing flexes upward in flight the dihedral effect will not be too large.
Dan