See dihedral

Oblique views and side views of aircraft with dihedral

Steve Seibel
www.aeroexperiments.org

This page is still under construction!
This page was last modified on August 19, 2006

 

In each of these photos (model), the bottom surface of the wing nearest the viewer is visible, and the top surface of the wing furthest from the viewer is visible.

Now, imagine that each of the above aircraft is moving DIRECTLY TOWARD THE VIEWER, so that the relative wind is blowing straight FROM THE VIEWER TO THE AIRCRAFT. See that the relative wind will strike the bottom surface of the wing nearest the viewer, creating positive lift. See that the relative wind will strike the top surface of the wing furthest from the viewer, creating negative lift.

This will create a roll torque in the "downwind" direction, i.e. away from the viewer.

These exaggerated examples show how dihedral creates a "downwind" roll torque whenever the relative wind has a sideways component.

In each of these photos (photos to be inserted), only the bottom surfaces of the wings are visible, but the wing nearest the observer is still presenting a noticeably larger "visual angle of attack" than is the wing furthest from the observer. Again, imagine that each of these aircraft is moving DIRECTLY TOWARD THE VIEWER, so that the relative wind is blowing straight FROM THE VIEWER TO THE AIRCRAFT. See that the wing nearest the viewer will meet the relative wind at a high angle of attack (creating lots of lift), while the wing furthest from the viewer will meet the relative wind at a lower angle of attack (creating less lift). Again, this will create a roll torque in the "downwind" direction, i.e. away from the viewer. These more realistic examples show how dihedral creates a "downwind" roll torque whenever the relative wind has a sideways component.

More views of aircraft with dihedral (photos to be inserted). In each of these photos we can see the bottom surface of the near wing and the top surface of the far wing.

More views of aircraft with dihedral (Superfloater). In each of these photos we can see the bottom surface of the near wing, but we can't see the bottom surface of the far wing.

More views of aircraft with dihedral (photos to be inserted). In each of these photos we can see the top surface of the far wing, but we can't see the top surface of the near wing.

Every one of the above photos shows that whenever the relative wind has a sideways component, if an aircraft has dihedral, the "upwind" wing will experience a higher angle-of-attack and create more lift, while the "downwind" wing will experience a lower angle-of-attack and create less lift.

In other words: dihedral will create a "downwind" roll torque whenever the nose of an aircraft is yawed to point in a different direction than the aircraft is actually travelling through the air.

Or to put it yet another way: dihedral will create a "downwind" roll torque whenever an aircraft is moving through the air in a different direction than the nose is actually pointing (this is called a "slip").

In fact, we'll use this idea to define dihedral--more on this in the next section of this tutorial.

 

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