See "M"-shaped wings

Oblique and side views of "M"-shaped wings

Steve Seibel
www.aeroexperiments.org

This page is still under construction!
This page was last modified on August 3, 2006

 

On this page, we'll explore oblique and side views of the "gull wing". As seen from the front, the "gull wing" looks like a stretched-out "M".

On this sailplane, note that we can see the bottom surface of the inboard panel of the aircraft's left wing, and we can see the top surface of the inboard panel of the aircraft's right wing. Clearly, the inboard wing panels have dihedral

We are viewing the outboard wing panels of both the left and right wings nearly edge-on. With a bit of imagination, you can visualize that if the outboard wing panels had just a bit of "droop" as they ran out to the wingtips, we would be able to see the top surface of the outboard panel of the aircraft's left wing, and we would be able to see the bottom surface of the outboard panel of the aircraft's right wing. This would indicate that the outboard wing panels had anhedral. Since we cannot see this geometry, it's clear that the outer wing panels of this glider do not actually have significant anhedral. (A 3-view drawing for this glider shows the bottom surfaces of the outer panels as being flat, and the top surfaces of the outer panels as having a very slight anhedral geometry due to the way that the panels are thinnest at the wingtips and thicker inboard. The geometry in actual flight may be slightly different.)

On this bird (photo to be posted), the left wing is nearest the camera and the right wing is furthest from the camera. We can see the top surface of the outboard panel of the left wing, and we can see the bottom surface of the outer panel of the right wing. We can also see the bottom surface of the inboard panel of the left wing, and we can also see the top surface of the inboard panel of the right wing. It's clear that the inboard wing panels have dihedral and the outboard wing panels have anhedral.

Since the outboard wing panels have anhedral, if the bird were moving directly toward the camera, so that the relative wind were blowing directly from the camera to the bird, the resulting sideways airflow over the outboard wing panels would cause the outboard wing panel nearest the camera to experience a lower angle-of-attack than the outboard wing panel furthest from the camera. This difference in angle-of-attack and lift would create an "upwind" roll torque, toward from the camera.

Also, since the inboard wing panels have dihedral, if the bird were moving directly toward the camera, so that the relative wind were blowing directly from the camera to the bird, the resulting sideways airflow over the inboard wing panels would cause the inboard wing panel nearest the camera to experience a higher angle-of-attack than the inboard wing panel furthest from the camera. This difference in angle-of-attack and lift would create an "downwind" roll torque, away from the camera.

Since the outboard, anhedral wing panels are much further from the bird's CG than the inboard, dihedral wing panels, the outboard panels will create much more roll torque than will the inboard panels. The net effect will be as though the entire wing had some anhedral. If the bird were moving straight toward the camera, so that the relative wind were blowing straight from the camera to the bird, the net effect of the wing's "M"-shaped geometry would be an "upwind" roll torque, toward the camera.

(Important note: for the moment, we're only considering the roll torque arising from the anhedral/ dihedral wing geometry, not the roll torque from the "pendulum" effect arising from the fact that the CG of the bird's body is located below the wing, or the roll torque from the aerodynamic interference between the body and the high-mounted wing, both of which could create dihedral-like effects.)

Here are more illustrations. In every one, note how we can see the top surface of the outboard wing panel nearest the camera, and we can see the bottom surface of the outboard wing panel furthest from the camera, and we can see the bottom surface of the inboard wing panel nearest the camera, and we can see the top surface of the inboard wing panel furthest from the camera.

(Photos to be added.)

 

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