I have a vertical panel which turns about a vertical axis somewhat less than 90 degrees slowly from one position to another. I am envisioning a spring, shaped something like the letter "C", laid horizontally, perpendicular to the panel's vertical axis of rotation.

At each end of the C, a protruding end would angle out at 90 degrees, normal to the plane of the "C" and parallel to the panel's axis of rotation. One protrusion up, one down.

Anchor one protruding end to movable panel, other end to the housing.

The "C" can go around the pivot point, guarding/ concealing the spring most of the time.

Anchors I would like to locate such that with the panel at one position, the spring provides little or no rotational force to the panel, but when panel is at/near the other position, the spring will force the panel towards this position much more enthusiastically. Sort of a snap shut, hang open situation.

I know I have seen this type of spring somewhere before. Vehicle fuel tank door perhaps? That's more of a snap-open, snap-shut design, but I think that careful anchor location selection can attain "hang open, snap shut."

Can anyone point me to any reference material or a favorite web site that can provide pointers such as anchor locations that would do what I want? Similar applications perhaps?

All input appreciated.