How does a tumblewing work?

Any object which spins as it moves through the air will be subject to a force perpendicular to its motion and the axis of rotation (known as the Magnus effect). The tumblewing spins so as to produce an upward force (lift). A baseball pitch with spin is subject to the same force, but the baseball can be spun in any number of ways to make it "float", "sink" or curve right or left. See the NASA site on the Curveball Aerodynamics.

Tumblewings actually do produce lift. There are three phases to this process:

Falling: acceleration down (tumblewing in vertical position) which also produces horizontal motion.

Generating lift: angle of attack increasing, pulling air down on top of wing and pushing air down on bottom of wing (how a regular wing works) until:

Stall: air separates from top of wing, downwash continues down,

Repeat cycle back to falling.

Here is an airplane which uses tumbling wings to produce lift:

The rotating wings can be powered and the airplane can fly without a propeller:

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