mighty fan

Cross-flow fans are mostly used for the even "curtain" of airflow produced that is as wide as they are long. They are also used when a product's form factor favours their long, narrow shape. The problem is that they are not particularly efficient by any measure. I have contemplated a few variations around optimizing individual blade pitch. The result is improved efficiency at the cost of increased complexity and weight. Other possible variables include optimal rotational speed and noise levels.

I will start with the least complex variation. Each blade of the fan pivots independently with the pitch determined by a sprung linkage that follows a cam on the hub of the fan barrel. In this way the blades can be pitched to draw in air on the intake side and push out air on the exhaust side.

Next alternative is a gearset to rotate the blades counter to and at exactly half the frequency of the fan barrel.

An advanced variation would be flexible blades and an additional mechanism to reverse the orientation of the aerofoil to capture extra lift forces.

The engineering maths is beyond me but I might build a model one day. I found one design online that used a similar concept except purposed for wind power generation and will link to it below.