In a bubble test, air is blown in front of the spinning propeller to visualize the flow of the water. This revealed some stalling on the bi-blade and the toroidal design too, which would explain ...

Inspired by the machine gun setups on World War I planes he wanted to make a gun that can shoot between the blades of a spinning propeller. The original guns used an interrupter gear that ...

The two propellers spin in opposite directions, and power is transferred from the engine through a planetary gear or spur ...

It turns out that not even BMW's spokespeople know that its Roundel emblem wasn't inspired by a spinning propeller. It's a common misconception, one that's finally been cleared up by BMW spokesman ...