And the way it does it, is it takes its tail and it swings it one way to yaw left, and it swings its other way to yaw right.

And that four dimensional space consists of X, Y, Z and then the yaw angle.

By controlling the speeds of these four propellers, these machines can roll, pitch, yaw, and accelerate along their common orientation.

We relinquish control of yaw, but roll, pitch and acceleration can still be controlled with algorithms that exploit this new configuration.

Conventional wisdom says that you need at least four fixed motor propeller pairs in order to fly, because there are four degrees of freedom to control roll, pitch, yaw and acceleration.

For many years, this question was framed according to the lean versus clean debate Should central banks lean against bubbles, damping down asset prices that create risks to financial stability, or just clean up the mess after bubbles burst? Proponents of the latter approach, such as former Fed Chair Alan Greenspan, express doubt that policymakers can reliably identify bubbles, and are generally uneasy about managing asset prices.