How our aircraft work

Any spinning device is a gyroscope; try to tilt it one way and instead it will want to tilt in a direction 90 degrees from the one you intended. In the realm of aircraft propellers this property has been a nuisance in the past, but we have used it to advantage to control of our aircraft.

Tilting their oppositely-spinning propellers (represented as solid discs in the figure at top right) towards or away from one another generates powerful gyroscopic moments about the aircraft pitch axis. We use these moments to control the pitch of the aircraft - without having to resort to a third propeller or other devices.

The concept is not entirely new, only the application is. Both the International Space Station (ISS, right) and the Hubble Space Telescope tilt pairs of large Control Moment Gyroscopes (CMGs, bottom right) toward or away from one another to change the spacecraft's attitude about an axis in space. In fact, since their is no air to slow them down, the spacecraft will continue to rotate about that axis indefinitely until the CMGs are brought back to their original position.

Because they operate in air there is somewhat more to controlling our models than just the above; tilting the propellers longitudinally while tilting them sideways provides thrust vectoring for better forward motion control. But the essence of the control system, whereby extremely large and enabling control moments are generated, is the propellers being used as gyroscopes.