Manufacturers of robust VTOL air vehicles for large payloads, precision hovers, and high speed flight.
How our aircraft work
Basic:
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 there 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 immediate control moments are generated, is the propellers being used as gyroscopes.
Advanced:
Adverse inertial reaction due to fore-aft tilting of the propellers is always present, but it is effectively mitigated by the gyroscopic moments associated with tilting the props sideways at the same time. The resulting tilt path is oblique, somewhere between longitudinal and lateral. The simplist path is planar (single axis tilting), with the vertical plane oriented 45 degrees away from the longitudinal. This is what the Vaders use. Their pitch control comes from a combination of thrust vectoring, gyroscopic moments, and aerodynamic counter-torque (the former from the fore-aft component of the tilting, the latter two from the sideways component).
The counter-rotating propeller spin directions dictate whether the props should be tilting outward or inward when also tilting (say) forward. The resulting gyroscopic pitching moment is in the right direction when it tends to push the nose down.
Inertial reaction is, of course, a function of angular acceleration, and gyroscopic moments are proportional to angular velocity (of the tilting). So, for a planar - or linear - tilt path, there will be a net pitching moment acting in the wrong direction initially. But it's duration is very brief, as it is quickly overcome by the rate-based gyroscopic moment.
Thrust vectoring by itself on the other hand, a function of just the tilt angle, is hardly ever powerful enough or quick enough to overcome the adverse inertial reaction from tilting. Exceptions are gimballed exhaust nozzles on rockets and jet fighters, or elevators and rudders on conventional a/c's performing torque rolls - they are light in comparison to the vehicle, and are at a considerable distance from the vehicle's center of gravity (long moment arms).
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 there 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 immediate control moments are generated, is the propellers being used as gyroscopes.
Advanced:
Adverse inertial reaction due to fore-aft tilting of the propellers is always present, but it is effectively mitigated by the gyroscopic moments associated with tilting the props sideways at the same time. The resulting tilt path is oblique, somewhere between longitudinal and lateral. The simplist path is planar (single axis tilting), with the vertical plane oriented 45 degrees away from the longitudinal. This is what the Vaders use. Their pitch control comes from a combination of thrust vectoring, gyroscopic moments, and aerodynamic counter-torque (the former from the fore-aft component of the tilting, the latter two from the sideways component).
The counter-rotating propeller spin directions dictate whether the props should be tilting outward or inward when also tilting (say) forward. The resulting gyroscopic pitching moment is in the right direction when it tends to push the nose down.
Inertial reaction is, of course, a function of angular acceleration, and gyroscopic moments are proportional to angular velocity (of the tilting). So, for a planar - or linear - tilt path, there will be a net pitching moment acting in the wrong direction initially. But it's duration is very brief, as it is quickly overcome by the rate-based gyroscopic moment.
Thrust vectoring by itself on the other hand, a function of just the tilt angle, is hardly ever powerful enough or quick enough to overcome the adverse inertial reaction from tilting. Exceptions are gimballed exhaust nozzles on rockets and jet fighters, or elevators and rudders on conventional a/c's performing torque rolls - they are light in comparison to the vehicle, and are at a considerable distance from the vehicle's center of gravity (long moment arms).
______________Gress Aeronautics, Toronto, ON, Canada. Tel: 416-763-4482__________
