Natural Pitch Stabilization of Bicopters in Hover Using Lift-Propeller Gyroscopics

  • G. R. Gress
  • Journal of Guidance Control and Dynamics, February 2018, American Institute of Aeronautics and Astronautics (AIAA)
  • DOI: 10.2514/1.g002468

Hovering Stably with Just Two Airplane Propellers and without Sensors

What is it about?

It is a theoretical investigation of the hover stability of a VTOL aircraft having two conventional airplane propellers (in a side-by-side configuration) for lift. It finds that this aircraft type's pitch rate can be stabilized (naturally go to zero) without electronics and actuator servos - if the propellers are allowed to tilt in oblique directions. This direction introduces propeller gyroscopic moments which act on the aircraft in a favorable way; the propellers in effect become both the attitude sensors and the control effectors. The same is true of roll, but its thorough investigation is saved for a subsequent paper.

Why is it important?

It reveals a new class of aircraft - in addition to helicopters with flybars - whose pitch and roll rates are inherently stabilized, but which does not require cyclic blade-pitch control. It's two lift-propellers can therefore be of much smaller diameter than a helicopter rotor for a given load. With its inherent stabilization, the aircraft does not require electronic pitch and roll sensors nor high-frequency tilt actuators. This lowers stresses, weight and energy usage. And the side-by-side propeller configuration is ideally suited for transitioning to airplane mode.


Gary Gress
University of Calgary

Writing this paper helped make the concept concrete, and provided directions for next steps and future investigations. I plan to use it as a template for writing a subsequent roll-yaw stability paper.

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