Attempts to combine the vertical take-off and landing (VTOL) capabilities of a helicopter with the high-speed flight and long range capabilities of a fixed-wing aircraft have been tackled in a number of different ways – from tiltrotor designs, such as the V-280 Valor and Project Zero, to fixed rotor aircraft that transition from vertical to horizontal flight, such as the SkyTote and Flexrotor. Australian company StopRotor Technology has taken a different approach with its Hybrid RotorWing design concept which features a main rotor that switches from fixed rotor to fixed wing in mid air.

Similar to the SiMiCon Rotor Craft concept, StopRotor Technology’s Hybrid RotorWing can take off vertically and hover with the main rotor spinning like a helicopter’s, or take off and fly like a conventional fixed wing aircraft. To transition between rotary and fixed wing flight modes, the aircraft is plunged into a fall involving high angle of attack flight that aligns the airflow with the rotation axis of the rotor system. This symmetrical airflow over the main rotor provides a stable environment that allows the blades to be started or stopped.

The design features a powered main rotor, anti torque system and forward propulsion engines. These various components can either all be powered by a single engine with appropriate transmissions, or by multiple engines performing dedicated roles.

The Hybrid RotorWing can operate in five different flight modes.

  • Fixed Wing Flight: where the RotorWing is locked to operate as a fixed wing
  • Rotary Wing Flight: The RotorWing rotates like a helicopter rotor providing sustained hover capability
  • Compound Rotary Wing Flight: where the rotors requirement to produce lift and thrust is off loaded to other lifting surfaces or propulsion engines
  • Autogiro Flight: a form of rotary wing flight where the rotor is driven by the relative airflow and not directly by the engine
  • Transition Flight Mode: where the conversion from fixed to rotary or rotary to fixed wing flight occurs

The company says this versatility translates into unprecedented adaptability with conventional, short or vertical takeoff and landing options, plus on-ground as well as in-flight mode transition with no negative impact on load capacity. The design also features a conventional fuselage that helps open up the technology to a host of applications.

While the StopRotor team says the design is suitable for scaling up to manned applications, the unmanned and remote piloted aerial vehicles market is seen as the natural first step for the technology.

While other potential applications include search and rescue, surveillance and corporate transport, military applications are likely to come first since StopRotor Technology is keen to develop the Hybrid RotorWing for inclusion in DARPA’s VTOL X-Plane program, which was launched in February. The company is looking to collaborate with leading aerospace companies to reach this goal.

"For the past 50 years, we have seen jets go higher and faster while VTOL aircraft speeds have flat-lined and designs have become increasingly complex," said Ashish Bagai of DARPA. "To overcome this problem, DARPA has launched the VTOL X-Plane program to challenge industry and innovative engineers to concurrently push the envelope in four areas: speed, hover efficiency, cruise efficiency and useful load capacity."

So far, a number of physical models built with rapid prototyping have successfully demonstrated the potential behind this approach. Each model had a virtual counterpart, which allowed for numerous designs to be tested and improved upon in a relatively short time frame. While the project is still in very early stages of development, the StopRotor Technology team believes that at the very least it could fulfill a useful role in the rapidly expanding UAV industry.

An overview of the Hybrid RotorWing design and its transition flight mode capabilities are shown in the first video below, with the following videos showing some various prototype test flights.

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