Performance
- Increased high/hot hover capability
- Coaxial rotor power required to hover is 15-18% less than single rotor + tail rotor
- Rotor-on-rotor wake interaction reduces power 5-6%
- Eliminating anti-torque power saves 10-15% of power required
- Increased cruise speed, range and endurance
- Induced power in cruise is 20% less than single rotor + tail rotor
- Fan propulsive efficiency is higher than tilting rotor for propulsion
- Fans act as stabilizers and are in axial flow
- Potentially less susceptible to “brownout”
- Fans can be used to decelerate, eliminating need for flare to a hover
- Easier to fly (safer) than conventional helicopter
- Fixed-wing flying qualities
- There is no coupling between the collective and pedals
Productivity
When the increase in payload and cruise speed are combined, a significant increase in productivity of the AVX configuration is realized – productivity is up to 60% greater than that of conventional helicopters.
Per seat mile, the coaxial rotor, dual ducted fan AVX configuration yields approximately 20-30% greater fuel efficiency than conventional helicopters as well.
Hover Performance
A counter rotating coaxial main rotor does not require an anti-torque device as the upper and lower rotor’s collective pitch are rigged such that the driving torques are equal and opposite. Because the coaxial rotor does not require an anti-torque device such as a tail rotor, Fenestron, or Notar, a coaxial rotor helicopter requires about 10% less power than a single rotor/tail rotor helicopter.
In addition to the power saved by eliminating the anti-torque device, a coaxial rotor requires less power due to favorable interaction of the upper and lower rotor wakes. The coaxial rotor’s reduced power required relative to other rotor configurations can be used in several ways:
- For the same rotor diameter and power the coax will lift approximately 11% more weight (9% net of weight empty increase). This equates to 30% greater useful load, which means more payload or fuel. The coax helicopter can hover at a 6000 ft higher altitude, or at a higher temperature.
- The diameter of the coax rotor can be reduced by up to 15% to reduce rotor and drive system weight resulting in a lower total aircraft weight.
- The diameter can be reduced by something less than 15% to both reduce weight and increase hover capability.
Cruise Performance
The AVX coaxial main rotor/dual ducted fan configuration achieves a higher speed than conventional helicopters (coax, single rotor, or tandem) by virtue of auxiliary propulsion (the ducted fans), maintaining a level fuselage attitude, and low drag airframe design. The ducted fans provide all of the propulsive force to overcome parasite drag; the rotor only provides lift in cruise.
In conventional helicopters the rotor is “tilted” to provide the propulsive force. The rotor incurs an increase in profile power and induced power when it provides the propulsive force, which makes it less efficient than the ducted fans as a source of propulsive force. When the rotor is tilted to provide the propulsive force the fuselage pitches nose down which increases fuselage parasite and trim drag and aerodynamic download that requires an increase in rotor thrust; these effects increase power required.
The AVX coaxial rotor/dual ducted fan configuration is based on minimizing the parasite drag of the airframe and the rotor hubs and controls. These design features result in a cruise speed higher than conventional helicopters.