Airbus Helicopters continues to eye novel architectures for future rotorcraft designs, including new compound and tail rotor-free configurations, patent applications reveal.
A pair of filings – published in recent weeks but applied for over the last two years – show the manufacturer attempting to address the drawbacks of current anti-torque systems.
Both outline concepts for an “improved anti-torque device that exhibits a comparatively low overall system complexity and a reduced overall weight” against existing solutions, it says.
Airbus Helicopters has traditionally opted for standard tail rotor designs on the majority of its rotorcraft, with the only excpetion its Fenestron ducted fan design that is used on certain models, including its newest helicopter, the H160 medium-twin.
For conventional rotorcraft, Airbus Helicopters proposes a passive anti-torque design that features an asymmetrical rear fuselage, a separate vertical support wing, and a box-shaped rear stabiliser arrangement.
These features would be configured to use the downwash from the main rotor in order to generate “sideward thrust”, says the application.
It suggests the rear fuselage could have a profile similar to a high-lift aerofoil, so that “comparatively high sideward thrust may already be generated at comparatively low downwash air speed”.
“This passive anti-torque device does not require any complex actuating mechanisms, thereby avoiding the weight and the need for redundancy of an active system,” it says, and would also reduce the “required maintenance effort”.
Additionally, the design does not incur the power loss associated with the operation of a conventional tail rotor while hovering – Airbus Helicopters says this is around 13% of the overall consumption – cutting fuel burn and increasing the power available.
Rudders could also be added to the vertical portion of the rear stabiliser arrangement, allowing control, potentially through the pedals, of the sideward thrust in forward flight, the patent filing says.
The horizontal part of the stabiliser would be at a height similar to that of a conventional T-tail, but with additional stiffness thanks to the box shape of the overall design. A vertical “support wing” – again with an aerofoil profile – would also connect the stabiliser to the engine deck of the helicopter.
Such a structure would be required “as there is no centre part of the rear section of the fuselage, compared to a tail boom of a conventional helicopter”.
By eliminating the need for a tail rotor and associated driveshaft, the design cuts weight and complexity and enables a radical reconfiguration of the helicopter’s aft section, opening up previously unusable space.
Airbus Helicopters also contemplates the addition of moveable canard-type wings on the forward fuselage to generate additional sideward thrust.
These would be vertically orientated during the hover to limit the impact of main rotor downwash, and then tilted through 90° to enable the generation of lift in forward flight; the canards could variously be independently adjusted or have different profiles to generate higher levels of lift as required.
Another application, filed in July 2021, outlines the manufacturer’s anti-torque solution for a compound rotorcraft.
Here a “shrouded duct” is positioned at the rear of the fuselage. This would be shaped to generate sideward thrust and also contain a propeller for use in forward flight.
The profile of the duct – its length, symmetry, angle-of-attack and position relative to the propeller disc – would be optimised for the generation of sidewards thrust and to minimise drag caused by the main rotor downwash, particularly during the transition from hover to forward flight.
An asymmetrical main fuselage could generate additional anti-torque performance from the main rotor downwash, the application states.
Indeed, similar to the design for the conventional rotorcraft, Airbus Helicopters proposes that the rear fuselage is shaped like a high-lift aerofoil in order to further increase generation of sideward thrust; a support wing is also envisaged.
While the manufacturer sees the potential to generate some anti-torque movement from the spinning propeller driveshaft, it also outlines a means of eliminating the part, suggesting that the propeller could instead be powered by a second engine situated at the rear of the helicopter.
This, it says, would enable “engine hybridisation” and increase redundancy.
Although the manufacturer has gone so far as to file patent applications for its designs, there is no guarantee they will make it into production.
To date, Airbus Helicopters’ interest in compound rotorcraft design has been confined to the Racer – a high-speed demonstrator aircraft being developed as part of the EU’s Clean Sky 2 programme.
In addition to the conventional main rotor, the Racer features twin pusher propellers mounted on V-wings for high-speed flight; it is due to perform a maiden sortie later this year.
That design is also the subject of a separate patent application, filed in December 2020, relating to the implementation of a floatation system for “a compound helicopter with braced wings in a joined-wing configuration”.