Paris Air Show 2017: Airbus' Racer high-speed rotorcraft concept.

The Racer concept utilises a main rotor for lift and basic flight modes, along with two lateral pusher rotors that generate thrust in forward flight and a box-wing to provide lift in cruise mode.

“Seventy years ago, [American test pilot] Chuck Yeager broke the sound barrier,” said Guillaume Faury, CEO of Airbus Helicopters, at the Racer announcement press conference. Now, he said, “we’re trying to break the cost barrier. It cannot be ‘speed at any cost.’”

Racer builds on the expertise Airbus Helicopters developed with its self-funded X3 high-speed demonstrator, which also was a compound rotorcraft design that set a speed record in June 2013 of 255 kts in forward flight.

“The X3 demonstrator showed that high speed, highly efficient results can be obtained when the main rotor’s rotational speed is slowed down during forward flight, and thrust is provided by propellers mounted on a wing that provides lift,” explained Tomasz Krysinski, the Vice President – Research & Innovation at Airbus Helicopters.

To facilitate the X3 demonstrator’s development and to manage costs, the X3 used off-the-shelf components from Airbus Helicopters’ in-production product line.

“The X3 flew a total of 350 hours with excellent results – which were confirmed by pilots from many countries who were given the opportunity of being at the controls,” Krysinski added. “In the second step with Clean Sky 2, we are now taking a clean-sheet approach in creating a new demonstrator that shows its suitability for the missions – which include emergency medical services, search and rescue, public services, along with commercial and business aviation.”

A notable feature of Racer is the staggered, step-wing arrangement – called the box-wing – which Krysinski describes as bringing a “virtuous circle” of improvements.

“The staggered-type box-wing has a smaller overall surface than a normal wing, so it is less affected by performance-reducing rotor downwash; and therefore, less power is required to hover,” Krysinski said. “However, the box-wing’s upper and lower segments create all the lift we need in forward flight.”

Another advantage is the ability to integrate the landing gear into the box wing’s lower segment. This facilitates the kinematics for the landing gear’s retraction, while also providing lower weight and lower cost.

For the Racer demonstrator, its propellers are installed on the back of the box-wing in a pusher arrangement (compared to the forward-mounted puller configuration on the X3), reducing the power required during forward flight by 10 per cent – thereby lowering fuel consumption and increasing flight range. An additional benefit is increased safety, as the pusher propellers are positioned farther away from the doors used for boarding and deplaning – with extra protection provided by the double wing itself.

Final assembly of the Racer demonstrator is planned to start at Airbus Helicopters in 2019, with a first flight the following year. It will be based on a hybrid metallic-composite airframe, with the two RTM322 turboshaft engines linked by a supercritical shaft to drive the main rotor and pusher propellers. An electrically-powered “eco mode” will allow one of the RTM322 powerplants to be stopped in flight – and quickly restarted when needed – thus generating fuel savings and increasing range.