In the chimeric world of vertical-takeoff-and-landing (VTOL) aircraft, the most common hybrid one finds are tiltrotor planes with helicopter-like abilities. But the X3 prototype from Airbus took the opposite approach. It transformed a traditional helicopter into a high-speed turboprop.
There’s always been a distinction between aeroplanes and helicopters in that planes can fly farther and faster but need landing strips, while choppers are slower with shorter ranges but can set down just about anywhere. However there is a strange middle ground between these two platforms, one that mixes the capabilities of each either through tilting wings, tilting rotors, or in the case of the X3, tilting propellers.
The X3 prototype was developed between 2010 and 2013 as part of the company’s efforts to advance rotorcraft technology and capabilities. Specifically, the demonstrator was built to show that high-speed helicopter flight could be achieved by slowing the rotor speed by 15 per cent (which avoids drag from the blade tip) and employing winglets to generate a majority of the helicopter’s lift.
Based on the Eurocopter AS365 Dauphin, the X3 featured a primary 5-blade 41 foot rotor driven by a pair of 2270 HP Rolls-Royce turboshaft engines as well as two smaller 5-blade propellers driven via a tractor gear from the main engines affixed to the front of the helicopter’s winglets. What the X3 lacked, however, was the tail rotor you’d find on conventional whirlybirds. Instead, Airbus engineers countered the torque of the main rotor by giving the starboard propeller a higher rotational speed than the port propeller.
This design proved immediately successful. The X3 made its maiden flight in 2010. By 2011 it had demonstrated a speed of 232 knots (430km/h) using less than 80 per cent of its available power, and in 2013 broke the unofficial speed record for non-jet-assisted compound helicopters previously held by the Sikorsky X2 when it hit 255 knots (472km/h) in level flight last June.
While the demonstrator itself has been retired and is now being inducted into the prestigious Musée de l’Air et de l’Espace, Airbus hopes to further develop the technology demonstrated aboard the X3 into a variety of military, SAR and commercial platforms by the end of the decade. [Airbus – Wiki]