Having already comfortably beaten an earlier target, Airbus Helicopters has a new cruise speed goal for its Racer compound demonstrator: 240kt (444km/h).
On top of which, the airframer is increasingly confident that the Racer is more fuel efficient than predicted, achieving a fuel saving of almost 30% against a comparatively-sized conventional helicopter.
Racer chief engineer Brice Makinadjian says that based on the performance of the Racer in testing so far, the higher cruise speed is well within reach.
“We are currently preparing the second flight-test campaign. During this campaign we will have more speed.
“We will target 240kt in cruise due to the low drag we have,” he said during the Royal Aeronautical Society’s Cierva lecture in London on 2 October.
The Racer’s maiden sortie only took place on 25 April and by its sixth flight on 13 June it had already hit 227kt true air speed in level flight – 7kt more than the programme’s original goal. It was also a target the airframer only expected to reach by the end of 2024.
To date, the demonstrator has accumulated around 8 flight hours but has been laid up since its last sortie in late June.
Makinadjian expects to have the Racer back in the air by the end of the year as the second phase of flight testing gets under way.
Changes to the configuration include the installation – taking place this week – of a low-drag main rotor fairing and landing gear doors, components that were unavailable for the first test phase but that will further refine its performance.
Airbus Helicopters predicts that the main rotor fairing will cut drag at that location by 25%.
“We have already showed 45% of the drag when we compare to helicopters that are in the same range in term of mass,” adds Makinadjian.
Due to its narrow fuselage and other aerodynamic improvements, he claims the 8-9t Racer has a drag coefficient equivalent to that of the smallest conventional helicopter in the manufacturer’s range: the 2.2t H125.
“Analysing all the flight data we have discovered that we have been able to surpass all the targets in terms of drag reduction,” he says.
In fact, the Racer has a lower drag coefficient than even its X3 predecessor – an earlier compound helicopter demonstrator that underwent a “special effort” to reduce drag ahead of its record-breaking 255kt flight in 2013.
Based on the flight-test data so far, Makinadjian says the Racer is “more than 20% lower in terms of fuel consumption” than a conventional helicopter with a similar maximum take-off weight. When pressed, he says the figure is “almost 30%”.
“We have been able to decrease sufficiently the fuel consumption so that it’s close to the consumption [of a helicopter] with the same size cabin,” he says.
Capable of carrying around 10 passengers, the Racer demonstrator is roughly the same size as other twin-engined types like the company’s H145 or AS365 Dauphin.
Range, too, is likely to be in excess of the current 400nm (740km) target, he adds.
Makinadjian sees even bigger fuel-burn gains as being possible. “If we take into account the expected performance when we have eco-mode we will be even lower than we are today,” he adds.
Eco-mode is a development in conjunction with propulsion supplier Safran Helicopter Engines that allows one of the Racer’s two Aneto-1X turboshafts to be idled – and rapidly restarted when needed – during the cruise phase, with the remaining engine optimised for the flight phase.
“Theoretically with the low amount of drag that we have we will be able to fly at 180kt with only one engine.” This will contribute a further 15% fuel-burn reduction.
Evaluation of eco-mode will form a core pillar of the next flight-test phase, he says.
Engine restart will be achieved with a high-power battery that can “provide a huge amount of energy in a very small amount of time”; an emergency restart will be as little as 5-7s, while a planned restart could take 20-30s, he adds.
Safran has previously indicated the battery and electric motor would be in the 100kW range.
Other aspects to be evaluated in the forthcoming flight tests will include mission demonstrations – both civil and military – to prove the real-world utility of the architecture.
Potential civil roles include search and rescue or an inter-city shuttle, for instance linking Paris and London “door to door”.
On the military side, Airbus Helicopters may invite pilots to “demonstrate the capability of this aircraft – not only the speed but also the manouevrability” where it is “comparable or even a little bit better” than a conventional helicopter.
Airbus Helicopters also intends to validate the Racer’s low-noise performance during the next flight phase, including functionality within the autopilot that will control the trajectory of the main rotor blades to minimise noise during take-offs or landings.
While conceived as a demonstrator, Makinadjian says the airframer has ensured it is as close to a serial helicopter as possible.
“In the specification of the Racer we took a specification that was really, really close to a serial specification,” he says. That includes designing the airframe so that it is capable of withstanding thousands of hours of operation, rather than the 200h necessary for the demonstration campaign.
“If we were to do this aircraft as a serial, it would look like it is at the moment.”
Airbus Helicopters would look to certify such a design under the European Union Aviation Safety Agency’s CS-29 regulations for large rotorcraft “plus some special amendments”, he says.
“We consider this aircraft is still a rotorcraft – when we fly at 220kt, we have 51% of the lift from the main rotor and 49% from the wing.”
Development of the Racer has been part-funded by the EU’s Clean Sky 2 programme.
