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The search for speed is a risky business. For rotorcraft, immutable laws of physics provide limits on the speed of a helicopter.
But a desire for faster travel remains strong, and drives development work particularly in the world of helicopters and related vehicles.
Rotorcraft — which depend on rotor blades for lift — may be able to take off and land vertically, but the advantage of cutting their passengers’ overall journey times from point A to point B — without the need for airports — is often undone by limited top speeds.
The market for rotorcraft to reach offshore oil and gas rigs may have slackened in the wake of the fall in the oil price. But new designs continue to be pursued, and analysts point out that the market for emergency medical and search helicopter still has room for growth.
Military buyers, understandably excited by the idea of aircraft that are both fast and can land vertically, have funded the best-known combination of helicopter and aeroplane, the Bell-Boeing V-22 Osprey tilt-rotor. Its transition from concept to working product was costly, both in dollars and lives lost in crashes in testing, but the technology is now proven, and the V-22 has a speed capability of 275 knots (509kph).
The civilian version, the much smaller nine-seat AW609 tilt-rotor, is still in development and the timetable for first deliveries has slipped from 2007 to 2018. The project started as a collaboration between Bell of the US and Agusta of Italy, but was taken over completely in 2011 by AgustaWestland, which is now known as Leonardo Helicopters.
Much like the V-22, the project has also suffered setbacks. Preliminary findings of an inquiry into a fatal crash in Italy during high-speed testing in 2015 were released last month and indicate a conflict between pilot input and the logic of the fly-by-wire software. Leonardo has said it has a solution to the problem and has resumed flight tests.
Airbus Helicopters, the European consortium, has a more elegantly simple solution to wringing more speed out of vertical-lift craft. Its X3 technology demonstrator replaced the anti-torque tail rotor of a conventional helicopter — which stops the aircraft body turning in the opposite direction to the main rotor — with two forward-facing rotors on stubby wings alongside the cabin. The combination produced the necessary anti-torque effect, generated forward thrust and eased the workload of the main rotor by the stub wings generating lift.
The X3 set a speed record of 472kph in level flight in 2013. Last month, Airbus announced that a rotorcraft building on the X3’s architecture, the LifeRCraft high-speed demonstrator, has had its initial layout validated by wind tunnel tests.
The rotorcraft’s increased speed results in “less fuel and smaller noise footprint for the same mission”, according to Tomasz Krysinski, head of research and innovation at Airbus Helicopters. Flight testing of a prototype could start as early as 2019.
As a project backed by a pan-European company with a substantial presence in the UK, this aircraft development could be affected by the UK referendum vote at the end of June to leave the EU. However, Airbus says that with contracts not due to be awarded until around 2020, it is too early to make any firm predictions of any Brexit fallout.
Leonardo Helicopters says it is considering development of the tilt-rotor.
Other manufacturers have their own solutions to speed. Sikorsky of the US, bought by defence company Lockheed Martin at the end of 2015, also funded its own high-speed demonstrator, the X2. That used a rearward-facing propeller for thrust and twin coaxial, counter-rotating main rotors for lift and it achieved a speed of 460kph. The technology has been used for the company’s proposed S-97 Raider military helicopter design.
Away from the quest for speed, safety remains one of the biggest issues. Some variants of an Airbus heavyweight helicopter have been grounded by regulators in the wake of the crash of a Super Puma in Norway in April, killing all 13 aboard.
Norwegian safety investigators have pointed in a preliminary finding towards the failure of a gearbox component as a possible cause, causing the lifting rotor to detach itself from the helicopter. As a result, the European safety agency banned operation of H225 LP and AS332 L2 Super Pumas last month. Aircraft in some other regulatory environments are still permitted to fly, however, and Airbus says it is “putting precautionary measures in place to support our customers and address potential initiating events”.
Some North Sea operators have drafted in Sikorsky S-92 helicopters, which are a similar size, as they did after the 2012 grounding of Super Pumas. Airbus’s re-engineering of a component, a bevel gear shaft, allowed the Super Pumas to return to service in 2013.
Keeping even conventional helicopters in the air means juggling competing forces such as lift and weight. Add pushing the envelope on speed, and the task becomes much more complex.