UNLIKE a helicopter, aeroplanes are inclined to fly, Harry Reasoner, a veteran American newsman, wryly observed after watching choppers in action during the Vietnam war. He wrote:
A helicopter does not want to fly. It is maintained in the air by a variety of forces and controls working in opposition to each other, and if there is any disturbance in the delicate balance, the helicopter stops flying, immediately and disastrously.
Despite their mechanical complexity and the need for piloting skills akin to riding a unicycle, a helicopter’s idiosyncrasies can quickly be forgiven. It does things aeroplanes cannot. The ability to take off and land vertically, and to hover, have made helicopters indispensable to the military since their first mass deployment by America in Vietnam, where the ubiquitous UH-1 “Huey” led to that conflict becoming known as “the helicopter war”. Civilian roles are just as vital, from rescuing people stranded on mountains to use as air ambulances, from putting out wildfires to carrying people and presidents to and from places where there are no runways.
The helicopter, though, has a new rival. Some drones also take off and land vertically, and with rotors powered by electric motors, they are mechanically more straightforward. Drones are also quieter, cheaper and easier to fly because they operate largely autonomously, and can be controlled by someone on the ground and who does not need a pilot’s licence. Unsurprisingly, drones are already taking work away from helicopters, in military tasks like reconnaissance and in civilian ones such as filming, surveying and delivering goods. They are also being developed to carry passengers. The differences between helicopters and drones are vanishing.
For now, companies that make helicopters think their machines have a long life ahead of them. Batteries are currently unable to provide electric rotorcraft with extended flight times or the ability to carry heavy loads. And many helicopter missions are still likely to require crew on board—think of winchmen for an air-sea rescue. Nor would most hovering drones stand a chance in the intense storms and blizzards that helicopters sometimes have to fly into. But that does not mean helicopters of the future will still fly in the same way, or that they will always have a pilot.
A number of new ideas for future helicopters are whirring. Among them are the “X2” technology, which is being developed by Sikorsky, a Connecticut-based firm founded by Igor Sikorsky, who produced the first practical helicopter in 1939. The V-280 Valor (pictured above), which is a striking “tilt-rotor” design, is being championed by Bell, the Texas-based producer of the old Huey. Both companies aim to overcome one of the helicopter’s inherent shortcomings: a limited top speed.
Pulling on the collective
A helicopter’s speed is restricted by the way it flies. An aeroplane obtains lift by air passing over the aerofoil shape of its wing. The blades of a helicopter have a similar shape and work like a revolving wing. The trouble is that, in forward flight, the airflow over the blade advancing into the oncoming air is greater than that over the blade that is retreating. This produces a lopsided amount of lift, which is compensated for by adjusting the angle of the blades as they rotate to achieve an equal amount of lift on both sides. Once the speed exceeds about 280kph (174mph), increasing the angle of the retreating blade any more results in a “stall”, which produces no lift at all. By then the helicopter is likely to be vibrating dangerously and it could flip over.
A tilt-rotor overcomes this problem with a pair of counter-rotating rotors mounted on a set of wings. This arrangement effectively converts a helicopter into an aeroplane for faster forward flight, by tilting the rotors forward, and then back into a helicopter to land and take-off vertically by pointing the rotors upwards. Bell’s V-280 tilt-rotor can nip along at 520kph (280 knots, hence the name) and has a range of almost 1,500km, even when weighed down by four crew and 14 fully-kitted combat troops.
An older and bigger tilt-rotor called the V-22 Osprey is produced by Bell in partnership with Boeing. This too is faster and can travel farther than a standard helicopter. It is used by the US Marines. The V-22, however, tilts both its rotors and engines. The V-280 simplifies this design and reduces the amount of weight that has to be rotated by having the engines remain in place and tilting only the driveshafts and rotors.
The new design could be scaled up to produce much bigger craft, says Vince Tobin, Bell’s head of military business. Bell is also looking at electric flight systems for sometime in the future.
Look, no hands
The V-280 will be “pilot optional”. Some passengers might be happier with a human in the cockpit, but much depends on the mission. “If picking up a downed pilot in a hostile situation, they’ll take any ride out, manned or unmanned,” says Mr Tobin, a former US Army helicopter pilot. In civilian use a tilt-rotor opens up all sorts of travel opportunities with their speed and range, he adds. That could be from roof tops to heliports, saving on land occupied by conventional airports.
Sikorsky’s X2 system uses two rotors mounted on the top of the helicopter, one above the other but turning in opposite directions. This so-called coaxial arrangement has long been employed by some Russian helicopters because it makes the tail rotor redundant, which is useful when flying in and out of tight spots. On a conventional helicopter the tail rotor counters “torque”, a twisting force induced by the main rotor. Coaxial rotors (and counter-rotating tilt-rotors) cancel out torque.
Where the design differs from previous coaxial helicopters, is that Sikorsky fits a propeller at the rear to push the helicopter along much faster. Another difference is that the four blades on each rotor are made much stiffer than is usual so that the rotors can be placed closer together without their blades colliding. The result is that at high speeds retreating-blade stall is overcome because there is always a blade advancing in the direction of travel on either side of the helicopter to provide a balanced lift.
Such an arrangement makes a helicopter faster and more manoeuvrable. It is also quieter because the rear propeller can be used for most of the forward thrust, allowing the rotors to run more slowly, says Chris Van Buiten, head of Sikorsky innovations. The company has two versions using the technology. One, the S-97 Raider (pictured above), carries six passengers and can fly at more than 400kph. A bigger model being developed with Boeing, the SB-1 Defiant, is due to begin test flights later this year. It can carry a dozen troops. Civilian versions of both are planned
All these new helicopters will be made easier to fly using computerised flight controls. Sikorsky, for instance, is working on a system in which pressing a single button is all that is required to take-off and hover. This level of automation makes autonomous operations possible. That could be for pilotless missions or as a back-up for single-pilot use, allowing a helicopter to return to base if that pilot was incapacitated, says Mr Van Buiten. When Sikorsky began experimenting with autonomous flight systems some ten years ago, the entire cabin of a test helicopter was filled with computers. Now the required kit is the size of a toaster. Whether they end up carrying people or not, the difference between drones and helicopters is starting to narrow.