Altitudes Arabia #16

T E C H N O LO G Y

FLYING MACHINES

OF PANDORA

SEE THE FUTURE AT A HELIPAD NEAR YOU Looking at some modern helicopter developments brings to mind the record-breaking sci-fi blockbuster, Avatar, which most have seen more than once.

They don’t only look stunning – they perform accordingly. BY Ivan Veretennikov

6 8 I ALTITUDESARABIA

T E C H N O LO G Y

The Eurocopter X3 concept (left) somehow resembles the Fairey Rotodyne of the 50s (bottom left), while the V-22 (bottom right) is completely different from the two.

T

he helicopter has always been a special machine. Its unique capabilities were understood by the great minds of the past, and vertical flight had been anticipated long before Igor Sikorsky took a ride in his VS-300, the first truly successful rotorcraft, in 1939. It is the year 2011, a date people in the 70s would look to as a distant and surely marvellous future. If we look at modern helicopters, however, we notice that they’re not so different from the initial concept – they come in a variety of sizes, have comfortable cabins, and are equipped with reliable engines, but quintessentially they are the same: a main rotor to provide lift and a tail rotor to counter torque. And once you’ve seen many of them, they don’t look spectacular enough. So you go to the cinema to see something more interesting. Or you take a look around and find the future just round the corner.

D ouble D utch The future comes with its own set of exotic words:Fenestron, tiltrotor, tiltwing, proprotor... You really have to know your way around these things before you venture into the world of 21st Century rotorcraft. So a brief explanation of the terms:STOL stands for ‘ short takeoff and landing’ and VTOL – for ‘ vertical takeoff and landing’. The Fenestron is a trademark of Eurocopter, and it describes the shrouded tail rotor used instead of a conventional one. You can see it on the tail of the EC135, for example. The tiltrotor and tiltwing are similar concepts of V/STOL vehicles – in one, the engine nacelles, with propeller-rotors (these are the proprotors) at the end of the wings, turn for a transition between vertical and horizontal flight, in the other, it is the entire wing that does the turning. And there’s also the compound helicopter that features a rotor for takeoff and propellers for horizontal flight. When this aircraft gains speed, the rotor spins in autorotation creating lift like a wing.

ALTITUDESARABIA I 6 9

T E C H N O LO G Y

7 0 I ALTITUDESARABIA

T E C H N O LO G Y

The Compound Story The dream to build an aircraft that would take off and land vertically, requiring the smallest of patches in busy cities or thick forests, but fly at speeds comparable to that of a fixed-wing, has occupied the minds of engineers and inventors since the first flight of man. The 30s saw rotorcraft take shape as practical vehicles, then came the bounteous postwar period when almost every engineer offered his own vision of the rotorcraft of the future. My personal favourite from that time is the Fairey Rotodyne, an absolutely magnificent aircraft using a tip-jet-powered main rotor driven by two turboprop engines that also provided forward thrust through propellers after takeoff. Driving the main rotor by air from compressors, as opposed to a shaft, helped it avoid torque. The Rotodyne completed 455 test flights without a single accident and achieved speeds of over 165 knots (307 km/h). It showed great promise, but, after a restructuring of the British aviation industry, the project was scrapped and the only existing prototype destroyed. Come the Eurocopter X3, using a different philosophy but looking a lot like the gyroplane from the 50s. It is basically a modified EC155 with its two turboshaft engines powering the main rotor and the two props. Torque is countered by varying pitch of the propeller blades. Eurocopter is aiming to reach speeds of over 220 knots (410 km/h) with this concept, and sees its main advantage in the ease and relative cheapness of the conversion; it’s not an entirely new type that will need separate certification, and it doesn’t require special pilot training since it flies like a normal helicopter.

The Sikorsky X2 (top left) looks like a promising platform for compound helicopters, while the future of the BA609 (bottom left and above) is still uncertain.

Tilt For Speed Tiltrotors and tiltwings are exceptionally complex machines, a fact confirmed by the immense programme costs of the Bell-Boeing V-22 Osprey, the futuristic and striking machine that has gone through a lot of controversy, incidents, and design changes to emerge as the first successful tiltrotor in history. This amazing piece of pure technology is undeniably a revolution in aviation. It indeed takes off and lands like a helicopter – and even flies backwards – and then it seamlessly transforms into an aircraft and shoots off at up to 305 knots (565 km/h).

Plus, it’s involved in real combat. Such success does come at a cost – the programme is said to have cost $27 billion, and each new unit is valued at $67 million (how about a V-22 instead of a G650?). The aircraft is equipped with complex avionics and a triplex fly-by-wire system for redundancy, and it requires the pilot to be capable of flying both for fixed-wing aircraft and rotorcraft. And if anyone was ever to certify it for civil use, they would have to go through a lot of hard (paper) work... ...which is what AgustaWestland is planning to do, it seems, with their partner Bell, or without. The Finmeccanica subsidiary is pushing forward

ALTITUDESARABIA I 7 1

T E C H N O LO G Y

MD's NOTAR is completely different to traditional designs. There's no tail rotor of any kind, its place taken by pressurised air and a rotating drum.

with the BA609 civil tiltrotor, even though Bell is not so sure that the market for this aircraft is quite there. The most compelling ability of this machine is to land in congested city centres, right on the rooftops of buildings where meetings are to take place, while cruising at 275 knots (509 km/h) to connect city pairs. It looks much like its military counterpart, and no surprise – with Bell being the partner in both programmes.

Although the BA609 is successful in that it does everything a tiltrotor should, some estimates say that its price will be as high as $20 million, and at a maximum of nine passengers and a range of 750 nm (1390 km) you wouldn’t call that a bargain, whatever the capabilities.

B ig Surprise As opposed to the layouts proposed by the X3, V-22, and BA609, you won’t find a coaxial helicopter with a pusher propeller in archives dating back to the 50s. The Sikorsky X2 is as fresh an idea as can be, born in the early 70s (yes, modern technology isn’t actually that modern), when the company was flying its S69, a coaxial aircraft built to test the Advancing Blade Concept. The speed of a helicopter is limited by the difference in airspeed of the advancing blade and retreating blade and, at a certain speed, the rotor stops providing adequate lift. Sikorsky used coaxial rotors to provide advancing blades on both sides, thus maintaining lift at higher speeds. The X2 takes this a step further using the engineering experience of the last forty years. This is just a technology demonstrator, however, while the rotorcraft above are not only fast, but functional. The X2 has achieved its design goal of 250 knots (463 km/h) on 15 September 2010 and looks a likely base for a new rotorcraft type.

7 2 I ALTITUDESARABIA

T E C H N O LO G Y

The Fenestron

by Eurocopter has seen success on many models since introduction.

What a Tail!

Probably, no other part of the helicopter has been looked at by perfectionists with such dismay. The tail rotor is there because it has to be, and it’s noisy, and can be dangerous. There have been many ideas over the years, but as of today only two alternatives have really stuck – Eurocopter’s Fenestron and NOTAR used exclusively by MD H elicopters.

Both of them look a lot more advanced and would fit in nicely in a futuristic setting. The Fenestron is essentially a ducted fan within a redesigned tail. It is safer and doesn’t really affect handling or performance. The only limitation is that it is practical on helicopters up to five tonnes due to size limitations. As for NOTAR, this is a different technology altogether, having nothing to do with rotors. A fan inside

the base of the tail boom drives pressurised air toward the aft end, and part of it exits through slots on the side of the boom. The occurring wave affects the downwash from the main rotor, causing the air to go around the boom and to the side, thus combating torque. A rotating drum at the end of the tailboom is used for control. Such a solution makes the helicopter a lot quieter and safer, while the resulting exterior look is very unusual and hi-tech. It is worth mentioning just one thing in conclusion: Bell and Boeing are developing the Q uad Tilt Rotor, a large four-rotor derivative of the V-22. It will be the size of a C-130 H ercules and fly at 250 knots (460 km/h) with a payload of around nine tonnes. It doesn’t have guns and ducted fans instead of rotors, but otherwise it’s just a step away from that huge flying thing in Avatar. ❚

ALTITUDESARABIA I 7 3