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On the Subject of Innovation: Helicopter Developments

Airbus X3 Helicopter

The test flight of the Eurocopter X³ technology demonstrator (First unveiled in February 2009) has shown another company‘s vision of the helicopter of the future.  With the traditional ‘Penny Farthing’ layout beginning to reach its upper technological limit, alternative layouts and composite designs will need to be thoroughly investigated in the near future.

The X³ (or X Cube Eurocopter parlance and suitably registered F-ZXXX) flew on 6 September and is truly a composite helicopter, not just in the sense of its layout.  It utilises an AS365N3 Dauphin fuselage coupled with a modified EC175 transmission, in addition to the EC 155 main rotor.  Many other components of the aircraft were also lifted from the Eurocopter spare parts bin, including the EC145.

The missions envisaged by Eurocopter for the X³ include oil and gas exploration and support, passenger transport, search and rescue and of course, military.  Although not just simply a ‘Poor man’s V-22 Osprey’, the stub wings and propellers offer significantly higher forward speeds and range.

At high speeds the disc load on the main rotor is off-loaded by lift from the stub wings, this helps reduce the drag from the main rotor by allowing it to rotate at a slower speed, in an attempt to keep the blade tips sub-sonic.   The stub wings also off-set retreating blade stall, inherent in a helicopter with a high forward speed.

The engines for the aircraft have been described as coming from the NH90, by this we can guess they are Rolls Royce RTM322’s.  The drive to the two wing-mounted rotors is provided by two small turbo-prop engines, although the promotional video suggested transmission take-off drives.  From this, it could be construed that there is an element of redundancy with direct drive from the main transmission in the event of engine failure, necessary if the props also provide yaw and anti-torque control.  From the video, it appears that the two drive propellers rotate in opposite directions, the port propeller clockwise (when viewed from the front), and the starboard propeller counter-clockwise.

Initial viewing suggests that the X³ is a very logical layout and an ideal solution to the problems of high-speed rotary performance.  However, from a military perspective, the design does have a number of limitations.

Firstly, the additional engines for the drive props would introduce an additional large component into the maintenance and logistics chain, its also one more thing to go wrong or get hit by enemy fire, despite the suggestion of mechanical redundancy.

Secondly, admittedly this is purely a technology demonstrator, the forward drive props in their present position do risk decapitating and dismembering deplaning personnel.  This risk would undoubtedly be reduced if an aircraft like the NH90 was adapted, however, the anhedral design of the wings may still pose an inherent problem.  Although these are necessary to keep the propellers and main rotors at a safe distance from each other in the event of blade flapping in high winds or heavy landings.

Ducting the props or converting them to a pusher configuration may mitigate some of these issues. Some years ago Dowty trialled ducted turbofans on a Britten Norman Islander.

Thirdly, from a military perspective, the stub wings are an ideal place to hang additional stores, such as weapons and drop tanks.  Spinning a large propeller at the front would preclude the aircraft from firing rockets or missiles unless they were fuselage-mounted.

As an alternative design, the tail-mounted Vectored Thrust Ducted Propeller (VTDP) demonstrated on Piasecki’s modified Sikorsky Seahawk, offers a safer and less complex solution.  It would allow use of the stub wings for the stores and put the danger of a rotating propeller where soldiers expect it to be, at the end of the tail at the back.

Sikorsky has also recently shown an advanced technology demonstrator, the X2.

The single-engined fly-by-wire aircraft features coaxial rotors and a pusher propeller that Sikorsky believes will revolutionize the helicopter world with cruise speeds of up to 250 kts, some 100 kts faster than current production helicopters. “This isn’t an aeroplane we are training to hover. It’s a helicopter that will go very, very fast,” said Sikorsky CEO Jeff Pino. “I think it will get to 260 kts.” (The helicopter world speed record is held by a Westland Lynx at 216.45 kts).

It is good to see companies exploring different avenues to try and resolve current design issues and limitations.  For the X³ I would give Eurocopter a ten out of ten for ingenuity and courage.

The question is, are we going to see something as innovative as this or the Sikorsky X2 from our very own AgustaWestland?

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13 Responses

  1. Nice blog post on Choppas, the Eurocopter X3 is news to me and i’ve no idea how on earth i had never heard about it before:| Anyway did anyone else notice quite a bit of wobble of the surfaces in the video, is it anything worth mentioning? I don’t really know.

    I would Also like to see AW come up with something innovative but they don’t have access to major French and German funding. However i feel they really have no choice as it’s survival of the fittest or the best at getting tax payers money.

  2. Why not dust off the plans of the Fairey Rotordyne, then update the design with modern materials, avionics and engines. The result would very likely at least match the Osprey.

  3. But, remember the ACH lynx :…cians-oppose-RTM322.html

    GKN Westland Helicopters plans to modify a Lynx helicopter as a compound demonstrator. However, the proposal is being delayed by a lack of funding and problems in finding a suitable airframe. The ACH or Advanced Compound Helicopter project proposes to install swept wings with trailing edge flaps, a rudder to off-load the tail rotor at high forward speeds and a new all-moving tailplane on an Army Lynx airframe. Two RTM322 turboshafts with variable-area nozzles will replace the Rolls-Royce Gem engines to give an adjustable mix of shaft horse power and direct thrust.”

  4. How about slowed rotor configurations such as the Boeing A160 Hummingbird, its got 12hrs+ endurance which is always useful.

  5. I’d very much like to see AgustaWestland produce a Merlin configured like the proposed Kamov Ka-92:

    I know AW are working on the BA609 tiltrotor, which they inherited from Agusta, but I don’t know how things are progressing or if its been put on hold.

  6. Euan, I saw the ‘wobble’ on the X3 stub wings and tail surfaces, although they should carry out sufficient vibration testing on the ground and in the hover before the maiden test flight. I found the following on youtube which demostrates what happens when a ‘wobble’ turns into resonance, which is the real killer.

  7. Thanks for the Video link Richard that is rather nail bitingly scary to watch it wobble, fail and then spin out like that. All I thought is that an aircraft or any structure is not meant to ‘wobble’ like that so watching the X3 I really noticed and was wondering if that was really something to worry about. As for the proposed Kamov Ka-92 I would really like to see one of them fly as it looks as if it could really steal the lead from Sikorsky and their X2 demonstrator.

  8. Rafer – yep, the Fairey Rotodyne was one of the big missed opportunities of British aviation. Its load-carrying, range and speed performance were all way above any helo of the time and would be competitive even today, so an updated one should be impressive. Sadly, the idea of a VTOL passenger transport going from city-centre to city-centre never caught on, and the military didn’t see any use for a VTOL transport which could carry a large number of troops at high speed…

    You can see it performing in this video:

    This has inspired a US company, Groen Brothers, to keep developing the gyrodyne concept, including taking the opposite approach to Eurocopter – instead of getting a helo to go faster, give a conventional plane a rotor. They have proposed adding one to a Hercules! See:

  9. There is nothing new in the EADS Copter.

    People have been strapping thrust engines to choppers for decades.

    Same propblems always stop them.

    To many engines= not enough payload and v expensive
    lousy handling when ‘In flight’ due to differential lift on the small wings. (Ask Pilots who have flown the Hind about vicious snap roles.
    Vibration problems.

    Sikorsky though has legs as do the Kamov designs.

  10. Any thoughts on a skew-wing single rotor hybrid? The problems with vibration and control experienced fifty years ago could be resolved with improvements in materials and fly by wireless digital flight control. Vectored exhaust nozzles on the ends of the rotror blade would replace ailerons. The fewer moving parts the better and if a single wing/rotor can do the work of two components, one of which will be redundant weight or underused during its partner’s flight mode so much the better. That was Sir Sidney Camm’s reasoning for having a single Pegasus in his P1127 rather than an Avon and several RB162 lift engines and he knew a bit about nailing aeroplanes together.

  11. What about the Cheyenne – promising design that was ahead of its time, but could be made to work with today’s technology.

  12. sikorsky are showing their mil version of the X2 it’s called the S-97 raider hoping to have 2 prototypes flying by 2014

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