Sikorsky’s X2 demonstrator outpaces conventional helicopters at 208 mph

[a_majoor]

Another really fast helicopter concept:

http://www.gizmag.com/sikorsky-x2-demonstrator-181-knots/15277/

Sikorsky’s X2 demonstrator outpaces conventional helicopters at 208 mph

By Darren Quick

01:37 June 1, 2010

Sikorsky Aircraft’s goal of producing the fastest helicopter ever built has taken another step towards becoming a reality. Its coaxial X2 Technology demonstrator has achieved a speed of 181 knots (208 mph) in a test flight – faster than the 160-170 knot speeds generally possible with conventional helicopters and edging closer to the eventual aim of delivering 250 knot (288 mph) cruising speeds.

As we’ve reported previously, the X2 demonstrator combines an integrated suite of technologies intended to advance the state-of-the-art, counter-rotating coaxial rotor helicopter. These include fly-by-wire flight controls, counter-rotating rigid rotor blades, hub drag reduction, active vibration control and an integrated auxiliary propulsion system.

After the latest test flight Jim Kaglis, Program Manager, Sikorsky Advanced Programs for Sikorsky, said, “the X2 Technology demonstrator today exceeded average helicopter speeds of a conventional helicopter, generally 160-170 knots.”

“The demonstrator is proving out the technologies very well, from the active vibration control system to the fly-by-wire controls. There are no show stoppers here so far, and now the program turns a corner, as this completes phase three of four. We are flying forward to the 250-knot cruise speed," Kaglis added.

Naturally speed isn’t the only feature Sikorsky is aiming for with its new helicopter technology. Attributes such as excellent low-speed handling, efficient hovering, and a seamless and simple transition to high speed are also desirable, and are all things that were successfully demonstrated on previous test flights.

In case you were wondering, the record of the world's fasdest helicopter has been held for over 20 years by the British built Westland Lynx ZB-500, which reached 249.1 miles per hour (400.8 kmh) at a European air show in 1986.

 

[KingKikapu]

Yes, but can they build it on time and on budget?


That's a joke, eh.

 

[SeanNewman]

Isn't having a separate (rear) propulsion system kind of cheating? The Osprey can do 250 kts, too, so would the X2 really be the first?

 

[Good2Golf]

Isn't having a separate (rear) propulsion system kind of cheating? The Osprey can do 250 kts, too, so would the X2 really be the first?

Not considered so when it is auxiliary propulsion...and it wasn't the first either.  AH-56 Cheyenne was considered "helicopter" even though it too had a pusher prop to augment its speed.  Of note, the Cheyenne flew at 247 mph level and 288 mph in a slight dive, and wasn't even trying to set records, prior to its 1972 cancellation.  Some posit that the AH-56 was starting to get a bit to close to the USAF's CAS-role, and that some inter-service political skullduggery was going on behind the scenes.

Interesting concept if Sikorsky gets the X2 going. 

 

[ArmyRick]

I remember reading about the cheyenne helicopter. It looked like a great idea. If they had gone ahead with it, maybe the Apache would have turned out considerably different today?

Aircraft that are tilt rotors, are they considered helicopters or are they going into a whole new class of their own?

 

[a_majoor]

Tiltrotors and tilt wings are forms of aircraft, since they derive their lift in forward flight from their wings. The Cheyenne is considered a "compound" aircraft, since a large portion of the lift in forward flight was derived from wings and the rest from the rotor. Interestingly, if the Cheyenne had no wings, it might be considered an autogyro, since the rotor was unloaded in forward flight, and most of the engine power sent to the pusher prop in the rear.

Legend has it the Airforce was concerned about the speed of the Cheyenne being comparable to many COIN aircraft and therefore in violation of the so called "Key West" agreement (Zoomies fly aircraft, the Army gets rotary wings), but the protracted development and escalating costs were probably a much greater factor.

 

[GK .Dundas]

Legend has it the Airforce was concerned about the speed of the Cheyenne being comparable to many COIN aircraft and therefore in violation of the so called "Key West" agreement (Zoomies fly aircraft, the Army gets rotary wings), but the protracted development and escalating costs were probably a much greater factor.

Ah yes the "Infamous Key West  agreement "....also know as the treaty of Key West I have always been amused by the  US Air Force' s absolute insistence that every paragraph and codicil pertaining to their rights and privileges regarding fixed wing A/C be enforced  like a medieval papal bull.One half expects to find that they've rerouted Spy satellites to keep watch on Fort Rucker.
Yet at the same time they have very little interest in CAS that part of the agreement  they seem to almost blissfully  unaware of it
Ironic to say the least

 

[Zoomie]

Isn't having a separate (rear) propulsion system kind of cheating?

Airwolf had twin afterburners - it went super fast.

 

[SeanNewman]

Airwolf had twin afterburners...

And one of the coolest show theme songs of all time.

 

[REDinstaller]

I'm not too sure of what value a 250mph helo is. Just like the Griffon airmobile taxi, once it would have mission specific kit added to it the ability to hit and maintain those high speeds is gone. At least the Lynx is a capable aircraft in its intended form, the speed setter was evolved from a proven airframe. Not an experimental airframe with the hopes of making it financialy viable.

 

[Good2Golf]

...At least the Lynx is a capable aircraft in its intended form, the speed setter was evolved from a proven airframe...

Except for when they pull it from theatre because of the hot, thin air... 

Cheers
G2G

 

[REDinstaller]

This affects all aircraft wrt loading and performance, minus the relocation of the fleet out of theater.

 

[Good2Golf]

This affects all aircraft wrt loading and performance, minus the relocation of the fleet out of theater.

...which is not an insignificant factor, and which was my original point to your comment on the Lynx.  There are time where it is an INCAPABLE aircraft in its intended form.  249 mph top speed does SFA in Helmand/RC(S) when the aircraft is 10,500km back in England because it doesn't have usable capability in the hot weather.

Adjusting an aircraft's load due to density altitude is one thing, removing it entirely from theatre because of the conditions is another...


Regards
G2G

 

[SeanNewman]

For you pilot types, does an acceptable loss of performance ever play into a desire to buy something over-capable?

For example, say these helicopters are over-performers, but something like our Griffs were "just okay" while still in Canada. 

Knowing you are going to take a temperature and altitude drop in some locations, would you not want the over-performer?

 

[REDinstaller]

You would need a crystal ball in order to plan what conditions an AC will be operating in over its life span. What has the right performance in TFA, might be totally unsuitable in a maritime enviorment.

 

[Good2Golf]

Petamocto, in a perfect world, you would like a "good-enough-performer" wherever you reasonably expect to operate, no matter where that may be. 

That said, there are things we do in the requirement specification world where we try to ensure this as much as possible.  In regards to helicopters, we call that "ISA +30", or "international standard atmosphere + 30 degrees C".  This means we want the aircraft to be able to perform as rated in an environment that is 30 degrees C hotter than the standard atmosphere.  ISA is 15*C at sea level (101.3kPa) with a decrease in temperature of 2*C per 1000' increase in altitude.  Say in Kandahar (~3000'ASL), the ISA temp would be 15 - 3x2 = 9*C.  IAS + 30 in KAF would be 39*C.  If it's hotter than 39*C, there may be some reduction in aircraft performance.  How much the overall performance decrease is depends on a number of factors, and how that decrease in performance affects a particular mission depends on the demands of that mission.  The US Army describes things a bit differently, they call it a "High/Hot" spec, and it mandates that a helicopter be able to hover out of ground effect (not using the cushion of air close to the ground) at 4000' altitude above sea level and 95 degrees F (aka  4K/95-spec).  The also require that the helicopter be capable of climbing away with at least 500 feet per minute climb rate from that hover.  By placing these specifications into a helicopter's requirement documentation, we are assured of a certain level of performance of the aircraft so long as we know what the environmental conditions are that we expect to operate within. 

Sure, we can't know everywhere that we will operate over the life of the aircraft, but we really don't need to...we know that the machine will perform reasonably, as advertised (if not abused, or over-loaded) in an atmosphere 30 degrees C hotter than the international standard atmosphere.  Are some places hotter, with thinner air even than ISA +30?  Yup.  But we know that, we crunch the numbers and we advise on what exactly we can do and how best to employ the machine, given those conditions.

On thing I find very unfortunate is when information is presented out of context...Griffon is a good example.  Many folks say it's a piece of crap and can't do a decent job.  Some even go as far as to say things like, "the Huey was much better!"  I take that with a grain of salt, because often it comes anecdotally from people not qualified to assess capabilities of the system in question.  With thousands of hours of flight time accumulated on a number of helicopters, including Chinooks, Hueys and Griffons (and Kiowa, but that was less than a hundred hours and in training so I won't count that), I will definitively say I would take a Griffon over a Huey EVERY TIME!  It may have some hiccups, but it is a damn good machine, way more power than a Huey, faster, smoother and better avionics for making sure I get where I'm supposed to be going.  I and others have had a Griffon pull our butts out of a sling when a Huey would have taken us to the crash site.  Perfect? No.  Good?  Darned right it is!

It all comes down to how you use an aircraft.  Use the Griffon more appropriately, like we are now doing in Afghanistan, as a light utility and armed escort, and the troops get thousands of rounds a minute of 7.62 raining down from overhead when they need help, or eyes on from many kilometers away giving SA to others who can't see as far -- it's doing its job.  Need to lift tons of stuff or a whole platoon?  Then do it with the right machine, the Chinook.  I once lifted 26,500lbs with a Chinook - pretty amazing capability.  Can we lift that much in AFG now?  Now way, not even close, but we're still happy with what the machine can do.  That's to say that even machines that folks think are the 'be all and end all' have their limitations.

T18A, you can do a reasonable job forecasting the environments that an aircraft will be used in.  A rather sizable portion of an aircraft's Statement of Operational Requirement (SOR) outlines precisely this information.


Cheers
G2G

 

[GAP]

Thanks, that cleared up a lot of questions.....excellent points..

 

[SeanNewman]

Yes, that was a fantastic write-up, thank you.

 

[a_majoor]

Project continues, video of the next record flight here

 

[a_majoor]

And now Eurocopter is in the race:

http://www.newscientist.com/article/mg20827826.500-airwolf-2010-the-race-to-build-superfast-choppers.html

Airwolf 2010: The race to build superfast choppers

IN the TV series Airwolf and Blue Thunder, the helicopters are revered almost as much as the actors or the plot. These fictional flying machines now have some serious competition in the speed stakes. High-speed prototypes capable of 500 kilometres per hour are taking to the skies for real.

These experimental craft are the work of Sikorsky Aircraft in the US and Eurocopter in Germany. Sikorsky's X2 and Eurocopter's X3 (pronounced X-cubed) have propellers for additional thrust. The firms' technology could help commercial chopper speeds rise by 60 per cent within five years.

A combination of fundamental aerodynamic limits and the need for fuel efficiency mean helicopters today have a top cruising speed of around 300 kilometres per hour. "Helicopters don't fly fast, managing only about half the speed of an airplane. That's a severe limitation," says Gordon Leishman, a helicopter aerodynamicist at the University of Maryland in College Park.

Choppers are often needed where speed is crucial, but injured people plucked from road accidents, oil rigs or mountain ledges, face a slow ride to the ER. "While the helicopter's hovering ability makes it extremely useful, its lack of speed often means people cannot be treated in what medical teams call the 'golden hour', where the ability to save life is strongest," says Leishman.

Coaxing extra speed from a helicopter is complex - you can't just soup up the engine and shovel in fuel. The top rotor blades, which generate both lift and forward thrust, can only turn so fast. If the rotor spins at just under the speed of sound, the "advancing" blade - moving at helicopter airspeed plus rotor speed - would reach supersonic velocity. Meanwhile, the retreating blade on the opposite side will remain subsonic. Because aerodynamic forces are different in the supersonic and subsonic regimes, that would cause instability and a dangerous loss of lift, says Jean-Michel Billig of Eurocopter in Ottobraun, Germany.
You can't just soup up the engine and shovel in fuel to coax more speed from a helicopter

The only option is to add thrust by other means: adding a separate propeller or jet engine. In the 1970s, for example, Sikorsky, alongside NASA and the US army, designed a helicopter called the XH59A, which had two jet engines that pushed its speed up to 400 km/h.

However, the transition from hovering using a rotor to jet-powered flight was difficult and mechanically stressful. "We couldn't bring it into production because its total of four engines had high fuel demand, it had very high vibration levels," says Steve Weiner, Sikorsky's chief engineer on the X2 project. What's more, two pilots were needed to fly it.

Modern vibration controls and computers that help a single pilot to fly such a complex craft have given Sikorsky another shot, Weiner says. For fuel efficiency, the X2 uses a "pusher" propeller at the back of the craft, rather than added fuel-guzzling engines.

The engineers needed to live without the tail rotor of a typical helicopter so the craft could use its drive shaft to turn the rear propellor. This presented some problems: a tail rotor stops a helicopter spinning in circles, and helps with steering.

Sikorsky solved this by adding two contra-rotating sets of rotor blades on top. These balance each other's torque so the helicopter doesn't spin. To steer at speeds up to 110 km/h, the angle - or pitch - of the top set of rotor blades is adjusted. Above that speed, the X2 steers using rudders on its tail fins.

With a propeller and rudders, though, isn't it close to being a plane? "In a sense, yes," says Weiner. "But all the lift still comes from the rotor. We have no wings."

Eurocopter's X3 does have wings, however, which support two propellers. At high speeds, those wings contribute 40 per cent of its lift, so the single rotor doesn't have to work so hard.

Like the X2, it has no tail rotor - so the pitch of the left and right propeller blades subtly adjust automatically in flight to maintain stability and to provide steering, says Billig, but the pilot still controls the craft as they would a regular helicopter.

The X3 has so far only flown once, in a 35-minute flight that tested its hovering behaviour and Billig says it performed as designed. It won't be going for any high speed attempts until late 2011, but they are initially aiming to bust 400 km/h.

Sikorsky is already well on the way to achieving its speed aim of over 500 km/h. In a test flight in September, the X2 unofficially broke the previous record of 400 km/h, which was set by the Westland Lynx in 1986. The X2 achieved 463 km/h, but due to its propellers, it is unclear if the craft will be recognised in the same category by the FAI, the world's air sports federation based in Lausanne, Switzerland, that oversees aviation records.

That won't stop Eurocopter, or indeed Sikorsky from trying to push choppers to ever higher speeds. "The physics of the X2 design certainly don't limit it," says Weiner. "By solving other issues it could go to 550 km/h."

Sikorsky and Eurocopter have enlivened a moribund industry, says Leishman. "For too long the rotorcraft industry has not built exciting, advanced demonstrators like X2 and X3. And we may yet see more manufacturers pick up on this speed challenge."