Super fast helicopters
Discussion
Interesting article from new scientist about new helictopers that are being developed to travel u p to 500 kph.
http://www.newscientist.com/article/mg20827826.500...
http://www.newscientist.com/article/mg20827826.500...
newscientist said:
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."
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."
What they should do is take something like a Blackhawk and fit turboprops on stub wings. They could then use the high pressure air feed from the engines to augment the main rotor power, turning it into a partial autogyro. Intect and ignite fuel at the rotor tips if you want instant boost power for takeoff.
Then you could call it something futuristic like the Rotodyne.
Then you could call it something futuristic like the Rotodyne.
Zad said:
What they should do is take something like a Blackhawk and fit turboprops on stub wings. They could then use the high pressure air feed from the engines to augment the main rotor power, turning it into a partial autogyro. Intect and ignite fuel at the rotor tips if you want instant boost power for takeoff.
Then you could call it something futuristic like the Rotodyne.
Whaat? Whaaaat?......what's that you say?Then you could call it something futuristic like the Rotodyne.
Go to dine? - sorry, old boy, already eaten.
Can't really hear a word you're saying. Bloody Rotodyne thing, you see. Always made an ungodly amount of noise. You could hear it from the next county. Deaf as a post now.
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