Tuesday, December 8, 2009

X2 Advanced Technology Helicopter

X2 prototype

Now that the Marines have fielded the revolutionary MV-22 Osprey Tilt Rotor aircraft, they have some problems. The one we will deal with today is that the usual gunship escort of the Marines, the AH-1 Cobra, is not really fast enough to keep up with the Osprey.

The Department of Defense has been trying to make a faster and more capable helicopter for many years now. The Osprey Tilt Rotor is one of the ways that they were able to make an aircraft with the vertical take off and landing capabilities of a helicopter and the fast flight of a fixed wing aircraft.
Although the Osprey has had its share of problems, we won't go into that today.

X2 in testing

So that brings us to the Sikorsky X2. The X2 is a technology demonstrator from helicopter pioneers Sikorsky and is still in testing. It differs from most traditional helicopters in that it has two blades on top of each other that spin in opposite directions. This design has been used on other helicopters, notably the Russian Ka-50 Black Shark attack helicopter. However the X2 also incorporates an auxiliary propeller on the tail to increase its speed in forward flight. The rear propeller is not a new idea either and had been a feature on the AH-56 Cheyenne helicopter. In addition to the obvious changes, it also makes use of technologies gleaned from the canceled Comanche Helicopter project such as the composite rotor blades and an advanced transmission. The X2 also uses of improved set of fly by wire controls developed for the Cypher VTOL UAV.

AH-56 Cheyenne

Russian Ka-50 Black Shark

AH-66 Comanche

The X2 is said to have a cruising speed of 287 miles per hour which is comparable to the Osprey's cruising speed of 277 mph. In comparison, the AH-1F "Modernized"Cobra's maximum speed is listed as 172 mph, and its normal cruising speed would likely be somewhat lower. An additional benefit of the new design is that the aircraft is not completely dependent on the tail rotor to maintain control and stability. The elimination of the tail rotor is a major advantage because the torque-countering tail rotor can use up to 30% of engine power. Furthermore, the vulnerable boom and rear gearbox are fairly common causes of helicopter losses in combat. The tail rotor is one of the more vulnerable areas of helicopters and all you need to do is watch Tru TV or Blackhawk Down to see what happens when they break. Since the speed of the advancing rotor tip is the main limitation to the maximum speed of a helicopter, the twin rotor allows for a higher maximum speed than other helicopters.

Artist's concepts of X2 attack helicopters

The X2 will likely not see any military service for some time though. The Osprey first flew in 1985, and was not really used until this year. Hopefully the X2 will have an easier time working out its bugs. When it does enter service, it will bring capabilities that no one in the world can match. (For now)


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  2. Just wanted to clarify your comment about the advancing tip speed limitation for most rotorcraft. For normal helicopters, the primary level flight speed limitation is just the drag of the airframe and rotor increasing far faster than one can produce forward thrust with a rotor. This explains the "compound" nature (the prop on the back) to direct more energy to pure thrust than one can produce with the rotor disk alone. You'll also notice how "clean" the X2 is, including faired rotorhead to reduce drag. The tip speed issue comes into play at higher speeds than most helos can achieve under normal level flight conditions. The contra-rotating rotor does two things to avoid this, first, it slows down at very high forward speed to reduce the tip velocity (to keep it subsonic) in comparison to the aircraft speed and second, since there is always one side of the two rotors moving forward, it prevents assymetry of lift produced by the retreating side of the rotor disk.

    . . . and I quite agree, the X2 has huge potential.

    Another interesting thing about it, it is being developed by company funds only - probably a reaction to Pentagon "suits" who are constantly trying to "Sovietize" and centralize US rotary wing industry. Of course, with DoD civilian "experts" directing it all from the 3rd floor of the Pentagon - this drives our military guys and industry insane - so, it forces the company to forego DoD funding, extends development time, slows innovation, but we have to do it that way, to avoid getting F'd with and having OSD dweebs screw it up.

  3. Thanks for the info, Man you should write your own blog. Seriously, you clearly know more about this than I do. I just read that shit about the rotors on wikipedia.