Special ops gets stealth drone chopper

Danger Room:

This month, U.S. Special Forces Command is quietly taking delivery of a radical new drone: the Boeing A160T Hummingbird, which rewrites the rules for helicopters. Thanks to a remarkable piece of design, the Hummingbird can go further, longer, higher – and quieter – than anything else around.

According to Jane's, 10 Hummingbirds are supposed to be delivered this month, under a joint SOCOM-DARPA program known as the Special Operations Long Endurance Demonstration (SLED).

"The Hummingbird is designed to fly 2,500 nautical miles with endurance in excess of 24 hours and a payload of more than 300 pounds. The autonomously-flown A160 is 35 feet long with a 36-foot rotor diameter," according to Hummingbird-maker Boeing's rather brief entry on the craft. "It will fly at an estimated top speed of 140 knots at ceilings up to 30,000 feet, which is about 10,000 feet higher than conventional helicopters can fly today.

This impressive performance is achieved by reworking traditional helicopter design. Normal helicopters work at a fixed rate of rotor revolutions per minute. Rotors are flexible, articulated and have a complex pattern of vibration; changing speed would cause potentially dangerous vibration. In addition, the rotor speed is generally as high as possible; this is an advantage when the helicopter is moving fast, so that the retreating blade still provides some lift. As a result, normal helicopters are noisy (sound is directly related to rotor speed) and wasteful, as most of the time the high rotor speed is not essential.

The key feature of the A160 is its redesigned rotor blade:

To avoid vibration problems, the rotor blades are light and stiff, and their stiffness in flap, lag and torsion is progressively reduced from root to tip, so that the tips are more flexible than the root. This is made possible by the use of tailored carbon fiber construction. The A160 rotor is hingeless and rigid, and has a larger diameter and lower disc loading than a conventional helicopter rotor with the same maximum lift.

This allows the A160 to operate at a wide range of different RPM -- from a high rate for maximum speed, to a very slow and quiet mode that is highly fuel-efficient. The early prototypes were fitted with a modified Subaru automotive engine (!). Later versions had the Pratt & Whitney PW207D turboshaft, but a more efficient engine may be in the works.

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So what are the new Special Forces birds going to be used for? According the Jane's, the Hummingbirds are expected to be fitted with a new ground surveillance radar called FORESTER (Foliage Penetration Reconnaissance, Surveillance, Tracking and Engagement Radar). This is another DARPA project which the developers say will "provide robust, wide-area, all-weather, persistent stand-off coverage of moving vehicles and dismounted troops under foliage."

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The real advantage of a rotorcraft – apart from being able to sneak around the treeline, quiet and unseen – is vertical takeoff and landing, This will make it useful for the other role mentioned by Boeing, precision re-supply. Three hundred pounds is quite a useful load for a Special Forces team; it's also enough for the Hummingbird to be used for emergency casualty evacuation (though it is not rated for this – yet).

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Here is a photo of the chopper drone.

It appears mainly as an enhancement of current special ops ability that was used to destroy al Qaeda and the Mahdi army in Iraq. Its ability to linger on station has to be a plus. It apparently does not have the lift capacity to fire Hellfire missiles, but could fire some lighter ones. The emergency extraction capability would be limited to one guy it appears.

I think it is a pretty cool weapon and is probably just the beginning of this class of weapon. There will be a lot of innovation in the coming years on UAVs in general and the choppers in particular.