Demand on the rise for small hovering drones.

The market for small, hovering drones will continue to grow, possibly at the expense of larger unmanned aircraft, experts say.

Small "ducted fan" drones--classified as weighing less than 50 pounds--have gained more attention in recent years because of their size and their advantages over fixed-wing unmanned aircraft, says Basil Papadales, principal with Moire Inc., a consulting firm in Issaquah, Wash.

Ducted fan drones, unlike fixed-wing unmanned aircraft, fly like helicopters, but have propellers enclosed inside a duct.

Ducted fan vehicles have the "classic advantage of taking off and hovering," he says. They also are easier to transport than the bulkier fixed-wing drones.

"Everything works in favor of small ducted fan UAVs," Papadales asserts.

The hovering feature has been critical for U.S. forces in Iraq that search for roadside bombs. Army convoys have been using a vehicle called the RQ-16A micro air vehicle to fly ahead of the pack and scan the roads, he says.

"Ducted fan UAVs are the [military's] choice," asserts Papadales. "There is no doubt that the Army will have thousands of them."

Right now, the Army is flying about 40 micro air vehicles, or MAVs, that are manufactured by Honeywell International Inc., says Dan Fouts, the company's manager of customer sales. The Defense Advanced Research Projects Agency initially awarded Honeywell a contract for 50 MAVs. The Army is flying aircraft that were purchased under that contract, but is currently working to buy more, Fours says.

The drone's popularity has quickly spread to other services as well.

The Navy announced a surprise order in January for 185 of the two-vehicle MAV systems, for a total of 370 vehicles. They will be shipped to explosive ordnance disposal units beginning in June.

Meanwhile, the market for larger ducted fan vehicles is not faring as well, Papadales says. Several companies are trying to sell large hovering drones as the next revolution for urban warfare, but the market is not yet there.

One company, Urban Aeronautics, based in Yavne, Israel, is developing two large ducted fan aircraft as a replacement for helicopters. The company believes helicopters are ill suited for urban operations.

"Helicopters are limited in urban areas because of large rotors and exposed rotor blades," says Janina Frankel-Yoeli, vice president of marketing at Urban Aeronautics.

The company is offering the "X-Hawk" vehicle for picking up and dropping off troops in tight urban areas and the "Mule" for medical evacuation missions. The Mule comes in an unmanned configuration.

Both vehicles employ patented "fan-craft" technology, which includes a front grill that can open or close to reveal a full duct, and a vane control system with ducts on the inflow and outflow, Yoeli explains.

On the X-Hawk, the ducts are laid over a Bell Helicopter 206 fuselage. Urban Aeronautics is working with the helicopter manufacturer to break into the U.S. military market. Bell displayed a full size mock-up of the X-Hawk at the 2006 Farnborough international air show in the United Kingdom.

"The aircraft can safely operate near objects such as electrical wires, trees and buildings," the company says.

Papadales agrees that ducted fan systems solve the trouble of exposed rotor blades, but argues that large ducted fan aircraft have a "problem of scale."

The mechanics of large systems have not been solved, he says. He notes that the largest working ducted fan aircraft--which weighs in at about 120 pounds--is much smaller than a helicopter-sized vehicle such as those proposed by Urban Aeronautics.

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In addition, large ducted fan aircraft are expensive and would need to fill many missions in order to be of value to the U.S. military, Papadales says.

Yoeli agrees, saying that the vehicle "has to be multi-mission because of the expense of the aircraft." She says that Mule and X-Hawk could be used for everything from medical evacuation to humanitarian missions and emergency rescue.

Even if that is the case, Papadales contends, the U.S. military just doesn't have use for such a vehicle.

Those aircraft "might be good for them in Israel in their small little world," but if you overlay that in Iraq, the scale and scope is completely different, he says. "It doesn't fit in the way we go to war."

Another larger ducted fan aircraft, called the Golden Eye 80, is being offered by Aurora Flight Sciences of Manassas, Va.

The 120-pound drone--the largest ducted fan vehicle on the market--is built with longer ducts and also has small wings, which makes it "aerodynamically very different" from other types of ducted fan systems, Papadales says.

Aurora competed with BAE Systems and Honeywell for DARPA's organic air vehicle program contract. After losing that contract, the company competed for the second organic air vehicle program, but it was canceled last year.

The company then decided to go after a Marine Corps UAV contract, but that program was also killed, Papadales says.

Aurora has in the past marketed the Golden Eye 80 to the U.S. Special Operations Command. After a string of program failures, the vehicle may finally have use in this area, he suggests. The company may find it hard to sell to the Army, Air Force and Navy because the services are reducing procurement of new types of UAVs.

In the future, larger ducted fans drones will continue to struggle to find a niche, Papadales predicts, while smaller hovering drones such as the micro air vehicle will continue to be a battlefield need. "For the counter-IED and counterinsurgency role, they will be useful."