from the June 2009 issue

Unmanned rotorcraft for urban operations

Israel's Urban Aeronautics is readying for the first flight of its multimission MULE, an unmanned vertical takeoff-and-landing (VTOL) aircraft tailored for urban operations.

Now in final assembly at company facilities, the midsize MULE demonstrator is scheduled to take to the sky by June, following full-power ground tests planned for next month.

If extensive flight testing validates the MULE's hidden-rotor, internal-lift design - as it has thus far in wind tunnel tests and in the company's scaled-down Panda UAV, flying since late 2007 - Urban Aeronautics can claim a significant aerospace milestone: the world's first Federal Aviation Administration (FAA)-certifiable "rotorless" VTOL capable of ferrying cargo and passengers in and out of constricted areas.

Built around company-patented Fancraft propulsion, flight control and aerodynamic technologies, the internally powered and controlled MULE is designed to take off and land like a helicopter, but without the safety hazards, flight restrictions and noise of large rotors and exposed rotor blades. With a maximum gross takeoff weight of 2,400 pounds, the midsize system is designed to carry a 500-pound payload nearly 300 miles - about two hours worth of flight time - while traveling at speeds of up to 100 knots.

Under the firm's preliminary concept of operations, MULEs would be loaded with logistics supplies, fly via GPS satellite coordinates to designated offload areas, and land at locations selected by beacon-bearing ground spotters. The rotorless external configuration renders approach on landing and offloading of supplies much safer and faster than with conventional aircraft, company executives here say. Once emptied, each MULE can evacuate two wounded on its return flight to forward or rear bases.

"Everything's inside the body of the aircraft; there are no exposed rotors, and this opens up a world of operational possibilities for military and civil use," said UrbanAero President Rafi Yoeli. According to Yoeli, the unmanned MULE as well as the company's X-Hawk, a larger, twin-rotor, 11-passenger manned demonstrator now in development, are designed to fly with precision and relative stealth in urban, forested and other areas now off-limits to conventional tactical aircraft.

"The tips of the rotors are protected inside the ducts, and deliberately turn slowly, so MULE will be very stealthy," Yoeli said. He added that infrared and radar signatures have been kept very low to ensure survivability.

In an interview at UrbanAero's headquarters here, Yoeli noted that the basic concept driving the firm's internal rotor Fancraft design has been around for decades, yet never proved practical due to inherent instability and aerodynamic inefficiencies. However, thanks to new lightweight composite materials, high-thrust engines, powerful micro-processors, quadruple fly-by-wire flight controls and company-patented aerodynamic innovations, "what was once a mere design curiosity is now a reality."

Yoeli said MULE relies on existing and proven technologies, is built in accordance with FAA-specifications and has passed a U.S. Navy-funded risk reduction and safety assessment program conducted jointly with Bell Helicopter and Penn State University.

"We're building an air vehicle that is as safe or safer than anything flying today," he said.

Ovadia Harari, a nationally recognized aerospace pioneer who agreed to serve as UrbanAero's chairman after nearly 40 years at state-owned Israel Aerospace Industries, credited Yoeli for designing and essentially hand-crafting the MULE prototype and the unmanned Panda - a tactical surveillance system that doubles as a flying test bed - in a fraction of the time and cost required of conventional aerospace firms.

"He raised nearly $10 million until now from good people who believe in his maverick ideas and practical smarts. In an industry which is so conservative and risk-averse, Yoeli inspires others to invest in his dream," said Harari.

Aside from a 2008 agreement with Tata Advanced Systems to jointly market and produce MULE for the Indian market, UrbanAero is discussing a potential strategic partnership with a major European aerospace firm, he said.

"Once MULE starts flying, the interest in this system will increase substantially," Harari said.

Data culled from flight testing of the firm's scaled-down, 35-pound Panda and ground subsystem tests indicate that the 2,400-pound MULE demonstrator will be highly stable, drag-resistant at sustained forward speeds of up to 100 knots and able to withstand gusts of up to 50 knots. Yoeli attributed performance breakthroughs mostly to the company's Vane Control System, a row of vanes on the inlet and outlet of the fan ducts that provide maximum maneuverability without having to tilt the body of the aircraft.

"Vanes mounted at the outlet of the ducts are an old idea, but for some reason, nobody ever put vanes on the inlet side. But we found they are as effective as the lower set of vanes and when all are moved in coordination, they act as a sum of tens of individual lifting surfaces, capable of generating a multitude of overall force and movement combinations," explained Janina Frankel-Yoeli, UrbanAero's vice president for marketing.

"For the first time, we have a vehicle that can move sideways without the need to roll, and vice versa," Frankel-Yoeli said.

She added that aerodynamic tailoring between the lift rotors and fuselage allows the fuselage to provide about 70 percent of the lift it needs when operating at high speeds, with the remaining 30 percent of lift provided from the internal rotor.

UrbanAero was exploring development of two additional MULE versions: a two- to four-seater manned vehicle and a faster, unmanned aircraft capable of flying upward of 250 knots, Frankel-Yoeli said.

"We've done wind-tunnel tests of the high-speed variant and have gotten excellent results and our existing MULE demonstrator can be adapted quite easily to hold up to four people," she said.

First flights will be very brief, low-altitude hovers, with the MULE vehicle tethered to the tarmac by safety wires. Later this summer, the firm plans to transition to high-altitude flight, after which the MULE vehicle will be ready for demonstrations for prospective customers, company executives said.

Reprinted from the Israel High-Tech & Investment Report June 2009

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