Ducted Fan Designs Lead to Potential New Vehicles
- Friday, 01 January 2010
From the myth of Icarus, who flew too close to the Sun on wings made of wax, to the designs Leonardo da Vinci drew of flying machines that mirrored the wing patterns of birds, people have always dreamed of personal flight. In 1903, on a cold December morning in North Carolina, the Wright brothers made the dream a reality with the first manned flight. It lasted only 12 seconds, but initiated a rapid evolution in aircraft design, and within a few years there was an aircraft industry.
In the early days of manned flight, though, one idea persisted: the personal air vehicle. At the time, the concept of personal flight was still a thing of the imagination—epitomized in 1928 by the fictional character Buck Rogers, complete with his rocket belt.
In the 1950s, Bell Aerospace took the dream one step closer to reality with its unveiling of the jet belt, a small, low-thrust rocket that strapped to the operator’s back. The short flight of 20 or 30 seconds, however, was not enough to make it viable for anything practical.
In 1955, with funding from the U.S. Navy, Hiller Aviation created the Hiller Flying Platform, a rotorcraft that was essentially a disk with a helicopter underneath. The operator stood on the platform and steered by shifting weight. Although there was interest and the prototype showed promise, the craft never went into production, as the standard helicopter proved more practical. For the next few decades, most of the interest in flight focused on the jet engine, and personal aircraft design was again relegated to the stuff of fiction.
For the centuries that people had dreamed of personal flight, there were countless great ideas, thousands of drawings, and hundreds of planned attempts. The only problem was that none of them stayed in the air long enough, so the dream lay dormant. But in the 1990s, new, lighter, stronger materials and advanced computer design systems awakened that dream.
In 1994, two aerospace engineers, Rob Bulaga and Mike Moshier, drew sketches for an aircraft they believed could prove viable, and by 1996, had formed a company, Trek Aerospace Inc. The company, based in Folsom, California, took full advantage of its proximity to NASA’s Silicon Valley-based Ames Research Center for a great deal of testing, results of which have provided greater lift, lowered weight, more power, and improved maneuverability.
In 2000, using a wind tunnel at Ames, the engineers improved their designs. They tested their duct and fan system at the NASA site and were able to watch the flow of air over the ducts at various angles, finding that there was a very small stall area, and that for the most part, the flow did not separate. This clean airflow showed them that the craft was accomplishing 40 percent of its lift out of the duct system, which meant that the engineers could accomplish lift with a significantly smaller, lighter engine.
The experience gave the engineers a better understanding of how their craft worked and led to several design changes, including the use of a fly-by-wire system. The original prototype had handgrips and relied on the operator to shift his weight in order to operate the vehicle, but the wind tunnel testing suggested that this would not give the pilot adequate control of the vehicle. The fly-by-wire solution replaces the handgrips with two joysticks, one for controlling altitude and the other for turns. Information from the joysticks is fed into an onboard computer.
All of Trek Aerospace’s aircraft employ ducted, counter-rotating fans attached to a central gearbox and drive train, connected to a power source. The ducts allow the craft to fly into tight spaces without fear of damaging the rotors or anything else with which the rotors would otherwise come in contact. While seemingly simple, the company suggests that its success with the vehicles is the right combination of devices and how to make them interact effectively. The technology has been applied to three models: the Dragonfly UMR-1, the Springtail EFV, and the OVIWUN.