"Overall, it worked quite excellent," said Rik Meininger, the Helios Prototype project manager, of the airplane he calls a "Hershey bar flying wing."
The wings the thing
The unconventional airplane, built by Monrovia, Calif.-based AeroVironment Inc., has a wingspan 53 feet longer than that of a Boeing 747, yet it weighs just 1,861 pounds -- with ballast. It takes off and lands at bicycle speed and cruises at 25 m.p.h. (40 kilometers per hour) on average.
The flying wing concept is nearly 20 years old. A previous incarnation, the Pathfinder, flew to 80,201 feet in 1998, setting a record for a propeller-driven and solar-powered aircraft. The Helios Prototype hopes to soon smash that record.
A propeller-driven satellite
Developed under NASAs Environmental Research Aircraft and Sensor Technology (ERAST) project, the high-flying Helios Prototype may one day rival satellites when it comes to certain remote-sensing applications, like monitoring forest fires and storms.
In 2001, flight tests will move to Hawaii, where engineers will attempt to prove it can fly that high, by taking it to 100,000 feet. At that altitude, the atmosphere is 1 percent as dense as it is at sea level, or about the same as it is on Mars. (No coincidence, AeroVironment has also built a prototype of an airplane that NASA hopes to fly on the Red Planet, possibly as soon as 2005 or 08.)
That and subsequent flights will rely on $8 million worth of solar panels stitched to the wings to generate up to 30 kilowatts of power to drive its propellers. The plane itself -- a high-tech gumbo of carbon fiber, plastic skin, Kevlar and epoxy -- only costs a couple million dollars to build.
Two years after the Hawaii flight, engineers aim to prove it can fly long, by sending it soaring for 96 hours at a time. Excess energy produced by the solar arrays during the day will be stored and drawn upon at night to keep the airplane aloft.
The eternal airplane
Eventually, the self-sufficient airplane should be able to fly at altitudes around 60,000 feet for extended periods of time, carrying payloads of up to 600 pounds. And unlike a satellite in Earth orbit, the airplane will be able to take off and land, swapping one payload for another.
"Its a poor mans satellite," said John Del Frate, NASA program manager for ERASTs solar projects. "Its being able to park an antenna at 50,000 feet."
Eventually, it could fly for 5,000 hours -- more than 200 days -- at a time, a single stretch that surpasses the entire life span of a fighter jet.
Wheres the rest of it?
In flight, the plane bows like a smiley face, but on purpose. The upsweep of the wings, or dihedral, gives it more lateral stability.
The Helios Prototype also has no tail, which prompts more than a few comments.
"I had a 10-year-old little girl ask me the other day where the rest of the airplane was," Meininger said.
The airplane with almost no moving parts
With no tail and hence no rudder, the Helios Prototype steers by retarding and advancing -- slowing down and speeding up -- the power it delivers to each propeller. Its a bit like canoeing, where a furious paddle on the right will steer the boat to the left.
In fact, during a tight turn to the left, say, during Wednesdays flight, the planes leftmost propellers all but stopped, while those more than two hundred feet away on the far right wingtip cranked for all they were worth.
By differentiating the power delivered to the outermost and innermost motors, flight engineers can also control the pitch of the airplane, proving Wednesday that it can both take off and land while its elevators stand idle.
Eventually, AeroVironment would like to eliminate the elevators all together.
"What we are trying for is the ultimate in reliability," Meininger said. "If a part isnt there, it cant fail."
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