A Little Lift
Gliders so responsive they can stay up on a breath of fresh air.
- By Paul Ciotti
- Air & Space magazine, May 2005
It is shortly after eight in the morning at El Mirage dry lake, a cracked and dusty expanse in the high desert 55 miles northeast of Los Angeles. Despite the big plumes of yellow smoke from wildfires on the far side of the San Gabriel Mountains to the south, up here on the lakebed it is clear and quiet as sailplane designer Danny Howell does a preflight checkout of his ultra-lightweight sailplane, the LightHawk.
“There’s not a straight line on it anywhere,” boasts the Northrop Grumman engineer, sighting the prototype’s gently swelling 15-meter (49 feet) elliptical wings. From above, the wings look more like those of a large seabird than anything you’d see on an airplane. According to Howell, that’s the whole idea: to build an unpowered aircraft that not only imitates the efficiency of soaring birds but also can fly as slowly as they do…in the LightHawk’s case, a mesmerizingly slow 23 mph.
This morning’s flight will be only the seventh time the LightHawk has been in the air, so Howell and his half-dozen crew members are extremely cautious. After a prolonged inspection of the aircraft, Howell gives the go-ahead to test pilot Galen Fisher. Fisher calls the driver of the tow vehicle, 1,800 feet down the lakebed, to tell him to get moving, and in 30 seconds Fisher has risen to 600 feet, where he releases the tow rope, eases into a right turn over the scrub and Joshua trees, and begins to search for rising air.
There’s not much out there this early in the day, and within a few minutes Fisher has fallen to 200 feet and is starting to think about landing when he notices a raven slowly circling nearby. Fisher maneuvers over to join him, and soon they both are slowly rising at a nearly imperceptible hundred feet per minute. The higher they go, the better the lift seems to be, and within half an hour Fisher is cruising comfortably at 8,500 feet, where the sailplane sinks at such a slow rate—Howell estimates just 1.3 feet per second—that in the words of one test pilot, the craft appears to “fly around horizontally.”
At 200 pounds, the LightHawk, which has gone on to make 20 flights, is the latest and most technologically sophisticated entry in an emerging class of low-inertia sailplanes—super-light, super-efficient gliders with such low airspeeds and sink rates that they can stay aloft far longer than every other kind of sailplane. This class includes the 101-pound, Swiss-built, open-cockpit Archaeopteryx, the German-made ULF-1 glider, increasingly efficient rigid-wing hang gliders, and the venerable 145-pound Carbon Dragon, a balsa wood and carbon-fiber sailplane that in recent years has acquired almost mythic status for its unique ability to stay aloft on “micro-lift”—the weak energy that can be extracted from the fleeting gusts, burbles, and meandering air streams found below 1,000 feet.
Designer Jim Maupin first conceived of the Carbon Dragon in the late 1970s, when there was no such thing as a low-inertia sailplane. He intended the Carbon Dragon to be a superlight craft that would have the maneuverability of a slow-flying hang glider but the high lift-to-drag ratio of a rigid-wing sailplane.
“His goal was to set a world [distance] record from a foot-launched aircraft,” says Dan Armstrong, a Tehachapi, California-based aeronautical engineer who at the time was one of the young soaring enthusiasts helping Maupin build the sailplane. In time, the sailplane would fulfill the dream; Wichita-based entrepreneur Gary Osoba now owns the prototype, which he has flown to four distance world records and one speed-over-distance record. Its unique characteristics also have opened up a whole new method of soaring. With a 44-foot wingspan, a 1.7-foot-per-second minimum sink rate, a 20 mph stall speed (in contrast to a typical 15-meter ship’s 40 mph), and a roll rate of about 27 degrees per second, the Carbon Dragon was the first sailplane to take advantage of micro-lift, using a technique known as dynamic soaring.
Unlike conventional soaring, in which pilots attempt to lift their sailplanes to higher altitudes by seeking air rising along ridges or in the form of columns called thermals, dynamic soaring provides speed or altitude by exploiting micro-lift and wind gradients—differing rates of movement in neighboring air masses. “You’re looking more to try to bounce off gusts of air and get energy from air that’s much more complex than just [a thermal],” says Taras Kiceniuk Jr., a hang gliding pioneer who has done much to put dynamic soaring on a sound mathematical basis.