Volunteer Science Team Probes Skies in State-of-the-Art Motorglider: Better Forecasts and Better Soaring Could Result
BOULDER -- A volunteer team of scientists, glider pilots, and technicians spent the spring exploring an elusive atmospheric phenomenon from a high-performance, hybrid aircraft. With support from the National Science Foundation (NSF) and the University Corporation for Atmospheric Research (UCAR), the scientists are now analyzing what they learned about thermal waves--the gravity waves that sometimes form above thermals. Thermals are rising columns of warm air used by eagles and other raptors, as well as gliders or sailplanes, to gain altitude in motorless flight.
Thermal waves, which have eluded thorough scientific measurement until now, may hold one key to better weather forecasts. For glider pilots, the ability to extend flights over greater distances is an extra benefit of the research.
The volunteers are from the Soaring Society of Boulder (SSB). Volunteer Phil Ecklund, a senior captain for United Airlines with 27,000 hours of flight time, explains the effort: "It's a labor of love for all of us. And the chance to be involved in a scientific mission was too good to miss."
A powered aircraft can't make the tight turns to maneuver in and around thermal columns, which have diameters of less than half a kilometer (a third of a mile). Conventional gliders can make the turns, but they lose altitude too quickly to get a complete picture within the lifetime of a thermal. To study the fine structure of thermal waves, the researchers needed an aircraft combining the maneuverability of a high-performance glider with a motor to stay airborne and travel long distances. Project director Joachim Kuettner of UCAR knew that the Stemme S-10VT motorglider developed by his German colleague Reiner Stemme had those capabilities, so he worked hard to bring one to Boulder for the experiment, named THERMEX. Kuettner holds the UCAR Distinguished Chair for Atmospheric Science and International Research, which is funded by NSF.
Like something out of a James Bond movie, the motorglider takes off and climbs using its turbocharged engine, draws in its propeller, and becomes a high-performance glider. "It's the only sailplane that retracts its propeller completely inside the nose while in flight," says Kuettner, explaining the secret of its performance capabilities. While gliding, the pilot can restart the engine, pop the propeller out, and resume powered flight. These features allowed the researchers to gather more data from individual thermals and to travel between and above promising cloud structures in search of the waves. With the craft's 77- foot wingspan and 1,000-mile range, the team was able to venture from Boulder to explore thermal waves in South Dakota and Nebraska without interference from the mountain waves that form over the Rocky Mountains.
A volunteer effort
"In order to pull a research project off, you need money or you need volunteers," says Kuettner, who serves on the Board of Directors of the SSB. When he explained his plan to SSB members, he found many skilled volunteers interested in the project. He notes that, "Although a volunteer effort is, by its nature, less efficient than a fully funded project, the community-building and educational benefits make it very worthwhile."
The SSB volunteers had already logged many hours in conventional gliders contributed by the society. After putting the Stemme through its paces, Ecklund remarked, "It was some of the most interesting and challenging flying I've done. It was really a thrill to see what the motorglider could do." For this spring's flights out of Boulder Municipal Airport, engineering consultant Jim Hauser and software consultant Colin Barry each contributed specialized data-handling software of their own design. Barry, who is also president of SSB, and Rod Smythe, a retired University of Colorado physics professor, were scientific observers. They took turns flying in the copilot seat, taking notes and running the data-gathering programs on a laptop computer. Volunteer Dave Campbell, who owns Mile High Gliding and DC Auto Electric, worked on the scientific instruments that gathered the data. THERMEX codirector Robert Grossman shared forecasting duties with Kuettner and was observer on several missions. Grossman is an atmospheric scientist at CU and a visiting scientist at the National Center for Atmospheric Research (NCAR). Kuettner also brought in one paid participant, physicist Wolf Dietrich Herold, who is also a highly skilled pilot. Formerly a visiting scientist at NCAR, Herold traveled to Boulder from Zurich, Switzerland, just for the mission.
Riding the waves
"It was all stories and theory for me until we caught a thermal wave just upwind of the top of a cloud over southeastern Colorado," says Grossman. "Suddenly we were in this really smooth lift, and--whoosh!--we were well above the cloud and still going up. Wolf's hand left the controls just long enough for a high five."
Thermal waves were once a well-kept secret of champion long-distance glider pilots. Mastering them can greatly extend the duration and distance of unmotorized flight. "What is learned from THERMEX is certain to find its way into international gliding circles," says Kuettner. A pioneer in the use of gliders for atmospheric research, Kuettner also served for many years as scientific chair of the International Scientific and Technical Organization for Gliding.
Thermal waves form over thermals and shallow cumulus clouds if vertical wind shear is present. The rising warm air currents, or convective currents, in which the clouds form act as obstacles to the higher winds aloft, creating "virtual mountains." However, in contrast to mountain waves, thermal waves occur over flat lands and oceans. The team hopes to learn more about the interaction of thermal waves with the convective currents in the boundary layer (the lowest kilometer or so of the atmosphere).
Skilled glider pilots have known about the extra "lift" in thermal waves for some time. But these atmospheric structures haven't been studied systematically until now "because we had no way to do it before the Stemme S-10VT," says Kuettner. To understand how thermal waves form, the team gathered data on their height range, horizontal velocity, tilt with height, and intensity. They encountered waves reaching as high as 24,000 feet (some can reach altitudes of 30,000 feet).
According to Grossman, better understanding of thermal waves could lead to improvements in the forecasting ability of computer models. He explains that global winds are slowed by friction, or drag, from the earth's surface. Modern computer models used to forecast winds include a way to account for the drag exerted by real mountains, but not the virtual ones formed by thermal waves. Grossman suspects thermal waves are playing a hidden role because global satellite images show fields of small cumulus all over the world, every day. "Even though not every cloud produces a thermal wave, there are probably enough being produced each day to make a substantial contribution to the global drag problem," Grossman says.
The University Corporation for Atmospheric Research is a consortium of more than 60 universities offering Ph.D.s in atmospheric and related sciences. UCAR manages NCAR under primary sponsorship of the National Science Foundation.
Visuals: The photo accompanying this news release is available via the Internet using anonymous ftp: Log on to ftp.ucar.edu, using the userid: anonymous; password: [your e-mail address]; directory: /communications [include the slash]; filename: thermex.tif
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The University Corporation for Atmospheric Research (UCAR) is a not-for-profit university membership consortium which carries out programs to benefit the atmospheric, oceanic, and related sciences. Among other activites, UCAR operates the National Center for Atmospheric Research with National Science Foundation sponsorship.
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