AeroAstro Magazine Highlight

Faculty profile: Mark Drela’s research — and his teaching — offer beauty and functionality

By Lauren Clark

World-renowned as an aerodynamicist, and human-powered vehicle expert, Professor Mark Drela is also admired by his colleagues and students as a superb — and fun — teacher.

Aero-Astro Professor Mark Drela. "An awesome teacher and gifted engineer." (William Litant photograph)

In 1988, Daedalus, a lightweight aircraft designed by MIT Professor Mark Drela, set the world distance record for human-powered flight by traveling 72.4 miles from Crete to the Greek island of Santorini. That accomplishment put Drela on the map as a leading expert on human-powered flight. However, even more significant than the world record was the advance in computational aerodynamic design that went into building Daedalus. It ensured Drela would be recognized as one of the best aerodynamicists and airplane designers in the world.

To design and test Daedalus, Drela developed a software program called XFOIL. A kind of MATLAB for aerodynamicists, XFOIL wrapped established computational techniques for airfoil design in a graphical, intuitive interface. The program’s ease of use and reliability enabled the Daedalus team to test and retest aircraft designs much more rapidly than previous, more cumbersome programming methods. Like MATLAB, XFOIL “does all the grungy details for you, so you can think more conceptually. And that really fits into how engineers do their job,” says Drela.

MIT Professor Emeritus Jack Kerrebrock, a mentor during Drela’s early days in the Department of Aeronautics and Astronautics, says that his colleague’s designs for human-powered aircraft and watercraft “have the beauty that stems from perfect functionality, and they were executed at an extraordinary level of precision using design tools of his own development. The aerodynamic design tools that he has developed have set a new standard of accuracy and usefulness for the aeronautical industry and are widely used in the design of commercial and military aircraft and their engines.”

Drela not only designs human-powered aircraft, but has also engineered aircraft for Boeing, the wing for the Predator UAV, the keel of America’s Cup yachts, and experimental aircraft used by NASA. In addition to XFOIL, he has written design programs for rotorcraft, machinery blading, and axisymmetric bodies such as zeppelins. All of these programs have been “developed in actual use, by myself and other people,” he says.

Mark Drela's enthusiasm for aircraft design and flying model planes is highly contagious, say his students. (William Litant photograph)

A role-model educator

Department colleagues point admiringly to Drela’s skill as an educator. “Mark is an awesome teacher and gifted engineer. His lectures and papers are laced with original insight and intellectual nuggets. He is always available – 24/7 – to help any student or participate in any undertaking. Mark is a role model for many of us who try to reach his level of excellence,” says Department Deputy Head, Professor Earll Murman.

Drela came to MIT as a freshman in 1982 and went on to receive the SB, SM, and PhD in aeronautics and astronautics. “ I was in aero since I was five years old,” he laughs, recalling building his first model airplane in his native Poland. He attended high school in the Philadelphia suburbs after his family emigrated to the U.S.

When he arrived at the Department, the field and its students were shifting focus from “hands-on, hardware stuff” to the computer- and information-science realm of aircraft engineering. Drela melded expertise in both areas to great effect by creating computer software that made aerodynamic design easier and faster.

Sitting in his office, surrounded by model aircraft he built, Drela describes XFOIL and similar programs he has written as “numerical wind tunnels. If you have a wing or an airfoil, and you need to find out how it does – what the drag is, what the lift is – you can actually compute it. It can be 1,000 times less expensive in terms of time and money to compute something on the computer instead of in a wind tunnel, which means that instead of testing one design you can test 1,000 designs. Nowadays, a freshman (using XFOIL on a desktop computer) can do the same work that required a team of computer operators 30 years ago. It’s a huge change in capability.”

After Daedalus made its unprecedented flight, Drela used XFOIL to design a new record-setting craft: the Decavitator, a human-powered hydrofoil that he pedaled to a world-record speed of 18.5 knots over a 100-meter race course on Boston’s Charles River in 1991. Both Daedalus and Decavitator are on display at the Boston Museum of Science.

Five years ago, Drela made XFOIL freely available on the Web under the General Public License. Since then, students, researchers, engineers, and aviation enthusiasts around the world have downloaded the program for both teaching and practice. XFOIL is used not only to design aircraft, says Drela, but also sailboats, propeller blades, windmills – “essentially any kind of lifting device that has air going over it.”

In early April 2006, Unified students organized a display of devotion to Professor Mark Drela by donning t-shirts bearing an alpha (angle of attack) on the front, and, on the back, a drawing of superhero Drela ripping open his shirt to reveal another alpha and the legend “Airdrela.” (James Houghton photograph)

Flying noodles and ASWING

A recent area of focus for Drela has been modeling very flexible airplanes. He consulted on an experimental unmanned aircraft called Helios, built by AeroVironment Inc. under NASA sponsorship. Intended as a satellite substitute, the solar-powered craft flies in the thin upper atmosphere two to three times higher than a typical crusing jetliner. For this reason, it must be light and flexible. Nicknamed “the flying noodle,” Helios is essentially a large, undulating wing with several small propellers.

“Designing an airplane like that is very hard, because you can’t assume what the shape is,” says Drela. “The shape depends on the air load and the air load depends on the shape. So you have this problem where you design the structure and the aerodynamics all at once.”

To tackle the problem, Drela developed a nonlinear modeling program called ASWING. Whereas Helios engineers started out having to combine separate aerodynamic- and structural-analysis tools in an ad hoc way, ASWING “put these things together and made them easier to use and essentially solved the whole problem in an integrated fashion rather than piecemeal.”

Drela plans to continue moving toward the design of vehicle systems rather than components. He is developing a design package that would enable rapid modeling and immediate flight simulation of an aircraft. “This prototyping system will fit well into the CDIO (conceive, design, implement, operate) structure of the Aero-Astro curriculum,” he says.

Drela teaches aircraft design fundamentals, external aerodynamics, and fluid mechanics of boundary layers to both undergraduate and graduate students. He notes how aero and astro students have shifted over the years from “mechanical types” who build model airplanes to those whose knowledge of aircraft has come almost purely from computer simulations. This poses a challenge to Drela as an instructor. “Doing stuff in software is fine, but ultimately, (aircraft modeling) has to be done.” He pats the PC on his desk. “Even a computer is made of something.”

Lauren Clark is a freelance writer and a communications assistant in the MIT School of Engineering Dean’s Office. She may be reached at ljclark@mit.edu