Alumni Glider Pilots Take to the Sky

Flying without engine power takes  strategy, focus, and a dash of luck. Two Caltech alumni, separated by seven decades, have soared to success as glider pilots.

By Judy Hill

On a good day, if he leaves his Pasadena apartment early enough, Michael Marshall (MS ’17) can be gliding over the Tehachapi Mountains by 10:30 am. With the baking Mojave Desert out to the east and the San Joaquin Valley’s flatlands unfurling to the west, Marshall is in his element. Wedged into the tiny cockpit of his single-seat racing sailplane, he knows that what happens next depends on two things: his skill as a glider pilot and the day’s weather conditions. 

Those skills are paramount. Without them, a glider will naturally return to the earth in just a few minutes after being towed by an airplane to an altitude of 2,000 to 3,000 feet. To keep the plane buoyant, the pilot has to seek out sources of thermal lift, the buoyancy provided by columns of heated rising air called thermals. 

“The big drivers are wind and sun,” explains Marshall, a Caltech aerospace graduate student who competed this summer with the U.S. Soaring Team in the Junior World Gliding Championships in Szeged, Hungary. Two years ago, Marshall was awarded the Soaring Society of America’s Rudolph W. Mozer Trophy when he won the title of Junior National Champion as  the highest-ranking contestant.

On the other hand, Marshall adds, as he continues to explain some of the factors a glider pilot must consider, clouds are a mixed bag: “Some clouds mean rain, some just shadow the ground. Shadows usually mean there’s no lift. If you have puffy white cumulus clouds, those are good markers of lift. When it’s really hot, you usually get strong thermals.”

Caltech aerospace graduate student Michael Marshall with the single seat racing sailplane he flew in the Junior World Gliding Championships in Szeged, Hungary in August.

Mountains also play a role. “In the morning, the eastern-facing slopes of the mountains get more sunlight so they’re more likely to trigger a thermal,” Marshall explains. “Air usually runs up the slopes and converges at the mountain peaks.” When seeking out thermals in the flatlands of the Midwest or East Coast, he is more likely to look for man-made infrastructures, such as a parking lot or a Walmart. 

Using these thermals, Marshall can log more than 300 miles on an average soaring day, staying in the air for seven hours or more. A recent flight took him from Tehachapi, up 15,000 feet, and over into the Owens Valley. “That was a short one, just four hours,” he says. “I had to get back for a conference call.”

The son of a pilot, Marshall made his first solo flight in a glider at the age of 14. By 16, he had earned his pilot’s license, and his family had moved to Minden, a town in northern Nevada. “The place was about an hour south of Reno, which is one of the top three or four places in the world to fly gliders,” he explains. “Someone would say, ‘I just flew to Mount Whitney and back,’ which is 400 miles, and they’d do that in an afternoon! I thought, ‘That would be fun. Let’s do that!’ That’s really where it all got started.”

Marshall has since flown in about a dozen competitions, in Florida, South Carolina, and across the western United States. But wherever Marshall flies, he relies on a device (now an algorithm) developed by a fellow Caltech alumnus. 

The instrument is called the MacCready Ring, and its inventor, the late Paul MacCready (MS ’48, PhD ’52), was also a glider pilot. He won the National Soaring Championship three times while at Caltech, became a pioneer in human-powered flight during the 1970s (see sidebar, next page), and made a career as an aeronautical engineer, and was the founder of the unmanned aircraft manufacturer, AeroVironment. 

“Every glider pilot around the world knows about Paul MacCready,” says Marshall. “He came up with the optimal speed-to-fly theory. There have been other people who have added little bits and pieces to it, but at the end of the day, the fundamental theory on optimal speed-to-fly is still MacCready’s.”

The MacCready Ring was originally a physical device, but the theory behind the MacCready Ring is now implemented in a glider’s flight computer. Based on his speed-to-fly principle, it calculates the speed and altitude necessary to glide to a particular destination. The indications for when to speed up and slow down change depending on the rate of climb that is set; with higher climb rates, it is more optimal to fly faster, which consequently uses up more altitude when gliding between thermals.

MacCready’s affiliation with Caltech was part of the reason Marshall wanted to come to the Institute, he says. “There’s a lot of soaring, aviation, and aerospace history associated with Caltech, and MacCready played a large part in it. I hope to emulate some of his successes one day, in both soaring and aerospace.”

MacCready, who died in 2007, achieved early gliding success in a Pasadena-made sailplane called the Screaming Wiener. He won national soaring championships in that glider, and its successors, in 1947, ’48, ’49, and ’53. He also competed in England, Spain, and Sweden, winning the World Championship in France in 1956. “I quit soaring after that contest,” said MacCready in a 2003 oral history conducted by the Caltech Archives. “It was a very extreme day. … The wind was, oh, 60 miles an hour or more, and you’d get a down-current behind the slope, maybe 100 feet a second down, mingled with currents of 100 feet per second up. And it was luck as to whether you made it there.”

Although he achieved remarkable success in soaring, MacCready never saw himself as an instinctive pilot. Instead, he said, “I used my brain power in the important part of the flight. Those contests wouldn’t be won by somebody who could do turns effortlessly but by somebody who knew where the next thermal was. I would concentrate very hard.”

Marshall, too, says he is not necessarily a natural flyer. “I do think that good glider pilots usually fall into one of two categories: tactical pilots, who understand the fundamentals of soaring and how to apply them, and intuitive pilots, who are very good at reading the sky and sensing the air around them,” he says. “I fall more into the former category, though I’m trying to get more over to the other side, too.”

The sport, adds Marshall, tends to appeal to mathematicians, scientists, and engineers, and while his graduate research on the dynamics and control of flexible spacecraft has no direct correlation with soaring, he feels sure that he benefits from his analytical background. “I have a reasonably good understanding of how things fly. Just being an aerospace engineer is beneficial. The challenges in engineering and research are similar to the challenges in soaring: they’re both difficult problems that you tackle with a set of fundamental principles and judgment formed from experience. It’s just that the consequences if something goes wrong in soaring are often higher than the consequences in research.”

Preparing for competition means researching the local terrain as well as the likely weather conditions. For instance, he says, flying on the West Coast is not great practice for flying in Europe, since European thermals are slower and the highest a glider pilot is likely to reach is around 5,000 feet, while on an average day in the western United States, a sailplane might reach an altitude of 15,000 feet. And, with fewer mountains in some parts of Europe, features like lakes, forests, and even roads can have a significant effect on gliding conditions.

It also helps to know who else is in the race. “You want to know who the really good pilots are,” says Marshall. Equally important, he says, is knowing the pilots who have historically made bad decisions and then both literally and metaphorically steering clear of them.

Even with careful planning and smart strategy, every flight holds some surprises. One day in Florida, Marshall recalls, he found himself sharing a thermal with a bald eagle. Another day, during a competition in central Utah, he says, “We were flying down a ridge that was maybe 70 miles long, and it ended up being a pack of gliders all basically hugging the top of the ridge, cruising at like 80 to 90 miles an hour just a couple hundred feet above the ground. We were basically in formation flying down the ridge, a flock of gliders. So that was unexpected but pretty exciting.”

When Marshall tells people he’s a glider pilot, they often muse about how peaceful it must be up in the skies without any engine noise. “But it’s not as quiet as people think,” he admits. “You have instruments beeping at you. And then there’s the wind noise. It looks peaceful, but sometimes it can be a lot more like a roller coaster.”

There is nowhere he would rather be, though, on a day away from his research on campus. “There are a lot of puzzle pieces that need to be put together to do well,” he says of his intellectually challenging sport. “I have some of the pieces but not all of them. I don’t think you can ever really get all of them.” 

See related story, “People-Powered Flight.”