Weighing only 3 grams, DelFly Micro is the world's smallest camera-carrying Micro Aerial Vehicle. Image: Delfly.nl
Growing up in the Netherlands, David Lentink started to see his future in the skies. But although he would build a string of model airplanes, it would be a much earlier flying model that would truly catch his eye: insects and birds.
Later on, with limitations on professors and labs in his part of the world, he sent a letter to Michael Dickinson, a professor of bioengineering at the California Institute of Technology, and was invited to do research in his lab during the summer. “For example, I had a chance to measure this 3-D flying robot. It helped to better understand how insect flight can develop a vortex to their wing, forming parallels and helping the wing to generate lift from high angles. I also wondered if the wing was stable at different scales: a fruit fly, housefly, insects like that. I found the forces were remarkably similar.”
Then Lentink got students involved. “I think these observations had me thinking differently than other engineers and I wanted to try and build a very small micro air vehicle with students.” Lentink said the challenge there wasn’t to find the right parts, but getting the students to see the right mindset. “I used to give ballpark measures so they would head in the right direction,” he recalls. “I said it should weigh no more than 60 grams and they really thought I meant 160. It was hard for them to picture. But, in the end, what’s great about young people is they may think something is difficult but they’ll still try.”
It worked and became known as the original “DelFly.” And the latest iteration described by the DelFly website as “the smallest flying ornithopter carrying a camera in the world,” actually has specs of 3 grams in weight and 10 cm in wingspan, a connected camera and transmitter coming in at 0.4 grams.
DelFly Micro in the hand. Image: Delfly.nl
Lentink, who has a Bachelor’s and Master’s in aerospace engineering and a Ph.D. in experimental zoology, naturally moved into bird research, focusing on birds from the swift family. Assessing the wings of swifts in a wind tunnel, he was fascinated by this animal, which lives almost it’s entire life up in the air, catching up to 20,000 insects a day.
“I looked at how wing morphing could improve its performance,” he says. “One theory was the bird swinging backwards could boost lift. Another idea was the wing is much smaller so it might just be generating that drag. No one knew. No one looked at wings and drag of birds as they morph; they only looked at it in a wind tunnel with fully extended wings. I measured and found we could add numbers to have it glide 60 percent further and 100 percent longer and get better turns. The reason it can do these things is it can change wing shape. Big wings generate drag and small wings can get the lift. But big wings are helpful when going slow because there isn’t a lot of push from the air.”
The robot that eventually followed was the RoboSwift and, as its website describes, it can “fold its feathers backwards, thereby changing its wing area, sweep, slenderness, and camber.”
So what can result from the research? To Lentink, now an assistant professor in mechanical engineering at Stanford University, it seems more like: “What can’t?”
One possibility he sees is creating a micro air vehicle to help with rescue. “We need to look further at how birds avoid clutter and that could be a strong aid to helicopters,” he says. “In disasters, a lot of the time the problem is it’s hard for anything to get through.” And, for everyday use, he believes even your phone could take flight. “Look at how many pictures we take,” he says, “and now imagine if you’re trying to sell your house. If your phone can fly, now you can take aerial shots. Or, you’re on vacation, and you’d like to have shots from above of the great views you saw. That would be fun!”